The effect of high thermal insulation on high thermal mass Is the dynamic

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高导热绝缘复合材料的研究

13524137719@163.C OM高导热绝缘复合材料的研究Ξ张志龙1)　吴　昊2)　景录如1)(中国地质大学材料科学与化学工程学院1)　武汉　430074)(华东交通大学信息工程学院2)　南昌　330013)摘　要:综述了高导热绝缘复合材料的导热机理和常用的导热理论模型,介绍了基体材料和填料的研究进展,复合技术的进展及其在电子、电机行业的应用前景。

关键词:高导热;绝缘;复合材料;应用中图分类号:TQ330Study of the High Thermal Conductivity and Electrical Insulation CompositeZhang Zhilong 1)　Wu H ao 2)　Jing Luru 1)(College of Material Science and Chemical Engineering ,CU G 1),Wuhan 430074)(School of Information Engineering ,East China Jiaotong University 2),Nanchang 330013)Abstract :The heat conduction mechanism and normally used theoretical models of high thermal conducting and electrical insu 2lating composite are summarized in the paper.The progress in the polymer material ,filler and the fabricated techniques is intro 2duced ,otherwise ,the prospect of such materials applied in electronic field and electromotor is presented and predictedK ey w ords :high thermal conductivity ,electrical insulation composite ,application.Class number :TQ330 随着高分子材料在各行业应用的日渐普及,人们对其综合性能的要求不断提高。

Thermal gravitational waves

v12
3kTc . 12
For a core temperature of Tc 10 7 K , the velocity of the particles is of the order of
8 10 5 m / s . For a star of density 200 g / cc 2 10 5 kg / m 3 , the numbeting in these values we get the power of thermal gravitational waves emitted as,
10 9 Watt at a frequency of 1017 Hz . E
2
The flux of thermal gravitational waves from the sun, received at earth is of the order of half a watt. 2. Thermal gravitational waves from compact stars In the case of white dwarfs, the number density is of the order of n1 n2 10 37 m 3 , and the velocity corresponding to the white dwarf temperature of Tc 10 8 K , is of the order of 2 10 6 m / s . The volume of the white dwarf is of the order of 4 1018 m 3 and the frequency corresponding to the temperature Tc 10 8 K is And for a white dwarf,

跨季节蓄热太阳能的英文文献

跨季节蓄热太阳能的英文文献Harnessing the Power of the Sun: A Seasonal Thermal Storage ApproachThe pursuit of sustainable energy solutions has become a global imperative, and one of the most promising avenues is the utilization of solar energy. As the world grapples with the pressing need to reduce greenhouse gas emissions and mitigate the effects of climate change, the exploration of innovative technologies that can harness the abundant and renewable power of the sun has become a focal point of research and development. One such approach is the concept of cross-seasonal thermal storage, which holds the potential to revolutionize the way we generate and utilize solar energy.The fundamental premise of cross-seasonal thermal storage is the ability to capture and store the sun's heat during periods of high solar irradiation, typically during the warmer months, and then release that stored energy during periods of lower solar availability, such as the colder seasons. This concept addresses a critical challenge faced by traditional solar energy systems, which often struggle to meet the energy demands of buildings and communities during periods of low sunlight.The process of cross-seasonal thermal storage involves a multi-step approach. First, solar thermal collectors, such as flat-plate or evacuated tube collectors, are used to absorb the sun's energy and convert it into thermal energy. This thermal energy is then stored in a suitable medium, such as water, rock, or phase-change materials, within an insulated storage system. The stored thermal energy can then be retrieved and utilized for heating, cooling, or other applications when the demand for energy is higher, effectively bridging the gap between the availability of solar energy and the energy needs of the end-users.One of the key advantages of cross-seasonal thermal storage is its ability to improve the overall efficiency and reliability of solar energy systems. By storing excess heat generated during the warmer months, the system can provide a consistent and reliable source of thermal energy during the colder seasons, reducing the reliance on fossil fuels or other energy sources for heating and cooling. This not only contributes to a reduction in greenhouse gas emissions but also enhances the energy security and self-sufficiency of communities and regions that adopt this technology.Moreover, cross-seasonal thermal storage can have a significant impact on the economics of solar energy systems. By providing a means to store and utilize solar energy throughout the year, thetechnology can help to mitigate the seasonal fluctuations in energy demand and supply, leading to a more stable and predictable energy market. This, in turn, can attract greater investment and support for the adoption of solar energy, further accelerating the transition towards a more sustainable energy future.The implementation of cross-seasonal thermal storage systems, however, is not without its challenges. One of the primary obstacles is the development of efficient and cost-effective thermal storage technologies that can maintain the integrity of the stored energy over extended periods. Additionally, the integration of these systems into existing energy infrastructure and building designs requires careful planning and coordination to ensure optimal performance and integration.Despite these challenges, the potential benefits of cross-seasonal thermal storage are substantial, and researchers and engineers around the world are actively exploring innovative solutions to overcome the barriers to widespread adoption. From the development of advanced insulation materials to the optimization of storage media and system designs, the field of cross-seasonal thermal storage is witnessing a surge of technological advancements that hold the promise of a more sustainable and resilient energy future.As the world continues to grapple with the urgent need to address climate change and energy security, the concept of cross-seasonal thermal storage stands as a shining example of the ingenuity and dedication of the scientific community. By harnessing the power of the sun and leveraging the principles of thermal energy storage, this technology has the potential to transform the way we generate, distribute, and consume energy, ultimately paving the way for a more sustainable and equitable energy landscape for generations to come.。

CCD-based thermoreflectance microscopy principles and applications

Home Search Collections Journals About Contact us My IOPscienceCCD-based thermoreflectance microscopy: principles and applicationsThis article has been downloaded from IOPscience. Please scroll down to see the full text article.2009 J. Phys. D: Appl. Phys. 42 143001(/0022-3727/42/14/143001)View the table of contents for this issue, or go to the journal homepage for moreDownload details:IP Address: 222.190.117.205The article was downloaded on 27/05/2013 at 02:46Please note that terms and conditions apply.IOP P UBLISHING J OURNAL OF P HYSICS D:A PPLIED P HYSICS J.Phys.D:Appl.Phys.42(2009)143001(20pp)doi:10.1088/0022-3727/42/14/143001TOPICAL REVIEWCCD-based thermoreﬂectance microscopy:principles and applications M Farzaneh1,8,K Maize2,D L¨uerßen3,4,9,J A Summers3,P M Mayer4,10,P E Raad5,6,K P Pipe7,A Shakouri2,R J Ram4and Janice A Hudgings31Department of Physics,Kenyon College,Gambier,OH43022,USA2Department of Electrical Engineering,University of California Santa Cruz,Santa Cruz,CA95064,USA3Department of Physics,Mount Holyoke College,South Hadley,MA01075,USA4Research Laboratory of Electronics,Massachusetts Institute of Technology,Cambridge,MA02139,USA5Department of Mechanical Engineering,Southern Methodist University,Dallas,TX75275,USA6TMX Scientiﬁc,Inc.,Dallas,TX75024,USA7Department of Mechanical Engineering,University of Michigan,Ann Arbor,MI48109,USAE-mail:farzanehm@Received23February2009,inﬁnal form5May2009Published29June2009Online at /JPhysD/42/143001AbstractCCD-based thermoreﬂectance microscopy has emerged as a high resolution,non-contactimaging technique for thermal proﬁling and performance and reliability analysis of numerouselectronic and optoelectronic devices at the micro-scale.This thermography technique,whichis based on measuring the relative change in reﬂectivity of the device surface as a function ofchange in temperature,provides high-resolution thermal images that are useful for hot spotdetection and failure analysis,mapping of temperature distribution,measurement of thermaltransient,optical characterization of photonic devices and measurement of thermalconductivity in thinﬁlms.In this paper we review the basic physical principle behindthermoreﬂectance as a thermography tool,discuss the experimental setup,resolutionsachieved,signal processing procedures and calibration techniques,and review the currentapplications of CCD-based thermoreﬂectance microscopy in various devices.(Someﬁgures in this article are in colour only in the electronic version)1.IntroductionOne of the biggest challenges in operation of electronic and optoelectronic devices and integrated circuits(ICs)is the generation of excess heat and increase in temperature under operating conditions.This can cause the loss of reliability,affect the performance or result in catastrophic failure of the device[1].Additionally,by miniaturization and monolithic integration of sub-micrometre devices on a chip, access to individual elements of an IC becomes restricted, 8Author to whom any correspondence should be addressed.9Current address:Oxford Gene Technology,Oxford OX51PF,UK.10Current address:Physical Sciences Inc.,20New England Business Center, Andover,MA01810,USA.which renders the characterization of these components difﬁcult.Understanding the temperature distribution and thermal characteristics of a device is an important step in thermal management and improving device performance;in addition,thermal proﬁling can be used to extract material parameters and to characterize the optical performance of photonic ICs.Ultimately this knowledge can lead to better device designs and chip layouts.Several thermography techniques have been used for temperature measurement of micrometre and sub-micrometre electronics and optoelectronic devices.Among them, infrared(IR)thermometry is perhaps the most widely used technique for temperature measurements of electronic devices, particularly ICs[2].IR thermometry is based on determiningthe spatial distribution of IR thermal radiation emitted from the surface of a solid[3,4].Based on Planck’s law of blackbody radiation,the maximum spectral power density of an ideal blackbody at thermal equilibrium will shift to lower wavelengths with increasing temperature.Since,in practice the surface of a device under study is not a blackbody and reﬂects some of the incident radiation,the blackbody law must be scaled by a material dependent factor known as the emissivityε.The total thermal radiation W integrated over the entire spectral rangeλis given by W=εσT4,where σ=5.7×10−12W cm−2.Emissivity depends on the surface property and geometry,wavelength and temperature of the object,and must be known for each surface in order to obtain an accurate thermal proﬁle.Silicon is largely transparent to near IR radiation,making IR thermography a valuable tool for thermal mapping of IC backplanes and hot spots.The thermal resolution of IR cameras(detectors)can be10–20mK,but their spatial resolution is mainly determined by the diffraction limit for the range of wavelengths to which the detector is sensitive.The most sensitive IR cameras work at3µm wavelength[3],which is ill-suited to the length scales of many modern electronic and optoelectronic e of a solid immersion lens can improve the resolution to sub-micrometre range,but low signal-to-noise ratios can still be a concern.Apart from the sub-optimal spatial resolution of IR thermography,other drawbacks include inaccuracy due to the attenuation of radiation between the target and the detector,uncertainty in the emissivity of the device surface and background radiation[4].Furthermore,the low emissivity of metals,which are widely used as electrical contacts in devices, limits the application of IR thermography.In the liquid crystal thermography(LCT)technique[3,4], the surface of the device under study is covered with a thin layer of liquid crystal and illuminated with white light. At different temperatures,the liquid crystal layer reﬂects different wavelengths of this incident light.To improve the spatial resolution of the method,the nematic–isotropic phase transition of liquid crystal which occurs at the clearing point of the crystal,T c,is used[5].Below T c the liquid crystal is in the nematic phase which scatters light and rotates the plane of polarization of the light and appears bright under a polarizing microscope.Above T c,where the liquid crystal is in the isotropic phase,the plane of polarized light does not change and the imageﬁeld appears dark.Taking advantage of the nematic–isotropic phase transition has given the LCT method a spatial resolution of2–4µm.The thermal resolution of LCT is approximately0.1K near the phase transition.Although LCT is less expensive than IR imaging,it is a semi-invasive technique and the thermal conductivity and heat capacity of the liquid crystal coating can affect the device under test.In addition,the uniformity and thickness of the liquid crystal layer are important factors in the accuracy and resolution of the technique[3].Fluorescent micro-thermography(FMT)[6,7]utilizes the temperature-dependent quantum efﬁciency of photolumines-cent rare earth dyes.In this technique,the sample surface is coated with a thinﬁlm of such dyes and is then illuminated by ultraviolet(UV)light.FMT can be used for thermal imag-ing of electronic and bio sensing devices as well as hot spot detection and thermal mapping of ICs.A spatial resolution of 0.3µm and a thermal resolution of1mK have been reported for FMT[4],although sample preparation and optical system design require special consideration.Photon shot noise,UV bleaching,ﬁlm dilution andﬁlm preparation can have a signif-icant impact on the quality of FMT thermal images.Using micro-thermocouples as inexpensive point mea-surement contact probes can provide accurate temperature readings with a thermal resolution of0.01K.However,the large size of the thermocouple wires(∼25–50µm in diameter) results in a poor spatial resolution.In addition,difﬁcul-ties in maintaining good thermal contact between the micro-thermocouple junction and the surface of a device can lead to erroneous readings.Finally,as point-based measurement tools,micro-thermocouples cannot be used for imaging with-out implementing complicated translation stages[3].A thermography technique with very high spatial resolution is scanning thermal microscopy(SThM)which takes the use of micro-thermocouples to the nanometre scale. The SThM probe consists of a thermocouple fabricated on the tip of an AFM cantilever[8].When the probe is scanned in contact mode over the surface of a sample,localized heat transfer between the sample surface and the probe tip leads to a change in the tip temperature that is measured by the thermocouple.In this way,both the tip–sample heat transfer across the entire surface and the sample topography can be obtained simultaneously with sub-micrometre spatial resolution(∼0.05µm)and a thermal resolution of0.1K[4]. However,the roughness of the sample surface can cause variations in the tip-surface thermal contact,leading to noise in the thermal signal.Furthermore,the SThM experimental setup is complicated and expensive,and data acquisition can be time-consuming due to the required scanning methods[3].A major limitation of SThM is the liquid meniscus that forms between the tip and the sample,which is intrinsic to contact measurements done in atmosphere and limits the resolution of the technique.Finally,SThM cannot be used easily on light emitting surfaces of optoelectronic devices such as vertical cavity surface emitting lasers(VCSELs),because the light is absorbed by the SThM thermocouple and causes errors in temperature measurement[9].In addition to the above-mentioned techniques,other methods of thermography include acoustic thermography[10], near-ﬁeld scanning optical microscopy(NSOM)adapted for temperature measurement[11],Raman spectroscopy[12]and thermoreﬂectance microscopy.Thisﬁnal technique is the focus of this review and will be discussed in detail.Thermoreﬂectance microscopy is based on measurement of the relative change in the reﬂectivity of a sample(device) surface as a function of change in temperature.As the temperature of the sample changes,the refractive index,and therefore the reﬂectivity,varies.The relation between the relative change in reﬂectivity and the temperature change can be approximated toﬁrst order asRR=1R∂R∂TT=κ T,(1)whereκ,which is typically of the order of10−2–10−5K−1, is the thermoreﬂectance calibration coefﬁcient that dependson the sample material,the wavelength of the illuminating light,the angle of incidence(and thus,by extension,the surface roughness)and the composition of the sample in the case of multi-layer structures.Thermoreﬂectance spectroscopy has been used exten-sively since the1960s to study the band structure and dielectric response functions of semiconductors[13].As an imaging thermography technique,it has been utilized in point-based laser scanning methods[14],and with multi-point detection systems.For the latter,both non-CCD photodiode array-based systems[15],and CCD-based schemes have been applied to study thermal proﬁles of electronic and optoelectronic devices [16,17].Thermoreﬂectance has also been employed in pump–probe conﬁguration to study phonon transport and the thermal relaxation of carriers on picosecond time scales[18].Transient thermoreﬂectance(TTR)[19]and photomodulated thermore-ﬂectance[20]have been used to characterize thermal diffusiv-ity and other thermal properties of thinﬁlms.It has been shown that the thermal and spatial resolutions of CCD-based thermoreﬂectance can be as low as10mK and 250nm,respectively[21],but the fundamental temperature limit is not known yet.The high resolution of CCD-based thermoreﬂectance microscopy,its relatively short data acquisition times compared with other techniques and its suitability to a wide range of materials including metals and light emitting surfaces make it a leading method for studying thermal transport in electronic and optoelectronic devices under operating conditions.This technique is also applicable for studying thermal transients and heat transfer in thinﬁlms and low dimensional structures such as multilayers and superlattices[22].In the following sections of this review,we present an overview of the physical basis of thermoreﬂectance,the most common experimental setup variations and signal processing and calibration techniques.We also review applications of CCD-based thermoreﬂectance microscopy in measuring temperature distributions of various devices.2.Principles of thermoreﬂectanceSince the1960s,optical modulation techniques have been used extensively to study the band structure of semiconductors at energies higher than the fundamental gap[13,23–29].In these techniques the response of the optical constants of a solid to a periodic change in a parameter such as electricﬁeld, pressure,temperature or wavelength of the incident radiation is measured[30].The resulting spectra show well-resolved features stemming from critical points of the band structure that are isolated and separated from the background which is less sensitive to modulation.A temperature increase creates a shift in the energy gap and also broadens the critical point involved.The shift of the energy gap involves two components,one due to thermal expansion and the other due to electron–phonon interaction. The thermal-expansion shift has the same sign as the phonon shift for most critical points observed,with comparable magnitude.The broadening is only due to the electron–phonon interaction,and is small compared with the total shift[13].For non-magnetic,isotropic,homogeneous media,in which the optical constants can be treated as scalars,the phenomenological basis of thermoreﬂectance spectroscopy [30]can be understood by studying the change in the complex dielectric functionˆε(E)=ε1(E)+iε2(E),whereε1andε2 are the real and imaginary parts of the dielectric function, respectively,and E is energy.The optical constantε2is related to the band structure through the joint density of states function[29]:ε2(E)=4e2¯h2πµ2E2d k|P cv(k)|2δ[E c(k)−E v(k)−E],(2)whereµis the combined density of states mass,the Diracδfunction represents the joint spectral density of states between the conduction(c)and valence(v)band states which differ by the energy E c(k)−E v(k)=¯hωof the incident light,P cv(k) is the momentum matrix element between the conduction and valence band states,and the integration is performed over the ﬁrst Brillouin zone.The reﬂectivity R of the material for normal incidence of light has the formR=(n−1)2+k2(n+1)2+k2,(3)where n and k are the index of refraction and the extinction coefﬁcient,respectively,and can be written as real and imaginary parts of the complex index of refractionˆn=n+i k. Since Maxwell’s equations yield the relationˆε=ˆn2,it follows thatε1=n2−k2,(4a)ε2=2nk.(4b) Solving these equations for n and k,one obtains[30]n=(ε21+ε22)1/2+ε121/2,(5a)k=(ε21+ε22)1/2−ε121/2.(5b)In thermoreﬂectance spectroscopy experiments,it is the rela-tive change in reﬂectivity( R/R),resulting from the modu-lation of temperature,which is measured.The contributions of n and k to the modulated reﬂectance can be obtained by differentiating(3),yieldingRR=4(n2−k2−1) n+8nk k[(n+1)2+k2][(n−1)2+k2],(6)where n and k are the changes in n and k resulting from the modulation.Substituting(5a)and(5b)into(6)yieldsRR=α(ε1,ε2) ε1+β(ε1,ε2) ε2,(7)withα=2AA2+B2,(8a)β=2BA2+B2,(8b)whereA=n(n2−3k2−1),(9a)B=k(3n2−k2−1).(9b) The coefﬁcientsαandβ,which are functions of n and k and thus the photon energy,weight the contributions of ε1 and ε2to the modulated reﬂectance,respectively.Their signs and magnitudes determine the response in different spectral regions,and have been derived for electroreﬂectance analysis[31].It should be noted thatε1(ω)andε2(ω),and therefore their modulations,are not independent and are related explicitly by the Kramers–Kronig transformation.According to this relation,the temperature induced change inε2(ω)causes a related change inε1(ω),given byε1(ω)=2πP∞ω ε2(ω )ω 2−ω2dω ,(10)where P denotes the principal value of the integral.If ε1and ε2can be calculated from some suitable theory as a function of change in temperature,then the theoretical thermoreﬂectance spectrum of R/R can be obtained via(7).An interpretation is possible if an agreement between experimental and theoretical spectra exists.As mentioned earlier,the temperature increase causes a shift in the energy gap and broadens the critical point involved. Combining these two effects,one can writeˆε=dˆεd E gd E gd TT+dˆεddd TT,(11)where E g is the energy gap and the broadening is accounted for, phenomenologically,by the broadening parameter .Near the fundamental absorption edge of the semiconductor,it can be found approximately that[30]ε1∝−11x+1dd T−xx+1d E0d TT,(12a)ε2∝−1xx2+1dd T+1x2+1d E0d TT,(12b)where x=(¯hω−E0)/ and E0is the inter-band energy at the critical point.When the broadening parameter is assumed to be constant(d /d T=0),the thermoreﬂectance spectrum is simply theﬁrst derivative with respect to the optical frequency of the joint electronic density of states in(2).For this reason, thermoreﬂectance is referred to as aﬁrst-order modulation spectroscopy(as opposed to electroreﬂectance,which is a third-order modulation spectroscopy).While thermoreﬂectance spectroscopy is a powerful tool for studying the band structure and dielectric response function of semiconductors,here we focus on its application in thermography as described by(1)in which all of the effects of the material’s reﬂectance modulation are lumped into the thermoreﬂectance calibration coefﬁcientκ(λ).Becauseκ(λ) can vary sharply within the spectral region of interest(often the visible spectrum),the choice of illumination wavelength determines not only the spatial resolution of the technique but also the sensitivity[32].For most metals and semiconductors, the thermoreﬂectance coefﬁcient is only in the range of 10−5–10−2K−1.Therefore,for most practical applications,a highly sensitive measurement is required to obtain quantitative information about the temperature of the device under test.The change in reﬂectance of the material under study can also result from modulation induced changes other than the temperature change.For example,in semiconductor lasers and ampliﬁers,the change in carrier density,as a result of change in device bias,can alter the index of refraction.The subsequent change in reﬂectivity combines with that due to temperature change,potentially complicating interpretation of the results[33].3.Experimental setupThe development of thermoreﬂectance as a thermography tool has mainly focused on two realizations:point measurements and CCD-based measurements[16].In the former,a focused laser beam is used as the illumination source and a single element photodiode,coupled with a lock-in ampliﬁer,is used as the detector.The sample is usually placed on a translation stage and the measurement is made for each point.Scanning the sample surface with the laser beam provides the thermal image.This technique has a very high sensitivity and is capable of detecting relative changes in reﬂectivity less than R/R=10−6.The disadvantage of this method is that it is time consuming with a typical500×500pixel scanned image requiring approximately an hour to acquire.Various improvements have been employed to reduce the acquisition time in laser scanning thermoreﬂectance,without loss of sensitivity.In one such case,a photodiode array with synchronous multiple point bandwidthﬁltering is used as the basis for a thermal imaging microscope[15].This state-of-the-art diode array camera achieves thermoreﬂectance imaging with10mK resolution in1s,while by combining multiple frames,a spatially enhanced image can be obtained in minutes [3].The photodiode array camera has a higher dynamic range and sensitivity than a CCD camera,because each diode in the array is ac-coupled with an analog ampliﬁer and a precision24-bit,40kHz,analog–digital(A/D)converter.The ac coupling at each pixel allows the signal to be boosted without saturation of the dc component.Such performance,however, greatly increases system complexity;current versions of the system include only16×16pixels,much fewer than a standard CCD.Another improvement upon laser scanning thermore-ﬂectance has been achieved by using a fast scanner made of two galvanometric mirrors,which sweeps a focused laser beam across the device[34].This method has achieved a spatial res-olution of the order of the diffraction limit(∼300nm),which is comparable to that attained by CCD-based thermoreﬂectance, and a R/R resolution of10−5.One limitation of this setup is the range of the temperature modulation frequency,which isFigure1.Schematic depiction of a homodyne thermoreﬂectance microscopy setup.on the order of a few tens of kilohertz.This can be a drawback because the temperature variation amplitude of the thermal modulation decreases as the frequency increases.The basic experimental setup for a high spatial-resolution CCD-based thermoreﬂectance is shown inﬁgure1.The setup consists of a visible light CCD camera and a light emitting diode(LED)illumination source that is focused onto the sample by a microscope objective[16].The light reﬂected back to the CCD in response to modulation of the sample temperature is then analysed by a computer.The use of an incoherent light source(LED)instead of a focused laser beam eliminates speckle or fringe type interference patterns that may occur with coherent illumination.Various modulation schemes can be used to detect the relative change in reﬂectivity of the sample surface,including the homodyne method,the heterodyne method and the techniques for studying transients, as described below.Recognizing that the thermoreﬂectance coefﬁcientκis strongly dependent on the probe wavelength,the R/R response is signiﬁcantly enhanced near the wavelengths where d R/d T has a maximum value and the reﬂectivity R is minimum(see(1)).Therefore,the choice of probe wavelength plays an important role in determining the sensitivity of CCD-based thermoreﬂectance.3.1.Homodyne techniqueIn the homodyne technique,the temperature of the sample is modulated using a signal generator that is phase-locked to the CCD frame trigger,and the LED illumination is in the continuous wave(CW)mode.The modulation frequency of the sample temperature is f,which also implies a modulation of reﬂectivity at the same frequencyR(x,y,t)=R0(x,y,t)+ R(x,y,t)cos(2πf t+ϕ(x,y)+ψ),(13) whereϕ(x,y)is the phase shift due to the thermal modulation andψis an arbitrary uniform phase shift accounting for any overall delay between the modulation signal and the camera trigger[21].Using a multichannel lock-in scheme and triggering the camera at a frequency of f c=4f,a 2D image can be obtained that represents the modulated reﬂectivity R(x,y),and through a calibration,the modulated temperature T(x,y).Choosing f c to be four times the frequency of temperature modulation causes the camera to take four images during each period T of the temperature modulation,with these images corresponding to the following four integrals[16]:I1=T/4R(x,y,t)d t,I2=T/2T/4R(x,y,t)d t,I3=3T/4T/2R(x,y,t)d t,I4=T3T/4R(x,y,t)d t,(14) The modulation amplitude R(x,y),the dc image R0(x,y) and the relative phaseϕ(x,y)+ψcan then be obtained through the following relations:R(x,y)=4π√2T(I13)2+(I24)2,R0(x,y)=2T(I1+I2+I3+I4),ϕ(x,y)+ψ=2πarctanI1+I2−I3−I4I123+I4.(15)The normalization of the modulated signal by the dc signal allows extraction of the relative change in reﬂectivity described in(1):R(x,y)R0(x,y)=√2π(I1−I3)2+(I2−I4)2I1+I2+I3+I4(16)This lock-in measurement technique(which is sometimes referred to as the‘four bucket’technique),makes best use of the CCD array’s slow readout speed by simply accumulating a number of identically phased images in each bin(I1,I2,I3or I4) and recording a cumulative average of the contents.Thus,even if many images are captured(increasing the sensitivity of the technique),only four image buffers(one for each phase bin) need be kept in memory throughout the procedure[33].3.1.1.Signal processing and noise analysis.Since the thermoreﬂectance coefﬁcient of some materials over accessible wavelengths can be quite low(e.g.10−5K−1), it is important to consider whether the CCD approach has the required sensitivity for imaging small(<1K)changes in temperature.For example,without boosting the resolution of the camera using this averaging,the thermal resolution for a typical thermoreﬂectance measurement would be at mostκ−1/2b,whereκis the thermoreﬂectance coefﬁcient and b is the bit depth of the camera.For a material with κ=1×10−4K−1and for a typical camera with b=12, this worst-case resolution is approximately2.5K.However, for a wide range of practical measurement scenarios,the shot noise present in the incident photons and the thermal noise present at the input of the A/D converter can provide a sufﬁcient amount of dither to resolve sub-quantization leveltemperatures via the phenomenon sometimes referred to as ‘stochastic resonance’[35].L¨u erßen et al ,provide empirical evidence for 10mK temperature resolution on a gold surface,using an illumination wavelength optimized for the material [36].This corresponds to an equivalent bit depth of 18bits rather than the 12bits offered nominally by the camera.This extra resolution results from the repeated averaging of the quantized signal in the presence of a sufﬁciently large noise,which causes the camera pixel’s signal to switch between adjacent quantization levels.In order to obtain sub-quantization level thermal images,averaging must be performed over many images.Mayer et al [21]have analysed the number of iterations required to achieve a given temperature resolution (and the speciﬁc form of the convergence)by propagating the approximately Gaussian fundamental noise sources (thermal or shot noise)present at the input of the measurement through the signal processing chain.They constructed an estimator of the temperature ﬂuctuation present in the sample based on the observable reﬂected light and the various measurement parameters which impact the accuracy of the measurement including the depth of the thermal and reﬂectance modulation,the mean level of reﬂected light,the number of iterations (thermal cycles)that are averaged over and the intrinsic noise present in a pixel (thermal,shot or quantization noise).The estimator takes the form of a Rice distribution.By taking the difference of the estimator with respect to the true thermal signal and the standard deviation of the estimator,the dependence of the thermoreﬂectance error as a function of the measurement conditions can be found.The errors in both the ﬁrst moment (mean)and the second moment (variance)decrease as average signal level and the number of iterations increase.The errors also decrease as the fundamental noise sources at the pixel decrease,provided that sufﬁcient noise is present to bump the signal between different quantization bins of the analogue to digital (A/D)converter in the camera.This can be used to plan measurements and make a statistical prediction of a measurement’s accuracy;alternatively,the measurement can simply be run until the value of the thermoreﬂectance is converged,since it is shown that for sufﬁcient averaging the thermoreﬂectance estimator is unbiased [21].A useful and intuitive result of the detailed analysis is that in the limit of a small thermoreﬂectance signal the accuracy of the measurement (the standard deviation)scales as 1/√N ,where N is the number of thermal oscillations measured (i.e.the amount of averages taken).Hence,to double the accuracy of the measurement,it must typically be run for four times as long.The model of [21]was experimentally conﬁrmed by performing sub-quantization threshold imaging of a diffused resistor in a Si wafer.Mayer et al [33]further discussed the conditions required for stochastic resonance,the optimal noise signal size (∼1/2LSB of the A/D converter),the impact of quantization noise and the functional form of both the magnitude and phase probability distribution functions (PDFs)as a function of the measurement and system variables.The ultimate temperature resolution using this method is set by the ideality (integral and differential non-linearity)of the A/Dconverter.This was illustrated using a Monte Carlo analysis [21].Using this method of averaging,the discrete limit for the 12-bit system can be lowered to R/R =2.5×10−6and possibly beyond,with a corresponding expansion in dynamic range from 72to bined with appropriate selection of illumination wavelength,stochastic resonance CCD systems have achieved thermal resolution of 10mK and spatial resolution of 250nm [21].The homodyne thermoreﬂectance techniques are suitable for obtaining thermal images of low-frequency phenomena,since the frequency of temperature modulation is limited by the frame rate of the CCD camera.In order to image high-frequency thermal phenomena,a modiﬁcation of the homodyne technique has been developed by Grauby et al [16]as discussed in the next section.3.2.Heterodyne techniqueIn this method,the temperature (and reﬂectivity)of the sample is modulated with a frequency f 1,as in (13)and LED illumination is modulated at a slightly different frequency f 2,with its ﬂux given byφ(t)=φ12[1+cos (2πf 2t)].(17)Using the same multichannel lock-in scheme as in the homodyne method,the slow difference frequency F =f 2−f 1component of the reﬂected signal can be detected by triggering the camera at a frequency f c =4F ;the ﬂux reﬂected back to the camera can be written ass(x,y,t)=φ12R 0(x,y,t)+φ14R(x,y,t)cos[2πF t −ϕ(x,y)−ψ].(18)For example,if the sample temperature is to be modulated at f 1=1MHz,then with the LED modulated at f 2=1MHz +10Hz,the blinking term F =f 2−f 1is only 10Hz,and the camera can be easily triggered at 4F =40Hz.Synchronization between the camera control,LED and device heating can be achieved using a phase-locked system and synchronous counters.Grauby et al have used this method to obtain amplitude and phase images of the Joule and Peltier heat exchange in a polycrystalline silicon resistor [16].3.3.Transient thermal imaging using thermoreﬂectance In both of the above frequency domain measurement techniques,a lock-in method captures the steady-state thermal signal but provides limited information about thermal transients.However,it is often desirable to observe how devices thermally evolve in time.Due to the size of typical electronic and optoelectronic devices,thermal effects can occur on a millisecond or microsecond time scale or faster.Thermoreﬂectance methods based on time domain analysis can characterize fast transient heating effects such as the thermal rise time by reconstructing the time varying reﬂectance signal.While CCD frame rates are typically much slower than device thermal time constants,single point TTR。

我的发现之热胀冷缩原理英语作文

我的发现之热胀冷缩原理英语作文Thermal Expansion and Contraction: A Fundamental Principle of Physics.Thermal expansion and contraction are fundamental physical phenomena that describe the change in size and shape of materials due to variations in temperature. This phenomenon is observed in solids, liquids, and gases and plays a crucial role in various scientific and engineering applications.Microscopic Origin of Thermal Expansion.At the microscopic level, thermal expansion and contraction can be attributed to the vibrations of atoms or molecules within a material. As the temperature of a material increases, the average kinetic energy of its individual particles increases. This leads to an increase in the amplitude of their vibrations, causing the particles to occupy a larger average volume. Consequently, thematerial expands. Conversely, when the temperature decreases, the average kinetic energy of the particles decreases, and the particles move closer together,resulting in contraction.Linear, Area, and Volume Expansion.Thermal expansion can occur in one dimension (linear expansion), two dimensions (area expansion), or three dimensions (volume expansion). Linear expansion refers to the change in length of an object along a specific direction. Area expansion pertains to the change in the surface area of an object, while volume expansion describes the change in the total volume of an object. The extent of expansion or contraction depends on the material's coefficient of thermal expansion, which quantifies the amount of expansion or contraction per unit temperature change.Types of Thermal Expansion.There are two main types of thermal expansion:isotropic and anisotropic. Isotropic expansion occurs whena material expands or contracts uniformly in all directions. This behavior is observed in amorphous solids and liquids. Anisotropic expansion, on the other hand, occurs when a material expands or contracts differently in different directions. This phenomenon is common in crystals, wherethe arrangement of atoms or molecules can lead to varying degrees of expansion along different axes.Applications of Thermal Expansion.Thermal expansion has numerous practical applicationsin various fields. In engineering, it is crucial for designing structures that can withstand temperature variations without catastrophic failure. For example, bridges, buildings, and pipelines are designed to accommodate thermal expansion and contraction to prevent cracking or buckling.In metrology, thermal expansion must be taken into account when measuring the dimensions of objects with high precision. Precision instruments like calipers andmicrometers are often calibrated at specific temperatures to ensure accurate measurements regardless of temperature fluctuations.Additionally, thermal expansion is utilized in various temperature-sensing devices, such as thermostats and bimetallic strips. In a thermostat, a bimetallic strip composed of two metals with different coefficients of thermal expansion is used to detect temperature changes. As the temperature varies, the strip bends due to the differential expansion of the two metals, actuating a switch to control heating or cooling systems.Conclusion.Thermal expansion and contraction are fundamental physical principles that describe the change in size and shape of materials due to temperature variations. Understanding this phenomenon is essential for a wide range of scientific and engineering applications, from the design of structures to the development of temperature-sensing devices. By harnessing the effects of thermal expansion,engineers can create innovative solutions that improve our lives and enhance technological advancements.。

泰山地形对一次副高边缘大暴雨过程影响的观测分析

doi:10.11676/qxxb2024.20230094气象学报泰山地形对一次副高边缘大暴雨过程影响的观测分析*郑丽娜1 孙继松2ZHENG Lina1 SUN Jisong21. 济南市气象台，济南，2501022. 中国气象科学研究院灾害天气国家重点实验室，北京，1000811. Jinan Meteorological Observatory，Jinan 250102，China2. State Key Laboratory of Severe Weather，Chinese Academy of Meteorological Sciences，Beijing 100081，China2023-06-16收稿，2023-09-04改回.郑丽娜，孙继松. 2024. 泰山地形对一次副高边缘大暴雨过程影响的观测分析. 气象学报，82（2）：155-167Zheng Lina， Sun Jisong. 2024. Observational analysis of the topographic effect of Mount Tai on an extreme rainfall event occurring at the edge of the subtropical high. Acta Meteorologica Sinica， 82（2）:155-167Abstract Intense observations of precipitation around the Mount Tai during an extreme heavy rain event in autumn 2022 in Shandong province by regional automatic weather stations, radars, wind profilers and satellites are analyzed and possible reasons for the precipitation distribution are explored. The results are as follows：(1) The heavy rain event in Shandong occurred under the background of strong southerly flow in the middle and lower troposphere, and the period of heavy rainfall was concentrated from 23:00 BT 1 October to 02:00 BT the next day. The 100 mm rainfall contour showed a "reverse bow" shape, stretching across the north and west sides of the Mount Tai, with over 170 mm of precipitation at each center. In contrast, rainfall on the south side of the Mount Tai was significantly weaker. (2) Heavy rain belts corresponded to the convergence line-mesoscale vortex system on the ground. The mesoscale vortex on the west side of the Mount Tai formed due to the encounter of the cold flow around the north side of the mountain and the warm flow around the south side. It resulted in a strong precipitation center with single-peak precipitation on the west side of the Mount Tai. The convergence line on the north side of the mountain was sustained and rebuilt, resulting in longer precipitation time and greater accumulated precipitation on the north side of Mount Tai. Hourly precipitation on the north side exhibited a double peak pattern. (3) The two precipitation peaks observed on the north side of the Mount Tai corresponded to the two parallel echo bands of radar reflectivity. The first echo band was located on the north slope of the Mount Tai and remained quasi-stationary for a long time, which corresponded to the ascending branch of the horizontal vorticity circulation on the north side of the Mount Tai. Its formation mechanism is the strong development and maintenance of horizontal vorticity due to the southwesterly low-level jet with strong vertical shear and the northeasterly airflow obstructed by the mountain at low levels in nighttime. The second precipitation echo band corresponded to a cold front cloud system. When it approached the north side of the Mount Tai, it was influenced by the leeward upslope southwesterly low-level airflow, resulting in an increase in the radar reflectivity factor. The corresponding ground wind field was featured by a reconstruction process of the convergence line. (4) On the west side of the Mount Tai, the ground convergence line moved southeastward under the drive of low-level cold air, causing the echo band to gradually evolve into a "reverse bow" shape and the heavy rain band also exhibited a "reverse bow" distribution. The south side of the Mount Tai is located under the subsidence branch of the horizontal vorticity formed by strong vertical shear low-level jet, where precipitation was significantly less compared to that in the north and west sides.Key words Mount Tai range， Circumferential motion， Low-level jet， Horizontal vorticity circulation* 资助课题：2023年中国气象局复盘专项（FPZJ2023—074）、中国气象局气象软科学重点项目（2023ZDIANXM03）。

蒸汽管线绝热材料保温性能衰减影响研究

引文：王克平，李栋，张谧，等．蒸汽管线绝热材料保温性能衰减影响研究[J]．石油石化节能，2023，13（3）：74-78.WANG Keping，LI Dong，ZHANG Mi，et al．Research on the decaying effect of thermal insulation performance for the insulation materials of steam pipeline[J]．Energy Conservation in Petroleum&PetroChemical Industry，2023，13（3）：74-78.蒸汽管线绝热材料保温性能衰减影响研究王克平1李栋2张谧3李天奎4刘屹然2孙伟栋5吴洋洋2花凌旭6（1.东北石油大学机械科学与工程学院；2.东北石油大学土木建筑工程学院；3.中国石油海洋工程有限公司工程设计院；4.青岛市特种设备检验检测研究院；5.管网集团（徐州）管道检验检测有限公司；6.新疆油田公司采油一厂）摘要：绝热材料是保证蒸汽管线保温效益的关键，而绝热材料老化则会造成保温性能衰减影响其保温效益。

为提高保温性能，建立了蒸汽管线保温效益理论分析模型，研究了三种绝热材料老化引起保温性能衰减对蒸汽管线保温效益的影响，并分析了绝热材料服役年限的影响。

研究结果表明：服役时间为20a时，硅酸盐毡绝热材料老化对其保温性能影响结果最大，与未考虑老化时相比，其经济厚度、热量损失以及年平均总费用增幅分别为15.15%、36.14%、33.83%；服役时间较短时建议选用硅酸盐瓦绝热材料，当服役时间较长时选用气凝胶绝热材料。

关键词：绝热材料；蒸汽管线；保温效益；保温性能；经济厚度DOI:10.3969/j.issn.2095-1493.2023.03.016Research on the decaying effect of thermal insulation performance for the insulation materials of steam pipelineWANG Keping1，LI Dong2，ZHANG Mi3，LI Tiankui4，LIU Yiran2，SUN Weidong5，WU Yangyang2，HUA Lingxu61School of Mechanical Science&Engineering，Northeast Petroleum University2School of Civil Engineering，Northeast Petroleum University3Engineering Design Institute，CPOE4Special Equipment Inspection and Testing Institute of Qingdao5Pipeline Inspection and Testing Co．，Ltd．，PipeChina(Xuzhou)6No.1Oil Production Plant of Xinjiang Oilfield CompanyAbstract：The insulation material is the key to ensure the thermal insulation benefits of steam pipeline．However，the decaying effect of thermal insulation performance caused by aging of insulation material is affected its thermal insulation benefit．The theoretical analysis model of thermal insulation benefit of steam pipeline was established．The influence of aging on the thermal insulation performance of three kinds of insulation materials for the thermal insulation benefits of steam pipeline was studied，and the influence of service life of insulation materials was analyzed．The results show that when the service time is20years，the aging of silicate felt insulation material has the greatest impact on its thermal insula-tion pared with that without aging，the increase of economic thickness，heat loss and annual average total cost are15.15%，36.14%and33.83%respectively．When the service time is short，silicate tile insulation material is recommended.Aerogel insulation material is chosen when the service time is longer.Keywords：insulation materials；steam pipeline；thermal insulation benefits；thermal insulation per-formance；economic thickness第一作者简介：王克平，在读硕士研究生，2021年就读于东北石油大学（能源动力专业），主要研究方向：油田节能降耗，152****7085，********************，黑龙江省大庆市高新技术开发区学府街99号东北石油大学，163318。

温度对半导体影响的书

温度对半导体影响的书英文回答：The effect of temperature on semiconductors is acrucial aspect to consider in the field of electronics. As temperature changes, it can have both positive and negative impacts on the performance and reliability of semiconductor devices.One of the main effects of temperature on semiconductors is the change in electrical conductivity. Generally, as temperature increases, the conductivity of a semiconductor also increases. This is due to the increased thermal energy, which allows more charge carriers to move freely within the material. As a result, the resistance of the semiconductor decreases, and it becomes more conductive.However, this positive effect of temperature on conductivity can also have negative consequences. For instance, if the temperature rises too high, it can lead tothermal runaway, where the increased conductivity causes excessive heating and further increases the temperature. This can ultimately result in the device failing or even burning out.Another important effect of temperature on semiconductors is the impact on bandgap energy. The bandgap energy is the energy difference between the valence band and the conduction band in a semiconductor. At higher temperatures, the bandgap energy decreases, which meansthat the semiconductor becomes more conductive and allows more charge carriers to move across the bandgap. This can affect the performance of devices such as diodes and transistors, as it can lead to increased leakage currents and reduced efficiency.Furthermore, temperature can also affect the mobility of charge carriers in semiconductors. Mobility refers to the ease with which charge carriers can move through the material. At higher temperatures, the mobility of both electrons and holes in a semiconductor generally increases. This can lead to improved device performance, as the chargecarriers can move more freely and quickly. However, at extremely high temperatures, the mobility can besignificantly reduced due to scattering effects, which can negatively impact device performance.In addition to these electrical effects, temperaturecan also affect the mechanical properties of semiconductors. For example, as the temperature changes, the coefficient of thermal expansion of the semiconductor material can cause stress and strain in the device. This can lead to mechanical failure or even cracking of the semiconductor.中文回答：温度对半导体的影响是电子领域中需要考虑的一个关键因素。

热红外传感史

History of infrared detectorsA.ROGALSKI*Institute of Applied Physics, Military University of Technology, 2 Kaliskiego Str.,00–908 Warsaw, PolandThis paper overviews the history of infrared detector materials starting with Herschel’s experiment with thermometer on February11th,1800.Infrared detectors are in general used to detect,image,and measure patterns of the thermal heat radia−tion which all objects emit.At the beginning,their development was connected with thermal detectors,such as ther−mocouples and bolometers,which are still used today and which are generally sensitive to all infrared wavelengths and op−erate at room temperature.The second kind of detectors,called the photon detectors,was mainly developed during the20th Century to improve sensitivity and response time.These detectors have been extensively developed since the1940’s.Lead sulphide(PbS)was the first practical IR detector with sensitivity to infrared wavelengths up to~3μm.After World War II infrared detector technology development was and continues to be primarily driven by military applications.Discovery of variable band gap HgCdTe ternary alloy by Lawson and co−workers in1959opened a new area in IR detector technology and has provided an unprecedented degree of freedom in infrared detector design.Many of these advances were transferred to IR astronomy from Departments of Defence ter on civilian applications of infrared technology are frequently called“dual−use technology applications.”One should point out the growing utilisation of IR technologies in the civilian sphere based on the use of new materials and technologies,as well as the noticeable price decrease in these high cost tech−nologies.In the last four decades different types of detectors are combined with electronic readouts to make detector focal plane arrays(FPAs).Development in FPA technology has revolutionized infrared imaging.Progress in integrated circuit design and fabrication techniques has resulted in continued rapid growth in the size and performance of these solid state arrays.Keywords:thermal and photon detectors, lead salt detectors, HgCdTe detectors, microbolometers, focal plane arrays.Contents1.Introduction2.Historical perspective3.Classification of infrared detectors3.1.Photon detectors3.2.Thermal detectors4.Post−War activity5.HgCdTe era6.Alternative material systems6.1.InSb and InGaAs6.2.GaAs/AlGaAs quantum well superlattices6.3.InAs/GaInSb strained layer superlattices6.4.Hg−based alternatives to HgCdTe7.New revolution in thermal detectors8.Focal plane arrays – revolution in imaging systems8.1.Cooled FPAs8.2.Uncooled FPAs8.3.Readiness level of LWIR detector technologies9.SummaryReferences 1.IntroductionLooking back over the past1000years we notice that infra−red radiation(IR)itself was unknown until212years ago when Herschel’s experiment with thermometer and prism was first reported.Frederick William Herschel(1738–1822) was born in Hanover,Germany but emigrated to Britain at age19,where he became well known as both a musician and an astronomer.Herschel became most famous for the discovery of Uranus in1781(the first new planet found since antiquity)in addition to two of its major moons,Tita−nia and Oberon.He also discovered two moons of Saturn and infrared radiation.Herschel is also known for the twenty−four symphonies that he composed.W.Herschel made another milestone discovery–discov−ery of infrared light on February11th,1800.He studied the spectrum of sunlight with a prism[see Fig.1in Ref.1],mea−suring temperature of each colour.The detector consisted of liquid in a glass thermometer with a specially blackened bulb to absorb radiation.Herschel built a crude monochromator that used a thermometer as a detector,so that he could mea−sure the distribution of energy in sunlight and found that the highest temperature was just beyond the red,what we now call the infrared(‘below the red’,from the Latin‘infra’–be−OPTO−ELECTRONICS REVIEW20(3),279–308DOI: 10.2478/s11772−012−0037−7*e−mail: rogan@.pllow)–see Fig.1(b)[2].In April 1800he reported it to the Royal Society as dark heat (Ref.1,pp.288–290):Here the thermometer No.1rose 7degrees,in 10minu−tes,by an exposure to the full red coloured rays.I drew back the stand,till the centre of the ball of No.1was just at the vanishing of the red colour,so that half its ball was within,and half without,the visible rays of theAnd here the thermometerin 16minutes,degrees,when its centre was inch out of the raysof the sun.as had a rising of 9de−grees,and here the difference is almost too trifling to suppose,that latter situation of the thermometer was much beyond the maximum of the heating power;while,at the same time,the experiment sufficiently indi−cates,that the place inquired after need not be looked for at a greater distance.Making further experiments on what Herschel called the ‘calorific rays’that existed beyond the red part of the spec−trum,he found that they were reflected,refracted,absorbed and transmitted just like visible light [1,3,4].The early history of IR was reviewed about 50years ago in three well−known monographs [5–7].Many historical information can be also found in four papers published by Barr [3,4,8,9]and in more recently published monograph [10].Table 1summarises the historical development of infrared physics and technology [11,12].2.Historical perspectiveFor thirty years following Herschel’s discovery,very little progress was made beyond establishing that the infrared ra−diation obeyed the simplest laws of optics.Slow progress inthe study of infrared was caused by the lack of sensitive and accurate detectors –the experimenters were handicapped by the ordinary thermometer.However,towards the second de−cade of the 19th century,Thomas Johann Seebeck began to examine the junction behaviour of electrically conductive materials.In 1821he discovered that a small electric current will flow in a closed circuit of two dissimilar metallic con−ductors,when their junctions are kept at different tempera−tures [13].During that time,most physicists thought that ra−diant heat and light were different phenomena,and the dis−covery of Seebeck indirectly contributed to a revival of the debate on the nature of heat.Due to small output vol−tage of Seebeck’s junctions,some μV/K,the measurement of very small temperature differences were prevented.In 1829L.Nobili made the first thermocouple and improved electrical thermometer based on the thermoelectric effect discovered by Seebeck in 1826.Four years later,M.Melloni introduced the idea of connecting several bismuth−copper thermocouples in series,generating a higher and,therefore,measurable output voltage.It was at least 40times more sensitive than the best thermometer available and could de−tect the heat from a person at a distance of 30ft [8].The out−put voltage of such a thermopile structure linearly increases with the number of connected thermocouples.An example of thermopile’s prototype invented by Nobili is shown in Fig.2(a).It consists of twelve large bismuth and antimony elements.The elements were placed upright in a brass ring secured to an adjustable support,and were screened by a wooden disk with a 15−mm central aperture.Incomplete version of the Nobili−Melloni thermopile originally fitted with the brass cone−shaped tubes to collect ra−diant heat is shown in Fig.2(b).This instrument was much more sensi−tive than the thermometers previously used and became the most widely used detector of IR radiation for the next half century.The third member of the trio,Langley’s bolometer appea−red in 1880[7].Samuel Pierpont Langley (1834–1906)used two thin ribbons of platinum foil connected so as to form two arms of a Wheatstone bridge (see Fig.3)[15].This instrument enabled him to study solar irradiance far into its infrared region and to measure theintensityof solar radia−tion at various wavelengths [9,16,17].The bolometer’s sen−History of infrared detectorsFig.1.Herschel’s first experiment:A,B –the small stand,1,2,3–the thermometers upon it,C,D –the prism at the window,E –the spec−trum thrown upon the table,so as to bring the last quarter of an inch of the read colour upon the stand (after Ref.1).InsideSir FrederickWilliam Herschel (1738–1822)measures infrared light from the sun– artist’s impression (after Ref. 2).Fig.2.The Nobili−Meloni thermopiles:(a)thermopile’s prototype invented by Nobili (ca.1829),(b)incomplete version of the Nobili−−Melloni thermopile (ca.1831).Museo Galileo –Institute and Museum of the History of Science,Piazza dei Giudici 1,50122Florence, Italy (after Ref. 14).Table 1. Milestones in the development of infrared physics and technology (up−dated after Refs. 11 and 12)Year Event1800Discovery of the existence of thermal radiation in the invisible beyond the red by W. HERSCHEL1821Discovery of the thermoelectric effects using an antimony−copper pair by T.J. SEEBECK1830Thermal element for thermal radiation measurement by L. NOBILI1833Thermopile consisting of 10 in−line Sb−Bi thermal pairs by L. NOBILI and M. MELLONI1834Discovery of the PELTIER effect on a current−fed pair of two different conductors by J.C. PELTIER1835Formulation of the hypothesis that light and electromagnetic radiation are of the same nature by A.M. AMPERE1839Solar absorption spectrum of the atmosphere and the role of water vapour by M. MELLONI1840Discovery of the three atmospheric windows by J. HERSCHEL (son of W. HERSCHEL)1857Harmonization of the three thermoelectric effects (SEEBECK, PELTIER, THOMSON) by W. THOMSON (Lord KELVIN)1859Relationship between absorption and emission by G. KIRCHHOFF1864Theory of electromagnetic radiation by J.C. MAXWELL1873Discovery of photoconductive effect in selenium by W. SMITH1876Discovery of photovoltaic effect in selenium (photopiles) by W.G. ADAMS and A.E. DAY1879Empirical relationship between radiation intensity and temperature of a blackbody by J. STEFAN1880Study of absorption characteristics of the atmosphere through a Pt bolometer resistance by S.P. LANGLEY1883Study of transmission characteristics of IR−transparent materials by M. MELLONI1884Thermodynamic derivation of the STEFAN law by L. BOLTZMANN1887Observation of photoelectric effect in the ultraviolet by H. HERTZ1890J. ELSTER and H. GEITEL constructed a photoemissive detector consisted of an alkali−metal cathode1894, 1900Derivation of the wavelength relation of blackbody radiation by J.W. RAYEIGH and W. WIEN1900Discovery of quantum properties of light by M. PLANCK1903Temperature measurements of stars and planets using IR radiometry and spectrometry by W.W. COBLENTZ1905 A. EINSTEIN established the theory of photoelectricity1911R. ROSLING made the first television image tube on the principle of cathode ray tubes constructed by F. Braun in 18971914Application of bolometers for the remote exploration of people and aircrafts ( a man at 200 m and a plane at 1000 m)1917T.W. CASE developed the first infrared photoconductor from substance composed of thallium and sulphur1923W. SCHOTTKY established the theory of dry rectifiers1925V.K. ZWORYKIN made a television image tube (kinescope) then between 1925 and 1933, the first electronic camera with the aid of converter tube (iconoscope)1928Proposal of the idea of the electro−optical converter (including the multistage one) by G. HOLST, J.H. DE BOER, M.C. TEVES, and C.F. VEENEMANS1929L.R. KOHLER made a converter tube with a photocathode (Ag/O/Cs) sensitive in the near infrared1930IR direction finders based on PbS quantum detectors in the wavelength range 1.5–3.0 μm for military applications (GUDDEN, GÖRLICH and KUTSCHER), increased range in World War II to 30 km for ships and 7 km for tanks (3–5 μm)1934First IR image converter1939Development of the first IR display unit in the United States (Sniperscope, Snooperscope)1941R.S. OHL observed the photovoltaic effect shown by a p−n junction in a silicon1942G. EASTMAN (Kodak) offered the first film sensitive to the infrared1947Pneumatically acting, high−detectivity radiation detector by M.J.E. GOLAY1954First imaging cameras based on thermopiles (exposure time of 20 min per image) and on bolometers (4 min)1955Mass production start of IR seeker heads for IR guided rockets in the US (PbS and PbTe detectors, later InSb detectors for Sidewinder rockets)1957Discovery of HgCdTe ternary alloy as infrared detector material by W.D. LAWSON, S. NELSON, and A.S. YOUNG1961Discovery of extrinsic Ge:Hg and its application (linear array) in the first LWIR FLIR systems1965Mass production start of IR cameras for civil applications in Sweden (single−element sensors with optomechanical scanner: AGA Thermografiesystem 660)1970Discovery of charge−couple device (CCD) by W.S. BOYLE and G.E. SMITH1970Production start of IR sensor arrays (monolithic Si−arrays: R.A. SOREF 1968; IR−CCD: 1970; SCHOTTKY diode arrays: F.D.SHEPHERD and A.C. YANG 1973; IR−CMOS: 1980; SPRITE: T. ELIOTT 1981)1975Lunch of national programmes for making spatially high resolution observation systems in the infrared from multielement detectors integrated in a mini cooler (so−called first generation systems): common module (CM) in the United States, thermal imaging commonmodule (TICM) in Great Britain, syteme modulaire termique (SMT) in France1975First In bump hybrid infrared focal plane array1977Discovery of the broken−gap type−II InAs/GaSb superlattices by G.A. SAI−HALASZ, R. TSU, and L. ESAKI1980Development and production of second generation systems [cameras fitted with hybrid HgCdTe(InSb)/Si(readout) FPAs].First demonstration of two−colour back−to−back SWIR GaInAsP detector by J.C. CAMPBELL, A.G. DENTAI, T.P. LEE,and C.A. BURRUS1985Development and mass production of cameras fitted with Schottky diode FPAs (platinum silicide)1990Development and production of quantum well infrared photoconductor (QWIP) hybrid second generation systems1995Production start of IR cameras with uncooled FPAs (focal plane arrays; microbolometer−based and pyroelectric)2000Development and production of third generation infrared systemssitivity was much greater than that of contemporary thermo−piles which were little improved since their use by Melloni. Langley continued to develop his bolometer for the next20 years(400times more sensitive than his first efforts).His latest bolometer could detect the heat from a cow at a dis−tance of quarter of mile [9].From the above information results that at the beginning the development of the IR detectors was connected with ther−mal detectors.The first photon effect,photoconductive ef−fect,was discovered by Smith in1873when he experimented with selenium as an insulator for submarine cables[18].This discovery provided a fertile field of investigation for several decades,though most of the efforts were of doubtful quality. By1927,over1500articles and100patents were listed on photosensitive selenium[19].It should be mentioned that the literature of the early1900’s shows increasing interest in the application of infrared as solution to numerous problems[7].A special contribution of William Coblenz(1873–1962)to infrared radiometry and spectroscopy is marked by huge bib−liography containing hundreds of scientific publications, talks,and abstracts to his credit[20,21].In1915,W.Cob−lentz at the US National Bureau of Standards develops ther−mopile detectors,which he uses to measure the infrared radi−ation from110stars.However,the low sensitivity of early in−frared instruments prevented the detection of other near−IR sources.Work in infrared astronomy remained at a low level until breakthroughs in the development of new,sensitive infrared detectors were achieved in the late1950’s.The principle of photoemission was first demonstrated in1887when Hertz discovered that negatively charged par−ticles were emitted from a conductor if it was irradiated with ultraviolet[22].Further studies revealed that this effect could be produced with visible radiation using an alkali metal electrode [23].Rectifying properties of semiconductor−metal contact were discovered by Ferdinand Braun in1874[24],when he probed a naturally−occurring lead sulphide(galena)crystal with the point of a thin metal wire and noted that current flowed freely in one direction only.Next,Jagadis Chandra Bose demonstrated the use of galena−metal point contact to detect millimetre electromagnetic waves.In1901he filed a U.S patent for a point−contact semiconductor rectifier for detecting radio signals[25].This type of contact called cat’s whisker detector(sometimes also as crystal detector)played serious role in the initial phase of radio development.How−ever,this contact was not used in a radiation detector for the next several decades.Although crystal rectifiers allowed to fabricate simple radio sets,however,by the mid−1920s the predictable performance of vacuum−tubes replaced them in most radio applications.The period between World Wars I and II is marked by the development of photon detectors and image converters and by emergence of infrared spectroscopy as one of the key analytical techniques available to chemists.The image con−verter,developed on the eve of World War II,was of tre−mendous interest to the military because it enabled man to see in the dark.The first IR photoconductor was developed by Theodore W.Case in1917[26].He discovered that a substance com−posed of thallium and sulphur(Tl2S)exhibited photocon−ductivity.Supported by the US Army between1917and 1918,Case adapted these relatively unreliable detectors for use as sensors in an infrared signalling device[27].The pro−totype signalling system,consisting of a60−inch diameter searchlight as the source of radiation and a thallous sulphide detector at the focus of a24−inch diameter paraboloid mir−ror,sent messages18miles through what was described as ‘smoky atmosphere’in1917.However,instability of resis−tance in the presence of light or polarizing voltage,loss of responsivity due to over−exposure to light,high noise,slug−gish response and lack of reproducibility seemed to be inhe−rent weaknesses.Work was discontinued in1918;commu−nication by the detection of infrared radiation appeared dis−tinctly ter Case found that the addition of oxygen greatly enhanced the response [28].The idea of the electro−optical converter,including the multistage one,was proposed by Holst et al.in1928[29]. The first attempt to make the converter was not successful.A working tube consisted of a photocathode in close proxi−mity to a fluorescent screen was made by the authors in 1934 in Philips firm.In about1930,the appearance of the Cs−O−Ag photo−tube,with stable characteristics,to great extent discouraged further development of photoconductive cells until about 1940.The Cs−O−Ag photocathode(also called S−1)elabo−History of infrared detectorsFig.3.Longley’s bolometer(a)composed of two sets of thin plati−num strips(b),a Wheatstone bridge,a battery,and a galvanometer measuring electrical current (after Ref. 15 and 16).rated by Koller and Campbell[30]had a quantum efficiency two orders of magnitude above anything previously studied, and consequently a new era in photoemissive devices was inaugurated[31].In the same year,the Japanese scientists S. Asao and M.Suzuki reported a method for enhancing the sensitivity of silver in the S−1photocathode[32].Consisted of a layer of caesium on oxidized silver,S−1is sensitive with useful response in the near infrared,out to approxi−mately1.2μm,and the visible and ultraviolet region,down to0.3μm.Probably the most significant IR development in the United States during1930’s was the Radio Corporation of America(RCA)IR image tube.During World War II, near−IR(NIR)cathodes were coupled to visible phosphors to provide a NIR image converter.With the establishment of the National Defence Research Committee,the develop−ment of this tube was accelerated.In1942,the tube went into production as the RCA1P25image converter(see Fig.4).This was one of the tubes used during World War II as a part of the”Snooperscope”and”Sniperscope,”which were used for night observation with infrared sources of illumination.Since then various photocathodes have been developed including bialkali photocathodes for the visible region,multialkali photocathodes with high sensitivity ex−tending to the infrared region and alkali halide photocatho−des intended for ultraviolet detection.The early concepts of image intensification were not basically different from those today.However,the early devices suffered from two major deficiencies:poor photo−cathodes and poor ter development of both cathode and coupling technologies changed the image in−tensifier into much more useful device.The concept of image intensification by cascading stages was suggested independently by number of workers.In Great Britain,the work was directed toward proximity focused tubes,while in the United State and in Germany–to electrostatically focused tubes.A history of night vision imaging devices is given by Biberman and Sendall in monograph Electro−Opti−cal Imaging:System Performance and Modelling,SPIE Press,2000[10].The Biberman’s monograph describes the basic trends of infrared optoelectronics development in the USA,Great Britain,France,and Germany.Seven years later Ponomarenko and Filachev completed this monograph writ−ing the book Infrared Techniques and Electro−Optics in Russia:A History1946−2006,SPIE Press,about achieve−ments of IR techniques and electrooptics in the former USSR and Russia [33].In the early1930’s,interest in improved detectors began in Germany[27,34,35].In1933,Edgar W.Kutzscher at the University of Berlin,discovered that lead sulphide(from natural galena found in Sardinia)was photoconductive and had response to about3μm.B.Gudden at the University of Prague used evaporation techniques to develop sensitive PbS films.Work directed by Kutzscher,initially at the Uni−versity of Berlin and later at the Electroacustic Company in Kiel,dealt primarily with the chemical deposition approach to film formation.This work ultimately lead to the fabrica−tion of the most sensitive German detectors.These works were,of course,done under great secrecy and the results were not generally known until after1945.Lead sulphide photoconductors were brought to the manufacturing stage of development in Germany in about1943.Lead sulphide was the first practical infrared detector deployed in a variety of applications during the war.The most notable was the Kiel IV,an airborne IR system that had excellent range and which was produced at Carl Zeiss in Jena under the direction of Werner K. Weihe [6].In1941,Robert J.Cashman improved the technology of thallous sulphide detectors,which led to successful produc−tion[36,37].Cashman,after success with thallous sulphide detectors,concentrated his efforts on lead sulphide detec−tors,which were first produced in the United States at Northwestern University in1944.After World War II Cash−man found that other semiconductors of the lead salt family (PbSe and PbTe)showed promise as infrared detectors[38]. The early detector cells manufactured by Cashman are shown in Fig. 5.Fig.4.The original1P25image converter tube developed by the RCA(a).This device measures115×38mm overall and has7pins.It opera−tion is indicated by the schematic drawing (b).After1945,the wide−ranging German trajectory of research was essentially the direction continued in the USA, Great Britain and Soviet Union under military sponsorship after the war[27,39].Kutzscher’s facilities were captured by the Russians,thus providing the basis for early Soviet detector development.From1946,detector technology was rapidly disseminated to firms such as Mullard Ltd.in Southampton,UK,as part of war reparations,and some−times was accompanied by the valuable tacit knowledge of technical experts.E.W.Kutzscher,for example,was flown to Britain from Kiel after the war,and subsequently had an important influence on American developments when he joined Lockheed Aircraft Co.in Burbank,California as a research scientist.Although the fabrication methods developed for lead salt photoconductors was usually not completely under−stood,their properties are well established and reproducibi−lity could only be achieved after following well−tried reci−pes.Unlike most other semiconductor IR detectors,lead salt photoconductive materials are used in the form of polycrys−talline films approximately1μm thick and with individual crystallites ranging in size from approximately0.1–1.0μm. They are usually prepared by chemical deposition using empirical recipes,which generally yields better uniformity of response and more stable results than the evaporative methods.In order to obtain high−performance detectors, lead chalcogenide films need to be sensitized by oxidation. The oxidation may be carried out by using additives in the deposition bath,by post−deposition heat treatment in the presence of oxygen,or by chemical oxidation of the film. The effect of the oxidant is to introduce sensitizing centres and additional states into the bandgap and thereby increase the lifetime of the photoexcited holes in the p−type material.3.Classification of infrared detectorsObserving a history of the development of the IR detector technology after World War II,many materials have been investigated.A simple theorem,after Norton[40],can be stated:”All physical phenomena in the range of about0.1–1 eV will be proposed for IR detectors”.Among these effects are:thermoelectric power(thermocouples),change in elec−trical conductivity(bolometers),gas expansion(Golay cell), pyroelectricity(pyroelectric detectors),photon drag,Jose−phson effect(Josephson junctions,SQUIDs),internal emis−sion(PtSi Schottky barriers),fundamental absorption(in−trinsic photodetectors),impurity absorption(extrinsic pho−todetectors),low dimensional solids[superlattice(SL), quantum well(QW)and quantum dot(QD)detectors], different type of phase transitions, etc.Figure6gives approximate dates of significant develop−ment efforts for the materials mentioned.The years during World War II saw the origins of modern IR detector tech−nology.Recent success in applying infrared technology to remote sensing problems has been made possible by the successful development of high−performance infrared de−tectors over the last six decades.Photon IR technology com−bined with semiconductor material science,photolithogra−phy technology developed for integrated circuits,and the impetus of Cold War military preparedness have propelled extraordinary advances in IR capabilities within a short time period during the last century [41].The majority of optical detectors can be classified in two broad categories:photon detectors(also called quantum detectors) and thermal detectors.3.1.Photon detectorsIn photon detectors the radiation is absorbed within the material by interaction with electrons either bound to lattice atoms or to impurity atoms or with free electrons.The observed electrical output signal results from the changed electronic energy distribution.The photon detectors show a selective wavelength dependence of response per unit incident radiation power(see Fig.8).They exhibit both a good signal−to−noise performance and a very fast res−ponse.But to achieve this,the photon IR detectors require cryogenic cooling.This is necessary to prevent the thermalHistory of infrared detectorsFig.5.Cashman’s detector cells:(a)Tl2S cell(ca.1943):a grid of two intermeshing comb−line sets of conducting paths were first pro−vided and next the T2S was evaporated over the grid structure;(b) PbS cell(ca.1945)the PbS layer was evaporated on the wall of the tube on which electrical leads had been drawn with aquadag(afterRef. 38).。

the tyndall effect介绍英文

the tyndall effect介绍英文English:The Tyndall effect, also known as Tyndall scattering, is the effect of light scattering in colloidal dispersion or in clear fluids with very small particles. When a beam of light passes through a colloid or a very fine suspension, the light is scattered by the particles, making the beam visible. This effect is named after John Tyndall, who first demonstrated it in 1869. The Tyndall effect is the reason why the sky appears blue, as the shorter wavelength blue light is scattered more than the longer wavelength red light by the gas molecules in the Earth's atmosphere, making the blue light more visible to the human eye. This effect is also commonly seen in everyday life, such as in the way light passes through a glass of water, making the beam visible. The Tyndall effect has important applications in various fields, including environmental monitoring, pharmaceuticals, and the food industry, where it can be used to determine the size and concentration of particles in a solution.中文翻译:泰德尔效应，也称为泰德尔散射，是指光在胶体分散体或具有微小颗粒的清澈液体中散射的效应。

大功率永磁同步发电机定子冷却系统优化分析

大功率永磁同步发电机定子冷却系统优化分析陈秀平，徐起连，李岩（江苏中车电机有限公司，江苏盐城224115）[摘要]为解决大功率永磁同步风力发电机发热问题，本文采用计算流体力学的方法对大功率永磁同步风力发电机定子冷却系统进行了优化分析。

结果表明：水冷系统的冷却管外壁与铁心之间存在的管孔间隙是影响铁心温度不可忽略的因素，采用工业导热硅脂进行填充，会很大程度上减小冷却管与铁心之间的接触热阻，降低铁心与绕组温度；电机运行时温度较高，乙二醇很容易酸败，造成的危害不容忽视，采用抑制性乙二醇水溶液可以解决其酸败问题。

[关键词]风力发电机；分析优化；导热硅脂；抑制性乙二醇[中图分类号]TM301.4+1[文献标志码]A[文章编号]1000-3983(2020)05-0029-05Optimal Analysis of Stator Cooling System ofLarge Power Permanent Magnet Synchronous GeneratorCHEN Xiuping,XU Qilian,LI Yan(CRRC Jiangsu Electric Co.,Ltd.,Yancheng224115,China)Abstract:The stator cooling system of medium-speed permanent magnet synchronous wind turbine is optimized by computational fluid dynamics.The results obtained are as follows:The effect of the gap between the outer wall of cooling pipe and iron core is not negligible,and the thermal contact resistance is reduced when the gap is filled with thermal conductive silicone grease,causing reduction of the temperature of iron core and winding.On the premise that the pressure difference between the inlet and outlet of water cooling system is less than3bar,the cooling effect is better with the increase of the flow rate of refrigerant.The temperature of turbine is high when it works,and glycol is easy to be acidified,and this problem can be solved by using inhibitory ethylene glycol.Key words:wind power generator;analysis and optimization;thermal conductive silicone grease; inhibitory ethylene glycol0前言随着大型电机制造技术的发展，大型电机内部单位体积内发热量随之增加，这样对电机通风散热就提出了更高的要求，通风系统的研究已成为电机设计研究的热点[1-4]。

伊士达高Tg、低CTE、多功能填充环氧树脂和酚醛固化层压板和预浸料IT-180ABS IT-180A

IT-180ABS/IT-180ATCHigh Tg, Low CTE, Multifunctional Filled Epoxy Resin and Phenolic-Cured Laminate & PrepregIT-180A is an advanced high Tg (175℃ by DSC) multifunctional filled epoxy with low CTE, high thermal reliability and CAF resistance. It’s design for high layer PCB and can pass 260℃ Lead free assembly and sequential lamination process.Key Features =============================== Advanced High Tg Resin TechnologyIndustrial standard material with high Tg (175℃ by DSC) multifunctional filled epoxy resin and excellent thermal reliability.Lead-Free Assembly CompatibleRoHS compliant and suitable for high thermal reliability needs, and Lead free assemblies with a maximum reflow temperature of 260℃. Friendly Processing and CAF ResistanceFriendly PCB process like high Tg FR4. Users can short the learning curve when using this material.CAF ResistanceLow thermal expansion coefficient (CTE) helps to excellent thermal reliability and CAF resistance providing long-term reliability for industrial boards and automobile application.Available in Variety of ConstructionsAvailable in a various of constructions, copper weights and glass styles, including standard(HTE), RTF and VLP copper foil. ApplicationsMultilayer and High Layer PCB AutomobileBackplanesServers and Networking TelecommunicationsData StorageHeavy Copper ApplicationIndustrial ApprovalUL 94 V-0IPC-4101C Spec / 99/ 101/ 126 RoHS CompliantGlobal AvailabilityArea Address Contact e-mail TELTaiwan 22,Kung Yen 1st Rd. Ping Chen Industry Zone. Ping Chen,Taoyuan, Taiwan, R.O.C.Sales: *************.twTechnician: *****************.tw886-3-4152345 #3168886-3-4152345 #5300East China Chun Hui Rd., Xishan Economic Development Zone,Wuxi City, Jiangsu Province, ChinaSales : ****************Technician: *********************86-510-8223-5888 #516886-510-8223-5888 #3000South China168, Dongfang Road, Nanfang Industrial Park, BeiceVillage, Humen Town, Dongguan City, Guangdong Province, China Sales: ***********.cnTechnician : ***************.cn86-769-88623268 #32086-769-88623268 #550Japan No.2, Huafang Rd, Yonghe Economic Zone, Economic andTechnological Development Zone, Guangzhou,Guangdong Province, ChinaSales: ****************.cnTechnician : *****************.tw86-20-6286-8088 #8027886-3-4152345 #5388USA Tapco Circuit Supply1225 Greenbriar Drive, Suite AAddison, IL 60101, USASales: *******************************Technician : ********************************1-614-937-52051-310-699-8028Europe ITEQ Europe,Via L. Pergher, 16 38121 Trento, Italy Sales: ********************Technician : *********************39-0461-82052639-0461-820526REV 06-12ITEQ Laminate/ Prepreg : IT-180ATC / IT-180ABS IPC-4101C Spec / 99 / 101 / 126LAMINATE( IT-180ATC)Thickness<0.50 mm[0.0197 in] Thickness≧0.50 mm[0.0197 in] Units T est MethodPropertyTypical Value Spec Typical Value SpecMetric(English)IPC-TM-650(or as noted)Peel Strength, minimumA. Low profile copper foil and very low profile copperfoil - all copper weights > 17µm [0.669 mil]B. Standard profile copper foil1.After Thermal Stress2.At 125°C [257 F]3.After Process Solutions 0.88 (5.0)1.23 (7.0)1.05 (6.0)1.05 (6.0)0.70 (4.00)0.80 (4.57)0.70 (4.00)0.55 (3.14)0.88 (5.0)1.40 (8.0)1.23 (7.0)1.23 (7.0)0.70 (4.00)1.05 (6.00)0.70 (4.00)0.80 (4.57)N/mm(lb/inch)2.4.82.4.8.22.4.8.3Volume Resistivity, minimumA. C-96/35/90B. After moisture resistanceC. At elevated temperature E-24/125 3.0x1010--5.0x1010106--103--3.0x10101.0x1010--104103MΩ-cm 2.5.17.1Surface Resistivity, minimumA. C-96/35/90B. After moisture resistanceC. At elevated temperature E-24/125 3.0x1010--4.0x1010104--103--3.0x10104.0x1010--104103MΩ 2.5.17.1Moisture Absorption, maximum -- -- 0.12 0.8 % 2.6.2.1 Dielectric Breakdown, minimum -- -- 60 40 kV 2.5.6 Permittivity (Dk, 50% resin content)(Laminate & Laminated Prepreg)A. 1MHzB. 1GHzC. 2GHzD. 5GHzE. 10GHz 4.44.44.24.14.05.44.44.44.34.14.15.4 --2.5.5.92.5.5.13Loss Tangent (Df, 50% resin content) (Laminate & Laminated Prepreg)A. 1MHzB. 1GHzC. 2GHzD. 5GHzE. 10GHz 0.0150.0150.0150.0160.0170.0350.0140.0150.0150.0160.0160.035 --2.5.5.92.5.5.13Flexural Strength, minimumA. Length directionB. Cross direction ----------------500-530(72,500-76,850)410-440(59,450-63,800)415(60,190)345(50,140)N/mm2(lb/in2)2.4.4Arc Resistance, minimum 125 60 125 60 s 2.5.1 Thermal Stress 10 s at 288°C [550.4F],minimumA. UnetchedB. Etched PassPassPass VisualPass VisualPassPassPass VisualPass VisualRating 2.4.13.1Electric Strength, minimum(Laminate & Laminated Prepreg)45 30 -- -- kV/mm 2.5.6.2 Flammability,(Laminate & Laminated Prepreg)V-0 V-0 V-0 V-0 Rating UL94 Glass Transition Temperature(DSC) 175 170 minimum 175 170 minimum ˚C 2.4.25Decomposition Temperature-- -- 345 340 minimum ˚C2.4.24.6 (5% wt loss)X/Y Axis CTE (40℃ to 125℃) -- -- 10-13 -- PPM/˚C 2.4.24 Z-Axis CTEA. Alpha 1B. Alpha 2C. 50 to 260 Degrees C ------------452102.760 maximum300 maximum3.0 maximumPPM/˚CPPM/˚C%2.4.24Thermal ResistanceA. T260B. T288 -------->60>3030 minimum15 minimumMinutesMinutes2.4.24.1CAF Resistance -- -- Pass AABUS Pass/Fail 2.6.25The above data and fabrication guide provide designers and PCB shop for their reference. We believe that these information are accurate, however, the data may vary depend on the test methods and specification used. The actual sales of the product should be according to specification in the agreement between ITEQ and its customer. ITEQ reserves the right to revise its data at any time without notice and maintain the best information available to users.REV 06-12。

Effect of high temperature treatment on the mechanical

Abstract The thermal treatment of wood is an alternative to the chemical treatment for preservation purposes.The heat treatment process improves wood’s resistance to decay and its dimensional stability.However,mechanical strength decreases as a result of heat treatment.Therefore,the treatment parameters have to be optimized to keep this loss at a minimum while improving other properties.Thermal treatment is new in North America,and its parameters are not yet ad-justed for the Canadian species.Carrying out the parameter adjustment in an industrial furnace requires many trials which are costly in terms of material and man-power.A laboratory study was carried out to determine the effect of different parameters of the heat treatment on the mechanical properties of birch in order to optimize this process.A thermogravimetric analyzer was built to carry out the laboratory tests.The impact of the process parameters–such as maximum treat-ment temperature,holding time at this temperature,heating rate,and gas humidity–on the mechanical properties of birch was investigated.Temperature distributions in wood and in gas as well as the weight loss of wood were measured during the experiments.Afterwards,hardness,modulus of elasticity,modulus of rupture,and resistance to screw withdrawal of the samples were measured.The relation between the process parameters and the resulting mechanical properties was examined.S.Poncsa´k (&)ÆD.Kocaefe ÆM.Bouazara Department of Applied Sciences,University of Quebec at Chicoutimi,555,boul.de l’Universite´,Chicoutimi,QC,Canada G7H 2B1e-mail:sponcsak@uqac.caA.PichetteDepartment of Fundamental Sciences,University of Quebec at Chicoutimi,Wood Sci Technol (2006)40:647–663DOI 10.1007/s00226-006-0082-9O R I G I N A LEffect of high temperature treatment on the mechanical properties of birch (Betula papyrifera )Sa ´ndor Poncsa ´k ÆDuygu Kocaefe ÆMohamed Bouazara ÆAndre PichetteReceived:21October 2005/Published online:18May 2006ÓSpringer-Verlag 2006List of symbolsb width of the sample(mm)d thickness of the sample(mm)d B diameter of the penetrating ball(mm)h penetration depthL plate separation(mm)m mass of wood sample(g)m0initial mass of wood sample(g)MOE modulus of elasticity(N/mm2)MOR modulus of rupture(N/mm2)P maximum load before rupture(N)P1load at the limit of the range of elasticity(N)P p maximum load applied during the penetration of steel ball into the wood sample(N)t time(min)t max duration of the heat treatment(min)t ref duration of the base case of the heat treatment(Table1)[min]y1displacement of the sample center at the limit of the range of elasticity (mm)W relative weight loss(non-dimensional)IntroductionThe most commonly used method of wood preservation is chemical treatment which involves the impregnation of chemical substances such as traditional oil(creosote, pentachloro-phenol)and chromated copper arsenate into the wood.Different preservation methods are sought in order to avoid the toxic effects of these chem-icals.Wood treatment at high temperature(thermo-transformation)is a very promising alternative to the chemical treatment.This method is different than conventional drying as explained below.During conventional drying,wood is heated to approximately120°C with exter-nally supplied superheated steam.During drying no structural change takes place in the wood,and water is only removed by evaporation.A minimum temperature of 140°C and prolonged drying times are required to remove the total moisture content (Amy1961).The absence of moisture in wood prevents the undesirable biochemical reactions and microbiological attacks.Full descriptions of the moist air and super-heated steam drying models are given in various papers(Pang et al.1994;Fhyr and Rasmuson1997;Johanson et al.1997;Pang1998).During the high temperature treatment,the wood species are heated slowly up to200–230°C in humid inert gas.This treatment reduces the hydrophilic behavior of the wood by modifying the chemical structure of some of its components (Raimo et al.1996;Gailliot1998).This modiﬁcation prevents the re-absorption of water which promotes wood decay.When wood absorbs humidity from its sur-roundings,water molecules are inserted between and within the wood polymers (lignin,cellulose,and hemicelluloses),and hydrogen bonds are formed.This phenomenon makes the wood swell.During the heat treatment,the number of(Hinterstoisser et al.2003).The latter creates cross-links between woodﬁbers and thus it signiﬁcantly reduces the ability of the water to penetrate into the wood (Homan et al.2000).The wood becomes dimensionally more stable compared to the untreated wood.Elimination of hydroxyl groups also reduces the number of potential anchor-points for fungi.During the heat treatment process,many volatile organic compounds–such as alcohols,resins,terpenes etc.–are produced and released from the wood (Manninen et al.2002;Graf et al.2003).Signiﬁcant decrease of hemicellulose content is also reported in the literature(Pavlo and Niemz2003).The hemicel-luloses degradeﬁrst(between160and260°C)since their low molecular weight and their branching structure facilitate a faster degradation compared to the other components present in wood(Fengel and Wegener1984).Hemicelluloses are nutrients to various kinds of fungi;therefore,they are one of the key components effecting wood decay(Fengel and Wegener1984).The removal of the branched hemicelluloses increases the crystallinity index of the cellulose between160and 220°C as reported in the literature(Fengel and Wegener1984;Weiland and Guyonnet2001).However,at temperatures higher than220°C,it decreases again. Cellulose is composed of linear chains which can crystallize,and hemicelluloses have an amorphous branched structure.As the hemicelluloses are eliminated,the crystallinity of wood increases temporarily around160–200°C.The exact tem-perature depends on the type of wood species.At the end of the thermal treat-ment,the wood is abruptly cooled down with a spray of water.During this period, the extractives and other water soluble secondary substances with low molecular weights which come from the decomposition of various wood components are partially captured by water.Their quantity depends on the wood species,tem-perature,and time of the heat treatment as well as on the moisture content of wood.Thermal treatment improves durability,prevents swelling and shrinking(Stamm et al.1946;Stamm1956),and gives a valuable dark color to the wood.It also modiﬁes the mechanical properties.Wood becomes more rigid and fragile,and the mechanical resistance decreases.Depending on the treatment parameters such as the maximum treatment temperature,the heating rate,the holding time at the maximum temperature or the gas humidity,cracks can appear and the cell structure can be partially degraded as well.Individual optimization of these parameters must be carried out separately for each wood species.Even the same wood species coming from places with different climates can have signiﬁcant dif-ferences in their cellular structures;therefore,they may require different treatment conditions.There are many technologies used for wood heat treatment in Europe:the PLATO process(Holland),the Retiﬁcation process(France),Bois Perdure process (France),OHT process(Germany),and the Thermo Wood process(Finland).The differences between these technologies are due to the design of the furnaces,gas composition,and the process parameters used(Militz2002).These processes have to be adapted to the Canadian wood species.This paper focuses on the inﬂuence of thermal treatment parameters on the mechanical properties of Canadian birch.The weight losses vs.time data measured during the experiments are analyzed,and the results are presented.Experimental set-up and experimental conditionsThermogravimetric systemA thermogravimetric analyzer was built to study the effect of the heat treatment parameters(maximum treatment temperature,heating rate,holding time,and gas humidity)on the birch quality(Fig.1).The variation of the temperature distribution within the wood and the weight loss of the wood were recorded during the treat-ment.The analyzer consists of an electrical furnace,a temperature controller,and a balance.The wood sample was suspended from the balance into the furnace.In industry,wood is heated with hot combustion gases.In this study,a mixture of inert gases with a composition similar to that of the industrial furnace is used to heat the wood sample.A programmable temperature controller assured the desired evolution of temperature in the furnace.The inert gas mixture(nitrogen,carbon dioxide,and water vapor)was used in order to prevent the oxidation reactions in the laboratory furnace.Nitrogen and carbon dioxideﬂow rates were controlled withﬂow meters.The gas humidity was adjusted using a second furnace which was placed directly under the main furnace. The latter was used to evaporate water and generate steam.Veryﬁne water droplets were injected into this furnace via a valve.The high temperature maintained in this furnace assured the instantaneous vaporization of water and thus the creation of hot steam.A second valve was used to evacuate the excess vapor.The opening and closing of both valves were done with a controller.Then,the steam was injected into the main furnace in order to adjust the humidity of the gas which was in contact with the wood sample.The presence of water vapor in gas is particularly important. Without humidity,wood dries too fast which increases the risk of crack formation (McCabe et al.1985).The outlet gas is evacuated from the system with a suction pump.An ice bed,as shown in Fig.1,was used to cool and collect condensable by-products,released from the wood.Parallel lines,equipped with timer controlled valves,were used to sepa-rate condensed by-products that were collected at different temperature intervals.Mechanical properties such as MOR,MOE,hardness,and resistance against screw withdrawal(RASW)of the wood were measured after treatment in order to study the impact of the heat treatment parameters on the birch quality.Preparation of the wood samplesThe birch(Betula papyrifera)samples treated during this study were obtained from a local sawmill of the Saguenay-Lac-Saint-Jean region of Quebec,Canada.The dimensions of the samples were0.035·0.035·0.2m3.They were pre-dried in air, and their initial moisture contents were5–12%before the heat treatment. Experimental procedureThe experiments were conducted in a thermogravimetric analyzer.Two groups of experiments were carried out.During theﬁrst group of experiments,the weight loss of the sample was continuously measured.In the second group,the same experi-ments were repeated under the same condition as that used for theﬁrst group;measured.For the temperature measurement experiments,the samples were equipped with ﬁve thermocouples as shown in Fig.2.An additional thermocouple was used to measure the gas temperature near the sample.The weight or temper-ature measurements were registered using a data acquisition system.During the experiments,wood samples were ﬁrst heated up to 120°C with a predetermined heating rate.The furnace temperature was kept constant at 120°C for half an hour to reduce the water content of wood before starting the thermo-chemical treatment which occurs at higher temperatures.Then,the samples were heated to a ﬁnal desired temperature with the same heating rate.In order to study the effect of the holding time at the maximum treatment temperature,the tem-perature was kept constant for a known period of time at the end of the treatment.Fig.1Schematic view of the thermogravimetric system:1sample,2main furnace,3temperature controller,4balance,5data acquisition system,6secondary furnace for steam generation,7water supply,8humidity controller,9valves,10gas,11gas and vapor evacuation line,12timer controlled valves,13Lixivia collection system,14cooling ice bed,15ﬂow meters,16suction pump,17aeration systembase case,the heating rate was 20°C/h,the maximum treatment temperature was 220°C,the gas humidity was 100g water/m 3gas,and there was no holding time.Only one parameter at a time was changed during the following experiments,and the effects of this parameter on the weight loss and mechanical properties were studied.Figure 3shows the heat treatment recipe used for the base case.Table 1presents the heat treatment parameters used during the experiments.Measurement of mechanical propertiesIn order to determine the effect of the treatment parameters on the mechanicalFig.3Recipe of the base case of the heat treatment of the wood samples used in the thermogravimetric analyzerrupture (MOR)measurements],the hardness,and screw withdrawal tests were carried out for the untreated and treated samples.Tests were carried out using the MTS ALLIANCE RT 100Universal Mechanical Test Machine and standard pro-cedures were respected.The relationship between the treatment conditions and the mechanical properties was examined.Three point static bending testThe ASTM D-143standard was followed during these tests.Ten to twelve birch samples (dimensions 1·1·20cm 3)were tested for each set of parameters.The plate separation (L)was 15.24cm and the vertical speed of the mobile head was1.3mm/min.The force was applied to the middle of the upper face of the sample in a radial direction.The MOE and the MOR were determined from the measured load–deformation curves using the equations given below (ASTM 2004):MOE ¼P 1L 34bd 3y 1ð1a ÞMOR ¼3PL ;ð1b Þwhere P is the maximum load before rupture,P 1and y 1denote the load and the displacement of the sample center at the limit of the range of elasticity,and b and d are the width and thickness of the samples,respectively (Fig.4a).Tests were re-peated ten times for every treatment parameter in both the radial and tangential directions.Penetration hardness testThe ASTM D-1324-83standard was followed during the test.Three samples (dimensions 3.5cm ·3.5cm ·20cm)were used for each set of parameters and the tests were repeated six times at both the radial and tangential faces for each sample.Figure 4b shows the hardness measurement and its parameters schematically.This Table 1Summary of heattreatment parameters a Base caseMaximaltemperature(°C)Heating rate (°C/h)Holding time (min)Humidity (g water vapor/m 3dry gas)120200100160200100200200100210200100220a2001002201001002203001002202015100220203010022020451002202000230200100penetration of a steel ball of11.3mm diameter(d B)at a constant penetration rate of 6mm/min.The tests were stopped when400N(P p)was reached and the penetration depth(h)was measured.During the tests,the displacement of the sample surfaces was also measured using a micrometer,and the results were corrected according to this measurement.Equation2shown below was used to determine the penetration hardness(H m)(ASTM2004):H m¼P pp d B hP p¼400N:ð2ÞThe tests were repeated eight times for every treatment parameter.Screw withdrawal testThis test,which was carried out according to the ASTM D-1761-88standard, permits the evaluation of the screw(N°10,25mm length)withdrawal resistance of wood.During such a test,the force required to pull out a screw from the wood sample is measured.This is another method to determine the mechanicalhstrength of wood.The screws were inserted at the middle of the sample top to the depth of2/3samples width.The speed of withdrawal of the screw was constant(2.54mm/min).The tests were repeated six times for every treatment parameter.The size of the samples was smaller than that required by the ASTM standards since the samples that can be treated in the thermogravimetric analyzer were small (0.035m·0.035m·0.2m).Using a small sample insures a more uniform tem-perature distribution during the treatment,and a uniformly treated product is ob-tained at the end of the treatment.Therefore,the standard tests were adjusted to the sample dimensions used in the experiments.The purpose here was to carry out only a comparative study in order to investigate and compare the effect of the treatment parameters on the mechanical properties.Results and discussionTemperature distribution in the wood sample during thermal treatmentFigure5shows the temperature distribution in the direction perpendicular to the sample length(horizontal direction).Theﬁgures showing the temperature effects are normalized using t max which is the total treatment time of a given experiment. It can be seen from thisﬁgure that the temperature of the birch sample follows the gas temperature with a small time-lag up to140–150°C.During this part, which is also called‘‘drying’’period,the maximum temperature difference ob-served between the center of the wood and the gas is20°C.The temperature at the center(TC4)of the sample is slightly lower than that close to the surface (TC2,TC5)as expected because the external surface of the wood is heated by hot gas.Around150±5°C,exothermic chemical reactions begin to take place within the wood.These reactions generate heat,and consequently,accelerate the rise of wood temperature which exceeds the gas temperature around170±5°C.Due to the heat generated by the exothermic reactions above150°C,the difference between the surface and the center temperatures disappears.The occurrence of these reactions atthe onset of thermo-transformation is also reported in the literature.Fengel isolated depolymerization products from wood treated at150°C in a nitrogen atmosphere (Fengel and Wegener1984).At higher temperatures,the wood temperature be-comes higher than the gas temperature.A maximum temperature difference of10°C is observed during the experiments.The wood temperatures recorded by the ther-mocouples TC2and TC5coincide perfectly showing that the temperature distribu-tion in the sample is symmetrical.Figure6shows the temperature distribution parallel to the sample length (vertical direction),measured by the thermocouples TC1,TC3(top and bottom), and TC4(center).The center temperature is slightly lower compared to those of the top and bottom before the onset of chemical reactions.As soon as chemical transformation begins,the center temperature increases and catches up with the top and bottom temperatures resulting in a uniform temperature distribution within the sample.Weight loss of the sample during thermal treatmentFigure7shows how the weight loss changes with time,measured with the thermo-gravimetric system for differentﬁnal temperatures at a constant heating rate of 20°C/h.The relative weight loss(W)is deﬁned as the ratio of the actual weight loss (m–m0)to the initial sample weight(m0)as shown below:W¼m0Àmm0:ð3ÞThe slight differences between the curves show the good repeatability of the tests. These differences are most likely the result of differences in initial humidity of the wood samples which varied between5and12%.The presence of two inﬂection points at each curve can be seen in thisﬁgure.Theﬁrst inﬂection point is observed at t/t max%0.48and T wood%110±5°C;and it corresponds to the drying process.Water starts to evaporate even at lower temperatures,but this phenomenon becomes sig-niﬁcant above100°C.This can be explained by the fact that the molecular diffusivityof water in wood increases with increasing temperature.Also,at high temperatures, the physical bonds between water and the hydrophilic groups of the wood are broken which facilitate the movement of water.These phenomena accelerate the weight loss rate with increasing temperature in this region.However,the quantity of water in the wood is limited.After a maximum rate,the weight lost slows down as water is depleted.In the second inﬂection point at t/t max%0.88and T wood%175±5°C,acceleration of the weight loss observed is probably caused by the release of different by-products during the degradation of the wood components such as hemicelluloses(heat treatment or thermal transformation period).Figure8shows the effect of heating rate on the weight loss.Since the time of treatment changes with heating rate,the total treatment time(t ref)of the base case (20°C/h heating rate)is chosen to calculate the relative time(t/t ref).Two inﬂection points described above are observed for the cases with10and20°C/h heating rates. For the case with the highest heating rate(30°C/h),it is not possible to observeclearly separate drying and heat transformation regions on the weight loss curve. This might be due to the lack of sufﬁcient time to eliminate the water,and the wood still contains a signiﬁcant quantity of moisture when chemical transformation begins. The presence of water in wood during the heat treatment catalyses the chain splitting by acidic hydrolysis and thus promotes the degradation of wood polymers(Raimo et al.1996;Kirk and Farell1987).On the other hand,the transformation of hemi-celluloses by water catalyzed hydrolysis makes the wood more resistant to mold attack(Kirk and Farell1987).The effect of gas humidity on the sample weight loss is shown in Fig.9.In this ﬁgure,the weight loss data are presented for two experiments carried out with humid (100g water vapor/m3)and dry gases.The absence of gas humidity causes a slight increase in the weight loss rate.If the humidity of gas is low,the difference between the moisture contents of the gas and the initially humid wood(moisture concen-tration gradient)is high.This increases the moisture removal rate and might cause crack formation in the wood especially around the knots as shown in Fig.10.In the absence of humidity in the heating gas,one to three cracks per samples were observed.No such failures were found in the samples treated in the presence of water vapor.Fig.10Crack formation on the wood sample heat treated with dry gas123Mechanical propertiesWood is a non-homogenous material;consequently,its mechanical properties can differ from one sample to the other.Therefore,mechanical tests were repeated6–12 times depending on the speciﬁc test in order to obtain statistically valid average values as explained below.Three point static bending testThis test shows the maximum load-carrying capacity of the sample.Figure11shows the inﬂuence of the maximum treatment temperature,holding time,heating rate, and gas humidity on the MOR.The effects of the same operating conditions on the MOE are presented in Fig.12.The results show that,the more the birch is subjected to heat(by using higher maximum temperatures or lower heating rates),the lower the MOR(Fig.11).This is probably due to the break-up of the hemicelluloses and cellulose polymers.It can be seen from thisﬁgure that the failure rate increases signiﬁcantly after200°C,although the exothermal chemical reactions begin between 150and160°C.A faster heating rate or a shorter holding time decreases the contact time between the hot gas and wood.Thus,the mechanical property loss is smaller compared to the samples subjected to hot gas for longer times.However,the impact of the holding time is not signiﬁcant;it is within the experimental error range.The elasticity of birch seems to be more or less constant under the experimental con-ditions used(Fig.12).Pavlo et al.reported similar tendencies.They found that MOR decreases when the heat treatment temperature decreases while MOE does not seem to be affected signiﬁcantly by the temperature(Pavlo and Niemz2003).Figures11d and12d show the effect of gas humidity on the MOR and the MOE, respectively.The MOR increases clearly with increasing gas humidity while the MOE shows a slight increase.The relative error of the bending test was±5–10%.Penetration hardness testThe hardness of birch in the tangential direction was found to be higher com-pared to that in the radial direction under various operating conditions as can be seen from Fig.13.As it can be seen from thisﬁgure the hardness increases slightly with temperature,especially above200°C.Around160°C a local maxi-mum of the hardness was observed,but the explanation of this phenomenon requires additional investigation.Those observations are in accordance with the literature(Pavlo and Niemz2003).The hardness of birch decreases with increasing holding time at the maximum treatment temperature(220°C)probably due to further structural degradation.Gas humidity and the heating rate do not seem to have a signiﬁcant effect on hardness(Fig.13c,d).The relative error of the screw hardness test was±2–8%.Screw withdrawal testThe results of the screw withdrawal tests are shown in Fig.14.The RASW starts to decrease gradually above200°C(Fig.14a).On the other hand,the holding time(Table1)at220°C does not seem to affect this property of the birch signiﬁcantly(Fig.14b).RASW increases with increasing heating rate(lower degradation)and decreases with increasing humidity of the drying gas(Fig.14c, 123d).It seems that changes in RASW and in MOR follow similar trends with respect to the treatment parameters.The relative error of the screw withdrawal test was ±3–5%.123ConclusionsThe principal conclusions of this study are summarized below.•When the heating rate is low,the drying and the thermal transformation periods can be clearly distinguished on the weight loss versus time diagrams of birch.At higher heating rates,these two phenomena can overlap.In this case,the wood moisture content cannot be eliminated during the drying period;therefore,wood still contains some moisture when the transformation starts at higher tempera-tures.This moisture might have some impact on the wood polymer degradation.•The temperature versus time diagrams show that exothermic reactions start be-tween150and160°C for birch.Below this temperature,only moisture and some extractives are removed by evaporation.The heat generated by the exothermic reactions above these temperatures causes an additional increase in wood tem-peratures.Wood temperature starts to exceed the gas temperature around170°C.The temperature distributions inside the birch samples were found to be sym-metrical.•Although the thermo-transformation(exothermic reactions)of wood begins around150–160°C,it accelerates signiﬁcantly only above200°C as indicated by the sample weight loss.This phenomenon coincides perfectly with the decrease in mechanical strength.•Mechanical properties such as the MOR and the RASW decrease with increasing treatment temperature,especially above200°C.The hardness increases slightly with temperature above200°C.Dry gas(0%humidity)can provoke crack for-mation which decreases theﬂexibility of birch.Slow heating rate has a similar impact on the mechanical properties as the higher treatment temperatures or the holding time at maximum treatment temperature.Due to a long contact time between hot gas and wood they cause deterioration in the mechanical strength of the birch.Fast heating rate can result in non-homogeneous and partially trans-formed wood especially for large samples.Acknowledgements The authors would like to thank the administration of the University of Quebec at Chicoutimi(UQAC),especially Mr.Sylvain Cloutier;the Foundation of University (FUQAC);our partners,especially,Mr.Adam Lapointe and Mr.Denis Lapointe of PCI Industries; Mrs.Josette Ross,expert in wood chemistry at UQAC;our technicians,Mr.Patrice Paquette,Mr. Julien Tremblay,and Mr.Jacques Allaire for their support and contributions.ReferencesAmy L(1961)The physico-chemical bases of the combustion of cellulose and ligneous materials.Cah du Centre Tech Du Bois45:30ASTM International(2004)Annual book of ASTM standards,Section4(construction),4.10(wood) Fengel D,Wegener G(1984)Wood,chemistry,ultrastructure,reactions.Walter de Gruyter&Co, BerlinFhyr C,Rasmuson A(1997)Some aspects of the modelling of wood chips drying in superheated steam.Int J Heat Mass Transfer40(12):2825–2842Gailliot FP(1998)Extraction and product capture in natural product isolation,Cannell.Humana Press,Totowa,pp59–68Graf N,Haas W,Bo¨chzelt H(2003)Characterization of gaseous emission from a small-size industrial plant for thermal wood modiﬁcation by GC/MS,In:van Acker J,Hill C(eds)The1st European 123。

New Perspectives on the Structure of Graphitic Carbons

Critical Reviews in Solid State and Materials Sciences,30:235–253,2005 Copyright c Taylor and Francis Inc.ISSN:1040-8436printDOI:10.1080/10408430500406265New Perspectives on the Structure of Graphitic CarbonsPeter J.F.Harris∗Centre for Advanced Microscopy,University of Reading,Whiteknights,Reading,RG66AF,UKGraphitic forms of carbon are important in a wide variety of applications,ranging from pollutioncontrol to composite materials,yet the structure of these carbons at the molecular level ispoorly understood.The discovery of fullerenes and fullerene-related structures such as carbonnanotubes has given a new perspective on the structure of solid carbon.This review aims toshow how the new knowledge gained as a result of research on fullerene-related carbons canbe applied to well-known forms of carbon such as microporous carbon,glassy carbon,carbonﬁbers,and carbon black.Keywords fullerenes,carbon nanotubes,carbon nanoparticles,non-graphitizing carbons,microporous carbon,glassy carbon,carbon black,carbonﬁbers.Table of Contents INTRODUCTION (235)FULLERENES,CARBON NANOTUBES,AND CARBON NANOPARTICLES (236)MICROPOROUS(NON-GRAPHITIZING)CARBONS (239)Background (239)Early Models (241)Evidence for Fullerene-Like Structures in Microporous Carbons (242)New Models for the Structure of Microporous Carbons (242)Carbonization and the Structural Evolution of Microporous Carbon (243)GLASSY CARBON (244)CARBON FIBERS (245)CARBON BLACK (248)Background (248)Structure of Carbon Black Particles (249)Effect of High-Temperature Heat Treatment on Carbon Black Structure (250)CONCLUSIONS (250)ACKNOWLEDGMENTS (251)REFERENCES (251)INTRODUCTIONUntil quite recently we knew for certain of just two allotropes of carbon:diamond and graphite.The vast range of carbon ma-∗E-mail:p.j.f.harris@ terials,both natural and synthetic,which have more disordered structures have traditionally been considered as variants of one or other of these two allotropes.Because the great majority of these materials contain sp2carbon rather than sp3carbon,their struc-tures have been thought of as being made up from tiny fragments235236P.J.F.HARRISFI G.1.(a)Model of PAN-derived carbon ﬁbres from the work of Crawford and Johnson,1(b)model of a non-graphitizing carbon by Ban and colleagues.2of crystalline graphite.Examples of models for the structures of carbons in which the basic elements are graphitic are reproduced in Figure 1.The structure shown in Figure 1(a)is a model for the structure of carbon ﬁbers suggested by Crawford and Johnson in 1971,1whereas 1(b)shows a model for non-graphitizing car-bon given by Ban and colleagues in 1975.2Both structures are constructed from bent or curved sheets of graphite,containing exclusively hexagonal rings.Although these models probably provide a good ﬁrst approximation of the structures of these car-bons,in many cases they fail to explain fully the properties of the materials.Consider the example of non-graphitizing carbons.As the name suggests,these cannot be transformed into crystalline graphite even at temperatures of 3000◦C and above.I nstead,high temperature heat treatments transform them into structures with a high degree of porosity but no long-range crystalline order.I n the model proposed by Ban et al.(Figure 1(b)),the structure is made up of ribbon-like sheets enclosing randomly shaped voids.It is most unlikely that such a structure could retain its poros-ity when subjected to high temperature heat treatment—surface energy would force the voids to collapse.The shortcomings of this and other “conventional”models are discussed more fully later in the article.The discovery of the fullerenes 3−5and subsequently of re-lated structures such as carbon nanotubes,6−8nanohorns,9,10and nanoparticles,11has given us a new paradigm for solid car-bon structures.We now know that carbons containing pentago-nal rings,as well as other non-six-membered rings,among the hexagonal sp 2carbon network,can be highly stable.This new perspective has prompted a number of groups to take a fresh look at well-known forms of carbon,to see whether any evidence can be found for the presence of fullerene-like structures.12−14The aim of this article is to review this new work on the structure of graphitic carbons,to assess whether models that incorporate fullerene-like elements could provide a better basis for under-standing these materials than the conventional models,and to point out areas where further work is needed.The carbon ma-terials considered include non-graphitizing carbon,glassy car-bon,carbon ﬁbers,and carbon black.The article begins with an outline of the main structural features of fullerenes,carbon nanotubes,and carbon nanoparticles,together with a brief dis-cussion of their stability.FULLERENES,CARBON NANOTUBES,AND CARBON NANOPARTICLESThe structure of C 60,the archetypal fullerene,is shown in Figure 2(a).The structure consists of twelve pentagonal rings and twenty hexagons in an icosahedral arrangement.I t will be noted that all the pentagons are isolated from each other.This is important,because adjacent pentagonal rings form an unstable bonding arrangement.All other closed-cage isomers of C 60,and all smaller fullerenes,are less stable than buck-minsterfullerene because they have adjacent pentagons.For higher fullerenes,the number of structures with isolated pen-tagonal rings increases rapidly with size.For example,C 100has 450isolated-pentagon isomers.16Most of these higher fullerenes have low symmetry;only a very small number of them have the icosahedral symmetry of C 60.An example of a giant fullerene that can have icosahedral symmetry is C 540,as shown in Figure 2(b).There have been many studies of the stability of fullerenes as a function of size (e.g.,Refs.17,18).These show that,in general,stability increases with size.Experimentally,there is evidence that C 60is unstable with respect to large,multiwalled fullerenes.This was demonstrated by Mochida and colleagues,who heated C 60and C 70in a sublimation-limiting furnace.19They showed that the cage structure broke down at 900◦C–1000◦C,although at 2400◦C fullerene-like “hollow spheres”with diameters in the range 10–20nm were formed.We now consider fullerene-related carbon nanotubes,which were discovered by Iijima in 1991.6These consist of cylinders of graphite,closed at each end with caps that contain precisely six pentagonal rings.We can illustrate their structure by considering the two “archetypal”carbon nanotubes that can be formed by cutting a C 60molecule in half and placing a graphene cylinder between the two halves.Dividing C 60parallel to one of the three-fold axes results in the zig-zag nanotube shown in Figure 3(a),whereas bisecting C 60along one of the ﬁvefold axes produces the armchair nanotube shown in Figure 3(b).The terms “zig-zag”and “armchair”refer to the arrangement of hexagons around the circumference.There is a third class of structure in which the hexagons are arranged helically around the tube axis.Ex-perimentally,the tubes are generally much less perfect than the idealized versions shown in Figure 3,and may be eitherNEW PERSPECTIVES ON GRAPHITIC CARBONS STRUCTURE237FI G.2.The structure of (a)C 60,(b)icosahedral C 540.15multilayered or single-layered.Figure 4shows a high resolu-tion TEM image of multilayered nanotubes.The multilayered tubes range in length from a few tens of nm to several microns,and in outer diameter from about 2.5nm to 30nm.The end-caps of the tubes are sometimes symmetrical in shape,but more often asymmetric.Conical structures of the kind shown in Fig-ure 5(a)are commonly observed.This type of structure is be-lieved to result from the presence of a single pentagon at the position indicated by the arrow,with ﬁve further pentagons at the apex of the cone.Also quite common are complex cap struc-tures displaying a “bill-like”morphology such as thatshownFI G.3.Drawings of the two nanotubes that can be capped by one half of a C 60molecule.(a)Zig-zag (9,0)structure,(b)armchair (5,5)structure.20in Figure 5(b).21This structure results from the presence of a single pentagon at point “X”and a heptagon at point “Y .”The heptagon results in a saddle-point,or region of negative curvature.The nanotubes ﬁrst reported by Iijima were prepared by va-porizing graphite in a carbon arc under an atmosphere of helium.Nanotubes produced in this way are invariably accompanied by other material,notably carbon nanoparticles.These can be thought of as giant,multilayered fullerenes,and range in size from ∼5nm to ∼15nm.A high-resolution image of a nanopar-ticle attached to a nanotube is shown in Figure 6(a).22In this238P.J.F.HARRISFI G.4.TEM image of multiwalled nanotubes.case,the particle consists of three concentric fullerene shells.A more typical nanoparticle,with many more layers,is shown in Figure 6(b).These larger particles are probably relatively im-perfect instructure.FI G.5.I mages of typical multiwalled nanotube caps.(a)cap with asymmetric cone structure,(b)cap with bill-like structure.21Single-walled nanotubes were ﬁrst prepared in 1993using a variant of the arc-evaporation technique.23,24These are quite different from multilayered nanotubes in that they generally have very small diameters (typically ∼1nm),and tend to be curledNEW PERSPECTIVES ON GRAPHITIC CARBONS STRUCTURE239FI G.6.I mages of carbon nanoparticles.(a)small nanoparticle with three concentric layers on nanotube surface,22(b)larger multilayered nanoparticle.and looped rather than straight.They will not be considered further here because they have no parallel among well-known forms of carbon discussed in this article.The stability of multilayered carbon nanotubes and nanopar-ticles has not been studied in detail experimentally.However,we know that they are formed at the center of graphite electrodes during arcing,where temperatures probably approach 3000◦C.I t is reasonable to assume,therefore,that nanotubes and nanopar-ticles could withstand being re-heated to such temperatures (in an inert atmosphere)without signiﬁcant change.MICROPOROUS (NON-GRAPHITIZING)CARBONS BackgroundIt was demonstrated many years ago by Franklin 25,26that carbons produced by the solid-phase pyrolysis of organic ma-terials fall into two distinct classes.The so-called graphitizing carbons tend to be soft and non-porous,with relatively high den-sities,and can be readily transformed into crystalline graphite by heating at temperatures in the range 2200◦C–3000◦C.I n con-trast,“non-graphitizing”carbons are hard,low-densitymateri-FI G.7.(a)High resolution TEM image of carbon prepared by pyrolysis of sucrose in nitrogen at 1000◦C,(b)carbon prepared bypyrolysis of anthracene at 1000◦C.I nsets show selected area diffraction patterns.30als that cannot be transformed into crystalline graphite even at temperatures of 3000◦C and above.The low density of non-graphitizing carbons is a consequence of a microporous struc-ture,which gives these materials an exceptionally high internal surface area.This high surface area can be enhanced further by activation,that is,mild oxidation with a gas or chemical pro-cessing,and the resulting “activated carbons”are of enormous commercial importance,primarily as adsorbents.27−29The distinction between graphitizing and non-graphitizing carbons can be illustrated most clearly using transmission elec-tron microscopy (TEM).Figure 7(a)shows a TEM image of a typical non-graphitizing carbon prepared by the pyrolysis of sucrose in an inert atmosphere at 1000◦C.30The inset shows a diffraction pattern recorded from an area approximately 0.25µm in diameter.The image shows the structure to be disordered and isotropic,consisting of tightly curled single carbon layers,with no obvious graphitization.The diffraction pattern shows symmetrical rings,conﬁrming the isotropic structure.The ap-pearance of graphitizing carbons,on the other hand,approxi-mates much more closely to that of graphite.This can be seen in the TEM micrograph of a carbon prepared from anthracene,240P.J.F.HARRI Swhich is shown in Figure 7(b).Here,the structure contains small,approximately ﬂat carbon layers,packed tightly together with a high degree of alignment.The fragments can be considered as rather imperfect graphene sheets.The diffraction pattern for the graphitizing carbon consists of arcs rather than symmetrical rings,conﬁrming that the layers are preferentially aligned along a particular direction.The bright,narrow arcs in this pattern correspond to the interlayer {0002}spacings,whereas the other reﬂections appear as broader,less intense arcs.Transmission electron micrographs showing the effect of high-temperature heat treatments on the structure of non-graphitizing and graphitizing carbons are shown in Figure 8(note that the magniﬁcation here is much lower than for Figure 7).I n the case of the non-graphitizing carbon,heating at 2300◦C in an inert atmosphere produces the disordered,porous material shown in Figure 8(a).This structure is made up of curved and faceted graphitic layer planes,typically 1–2nm thick and 5–15nm in length,enclosing randomly shaped pores.A few somewhat larger graphite crystallites are present,but there is no macroscopic graphitization.n contrast,heat treatment of the anthracene-derived carbon produces large crystals of highly or-dered graphite,as shown in Figure 8(b).Other physical measurements also demonstrate sharp dif-ferences between graphitizing and non-graphitizing carbons.Table 1shows the effect of preparation temperature on the sur-face areas and densities of a typical graphitizing carbon prepared from polyvinyl chloride,and a non-graphitizing carbon prepared from cellulose.31It can be seen that the graphitizing carbon pre-pared at 700◦C has a very low surface area,which changes lit-tle for carbons prepared at higher temperatures,up to 3000◦C.The density of the carbons increases steadily as thepreparationFI G.8.Micrographs of (a)sucrose carbon and (b)anthracene carbon following heat treatment at 2300◦C.TABLE 1Effect of temperature on surface areas and densities of carbonsprepared from polyvinyl chloride and cellulose 31(a)Surface areas Speciﬁc surface area (m 2/g)for carbons prepared at:Starting material 700◦C 1500◦C 2000◦C 2700◦C 3000◦C PVC 0.580.210.210.710.56Cellulose 4081.601.172.232.25(b)Densities Helium density (g/cm 3)for carbons prepared at:Starting material 700◦C 1500◦C 2000◦C 2700◦C 3000◦C PVC 1.85 2.09 2.14 2.21 2.26Cellulose1.901.471.431.561.70temperature is increased,reaching a value of 2.26g/cm 3,which is the density of pure graphite,at 3000◦C.The effect of prepara-tion temperature on the non-graphitizing carbon is very different.A high surface area is observed for the carbon prepared at 700◦C (408m 2/g),which falls rapidly as the preparation temperature is increased.Despite this reduction in surface area,however,the density of the non-graphitizing carbon actually falls when the temperature of preparation is increased.This indicates that a high proportion of “closed porosity”is present in the heat-treated carbon.NEW PERSPECTIVES ON GRAPHITIC CARBONS STRUCTURE241FI G.9.Franklin’s representations of(a)non-graphitizing and(b)graphitizing carbons.25Early ModelsTheﬁrst attempt to develop structural models of graphitizingand non-graphitizing carbons was made by Franklin in her1951paper.25In these models,the basic units are small graphitic crys-tallites containing a few layer planes,which are joined togetherby crosslinks.The precise nature of the crosslinks is not speci-ﬁed.An illustration of Franklin’s models is shown in Figure9.Using these models,she put forward an explanation of whynon-graphitizing carbons cannot be converted by heat treatmentinto graphite,and this will now be summarized.During car-bonization the incipient stacking of the graphene sheets in thenon-graphitizing carbon is largely prevented.At this stage thepresence of crosslinks,internal hydrogen,and the viscosity ofthe material is crucial.The resulting structure of the carbon(at ∼1000◦C)consists of randomly ordered crystallites,held to-gether by residual crosslinks and van der Waals forces,as inFigure9(a).During high-temperature treatment,even thoughthese crosslinks may be broken,the activation energy for themotion of entire crystallites,required for achieving the struc-ture of graphite,is too high and graphite is not formed.Onthe other hand,the structural units in a graphitizing carbon areapproximately parallel to each other,as in Figure9(b),and thetransformation of such a structure into crystalline graphite wouldbe expected to be relatively facile.Although Franklin’s ideason graphitizing and non-graphitizing carbons may be broadlycorrect,they are in some regards incomplete.For example,thenature of the crosslinks between the graphitic fragments is notspeciﬁed,so the reasons for the sharply differing properties ofgraphitizing and non-graphitizing carbons is not explained.The advent of high-resolution transmission electron mi-croscopy in the early1970s enabled the structure of non-graphitizing carbons to be imaged directly.n a typical study,Ban,Crawford,and Marsh2examined carbons prepared frompolyvinylidene chloride(PVDC)following heat treatments attemperatures in the range530◦C–2700◦C.I mages of these car-bons apparently showed the presence of curved and twistedgraphite sheets,typically two or three layer planes thick,enclos-ing voids.These images led Ban et al.to suggest that heat-treatednon-graphitizing carbons have a ribbon-like structure,as shownin Figure1(b).This structure corresponds to a PVDC carbonheat treated at1950◦C.This ribbon-like model is rather similar to an earlier model of glassy carbon proposed by Jenkins andKawamura.32However,models of this kind,which are intendedto represent the structure of non-graphitizing carbons follow-ing high-temperature heat treatment,have serious weaknesses,as noted earlier.Such models consist of curved and twistedgraphene sheets enclosing irregularly shaped pores.However,graphene sheets are known to be highlyﬂexible,and wouldtherefore be expected to become ever more closely folded to-gether at high temperatures,in order to reduce surface energy.Indeed,tightly folded graphene sheets are quite frequently seenin carbons that have been exposed to extreme conditions.33Thus,structures like the one shown in Figure1(b)would be unlikelyto be stable at very high temperatures.It has also been pointed out by Oberlin34,35that the modelsput forward by Jenkins,Ban,and their colleagues were basedon a questionable interpretation of the electron micrographs.In most micrographs of partially graphitized carbons,only the {0002}fringes are resolved,and these are only visible when they are approximately parallel to the electron beam.Therefore,such images tend to have a ribbon-like appearance.However,because only a part of the structure is being imaged,this appear-ance can be misleading,and the true three-dimensional structuremay be more cagelike than ribbon-like.This is a very importantpoint,and must always be borne in mind when analyzing imagesof graphitic carbons.Oberlin herself believes that all graphiticcarbons are built up from basic structural units,which comprisesmall groups of planar aromatic structures,35but does not appearto have given a detailed explanation for the non-graphitizabilityof certain carbons.The models of non-graphitizing carbons described so farhave assumed that the carbon atoms are exclusively sp2and arebonded in hexagonal rings.Some authors have suggested thatsp3-bonded atoms may be present in these carbons(e.g.,Refs.36,37),basing their arguments on an analysis of X-ray diffrac-tion patterns.The presence of diamond-like domains would beconsistent with the hardness of non-graphitizing carbons,andmight also explain their extreme resistance to graphitization.Aserious problem with these models is that sp3carbon is unsta-ble at high temperatures.Diamond is converted to graphite at1700◦C,whereas tetrahedrally bonded carbon atoms in amor-phousﬁlms are unstable above about700◦C.Therefore,the242P.J.F.HARRI Spresence of sp 3atoms in a carbon cannot explain the resistance of the carbon to graphitization at high temperatures.I t should also be noted that more recent diffraction studies of non-graphitizing carbons have suggested that sp 3-bonded atoms are not present,as discussed further in what follows.Evidence for Fullerene-Like Structures in Microporous CarbonsThe evidence that microporous carbons might have fullerene-related structures has come mainly from high-resolution TEM studies.The present author and colleagues initiated a series of studies of typical non-graphitizing microporous carbons using this technique in the mid 1990s.30,38,39The ﬁrst such study in-volved examining carbons prepared from PVDC and sucrose,after heat treatments at temperatures in the range 2100◦C–2600◦C.38The carbons subjected to very high temperatures had rather disordered structures similar to that shown in Figure 8(a).Careful examination of the heated carbons showed that they often contained closed nanoparticles;examples can be seen in Figure 10.The particles were usually faceted,and often hexagonal or pentagonal in shape.Sometimes,faceted layer planes enclosed two or more of the nanoparticles,as shown in Figure 10(b).Here,the arrows indicate two saddle-points,similar to that shown in Figure 5(b).The closed nature of the nanoparticles,their hexagonal or pentagonal shapes,and other features such as the saddle-points strongly suggest that the parti-cles have fullerene-like structures.I ndeed,in many cases the par-ticles resemble those produced by arc-evaporation in a fullerene generator (see Figure 6)although in the latter case the particles usually contain many more layers.The observation of fullerene-related nanoparticles in the heat treated carbons suggested that the original,freshly prepared car-bons may also have had fullerene-related structures (see next section).However,obtaining direct evidence for this is difﬁ-cult.High resolution electron micrographs of freshly prepared carbons,such as that shown in Figure 7(a),are usuallyratherFI G.10.(a)Micrograph showing closed structure in PVDC-derived carbon heated at 2600◦C,(b)another micrograph of same sample,with arrows showing regions of negative curvature.38featureless,and do not reveal the detailed structure.Occasion-ally,however,very small closed particles can be found in the carbons.30The presence of such particles provides circumstan-tial evidence that the surrounding carbon may have a fullerene-related structure.Direct imaging of pentagonal rings by HRTEM has not yet been achieved,but recent developments in TEM imaging techniques suggest that this may soon be possible,as discussed in the Conclusions.As well as high-resolution TEM,diffraction methods have been widely applied to microporous and activated carbons (e.g.,Refs.40–44).However,the interpretation of diffraction data from these highly disordered materials is not straightforward.As already mentioned,some early X-ray diffraction studies were interpreted as providing evidence for the presence of sp 3-bonded atoms.More recent neutron diffraction studies have suggested that non-graphitizing carbons consist entirely of sp 2atoms.40It is less clear whether diffraction methods can establish whether the atoms are bonded in pentagonal or hexagonal rings.Both Petkov et al .42and Zetterstrom and colleagues 43have interpreted neutron diffraction data from nanoporous carbons in terms of a structure containing non-hexagonal rings,but other interpreta-tions may also be possible.Raman spectroscopy is another valuable technique for the study of carbons.45Burian and Dore have used this method to analyze carbons prepared from sucrose,heat treated at tem-peratures from 1000◦C–2300◦C.46The Raman spectra showed clear evidence for the presence of fullerene-and nanotube-like elements in the carbons.There was also some evidence for fullerene-like structures in graphitizing carbons prepared from anthracene,but these formed at higher temperatures and in much lower proportions than in the non-graphitizing carbons.New Models for the Structure of Microporous Carbons Prompted by the observations described in the previous section,the present author and colleagues proposed a model for the structure of non-graphitizing carbons that consists ofNEW PERSPECTIVES ON GRAPHITIC CARBONS STRUCTURE243FI G.11.Schematic illustration of a model for the structure of non-graphitizing carbons based on fullerene-like elements.discrete fragments of curved carbon sheets,in which pentagons and heptagons are dispersed randomly throughout networks of hexagons,as illustrated in Figure11.38,39The size of the micropores in this model would be of the order of0.5–1.0nm, which is similar to the pore sizes observed in typical microp-orous carbons.The structure has some similarities to the“ran-dom schwarzite”network put forward by Townsend and col-leagues in1992,47although this was not proposed as a model for non-graphitizing carbons.I f the model we have proposed for non-graphitizing carbons is correct it suggests that these carbons are very similar in structure to fullerene soot,the low-density, disordered material that forms on walls of the arc-evaporation vessel and from which C60and other fullerenes may be ex-tracted.Fullerene soot is known to be microporous,with a sur-face area,after activation with carbon dioxide,of approximately 700m2g−1,48and detailed analysis of high resolution TEM mi-crographs of fullerene soot has shown that these are consis-tent with a structure in which pentagons and heptagons are dis-tributed randomly throughout a network of hexagons.49,50It is signiﬁcant that high-temperature heat treatments can transform fullerene soot into nanoparticles very similar to those observed in heated microporous carbon.51,52Carbonization and the Structural Evolutionof Microporous CarbonThe process whereby organic materials are transformed into carbon by heat treatment is not well understood at the atomic level.53,54In particular,the very basic question of why some organic materials produce graphitizing carbons and others yield non-graphitizing carbons has not been satisfactorily answered. It is known,however,that both the chemistry and physical prop-erties of the precursors are important in determining the class of carbon formed.Thus,non-graphitizing carbons are formed, in general,from substances containing less hydrogen and more oxygen than graphitizing carbons.As far as physical properties are concerned,materials that yield graphitizing carbons usu-ally form a liquid on heating to temperatures around400◦C–500◦C,whereas those that yield non-graphitizing carbons gen-erally form solid chars without melting.The liquid phase pro-duced on heating graphitizing carbons is believed to provide the mobility necessary to form oriented regions.However,this may not be a complete explanation,because some precursors form non-graphitizing carbons despite passing through a liquid phase.The idea that non-graphitizing carbons contain pentagons and other non-six-membered rings,whereas graphitizing car-bons consist entirely of hexagonal rings may help in understand-ing more fully the mechanism of carbonization.Recently Kumar et al.have used Monte Carlo(MC)simulations to model the evo-lution of a polymer structure into a microporous carbon structure containing non-hexagonal rings.55They chose polyfurfuryl al-cohol,a well-known precursor for non-graphitizing carbon,as the starting material.The polymer was represented as a cubic lattice decorated with the repeat units,as shown in Figure12(a). All the non-carbon atoms(i.e.,hydrogen and oxygen)were then removed from the polymer and this network was used in the。

高温超导体的红外光学响应

高温超导体的红外光学响应英文回答：High-temperature superconductors (HTS) are materials that exhibit superconductivity at relatively high temperatures, compared to traditional superconductors. These materials have a wide range of applications, including in the field of infrared (IR) optics. The IR optical response of HTS materials is of great interest due to their potential use in various devices and systems.The IR optical response of HTS materials refers to how these materials interact with infrared light. This interaction can be characterized by various parameters, such as reflectivity, transmittance, and absorbance. These parameters determine how much of the incident IR light is reflected, transmitted, or absorbed by the HTS material.One important aspect of the IR optical response of HTS materials is their reflectivity. Reflectivity is a measureof how much of the incident IR light is reflected by the material. In the case of HTS materials, their reflectivity can be influenced by factors such as the material's crystal structure, composition, and surface quality. For example, a smooth and polished surface of an HTS material may have higher reflectivity compared to a rough or oxidized surface.Another important parameter is transmittance, which refers to the fraction of incident IR light that passes through the material. The transmittance of HTS materialscan be affected by factors such as the material's thickness, impurities, and defects. For instance, a thicker HTSmaterial may have lower transmittance compared to a thinner one due to increased absorption and scattering of the IR light.Absorbance is a measure of how much of the incident IR light is absorbed by the material. The absorbance of HTS materials can be influenced by factors such as thematerial's energy gap, impurity levels, and temperature.For example, at certain IR frequencies, HTS materials may exhibit strong absorbance due to their energy gap matchingthe energy of the incident light.Understanding the IR optical response of HTS materialsis crucial for the design and optimization of devices and systems that utilize these materials. For example, in the field of IR detectors, the IR optical response of HTS materials can affect their sensitivity and performance. By studying and manipulating the IR optical response, researchers can develop HTS-based devices with enhanced performance and capabilities.中文回答：高温超导体（HTS）是相对于传统超导体而言，在相对较高的温度下表现出超导性的材料。

光热发电吸热塔温度

光热发电吸热塔温度英文回答：Solar thermal power plants utilize concentrated solar radiation to generate heat, which is then used to produce electricity through a thermodynamic cycle. The efficiency of these plants is highly dependent on the temperature of the heat transfer fluid used to absorb solar radiation.In a solar thermal power plant, the heat transfer fluid is circulated through an array of mirrors or lenses, which focus sunlight onto a central receiver. The heat transfer fluid, typically a molten salt or synthetic oil, absorbs the concentrated solar radiation, heating up to temperatures ranging from 550 to 1,000 degrees Celsius.The temperature of the heat transfer fluid is critical because it directly affects the efficiency of the thermodynamic cycle used to generate electricity. A higher temperature heat transfer fluid can produce more steam ordrive a turbine more efficiently, resulting in a higher electrical output.However, the materials used in the heat transfer system, such as the pipes and receiver panels, must be able to withstand the high temperatures involved. This often limits the operating temperature of solar thermal power plants to less than 600 degrees Celsius.In recent years, research has been focused ondeveloping new heat transfer fluids and materials that can operate at higher temperatures. These advancements have the potential to improve the efficiency of solar thermal power plants and make them a more competitive source of renewable energy.中文回答：光热发电厂利用集中的太阳辐射来产生热量，然后通过一个热力循环来产生电力。

磁致热效应magnetothermaleffect在线英语词典英文翻译专业英语

磁致热效应magnetothermaleffect在线英语词典英文翻译专业英语1)magothermal effect 磁致热效应 2)magor;magric 磁致3)magostriction 磁致伸缩1.The study of anisotropy parameters of new magostriction material Tb_(0.27)Dy_(0.73)Fe_(1.95); 新型稀俗磁致伸缩材料Tb_(0.27)Dy_(0.73)Fe_(1.95)的各向异性参数研究2.Martensitic transformation and magostriction in Ni_(52)Mn_(23)Ga_(24.5)Sm_(0.5) alloy; Ni_(52)Mn_(23)Ga_(24.5)Sm_(0.5)合金的马氏体相变和磁致伸缩性能3.Giant magostriction of melt_spun Fe_(85) Ga_(15) ribbons; 甩带Fe_(85)Ga_(15)合金的巨磁致伸缩研究4)mago-vibration 磁致振动1.The relationship between mago-vibration and magic treatment induced tensile residual stress reduction in the steel 45 was studied. 研究了45钢脉冲磁处理过程中残余拉应力与磁致振动之间的相互作用关系。

5)mago-optical rotation 磁致旋光6)magic refrigeration 磁致冷1.The principle of magic refrigeration, proof-principle demonstration apparatus and its development are introduced. 介绍了室温磁致冷机的原理，对世界上最新发展的磁致冷原理样机和具有实用价值的磁致冷材料进行了介绍。

美国堪萨斯Nelson—Atkins美术馆

美国堪萨斯Nelson—Atkins美术馆THENELSoN-ATKlNSMUSEUMoFART—KANSASClTY—Mo—UNlTEDSTATES美国堪萨斯Nelson—Arkins美术馆目g#*目Nc1∞¨_Atkh~#*目itChrisMcV oy自^CI1丌sM目*MdrtlnCoxRchmTobias目∞…0…s2lIGabrl…nrMatth…】assMollyBlledenEIi……Csboides.Robert…ndssm10IIc…tra…l㈨r…r—?一:.U/:D7埔053I5+62Ol1B稠…一,UED]域市墉053I5+6I20tl匕r_一1]Nelson'Atkins美术馆的扩建与景观相融台旨在创造一座体验型的建筑它能让所有参观者通过自身在空间时间的移动感知该建筑的延展被命名为Block Building的扩建部分与现有的雕塑园联系密切从而使整座博物馆变成了游客体验专区扩建部丹沿校园东部展开分别被5片Lens(镜片}区分从现有建筑横穿雕塑公目以形成新的场所和视角景观建筑和艺术三者创新性的融台通过1尊物馆策展人与艺术家的密切协作得以实现目的是实现艺术与建筑之间动态互助的关系当参观者行走于这个新建筑的时候他们将感受到不同的景色和由内而外光线艺术建筑与景观的流动基于与文脉的敏感关系新建Lens优美流畅地编织在建筑与景观中.与大型建筑物不同的是新元素的出现与1933年原真经典的从寺庙到艺术的博物馆设计理念形成了互补对比.这些新的元素包括.原始建筑重密封景观的看有界定向活动独立新建建筑【互补对比度方面透明轻喈台被看无界自由活动成组的透明Lens第一组的5栋Lens咸7一个明亮透明的大堂其中包含咖啡厅艺术图书馆和书店当参观者前行向下进八花园的时候开放的大堂能够邀请公众通过坡道进^博物馆并鼓励他们参与活动这个在新十宇轴线的太堂与原有建筑的大空间相连在晚上发光的大堂玻璃体提供了一个极具吸引力的透明度促使参观者参与到事件和活动中半透明的ons通过多厍发的结合对周围的事物进行传播和折射有时候被物化22I白天廊中的光线会注八到不同的Lens中而夜晚整个建筑则在雕塑公园中{啦发着光芒.Lens以蜿蜒的路径在雕塑公园中穿过以开放的流动廊作为补充与下一级建筑形成连续的整体画廊按照顺序进行组织以支持整体的形式发展运渐连接到后面的公园并穿插着盎好的景观祝线新增加的设计采用的是可持续发展的建筑概念雕塑公开在Lens之间建立了雕坚庭院同时也提供了屋顶绿化以实现高隔热和控制雨水的目的在其他Lens的中心将一盏灯以殛空气分配器台并主要展现了一个结构性的概念.沿着弯曲的流线将光线一直续到画廊中同时又安装7悬浮的玻璃并冒有空调管道的位置该Lens的双层玻璃腔在冬日能够聚集阳光从而加热室内的空气而夏天则可以实现室内气的排出对于艺术媒体设施以爱各季节的夏活性要求主要通过电脑控制和嵌在玻璃腔的特殊半透明绝缘材料来确保最佳的光线艺术廊的地下室主要作为服务仓库和处理空间使用同时考虑该空间作为灵活的喘息徘徊空间使用.这个艺术与建筑巧妙融台体还包括了我们这个时代伟大的艺术家之一Walter deMaria的台作努力WalterdeMaria的雕塑——1个太阳/34个月亮是一个广阔的花岗岩铺成的反映池该雕塑形成7现有建筑物空间和新的大堂Lens彩人口广场的中心标志.艺术作品中的月亮是池底的圆形天窗通过水将光线折射到地下的车库中.感觉上就像一个可以直接穿过去的大堂车库空间的比倒很宽敞麸有两层且直接连接到新馆大堂并通过混凝±.波浪彩T拱磺跨越了连续起伏的仓库建筑理念及博物馆中重要的东方艺术馆蘸之间的密切关系主要体现在其中的永久收藏中如ChlangShen的青翠山峦f12世纪}ChouChin的北海f16世纪】遗充分表达了艺术建筑和景观的永恒结台这种新元素的渗八昭示着与新雕塑庭院的融台与现有的雕塑公园之问建立了相互的约束力睢量流高绝缘屋顶绿化与屋顶下层的结台极大地减少了展览斤严格韵环境标准的人工维护需求.5个Lens中的双层玻璃中均装配有一个能够提供最大自然光的构造从而实现对艺术品的保护目时实现酷暑季节中对热量的最小增加和冬季热损失的最大减少Lens的飒组装是由半透明并绝缘的OKALUX加压空气腔密封玻璃层内夹层和外层共同组成的车库是自然的无窗白天能最大限度减少电力耗景观中的小路梯口和远址的玻璃区域通过其中的景观及外观设计热岛防护树木灌木等元素来提供遮阴4955m(50ooo平方英尺j的绿色f植物】厦面{共3048cm厚}既为保温R值增加了3个点同时只减少了雨水径流白色薄膜卷材屋面减少了热量的碾收.同时较深的遮阳棚为西向的大玻璃面起到了良好的遮阳效果该建筑具有目前最小的热量热岛效应薰蕈辫一誉～懑一一龇一一雠矧一一一一～黜为张撕髓嗽釉一～饴候触州船舶觚鲔眦艏戡鲥雌狮m愀器,￡珊)J城市埔'设"0535+02011』UEDTOPIC]Ⅱ/博物口白gn计^RcHITEcTuR^LDESIGNoFMUSEUM 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3ThermalInsulation

A well-insulated structure and a poorly-insulated structure, which one will stay cooler in summer?
It is useful to remember that good thermal insulation will also reduce the flow of heat into a building, when the temperature outside is greater than the temperature inside.
H kA(1 2 )
t
d
Resistivity 热阻
Resistivity （r）is an alternative index of conduction is the reciprocal of（成反比） thermal conductivity, so that r = 1/lamda
The thermal conductivities of some building materials are given in table 3.1.
Standard U-values are calculated by making certain assumptions about moisture contents of materials and about rates of heat transfer at surfaces and in cavities.
3.1.4 Emissivity and absorptivity
发射率
吸收率
the ability of a material to absorb or give off radiant heat is a property of the surface of the material. Rough black surfaces absorb most heat and emit most heat. Conversely, shiny slivered surfaces absorb least heat and emit least heat.

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Energy and Buildings 88(2015)367–383Contents lists available at ScienceDirectEnergy andBuildingsj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /e n b u i ldThe effect of high thermal insulation on high thermal mass:Is the dynamic behaviour of traditional envelopes in Mediterranean climates still possible?Francesca Stazi a ,∗,Cecilia Bonﬁgli a ,Elisa Tomassoni a ,Costanzo Di Perna b ,Placido MunafòaaDipartimento di Ingegneria Civile,Edile e Architettura (DICEA),Facoltàdi Ingegneria,UniversitàPolitecnica delle Marche,Via Brecce Bianche,60131Ancona,Italy bDipartimento di Ingegneria Industriale e Scienze Matematiche,Facoltàdi Ingegneria,UniversitàPolitecnica delle Marche,Via Brecce Bianche,60131Ancona,Italya r t i c l ei n f oArticle history:Received 24July 2014Received in revised form 18November 2014Accepted 20November 2014Available online 26November 2014Keywords:Optimal building envelope Energy efﬁcient retroﬁtting Energy saving Comfort Global costDynamic thermal insulationa b s t r a c tThe paper aims at studying the effect of both high thermal insulation and high thermal mass techniques in buildings dynamic behaviour in Mediterranean climates.The two techniques can lead to conﬂicting requirements when considering winter and summer conditions,or even high daily temperature ranges.Therefore,the best solution for the summer can be the worst solution for the winter.It is necessary to identify insulation measures that conserve the mass dynamic behaviour.Experimental investigations were carried out on a single-family house to characterize the behaviour of two walls with different thermal inertia.Thermal simulations made it possible to explore differ-ent retroﬁt conﬁgurations also including dynamic strategies.The solutions were compared on comfort,energy savings and global cost.The study shows that the most suitable intervention is the maximization of the internal heat capacity and the introduction of an external insulation layer sealed in wintertime and ventilated in summer,thus maintaining the existing massive envelope seasonal dynamic behaviour by alternatively maximising thermal barrier effect and heat loss.Considering this,the authors introduced a recently patented dynamic system that reduces both summer discomfort levels and consumption,respectively,of about 20%and 43%respect to the worst retroﬁt solution.©2014Elsevier B.V.All rights reserved.1.IntroductionThe energy saving regulations developed on the last years have focused their attention on the problem of heating consumption reduction (common to all European countries)without consider-ing that in hot summer Mediterranean climates the predominant need is to guarantee indoor comfort during the warm period.This has led,even in warmer countries as in Italy,to the imposi-tion of thermal transmittance limit values,through stationary or periodic parameters.So,even in such climates,lightweight and super-insulated building envelopes have been adopted in new∗Corresponding author.Tel.:+390712204783/+393283098217;fax:+390712204378.E-mail addresses:f.stazi@univpm.it ,fstazi@yahoo.it (F.Stazi).constructions.Moreover,in existing buildings retroﬁt,considerable thicknesses of insulation layer were placed either on the external or internal side of the wall,regardless of the relative position between mass and thermal insulation.However many authors have already shown that differ-ent insulation–mass conﬁgurations differently impact on both heating–cooling consumptions and indoor comfort with a differ-ent and often opposite effect on the various aspects.The optimal stratigraphy varies based on the considered operational condi-tions (intermittent use [1],continuous use [2]),climate (extreme climate or with variable temperature range [3])and the speciﬁc analysed aspect between energy efﬁciency [4,5],comfort [6–8]or costs [9,10].So that the best solution identiﬁcation is still an open question and it could be with internal insulation (in studies focused on winter performance [1,11]),with external insulation (in stud-ies focused on summer performance [2,12–16]),or with insulation/10.1016/j.enbuild.2014.11.0560378-7788/©2014Elsevier B.V.All rights reserved.368 F.Stazi et al./Energy and Buildings88(2015)367–383Nomenclatureq volumetricﬂow through the opening(m3/s)P pressure difference across the opening/crack(Pa)nﬂow exponent varying between0.5for fully turbu-lentﬂow and1.0for fully laminarﬂow(–) Cﬂow coefﬁcient,related to the size of the open-ing/crack(–)P w wind surface pressure relative to static pressure in undisturbedﬂow(Pa)air density(kg/m3)v z mean wind velocity at height z(m/s)C p wind pressure coefﬁcient at a given position on thesurface(–)U thermal trasmittance(W/m2K)C G( )global cost referred to starting year 0(D/m2)C I initial investment cost(D/m2)C a,i(j)annual cost for component j at the year i(D/m2)R d(i)discount rate for year i(–)V f, (j)ﬁnal value of component j at the end of the calcula-tion period(D/m2)C m replacement costs(D/m2)C o operation cost(D/m2)R R real interest rate(–)p timing of the considered costs(–)placed on both sides of the wall[1,9,17,18].Very rarely studies have been performed on a multidisciplinary simultaneous evaluation of the different aspects.Focusing on the summer comfort optimization it is established in literature that thick insulation layers,imposed by energy sav-ings standards,whatever their position,act as a thermal barriers avoiding the heat loss with overheating risks.This has led to the increasing importance of the thermal mass in all climates[19–22]. In hot summer Mediterranean climate building envelopes with heavy“storing”masses that dynamically adapt to seasonal vari-ations,were found to be preferable.The traditional architectures are examples of a very close relationship with the speciﬁc climate because they have dynamically adapted to the external environ-ment without the use of the systems but through the adoption of passive strategies such as high massive envelopes[23–25]and natural cross ventilation[26].For new and retroﬁtted envelopes,various authors demon-strated that dynamic conﬁgurations should be preferred:not insulated walls[6,23];walls with seasonal deactivation of the insulation layer[27,28];walls with recently developed dynamic ﬁnishing materials(PCM)[29].Betweenthe above mentioned solutions,the former(not insulated solutions)are not suited for both summer and winter period;the dynamic insulation is mainly designed to enhance the indoor ventilation rather than maximize the dynamic behaviour of the massive layers of the envelope that should be a priority in the retroﬁt of existing massive envelopes; PCM materials work on the latent heat storage rather than on the interaction between natural ventilation and mass.Another solution to enhance the dynamic interaction with the environment is the ventilated external insulation layer,which con-sists in an external insulation separated from the internal massive wall by a channel that can be either ventilated in summer or closed in winter.This solution should resolve the posed question.The system was originated in Northern Europe with various patents [30–32]but has been rarely applied owing to its installation com-plexity and the poor winter thermal performance of the air vents, which are generally made of thin aluminium plates.For this reason, our research group has studied a pre-assembled system with airFig.1.External view of the case study.vents made of insulating material(registered trademark MUnSTa®) [33].This type of system could improve the dynamic behaviour of the inner mass but no studies in literature were performed on performance quantiﬁcation.In summary,various authors highlighted the overheating risk of the super-insulated envelopes newly introduced by the energy sav-ing standards,but the quantiﬁcation of the beneﬁces(on comfort, consumptions and global cost)of restoring the dynamic behaviour of the mass through the introduction of a ventilated layer is still lacking.The paper aims at studying the effect of both high thermal insu-lation and high thermal mass techniques in the dynamic behaviour of buildings in Mediterranean climates also considering the effect of natural ventilation(cross and interposed in the building elements).A multidisciplinary study was carried out including:an experi-mental investigation on a traditional detached building;analytical simulations of comfort levels and energy consumptions to deﬁne the most beneﬁcial mutual position between mass and insulation and to check the effect of the introduction of natural ventilated cavities on the external envelope;global cost comparison between different scenarios;integrated evaluation between the various aspects(comfort,energy saving,global cost).2.Phase,tools and methods2.1.PhasesThe research was carried out through experimental activities and analytical simulations according to the following phases:-On-site monitoring during summer and an intermediate season on four rooms(two at the groundﬂoor and two at theﬁrstﬂoor), characterized by different envelope inertia so as to assess the thermal performance and to obtain real data for comparison with simulation values;-dynamic simulations and model calibration through comparison with measured values;and-parametric analysis on the virtual model to extend the study for different seasons and to assess the comfort levels and energy saving potential of different retroﬁt scenarios.2.2.The case studyThe case study(Fig.1)is a single-family house located in the central Italy near the Adriatic coast(latitude43◦27 ,longitude 13◦37 ),characterized by1647degree-days.The building is a typi-cal example of traditional rural architecture.It was built up at the beginning of1900and theﬁrstﬂoor had been completed in the subsequent years(around1920)with a different constructive tech-nology.It consists in a volume of two storeys above ground level370F.Stazi et al./Energy and Buildings 88(2015)367–383Table 2Thermal properties of the main materials of the external envelope.[W/m K]c [J/kg K][kg/m 3]External/internal plaster 0.90010001900External plaster coating 0.70010001000Gypsum plasterboard 0.2501000900Clay panel 0.0471*******EPS insulation0.036148035Mineral wool insulation 0.036840175Wood ﬁbre insulation 0.0492100265Glass wool insulation 0.04067040Solid brick0.7809401500Semisolid brick 0.3608401100XLAM0.1301600500(S /V ratio =0.69),with its longitudinal axis inclined clockwise about 45◦with respect to the north–south direction.The ground ﬂoor has a high thermal inertia solid-bricks masonry wall (thickness:42cm),while the ﬁrst ﬂoor has a low thermal inertia semisolid-brick (called “occhialoni”)masonry wall (thickness:25cm).The ground ﬂoor is made up by a concrete slab directly laid above the ground level;the ﬂoors on the ﬁrst level and roof are reinforced brick −concrete slabs.The building has small size windows equipped with wooden frames and single glazing.The thermal characteristics of each envelope component are reported in Tables 1and 2(Scheme 0).2.3.Experimental studyThe present paper reports the experimental data from two mon-itoring campaigns conducted from September 9to 19(2006)and from July 27to August 2(2007),in order to record data on the behaviour of the walls at the two building levels.Two south facing rooms have been monitored (Fig.2):one at the ground ﬂoor and one at the ﬁrst ﬂoor.Since the boundary conditions of the two rooms are completely different the acquired data were useful both for model calibration and for a separate assessment of the two wall behaviour rather than for a direct comparison.Measurements were carried out accord-ing to ISO 7726:2002[34].Both monitoring activities involved the following investigations:-Outdoor environmental conditions :a weather station with a global radiometer,a combined sensor for wind speed and direction and a thermo hygrometer with a double screen anti-radiation was used;-indoor climate conditions :two indoor microclimate stations that included a thermo hygrometer and thermo resistances with a tolerance according to IEC 751were used;Table 3Calibration data.BedroomOccupancy offLiving roomMET :115W/person Density :0.2person/m 2Schedules :100%of occupancy from 6.00a.m.to 6.00p.m.on Monday and Sunday;20%ofoccupancy from midnight to 7.00a.m.and from 6.00p.m.to midnight,70%of occupancy from 7.00a.m.to 6.00p.m.from Tuesday to SaturdayVentilation schedulesAlways opened from 6.00a.m.to except for the 30th July during which the windows were always closed4ach at the ground ﬂoor 7ach at the ﬁrst ﬂoor Inﬁltration1ach-envelope performance :data loggers coupled to thermo resistances,with tolerance in accordance with IEC 751,were used to measure the internal and external surface temperatures of the walls.The uncertainty provided by the manufacturer for the used probes is shown below:-thermo resistances (surface temperatures and air temperatures ):0.15◦C (at 0◦C);-thermo hygrometer:0.15◦C (at 0◦C);UR 2%(5–95%,23◦C);-global radiometer:0.5%m.v.+5W/m 2;-wind direction :5◦;-wind velocity :2.5%m.v./reading;Data logger accuracy is 3%m.v./reading.2.4.Methods of thermal analysisThe monitoring activities only regarded the initial as built solu-tion.Analytical simulations of the thermal behaviour were carried out using Energy Plus dynamic software.A virtual model repro-ducing the as built solution was realized and calibrated through comparison with monitored values.In particular we developed a climatic input ﬁle containing the outdoor conditions measured dur-ing experiments,then the speciﬁc data regarding the real users proﬁles for the building (occupancy,ventilation schedules,air inﬁltration)were set in the model as detailed in Table 3.So the cor-respondence between the monitored and calculated values could be checked.The obtained model reproduces with a good approx-imation the observed values since the percentage errors between measured and calculated values were found to be about 1.3%for internal surface temperatures and 2.7%for external surface tem-peratures.Fig.3reports,as an example,the comparison of the monitored and simulated values for the south wall surface tem-peratures at the groundﬂoor.Fig.2.Plans indicating the measuring instruments.F.Stazi et al./Energy and Buildings88(2015)367–383371Fig.3.Calibration of the simulation model by comparison with the measured data.Incremental changes were subsequently made on the calibrated model by introducing an insulation layer in different positions (external or internal)within the horizontal and vertical stratig-raphy(groundﬂoor slab,roof,and walls)and also evaluating the introduction of a vented insulation layer.2.4.1.Retroﬁt scenariosThe retroﬁt measures were combined according to the following scenarios(Tables1–4):-As built scenario:groundﬂoor(G0),roof(R0),walls(W0)and windows as in the“as built”situation;-Scheme0:in the as built scenario(G0,R0,W0)the glazed area is increased until reaching the minimum health standards[35] and achieving an overall9%of window-to-wall ratio(against7% of the as built scheme);the glass−frame system performance is also improved(U≤2W/m2K[36]);-Scheme1:starting from Scheme0a retroﬁt on the groundﬂoor and roof was implemented by assuming two types of solutions: a.High capacityﬂoors:the insulating material is placed on theside facing outward thus leaving high mass on the inner side;b.Low capacityﬂoors:the insulating material is placed on theinternal face of theﬂoors;-Scheme2:the previous scenario(Scheme1)is completed by introducing the insulation layer also on the external walls assum-ing three solutions:a.High capacity building:the insulating material is applied in theouter side of the vertical envelope(adjacent to the existing wall);b.High capacity vented building:the insulating material is appliedin the outer side of the vertical envelope leaving an air cavity that could be alternatively closed(in the cold period)or vented (in the hot period through the vents opening);c.Low capacity building:the insulating material is applied on theinner side of the vertical building envelope.-Scheme3:new lightweight wooden building envelope typical of a constructive practice increasingly used in Italy.-Scheme4:improvement of the worst case(Scheme2c)through the introduction of a massive innerﬁnish[37]characterized by a good heat capacity.-Scheme5:further optimization of the preferable solution(namely Scheme2b)with the introduction of a ventilation layer even in the roof slab and the elimination of the atticﬂoor.Different insulation layer thicknesses and materials were used in the various conﬁgurations in order to provide the same station-ary and periodic thermal transmittance[36].The main difference between the walls is the thermal inertia on the inner side repre-sented by the parameter of internal areal heat capacity deﬁned by European standard EN ISO13786:2008[38].On Table1,the assumed values for each parameter are reported and also compared with the imposed(or suggested)limits.Table4Scheme of the studied scenarios.Windows Ground Roof WallAs built WWR7%U≈5W/m2K G0R0W0Scheme0WWR9%U≈2W/m2K G0R0W0Scheme1WWR9%U≈2W/m2K(a)High(HC ground)High(HC roof)W0(b)Low(LC ground)Low(LC roof)W0Scheme2WWR9%U≈2W/m2K(a)High(HC ground)High(HC roof)High(HC wall)(b)High(HC ground)High(HC roof)Vented(HC vented wall)(c)Low(LC ground)Low(LC roof)Low(LC wall)Scheme3WWR9%U≈2W/m2K Wood Wood WoodScheme4WWR9%U≈2W/m2K Low(LC ground)Low(LC roof)High(massive innerﬁnish) Scheme5WWR9%U≈2W/m2K High(HC ground)Vented(HC vented roof)Vented(HC vented wall)372F.Stazi et al./Energy and Buildings 88(2015)367–383Fig.4.Construction details .Between the abovementioned schemes,the Schemes 2b and 5include a dynamic insulation system.Thanks to an air gap introduced between the external insulation layer and the internal mass (walls or roof)and the introduction of vents,the envelope is able to dynamically adapt to the external climate with two conﬁg-urations,ventilated during the summer (vents open)and air-tight in winter (vents closed).The authors patented a system to enhance the vents perfor-mance and to simplify the realization [33].The system involves theuse of two panels,deﬁned “normal panels”and “special panels”.Both of them consist of an outer insulating layer (nos.1and 2in Fig.4)spaced from the internal massive wall (or ﬂoor)thanks to the use of cubical spacers (made by the same insulating material)thus creating an air gap (Fig.4with no.3).The anchorage of the panels to the massive support occurs as a normal external insulation,i.e.with adhesive and mechanical anchors both placed in correspon-dence of the spacers.The opening/closing of the ventilation channel takes place through vents positioned in the inferior/superiorF.Stazi et al./Energy and Buildings88(2015)367–383373“special panels”.These vents(Fig.4with no.4)are made of insu-lating material(shaped in a suitable manner),equipped with seals (the same used for windows)and handled by an electronic device similar to that used for the rolling shutters(no.5in Fig.4).The sys-tem could also be completed with sensors for automatic opening based on external temperature.The“special panels”come on site ready for installation previ-ously provided with the following elements:spacers,vents and electronic system(powered by electric cables or batteries)for vents opening,expanded metal mesh coupled with insect mesh at the openings(no.7in Fig.4),vertical elements of insulating material to avoid thermal bridges(no.6in Fig.4).This vented solution was simulated through Energy Plus Airﬂow Network Tool[39].The Airﬂow Network model calculates the air-ﬂows based on AIRNET[40].An airﬂow network consists of a set of nodes connected by airﬂow elements.The nodes represent rooms, connection points in ductwork,or the ambient environment.The airﬂow elements correspond to discrete airﬂow passages such as doorways,construction cracks,ducts,and fans.The assumption is made that there is a simple,nonlinear relationship between the ﬂow through a connection and the pressure difference across it. The problem therefore reduces to the calculation of the airﬂow through these connections with the internal nodes of the network representing certain unknown pressures.The pressure difference between two nodes and the external wind pressure are assumed to be governed by Bernoulli’s equation.A solution is achieved by an iterative mass balance technique in which the unknown nodal air pressures are adjusted by applying mass conservation.Based on the founded airﬂows the model then calculates node temperatures and humidity ing these values the sensible and latent loads are used to calculateﬁnal zone air temperatures,humidity ratios and pressures.The vented cavity was simulated as a unique thermal zone with openings(dimensions of0.08m×1m)in the upper and lower part (positioned with an interval of about2m where possible,for exam-ple not in correspondence of the windows).In this cavity forced ﬂow(due to pressure differences)and buoyancyﬂow(due to air density differences)co-exist.The ventilation rate(q)through each opening in the model is calculated based on the pressure difference using wind and stack pressure effects:q=C×( P)n(1) where q is the volumetricﬂow through the opening;C is theﬂow coefﬁcient,related to the size of the opening; P is the pressure difference between lower and upper openings;n is theﬂow expo-nent varying between0.5for fully turbulentﬂow and1.0for fully laminarﬂow.The wind pressure is determined by Bernoulli’s equation, assuming no height change or pressure losses:P w=0.5× ×C p×v2z(2) where P w is the wind surface pressure relative to static pressure in undisturbedﬂow[Pa], is the air density[kg/m3],v z is the mean wind velocity at height z[m/s],C p is the wind pressure coefﬁcient at a given position on the surface.It is a function of wind direction, position on the building surface and side exposure.Some authors[41]demonstrated that the Airﬂow Network model adopted by Energy Plus accurately simulates the airﬂow in naturally ventilated opaque cavities(for example in ventilated atria)and especially for low rise buildings[42]while major difﬁcul-ties have been found for the application of this model on double skin facades,characterized by an outer glazed surface[43,44],probably due to the difﬁculty of reproducing the real solar inputs[42].Table5Schedules of internal gains due to occupants and equipment for residential buildings.Days Hours Living roomand kitchen(W/m2)Otherrooms(W/m2) Monday−Friday07.00a.m.–05.00p.m.8.0 1.005.00p.m.–11.00p.m.20.0 1.011.00p.m.–07.00a.m. 2.0 6.0 Saturday–Sunday07.00a.m.–5.00p.m.8.0 2.005.00p.m.–11.00p.m.20.0 4.011.00p.m.–07.00a.m. 2.0 6.02.4.2.Energy and comfort analysisDynamic thermal simulations with Energy Plus software were performed to evaluate walls thermo-physical parameters,internal comfort conditions and energy consumptions.The inside surface temperatures of the vertical walls,the oper-ative temperatures and internal comfort of the two south-facing rooms(model calibrated with measures)have been examined dur-ing summer and intermediate season.The summer comfort was assessed with the adaptive model considering the category II,as indicated in standard UNI EN15251:2008[45],and the hours of discomfort(percentage of hours outside the range)were compared.In addition,the consumptions were calculated in order to com-pare the energy saving provided by each retroﬁt scenario.The introduction of a summer mechanical cooling system(as an alterna-tive to the base scenario with natural ventilation)was assumed to ﬁnd out summer consumptions.Since summer cooling is achieved by electrical power with low efﬁciency and winter heating by high efﬁciency fossil fuel,to make these two different forms of energy comparable,the consumptions were calculated in terms of primary energy by using two different conversion factors(1for fossil fuel and2.17for electric energy,as deﬁned by AEEG in EEN3/08[46]).To ensure that the study was not inﬂuenced by the speciﬁc use of the heating system,or a speciﬁc proﬁle of daily ventilation(as set in the calibrated virtual model),all the parametric variations were carried out considering the following assumptions:-Internal gains proﬁleﬁxed according to the Italian Standard UNI TS11300-1(Table5)[46];-Two heating operation programs:intermittent or continuous from November1to April15as established by Italian law[47,48] for zone D,with a set point of20◦C.The intermittent heating was switched on for a total of12h per day[47,48]distributed according to the following time slots:6.00a.m.−10.00a.m.,12.00 a.m.–4.00p.m.,and6.00p.m.–10.00p.m.;-Ventilation rate is set to0.3air change rate per hour(ach)dur-ing the winter period(UNI/TS11300-1)while in the summer a continuous proﬁle set to1.5ach was considered according to UNI 10375[49];-Summer cooling system with a set-point of26◦C.2.4.3.Method of global costs evaluationFinally an economic analysis according to the procedure described in the UNI EN15459[50]by using the global cost method-ology was carried out.The whole cost is determined by summing up the global costs of initial investment,periodic and replacement costs,annual costs and energy costs and subtracting the global cost of theﬁnal value.The global cost is directly linked to the duration of the calculation period and it can be written as:C G( )−C I+ji=0C a,i(j)×R d(i)−V f, (j)(3)where C G( )represents the global cost referred to starting year 0,C I is the initial investment cost,C a,i(j)is the annual cost for374F.Stazi et al./Energy and Buildings 88(2015)367–383Table 6Input data for the economic analysis.Input dataParameterValueComments/source Starting year for calculation 2013Calculation period30YearsAccording to Annex I of EU regulation Interest rate4%RealAssumed lifetimes of building elementsParameterValueComments/sourceInsulation (thermal protection)50Years UNI EN 15459[46]Window30Years Heating system 20Years Cooling system15YearsEnergy pricesParameterValueComments/sourceNatural gas 0.087D /kW h VAT and taxes excludedElectricity0.2D /kW h Energy price development2.8%RealSpeciﬁc cost [D /m 2](VAT excluded)Ground ﬂoor HC ﬂoor and LC ﬂoor :22.43Roof HC roof :39.33;HC vented roof :53.76;LC roof :42.22WallHC wall :53.12;HC vented wall :67.26;LC wall :48.78;LC wall with clay panel :56.13Attic ﬂoor removal20.20component j at the year i (maintenance,replacement and running costs),R d (i )is the discount rate for year i ,V f, (j )is the ﬁnal value of component j at the end of the calculation period (referred to the starting year 0).With regard to initial investment cost (C I ):the unit prices for products,including both furniture and application,were estab-lished from the current Italian pricelist.In particular the DEI pricelist [51]for the buildings recovery,renovation and mainte-nance was consulted.In order to evaluate the cost related to the innovative vented solution,additional costs respect to a traditional external insulation layer were applied due to:deeper wall mechan-ical fasteners,additional insulating material and workmanship for the spacers supply and installation,electronic system for vents opening and expanded metal mesh that were pre-assembled in the special panel.The prices were obtained from market compa-nies and considering the system as if it was industrially produced rather than handcrafted.The component (C a )includes maintenance/replacement costs (C m )and operation cost (C o ).For the maintenance costs only those connected to energy system were considered (2.75%of the invest-ment costs related to heating and cooling systems).The timing for replacement of systems and building components were acquired from the Annex A of EN 15459considering the same cost adopted for the initial investment.The operational costs for heating and cooling were obtained by multiplying the useful energy demands with the respective tariff (0.087D /kW h for natural gas and 0.2D /kW h for electricity after tax)[52].With regard to the discount rate (R d ):in order to refer the costs to the starting year the real discount rate is usedR d (p )=1(1+R R )/100p(4)where R R is the real interest rate and p is the timing of the consid-ered costs (i.e.number of years after the starting year).With regard to the ﬁnal value for each component (V f ),it is deter-mined by straight-line depreciation of the initial investment until the end of the calculation period and referred to the beginning of the calculation period.All the relevant input data are shown in Table 6.Afterwards the different cost components have been grouped into three categories:costs related to the building envelope,costs related to heating and cost related to cooling (Table 7).3.Results3.1.Summer comfort3.1.1.As builtFig.5shows the results of the monitored external climatic con-ditions.The period was characterized by mostly sunny conditions with external temperatures daily varying between 33◦C during the day and 20◦C during the night in the ﬁrst three days (27−30July).These could be considered typical summer season conditions.On July 31there was a sudden drop of temperature values down to 26◦C during the day and to about 16◦C at night.The relative humidity shows an almost uniform trend between 30%and 70%.Fig.6reports the external and internal surface and air temper-atures recorded during the summer experimental campaign at the two building levels.The monitored rooms have the same exposure (southern side)but present external walls with different inertia (solid bricks masonry and semisolid bricks masonry)and different elevations (ground ﬂoor and ﬁrst ﬂoor).The external surface temperatures reach their minimum value at around 5:00a.m.in both walls with lower values (about 2◦C)recorded in the ﬁrst ﬂoor lightweight wall.In the following hours,with the solar radiation rising,the external surface temperatures increase,with the same trend for the two walls (since they have the same external plaster ﬁnishing)reaching the maximum at about 11:00a.m.,with higher values (about 2◦C)for the low inertia wall.The difference could be ascribed to a different outgoing heat ﬂux for the two walls.The internal surface temperatures show different ﬂuctuations at the two levels with a maximum daily range of about 4◦C for lightweight wall and 1.5◦C for the massive ones.Moreover,the。