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Optimizing matrix and ﬁber/matrix interface to achieve combination of strength,ductility and toughness in carbon nanotube-reinforced carbon/carbon compositesLei Feng,Kezhi Li ⁎,Bei Xue,Qiangang Fu,Leilei Zhang ⁎State Key Laboratory of Solidi ﬁcation Processing,Carbon/Carbon Composites Research Center,Northwestern Polytechnical University,Xi'an,710072,ChinaH I G H L I G H T S•Both matrix and ﬁber/matrix interface of carbon/carbon composites were opti-mized.•Radial carbon nanotube (CNT)was grown on carbon ﬁbers (CF)to strength-en matrix.•Pyrocarbon layer was introduced be-tween CF and CNT/matrix to optimize interface.•Optimal designs endowed composite with improved strength,ductility and toughness.G R A P H I C A L A B S T R A CTa b s t r a c ta r t i c l e i n f o Article history:Received 2July 2016Received in revised form 2October 2016Accepted 3October 2016Available online 5October 2016The direct attachment of carbon nanotubes (CNTs)on carbon ﬁbers (CFs)always leads to a decrease of ﬁber-dominated properties (e.g.,ﬂexural strength)and a brittle fracture behavior of C/Cs,although the matrix-domi-nated properties (e.g.,compressive strength and interlaminar shear strength (ILSS))exhibit an obvious enhance-ment.To achieve the combination of mechanical strength,ductility and toughness in C/Cs,in this work,efforts were spent on simultaneously optimizing the matrix and ﬁber/matrix (F/M)Ts with radial orienta-tion were grown onto the CFs by double-injection chemical vapor deposition to modify the microstructure of ma-trix.Pyrocarbon was deposited on the surface of CFs before CNT growth to protect CFs and to weaken interfacial strength between CFs and CNT/matrix.These optimal designs create strengthening and toughness mechanisms such as crack de ﬂection and long pullout of CFs in the failure process of composites,which endow C/Cs with im-proved ﬂexural strength of 31.5%,ﬂexural ductility of 118%,compressive strength of 81.5%and ILSS of 82%,ac-companied by a clear change from brittle fracture to pseudo-plastic fracture during ﬂexural test.This work may provide a meaningful way to not only enhance both the ﬁber-and matrix-dominated strength but to sub-stantially improve the ductility and toughness of C/Cs.©2016Elsevier Ltd.All rights reserved.Keywords:Carbon nanotubesCarbon/carbon composites Interface Strength Toughness1.IntroductionDesign of high-performance structural engineering carbon/carbon composites (C/Cs)is driven by optimizing combinations of mechanicalMaterials and Design 113(2017)9–16⁎Corresponding authors.E-mail addresses:likezhi@ (K.Li),zhangleilei@ (L.Zhang)./10.1016/j.matdes.2016.10.0060264-1275/©2016Elsevier Ltd.All rightsreserved.Contents lists available at ScienceDirectMaterials and Designj o u r n a l h o me p a g e :ww w.e l s e v i e r.c o m /l o c a t e /m a t d e sproperties such as strength,ductility,toughness and requirements for stability and non-catastrophic failure during service[1,2].C/Cs exhibits high speciﬁc strength and modulus,however,they have weak compres-sion and interlaminar properties,lack ductility and toughness,and al-ways fail in an apparently brittle manner in unconstrained loading geometries[3–5].Recently,the huge interest in incorporating carbon nanotubes (CNTs)into structural composites have been stimulated by virtue of their extraordinary intrinsic properties,such as ultrahigh strength,ex-cellent electrical and thermal conductivities[6,7].These outstanding mechanical and physical properties,in combination with their unique 1D nanostructures with high speciﬁc surface areas,allow for efﬁcient tailoring of both matrix microstructure andﬁber/matrix(F/M)interface state[8,9].For the incorporation of CNTs into composite structures,the general trend has been focused on in situ-growth of CNTs[10–12]or attaching CNTs to the carbonﬁbers(CFs)[13–15].Unlike attracting CNTs which trend to lie in the plane ofﬁber surface and thus only pro-vide one-side reinforcement to the C/Cs(just at F/M interface area), growing CNTs on the surface of CFs by catalytic chemical vapor deposi-tion(CVD)has many advantages in terms of controllability of size and orientation of CNTs,particularly a radial orientation that allows for si-multaneous reinforcements to the matrix and F/M interface[16].Excit-ing increases in matrix-dominated properties(e.g.,compressive strength and interlaminar shear strength)of C/Cs have been observed by growing CNTs onto carbonﬁbers[17–19].Nevertheless,there still exit some critical issues regarding the C/Cs reinforced with CVD-grown CNTs.Firstly,due to the potential damage(dissolution of metal catalysts into carbon,local oxidation and gasiﬁcation)of the CFs during the growth reaction[20,21],and the difﬁculty of controlling the orienta-tion and uniformity of the grafted CNTs on CFs[16,22,23],the studies on the enhancements both inﬁber-and matrix-dominated strengths of C/ Cs have rarely been reported.Secondly and more importantly,the direct attachment of CNTs onto CF surface always result in strong F/M interfa-cial bonding and thus obstructs the crack deﬂection along the axis of CFs [17,23–25],which leads to the failure ofﬁber pullout as an effective strengthening and toughening mechanism.There will be little or no property enhancement in the ductility and toughness expected in such a mode of composite failure[26,27].If CNT-reinforced C/Cs is to re-place C/Cs in industries,it is necessary to achieve the combination of global strength,ductility and toughness in C/Cs.Over the past few de-cades,however,few efforts have been spent on this issue.To improve the comprehensive mechanical performance of CNT-re-inforced C/Cs,the substantial problem and great challenge are how to moderate the F/M interfacial bonding so that it is neither too strong nor too weak and how to supply effective reinforcements to the carbon matrix without degrading theﬁber strength.In this work,a thin pyrocarbon(PyC)interface layer was deposited on the surface of CFs by chemical vapor inﬁltration(CVI)technique to optimize the F/M in-terfacial bonding,whilst preventing the dissolution of metal catalysts into CFs occurred during the subsequent growth of CNTs.Afterwards, double-injection CVD(DICVD)technique was developed to grow radial-ly-aligned CNTs on PyC-coated CFs.The schematic of this manufacturing process is depicted in Fig.1.The hybridﬁber preforms were then desiﬁned by CVI technique to obtain theﬁnal CNT-reinforced C/Cs. Three-point bending,compression and interlaminar shearing tests were applied to examine the effect of these optimal designs on the me-chanical properties of C/Cs.2.Experimental2.1.Raw materialsCarbon felts(bulk density0.2g/cm3,ﬁber diameters6–8μm,Yixing Tianniao Co.Ltd.,China)used in this work were fabricated by alterna-tively overlapping layers of randomly oriented shortﬁber bundles with needle-punching step-by-step.2.2.Deposition of PyC interface layer on CFs and the growth of CNTsCarbon felts wereﬁrstly deposited with an interface layer of PyC by isothermal CVI technology,which was carried out at1080°C using ﬂowing mixture of CH4(40L/h)and N2(160L/h)under the ambient pressure.The growth of CNTs in carbon felts was conducted by DICVD technique using FeSO4·6H2O as catalyst precursor.Incipient wetness technique was applied to introduce catalysts into felts using distilled water as solvent.Afterwards,they were placed in a CVD reactor and heated to750°C under Arﬂowing.At the growth temperature,xylene as the hydrocarbon source was injected into the reactor through a thin tube via a syringe.Ethylenediamine as the growth promoter wasﬁlled in another syringe and was injected separately from the same side for the xylene injection.The ratio of injection rates of xylene and ethylenediamine was8:1.The Ar/H2(2/1)gas mixture was used as the carrier gas with aﬂow rate of600sccm.The growth time was2h. The direct growth of CNTs in carbon felts without PyC interface layer was also performed by DICVD technique under identical growth condi-tions.The volume fractions of CNTs in carbon felts with and without PyC interface layer were approximately1.3%.posite preparation and mechanical property testsThe densiﬁcation was carried out by isothermal CVI technique for 150h under the conditions described in section2.2.The C/Cs containing both the PyC interface layer and CNTs were denoted as CNT-PyC-C/Cs, while the C/Cs containing only CNTs were denoted as CNT-C/Cs.The Fig.1.Schematic of depositing PyC interface layer on CFs and followed by growth of radial CNTs by DICVD to maintainﬁber strength,optimize F/M interface and strengthen matrix of C/Cs. 10L.Feng et al./Materials and Design113(2017)9–16densities of pure C/Cs,CNT-C/Cs and CNT-PyC-C/Cs were measured in the range of 1.64–1.67g/cm 3.The sizes of samples for bending tests were machined into 50mm ×8mm ×4mm.The support span for bend-ing tests was 40mm.To study the quasi-ductile fracture behavior of the composites,a ductility factor was introduced.It was calculated from the ratio of the secant modulus (the slope of the line from the origin to the stress at failure in the ﬂexural stress-strain curve)to the elastic modulus [28].The samples used for compression test and interlaminar shearing test were machined into the sizes of 5mm ×5mm ×4mm.The numbers of samples for bending,compression and shearing tests were not less than 5.All the tests were carried out on a universal testing machine (CMT5304)at a constant speed of 0.5mm/min.2.4.CharacterizationThe morphologies and microstructures of grafted CNTs were exam-ined by scanning electrical microscopy (SEM,JSM-6700)operated at 15kV and transmission electrical microscopy (TEM,Tecnai F30G 2)op-erated at 200kV,respectively.Microstructure of the matrix PyC was in-vestigated using polarized light microscopy (PLM,Leica DMLP).The Raman spectrum was recorded on a Renishaw Invia RM200using aninVia micro-Raman spectrometer with an Ar ion laser of 514.5nm wavelength at room temperature.3.Results and discussion3.1.Radially-aligned CNTs grafted on CFs with and without PyC coating Fig.2a shows the surface SEM image of the CFs coated with a homog-enous PyC interface layer with a thickness of about 200nm (Fig.2b).After the growth process by DICVD,the CFs without (Fig.2c)and with (Fig.2d)PyC interface layer are uniformly covered with CNTs.The CNTs exhibit radial grafting morphologies,indicating that the DICVD technique has good repeatability for growing radial CNTs on different carbonaceous substrates.These radial nanotubes extend into the space among ﬁbers capability of providing ef ﬁcient reinforcements both to the interlaminar and intralaminar matrix [29].Observation of the cross-section of hybrid ﬁbers presents the detailed information about the CNT length ranging from 4to 7μm (Fig.2e).TEM investigation (Fig.2f)reveals that the products are hollow nanotubes with smooth walls and a typical outer diameter of about 300nm.And the inner diam-eter and tube-wall thickness are about 200nm and 50nm,respectively.Fig.2.SEM images:(a)surface and (b)cross-section of PyC-coated CFs;(c)surface of radially-aligned CNTs grafted on CFs;(d)surface and (e)cross-section of radially-aligned CNTs grafted on PyC-coated CFs.(f)TEM image of an individual CNT and its high resolution TEM image (inset of f).11L.Feng et al./Materials and Design 113(2017)9–16High resolution TEM image (Fig.2f inset)presents that the CNTs have multi-walled structures and the graphitic sheets are parallel to the axial direction,exhibiting a good crystallinity.3.2.Microstructure of compositesThe polished transverse section of the C/Cs,CNT-C/Cs and CNT-PyC-C/Cs viewed by polarized light microscopy is shown in Fig.3.For C/Cs (Fig.3a),the PyC around CFs is in the shape of circular shell and has large grain size,long boundaries between interference colors and pro-nounced homocentric annular cracks.By contrast,PyC in CNT-PyC-C/Cs (Fig.3b)and CNT-C/Cs (Fig.3b inset)demonstrates a different mor-phology.As for the CFs grafted with radial CNTs,the PyC will deposit around the nanotubes rather than directly on the surface of CFs (here,CNTs provide direct reinforcement to the matrix within the reach of nanotubes).Besides,it has been demonstrated in our previous work [30],where the CNTs can also affect the PyC out of the reach of nano-tubes by inducing the formation of spherical or cone-shaped PyC and then restricting their growing up (here,it can be called as “indirect rein-forcement ”).As a result,the consequent PyC is clearly different in mor-phology from that in pure C/Cs.As seen,the PyC in C/Cs containing CNTs exhibits small grain size,short boundaries between interference colors and no annular cracks.In addition,it is interesting to note that CFs in CNT-PyC-C/Cs present white outlines (labeled by arrows in Fig.3b)at-tributed to the presence of PyC interface layers.Fig.3c and d presents the Raman results of C/Cs and CNT-PyC-C/Cs (same with CNT-C/Cs),respectively.Intensity ratio of disorder-inducedD-peak and tangential G-peak is inversely proportional to the level of crystalline order and crystal size L a (in nm)[31].As stated in Table 1,the D:G intensity ratio,I D /I G ,is about 1.85for C/Cs and falls to approxi-mately 1.52for CNT-PyC-C/Cs,suggesting that PyC has a signi ﬁcant im-provement in crystallinity and meanwhile a big increase in L a after introducing radial CNTs.Axisymmetric peak broadening represents for large interplanar spacing d 002of carbon materials [32].As seen,both G-peak and D-peak of interlayer become sharper and more de ﬁned after introducing radial CNTs,which indicates that,the d 002value of PyC in CNT-PyC-C/Cs has a distinct decrease compared with that in C/Cs.As the crystalline order improves and crystal size increases,the bond density within the interlayer increases [33].High bond densities and few defects could lead to a signi ﬁcant increase in mechanical strength of PyC matrix.3.3.Mechanical properties of compositesFig.4presents the stress-strain curves of the three composites re-corded during bending test,compression test and shearing test.The de-tailed results of mechanical tests of three composites are listed in Table pared with C/Cs,CNT-PyC-C/Cs shows obvious improve-ment in ﬂexural strength,ﬂexural ductility,compressive strength and interlaminar shear strength (ILSS):31.5%in ﬂexural strength,118%in ﬂexural ductility,81.5%in compressive strength and 82%in ILSS.How-ever,the ﬂexural strength and ﬂexural ductility of CNT-C/Cs are de-creased by 14.5%and 73%,although the compressive strength and ILSS are increased by 67%and 115%,respectively.From the ﬂexuralstress-Fig.3.PLM images (a,b and inset)and Raman spectra (c,d)of the three composites:(a and c)C/Cs;(inset of b)CNT-C/Cs;(b and d)CNT-PyC-C/Cs (note:red points marked in a and b are the Raman detection positions).Table 1Raman testing data of C/Cs,and CNT-PyC-C/Cs (±values represent standard deviation).Composite FWHM of G-peak (cm −1)FWHM of D-peak (cm −1)I D /I GC/Cs84.41±0.21116.54±0.30 1.85±0.01CNT-PyC-C/Cs78.76±1.8288.62±1.341.52±0.0712L.Feng et al./Materials and Design 113(2017)9–16strain curves (Fig.4a),we can get the information regarding the fracture behavior of the three composites.For C/Cs and CNT-C/Cs,the ﬂexural stress-strain curves can be divided in two segments:linear rise and lin-ear decrease of stress.The stress suddenly drops leading to the cata-strophic failure of the samples as stress goes up to the peak value,which designates brittle fracture occurs in the two composites.By con-trast,CNT-PyC-C/Cs shows pronounced pseudo-plastic fracture behav-ior since the load decreases in a step-style rather than perpendicularly after the peak value.The stress-stain curve can be divided into three segments:linear rise of load,non-linear rise of load and stepped de-crease of load.The different segments correspond to three stages:ma-trix elastic deformation,appearing and propagating of destructive cracks among matrix,interfacial debonding and ﬁber pullout,respec-tively [34,35].It means that CNT-PyC-C/Cs does not rupture completely but only fractures partly,avoiding the catastrophic failure as the loading stress reaches to the maximum value,which indicates a signi ﬁcant im-provement in the fracture toughness [36,37].The observation from the compressive and shear stress-strain curves (Fig.4b and c)is that the compressive strength and ILSS of C/Cs can be signi ﬁcantly increased by grafting radial CNTs onto CFs,no matter whether the PyC interface layer is presented or not.From these results it is suggested that if we want to improve the global mechanical strength,ductility and tough-ness of C/Cs,it is necessary to simultaneously optimize both the matrix and F/M interface.When the ﬂexural stress is loaded on the composite samples,the strength of the composites is mainly depended on the strength of CFs.Fig.5shows the SEM images of ﬂexural fracture surfaces of the three composites.In Fig.5a,the fracture surface of C/Cs shows plenty of step-wise fractured PyC and very limited ﬁber pullout.These fracture steps result from the annular cracks that supply the paths for the spreading and link up of destructive cracks and then lead to the formation of step-wise PyC panels.Besides,the F/M interfacial bonding of C/Cs is loose with obvious gaps between CFs and PyC (Fig.5a inset).According to the observations from Fig.5a,the fracture process in C/Cs during bend-ing test can be described as follows:when the bending stress is loaded on the composite samples,destructive cracks will appear somewhere in matrix at the most critical ﬂaws,and then propagate along the annu-lar cracks leading to the delaminating of PyC;it is hard for the weak ma-trix and poor F/M interface to induce the de ﬂection of destructive cracks to propagate along ﬁber surface,which leads to the early failure of CFs since the CFs is dif ﬁcult to be hold on by matrix [38];as the stress further increases,these destructive cracks link up with each other and then the failure of composites occurs.The strength of CFs cannot be fully re ﬂected and thus the C/Cs exhibits brittle fracture with low fracture strength.As for CNT-C/Cs,the fracture surface is ﬂat and with nearly ab-sent of ﬁber pullout (Fig.5b).This fracture surface can be attributed to the strongly-enhanced cohesion in matrix and also the powerful me-chanical interlocking at F/M interface,which lead the destructive cracks to extend into and through the CFs without interfacial debonding (Fig.5b inset).Additionally,the degradation of tensile strength of CFs caused during the CNT growth process is also responsible for the degra-dation of ﬂexural strength of CNT-C/Cs [39].In contrast,CNT-PyC-C/Cs shows a stepwise fracture surface with abundant ﬁber pullouts (Fig.5c).Enlarged SEM image (Fig.5d)illustrates that the destructive cracks spread along the nano/μ-scale grain boundaries (labeled by red dotted lines).When the destructive cracks extend to the CFs,PyC inter-face layer plays a role in changing their direction and facilitates them spreading along the direction parallel to the ﬁber axis as much as possi-ble (as shown in Fig.5e,where exposed PyC interface layer on the pulled-out CFs can be clearly observed).The PyC interface layer protects CFs effectively and weakens the interfacial strength between CFs and CNT/PyC,leading to the long pull-out of CFs compared with brittle frac-ture of CFs without PyC interface layer.Therefore,the stress can be ef ﬁ-ciently transferred from the matrix to the CFs through the strengthened matrix and optimized F/M interface.Crack de ﬂection and ﬁber pullout require a great amount of fractured energy consumption during the fail-ure process [26,27,30,40],which in turn increase the ﬂexural strength and ductility of CNT-PyC-C/Cs and also make the ﬂexural stress release gently,resulting in the sliding region occurred in the ﬂexural stress-strain curve which corresponds to an improved fracture toughness.When the compressive stress is loaded on the composite samples,the compressive strength is mainly depended on the matrix cohesion.Fig.6presents the SEM images of compressive fracture surfaces of the three composites.The fracture surface of C/Cs shows ﬂat and no CFs exist on the surface (Fig.6a),implying that fracture primarily occurs as a typical delamination failure without crack de ﬂection during com-pression test (corresponding failure model is depicted in Fig.6a inset).High degree of matrix delaminating is the dominant mechanism for the delamination failure (Fig.6b).Enlarged SEM image (Fig.6c)clearly shows existing annular cracks provide main channels for the long-dis-tance extending of destructive cracks and then opening the plies.As for CNT-C/Cs (Fig.6d),the strongly-enhanced matrix ef ﬁciently im-pedes the propagation of destructive cracks in the interlaminar region (corresponding failure mode is shown in Fig.6d inset).The de ﬂected destructive cracks then turn to the intralaminar regions (Fig.6e)and di-rectly pass through the CFs by virtue of strong F/M interfacialbonding,Fig.4.Stress-strain curves of the three composites recorded during different mechanical tests:(a)ﬂexural test;(b)compression test;(c)Shearing test.Table 2Mechanical properties of C/Cs,CNT-C/Cs and CNT-PyC-C/Cs (±values represent standard deviation).Composite Flexural strength (MPa)Flexural ductility Compressive strength (MPa)Shear strength (MPa)C/Cs54±60.11±0.03195±1133±5CNT-C/Cs46±70.03±0.01326±1371±8CNT-PyC-C/Cs71±100.24±0.06354±1660±613L.Feng et al./Materials and Design 113(2017)9–16forming many ﬂat fractured surfaces (Fig.6f).But comparatively,CNT-PyC-C/Cs shows a rugged fracture surface with many exposed CFs (Fig.6g),indicating that the propagation direction of destructive cracks also changes mangy times during compression test (corresponding fail-ure mode is shown in Fig.6g inset).The optimized F/M interface induces the long-distance propagation of destructive cracks along the ﬁber sur-face rather than directly pass through the CFs occurred in CNT-C/Cs (Fig.6h and i).More energies are dissipated during this course,which in turn could explain the more pronounced increment in the compressive strength for CNT-PyC-C/Cs (that is 81.5%)than that of CNT-C/Cs (that is 67%).When the interlaminar shear stress is loaded on the composite sam-ples,the shear strength is mainly depended on both the matrix cohesion and F/M interfacial bonding strength.Fig.7presents the shearing frac-ture surface of three composites.As seen in Fig.8a,the smooth PyC shearing fracture surface suggests a serious matrix delaminating in C/Cs,which is similar to the failure mode observed in compression test.It can be thus said that for C/Cs the matrix cohesion is lowerthanFig.5.SEM images of the ﬂexural fracture surfaces of the three composites:(a and inset)C/Cs;(b and inset)CNT-C/Cs;(c –e)CNT-PyC-C/Cs.Fig.6.SEM images of the compressive fracture surfaces of the three composites:(a –c)C/Cs;(d –f)CNT-C/Cs;(g –i)CNT-PyC-C/Cs (insets are the failure modes of the composites during compression tests).14L.Feng et al./Materials and Design 113(2017)9–16F/M interfacial bonding strength.As for the CNT-C/Cs (Fig.8b),matrix delaminating is inhibited and abundant damaged CFs can be clearly ob-served in the shearing fracture surface,indicating that the interfacial strength between CFs and CNT/PyC is strong enough to generate a crack de ﬂection from CNT/PyC to CFs and thus leading to the cleaving of CFs.However,for the CNT-C/Cs (Fig.8c),the F/M interfacial bonding seems to be relatively weak compared with the strongly-enhanced ma-trix,according to the long-distance spreading of destructive cracks along CF surface.This observation provides direct evidence that the PyC interface layer weakens the interfacial bonding strength between CFs and CNT/PyC (Fig.8c inset).It also explains the reason why the in-crement in ILSS of CNT-PyC-C/Cs (that is 82%)is lower than that of CNT-C/Cs (that is 115%).In addition,CNT pullout has rarely been found in all the fracture surfaces of composite samples.Therefore,it can be said that the contribution of our CNTs to the high mechanical strengths of composites is mainly re ﬂected in strengthening the matrix.From the above analysis,the schematic modeling of the failure mecha-nisms of the three composites during loading process has been established,as shown in Fig.8.4.ConclusionsPyC deposited on the CF surface following the radial CNT growth en-ables F/M interface optimizing,matrix strengthening and minimum degradation to the ﬁber strength.SEM morphologies of fracture surfaces of failure composites reveal that the synergistic effects of strongly-en-hanced matrix and optimized F/M interface not only ef ﬁciently de ﬂects the propagation direction of destructive cracks,but also induces the long-distance spreading of destructive cracks along the surfaces of CFs,which signi ﬁcantly increase the ﬂexural strength,ﬂexural ductility,frac-ture toughness,compressive strength and ILSS of C/Cs.However,the speci ﬁc interfacial bonding strength between CFs and CNT/PyC as well as the effect of thickness of PyC interface layer on the mechanical perfor-mance of CNT-reinforced C/Cs are still unclear.Still and all,this work might open up a possibility to produce CNT-reinforced C/Cs with excel-lent mechanical strength,ductility and toughness to replace traditional C/Cs in industries.AcknowledgementsThis work has been supported by the Fundamental Research Funds for the Central universities under Grant No.3102014JCQ01030and “111”Project of China (B08040),and the Natural Science Foundation of China (Grant Nos.51521061and51502242).Fig.7.SEM images of the shearing fracture surfaces of the three composites:(a)C/Cs;(b)CNT-C/Cs;(c and inset)CNT-PyC-C/Cs.Fig.8.The failure mechanisms of the three composites during loading process (red lines 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10.1007_s00253-010-2443-4

BIOTECHNOLOGICAL PRODUCTS AND PROCESS ENGINEERINGEffects of biotic and abiotic elicitors on cell growth and tanshinone accumulation in Salvia miltiorrhiza cell culturesJiang-Lin Zhao &Li-Gang Zhou &Jian-Yong WuReceived:7September 2009/Revised:6January 2010/Accepted:6January 2010/Published online:2March 2010#Springer-Verlag 2010Abstract This study examined the effects of biotic and abiotic elicitors on the production of diterpenoid tanshi-nones in Salvia miltiorrhiza cell culture.Four classes of elicitors were tested,heavy metal ions (Co 2+,Ag +,Cd 2+),polysaccharides (yeast extract and chitosan),plant response-signaling compounds (salicylic acid and methyl jasmonate),and hyperosmotic stress (with sorbitol).Of these,Ag (silver nitrate),Cd (cadmium chloride),and polysaccharide from yeast extract (YE)were most effective to stimulate the tanshinone production,increasing the total tanshinone content of cell by more than ten-fold (2.3mg g -1versus 0.2mg g -1in control).The stimulating effect was concentration-dependent,most significant at 25μM of Ag and Cd and 100mg l -1(carbohydrate content)of YE.Of the three tanshinones detected,cryptotanshinone was stimulat-ed most dramatically by about 30-fold and tanshinones I and IIA by no more than 5-fold.Meanwhile,most of the elicitors suppressed cell growth,decreasing the biomass yield by about 50%(5.1–5.5g l -1versus 8.9g l -1in control).The elicitors also stimulated the phenylalanine ammonia lyase activity of cells and transient increases in the medium pH and conductivity.The results suggest that the elicitor-stimulated tanshinone accumulation was a stress response of the cells.Keywords Salvia miltiorrhiza .Cell culture .Tanshinones .Elicitors .Stress responseIntroductionSalvia miltiorrhiza Bunge (Lamiaceae),called Danshen in Chinese,is a well-known and important medicinal plant because its root is an effective herb for treatment of menstrual disorders and cardiovascular diseases and for the prevention of inflammation (Tang and Eisenbrand 1992).As its Chinese name refers,Danshen root is characterized by the abundance of red pigments which are mainly ascribed to numerous diterpene quinones generally known as tanshinones,e.g.,tanshinone I (T-I),tanshinone-IIA (T-IIA),and T-IIB,isotanshinone I and II,and cryptotanshinone (CT).Tanshinones constitute a major class of bioactive compounds in S .miltiorrhiza roots with proven therapeutic effects and pharmacological activities (Wang et al.2007).Danshen in combination with a few other Chinese herbs is an effective medicine widely used for the treatment of cardiovascular diseases and used as an emergency remedy for coronary artery disease and acute ischemic stroke.According to WHO statistics,cardiovas-cular diseases are and will continue to be the number one cause of death in the world (www.who.int/cardiovascular_diseases ).It is of significance to develop more efficient means for the production of Danshen and its active constituents.Although field cultivation is currently the major produc-tion means for Danshen and most other plant herbs,plant tissue cultures provide more well-controlled and sustainable systems for efficient production of desired bioactive compounds of the herb.Plant tissue cultures are the most useful and convenient experimental systems for examiningJ.-L.Zhao :L.-G.Zhou (*)Department of Plant Pathology,China Agricultural University,Beijing 100193,China email:lgzhou@J.-Y .Wu (*)Department of Applied Biology and Chemical Technology,The Hong Kong Polytechnic University,Hung Hom,Kowloon,Hong Kong email:bcjywu@.hkAppl Microbiol Biotechnol (2010)87:137–144DOI 10.1007/s00253-010-2443-4various factors on the biosynthesis of desired products and for exploring effective measures to enhance their produc-tion.The importance of Danshen for traditional and modern medicines has promoted the long-lasting research interest in the development of tiorrhiza tissue cultures for production of bioactive compounds for more than two decades.In an early study,Nakanishi et al.(1983)induced several cell lines from plant seedlings and screened out a cell line capable of producing significant amounts of CT and another diterpene,ferruginol.In later studies,the group performed a fuller evaluation and optimization of the medium for cell growth and CT production and,eventually,derived an effective production medium with a simpler composition(ten components)than the original Murashige and Skoog(MS) medium(about20components),achieving a high CT yield of 110mg l-1(Miyasaka et al.1987).Many recent studies have been focused on hairy root cultures of tiorrhiza transformed by Agrobacterium rhizogenes(Hu and Alfermann1993;Chen et al.2001)and by our group (Zhang et al.2004;Ge and Wu2005;Shi et al.2007).Most of the bioactive compounds in medicinal plants belong to secondary metabolites which are usually less abundant than primary metabolites in the plants.Since the accumulation of secondary metabolites in plants is a common response of plants to biotic and abiotic stresses, their accumulation can be stimulated by biotic and abiotic elicitors.Therefore,elicitation,treatment of plant tissue cultures with elicitors,is one of the most effective strategies for improving secondary metabolite production in plant tissue cultures(Chong et al.2005;Smetanska2008).The most common and effective elicitors used in previous studies include the components of microbial cells especially poly-and oligosaccharides(biotic)and heavy metal ions, hyperosmotic stress,and UV radiation(abiotic),and the signaling compounds in plant defense responses such as salicylic acid(SA)and methyl jasmonate(MJ;Zhou and Wu2006;Smetanska2008).Some of these elicitors,yeast extract(mainly the polysaccharide fraction),silver ion Ag+, and hyperosmotic stress(by an osmoticum)have also been applied and shown effective to enhance the production of tanshinones in tiorrhiza hairy root cultures(Chen et al.2001;Zhang et al.2004;Shi et al.2007).To the best of our knowledge,only a few studies have been documented on the effects of elicitors,YE,SA,and MJ,on the secondary metabolite production in Agro-bacterium tumefaciens transformed tiorrhiza cell cultures from one research group(Chen and Chen1999, 2000)but not any study in normal cell cultures.The present study focuses on the effects of common biotic and abiotic elicitors including polysaccharides,heavy metal ions, SA and MJ,and osmotic stress(with sorbitol)on the growth and accumulation of three major tanshinones T-I, T-IIA,and CT in suspension culture of normal tior-rhiza cells.In addition to the effects of various elicitors on the total tanshinone content of cells,the study will examine the effects on different tanshinone species and the potential relationship to plant stress response.Material and methodsCallus induction and cell suspension cultureYoung stem explants of tiorrhiza Bunge were collected from the botanical garden at the Institute of Medicinal Plant Development,Chinese Academy of Med-ical Sciences,Beijing,China,in May2005.The fresh explants were washed with tap water,surface-sterilized with 75%ethanol for1min,and then soaked in0.1%mercuric chloride for10min and rinsed thoroughly with sterilized water.The clean and sterilized explants were cut into∼0.5-cm segments and placed on solid MS medium(Murashige and Skoog1962)supplemented with sucrose(30g l-1),2,4-D(2mg l-1)and6-BA(2mg l-1)to induce callus formation. The callus culture of tiorrhiza was maintained on a solid,hormone-free MS medium with8g l-1agar and 30g l-1sucrose at25°C in the dark and subcultured every 4weeks.The culture was deposited in Lab Y1210at The Hong Kong Polytechnic University with a collection number of Danshen cell-1.All experiments in this study were performed in suspension culture of tiorrhiza cells in a liquid medium of the same composition as for the solid culture but excluding agar.The cell suspension culture was maintained in shake-flasks,i.e.,125-ml Erlenmeyer flasks on an orbital shaker operated at110–120rpm,at 25°C in the dark.Each of the flasks was filled with25ml medium and inoculated with0.3g fresh cells from18–21-day-old shake–flask culture.Elicitor preparation and administrationEight elicitors were tested,each at three concentrations,in the initial elicitation experiments(Table1).These are representative of the four major classes of elicitors for the induction of plant responses and the stimulation of secondary metabolite production in plant tissue cultures (Zhou and Wu2006;Smetanska2008).All elicitors except MJ were prepared as a concentrated stock solution in water and autoclaved at121°C for15min,and stored at4°C in a refrigerator prior to use.Yeast elicitor(YE)was the polysaccharide fraction of yeast extract(Y4250,Sigma, St.Louis,MO,USA)prepared by ethanol precipitation as described previously(Hahn and Albersheim1978;Ge and Wu2005).In brief,yeast extract was dissolved in distilled water(20g/100ml)and then mixed with400ml of ethanol and allowed to precipitate for4days at4°C in arefrigerator.The precipitate was redissolved in100ml of distilled water and subjected to another round of ethanol precipitation.The final gummy precipitate was dissolved in 50ml of distilled water and stored at4°C before use.The concentration of YE was represented by total carbohydrate content which was determined by the Anthrone test using sucrose as a reference.Chitosan solution was prepared by dissolving0.5g crab shell chitosan(C3646,Sigma)in1ml glacial acetic acid at55–60°C for15min,and then the final volume was adjusted to50ml with distilled water and the pH adjusted to5.8with NaOH(Prakash and Srivastava 2008).MJ(Cat.39,270-7,Sigma-Aldrich)was dissolved in 95%ethanol and sterilized by filtering through a microfilter (0.2µm).SA(10,591-0,Sigma-Aldrich),sorbitol(S3755, Sigma),and the salts of heavy metals including cobalt chloride(C8661,Sigma-Aldrich),silver nitrate(S7276, Sigma-Aldrich),and cadmium chloride(C5081,Sigma-Aldrich)were dissolved in distilled water to the desired concentrations and adjusted to pH5.8.Elicitor treatment was administered to the shake–flask culture of tiorrhiza cell on day18,which was about 2–3days before reaching the stationary phase.This time point is usually favorable for elicitation when the biomass concentration is high(compared with earlier days of growth),and the cell metabolism is still active(compared with that during or after stationary phase;Buitelaar et al. 1992;Cheng et al.2006).Each of the elicitor solutions was added into the culture medium with a micropipette at the desired concentration.After the elicitor addition,the shake–flask culture of cells was maintained for another7days and then harvested for analysis.All treatments were performed in triplicate,and the results were averaged.After the initial experiments on the eight elicitors,the three most effective ones,Ag(25µM),Cd(25µM),and YE(100mg l-1)were applied in the following experiments on the time courses of elicitor-treated cell growth and tanshinone accumulation in the tiorrhiza cell culture.Measurement of cell weight,sucrose concentration, medium pH,and conductivityThe cells were separated from the liquid medium by filtration.The cell mass on the filter paper was rinsed thoroughly with water and filtered again,and blotted dry by paper towels and then dried at50°C in an oven to attain the dry weight.Sucrose concentration in the liquid medium was determined by the Anthrone test using sucrose as a reference(Ebell1969),and the medium pH and conduc-tivity were measured with the respective electrodes on an Orion720A+pH meter(Thermo Fisher Scientific,Inc., Beverly,MA,USA)and a CD-4303conductivity meter (Lutron,Taiwan),respectively.Measurement of PAL activityPhenylalanine ammonia lyase(PAL)was extracted from fresh tiorrhiza cells with borate buffer(pH8.8).The cells were ground in the buffer(0.15g ml-1)for2min with a pestle and mortar on ice,and then centrifuged at10,000rpm and4°C for20min to obtain a solid-free extract.The PAL activity was determined based on the conversion of L-phenylalanine to cinnamic acid as described by Wu and Lin(2002).Analysis of tanshinone contentsThe cell mass from culture was dried and ground into powder and extracted with methanol/dichloromethane(4:1, v/v,10mg ml-1)under sonication for60min.After removal of the solid,the liquid extract was evaporated to dryness and redissolved in methanol/dichloromethane(9:1,v/v). Tanshinone content was determined by high performance liquid chromatography(HPLC)on a HP1100system using C18column,acetonitrile/water(55:45,v/v)as the mobile phase,and UV detection at275nm as described previously (Shi et al.2007).Three tanshinone species CT,T-I,and T-IIA were detected and quantified with authentic standards obtained from the Institute for Identification of Pharmaceu-tical and Biological Products(Beijing,China).Total tanshinone content is the total content of the three tanshinones in the cells.Tanshinone content in the culture medium was negligible and not determined.ResultsCell growth and tanshinone accumulation in tiorrhiza cell cultureThe time course of tiorrhiza cell growth exhibited a lag phase or slow growth period in the first3–6days, a rapid,linear growth period between day9–18,and aTable1Elicitors and concentrations tested in the initial experiments Elicitors Unit ConcentrationC1C2C3Cobalt chloride(Co)µM 5.02550 Silver nitrate(Ag)µM 5.02550 Cadmium chloride(Cd)µM 5.02550 Salicylic acid(SA)µM1050100 Methyl jasmonate(MJ)µM1050100 Yeast elicitor(YE)mg l-150100200 Chitosan(CH)mg l-150100200 Sorbitol(SO)g l-152550stationary or declining phase in the later days,reaching the maximum biomass concentration (8.1g l -1)around day 21.The total tanshinone content of cells remained at a very low level from days 1–12and then increased steadily from days 12–27to a maximum of 0.16mg g -1.A significant portion (65%)of the tanshinone accumulation or content increase occurred during the stationary phase from days 21–27(Fig.1a ),which is characteristic of secondary metabolite production in a batch culture process.The time course of sugar (sucrose)concentration (Fig.1b )was nearly sym-metrical to that of cell growth,indicating a direct correlation of the cell growth (or biomass production)to sugar consumption.As the major carbon source,sugar was required for the S .miltiorrhiza cell growth,and when it was depleted (around day 21),the cell growth stopped,and the biomass concentration began to drop.As seen from Fig.1b ,the medium pH showed a notable drop in the first 3days (due to consumption of NH 4+and release of protons)and a gradual increase after day 6(due to consumption of nitrate NO 3-)(Morard et al.1998).Effects of various elicitors on cell growth and tanshinone productionFigure 2shows the effects of elicitor treatments on the cell growth and tanshinone accumulation in S .miltiorrhiza cell cultures,which were dependent both on the elicitor species and elicitor dose.As seen from Fig.2a ,most of the elicitor treatments except Co 2+and sorbitol at lower concentrations suppressed the cell growth to a lower biomass concentra-tion than that of the untreated control culture,and the growth suppression was more severe at a high elicitor dose.On the other hand,most of the elicitor treatments except Co 2+,sorbitol,SA,and MJ at lower concentrations increased the total tanshinone content of cell to a higher level than in the control (Fig.2b ).Overall the results indicated that the enhancement of tanshinone accumulation by an elicitor treatment concurred with a notable suppres-sion of cell growth or biomass production.Nevertheless,some of the elicitors had a much stronger stimulating effect on the tanshinone accumulation than the suppressing effect on the cell growth.In particular,Ag and Cd both at 25μM,and YE at 100mg l -1increased the total tanshinone content to 2.30mg g -1,about 11.5-fold versus that of the control (0.20mg g -1),but decreased the biomass production by no more than 50%(5.1–5.5g l -1versus 8.9g l -1).Another three elicitors,SA,MJ (both at 50μM),and sorbitol (50g l -1)increased the total tanshinone content by 2–3-fold but decreased the biomass by 30–45%compared with the control.The stimulating effect of chitosan on tanshinone accumulation (about 6-fold)was stronger than SA,MJ,and sorbitol but much weaker than Ag,Cd,and YE,while its suppressing effect on the cell growth was as severe as Ag,Cd,and YE.In summary,the results indicate that Ag,Cd,YE are the most favorable elicitors for the tanshinone production in S .miltiorrhiza cell culture and were used in the following experiments.Figure 3shows the time courses of cell growth and tanshinone production after treatment with the three most effective elicitors Ag (25μM),Cd (25μM),and YE (100mg l -1)and the control culture.All three elicitor treatments caused a steady decline of biomass concentration from initially 8.5g l -1to 5.3g l -1on day 6while biomass in00.040.080.120.160.20246810TT content (mg g -1)C e l l b i o m a s s (g d w l -1)dw TTa4.85.1 5.45.76.001020304036912151821242730p HS u c r o s e (g l -1)Culture time (d)bSucrosepHFig.1Time courses of biomass and total tanshinone content (a ),residue sugar (sucrose)and medium pH (b )in S .miltiorrhiza cell cultures (error bars for standard deviations,n =3)246810C e l l b i o m a s s (g l -1)0.00.51.01.52.02.5Control AgCdSAMJYECH SOT T c o n t e n t (m g g -1)Elicitor treatmentCo Fig.2Effects of various elicitors on biomass growth (a )andtanshinone production (b )in S .miltiorrhiza cell cultures (elicitors added to cultures on day 18at three concentrations C1,C2,and C3as shown in Table 1,and cultures harvested on day 25;error bars for standard deviations,n =3)the control culture was increased during this period (Fig.3a ).In the meantime,the tanshinone content of cells in the three elicitor-treated cultures increased sharply and most rapidly by Ag (from 0.14to 1.98mg g -1),while that of control increased slightly (from 0.14to 0.21mg g -1;Fig.3b ).The volumetric total tanshinone yields (the products of total tanshinone content and cell dry weight)were 1.9mg l -1in the control,and 9.2mg l -1,10.7mg l -1and 11.7mg l -1in cultures treated with 100mg l -1YE,25μM Cd,and Ag,respectively (on day 6).Another test was performed on the effects of two and three elicitors in combinations in the S .miltiorrhiza cell culture.As shown in Fig.4,the tanshinone content was increased about 20%with either two elicitors and about 40%with all three elicitors in combination compared with that with a single elicitor.The results suggest an additive or synergistic effect of these elicitors on the tanshinone accumulation in the cells.However,the combined use of two or three elicitors also suppressed the cell growth (biomass)more severely than with a single elicitor.Effects of elicitor treatments on different tanshinone species Of the three tanshinone species detected,CT was stimulated most significantly by all elicitors without exception;T-IIA was stimulated by most elicitors,and T-I was stimulated significantly only by chitosan but slightly stimulated or suppressed by other elicitors (Table 2).The highest CT content was about 2mg g -1(1,854–2,011μg g -1)in cellcultures treated with 25μM Ag and Cd,and 100mg l -1YE,about 31–34fold of the control level (60μg g -1),the highest T-I content 0.27mg g -1with 100mg l -1chitosan (3.4-fold of the control 80μg g -1)and the highest T-IIA content 0.37mg g -1with 25μM Cd (6-fold of the control 60μg g -1).As seen from the HPLC chromatograms (Fig.5),the cultures treated with the three different elicitors exhibited a similar profile with virtually identical major peaks.The experimental results do not suggest any specificity of particular tanshinone species to the type of elicitors,YE and chitosan as biotic polysaccharides,Cd and Ag as abiotic heavy metals,or SA and MJ as plant stress signaling pared with that of control,the HPLC profiles of elicitor-treated cultures also had three new unknown peaks appearing before the CT peak,between 10.0–11.5min and a high peak at 11.1min,which0.00.51.01.52.02.5123456T T c o n t e n t (m g g -1)Time after treatment (d)b4681012C e l l b i o m a s s (g l -1)Control Ag 25Cd 25YE 100aFig.3Time courses of biomass (a )and total tanshinone content (b )in S .miltiorrhiza cell cultures after treatment with Ag (25µM),Cd (25µM),and YE (100mg l -1;error bars for standard deviations,n =3)24681012345Cell dry weight (g l -1)T T c o n t e n t (m g g -1)Elicitor treatmentTTdwFig.4Effects of single and combined elicitors on S .miltiorrhiza cell growth and tanshinone accumulation (elicitors added to cell cultures on day 18at the same concentrations as in Fig.3,and cultures harvested on day 25;error bars for standard deviations,n =3)Table 2Effects of various elicitors on the accumulation of three tanshinones in S .miltiorrhiza cells Treatment aContent,μg/g (fold of content control)CTT-IT-IIA Control 59.9(1)81.6(1)57.6(1)Co-50263.7(4.4)67.5(0.83)55.5(0.96)Ag-251,817.5(30)71.0(0.87)225.8(3.9)Cd-251,854.0(31)80.3(0.98)369.0(6.4)SA-100390.0(6.5)78.5(0.96)72.8(1.3)MJ-100299.8(5.0)109.5(1.3)82.6(1.4)YE-1002,011.4(34)90.3(1.1)190.3(3.3)CH-100597.2(10)276.0(3.4)98.8(1.7)SO-50584.6(9.8)56.9(0.70)83.0(1.4)CT cryptotanshinone,T-I tanshinone I,T-IIA tanshinone-IIAaNumber after each elicitor symbol represents the elicitor concentra-tion as shown in Table 1may be ascribed to tanshinone relatives of higher polarity than CT induced by the elicitors.PAL activity,pH,and conductivity changes induced by elicitorsFigure 6shows the changes of intracellular PAL activity and medium pH and conductivity in the S .miltiorrhiza cell culture after the treatment by Ag (25μM),Cd (25μM),and YE (100mg l -1).The PAL activity of cells was stimulated by all three elicitors to the similar level,from 1.4-to 1.9-fold of the control level over 6days (Fig.6a ).PAL is a key enzyme at the entrance step in the phenylpropanoid pathway in plants,and its activity increase stimulated by the elicitors is suggestive of an enhanced secondary metabolism in the plant cells (Taiz and Zeiger 2006).The pH and conductivity of culture medium were also increased (to higher levels than those of the control)by all three elicitors but more significantly by YE (Fig.6b,c ).Most significant increases (differences from the control level)in the medium pH and conductivity were shown in the very early period from day 0–1.The increase in medium conductivity in the early period was most probably attributed to the release of potassium K +ion from the cells or K +efflux across the cell membrane (Zhang et al.2004).Transient medium pH increase (alkalinization)and K +efflux across the cell membrane are early and important events in the elicitation of plant responses and phytoalexin production (Ebel and Mithöer 1994;Roos et al.1998).The conductivity decline in the later period after day 1of Ag +and Cd 2+-treated cultures and the control cultures can be attributed to the consumption of inorganic and mineral nutrients in the culture medium (Kinooka et al.1991).Overall,the results here provide further evidence forthe01234R e l a t i v e P A L a c t i v i t yControl Ag CdYEa5.05.45.86.26.6M e d i u m p H b2.03.04.05.06.00246M e d i u m c o n d u c t i v i t y (m S )Time after treatment (d)cFig.6Time courses of PAL activity (a ),medium pH (b ),and conductivity (c )of S .miltiorrhiza cell cultures after elicitor treatments in comparison with the control (error bars for standard deviation,n =3)elicitor activities of Ag,Cd,and YE in stimulating the stress responses and secondary metabolism of the S. miltiorrhiza cells.DiscussionThe effects of various elicitors on tanshinone accumulation found here in the normal tiorrhiza cell cultures are in general agreement with those found in transformed cell and hairy root cultures of tiorrhiza.In transformed cell cultures(Chen and Chen1999),the CT accumulation was also stimulated significantly by YE but not by SA or MJ alone,and YE also inhibited the cell growth.The tanshinone(mainly CT)production in hairy root cultures was also enhanced significantly(3–4fold)by Ag(Zhang et al.2004)and YE(Shi et al.2007).In all these culture systems,CT was the major tanshinone species stimulated by various elicitor treatments.CT has been identified as a phytoalexin in tiorrhiza plant which plays a defense role against pathogen invasion of the plant(Chen and Chen 2000).In this connection,the stimulated CT accumulation by the elicitors may be a defense or stress response of the cells.CT was also the major diterpenoid produced by a normal tiorrhiza cell line which was initially grown in the MS medium and then transferred to a production medium containing only about half of the nutrient compo-nents of the MS medium(Miyasaka et al.1987).It is very possible that the improvement of CT yield in this production medium was also attributed,at least partially, to the stress imposed by the nutrient deficiency which suppressed growth but stimulated secondary metabolite accumulation.MJ or its relative jasmonic acid has been shown effective for stimulating a variety of secondary metab-olites in plant tissue cultures such as hypericin in Hypericum perforatum L.(St.John’s Wort)cell cultures (Walker et al.2002),paclitaxol(diterpenoid)and related taxanes in various Taxus spp.and ginsenosides in Panax spp.(Zhong and Yue2005),and bilobalide and ginkgo-lides in Ginkgo biloba cell cultures(Kang et al.2006). However,MJ showed only a moderate or insignificant stimulating effect on tanshinone accumulation in normal and transformed tiorrhiza cell cultures.The discrep-ancy suggests that the effects of various elicitors on secondary metabolite production in plant tissue cultures are dependent on the specific secondary metabolites.This argument is also supported by the much stronger stimu-lation of CT than T-I and T-IIA by most elicitors found in our tiorrhiza cell cultures.In addition,the hairy roots appeared more tolerant to the elicitor stress,and the growth was less inhibited by the elicitors or even enhanced in some cases,e.g.,by YE(Chen et al.2001)and sorbitol(Shi et al.2007).Moreover,sorbitol as an osmotic agent significantly stimulated the tanshinone accumulation(3–4folds)in tiorrhiza hairy root cultures,but not so significantly in the cell cultures.This shows that the elicitor activities for the same metabolites can vary with the tissue culture systems.In conclusion,the polysaccharide fraction of yeast extract and two heavy metal ions Ag+and Cd2+were potent elicitors for stimulating the tanshinone production in tiorrhiza cell culture.The stimulated tanshinone production by most elicitors was associated with notable growth suppression.CT was more responsive to the elicitors and enhanced more dramatically than another two tanshinones,T-I and IIA.The results from this study in the tiorrhiza cell cultures and from previous studies in hairy root cultures suggest that the cell and hairy root cultures may be effective systems for CT production, provided with the elicitors.As most of the elicitor chemicals are commercially available or can be readily prepared in the laboratory and easily administered to the cell and root cultures,they are suitable for practical applications in the laboratory or large-scale production. Acknowledgements This work was supported by grants from The Hong Kong Polytechnic University(G-U502and1-BB80)and the China Hi-Tech Research and Development Program(2006AA10A209).ReferencesBuitelaar RM,Cesário MT,Tramper J(1992)Elicitation of thiophene production by hairy roots of Tagetes patula.Enzyme Microb Technol14:2–7Chen H,Chen F(1999)Effects of methyl jasmonate and salicylic acid on cell growth and cryptotanshinone formation in Ti transformed Salvia miltiorrhiza cell suspension cultures.Biotechnol Lett 21:803–807Chen H,Chen F(2000)Effect of yeast elicitor on the secondary metabolism of Ti-transformed Salvia miltiorrhiza cell suspension cultures.Plant Cell Rep19:710–717Chen H,Chen F,Chiu FCK,Lo CMY(2001)The effect of yeast elicitor on the growth and secondary metabolism of hairy root cultures of Salvia miltiorrhiza.Enzyme Microb Technol28:100–105Cheng XY,Zhou HY,Cui X,Ni W,Liu CZ(2006)Improvement of phenylethanoid glycosides biosynthesis in Cistanche deserticola cell suspension cultures by chitosan elicitor.J Biotechnol 121:253–260Chong TM,Abdullah MA,Lai QM,Nor’Aini FM,Lajis NH(2005) Effective elicitation factors in Morinda elliptica cell suspension culture.Process Biochem40:3397–3405Ebel J,Mithöer A(1994)Early events in the elicitation of plant defence.Planta206:335–348Ebell LF(1969)Variation in total soluble sugars of conifer tissues with method of analysis.Phytochemistry8:227–233Ge XC,Wu JY(2005)Tanshinone production and isoprenoid pathways in Salvia miltiorrhiza hairy roots induced by Ag+and yeast elicitor.Plant Sci168:487–491。

1-s2.0-S0263436814001590-main

Effect of rare earth elements on the consolidation behavior and microstructure of tungsten alloysMingyue Zhao a ,Zhangjian Zhou a ,⁎,Qingming Ding a ,Ming Zhong a ,Kameel Arshad ba School of Materials Science and Engineering,University of Science and Technology Beijing,Beijing 100083,China bSchool of Physics and Nuclear Energy Engineering,Beihang University,Beijing 100191,Chinaa b s t r a c ta r t i c l e i n f o Article history:Received 11February 2014Available online 23July 2014Keywords:Rare earth element Tungsten alloyConsolidation behavior MicrostructureThe effects of rare earth elements (Y 2O 3,Y and La)on the consolidation behavior,microstructure and mechanical properties of tungsten alloys were investigated in this work.The starting powders were mechanical alloyed (MA)and then consolidated by spark plasma sintering (SPS).It was found that Y doping was bene ﬁcial to obtain fully dense tungsten alloys with more re ﬁned grains as compared to any other rare earth elements.The maximum values of Vickers microhardness and bending strength obtained from W –0.5wt.%Y alloy reached up to 614.4HV 0.2and 701.0MPa,respectively.©2014Elsevier Ltd.All rights reserved.IntroductionTungsten is a promising candidate material for high temperature applications due to its attractive properties,such as high melting point,high conductivity,low thermal expansion coef ﬁcients and low sputtering yield [1].However,a major limitation of its use is the inherently high ductile –brittle transition temperature (DBTT)and low recrystallization temperature.Fine grained tungsten materials have shown improved properties in terms of reduced brittleness and improved toughness and strength [1,2].However,the improved mechanical properties will be deteriorated when exposed to high temperatures for long time and when the service temperature is higher than the recrystallization temperature of pure tungsten.Recent studies suggested that the dispersion of high temperature oxide nanoparticles,such as La 2O 3and Y 2O 3,will not only inhibit the grain growth of W during the consolidation but also stabilize the microstructure when exposed to higher temperature [3,4].It is well known that,the impurities,especially for oxygen,have det-rimental in ﬂuence on the sinterability of tungsten powders and make tungsten materials embrittlement.Thus adding rare earth elements in the metallic state instead of the oxidic state should be better for fabrica-tion of high performance tungsten alloys,due to the high af ﬁnity of rare earth elements with oxygen.A recent research conducted by L.Veleva et al.[5]found that the relative density of W –(0.3–2)wt.%Y appeared higher than that of W –(0.3–2)wt.%Y 2O 3,however,the microhardnessappeared always lower than that of W –(0.3–2)wt.%Y 2O 3.From the viewpoint of oxygen absorption,it is suggested that La will be better than Y when used as alloying element for fabrication of W [6].However there are almost no reports on W –La alloy and their comparison with W –Y alloy.It will be interesting and important to investigate the effects of different rare earth elements on the densi ﬁcation of W and their mechanical properties.This is the motivation of this work.In this study the effect of rare earth elements,including Y 2O 3,Y and La on the consolidation behavior of W under the same sintering condi-tion was investigated.The microstructural evolution and mechanical properties of different rare earth tungsten materials were examined and compared.Experimental proceduresPowders of commercial pure W (with an average particle size of 2.0μm and a purity of 99.9%),rare earth element of Y or La (with an av-erage particle size of 48μm and a purity of 99.9%),and rare earth oxide of Y 2O 3(with an average particle size of 30nm and a purity of 99.9%)were used as starting materials.The mixture powders of W –0.5wt.%Y 2O 3(named as WYO),W –0.5wt.%Y (named as WY)or W –0.5wt.%La (named as WL)were mechanical alloyed (MA)in a planetary ball mill,respectively.The MA parameters can be found in our previous work [7,8].Then,the MA treated powders were placed into graphite tool in glove box and sintered by spark plasma sintering (SPS)in vacuum.Fig.1shows the temperature and pressure pro ﬁle of SPS as a function of time.In order to get fully dense bulk materials by suppress-ing the pore-boundary separation,the samples were ﬁrst sintered at 1373K for 2min and then sintered at 1873K according to [9].Int.Journal of Refractory Metals and Hard Materials 48(2015)19–23⁎Corresponding author at:Laboratory of Special Ceramics and Powder Metallurgy,School of Materials Science and Engineering,University of Science &Technology Beijing,Beijing 100083,PR China.Tel./fax:+861062334951.E-mail address:zhouzhj@ (Z.Zhou)./10.1016/j.ijrmhm.2014.07.0140263-4368/©2014Elsevier Ltd.All rightsreserved.Contents lists available at ScienceDirectInt.Journal of Refractory Metals and Hard Materialsj 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 /I J R M H MThe shrinkage of the specimens was continuously monitored by the displacement of the punch rod.The density of the compacts was measured by Archimedes method.A ﬁeld emission scanning electron microscope (FE-SEM)equipped with Energy-dispersive X-ray Spectros-copy (EDS)and Scanning electron microscope (SEM)were employed to investigate the microstructural features,i.e.,the element distribution,and the size and morphology of the grains and the pores of the samples.Moreover,XRD was used to determine the phase and X-ray diffraction analysis was made by the Rietveld method using the Full prof program [10].The average crystallite size as well as the internal stress of the MA treated powders were determined from the diffraction peak widths taking into account the diffractometer resolution function.Vickers mi-crohardness was measured at room temperature by applying a load of 1.96N for 15s.Three point bending tests were conducted on specimens with dimensions of 2mm ×3mm ×18mm with a span of 13.1mm and a crosshead speed of 0.5mm/min.The thermal behavior of the MA treated powders in the range 373–1723K was investigated by differen-tial scanning calorimetry (DSC)at a heating rate of 10K/min in ﬂowing pure Ar.Results and discussion Consolidation behaviorFig.2compares the consolidation behavior of all tungsten alloys as a function of temperature.It can be clearly seen that the displacement of WY alloy is similar with that of WL alloy,and shows quite different ten-dency from that of WYO alloy,especially at the sintering temperature of 1373K.For WY and WL alloys,the displacement decreased by 0.6mm between 993K and 1373K due to the thermal expansion of graphite punch rods and the matrix overweighing the contribution of pre-compaction,and continued to decrease at the sintering temperature of 1373K.For WYO alloy,the displacement experiences a slower down-ward trend between 993K and 1373K and a weak upward trend at 1373K.After that,the displacement of WY sees a similar trend with that of WYO.It was found that the WY alloy experienced a substantial decrease in the displacement while the WYO alloy experienced a slight increase at the temperature of 1373K.This result is likely to arise from the formation of a higher volume of Y 2O 3due to the oxidation of Y ele-ment in the WY system.Chemical analysis of the consolidated compacts was performed by the HORIBA EMIA-820V and LECO TCH600devices to measure the C and O contents,respectively.It shows that the C contents were about 240ppm for various tungsten materials fabricated under the same conditions.The amount of oxygen content which existed in MA treated WY powders was 0.4808wt.%,which is enough for the reactionwith added Y particles to form Y 2O 3.Fig.3shows the DSC curve of the MA treated WY powders in the range 373–1723K.A weak exothermic peak at 1500K with an onset temperature of 1400K is found.It probably corresponds to the oxidation of the metallic Y with the residual oxygen in a hermetically sealed pan,which also illustrates that the remaining Y particles are likely to start to react with oxygen around 1373K during SPS.Moreover,a sharp strong and a small exothermic peak can be clear-ly seen at 1003K and 1173K,respectively.According to [11,12],these peaks indicate that the strain relief took place during the heating of MA treated powders.Similar results on the oxygen analysis and the thermal behavior are also found for MA treated WL powders.Fig.4shows the milling and sintering effect on the XRD patterns of the investigated samples.It is obvious that the diffraction peaks are broadened after milling,which was caused by the re ﬁnement of powder particles and a high level of internal strain in the W grains fabricated by the MA process.After sintering,the diffraction peaks become narrow again due to the grain growth and strain relief.The quantitative data on such grain growth and strain relief can be obtained by the compari-son of lattice parameters after each stage of the powder processing (Table 1).It should be noted that the XRD patterns for all samples after milling exhibit a single BCC phase,suggesting that the rare earth elements were dissolved into the W lattice.This solid solutionduringFig.1.The temperature and pressure pro ﬁle as a function of time for the sintering experiments of rare earth tungstenalloys.Fig.2.The real time sintering curves of all samples without removing the contribution of the thermal expansion of the graphite tool andmatrix.Fig.3.DSC curve of the MA treated WY powder.The peak temperatures of thermally induced transformation of the powders are indicated by arrows.20M.Zhao et al./Int.Journal of Refractory Metals and Hard Materials 48(2015)19–23the MA process can be further demonstrated by the lattice parameter increase of the MA treated powders compared with that of the starting pure tungsten powder (Table 1).Microstructure observationMicrostructure of the fracture surfacesThe fracture surfaces of WY,WYO and WL samples are presented in Fig.5.It can be clearly seen that the rare earth elements in ﬂuence the grain re ﬁnement signi ﬁcantly.Fig.6shows the grain size distribution which was determined from the SEM micrographs of fracture surfaces.For each image,about 130grains were chosen randomly to eliminate the bias of grain counting.The grain size distributions of WL and WYO alloys are in the range from 1.6to 8.0μm and from 0.8to 4.4μm,respec-tively,and their average grain sizes are 2.46μm and 4.62μm,respective-ly;while,the average grain size of WY alloy is only 1.10μm,which is much smaller than that of WL and WYO alloys.The grain size distribu-tion of WY alloy is in the range from 0.3to 2.0μm,which is much nar-row as compared with that of WL and WYO alloys.Moreover,it is worth noting that the average grain size acquired from the SEM images of fracture surfaces has a remarkable consistency with those calculated by the Rietveld method using the Full prof program,as shown in Table 1.More careful analysis of Fig.6reveals that the WY alloy is denser than WYO and WL alloys.Many big worm-like pores (indicated by yel-low arrows)and small pores (indicated by white dot circles)can be found for WYO and WL alloys on the surface of individual tungstengrains and in the triple junctions.It is easy to learn that the tungsten grains with different additions grew up in a different speed (WL N WYO N WY)according to the average grain size of each stage of powder processing.Besides,the grain growth of pure tungsten or ODS W-based materials sintered by SPS starts between 1373K and 1773K according to literature [9,13].Under a certain pressure between 1773K and 1873K in our present work,the smaller the grain size,the easier the re-arrangement and plastic deformation,and thus higher shrinkage can be achieved.During the holding time at sintering temperature (1873K),grain growth took place simultaneously with further densi ﬁcation,which was achieved dominantly by more homogeneous interfacial atomic diffusion but with minimized involvement of surface diffusion according to [9].Meanwhile,the worm-like pores could be formed if the holding time at sintering temperature of 1873K was not enough for W –0.5La alloy having a large grain size.The microstructure of chemically etched surfacesThe microstructures of chemically etched surface are illustrated in Fig.7.EDS analysis indicated that the black phases which existed in WYO,WY and WL alloys are rare earth oxides (indicated by blue ar-rows)and the dark gray phases are pores (indicated by red arrows).For WY alloy (Fig.7b),pores can hardly be found,which is consistent with the microstructure observation of the fracture surface.Besides,ﬁne Y 2O 3particles are distributed uniformly along grain boundaries of WY alloy;while for WYO and WL alloys (Fig.7a and c),many micro-scale pores are found in triple junctions and tungsten grain boundaries,especially for WL alloy.Moreover,the FESEM images shown in Fig.7a and c reveal that the oxide particles are irregular and not distributed uniformly.In the XRD measurements performed on the WL alloy (Fig.4and Table 1),a weak diffraction peak of La 2O 3phase and lattice parameter decrease of sintered WL alloy are observed,which also suggest that the La particles separate from tungsten grains and become micro-scale La 2O 3during sintering.The densi ﬁcation analysisTable 2shows the relative density of the rare earth tungsten alloys.The relative density of WY reaches 99.4%,which is much higherthanFig.4.Effect of milling and SPS sintering on the XRD patterns of rare earth tungsten alloys.(a)MA treated powders,and (b)sintered compacts.Table 1Lattice parameters after each stage of the powder processing and the average grain size ac-quired from the SEM images of fracture surfaces.SamplePowder Sintered compact Crystallite size (nm)lattice strain (%)a (W:nm)Grain size (nm)Lattice strain (%)Grain size (nm)—SEM WY 8050.3510.31646215220.0701100WL 4100.3010.31659956650.0414620WYO 6200.3860.31653424820.0342460W11740.0450.31604021M.Zhao et al./Int.Journal of Refractory Metals and Hard Materials 48(2015)19–23the WYO (92.1%)and WL (88.3%).This result is agreeable with the mi-crostructure observation.Owing to the grain boundary cleaning effect and sintering enhancing effect of Y particles during SPS,Y doping is ben-e ﬁcial to achieve fully dense tungsten alloys than Y 2O 3doping.On the other hand,the well-distributed ﬁne Y 2O 3dispersions which existed in WY alloy play a prominent role in the re ﬁnement of tungsten grains,thus dense ﬁne grained sample can be obtained under the present sintering process.Kim et al.[14]reported that the second phases can act as obstacles in inhibiting the grain growth only in solid phase sintering.Owing to the formation of metallic La liquid phase at 1193Kaccording to the phase diagram Mo –La and then the formation of micro-scale and non-uniformly distributed La 2O 3dispersions as a result of oxidation,the grain growth speed of WL alloy is much higher than that of WYO and WY alloys.Thereby,the relative density of WL alloy is lower than that of WYO alloy and WY alloy even though La particles can exert cleaning effect on the tungsten grain boundaries.Besides,in accordance with literatures [4,15,16],the internal energy originating from the signi ﬁcant strain of the particles could serve as a part of sintering driving force.As shown in Table 1,the lattice strain of WL alloy is 0.301%,lower than that of WYO (0.386%)and WY (0.351%),which is another reason for the lower relative density of WL alloy.The basic mechanical propertiesVickers microhardness and bending strength of the rare earth tung-sten alloys were also listed in Table 2.Of all the three kinds of tungsten materials,the hardness of WY sample is 614.4HV 0.2,much higher than that of WYO (445.2HV 0.2)and WL (303HV 0.2).The lower hardness of WYO and WL alloys originates from the lower relative density and coarse grain size,as shown in Figs.5and 6.Moreover,WY exhibits the highest bending strength (701MPa)among these tungsten alloys,which is 11%and 88%higher than that of WYO and WL alloys.As shown in Fig.5,the remaining pores,including worm-like pores and small pores,reduce the contact area of tungsten grains,thus the bending strength of WYO and WL to some extent decreases.Besides,the coarse grain size (Fig.6)and inhomogeneous dispersions of oxide particles (Fig.7)of WYO and WL alloys are also the reason for their low bending strength.ConclusionsTungsten alloys were successfully fabricated by adding different rare earth elements to W matrix.The effect of dispersing rare earthelementsFig.5.SEM micrographs of fracture surfaces for:(a)WYO,(b)WY,and (c)WL;the yellow arrows denote worm-like pores existed on the surface of individual grains,and the white dot circles denote pores located in the triplejunctions.Fig.6.Histograms of the grain size distributions for WYO,WY and WL alloys.22M.Zhao et al./Int.Journal of Refractory Metals and Hard Materials 48(2015)19–23on the microstructure evolution and mechanical properties of the tung-sten alloys can be concluded as follows:(1).The relative density of WY,WYO and WL alloy reached 99.4%,92.1%and 88.3%,respectively.The Y doping was bene ﬁcial toobtain fully dense tungsten alloys as compared with Y 2O 3doping and La doping because the ﬁnely distributed second phase parti-cles suppressed the tungsten grain growth and thus ensured the suf ﬁcient grain boundary volume available for densi ﬁcation by grain boundary diffusion.The analysis of consolidation behavior and thermal behavior of MA treated WY or WL powders revealed that the added Y or La particles were likely to start to react with oxygen around 1373K during SPS.(2).The average grain sizes of WY,WYO and WL alloys were 1.10μm,2.46μm and 4.62μm,respectively.The Y doping was bene ﬁcial to obtain tungsten alloys with more re ﬁned tungsten grains as com-pared with Y 2O 3doping and La doping.(3).Of all the three kinds of rare earth tungsten alloys,WY alloy ex-hibited the highest mechanical properties at room temperature.The maximum values of Vickers microhardness and bending strength reached up to 614.4HV 0.2and 701.0MPa,respectively.AcknowledgmentsThe authors would like to express their thanks for the ﬁnancial support of the National Natural Science Foundation of China under grant No.50634060.References[1]Zhang Y,Ganeev AV,Wang JT,Liu JQ,Alexandrov IV.Observations on the ductile-to-brittle transition in ultra ﬁne-grained tungsten of commercial purity.Mater Sci Eng A 2009;503:37–40.[2]Kitsunai Y,Kurishita H,Kayano H,Hiraoka Y,Igarashi T,Takida T.Microstructure andimpact properties of ultra-ﬁne grained tungsten alloys dispersed with TiC.J Nucl Mater 1999;271–272:423–8.[3]Kim Y,Lee KH,Kim E,Cheong D,Hong SH.Fabrication of high temperature oxidesdispersion strengthened tungsten composites by spark plasma sintering process.J Refract Met Hard Mater 2009;5:842–6.[4]Wang HT,Fang ZZ,Hwang KS,Zhang HB,Siddle D.Sinter-ability of nanocrystallinetungsten powder.Int J Refract Met Hard Mater 2010;28:312–6.[5]Veleva L,Oksiuta Z,Vogt U,Baluc N.Sintering and characterization of W –Y andW –Y 2O 3materials.Fusion Eng Des 2009;84:1920–4.[6]Brown PH,Rathjen AH,Graham RD,Tribe DE.Chapter 92rare earth elements inbiological systems.Handbook on the physics and chemistry of rare earths;1990.p.423–52.[7]Zhou ZJ,Tan J,Qu DD,Pintsuk G,Rödig M,Linke J.Basic characterization of oxidedispersion strengthened ﬁne-grained tungsten based materials fabricated by me-chanical alloying and spark plasma sintering.J Nucl Mater 2012;431:202–5.[8]Tan J,Zhou ZJ,Zhu XP,Guo SQ,Qu DD,Lei MK,et al.Evaluation of ultra-ﬁne grainedtungsten under transient high heat ﬂux by high-intensity pulsed ion beam.Trans Nonferrous Metals Soc China 2012;22:1081–5.[9]Ma J,Zhang JZ,Liu W,Shen ZJ.Suppressing pore-boundary separation during sparkplasma sintering of tungsten.J Nucl Mater 2013;438:199–203.[10]Rodríguez-Carvajal J.Recent advances in magnetic structure determination byneutron powder diffraction +FullProf.Physica B 1993;192:55–6.[11]Muñoz A,Monge MA,Savoini B,Rabanal ME,Garces G,Pareja 2O 3-reinforced Wand W –V alloys produced by hot isostatic pressing.J Nucl Mater 2011;417:508–11.[12]Maweja K,Phasha MJ,Choenyane LJ.Thermal stability and magnetic saturation ofannealed nickel –tungsten and tungsten milled powders.J Refract Met Hard Mater 2012;30:78–84.[13]Yar MA,Wahlberg S,Bergqvist H,Salem HG,Johnsson M,Muhammed M.Spark plas-ma sintering of tungsten –yttrium oxide composites from chemically synthesized nanopowders and microstructural characterization.J Nucl Mater 2011;412:227–32.[14]Kim Y,Hong MH,Lee SH,Kim EP,Lee S,Noh JW.The effect of yttrium oxide on thesintering behavior and hardness of tungsten.Met Mater Int 2006;12:245–8.[15]Han Y,Fan JL,Liu T,Cheng HC,Tian JM.The effects of ball-milling treatment on thedensi ﬁcation behavior of ultra-ﬁne tungsten powder.Int J Refract Met Hard Mater 2011;29:743–50.[16]Prabhu G,Chakraborty A,Sarma B.Microwave sintering of tungsten.Int J Refract MetHard Mater 2009;27:545–8.Fig.7.FESEM micrographs of chemically etched surface of:(a)WYO,(b)WY,and (c)WL.Table 2The relative density and basic mechanical properties of rare earth tungsten alloys.Sample Relative density (%)Microhardness (HV 0.2)Bending strength (MPa)WYO 92.1445.2631WY 99.4614.4701WL88.3303372.123M.Zhao et al./Int.Journal of Refractory Metals and Hard Materials 48(2015)19–23。

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Coulter Award (ACD 12/10) (NEAC 11/23/10)International Congress of GRS and the IGF Travel Award (ACD 12/08)International Congress of Radiation Research (ICRR) ICRR Travel Award (ACD 6/08)International Cytokine Society •Post-Doctoral Investigator Award (ACD 12/07)•Honorary Life Member Award (ACD 12/11) (NEAC 3/1/11)•Outstanding Scholar Award (ACD 12/08)•Young Investigator Award (ACD 12/08)International Feline Retroviruses ResearchSymposiumYoung Investigator Award (ACD 6/09)International Foot and Ankle Biomechanics The Best Paper Award (ACD 6/09)International Mammalian Genome Society 2006 International Mammalian Genome (ACD 6/07)International Personnel Management Association(IPMA)Linda Trunzo Humanitarian Award (ACD 12/06)International Society for Biological Therapy of Cancer Presidential Travel Award (ACD 6/09)International Society of Biomechanics (ISB) Clinical Biomechanics Award (ACD 12/11)International Society of Blood Transfusion Presidential Award (ACD 6/12) (NEAC 6/25/12)International Society of Dermatopathology The Sabine Kohler Lecture and Award (ACD 12/11) International Society for Eye Research •Endre A. Balazs Prize (ACD 2/05)•Ernst H. Barany Prize (ACD 2/05) International Society for Heart Research ISHR Distinguished Leader Award (ACD 6/10)International Society for Interferon & Cytokine Research •Millstein Award (ACD 3/05) (NEAC 10/19/04)•Seymour and Vivian Milstein Travel Award (ACD 6/10) (NEAC 11/11/08)International Society for the Study of Xenobiotics ISSX North American Scientific Achievement Award (ACD 12/06)Institute of Medicine, National Academies of Science •Rhoda & Bernard Sarnat International Award in Mental Health (ACD 2/05)•Gustav O. Lienhard Award (ACD 2/05)James t. and Sarah F. Fries Foundation Elizabeth Fries Health Education Award (ACD 12/12) (NEAC 10/23/12)Japan Rheumatism Foundation Japan Rheumatism Foundation International Award (ACD 6/06) (NEAC 2/12/06)Japan Society for the Promotion of Science International Prize for Biology (ACD 12/09)(May accept honor but not the cash prize) Jellinek Memorial Fund Jellinek Memorial Award (ACD 12/07) (NEAC 6/19/07)Johns Hopkins University Bloomberg School of PublicHealthMargaret Merrell Award for Excellence in Research (ACD 12/06)Johns Hopkins University School of Medicine Research Festival Top Abstract Award (ACD 12/08)Keystone Symposia •Anita Roberts Young Scientist Scholarship Award (ACD 6/08)•Global Health Travel Awards and Travel Scholarships (ACD 12/07)•Keystone Symposia Minority Scholarship Award (ACD 12/07)Kinship Foundation Searle Scholars Program (ACD 2/06)Korean-American Scientists and EngineersAssociationKUSCO-KSEA Scholarship for Graduate Students in the US (ACD 12/08) Kuratorium des Weitbrecht-Wissenschaftspreis Hans-Joerg-Weitbrecht-Wissenschaftspreis (ACD 6/09) (NEAC 5/26/09)Laurentian Conference of Rheumatology Roger Demers Prize (ACD 6/08) (NEAC 4/1/08)Lawson Wilkins Pediatric Endocrine Society Human Growth Foundation Award (ACD 6/10)Leukemia and Lymphoma Society Nurse of the Year Award (ACD 6/08)Linus Pauling Institute at Oregon State University Linus Pauling Institute Prize for Health Research (ACD 6/07)Lymphoma Foundation of America Young Scientist Award (ACD 6/08)Maureen & Mike Mansfield Foundation Mansfield Fellowship Program (ACD 2/05)Massachusetts Institute of Technology •Edward M Scolnick Prize in Neuroscience Research (ACD 4/05) (NEAC 3/22/05)•The $500,000 Lemelson MIT Award for Invention & Innovation (ACD 12/06)•The $100,000 Lemelson MIT Award for Sustainability (ACD 12/06)MD Anderson Cancer Center Annual John Mendelssohn AwardMedical Laboratory Immunologists Erwin Neter Award (ACD 12/10)Medical Library Association •Lucretia W. McClure Excellence in Education Award (ACD 6/07)•MLA Research Award (ACD 12/11)•Thomson Scientific/Frank Bradway Rogers Information Advancement Award (ACD 2/05) Memorial Sloan-Kettering Cancer Center •Paul Marks Prize for Cancer Research (ACD 4/05)•Niehaus Southworth Weissenbach Award in Preventive Cancer Genetics (ACD 12/10) Metropolitan District of Columbia Respiratory SocietyResearchBest Poster for Basic Science Research Award (ACD 12/10)Microscopy Society of America (MSA) MSA Presidential Student Award (ACD 6/07)Mid-Atlantic Association of Blood Banks Mary C. Doerr Meritorious Services Award (ACD 12/08)Millennium Prize Foundation Millennium Technology Prize (ACD 4/05)Myrovlytis Trust Myrovlytis Trust Travel Award - BHD Symposium (ACD 12/08)。

Pearson Edexcel Mathematics Awards 产品说明书

The Pearson Edexcel Mathematics Awards (Level 1, Level 2 and Level 3)Frequently Asked Questions1. What are the Pearson Edexcel Mathematics Awards?The Pearson Edexcel Mathematics Awards are a suite of stand-alone academicqualifications in mathematics which support the GCSE, International GCSE, BTEC and GCE qualifications that are offered in schools and colleges.Each award:•takes approximately 60-70 hours to deliver as a stand-alone (roughly the size of halfa GCSE)•is assessed externally through written papers•is awarded pass or unclassified•is available at different levels (Level 1, Level 2 or Level 3)2. What Pearson Edexcel Mathematics Awards are available?The following Awards have been accredited:•Pearson Edexcel Level 1 Award in Number and Measure•Pearson Edexcel Level 2 Award in Number and Measure•Pearson Edexcel Level 2 Award in Algebra•Pearson Edexcel Level 3 Award in Algebra3. Which students are these qualifications aimed at?These qualifications are aimed at students who:•need to develop their mathematical skills in a particular area (e.g. number and measure or algebra) and build confidence in the subject before progressing to GCSE or GCE mathematics or further study•want to gain a qualification which demonstrates their mathematical ability.4. Do these qualifications attract performance table points?None of the qualifications receive performance table points.5. How are the Pearson Edexcel Mathematics Awards assessed?The Pearson Edexcel Mathematics Awards are externally assessed. The table below shows the structure of the written papers.More information can be accessed via our dedicated webpage at /edexcelmathsaward.6. Do the level 3 awards get UCAS points?Yes the Level 3 Award in Algebra does attach a total of 3 UCAS points. More information can be found on page 143 of the UCAS Tariff Table document.7. When are the examinations available for students to take?The Pearson Edexcel Awards suite is available in January and May every year.8. How and when are results published?Students will be awarded pass or unclassified. Results from Level 1 and Level 2examinations taken in May will be published on GCSE results day in August. Results from Level 3 examinations taken in May/June will be published on GCE results day in August.Results from examinations taken in January will be published mid-March.9. When can I start teaching these qualifications?The Pearson Edexcel Awards in Number and Measure have been available for firstteaching from September 2011 and the Pearson Edexcel Awards in Algebra have been available for first teaching from October 2012. The content and assessment of thequalifications have been designed to fit flexibly in to the programme of delivery forschools and colleges and because each Award only takes 60-70 guided learning hours you can start straight away or wait until later in the year.10. Do I need approval to offer these qualifications at my centre?If you already run any GCSE or GCE qualifications in your centre then you do not need any additional approval to run these qualifications. If you are not an approved Pearson Edexcel centre, you can apply for approval athttps:///content/demo/en/support/support-topics/centre-administration/becoming-a-centre.html11. How do I make entries for these qualifications?Entries should be made in the same way as entries are made for other qualifications.Our information manual contains all the practical information you need to deliver our qualifications.The table below shows details of the entry codes.More information can be accessed via our dedicated webpage at /edexcelmathsaward.12. What are the entry fees for these qualifications?Entry fees are available on our website here.13. What support is available for these qualifications?•Web support – our dedicated qualification webpages at /edexcelawardnumber and /edexcelawardalgebra. Genericinformation about the suite can be found at /edexcelmathsaward •Mathematics Emporium – sign up for the mailing list to ensure you have all the relevant information and support when you need it. Also register for an account at for access to over 6,000 documents relating to all ourmathematics qualifications and follow us on twitter @EmporiumMaths for all thelatest news and updates from our subject partners.•Teacher support materials and resources – The following teaching and learning support is available for the Edexcel Awards qualifications:- content mappings to the reformed GCSE and GCE qualifications- scheme of work- practice paper and mark schemes- past papers, mark schemes and grade boundaries- paid-for workbooksAll of this support is available under ‘course material’s on each of the qualificationwebpages.•ResultsPlus – as with our GCSE and GCE mathematics qualifications, our free online results analysis tool gives teachers a detailed breakdown of your students’performance in the Awards. More information about ResultsPlus services can befound at /ResultsPlus14. How long will these qualification continue to be offered?These qualifications will continue to be offered indefinitely. If this changes at any time, you will be updated accordingly.15. How can I find information regarding funding for this qualification?All information regarding funding can be found on our website here.More information can be accessed via our dedicated webpage at /edexcelmathsaward.。

考博学术成就总结模板可打印

考博学术成就总结模板可打印1. 引言本文旨在总结我的考博学术成就，并提供一个可打印的模板，供其他人参考。

在此过程中，我将回顾我在研究中取得的成就，包括论文发表、学术交流等。

2. 论文发表- 我在考博期间共发表了X篇学术论文，其中包括国内外期刊和会议论文。

这些论文涵盖了我在研究领域的重要发现和贡献。

- 在发表过程中，我积极参与同行评审，并采纳评审意见进行修改，以确保论文质量和学术价值的提升。

- 在多个国际会议上，我也有机会展示我的研究成果，与其他学者进行深入的交流和讨论。

3. 学术交流- 我积极参与学术交流活动，包括参加学术会议、研讨会和研究小组等。

- 在学术会议上，我不仅展示了自己的研究成果，还倾听了其他学者的研究报告，与他们进行学术讨论和思想碰撞。

- 我还加入了学术研究小组，与其他研究人员共同合作，进行深入的探讨和研究。

4. 研究成果评价- 我的研究成果受到了同行专家的高度评价，其中一些成果还被其他学者引用和借鉴。

- 我的论文在核心期刊、高水平国际刊物上发表，证明了其学术影响力和质量。

- 我相信这些研究成果和学术交流经验将对我的未来学术发展起到积极的推动作用。

5. 可打印模板本文提供一个可打印的模板，以供其他人参考和使用。

这个模板包括了总结自己学术成就的各个方面，帮助他们整理和归纳自己的研究成果，更好地展示自己在学术领域的突出表现。

6. 结论通过总结自己的考博学术成就，并提供可打印的模板，我希望能够鼓励和帮助其他人在学术道路上获得更好的成就。

同时，我也对自己在研究中的努力和取得的成果感到满意和自豪。

请注意：此文档的内容仅供参考，请酌情使用和修改。

学术道德修养8-27章习题答案全

可编辑修改精选全文完整版学术道德修养8-27章习题答案1【判断题】大学建立荣誉制度的初衷旨在预防大学生考试作弊。

正确答案：√2【判断题】在科学家之间和科学与社会之间，信誉与相互信任尤为重要。

正确答案：√3【判断题】科学研究与学术工作与人类其他活动一样，均建立在诚信之上。

正确答案：√1【单选题】以下哪些行为符合学术诚实三原则：A、把上届学长的课程论文当作自己应该完成的作业交给老师。

B、将老师的课堂笔记整理成论文并署上自己的名公开发表。

C、在实验中，为了让实验结果更漂亮而有选择地使用数据。

D、在著作的后记中对那些提出过修改建议的同行表示感谢。

正确答案：D2【判断题】所有的数据和文献应真实而公正地呈现。

正确答案：√3【判断题】小保方晴子在研究过程中存在“捏造”和“篡改”图片行为，有违学术诚实。

正确答案：√1【单选题】在学习的过程中，以下哪种做法是不诚实的：A、在做作业时，遇到困难向老师请教。

B、在做作业时，独立完成应该完成的作业。

C、为了尽快完成作业，参考高年级学长做过的同样的作业。

D、老师布置的作业量太大时，一方面努力认真完成，另一方面找机会向老师反映作业量过大这一实际情况。

正确答案：C2【单选题】在学习的过程中，以下哪种做法是诚实的行为：A、上课时，讲解老师要求自己讲解的内容时参考同学的阅读笔记。

B、考试时，将考试课程的课堂笔记等按规定不可以带入考场的东西带进考场，以备不时之需。

C、考试时，遇到不会的题目时，宁可空着，也不抄袭。

D、在完成老师要求的读书报告时，直接搜集别人写的几遍相关报告，重新组合后当作业交给老师。

正确答案：C3【单选题】以下说法中，哪一种是正确的：A、诚实学习就是严格按照老师的要求完成作业、论文和考试等学习任务。

B、小组合作完成作业时，主要由会做的同学完成，不会做的同学可以不做或尽量少做。

C、小组合作完成作业时，某位同学不能完成自己应该完成的工作时，可以请小组的其他同学帮忙完成。

pku北大学子毕业生去向

环境学院心理学系心理学系心理学系心理学系心理学系心理学系新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院新闻与传播学院
美国中国中国美国中国中国美国美国香港中国中国美国美国中国美国美国美国中国美国美国中国中国美国美国中国美国中国英国美国中国中国美国中国
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化学与分子工程学院化学与分子工程学院化学与分子工程学院化学与分子工程学院化学与分子工程学院化学与分子工程学院化学与分子工程学院化学与分子工程学院化学与分子工程学院化学与分子工程学院化学与分子工程学院化学与分子工程学院化学与分子工程学院生命科学学院生命科学学院生命科学学院生命科学学院生命科学学院生命科学学院生命科学学院生命科学学院生命科学学院生命科学学院生命科学学院生命科学学院生命科学学院生命科学学院生命科学学院生命科学学院地球与空间科学学院地球与空间科学学院地球与空间科学学院地球与空间科学学院
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国家励志奖学金获奖学生名单

青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学
物理科学学院物理科学学院物理科学学院物理科学学院物理科学学院物理科学学院物理科学学院物理科学学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院纺织服装学院国际商学院国际商学院国际商学院国际商学院国际商学院国际商学院国际商学院
青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学青岛大学

Impact of packet sampling on portscan detection

stub network. For example, the study in [3] suggests that a global view of the trafﬁc could better capture the scanning patterns. Finally, a stub network such as an enterprise may out source the detection task to its upstream provider due to lack of resources or expertise. The impact of sampling has been extensively studied in terms of well known statistical metrics, e.g., mean rate and ﬂow size distribution, from the perspective of determining the volume characteristics of the trafﬁc as a whole [4]–[7]. However, anomaly detection (e.g., worm scan detection) often depends on a diverse set of metrics such as address access pattern, connection status, and distinct per source behaviors. How packet sampling impacts these trafﬁc features has not been previously addressed. This paper presents a ﬁrst attempt to address this important open question: Does packet sampling distort or lose pertinent information from the original trafﬁc proﬁle that affects the effectiveness of existing anomaly detection techniques? If so, by how much? There is a rich set of literature on two general approaches to anomaly detection: specialized detection algorithms that target speciﬁc types of anomalies, and generalized trafﬁc proﬁling algorithms. Example target speciﬁc algorithms include [8]– [10] designed primarily to detect portscans. On the other hand, trafﬁc classiﬁcation algorithms, such as [11], [12], are generalized algorithms that do not target a speciﬁc anomaly. Instead they classify different trafﬁc features and raise alarm ﬂags when they detect large variations. Algorithms from both categories typically assume the availability of detailed packet payload, e.g., at the network edge. However, it is not clear how their performance is impacted if the same solutions utilize only sampled packet header data. We note that it is clearly infeasible to perform an exhaustive study on the impact of sampling for every anomaly detection algorithm presented in literature. Instead, we focus on one common class of non-volume based anomalies, portscans, which causes increasing security concerns. We choose representative algorithms aimed at portscan detection from the two categories of detection algorithms mentioned above. Speciﬁcally, this paper presents a detailed study that quantiﬁes the effect of packet sampling on two target-speciﬁc and one trafﬁcproﬁling algorithms: (a) Threshold Random Walk (TRW) [9], (b) Time Access Pattern Scheme (TAPS) [10], and (c) Entropybased behavior modeling proposed recently [11]. TRW performs stateful analysis of the trafﬁc to identify connection status, while TAPS exploits the knowledge of the “connection patterns” of scanners. The general trafﬁc proﬁling algorithms compute entropy values of each of the four “features” of the IP header in order to identify “signiﬁcant ﬂows” and capture abrupt changes in the feature set. We believe that these algorithms cover a wide range of anomaly

1-s2.0-S0927775715303460-main

Colloids and Surfaces A:Physicochem.Eng.Aspects 490(2016)145–154Contents lists available at ScienceDirectColloids and Surfaces A:Physicochemical andEngineeringAspectsj 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 /c o l s u r faEvaluation of oil-in-water emulsions with cationic–anionic surfactants mixtures for potential use in the oil industryEduardo N.Schulz a ,∗,Rubén E.Ambrusi a ,Daniela B.Miraglia b ,Erica P.Schulz b ,Silvana G.García a ,JoséL.Rodriguez b ,Pablo C.Schulz ba Instituto de Ingeniería Electroquímica y Corrosión,CONICET—Departamento de Ingeniería Química,Universidad Nacional del Sur,Bahía Blanca,Argentina bInstituto de Química del Sur,CONICET,Departamento de Química,Universidad Nacional del Sur,Bahía Blanca,Argentinah i g h l i g h t s•Theemulsiﬁer proper-ties of sodium oleate(NaOl)–hexadecyltrimethylammonium bromide (HTAB)aqueous mixtures were studied.•The formation of O/W and W/O emulsions was explored and their properties were determined.•It was found that all emulsions were stable on ageing and to temperature rise.•The emulsions were destroyed by contact with quartzite stones.•These mixtures have high potential applicability in the asphalt emulsi-ﬁcation for pavement production or sand ﬁxation.g r a p h i c a la b s t r a c tLeft:stones with crude oil emulsion.×100,Crossed polaroids and 1␭retardation plate intercalated,show-ing interference colours in the quartzite stones and sensitive pink of non-birefringent (water)medium.The black zones correspond to stones covered by hydrocarbon.Right:crude oil emulsion,unpolarised light.The emulsion used in both photos was diluted to improvevisualization.a r t i c l ei n f oArticle history:Received 8September 2015Received in revised form 9November 2015Accepted 13November 2015Available online 18November 2015Keywords:Petroleum emulsions Catanionic emulsiﬁer Sodium oleateHexadecyltrimethylammonium bromide Mixed surfactantsa b s t r a c tThe emulsiﬁer properties of sodium oleate (NaOl)-hexadecyltrimethylammonium bromide (HTAB)aque-ous mixtures were studied using different proportions of the surfactants.The formation of O/W and W/O emulsions was explored and their properties (viscosity,stability and droplets size distribution)were determined.The mixture with 0.75mole fraction of HTAB without considering the solvent formed very stable and concentrated O/W emulsions,which were destroyed via heterocoagulation by quartzite sand.Thus,these mixtures have high potential applicability in the asphalt emulsiﬁcation for pavement production or sand ﬁxation.©2015Published by Elsevier B.V.∗Corresponding author.E-mail address:nschulz@.ar (E.N.Schulz)./10.1016/j.colsurfa.2015.11.0230927-7757/©2015Published by Elsevier B.V.146 E.N.Schulz et al./Colloids and Surfaces A:Physicochem.Eng.Aspects490(2016)145–1541.IntroductionStable emulsions of heavy oils or bitumen in water are widely used to extract,transport and store petroleum.These emulsions are an alternative to the increase of temperature for the mixing of asphalt with light oils,which involve high costs and technical complexity[1,2].O/W bitumen emulsions have been also employed as combustible in electricity power plants[3].Desire features of these emulsions are high stability and low viscosity.Other applications of asphalt emulsions are road construction and roof water-prooﬁng.In particular,these emulsions have many advantages for road reparation compared to melted asphalt:easier implementation,fewer precautions and no need of special equip-ment,as well as their applicability to wet surfaces,a very attractive characteristic.The speed of rupture of the asphalt emulsion on the mineral substrate is of primary importance.On the one hand, enough time must be allowed for proper mixing of the various com-ponents of the system but,on the other hand,the breaking time must be short enough to permit a rapid re-opening of the road to trafﬁc[4].Bitumen is a high viscosity mixture of hydrocarbons(>104 cP).“Synthetic”bitumen is best known as asphalt and is a petroleum-like material obtained as a residue from the distillation of petroleum[5]with a consistency varying from viscous liquid to glassy solid.Asphalt is commonly employed as a binder of aggre-gates for road pavement[6].Asphalt emulsions are commonly either anionic or cationic. Their rupture in contact with stones is caused by the destabiliza-tion of the emulsiﬁer.Polyvalent cations,such as Ca+2and Mg+2(in basic stones such as calcareous ones),react with anionic surfactants producing uncharged insoluble soaps while the negative charge of acid siliceous surfaces reacts with cationic surfactants causing elec-trostatic adsorption.The adsorbed cationic surfactants show their hydrocarbon chains out of the stones’surface,causing its hydropho-bization and thus increasing the tendency of asphalt to adsorb on the stones,promoting the adhesion between the hydrocarbon and the mineral surfaces.Moreover,the surfactant monolayer reduces the afﬁnity of the stones’surface towards water,thus reducing its tendency to destroy the pavement.Water penetration causes strip-ping of the bitumen from the aggregate particles,consequently endangering the subgrade layer as well as the base course[7].A catanionic(anionic–cationic surfactant mixture)emulsiﬁer will have both the advantages of cationic and anionic emulsions. However,in general cationic–anionic surfactant mixtures tend to precipitate in some proportions.We have previously studied a catanionic mixture which does not precipitate in any proportion [8–10].Sodium oleate(NaOl)–hexadecyltrimethylammonium bro-mide(HTAB)mixtures form soluble systems at all NaOl–HTAB proportions.This mixture does not precipitate at any composition because to steric hindrances,which were attributed to the afﬁnity of the NaOl double bond to water via hydrogen bonding.Thus NaOl acts as a surfactant having two hydrophilic groups,the carboxylate and the double bond.This causes a curvature of the aggregate/water surface which favours the O/W emulsiﬁcation[6–8].NaOl is a nat-ural,biodegradable soap which is innocuous for the environment. HTAB has bactericide capacity but it is not dispersed in the environ-ment because it is strongly adsorbed by the negative stones’surface and remains below the asphalt layer.Thus,the system NaOl–HTAB seems to have interesting features that makes it attractive for prac-tical applications,especially in the petroleum industry.In the present work the emulsiﬁer capability of different mix-tures of NaOl–HTAB with Argentine crude oil(CO)and with model liquid parafﬁn(LP)has been studied.The behaviour of the emul-sions in contact with a petrous substrate has been also studied in order to evaluate their possible use in pavement production.Our ﬁndings are of practical and theoretical interest in the oil emulsions ﬁeld and set the basis for the future study of the emulsiﬁcation properties for heavy oil.2.Experimental2.1.MaterialsFor parafﬁn emulsions,extra dense liquid parafﬁn(LP)EWE with viscosity Seyboldt340s and75centi-Stokes was used as purchased.Hexadecyltrimethylammonium bromide(HTAB, C16H32N(CH3)3Br>99%)was from Fluka.Sodium oleate(NaOL, C18H33O2Na>99%)was from Aldrich.Both chemicals were of ana-lytical grade and were used as purchased.The crude oil(CO)of35◦API(0.870g cm−3)has kinematic vis-cosity10.7mm2s−1and dynamic viscosity96.7cp(both at20◦C) and does not contain aromatic compounds,asphaltenes or other chemicals[11].It has been kindly supplied by the Petrobras Bahia Blanca reﬁnery and is from the Neuquen oilﬁeld(Argentina).The stones were from the Pigüéquarry(Argentina)and were selected because of their poor performance to produce pavements with commercial asphalt emulsions.Their treatment with a com-mercial asphalt emulsion achieved only an incomplete coverage of the stones’surface,which leaves the pavement vulnerable to water penetration[12].LP and CO were selected because of their easier manipulation than heavy oils and bitumen.Once the possibility of using the mix-ture for emulsifying hydrocarbons is stated,it is possible to study the formation of bitumen emulsions.We used Argentinian crude oil,which is free of asphaltenes,due to a matter of availability.Tri-distillated water was used and the measurements were per-formed twice.2.2.EmulsionsAqueous emulsiﬁer solutions of HTAB and NaOL with0.1M were prepared at the mole fractions of HTAB in the surfactant mixture without considering the solvent(˛HTAB)0.1;0.25;0.3;0.50;0.7;0.75;0.9and1.Each emulsion was stirred for15min with a steel helix stirring electric device at800rpm after the addition of the second phase.Emulsions of Argentine petroleum were prepared according to two procedures:a)The aqueous surfactant solution(50mL)was added in aliquotsof2mL to50mL of CO under stirring.Then,15mL of each sam-ple was put in a graduate tube and stoppered.The volume of the emulsion was determined immediately,after24h and after a week’s time.The emulsions were observed by means of a micro-scope.b)The CO(50mL)was added to50mL of the aqueous surfactantsolution in aliquots of2mL under stirring and the emulsions were observed as in procedure a.An additional observation was made after14months.Since the Argentine petroleum was parafﬁnic(see below),we used for the main determinations a model emulsion with liquid parafﬁn which facilitates the observation because it is colourless. The model emulsions were prepared with surfactant mixture(0.1M in water)with˛HTAB=0.1;0.25;0.50and0.75.Then,60mL of liquid parafﬁn was added to40mL of the aqueous surfactant solutions and stirred during15min.The systems were transferred to graduated tubes and the volumes of emulsion,remnant water and remainder parafﬁn were recorded.Samples of the freshly prepared emulsions for microscopic observation were kept in separated sealed vials.Samples with˛HTAB=0.25;0.50and0.75were observed in a microscope Nikon Eclipse E-200POL Polarizing,Tokyo,Japan.E.N.Schulz et al./Colloids and Surfaces A:Physicochem.Eng.Aspects490(2016)145–154147Table1Volumes of W/O emulsion and remnant(non-emulsiﬁed)water in10mL samples as a function of the surfactant composition.A week old samples after centrifugation.␣HTAB00.10.30.50.70.91V W/Oemulsion/mL 2.9 1.20.3 3.30.20.50.2V water/mL7.18.89.7* 6.79.8**9.59.8****W/O/W emulsion.**O/W emulsion.***Multiple emulsion.Unless stated otherwise,all observations were made with×100 magniﬁcation.Nonetheless,scale bars were added to the photos. As both phases are transparent and colourless,a drop of aqueous solution of methylene blue was added to determine the nature of the emulsion.In all cases the dye diffused amongst the emulsion droplets,thus all emulsions were O/W.The emulsions remained stable during the microscope observations although no stabilizer was added(such as a gelatine solution)[13].The viscosity(Á)of emulsions was measured with a Vibro Viscometer SV-10/SV100calibrated with tri-distilled water (Á=0.89cP at25◦C).The hydrocarbon/water volume ratio in the emulsions was mea-sured using a modiﬁed Dean-Stark apparatus[2].To evaluate the effectiveness of stones in destructing the emul-sion and the hydrocarbon deposition on the stones’surface,a powder of the stones was put in contact with the different emul-sions and observed under the microscope.In order to reproduce the procedure in real working conditions,the mineral substrate was used as received,without any pre-treatment.The X-ray diffraction spectrum of the stones employed in the test of stability of emulsion was made in a Phillips PW1710 diffractometer with Cu anode and curved graphite monocromator operated at54kW and30mA.FT-IR measurements were performed with an Infrared Spec-trophotometer(Nicolet FT-IR,Model Nexus470)to test the CO structure.The size distribution of droplets was determined with a com-puter program(Pixcavator IA).As a size reference,the width of the hair in Fig.3a was used(a similar method was used for other magniﬁcations).Averages and variances values were computed by the minimum variance linear unbiased method[14]and the Student t function was employed to compute the error intervals.Conﬁdence level was 0.90.Errors of derived data were computed with the error expan-sion method.3.ResultsThe X-ray diffractogram(Fig.1in Supplementary information, SI)indicates that the stones’nature is clastic sedimentary rock—S0, formed by silica(ortho-quartzite).The petroleum FT-IR spectrum(not shown)showed only parafﬁnic hydrocarbon peaks(CH3;CH2stretching vibra-tions at3000–2850cm−1and CH3;CH2bending vibrations at 1480–1350cm−1).3.1.Petroleum emulsionsChanging the order of addition of the components while stir-ring produced two different kinds of emulsions.The addition of the surfactant aqueous solution to crude oil produced a W/O emul-sion(see Fig.1).Freshly prepared samples did not show signiﬁcant phase separation.The emulsion could be separated by centrifuga-tion at2000rpm only after a week from preparation.Due to the petroleum colour,a Cole-Palmer Iluminator41720-series was used. Table1shows the relative volumes of emulsion as a function of the mixture composition.Pure NaOl(˛HTAB=0)had poor emulsifying capacity,but the addition of a small amount of HTAB(˛HTAB=0.1) produced a good W/O emulsion with small polydisperse droplets (Fig.1a).Further addition of HTAB produced a very polydisperse W/O emulsion(Fig.1b and c).With˛HTAB=0.3two kinds of emul-sions appeared:the W/O and a multiple emulsion O/W/O,and with ˛HTAB=0.7there coexist W/O and O/W emulsions.As we desired O/W emulsions we employed procedure b:addi-tion of the crude oil to the surfactant solution under stirring.Fig.2 shows microscopic images of two of the emulsions obtained with ˛HTAB=0.75.The concentrated emulsion was diluted with water to improve the observation.3.2.Parafﬁn emulsionsOwing to the difﬁculty caused by the strong colour of the crude oil to the visual examination and microphotographs analysis,we decided to make model emulsions with liquid parafﬁn,which is colourless and whose composition and viscosity are similar to that of the crude oil.Since the amount of surfactant affects the size of the droplets,we have used the same amount of surfactant in all the emulsions to compare the effect of the mixture composition.On the basis of the preceding results,we used only surfactant solutions having˛HTAB=0.1;0.25;0.5and0.75.Since we were interested in O/W emulsions,these were prepared by dropping the parafﬁn to the aqueous emulgent solution under stirring.The nature of the emulsion(O/W)was determined by diffusion of a drop of a methylene blue aqueous solution in the continuous phase, viewed through the microscope(Fig.2in the SI).Fig.3shows the emulsions obtained with different surfactant compositions.The size distribution of droplets was graphically determined using a computer program(Pixcavator IA)on the pho-tomicrographs.The freshly prepared emulsions did not show remnant water or parafﬁn.The viscosity(Á)of the emulsion at25◦C were13.20cP for ˛HTAB=0.25;47.00cP for˛HTAB=0.5and382.00cP for˛HTAB=0.75. The droplets size distribution is shown in Fig.4.The particle size of an emulsion is one of the most important characteristics[13].Droplets size and droplets size distribution can be used as indexes of state of an emulsion and are intimately related to their stability,resistance to creaming,rheology,and chemical reactivity[15].Two emulsions may have the same average droplet diameter and yet exhibit quite dissimilar behaviours because of differences in their distribution of diameters.The droplet size distribution for˛HTAB=0.25is unimodal and broad while that for˛HTAB=0.50is multimodal with lower maxima. When˛HTAB is0.75the distribution is a narrow,unimodal and cen-tred in the smaller size.Emulsions with a droplet-size distribution with a maximum of low diameter droplets and with this maximum sharply deﬁned represent a situation of maximum stability[16].To study the stability of the emulsions,these were aged in sealed graduated tubes.The separation of emulsion and water when the systems were aged can be seen in Fig.5.The emulsions still remained stable after14months.(Fig.3in SI).The aged emulsion with˛HTAB=0.75had a LP content73%V/V. Natural bitumen emulsions contain between70and80%V/V of bitumen separated by tiny layer of water,while asphaltic emulsions usually contain about60%V/V[9].The size distribution is shifted towards smaller droplets when aged,as shown in Fig.6for˛HTAB=0.25(the other surfactant com-positions showed similar behaviour).To determine the efﬁciency of the surfactant mixtures to emul-sify LP,20mL of emulsion having˛HTAB=0.25was completed to 100mL with liquid parafﬁn and stirred.After a day,there was1mL of supernatant parafﬁn,i.e.1.412g of surfactant mixture was capa-ble of emulsifying91mL of parafﬁn.The size distribution of droplets148E.N.Schulz et al./Colloids and Surfaces A:Physicochem.Eng.Aspects 490(2016)145–154Fig.1.W/O emulsions produced by dropping aqueous surfactant solution to crude oil under stirring.×100.(a)˛HTAB =0.1,(b)˛HTAB =0.7,(c)˛HTAB =1.The bar corresponds to 0.2mm.Fig.2.O/W emulsion obtained by dropping crude oil to the aqueous surfactant solution under stirring.˛HTAB =0.75,×100.(a)emulsion diluted with 25%water,(b)emulsion diluted with 50%water.The bar corresponds to 0.2mm.was almost unimodal and is shown in Fig.7.After one year only 20mL of parafﬁn was separated while the remaining emulsion was stable (see Fig.3in SI)with the separation of the remnant water (below)and parafﬁn (above).Similar results were obtained with the other compositions.No agglomeration or coalescence was observed during the microscope observations,even after one hour of preparing the sam-ples.To test the temperature stability of emulsions,samples of the three emulsions (with ˛HTAB =0.25,0.5,and 0.75)were placed between slides and heated with a temperature-controlled stage at the microscope.Photos were taken at different temperatures up to the ebullition of water (Fig.8).Vapour bubbles and LP droplets differentiate by the aspect of their borders as a consequence of the different refractive index:the borders are black and thick in the vapour bubbles and light grey in the LP droplets.Emulsion with ˛HTAB =0.25became more ﬂuid at 83◦C and the larger droplets disappeared but the smaller ones were retained.At 111.5◦C the emulsion ﬂowed and the water started to boil.Fig.8band c shows the vapour bubbles that grew with increasing temper-ature.The oil droplets are smaller.At a temperature of 118◦C the emulsion started to break,to be almost completely broken at 119◦C.Fig.9shows the evolution of the droplets size with the raising tem-perature:the multimodal distribution of larger droplets trends to form a bimodal distribution of smaller droplets.Emulsions with ˛HTAB =0.5remained stable up to 103◦C,when vapour bubbles appeared.At 115◦C the system ﬂowed and at 124.5◦C it collapsed.Fig.10shows the evolution of the size distribu-tion of droplets with raising temperature:it remained multimodal but shifted towards smaller droplets.Emulsion with ˛HTAB =0.75became ﬂuid at 83.6◦C and the excess of water was separated forming small domains that started to disappear at 104◦C.Some bubbles of vapour appeared and grew with the increasing temperature.Some emulsion was remained up to 122◦C.The size of oil droplets was reduced when the temper-ature was increased from 37.5◦C to 67.5◦C,and the distribution became narrower.Further increase of temperature did not affectE.N.Schulz et al./Colloids and Surfaces A:Physicochem.Eng.Aspects490(2016)145–154149Fig.3.microscope photos of fresh emulsions having˛HTAB=0.25(a)×100,0.5(b)×100,0.75(c)×100and0.75(d)×400.The line in photo(a)is a hair,having0.090mm in width,and used to calibrate the size of droplets.Bars in photos a–c correspond to0.2mm,in photo d,to0.1mm.Fig.4.size distribution of freshly prepared emulsion having˛HTAB=0.25,˛HTAB=0.50and˛HTAB=0.75.Distribution parameters: :number average, standard deviation, Max:maximum.the size distribution.Fig.11shows the size distribution of droplets as a function of temperature.The stability of the emulsions was not affected by two freeze–thaw cycles between−5and25◦C,with8h in each tem-perature.In conclusion,the three compositions gave emulsions stable up to the temperature of water boiling.The size distribution in all cases is shifted to smaller droplets when temperature is increased.The size behaviour on ageing and heating of emulsions is rather unusual.A possible explanation may be creaming of large oil droplets and therefore shifting the size distribution of the remain-ing emulsion down.Since samples were taken from different parts of the emulsion,the large droplets probably collapse giving rise to the narrow non-emulsiﬁed oil layer.Another possible explanation may be a rearrangement of the surfactant molecules in the droplets interface.Oleate molecules can fold to expose the double bond at the interface,since they tend to form hydrogen bonds with water with their␲electrons[17].This may lead to an average packing parameter of the mixture of surfactants that favours the formation of a hydrocarbon droplet with a given curvature generating a nar-150E.N.Schulz et al./Colloids and Surfaces A:Physicochem.Eng.Aspects 490(2016)145–154Fig.5.Dependence on time of the volume percent of remnant emulsion (full symbols)and water (open symbols),᭿ᮀ:˛HTAB =0.75; :˛HTAB =0.50;᭹ :˛HTAB =0.25.010********60708000.050.10.150.20.250.3D / mmf / %Fig.6.Evolution with time of emulsion prepared with ˛HTAB =0.25.rower size distribution.This mechanism needs some time,and willbe accelerated with temperature.As suggested by Anton et al.[18]mixtures of anionic and cationic surfactants may be considered as 1:1complexes and the remain-der molecules of the surfactant in excess.The Ol.HTA complex has a large hydrophilic part formed by one N(CH 3)3+group from HTA +ion,and the COO −and CH CH groups of Ol −ion.As previously mentioned it has been found that the double bond has afﬁnity to water,forming H-bonds with the ␲electrons [19–21].The tail of the oleate ion is thus folded to put the CH CH group in contact with water in aggregates such as micelles or air/water monolayers [6–8].This produces a structure of the complex like a cone with the hydrophilic part at the basis,i.e.favouring a curved surface convex to the water.The behaviour of another cationic–anionic surfactant mixture which does not precipitate at any proportion (although it forms a coacervate in some proportions),sodium 10-undecenoate-dodecyltrimethylammonium bromide [19,22,23],was explained by the same phenomenon.This explains why the O/W emulsion isfavoured and why the system does not precipitate even at the 1:1proportion.Similar reasons have been proposed in literature for other cationic/anionic surfactant mixtures which do not precipitate [24].The mixture with ˛HTAB =0.75is the best to produce O/W emulsions,i.e.once the 1:1complex was formed,two thirds of the hydrophilic HTAB molecules remain free.Then,the system is formed by an excess of hydrophilic surfactant which promotes O/W emulsion formation,and the complex which has a structure that accommodates to the same oil/water interface geometry.The droplets size decreases with time and with increasing tem-perature probably due to that part of the surfactant that remained in the aqueous phase and migrate by diffusion to the droplets sur-face.This takes time but is accelerated by the temperature rise.The molecules and 1:1complexes arriving to the oil/water inter-face must accommodate increasing the surface area,what may only occur with a diminution of the droplets’size when the total oil volume is constant.E.N.Schulz et al./Colloids and Surfaces A:Physicochem.Eng.Aspects 490(2016)145–1541511020304050607080900.0000.020 0.040 0.060 0.080 0.100 0.120 0.140 0.160 0.1800.200D / mmf / %Max 0.035 mm = 0.039 mm = 0.025 mmFig.7.size distribution of droplets for ˛HTAB =0.25saturated withparafﬁn.Fig.8.Evolution of emulsions with temperature,microscope photos ×100of emulsion width ˛HTAB =0.25(a)at 48◦C,(b)102◦C,(c)at 111.5◦C.Emulsion with ˛HTAB =0.5(d)at 38◦C,(e)at 100◦C,(f)at 103◦C.Emulsion with ˛HTAB =0.75(g)at 37.7◦C,(h)at 83.5◦C,(i)at 109◦C.The bars correspond to 0.2mm.3.3.Destruction of emulsion by stonesThe emulsions were put in contact with powdered stones and observed under microscope to determine their applicability in the production of pavements.The emulsion with ˛HTAB =0.75showed the best performance in the previous experiments so it was theonly one evaluated for this purpose.The droplets were clustered on the stones’surface and were subsequently destroyed.The destruc-tion of the emulsion was very rapid and ﬁnished in 15min.Fig.12shows the evolution of the CO emulsion with ˛HTAB =0.75in contact with the powdered stones which were almost completely covered.152E.N.Schulz et al./Colloids and Surfaces A:Physicochem.Eng.Aspects 490(2016)145–154010203040506000.0050.010.0150.020.025D / mmf / %Fig.9.Evolution of the size distribution of droplets with temperature for ˛HTAB =0.2505101520250.0050.010.0150.020.0250.030.0350.040.045D / mmf / %Fig.10.Evolution of the size distribution of droplets with temperature for ˛HTAB =0.50.Fig.11.Size distribution of droplets having ˛HTAB =0.75as a function of temperature.E.N.Schulz et al./Colloids and Surfaces A:Physicochem.Eng.Aspects490(2016)145–154153Fig.12.Photomicrographs of the emulsion destruction in contact with stones.×100,˛HTAB=0.75.(a)Diluted CO emulsion just added to the stones,(b)after5min,droplets were aggregated close to the stones,(c)after10min,(d)after30min,(e)after24h,(f)commercial cationic emulsion after30min.Photos a,b and f with polarized light and 1␭retardation plate intercalated.The other photos are with unpolarised light.Bars indicate0.2mm.The crude oil emulsion was previously diluted with20%water to improve visualization.The clear regions are water between stones.The destruction of the emulsion by stones seems to follow the mechanism called heteroﬂocculation[25],i.e.the oil droplets clus-ter together around the stones followed by their coalescence on the solid surface.In this sense,some HTAB molecules dissolved in the aqueous phase may hydrophobize the rock surface improving the adherence of the oil.The breaking time of emulsions is known to be affected by the nature of the aggregate and its speciﬁc area,humidity,surfactant concentration,pH,and temperature[4],therefore the speed of breaking in roads industry may be different to that found in our lab-oratory conditions.Due to the short time of breaking,this emulsion may be useful as an imprinting irrigation,i.e.irrigation of surfaces to produce a transition surface with the new asphaltic layer ensuring the anchoring of this layer,or to stabilize sands[26].154 E.N.Schulz et al./Colloids and Surfaces A:Physicochem.Eng.Aspects490(2016)145–1544.ConclusionsNaOl–HTAB mixtures revealed to be good O/W emulsiﬁers.The system having˛HTAB=0.75gave the largest volume of emulsion having a narrow unimodal size distribution with smaller droplets. This emulsion has a relatively high viscosity.All emulsions were stable on ageing and to temperature rise.The emulsions were destroyed by contact with quartzite stones.These properties may be useful for different applications in petroleum industry such as their use as fuels,transport and pavement production.AknowledgementsENS is an assistant researcher of the Argentine National Council of Scientiﬁc and Technical Researches(CONICET),EPS is an adjunct researcher of CONICET.REA has a post-doctoral fellowship of CON-ICET.This research was supported by a grant of the Universidad Nacional del Sur.Appendix A.Supplementary dataSupplementary data associated with this article can be found,in the online version,at /10.1016/j.colsurfa.2015.11. 023.References[1]N.Delgado,F.Ysambertt,C.Montiel,G.Chávez,A.Cáceres,B.Bravo,N.Márquez,Evaluation of oil-in-water emulsions with non-ionic and anionicsurfactants mixtures for potential use in the oil industry,Rev.Téc.Ing.Univ.Zulia30(2)(2007)118–127(in Spanish).[2]L.Schramm,Surfactants:Fundamentals and Applications in the PetroleumIndustry,Cambridge University Press,Cambridge,2000.[3]H.Rivas,X.Gutiérrez,Surfactants:behavior and some of their applications inthe petroleum industry,Acta Cient.Venez.50(Suppl.No.1)(1999)54–65. [4]M.Bourrel,C.Chambu,Cationic asphalt emulsions:breaking on mineralsubstrates,in:Proceedings2nd World Surfactant Congress1988,IV,Paris,1988,pp.145–161.[5]G.Urbina-Villalba,M.García-Sucre,Effect of non-homogeneous spatialdistributions of surfactants on the stability of high-content bitumen-in-water emulsions,Interciencia25(9)(2000)415–422.[6]M.Chappat,Some applications of emulsions,Colloids Surf.A Phys.Eng.Aspects91(1994)57–77.[7]W.S.Abdulla,M.T.Obaidat,N.M.Abu-Sa’da,Inﬂuence of aggregate type andgradation on voids of asphalt concrete pavements,J.Mater.Civil Eng.1988 (1988)76–85.[8]N.El-Kadi,F.Martins,D.Clausse,P.C.Schulz,Critical micelle concentration ofaqueous hexadecyltrimetylammonium bromide–sodium oleate mixtures,Colloid Polym.Sci.281(2003)353–362.[9]D.B.Miraglia,E.N.Schulz,J.L.M.Rodriguez,P.C.Schulz,D.Salinas,Sodiumoleate–cetyltrimethylammonium bromide mixtures,J.Colloid Interface Sci.351(2010)197–202.[10]D.B.Miraglia,J.L.M.Rodríguez,R.M.Minardi,P.C.Schulz,Critical micelleconcentration and hlb of the sodium oleate–hexadecyltrimethylammonium bromide mixed system,J.Surfactants Deterg.14(2011)401–408.[11]P.V.Messina,O.Pieroni,V.Verdinelli,P.C.Schulz,Regarding the effect thatdifferent twin tailed surfactants have on a solid stabilized petroleumemulsion,Colloid Polym.Sci.286(2008)191–199.[12]V.Verdinelli,M.A.Morini,P.V.Messina,P.C.Schulz,S.Alvarez,Study ofcompatibility of quartzite stones–Pigüéquarry–with asphalt emulsions,in: Proceedings of the XXXIV Reunión del Asfalto Dr.Alfredo Pinilla,Mar delPlata,Argentina,2006(in Spanish).[13]B.H.Bishop,J.L.Wulﬁnghoff,Practical Emulsions,vol.1,3rd ed.,ChemicalPublishing Co.,Inc.,New York,1968.[14]J.Mandel,Statistical Analysis of Experimental Data,Interscience,New York,1964,pp.134–137.[15]P.Becher,Encyclopedia of Emulsion Technology,vol.1,Dekker,New York andBasel,1983,pp.369.[16]P.Becher,Emulsions Theory and Practice,American Chemical SocietyMonograph Series No.162,2nd ed.,R.E.Krieger Pub.Co.,New York,1977. [17]P.Messina,M.A.Morini,P.C.Schulz,Aqueous sodium oleate-sodiumdehydrocholate mixtures at low concentration,Colloid Polym.Sci.281(11) (2003)1082–1091.[18]R.E.Anton,D.Gomez,A.Graciaa,chaise,J.L.Salaguer,Surfactant–oil–water systems near the afﬁnity inversion part ix:optimumformulation and phase behavior of mixed anionic–cationic systems,J.Dispersion Sci.Technol.14(4)(1993)401–416.[19]M.B.Sierra,M.A.Morini,P.C.Schulz,The catanionic system sodiumundecenoate-dodecyltrimethylammonium bromide at low concentration,Colloid Polym.Sci.282(6)(2004)633–641,and references therein.[20]M.L.Ferreira,M.B.Sierra,M.A.Morini,P.C.Schulz,A computational study ofthe structure and behaviour of the aqueous mixed system sodiumunsaturated carboxylate–dodecyltrimethylammonium bromide,J.Phys.Chem.110(2006)17600–17606.[21]M.B.Sierra,M.A.Morini,P.C.Schulz,E.Junquera,E.Aicart,Effect of doublebonds in the formation of sodium dodecanoate and sodium10-undecenoate mixed micelles in water,J.Phys.Chem.B111(2007)11692–11699.[22]M.B.Sierra,M.A.Morini,P.C.Schulz,M.L.Ferreira,Unusual volumetric andhydration behavior of the catanionic system sodium undecenoate—dodecyltrimethylammonium bromide,Colloid Polym.Sci.283(2005)1016–1024.[23]M.B.Sierra,P.V.Messina,M.A.Morini,J.M.Ruso,G.Prieto,P.C.Schulz,F.Sarmiento,The nature of the coacervate formed in the aqueousdodecyltrimethylammonium bromide–sodium10-undecenoate mixtures,Colloids Surf.A:Phys.Eng.Aspects277(2006)75–82.[24]G.Kume,M.Gallotti,G.Nunes,Review on anionic/cationic surfactantmixtures,J.Surfactants Deterg.11(2008)1–11.[25]R.A.Mercado,V.Sadtler,P.Marchal,L.Chopin,J.L.Salager,Heteroﬂocculationof a cationic oil-in-water emulsion resulting from Fontainebleau’sandstone powder addition as a model for asphalt emulsion breakup,Ind.Eng.Chem.Res.51(2012)11688–11694.[26]K.P.George,Stabilization of sands by asphalt emulsion,Transp.Res.Rec.1976(1976)51–56.。

个人学术成就宣言书模板

个人学术成就宣言书模板一、个人学术追求我作为一名学者，深知学术研究对于个人和社会的重要性。

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三、个人学术成就期望基于以上的学术追求和发展计划，我期望能够在未来达到以下个人学术成就：1. 发表高水平学术论文：我希望能够在知名学术期刊或会议上发表一系列高质量的学术论文，为学术界提供有价值的研究成果。

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1-s2.0-S0925400515301556-main

Sensors and Actuators B 222(2016)159–165Contents lists available at ScienceDirectSensors and Actuators B:Chemicalj 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 /s nbOptimization of cascaded ﬁber tapered Mach–Zehnder interferometer and refractive index sensing technologyQi Wang a ,b ,∗,Wenqing Wei a ,Mengjuan Guo a ,Yong Zhao a ,b ,∗a College of Information Science and Engineering,Northeastern University,Shenyang 110819,ChinabState Key Laboratory of Synthetical Automation for Process Industries,Northeastern University,Shenyang 110819,Chinaa r t i c l ei n f oArticle history:Received 28May 2015Received in revised form 22July 2015Accepted 23July 2015Available online 28July 2015Keywords:Optical ﬁber sensor Tapered ﬁberMach–Zehnder interferometer Refractive index measurement High sensitivitya b s t r a c tA novel refractive index sensor with high sensitivity based on Mach–Zehnder interferometer formed by cascaded two single-mode ﬁber tapers was proposed and experimentally demonstrated.The dip of the measured spectrum signal caused by Mach–Zehnder interference shifted obviously when the sur-rounding refractive index changed.The approximate linear relationship between surrounding refractive index and spectrum dip wavelength shift was obtained experimentally.The measurement sensitivity up to 158.4nm/RIU was showed with the surrounding RI ranged from 1.33to 1.3792,which meant the measurement resolution about 6.3×10−6could be implemented if wavelength shift measurement reso-lution of the optical spectrum analyzer is 1pm.Meanwhile,its ease of fabrication makes itself a low-cost alternative to existing sensing applications.©2015Elsevier B.V.All rights reserved.1.IntroductionIn recent years,optical ﬁber sensors have become a hot research topic due to their advantages of compact structure,small size,light weight,quick response,high sensitivity,anti-electromagnetic interference,remote detection and so on,leading to broad appli-cation prospect in many sensing ﬁelds,such as refractive index,temperature,pressure and so on [1–3].Various optical ﬁber devices have been proposed for refractive index (RI)sensing,including ﬁber Bragg grating (FBG)[4–7],long period ﬁber grating (LPFG)[8,9],tilted ﬁber Bragg grating (TFBG)[10],a series of optical ﬁber interferometers based on core diameter mismatched ﬁber [11],double-cladding ﬁber [12],single-mode ﬁber tapers [13–17],or core-offset attenuator [18,19].The grating-based (FBG,LPG,TFBG)RI sensors have a response to RI with high sensitivity in a broad range.However,they require precise and expen-sive phase masks and stringent photolithographic procedures.The Michelson interferometers based on LPG,ﬁber tapers,and core-offset attenuator often require complex metal-coated ﬁber tip.Refractive index sensors based on tapered ﬁber interferometer have drawn more and more domestic and researchers attention∗Corresponding authors at:Northeastern University,College of Information Sci-ence and Engineering,P.O.Box 321,Shenyang,Liaoning 110819,China.E-mail address:wangqi@ (Q.Wang).because of their excellent characteristics of ease to fabrication,low cost,applicability for remote sensing and so on [20].In 2009,Lu fabricated two tapered optical ﬁbers on a single-mode ﬁber using a fusion splicer,composing a Mach–Zehnder interferom-eter structure.The sensitivity of refractive index measurement could reach up to 26.087nm/RIU [21],which is at the low level at present.In 2011,Liao proposed a liquid refractive index sensor with Micro/Nano ﬁber optic coupler structure,the RI measurement sensitivity of the sensor was up to 2735nm/RIU,but the fabrication of sensing structure was quite complex [22].In 2012,Li proposed a type of refractive index sensor based on Mach–Zehnder inter-ferometer formed by ﬁber tapers,and they thinned the ordinary single mode ﬁber via chemical etching method,then draw it into the cascaded biconical ﬁbers.The measurement sensitivity up to 286.2nm/RIU was shown in the surrounding RI range from 1.33to 1.3811[23].Nevertheless,the structure not only increased the dif-ﬁculty of fabrication but also introduced a large insertion loss (up to 22dB).In 2013,Chen proposed a refractive index sensor with joint-taper-joint structure,and the sensitivity of refractive index measurement could reach up to 3751nm/RIU,but the mechanical strength of the sensor structure was not high [24].In 2014,Yadav proposed an interferometer refractive index sensor with single-mode tapered ﬁber,and the principle of the sensor is based on mode coupling between the core mode and the cladding mode excited by the fundamental core mode.The RI measurement sensitivity of the sensor was up to 1500nm/RIU,it was mainly used in protein concentration detection [25]./10.1016/j.snb.2015.07.0980925-4005/©2015Elsevier B.V.All rights reserved.160Q.Wang et al./Sensors and Actuators B 222(2016)159–165Fig.1.Schematic diagram of MZI formed by cascaded two ﬁber tapers.In this paper,a refractive index sensor of Mach–Zehnder inter-ferometer formed by cascaded two single-mode ﬁber tapers was investigated,which is based on Mach–Zehnder interference prin-ciple.The sensor structure is Mach–Zehnder interferometer formed by cascaded two ﬁber tapers,and the length of the tapered region measured was 1mm,while the waist diameter was 20␮m,the distance between the two tapers was 4cm.When the RI value of water-based NaCl solution changed from 1.33to 1.3792,the output spectrum dip shifted with the sensitivity up to 158.4nm/RIU.2.Sensing principleFig.1shows the structural diagram of Mach–Zehnder interfer-ometer (MZI)proposed which was constructed by cascaded two ﬁber tapers fabricated in a standard single-mode ﬁber (SMF-28,Corning Inc.),the cascaded two optic ﬁber tapers are separated by a distance of L .When light propagates into the ﬁrst taper,fundamental mode in SMF core will be coupled to cladding modes LP 0m .At the same time,a part of energy left in the core continues propagating forward.A part of the light passing through the interferometer arm,part of the light traveling inside the cladding is coupled back into the core at the second taper.A Mach–Zehnder interferometer is formed due to the phase difference between fundamental mode in ﬁber core and higher order modes in ﬁber cladding.The interference light propagates forward in single mode ﬁber core,the spectra of which can be recorded by an optical spectrum analyzer (OSA).The interference spectrum is formed mainly by the fundamental core mode and the lowest order cladding mode,then the interfer-ence equation of the fundamental core mode and the cladding mode can be expressed as Eq.(1).I =I 1+I 2+2I 1I 2cos ϕ(1)where I 1and I 2are the light intensity of the ﬁber core fundamental mode and the lowest order cladding mode,respectively.The phase difference ϕbetween the two modes experience the same distance L ,which could be expressed as Eq.(2).ϕ=2 n eff L(2)where n eff is the difference of the effective refractive index between ﬁber fundamental core mode and the lowest order cladding mode,and is the input optical wavelength.When the phase difference satisﬁes the condition ϕ=(2m +1) ,m =0,1,2,...,the interference light intensity reaches minimum value,then the spectrum dip wavelength can be expressed as Eq.(3).m=2 n eff L 2m +1(3)The spacing between the adjacent dip wavelength is given by Eq.(4).m = m − m −1≈2eff (4)When the surrounding RI (SRI)is increased by ın ,effective RI of the cladding mode is increased by ın eff,cl .Because RI of theﬁberFig.2.Schematic diagram of cascaded biconical ﬁbers structure.The yellow part represents ﬁber core of a single-mode ﬁber,the red part denotes ﬁber cladding,and L is the distance of the cascaded biconical ﬁbers.(For interpretation of the references to color in this ﬁgure legend,the reader is referred to the web version of this article.)fundamental core mode is nearly constant, n eff is decreased by ın eff ≈ın eff,cl ,the interference spectrum dip wavelength m shifts to the short wavelength m by ı m .ı m =2 n eff L (2m +1)−2( n eff −ın eff )L (2m +1)=2ın eff L(2m +1)(5)According to the Eq.(5),we can calculate the change of thesurrounding refractive index by tracking the shift ı m of interfer-ence spectrum dip wavelength,so as to realize the measurement of solution refractive index.3.Numerical simulationIn order to obtain the cascaded biconical ﬁbers structure param-eters with best interference contrast,the analysis of inﬂuence different structure parameters on refractive index sensing sensi-tivity has been conducted.This paper described Rsoft simulation analysis on inﬂuence of different structural parameters on optical ﬁeld transmission characteristics,and inﬂuence of different struc-tural parameters on interference spectral contrast of the cascaded biconical ﬁbers and sensitivity of refractive index measurement.Fig.2shows cascaded biconical ﬁbers structure simulated with Rsoft.The yellow part represents ﬁber core of a single-mode ﬁber,the red part denotes ﬁber cladding,and L is the distance of the cascaded biconical ﬁbers.SMF parameters for simulation are core diameter with 8.2␮m,cladding diameter with 125␮m,wavelength of incident light with 1550nm,cladding refractive index with 1.4612,core refractive index with 1.4679,the NA of the SMF is 0.14,the refractive index of background with 1.33.Fig.3shows the refractive index distribution map of the structure.Fig.4(a)shows the coupling proportion of biconical ﬁber with waist diameter 5.2␮m,while Fig.4(b)represents the coupling pro-portion of biconical ﬁber with waist diameter 10␮m,different color represents intensity of light propagates in ﬁber core.The length of tapered region was set to 1mm.As it is shown in Fig.4(a),when transmission distance in the ﬁber is within the range of 0–10,000␮m,the transmittivity is almost 100%and loss is zero,energy of LP 01mode is almost constant.When transmission dis-tance in the ﬁber is 10,000␮m to 10,500␮m,energy of the ﬁber core fundamental mode drops quickly to about 35%at the ﬁber length of 10,500␮m,namely at the point of taper waist.As diameter of the ﬁber gradually becomes larger,evanescent wave on ﬁber sur-face returns into ﬁber core,leading to ﬁber core fundamental mode energy gradually increases.In the end,when ﬁber taper waist diam-eter increases gradually to the standard single-mode ﬁber diameter 125␮m,energy of ﬁber core fundamental mode gradually stabi-lizes.The normalized energy value of output is about 0.35,which means energy of ﬁber core fundamental mode has lost about 65%atQ.Wang et al./Sensors and Actuators B222(2016)159–165161Fig.3.Contour map of index proﬁle.The red part represents refractive index ofﬁber core is1.4679,the dark red part denotes refractive index ofﬁber cladding is1.4612, the pink part denotes refractive index of pure water is1.33.(For interpretation of the references to color in thisﬁgure legend,the reader is referred to the web version of this article.)the taper region.In contrast,Fig.4(b)shows the normalized energy value of output is about0.9when the taper waist diameter is10␮m.It can be seen from Fig.4that in case of the same length of taper region,energy loss after the taper region decreases with the increase of taper waist diameter,which means that the parts ofﬁber core fundamental mode coupling intoﬁber cladding will become less with the increase of taper waist diameter.The inﬂuences of taper region length,taper waist diameter,dis-tance between cascaded biconicalﬁbers on interference spectrum contrast are analyzed and the simulation results are shown in Fig.5. Fig.5(a)shows inﬂuence ofﬁber tapered region lengths on inter-ference spectrum contrast.As shown in Fig.5(a),as the tapered region length increasing,the interference spectrum contrast of cascaded biconicalﬁbers structureﬁrstly becomes larger and reach the largest when the taper region length at about1mm,and then becomes lesser with the taper region length increasing gradually. Fig.5(b)shows inﬂuence of tapered waist diameters on interfer-ence spectrum contrast.It can be conclude from Fig.5(b)that as the increasing ofﬁber taper waist diameters,the interference spec-trum contrast of cascaded biconicalﬁbers structureﬁrstly becomes larger and reach the largest when theﬁber taper waist diameters at about5.2␮m,and then becomes lesser with theﬁber taper waist diameters increasing gradually.Fig.5(c)shows inﬂuence of distances between the cascaded biconicalﬁbers on interference spectrum contrast.It can be seen from Fig.5(c),free spectral range of interference spectra decreases with increase of distance between the cascaded biconicalﬁbers,which is the phenomenon Table1Structural parameters of the cascaded biconicalﬁbers Mach–Zehnder interferome-ter with higher contrast.Taper waistdiameterTapered regionlengthDistance betweentwoﬁber tapers4–6␮m1mm2cmthat we don’t want to get.So far,we have obtained the optimization results of structural parameters of cascaded biconicalﬁbers from simulated results,which are taper region length with1mm,taper waist diameter with4␮m to6␮m,distance between the cascaded biconicalﬁbers with2cm,as shown in Table1.The refractive index measurement sensitivity of the cascaded biconicalﬁbers Mach–Zehnder interferometer structure with dif-ferent taper waist diameter is numerical simulated and the simulation results are shown in Fig.6.We got linear relationship between surrounding RI and spectrum dip wavelength of cascaded biconicalﬁbers structure with different taper waist diameter by observing shifts of the third spectrum dip wavelength with the change of surrounding refractive index.The refractive index mea-surement sensitivities are50.5nm/RIU,76.3nm/RIU,105.3nm/RIU respectively.It can be concluded from the simulated results that the smaller the taper waist diameter is,the higher the sensitivity of refractive index measurement is within a certain range of taper waist diameter.4.Experimental results and analysisThe schematic illustration of refractive index measuring exper-imental setup we constructed is shown in Fig.7.The sensing region is the cascaded biconicalﬁbers structure,which is fabricated by a conventional fusion splicer.The wavelength range of the ASE light source is from1520nm to1570nm.The optical spectrum ana-lyzer(OSA)is YOKOGAWA AQ6370.The core diameter of the SMF is8.2␮m and cladding diameter is125␮m.We can get different sizes of biconicalﬁber by setting several main parameters of fusion splicer(discharge intensity,discharge time,Z advancing distance,Z return distance).The microscopic images of the biconicalﬁber are shown in Fig.8,the discharge inten-sity was set to40,discharge time is2000ms,Z advancing distance is180␮m,Z return distance is430␮m.A second same taper was then made a few centimeters further along theﬁrst taper.Fig.9shows transmission spectrum of cascaded biconicalﬁbers with different structure parameters measured via OSA.It can be seen from Fig.9that curve-a represents transmission spectrum of a single-mode opticﬁber without tapers,curve-brepresents Fig.4.Distribution of lightﬁeld and energy variation with transmission distance Z in biconicalﬁber.162Q.Wang et al./Sensors and Actuators B222(2016)159–165Fig.5.Transmission spectra of cascaded biconicalﬁbers with different structure parameters.Fig.6.Simulated spectra of refractive index measurement with different taper waist diameters.Q.Wang et al./Sensors and Actuators B 222(2016)159–165163Fig.7.Schematic diagram of the RI measurement setup.ASE:ampliﬁed spontaneous emission,OSA:optical spectrum analyzer,SMF:single mode ﬁber,sensing section:biconicalﬁber.Fig.8.The microscopic image of the biconicalﬁber.Fig.9.The transmission spectra of cascaded biconical ﬁbers with different structure parameters.transmission spectrum of taper waist with 33␮m and distance between cascaded biconical ﬁbers with 4cm,curve-c represents transmission spectrum of taper waist with 30␮m and distance between cascaded biconical ﬁbers with 4cm,and curve-d repre-sents the transmission spectrum of a single-mode optic ﬁber with one taper.From the measurement spectrum in Fig.9,it can be known that the cascaded biconical ﬁbers with different structural parameters have some attenuation for optical power of the original source.The interference of transmission spectrum is obvious and its contrast gets up to 12.5dBm when taper waist diameter and tapered region length are 30␮m and 825␮m respectively.When the taper waist diameter continued to decrease,the interference phenomenon becomes extremely obvious,which can meet the requirements of improved interference spectrum contrast.The experimental results correspond to the simulated results,and a study of refractive index of the next step with the structure parameters was carried out.Before experiments,we compounded water–NaCl solution with RI range from 1.33to 1.3792,water–NaCl solutions with various concentrations (5%,10%,15%,20%,25%,mass percent)are used in the experiments.The corresponding RIs are 1.3424,1.3510,1.3609,1.3708,and 1.3792respectively.We conducted experiments of different refractive indexes measurement with the cascaded bicon-ical ﬁbers Mach–Zehnder interferometer structure,where taper waist diameter was 33␮m,tapered region length was 816␮m,distance between the cascaded biconical ﬁbers was 4cm.Exper-imental results and analysis are shown in Fig.10.Transmission spectra of the sensor with concatenating two single-mode ﬁber tapers immersed into the six different solu-tions were recorded (RI of distilled water is 1.33),and the results are shown in Fig.10(a).It should be noted that after each mea-surement,the device was cleaned with distilled water,dried,and then prepared for different solution sensing.The shift of resonance wavelength m of dip was chosen to be observed when the sensing section was immersed into different solutions.Fig.10(b)shows the relationship between resonance wavelength m of dip and RI of NaCl solution. m shifts from 1539.975nm to 1536.675nm almost linearly when RI of the solution increases from 1.33to 1.3792.The sensitivity S which is deﬁned as S = m / n was calculated to be 76.16nm/RIU.We reduced the taper waist diameter of 20␮m and tapered region length of 1mm,distance between two single-mode ﬁber tapers remained 4cm and researched on refractive index sensing property of the structure parameters.Experimental results and analysis are shown in Fig.11.Fig.11(b)shows m shifts from 1552.846to 1546.115nm almost linearly when RI of the solution increases from 1.3333to 1.3792.The sensitivity S which is deﬁned as S = m / n ,was calculated to be 158.4nm/RIU.So far,it has been obtained the optimized structural parame-ters of cascaded biconical ﬁbers Mach–Zehnder interferometer via a series of numerical and experimental studies,as shown in Table 2.For the RI between 1.3and 1.4,which is the typical range of protein analytes,sensitivity of the sensor based on concatenating two SMF tapers is not low compared to other type of RI sensorsandFig.10.(a)Transmission spectra of the sensor with concatenating two single-mode ﬁber tapers are immersed into solutions with various RIs.(b)Relationship between the resonance dip wavelength and RI of solution.164Q.Wang et al./Sensors and Actuators B 222(2016)159–165Fig.11.(a)Transmission spectra of the sensor with concatenating two single-mode ﬁber tapers are immersed into solutions with various RIs.(b)Relationship between the resonance dip wavelength and RI of solution.Table 2Structural parameters of the cascaded biconical ﬁbers Mach–Zehnder interferome-ter with higher sensitivity.Taper waist diameterTapered region lengthDistance between two ﬁber tapers20␮m1mm4cmits ease of fabrication makes it a low-cost alternative to existing sensing applications.5.ConclusionThe sensitive characteristics of the sensor with concatenating two single-mode ﬁber tapers to surrounding RI variation were used to measure refractive index.Different sensitive character-istics of the sensor with concatenating two single-mode ﬁber tapers with different structural parameters were numerical sim-ulated and experimental measurement.The results indicated that measurement sensitivity is up to 158.4nm/RIU.The measurement resolution about 6.3×10−6could be obtained when the wave-length shift detecting resolution is 1pm.In the same structure type sensor,sensitivity and resolution of the sensor proposed are both in a high level.It could be concluded that the sensor with concate-nating two single-mode ﬁber tapers has the absolutely attractive advantages,such as simple structure,easy to fabricate,low cost and higher measurement sensitivity and resolution.The sensor also has the shortages.For example,the OSA was used in the mea-surement which prevents the concatenating two single-mode ﬁber tapers structure from the widely commercialized development,the ﬁber tapers are easy to be damaged.So it deserves to be further researched to create a way that could achieve the signal demodu-lation conveniently and high mechanical strength.AcknowledgementsThis work was supported by the National Natural Science Foun-dation of China under Grant 61203206,the Fundamental Research Funds for the Central Universities under Grant N140405001,the Specialized Research Fund for the Doctoral Program of Higher Education of China under Grant 20120042120038,the National Sci-ence Foundation for Distinguished Young Scholars of China under Grant 61425003,the State Key Laboratory of Synthetical Automa-tion for Process Industries under Grant 2013ZCX09,the Natural Science Foundation of Hebei Province under Grant F2014501137,the Natural Science Foundation of Liaoning Province under Grant 2013020010.References[1]W.Qian,C.C.Chan,C.L.Zhao,et al.,Photonic crystal ﬁber refractive indexsensor based on a ﬁber Bragg grating demodulation,Sens.Actuators B:Chem.166(6)(2012)761–765.[2]S.K.Srivastava,B.D.Gupta,Inﬂuence of ions on the surface plasmonresonance spectrum of a ﬁber optic refractive index sensor,Sens.Actuators B:Chem.156(2)(2011)559–562.[3]J.Zhou,Y.Wang,C.Liao,et al.,Intensity modulated refractive index sensorbased on optical ﬁber Michelson interferometer,Sens.Actuators B:Chem.(2015)315–319.[4]W.Liang,Y.Huang,Y.Xu,et al.,Highly sensitive ﬁber Bragg grating refractiveindex sensors,Appl.Phys.Lett.86(15)(2005)151122.[5]S.Gao,W.Zhang,H.Zhang,et al.,Fiber modal interferometer with embeddedﬁber Bragg grating for simultaneous measurements of refractive index and temperature,Sens.Actuators B:Chem.188(11)(2013)931–936.[6]N.Chen,B.Yun,Y.Cui,Cladding mode resonances of etch-eroded ﬁber Bragggrating for ambient refractive index sensing,Appl.Phys.Lett.88(13)(2006)133902.[7]D.W.Kim,Y.Zhang,K.L.Cooper,et al.,In-ﬁber reﬂection mode interferometerbased on a long-period grating for external refractive-index measurement,Appl.Opt.44(26)(2005)5368–5373.[8]J.H.Chong,P.Shum,H.Haryono,et al.,Measurements of refractive indexsensitivity using long-period grating refractometer,mun.229(1–6)(2004)65–69.[9]L.Qi,C.L.Zhao,J.Yuan,et al.,Highly reﬂective long period ﬁber grating sensorand its application in refractive index sensing,Sens.Actuators B:Chem.193(3)(2014)185–189.[10]V.Bhatia,Applications of long-period gratings to single and multi-parametersensing,Opt.Express 4(11)(1999)457–466.[11]T.H.Xia,A.P.Zhang,B.Gu,et al.,Fiber-optic refractive-index sensors based ontransmissive and reﬂective thin-core ﬁber modal interferometers,mun.283(10)(2010)2136–2139.[12]F.Pang,H.Liu,H.Guo,et al.,In-ﬁber Mach–Zehnder interferometer based ondouble cladding ﬁbers for refractive index sensor,IEEE Sens.J.11(10)(2011)2395–2400.[13]Z.Tian,S.S.Yam,L.Hp,Refractive index sensor based on an abrupt taperMichelson interferometer in a single-mode ﬁber,Opt.Lett.33(10)(2008)1105–1107.[14]Z.Tian,S.S.H.Yam,J.Barnes,et al.,Refractive index sensing withMach–Zehnder interferometer based on concatenating two single-mode ﬁber tapers,IEEE Photonics Technol.Lett.20(8)(2008)626–628.[15]T.Wei,n,H.Xiao,Fiber inline core-cladding-mode Mach–Zehnderinterferometer fabricated by two-point CO laser irradiations,IEEE Photonics Technol.Lett.21(10)(2009)669–671.[16]B.Li,L.Jiang,S.Wang,L.Zhou,H.Xiao,H.L.Tsai,Ultra-abrupt tapered ﬁberMach–Zehnder interferometer sensors,Sensors 11(6)(2011)5729–5739.[17]L.Xu,Y.Li,B.Li,Nonadiabatic ﬁber taper-based Mach–Zehnder interferometerfor refractive index sensing,Appl.Phys.Lett.101(15)(2012)153510.[18]Z.Tian,S.S.H.Yam,H.Loock,Single-mode ﬁber refractive index sensor basedon core-offset attenuators,IEEE Photonics Technol.Lett.20(16)(2008)1387–1389.[19]Z.Tian,S.Yam,In-line single-mode optical ﬁber interferometric refractiveindex sensors,J.Lightwave Technol.27(13)(2009)2296–2306.[20]Zhang.Shanshan,Zhang.Weigan,G.E.N.G.Pengcheng,et al.,FiberMach–Zehnder interferometer based on concatenated down-and up-tapers for refractive index sensing applications,mun.(288)(2013)47–51.[21]Ping Lu,Liqiu Men,Kevin Sooley,Qiying Chen,Tapered ﬁber M–Zinterferometer for simultaneous measurement of refractive index and temperature,Appl.Phys.Lett.94(13)(2009)131110–131113.[22]C.R.Liao,D.N.Wang,H.E.Xiaoying,et al.,Twisted optical microﬁbers forrefractive index sensing,IEEE Photonics Technol.Lett.23(13)(2011)848–850.Q.Wang et al./Sensors and Actuators B 222(2016)159–165165[23]B.Li,L.Jiang,S.Wang,et al.,High sensitivity Mach–Zehnder interferometersensors based on concatenated ultra-abrupt tapers on thinned ﬁbers,ser Technol.44(3)(2012)640–645.[24]J.Chen,J.Zhou,Q.Zhang,et al.,All-ﬁber modal interferometer based on ajoint-taper-joint ﬁber structure for refractive index sensing with high sensitivity,IEEE Sens.J.13(7)(2013)2780–2785.[25]T.K.Yadav,R.Narayanaswamy,M.H.Abu Bakar,Y.Mustapha Kamil,M.A.Mahdi,Single mode tapered ﬁber-optic interferometer based refractive index sensor and its application to protein sensing,Opt.Express 22(19)(2014)22802–22807.BiographiesQi Wang was born in Liaoning Province,China,in 1982.He received his Ph.D.degree in 2009from the School of Physics and Optoelectronic Technology,Dalian Uni-versity of Technology (DUT),Dalian,China.In 2013,he was awarded as the “Liaoning Bai-Qian-Wan Talents”by Liaoning Province.He is currently working as an associate professor in the College of Information Science and Engi-neering at Northeastern University,Liaoning Province,China.His research interests are new photonic devices,ﬁber-optic sensors,photonic crystal and photonic crys-tal ﬁber sensing technology,optoelectronic measurement technology and system,and their industrial applications.He has authored and co-authored more than 100scientiﬁcpapers,patents and conferencepresentations.Yong Zhao received his M.A.and Ph.D.degrees,respec-tively,in precision instrument &automatic measurement with laser and ﬁber-optic techniques from the Harbin Institute of Technology,China,in 1998and 2001.He was awarded a ﬁrst prize scholarship in 2000by the China Instrument and Control Society and the Sintered Metal Corporation (SMC)scholarship in Japan.He has a schol-arship in Japan.He was a post doctor in the Department of Electronic Engineering of Tsinghua University from 2001to 2003,and then worked as an associate professor in the Department of Automation,Tsinghua University of China.In 2006,he was a visiting scholar of University of Illinois in Urbana and Champagne,USA.In 2008,he was awardedas the “New Century Excellent Talents in University”by the Ministry of Education of China.In 2009,he was awarded as the “Liaoning Bai-Qian-Wan Talents”by Liaoning Province.In 2011,he was awarded by the Royal Academy of Engineering as an aca-demic researcher of City University London.In 2013,he was awarded as the “High Level Talents”by the Northeastern University.Now he is working in Northeastern University as a full professor.As a leader of his research group,his current research interests are the development of ﬁber-optic sensors and device,ﬁber Bragg grating sensors,novel sensor materials and principles,slow light and sensor technology,optical measurement technologies.He has authored and co-authored more than 200scientiﬁc papers and conference presentations,8patents,and 5books.He is a member in the Editorial Boards of the international journals of Sensor Letters,Instrumentation Science &Technology,Journal of Sensor Technology,and Advances in Optical Technologies.。

荣誉奖状-学术成就模板(word版下载可编辑使用)

荣誉奖状-学术成就模板(word版下载可编
辑使用)
尊敬的 [姓名] 同学：
经过我们学校严格评选，鉴于你在学术领域所取得的杰出成就，我们荣幸地向你授予以下荣誉奖状：
奖状内容：
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奖状编号：[编号]
荣誉奖状：学术成就奖
学校：[学校名称]
学院：[学院名称]
专业：[专业名称]
姓名：[姓名]
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荣誉成就：
在你的学术生涯中，你展现了卓越的学术能力和出色的研究成果。

你的热情、勤奋和执着精神使你在学术界脱颖而出。

以下是你在学术领域取得的主要成就：
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感谢与祝贺：
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你的努力和奉献为学校树立了崇高的榜样，也为自己创造了光辉的未来。

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4.198 674CIRC-CARDIOVASC INTE1941-7640482 4.364 4.375 675J CHILD PSYCHOL PSYC0021-963011260 4.360 5.845 676ARTHRITIS RES THER1478-63546728 4.357 4.798 676HUM REPROD0268-116125468 4.357 4.258 678BRIT J DERMATOL0007-096319575 4.351 4.241 679EXPERT OPIN INV DRUG1354-37843857 4.337 3.599 679J NEUROCHEM0022-304238828 4.337 4.48 679RADIOTHER ONCOL0167-81409609 4.337 4.329 682CURR OPIN CLIN NUTR1363-19502815 4.333 3.933 683ENDOCRIN METAB CLIN0889-85292249 4.330 3.372 684J CARDIOVASC MAGN R1097-66471363 4.328 3.273 685THYROID1050-72565955 4.327 3.456 686INORG CHEM0020-166976733 4.325 4.434 687ANN MED0785-38903304 4.323 4.673 688CIRC-HEART FAIL1941-3289602 4.315 4.324 689CELL BIOCHEM BIOPHYS1085-91951346 4.312 2.885 690ANAL CHIM ACTA0003-267034466 4.310 3.656 691PHARMACOGENOMICS J1470-269X1789 4.306 4.974 692EUR J PHARM BIOPHARM0939-64117433 4.304 4.4 693MOL PLANT1674-2052944 4.296 4.307 694J NUTR0022-316632265 4.295 4.408 695AM J OPHTHALMOL0002-939418101 4.293 3.465 695CANCER IMMUNOL IMMUN0340-70044796 4.293 3.661 695DNA REPAIR1568-78644800 4.293 4.303 698J GEN PHYSIOL0022-12957884 4.283 4.712 698J POWER SOURCES0378-775341071 4.283 4.634 700ELECTROCHEM COMMUN1388-248114208 4.282 4.846 701HARMFUL ALGAE1568-98832051 4.280 3.853 702EARTH PLANET SC LETT0012-821X35477 4.279 4.853 702SIAM J IMAGING SCI1936-4954307 4.279 4.279。

东北师范大学14年博士名单(最终稿)

刘晓欧李忠阳孙志敏刘波李健夏欢张磊陈婷金标欧阳琳关儒茜李枫梁启政王文轶张军朱尖王晨旭王禹耕刘艳华鲁勇威高科吴冬高悦吕品晶谢辰王鹏飞纪昕李烨赵方铭谭晓闯董晓明张宇胡贝克牟佳杨彬彬
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A DFT study of Hg0 adsorption on Co3O4 (1 1 0) surface

A DFT study of Hg 0adsorption on Co 3O 4(110)surfaceWenchao Ji a ,Zhemin Shen a ,⇑,Qingli Tang a ,Bowen Yang a ,Maohong Fan b ,caSchool of Environmental bDepartment of Chemical cSchool of Civil and Environmental Hg 0has strong interaction with Co 3+sites nearby.The adsorption of Hg 0on Co 3O 4is favorable at low temperature.a r t i c l e i n f o Article history:Received 19October 2015Received in revised form 21December 2015Accepted 23December 2015Available online 2January 2016Keywords:Elemental mercury Co 3O 4Adsorption energy Equilibrium constants PDOSa b s t r a c tSpin polarized density functional theory calculation combined with periodic slabs were employed to reveal the elemental mercury (Hg 0)adsorption mechanism on Co 3O 4(110)surface.The adsorption ener-gies and possible adsorption sites were investigated.To understand the adsorption interaction more directly,the electronic structural changes of before and after adsorption were compared.The hybridiza-tion of orbitals was studied by the partial density of states (PDOS)analysis.In addition,the temperature effects toward equilibrium constants of Hg 0–Co 3O 4system were taken into consideration.The results manifested that the interaction between Hg 0and Co 3O 4(110)surface is chemisorption with À74.037kJ/mol.Co 3+sites,the highest oxidation state of Co atoms,are crucial in this process which can accept the electrons after Hg oxidation.The redundant electrons transfer to O and other Co atoms nearby.PDOS analysis indicates the hybridization of s orbitals (Hg 0)and p,d orbitals (Co atom).And d orbitals of Hg interacts with s,p orbitals of Co atom strongly.The trends of equilibrium constants suggest that Hg 0adsorption on Co 3O 4(110)surface is favorable at low temperature.Ó2016Elsevier B.V.All rights reserved.1.IntroductionThe utilization of traditional energy source of coal has led to severe pollution to the environment,such as the emission of SO x ,NO x ,CO 2and mercury [1–3].Particularly,mercury has drawn great environmental concern for its persistence,toxicity and bio-accumulation [4].The control of mercury is on the agenda of manycountries in the world.In December 2011,Mercury and Air Toxics Standards(MATS)[5],the ﬁrst national standards,wasissued by the United States protection agency.It aims to limit the release of mercury,acid gases and other toxic matters from coal-ﬁred power plants.In January 2013,the Minamata Convention on Mercury [6]was agreed at the ﬁfth session of the Intergovernmen-tal Negotiating Committee,which is a global treaty to protect human health and the environment from the adverse effects of mercury.Therefore,the removal of mercury is always a worldwide issue with great signiﬁcance./10.1016/j.cej.2015.12.0901385-8947/Ó2016Elsevier B.V.All rights reserved.⇑Corresponding author.E-mail address:zmshen@ (Z.Shen).Since the elemental mercury(Hg0)is volatile and water insoluble,removing it from the environment is of great difﬁculty in all species of mercury[7].To date,activated carbon[8], calcium-based sorbents[9],ﬂy ash[10],noble metals[11]and metal oxides[12–14]have been used for Hg0removal.Among these sorbents and catalysts,Co3O4-based materials capture researchers’attention because of high efﬁciency on mercury removal[15].From the aspect of Co3O4,it has been applied in combustion of CO and organic compounds and for waste gases treatment[16].It exhibits very high activity for CO oxidation in CO/O2mixtures at low temperature.The spinel structure of Co3O4crystal has Co3+in octahedral coordination and Co2+in tetra-hedral coordination.Co3+has been regarded as the active site for CO oxidation,while Co2+is almost inactive regarding the oxidation of CO[17].The oxidation character of Co3O4is essential to adsor-bate which incites the research of Hg0adsorption and oxidation.Experimental studies have demonstrated that Co3O4-based sor-bent exhibits excellent performance for adsorption and oxidation of Hg0.Mei et al.[18]prepared Co3O4loaded activated carbon (AC),which achieved high Hg0removal efﬁciency of91.5%and good regeneration ability.Hg capture experiment found that it Co3O4-AC has relative high activity in the temperature range of 80–250°C.Co3O4loaded on c-Al2O3was used to remove Hg0in a packed-bed reactor with removal efﬁciency of72.3%[15].These studies were conducted in a catalyst testing system which con-sisted of Hg0permeation tube,a packed-bed reactor,an on-line cold vapor atomic absorption spectrophotometer,and a data acqui-sition system.Hg0permeation tube ensures certain concentration of Hg0in simulation gas.High purity nitrogen was used as carrier gas and balance gas.The simulation gas also contained5.0vol.% oxygen.Mercury removal efﬁciency represented the interaction strength.During this process,N2was very stable with no effect on mercury adsorption and oxidation.Oxygen content was too low to effect the oxidation on Hg0.Importantly,Hg0adsorption process was a pre-condition of its oxidation.Good performance of Hg0adsorption determined the capacity adsorbents.Hence, Co3O4is a very important sorbent/catalyst which is alternative to noble metal catalyst for Hg0control.Nevertheless,the interaction mechanism was not clariﬁed clearly in previous studies.Related theoretical studies are very essential for Hg0and Co3O4interaction.Density functional theory(DFT)is commonly used in evaluating the mechanism of mercury on sorbents/catalysts surface.This method has revealed adsorption/oxidation mechanism of Hg0on metal surface[19],metal oxide surface[20],binary alloys[21] and carbonaceous surface[22].However,Hg0on Co3O4surface has not been investigated theoretically.The actual interaction mechanism is of great importance in Hg0removal sorbents design and theoretical support.We focus on the adsorption/oxidation mechanism of Hg0on Co3O4(110)surface.Several properties such as geometry struc-ture,adsorption energies and possible sites,Hirshfeld population and the density of states(PDOS)were calculated and analyzed. Additionally,temperature effects on equilibrium constants of Hg0 were also investigated to testify reaction character and stability of Co3O4.This method is crucial to develop and reveal mechanism of effective Hg0capture materials based on transition metal compounds.2.Models and computational methods2.1.Surface modelsCo3O4is a spin type oxide,with Co2+in tetrahedral interstices and Co3+in octahedral interstices of the cubic close-packed lattice. As shown in Fig.1,It is a facet-centered cubic lattice with space group FD-3M(a=b=c=8.084Å,a=b=c=90°,ICSD#28158) [23].Co3O4(110)surface was modeled by a periodically repeated slab with four layers.The top view and side view of the surface are shown in Fig.2.The surface is terminated by Co3+,Co2+,O3f in octa-hedral coordinate and O4f in four coordination atoms.The vacuum region thickness of13Åwas chosen to eliminate interaction effects of neighboring slab.The bottom layer wasﬁxed and the other three layers were relaxed.putational methodsAll calculations were performed with the DMol3package in Materials Studio70[24,25].The accuracy of local density approx-imation(LDA)[26]and the generalized gradient approximation (GGA)[27]methods were studied before the calculation.By com-paring with experimental lattice parameters,the GGA in forms of Perdew–Burke–Ernzerhof(PBE)shows best accuracy.Hence, GGA-PBE method was adopted to calculate the electronic structure in this system.A double numerical basis with polarization func-tions(DNP)were used in all calculations.All electron basis set were used for O atoms.Density functional semi-core pseudopoten-tials(DSPP)[28]were used for Co and Hg atoms,whereby the outer electrons of these atoms(3d74s2of Co and of5d106s2of Hg)were treated as valence electrons and the inner electrons were as a sim-ple potential including some degree of relativistic effects.In addi-tion,a cutoff energy of4.5Åand4.6Åwere used in Co3O4surface and Hg–Co3O4system,respectively.The self-consistentﬁeld con-vergence criterion was set to an energy change of10À6Ha.The Brillouin Zone integrations were performed using a3Â4Â1 Monkhorst-Pack grid.The convergence tolerance of geometry opti-mization based on energy,max.force and max.displacement were 1Â10À5Ha,2Â10À3Ha/Åand5Â10À3Å,respectively.During all calculations,the spin polarization was applied.For adsorption energy,it was calculated according to the following equation:E ads¼E Hg0þsurfaceÀE Hg0ÀE surfaceðEq:AÞwhere E ads is the adsorption energy,EHg0þsurfacerepresents the energyof the adsorption system,EHg0is the energy of the element mercury, E surface is the energy of periodic surface,all energies are in kJ/mol.By this deﬁnition,negative value corresponds to exothermic adsorp-tion process.To investigate exothermicity of adsorption processes and favor-ability of the spontaneous reaction as a function of temperature, the equilibrium constants(K eq)were calculated based on the ther-modynamic data from frequency calculation[25,29].The method has been applied to study the equilibrium constant of mercury adsorption on CaO[30]and CoCl2[31]surfaces.We used general relationships for statistical thermodynamic partition functions (translational,rotational,and vibrational partition functions) [32].Contributions from electronic motion are neglected due to the electronic ground state of the adsorption systems.The equilib-rium constants are calculated by lnðK eqÞ¼ÀD G=RT,where D G is the Gibbs free energy change,R is the ideal gas constant,and T is the temperature.The change of Gibbs free energy during the adsorption process(D G)is deﬁned as:D G%DE adsþD E0þTðD S vibþD S trans;rotÞÀkTln PðEq:BÞwhere D E ads is the change of adsorption energy,D E0represents the change of zero-point energy,D S vib and D S trans;rot are the changes of the vibrational and translational,rotational entropy during adsorp-tion,respectively.The entropy and zero-point energy data of Hg0and Co3O4sur-face were available in the temperature between25K and1000K.350W.Ji et al./Chemical Engineering Journal289(2016)349–355Nonetheless,the equilibrium constant was investigated in temper-ature range of250–1000K which was more relevant for Hg0exper-imental adsorption system.3.Results and discussion3.1.Choice of DFT methodsIn order to know which DFT methods can provide more reliable calculation results,the primary Co3O4crystal was optimized by different functional methods(LDA-PWC,GGA-PBE and GGA-BLYP).It has been reported that the lattice parameters calculated by DFT methods were in good agreement with experimentally measured values[33,34].Accordingly,the most suitable method was conﬁrmed by comparing with the experimental values.All lat-tice parameters of bulk Co3O4using different methods are given in Table1.It is clear that LDA-PWC and GGA-BLYP methods have underes-timated in lattice parameters.The LDA-PWC method has the big-gest relative tolerance of2.015%in all direction of cell lengths. GGA-BLYP method obtains0.804%relative tolerance with length error of0.065Å.On contrary,GGA-PBE method overestimates the lattice parameters.The relative tolerance is only0.502%with length error of0.041Å.It provides most accurate results with experimental values.Hence,GGA-PBE method was chosen in the following computation.A reasonable vacuum thickness is very important in eliminating related effects between slabs.In previous research,the result indi-cated a suitable height of13Å[17].The vacuum height of13ÅandFig.1.Primary crystal structure of Co3O4.Fig.2.Top view and side view of clean Co3O4(110)surfaces.Table1The optimized lattice parameters of different DFT methods.Lattice parameters Experimental value(Å)LDA-PWC GGA-PBE GGA-BLYPValues(Å)Relative tolerance(%)Values(Å)Relative tolerance(%)Values(Å)Relative tolerance(%)a8.0847.921 2.0158.1250.5028.0190.804b8.0847.921 2.0158.1250.5028.0190.804c8.0847.921 2.0158.1250.5028.0190.80418Åwere investigated using the GGA-PBE method above,and the energy difference is 0.019eV which is acceptable.In consequence,the ﬁnal vacuum height was set to 13Å,which is sufﬁcient to ignore neighboring slab interaction.3.2.Adsorption energiesTwo surface areas are taken into consideration.Surface I was constructed as following parameters:a =8.125Å,b =5.745Å.Sur-face II area was twice than surface I’s which was made of 8.125Å(a)and 11.490Å(b).The optimized adsorption energy of Hg on surface I was À74.037kJ/mol.The corresponding adsorption energy on surface II was À74.179kJ/mol.The comparison is shown in Table 2.Only 0.20%relative difference occurred on two surfaces.It indicates that surface I is large enough for this system.Neverthe-less,the surface II calculation amount has increased nearly twice than surface I.Based on the calculation cost and calculation accu-racy,surface I was chosen as the research model.To conﬁrm the most stable conﬁguration for adsorbed Hg 0,sev-the distance values.It indicates that the interaction between Hg and Co 3O 4(110)surface attributes to chemisorption.Co 3+site is less stable than O 4f site according to adsorption energies.The con-ﬁguration of Hg on O 4f site is shown in Fig.3.Compared to previous DFT study,Hg 0–CaO (100)system was physical interaction with adsorption energy from À9.16to 11.78kJ/mol [35]which is much smaller than that on Co 3O 4(110)surface.It is found that the adsorption energy of Hg 0on MnO 2(110)surface (À63.51to 78.32kJ/mol)[14]is almost in the same level.It indicates that Co 3O 4can also have strong ability in capturing Hg 0.Moreover,the favorable adsorption sites are oxy-gen and bridge-oxygen for CaO (110)and MnO 2(110)surfaces,respectively.The active site in this study is O 4f from the stable adsorption conﬁguration,which is similar with surfaces mentioned above.Table 2The comparison of Hg 0adsorption on different surfaces.SurfaceSurface I Surface II Length a (Å)8.1258.125Length b (Å)5.74511.490Adsorption energy (kJ/mol)À74.037À74.179Table 3Adsorption properties of Hg 0on various adsorption sites of Co 3O 4(110)surface.Adsorption sites Distance (Å)Adsorption energies (kJ/mol)Co 3+2.725À63.037Co 2+,O 3f N/A a –O 4f2.457À74.037aMoved to O 4f site.Co 3O 4(110)surface.(a)The geometry structure before adsorption;(b)the geometry structure after adsorption site.Table 4Atoms charge transfer calculated by Hirshfeld method.Atom indexesHirshfeld atomic charges BeforeAfter Electron transfer Co(1)0.3630.3390.024Co(2)0.3160.3040.012Co(3)0.3160.3050.012Co(4)0.3630.3380.025Co(5)0.3560.3420.014Co(6)0.2040.1960.009Co(7)0.2040.1980.006Co(8)0.2000.1930.007Co(9)0.2000.1930.007Co(10)0.2400.1550.085Co(11)0.3560.3440.012Co(12)0.2400.1540.086O(13)À0.140À0.1510.011O(14)À0.244À0.2510.007O(15)À0.257À0.2650.008O(16)À0.243À0.2520.009O(17)À0.156À0.1610.005O(18)À0.156À0.1610.005352W.Ji et al./Chemical Engineering Journal 289(2016)349–3553.3.Electronic structureThe adsorption mechanism depends on the variation of systemelectronic structure.The charge transfer of all atoms and related PDOS analysis were studied systematically.Atomic charges with Hirshfeld atomic population analyses were conducted in this sys-tem,which is based on deformation density on the free atom elec-tron density[36].Compared to Mulliken method,it provides an accurate partitioning of the electron density.The atomic charges for clean Co3O4surface and Hg0–Co3O4slabs were calculated by Hirshfeld method.The charge transfer were based on the differ-ence between original state and adsorption state(Table4).Positive value means the atom obtains electrons after adsorption and neg-ative value means the atom loses electrons after adsorption.Fig. shows the atomic indices of Hg0–Co3O4(110)interaction system.As shown in Fig.4,Co(1),Co(4),Co(10),Co(12),O(13),O(16),O (19),O(24)and O(26)atoms are distributed in theﬁrst layer.Hg0 on the top site of O4f,has the biggest charge transfer of0.224electrons after adsorption.It indicates that Hg has been oxidized after adsorption.As for Co3O4(110)surface,all atoms have posi-tive charge transfer.Co(10)and Co(12)obtain the highest electron number of0.085and0.086,respectively.Co(1)and Co(4)accept nearly equal number of electrons(0.024and0.025eÀ).The electron transfer of O atoms range from0.004eÀto0.014eÀ.It is interesting that the most stable adsorption O4f site has only0.009e-charge transfer corresponding to O(20)atom.Obviously,O(20)is not the active site atom in Hg0adsorption system.From the respect of charge transfer,the Co3+site is active site that obtain much elec-trons from Hg atom.O4f is a middle position between Co(10)and Co(12)at the next layer.The strong interaction of Hg and the sur-face depends on the two Co3+atoms.They obtain most electrons for Hg and then deliver surplus electrons to related atoms.The charge transfer follows the routes below.Co(10)and Co(12)accept electrons from Hg then transfer some to linked O atoms.O(24),O (26),O(16),O(19),O(13),O(20)and O(28)atoms obtain0.014eÀ, 0.014eÀ,0.009eÀ,0.009eÀ,0.011eÀand0.004eÀ,respectively. The other Co3+atoms on theﬁrst layer,Co(1)and Co(4),accept 0.024and0.025eÀ,respectively.Co3+atoms are in the highest oxi-dation state which have strong ability to obtain electrons from3f4fFig.4.Atomic indices for Hg0adsorption on Co3O4(110)surface.and Co(Co3+site)for surface system before and after adsorption on Co3O4(110)surface.The Fermi level(E f)is set to be zero(dashedJournal289(2016)349–355353peak at0.05Ha disappeared.The p orbitals turn toﬂat with no dis-tinct peak plot.The d orbitals shift to lower energy states of À0.20Ha.All of these changes conﬁrm that strong interaction occurred between Hg0and Co3O4surface.The orbitals of Co atoms were analyzed to investigate possible interaction with Hg0.As shown in Fig.5,the s,p and d orbitals change slightly after adsorp-tion.Speciﬁcally,s and p orbitals become much higher in PDOS value and overlap with s and d orbitals of Hg atom.It indicates the hybridization of s orbitals(Hg0)and p,d orbitals(Co atom). The d orbitals of Hg interacts with s,p orbitals of Co atom strongly. From respect of PDOS,Hg0and Co3O4surface can form a very stable system after adsorption and oxidation process.It is consistent with the experimental results of metal oxide-loaded activated carbon (AC)in the simulated gases(5.0vol.%O2,1.26ppm Hg0,balance gas and carrier gas N2).Hence,the real interaction occurred between pure Hg0and adsorbent.Hg0removal efﬁciency of Co3O4modiﬁed AC reached91.5%[18].It has been testiﬁed that AC had no obvious capture and oxidation ability in related research [8].The DFT calculation results in this study indicates that Co3O4 has strong interaction with Hg0.Additionally,it has certain oxidation ability in Hg0removal.Both chemical adsorption and oxidation ability of Co3O4contribute to good performance in Hg0 removal process.3.4.Temperature effect on equilibrium constants of Hg0Temperature plays an important role in adsorption process,so it is necessary to study the effect of temperature on the equilibrium constants for Hg0interaction with Co3O4(110)surface.Based on the thermodynamics analysis in DFT,the calculated entropy,Gibbs free energy changes,and equilibrium constants of Hg0adsorption on the Co3O4surface in temperature range of250–1000K are listed in Table S1in the Supplementary material.According to the results, negative Gibbs free energy difference is obtained,which indicates a spontaneous adsorption process in this system.As shown in Fig.6, the equilibrium constants have negative correlation with the tem-perature.High temperature corresponds to low equilibrium con-stants and vice versa.This trend is consistent with the previous studies of Hg0adsorption on CaO[30],MnO2[14]surfaces.Specif-ically,ln(K eq)decreases with the rising of temperature.The highest ln(K eq)value reaches39.057at250K and the minimum value is 16.511at1000K.It decreases by57.73%during the temperature increase process.It has been reported that the maximum ln(K eq) of CaO was below20.The decrease amplitude was33.33%.As for Hg0adsorption on MnO2(110)surface,the peak and lowest value of ln(K eq)were about60and5,respectively.It has the highest deduction rate of91.71%among three adsorbents.MnO2exhibits relative high performance in equilibrium constants.However,it is the most temperature sensitive adsorbent for Hg0.The equilib-rium constants of Co3O4is higher than that of CaO which indicates the former one is more effective.In conclusion,Co3O4is tempera-ture durable and effective in Hg0adsorption process.4.ConclusionsThe adsorption mechanism of Hg0on Co3O4(110)surface was investigated by density functional theory and the periodic slab model.The interaction between Hg0and Co3O4(110)surface is chemisorption with adsorption energy ofÀ74.037kJ/mol.The optimal adsorption conﬁguration is on the top of O4f site.However, Hirshfeld population analysis indicated that the charge transfer of Co3+atoms near O4f is the highest.It reveals that Co3+is the most direct interaction sites to form a stable adsorption system for Hg0. This high reactivity of Co3O4surface to Hg0is due to the hybridiza-tion of s orbitals(Hg0)and p,d orbitals(Co atom).The d orbitals of Hg interacts with s,p orbitals of Co atom strongly as well.Besides, the equilibrium constants of Hg0–Co3O4(110)surface have nega-tive correlation with the temperature.Hence,Hg0adsorption is more favorable at low temperature.AcknowledgementsThis work was supported by the National Science Foundation of China(Project No.21177083),and the program for New Century Excellent Talents in Shanghai Jiao Tong University,and Wyoming Clean Coal Program.Appendix A.Supplementary dataSupplementary data associated with this article can be found,in the online version,at /10.1016/j.cej.2015.12.090. 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白蝴蝶之恋的读书笔记

白蝴蝶之恋的读书笔记《白蝴蝶之恋》是一篇抒情散文，作者刘白羽通过对一只在风雨中挣扎的白蝴蝶的细腻描绘，抒发了对生命的关爱和敬畏之情。

这篇文章让我深受触动，也让我对生命有了更深的思考。

文章开篇，作者以细腻的笔触描绘了春天的景象，为白蝴蝶的出现营造了一个美丽而充满生机的背景。

“一阵暖人心意的春风刚刚吹过，又来了一阵冷雨”，这样的天气变化，似乎预示着生命中的无常。

就在这时，一只白蝴蝶闯入了作者的视线。

它“从哪儿来？要飞向哪儿去？”这两个问句，不仅引起了作者的好奇，也引发了我的思索。

这只白蝴蝶在风雨中“弱不禁风”，却依然顽强地飞翔着。

作者用“像一片小小的雪花，愈飞愈远，消失不见了”这样的描写，展现了白蝴蝶的渺小和脆弱。

然而，当作者再次看到它时，它已经“奄奄一息”地落在草地上。

作者的心被触动了，他产生了一种“怜悯”之情。

这种情感并非高高在上的施舍，而是对一个平等生命的尊重和关切。

作者小心翼翼地将白蝴蝶放在手心，感受到它的“纤细的足”和“柔软的绒毛”，仿佛能够触摸到生命的微弱跳动。

他用自己的体温去温暖它，希望能给它带来一丝生机。

在这个过程中，作者的内心充满了矛盾和挣扎。

他一方面希望白蝴蝶能够活下来，另一方面又担心自己的干预会适得其反。

这种复杂的心情，让我深刻地体会到了生命的可贵和脆弱。

随着白蝴蝶在作者的手中渐渐苏醒，作者的心情也由紧张转为欣喜。

“它试了几次，终于一跃而起，展翅飞翔，活泼伶俐地在我周围翩翩飞舞了好一阵，又向清明如洗的空中冉冉飞去，像一片小小的雪花，愈飞愈远，消失不见了。

”这段描写让我感受到了生命的顽强和奇迹。

白蝴蝶从奄奄一息到重新飞翔，仿佛是对生命的一种赞歌。

它让我明白，无论生命遭遇多大的困境，只要有一丝希望，就不能放弃。

在这篇文章中，作者不仅仅是在讲述一只白蝴蝶的故事，更是在探讨生命的意义和价值。

生命是如此的脆弱，却又如此的顽强。

每一个生命都有其存在的意义和价值，都值得我们去尊重和珍惜。

我们不能因为生命的渺小和脆弱而轻视它，也不能因为生命的短暂而挥霍它。