Effect of friction heat on tribological behavior of M2 steel against GCr15 steel in dry sliding

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含氮硼酸酯添加剂的合成及其摩擦学性能研究

2008年8月第33卷第8期润滑与密封LUBR I C A TI ON EN GI N EER I N GA ug .2008V ol 133No 18收稿日期3作者简介张浩(3—),男,硕士研究生,研究方向含氮硼酸酯添加剂2@111含氮硼酸酯添加剂的合成及其摩擦学性能研究张　浩1　涂政文1　付尚发2(1.湖北省新型反应器与绿色化学工艺重点实验室　湖北武汉430074;2.武汉博达特种润滑技术有限公司　湖北武汉430074)摘要:合成了3种含有烷基醇酰胺基团的含氮硼酸酯,并利用红外光谱对其主要官能团进行了鉴定;考察了它们的水解稳定性能,利用四球试验机考察了它们在150S N 基础油中的摩擦学性能,并采用扫描电子显微镜观察分析钢球磨斑表面形貌。

结果表明:将烷基醇酰胺基团引入硼酸酯分子结构中能有效改善硼酸酯的水解稳定性能;含氮硼酸酯具有较好的极压抗磨性能,并具有较好的抗腐蚀性能。

关键词:含氮硼酸酯;烷基醇酰胺;水解稳定性;摩擦学性能中图分类号:T H11712;T Q 225126　文献标识码:A 文章编号:0254-0150(2008)8-094-4Syn thesis an d Tr ibologica l C ha ra cter istic of Nitrogen 2con ta i n i n g Bora te a s L ubr i can t Add itiveZha ng H ao 1　Tu Zhe ng w e n 1　F u S ha ngfa2(1.Hube i K ey Lab of Nove l R eac t or &Green Che m ical Technol ogy,W uhan Hubei 430074,China;2.W uhan BO DA Specia l Lubricant Co .,L td,W uhan Hube i 430074,China )A bstr ac t:Three k inds of nitr ogen 2contain ing borates includ ing alkanola mide were synthesiz ed and char acteriz ed by I Rs p ectrum .The hyd r olytic stab ilities and tribo l ogical characteristic of nitr ogen 2containing bo rates as add itive f o r 150S N o il were investigated on f ou r ball tester .The mo r phologies of the wo rn scars were observed by means of scann ing electr on mi 2cr osc op y .The results show that the bo r ates including alkanolamide have better hyd r olytic stabilities;nitr ogen 2contain ing bo 2r ates as add itive have better load 2carrying,anti 2wear ,fricti on 2reducing and an ti 2freting ca p ability .Keyword s :nitr ogen 2c on taining bo r ate;alkano la m ide;hydr o lytic stab ility;tribo logical characteristic　随着润滑油产品标准的不断提高和各国环保法规的越来越严格,传统的润滑油添加剂面临着巨大的挑战[1]。

冰冻浓缩效应绿色合成英文

冰冻浓缩效应绿色合成英文The "cryo-concentration effect" refers to the processin which a liquid mixture is cooled to a temperature below the freezing point of the solvent, causing the formation of ice crystals. This results in the separation of the solvent from the solute, leading to a more concentrated solution. The cryo-concentration effect is often utilized in various industries, such as the food and beverage industry, for the production of concentrated juices and other liquid products.On the other hand, "green synthesis" refers to the development of chemical processes for the production of various compounds and materials that are environmentally friendly. This approach aims to minimize the use of hazardous substances, reduce waste generation, and promote sustainable practices. Green synthesis methods ofteninvolve the use of renewable resources, non-toxic solvents, and energy-efficient processes.In summary, the "cryo-concentration effect" involvesthe separation and concentration of a liquid mixture through freezing, while "green synthesis" pertains to the environmentally friendly production of compounds and materials. Both concepts are important in their respective fields and contribute to sustainable and responsible manufacturing practices.。

化学机械抛光工艺中的抛光垫

第6期(总第151期)2008年12月机械工程与自动化M ECHAN I CAL EN G I N EER I N G &　AU TOM A T I ON N o 16D ec 1文章编号:167226413(2008)0620073203化学机械抛光工艺中的抛光垫3周　海1,王黛萍1,王　兵1,陈西府1,冶远祥2(1.盐城工学院,江苏　盐城　224051;2.兴化祥盛光电子材料公司,江苏　兴化　225761)摘要:抛光垫是晶片化学机械抛光中决定表面质量的重要辅料。

研究了抛光垫对光电子晶体材料抛光质量的影响:硬的抛光垫可提高晶片的平面度;软的抛光垫可改善晶片的表面粗糙度;表面开槽和表面粗糙的抛光垫可提高抛光效率;对抛光垫进行适当的修整可使抛光垫表面粗糙。

关键词:化学机械抛光;抛光垫;表面粗糙度中图分类号:T G 5801692 文献标识码:A3江苏省科技厅科技攻关项目(BE 2007077);江苏省自然科学基础研究项目(BK 2008197);江苏省高校自然科学基础研究项目(06KJB 460119);江苏省大学生实践创新训练计划项目(07SSJCX 026)收稿日期:2008210215作者简介:周海(19652),男,江苏滨海人,教授,博士,主要研究方向为CAD CAM 、超精密加工。

0　引言化学机械抛光(Chem ical M echan ical Po lish ing ,简称C M P )是化学反应、机械摩擦、流体动压综合作用的过程,通过纳米级粒子的研磨作用与抛光液的化学腐蚀作用的有机结合,使被抛光的工件表面光滑,从而得到其它平面加工手段很难达到的光滑平坦表面[1]。

自1991年I BM 公司首次成功地将C M P 技术应用到动态随机存储器的生产以来,化学机械抛光技术已成功用于集成电路中的半导体晶片、存储磁盘、精密陶瓷、磁头、精密阀门、光学玻璃等表面的平面化,成为应用最为广泛的全局平面化技术[2]。

Effect of Surfactants on the Interfacial

Effect of Surfactants on the Interfacial Tension and Emulsion Formation between Water and Carbon Dioxide Sandro R.P.da Rocha,Kristi L.Harrison,and Keith P.Johnston*Department of Chemical Engineering,University of Texas,Austin,Texas78712Received July8,1998.In Final Form:October7,1998 The lowering of the interfacial tension(γ)between water and carbon dioxide by various classes of surfactants is reported and used to interpret complementary measurements of the capacity,stability,and average drop size of water-in-CO2emulsions.γis lowered from∼20to∼2mN/m for the best poly(propylene oxide)-b-poly(ethylene oxide)-b-poly(propylene oxide)(PPO-b-PEO-b-PPO)and PEO-b-PPO-b-PEO Pluronic triblock copolymers,1.4mN/m for a poly(butylene oxide)-b-PEO copolymer,0.8mN/m for a perfluoropolyether (PFPE)ammonium carboxylate and0.2mN/m for PDMS24-g-EO22.The hydrophilic-CO2-philic balance (HCB)of the triblock Pluronic and PDMS-g-PEO-PPO surfactants is characterized by the CO2-to-water distribution coefficient and“V-shaped”plots of logγvs wt%EO.A minimum inγis observed for the optimum HCB.As the CO2-philicity of the surfactant tail is increased,the molecular weight of the hydrophilic segment increases for an optimum HCB.The stronger interactions on both sides of the interface lead to a lowerγ.Consequently,more water was emulsified for the PDMS-based copolymers than either the PPO-or PBO-based copolymers.IntroductionSupercritical fluid(SCF)carbon dioxide(T c)31°C,P c )73.8bar)is an environmentally benign alternative to organic solvents for waste minimization.It is nontoxic, nonflammable,and inexpensive.However,because of its very low dielectric constant, ,and polarizability per volume,R/v,CO2is a poor solvent for most nonvolatile lipophilic and hydrophilic solutes.1It may be considered a third type of condensed phase,different from lipophilic and hydrophilic phases.Consequently,it is possible to disperse either lipophilic or hydrophilic phases into CO2, in the form of microemulsions,emulsions,and latexes, given an appropriate surfactant.Because of the low values of and R/v for CO2,the most CO2-philic types of functional groups have low cohesive energy densities,e.g.,fluoro-carbons,fluoroethers,and siloxanes.2-6The solvent strength of carbon dioxide may be understood by the fact that the solubility of a polymer in carbon dioxide is highly correlated with the surface tension of the pure polymer melt.7For example,poly(fluoroacrylates)with low surface tensions of10-15mN/m are highly soluble,whereas poly-(dimethylsiloxanes)with surface tensions of20mN/m are moderately soluble,and hydrocarbon polymers with higher surface tensions show very low solubility.For nonpolar or slightly polar polymers,the surface tension is a measure of the van der Waals forces and is related to the cohesive energy density.Because R/v is so small for CO2,polymers with low cohesive densities and surface tensions are the most soluble.The first generation of research involving surfactants in SCFs addressed reverse micelles and water-in-SCF microemulsions,for fluids such as ethane and propane8,9 as reviewed recently.10,11Microemulsions are thermody-namically stable and optically transparent,with typical droplet diameters of about2-10nm.The mechanistic insight gained from these studies of phase equilibria, interfacial curvature,and droplet interactions in a su-percritical fluid is directly applicable to carbon dioxide. Attempts to form water-in-CO2(w/c)microemulsions have been elusive.6,12,13For PFPE COO-NH4+w/c microemul-sions,FTIR,UV-visible absorbance,fluorescence,and electron paramagnetic resonance(EPR)experiments have demonstrated the existence of an aqueous domain in CO2 with a polarity approaching that of bulk water,14as has also been shown by small-angle neutron scattering (SANS).15Organic-in-CO2microemulsions have also been formed for600molecular weight poly(ethylene glycol) (PEG600)and for polystyrene oligomers.16,17In many previous studies,surfactant activity in CO2has been characterized in terms of water uptake into a CO2 microemulsion.Since the results were negative most of the time,it has been difficult to determine how to design surfactants to the water-CO2interface.A more direct property,such as the interfacial tension,is needed to understand the activity of surfactants at various interfaces containing carbon dioxide.In SCF systems,only a few studies have measured the interfacial tension(γ)even for simple binary systems(1)O’Shea,K.;Kirmse,K.;Fox,M.A.;Johnston,K.P.J.Phys.Chem. 1991,95,7863.(2)McHugh,M.A.;Krukonis,V.J.Supercritical Fluid Extraction: Priciples and Practice,2nd ed.;Butterworth:Stonham,MA,1994.(3)Hoefling,T.A.;Newman,D.A.;Enick,R.M.;Beckman,E.J.J. Supercrit.Fluids1993,6,165-171.(4)Newman,D.A.;Hoefling,T.A.;Beitle,R.R.;Beckman,E.J.; Enick,R.M.J.Supercrit.Fluids1993,6,205-210.(5)DeSimone,J.M.;Guan,Z.;Elsbernd,C.S.Science1992,257, 945.(6)Harrison,K.;Goveas,J.;Johnston,K.P.;O’Rear,ngmuir 1994,10,3536.(7)O’Neill,M.L.;Cao,Q.;Fang,M.;Johnston,K.P.;Wilkinson,S. P.;Smith,C.D.;Kerschner,J.;Jureller,S.Ind.Chem.Eng.Res.1998, 37,3067-3079.(8)Fulton,J.L.;Smith,R.D.J.Phys.Chem.1988,92,2903-2907.(9)Johnston,K.P.;McFann,G.;Lemert,R.M.Am.Chem.Soc.Symp. Ser.1989,406,140-164.(10)Bartscherer,K.A.;Minier,M.;Renon,H.Fluid Phase Equilib. 1995,107,93-150.(11)McFann,G.J.;Johnston,K.P.In Microemulsions:Fundamental and Applied Aspects;Kumar,P.,Ed.;Dekker:New York,1998;Vol.in press.(12)Iezzi,A.;Enick,R.;Brady,J.Am.Chem.Soc.Symp.Ser.1989, No.406,122-139.(13)Consani,K.A.;Smith,R.D.J.Supercrit.Fluids1990,3,51-65.(14)Johnston,K.P.;Harrison,K.L.;Clarke,M.J.;Howdle,S.M.; Heitz,M.P.;Bright,F.V.;Carlier,C.;Randolph,T.W.Science1996, 271,624-626.(15)Zielinski,R.G.;Kline,S.R.;Kaler,E.W.;Rosov,ngmuir 1997,13,3934-3937.419Langmuir1999,15,419-428including carbon dioxide and a liquid phase.18-20None of these studies included a surfactant.Surfactants have been studied for the generation of CO2foams in water21typically for water-soluble surfactants.The effects of various surfactants on theγbetween supercritical CO2and PEG (600MW)were reported recently.16At276bar,the addition of1%PFPE COO-NH4+reducesγfrom3.2to2.1mN/m, and the interfacial area of the surfactant is437Å2/ molecule.Interfacial tension measurements have also been made between poly(2-ethylhexyl acrylate)(PEHA)and CO222and styrene oligomers and CO2.23As is well-known for water-in-oil(w/o)emulsions and microemulsions,the phase behavior,γ,and curvature are interrelated,as shown in Figure1.24A minimum inγis observed at the phase inversion point where the system is balanced with respect to the partitioning of the surfactant between the phases.25,26Upon change of any of the formulation variables away from this point,for example,the temperature or the hydrophilicity/hydro-phobicity ratio(in our case the hydrophilic/CO2-philic ratio),the surfactant will migrate toward one of the phases. This phase usually becomes the external phase,according to the Bancroft rule.27Unlike the case for conventional solvents,a small change in pressure or temperature can have a large influence on the density and thus on the solvent strength of a supercritical fluid.By“tuning”the interactions between the surfactant tail and the solvent,it becomes possible to manipulate the phase behavior,and therefore the activity of the surfactant at the interface and curvature,and also the extension of the surfactant tails.As an example of pressure tuning,a water-in-propane microemulsion is inverted to a propane-in-water microemulsion by varying the pressure by50bar in the C12EO6/brine/propane system, at constant temperature.28This system undergoes a phase inversion density,by analogy with the phase inversion temperature,for conventional systems.If the density is changed so that the surfactant prefers either phase over the other,the surfactant is less interfacially active and γincreases.16,22,23The objective of this study is to achieve a fundamental understanding of the lowering of the water-CO2inter-facial tension by different classes of surfactants and to use this knowledge to explain the formation and stability of water-in-CO2(w/c)emulsions.The surfactants include PFPE COO-NH4+,Pluronic R(PPO-b-PEO-b-PPO)and Pluronic L(PEO-b-PPO-b-PEO)triblock copolymers,poly-(butylene oxide-b-ethylene oxide)(PBO-b-PEO),and poly-(dimethylsiloxane)(PDMS)copolymers with PEO-PPO grafts(PDMS-g-PEO-PPO).Fromγmeasurements ver-sus concentration,the adsorption is investigated for PFPE COO-NH4+and used to determine the critical micro-emulsion concentration.For the PPO-and PDMS-based surfactants,the concept of a hydrophilic-CO2-philic bal-ance(HCB)is introduced by relatingγand the distribution coefficient of the surfactant to the EO fraction(see Figure 1).To understand howγand the HCB influence colloid stability,we chose to study w/c emulsions in contrast to previous studies of microemulsions,since so few of these surfactants form microemulsions.Emulsions are ther-modynamically unstable,but may be kinetically stable, with droplets from100nm to several micrometers in diameter.The presence of the surfactant at the interface lowers theγand thus the Laplace pressure,reducing the energy necessary to deform the interface.29The emulsions may be stabilized against flocculation due to van der Waals forces by steric stabilization,as has been analyzed theoretically,30-33and/or Marangoni stresses,due to gradients in interfacial tension at the interface.To characterize emulsion capacity,stability,and the average droplet size of the emulsions,an in-situ turbidity technique has been applied in addition to visual observations.The ability to design surfactants for the interface between CO2 and an aqueous phase based upon knowledge of the relationship between colloid formation and stability,phase behavior,andγis of interest for a wide variety of heterogeneous reactions and separation processes in CO2. Examples include dry cleaning,extraction with micro-(16)Harrison,K.L.;Johnston,K.P.;Sanchez,ngmuir1996, 12,2637-2644.(17)McClain,J.B.;Betts,D.E.;Canelas,D.A.;Samulski,E.T.; DeSimone,J.M.;Londono,J.D.;Cochran,H.D.;Wignall,G.D.;Chillura-Martino,D.;Triolo,R.Science1996,274,2049.(18)Heurer,G.Ph.D.Thesis,The University of Texas at Austin, 1957.(19)Chun,B.-S.;Wilkinson,G.T.Ind.Eng.Chem.Res.1995,34, 4371-4377.(20)Schiemann,H.;Wiedner,E.;Peter,S.J.Supercrit.Fluids1993, 6,181-189.(21)Lee,H.O.;Heller,J.P.;Hoefer,A.M.W.SPE Reservoir Eng. 1991,11,421-428.(22)O’Neill,M.;Yates,M.Z.;Harrison,K.L.;Johnston,P.K.;Canelas,D.A.;Betts,D.E.;DeSimone,J.M.;Wilkinson,S.P.Macromolecules1997,30,5050-5059.(23)Harrison,K.L.;da Rocha,S.R.P.;Yates,M.Z.;Johnston,K. P.;Canelas,D.;DeSimone,ngmuir1998,14,6855-6863.(24)Aveyard,R.;Binks,B.P.;Clark,S.;Fletcher,P.D.I.J.Chem. Technol.Biotechnol.1990,48,161-171.(25)Bourrel,M.;Schechter,R.S.Microemulsions and Related Systems:Formulation,Solvency and Physical Properties;Marcel(27)Ruckentein,ngmuir1996,12,6351-6353.(28)McFann,G.J.;Johnston,ngmuir1993,9,2942.(29)Walstra,P.Chem.Eng.Sci.1993,48,333-349.(30)Peck,D.G.;Johnston,K.P.Macromolecules1993,26,1537.(31)Meredith,J.C.;Johnston,K.P.Macromolecules1998,31,5507-5555.(32)Meredith,J.C.;Sanchez,I.C.;Johnston,K.P.;Pablo,J.J.d.Figure1.Schematic representation of phase behavior andinterfacial tension for mixtures of water,CO2,and nonionicsurfactants as a function of formulation variables.420Langmuir,Vol.15,No.2,1999da Rocha et al.emulsions and emulsions,phase transfer reactions,34,35and emulsion polymerization.36Experimental SectionMaterials.All of the surfactants were used as received,unless indicated.The CF 3O(CF 2CF(CF 3)O)∼3CF 2COO -NH 4+(PFPE COO -NH 4+),a gift from A.Chittofrati,37was stored in a desiccator.The single tail Krytox-sulfate,R -COOCH 2CH 2OSO 3--Na +,where R )CF 3(CF 2CF(CF 3)O)n CF 2CF 2-,and the triple tail Krytox-sorbitol surfactants were synthesized by E.Singley and Dr.E.J.Beckman at the University of Pittsburgh.38Pluronic L,PEO-b -PPO-b -PEO (PEO -PPO -PEO),and Pluronic R,PPO-b -PEO-b -PPO (PPO -PEO -PPO),surfactants were a gift from BASF.The block copolymer PEO-b -PBO (EO 15-BO 12,SAM185)(where the subscripts indicate the number of repeat units of each moiety)was provided by Pittsburgh Paint and Glass.The surfactant (CH 3)3SiO[Si(CH 3)2O]20[Si(CH 3)(R)]2OSi(CH 3)3,with graft R )(CH 2)3O(C 2H 4O)∼11H,(PDMS 24-g -EO 22),M w ∼2600,was a gift synthesized by Unilever.7SILWET L-7500(M w )3000),(CH 3)3SiO(Si(CH 3)2O)x (Si(CH 3)(R))y OSi(CH 3)3,with R )(CH 2)3O-(C 3H 6O)n Bu (PDMS 11-g -PO 39),with n ,x ,and y not specified,and SILWET L-7622(M w )10000),with a similar backbone,but R )(CH 2)3O(C 2H 4O)m Me (PDMS 105-g -EO 68),were provided by OSi Specialties,Inc.ABIL B 8851(M w ∼6000),(CH 3)3SiO(Si-(CH 3)2O)22(Si(CH 3)(R)O)4Si(CH 3)3,with R )(CH 2)3O(C 2H 4O)∼17-(C 3H 6O)∼4H (PDMS 28-g -EO 67-PO 17),and ABIL B 88184(M w ∼13000),(CH 3)3SiO(Si(CH 3)2O)73(Si(CH 3)(R)O)4Si(CH 3)3,with R ∼(CH 2)3O(C 2H 4O)∼32(C 3H 6O)∼7H (PDMS 79-g -EO 126-PO 28)were obtained from Goldschmidt AG.PDMS homopolymer with a M w of 13000was synthesized by J.M.DeSimone at U.N.Carolina.Poly(ethylene glycol)with a molecular weight of 600was obtained from Polysciences,Inc.Poly(butylene glycol)monoether,composed of an ethylene oxide backbone with an ethyl side group (PBO,800g/mol)was supplied by Air Products.Poly(propylene glycol)(1025g/mol)was obtained from Polysciences,Inc.,and used as received.Deionized water (NANOpureII;Barnstead)and instrument grade carbon dioxide (99.99%)were used for all experiments.Phase Behavior.Phase boundaries were determined in the variable-volume view cell as described in further detail else-where.7For a given weight of surfactant and CO 2,the pressure of the system was increased until a single phase was observed in the view cell.The pressure was then decreased slowly until the solution became slightly turbid.The pressure was then increased again,and the process was repeated.The pressure where the system became turbid was classified as the cloud point pressure.The pressure and temperature were measured to (0.2bar and (0.1°C,respectively.Interfacial Tension Measurements.The tandem variable-volume pendant drop tensiometer described previously 16was used to measure the interfacial tension between CO and water (γ).The apparatus consisted of two variable volume view cells (the drop phase cell and the measurement cell (continuous phase cell)),an optical rail for proper alignment,a light source,a video camera,and a computer.The drop phase cell contained water saturated with an excess amount of pure CO 2,and the continuous phase cell contained CO 2and surfactant (if present).In this configuration,the surfactant only has to diffuse short distances in the small volume of the droplet phase.Pendant drops were formed on the end of a stainless steel or PEEK capillary tube with an inside diameter ranging from 0.01to 0.03in.Once a suitable drop was formed,the six-port switching valve connecting the two cells was closed and timing of the drop age was started.Several images were recorded as a function of drop age.Images of the drop were obtained in a tagged imagefile format (TIFF)and the edge of the drop was extracted from data at various global threshold values using a C ++program.From the shape of the interface,the γmay be obtained from the Laplace equationwhere ∆P is the pressure differential across the interface,R 0is the radius of curvature at the apex of the drop,and z is the vertical distance from the apex.A set of three first-order differential equations was used to express Laplace’s equation,and a computer program 39,40was used to solve for γ.The density difference between the two phases was calculated by using an equation of state for pure CO 241and steam tables for pure water.The aqueous phase density was assumed to change less than 0.0025g/cm 3for the concentrations of surfactant studied.Emulsion Formation,Stability,and Average Droplet Size Estimation.Figure 2shows a schematic representation of the experimental apparatus,similar to a previous version,for turbidimetric measurement and visual observation of emulsion formation and stability.22The system consists of a 28-mL variable-volume view cell,an optical cell (0.1cm path length)which was mounted in a spectrophotometer (Cary 3E UV -vis),a high-pressure reciprocating pump (minipump with a flow rate of 8-80mL/min),and a manual pressure generator (High-Pressure Equip.,model 87-6-5).A six-port switching valve (Valco Instru-ments Co.,Inc.)with an external sampling loop was used to add water to the system.The pressure was monitored to (0.2bar with a strain gauge pressure transducer (Sensotec),and the temperature was controlled to within (0.1°C.Surfactant was initially loaded into the view cell,and the desired amount of CO 2was added with the pressure generator.The pressure was increased,and the system equilibrated at the desired T ,for ∼2h,by using a magnetic stir bar.The cloud point of the surfactant was obtained as described above.The solution was then recirculated,and deionized water was injected into the system via the 150-µL sample loop in the switching valve.The solution was sheared through a 130µm i.d.×50mm long stainless steel capillary tube upstream of the optical cell.Emulsion formation and stability were characterized based upon turbidity measurements versus time (t )at a constant wavelength (λ)650nm)and also visual observation.The turbidity is a measure of the reduction in transmitted intensity,τ)(1/l )ln(I 0/I ),where l is the path length and I 0and I are the incident and transmitted intensities,respectively.After the injection of each increment of water,the emulsion was stirred and recirculated for ∼20min (approximate time required for the absorbance to reach a maximum value).Immediately after recirculation and stirring were stopped,τmeasurements started.The stability was assessed from τas a function of t ,while the(34)Jacobson,G.B.;Lee,C.T.;daRocha,S.R.P.;Johnston,.Chem.,in press.(35)Jacobson,G.B.;Lee,C.T.;Johnston,.Chem.,in press.(36)Adamsky,F.A.;Beckman,E.J.Macromolecules 1994,27,312-314.(37)Chittofrati,A.;Lenti,D.;Sanguineti,A.;Visca,M.;Gambi,C.M.C.;Senatra,D.;Zhou,Z.Prog.Colloid Polym.Sci.1989,79,218-(39)Jennings,J.W.;Pallas,ngmuir 1988,4,959-967.Figure 2.Apparatus for emulsion formation and turbidimetry measurement.∆P )2γ/R 0+(∆F )gz(1)Surfactant Effect on Interfacial Tension Langmuir,Vol.15,No.2,1999421effective average droplet size was determined fromτversusλ.For a monodisperse system of nonabsorbing spheres in theabsence of multiple scatteringτis given byτ)3K*φ/2D,42where φis the dispersed phase volume fraction,D is the droplet diameter, and K*is the scattering coefficient.According to Mie theory,Κ*is a complex function of R(R∼D/λ,whereλis the wavelengthof the incident light)and m the ratio of the refractive indices ofthe dispersed and continuous phases.The refractive indices wereapproximated by those of the pure components,water(1.333)and CO2.43By evaluation of turbidities at two wavelengths,theaverage droplet size can be determined by an iteration proce-dure.44Results and DiscussionInterfacial Tension of the CO2-Water Binary System.The interfacial tension between pure CO2and water is shown in Figure3for two temperatures as a function of pressure,along with the data of Heurer18and Chun and Wilkinson.19Our interfacial tensions were measured1h after drop formation.Theγvalues obtained by Chun and Wilkinson19were measured with the capillary rise technique.Whereas local equilibrium was achieved within the capillary tube,the entire system was not at equilibrium.Heurer used the pendant drop technique; however,the values reported were obtained from the drop profile within10s of drop formation.Therefore,the lower values ofγin the present study suggest a closer approach to true equilibrium.A simple physical picture may be used to explain the behavior for most of the pressure range studied.16At pressures below70bar,γdecreases with increasing pressure.The cohesive energy density or free energy density of CO2is well below that of water at all pressures. The density and free energy density of CO2change over a wide range with pressure,whereas the values for essentially incompressible water are constant.As the density of the CO2phase increases,its free energy density becomes closer to that of water,andγdecreases.At low pressures where the density and free energy density change a great deal with pressure,the decrease inγis pronounced.At high pressures,where CO2is more “liquidlike”,it is much less compressible and the decrease inγwith pressure is small.For the CO2-PEG600interface,γwas predicted quantitatively with a gradientmodel and the lattice fluid equation of state.16The latticefluid model is less applicable for water due to thecomplexities resulting from hydrogen bonding and car-bonic acid formation.A cusp in the curve ofγversus pressure is observed attemperatures and pressures near the critical point of CO2.The region of the cusp inγshifts to slightly higherpressures as the temperature is increased above the criticaltemperature of CO2.For supercritical temperatures,themagnitude of the cusp increases as the temperature isdecreased toward the critical temperature.At25,1935,and38°C,the cusp in the interfacial tension is verynoticeable,while it becomes small at45°C and is notvisible at71°C.18The following argument explains how the cusp is relatedto the large compressibility of CO2.An upward pointingcusp has been observed for the surface excess of ethyleneon graphitized carbon black.45The excess adsorption canbe defined in terms of the density of the bulk phase andthe density of the interfacial region46where F(z)is the molar density of the fluid at a distancez from the surface.At pressures below the critical pressureregion,F(z)can be much larger than F,due to attractionof solvent to the surface,leading to a largeΓex.At higherpressures,the bulk fluid is much denser,so that thedifference between F(z)and F is much smaller resultingin a smallerΓex.As temperature increases above thecritical temperature of the solvent,the tendency of thesurface to raise F(z)to“liquidlike”densities diminishesandΓex decreases.Similar arguments apply to theadsorption of CO2at the water-CO2interface.TheenhancedΓex is manifested as the downward cusp inγ.Inboth examples,the cusps become broader and shift tohigher pressures at higher temperatures.Similar behavioris observed for peaks in plots of the isothermal compress-ibility of pure CO2versus pressure at constant temper-ature.To put the above results in perspective,new interfacialtension data are shown for the PEG600-CO2interface tocomplement earlier data16only at45°C(Figure4).Thevalues ofγfor the water-CO2interface are considerablylarger than those for the PEG600-CO2,PS(M n)1850),23CO2-PEHA(M n)32k)interfaces.22This result is dueprimarily to the much larger surface tension of water,∼72mN/m,versus that of PEG,∼35mN/m,and PEHA, 30mN/m.However,it is interesting thatγbetween CO2and water at high pressures,20mN/m,is below that forwater-hydrocarbon interfaces.For heptane and octane,the hydrocarbon-waterγis about50mN/m.This lower γis consistent with the higher miscibility between CO2 and water47versus hydrocarbons and water.The stronger interactions between CO2and water versus hydrocarbons and water are due to the small size of CO2which causes a smaller penalty in hydrophobic hydration,CO2’s quad-rupole moment,and,finally,Lewis and Bronsted acid-base interactions.Over the entire pressure range for PEG600-CO2at25and45°C,the interfacial tension decreased monotonicallywith increasing pressure,unlike the case for CO2-water(42)Yang,K.C.;Hogg,R.Anal.Chem.1979,51,758-763.(43)Burns,R.C.;Graham,C.;Weller,A.R.M.Mol.Phys.1986,59,(45)Findenegg,G.H.In Fundamentals of Adsorption;Myers,A.L., Belfort,G.,Eds.;Engineering Foundation:New York,1983;p207.Figure3.Interfacial tension at the CO2-water interface asa function of pressure at various temperatures.Γex≡∫(F(z)-F bulk)d z(2) 422Langmuir,Vol.15,No.2,1999da Rocha et al.at 35°C.The lack of a dip near the critical pressure may be due to the much lower compressibility at 25and 45°C versus 35°C.This contrast in behavior may also be due to a difference in the density gradient and thickness in the interfacial region for the two systems,for example,greater miscibility for the CO 2-PEG600system.Interfacial Tension:PFPE Ammonium Carboxy-late.The addition of small amounts of PFPE COO -NH 4+decreases γsubstantially as shown at 45°C and 276bar in Figure 5.As the concentration is raised above 0.03%surfactant,a discontinuity is observed,and the magnitude of the slope becomes much smaller.Because it has been shown that w/c microemulsions are formed in this system,14the discontinuity can be attributed to a critical microemulsion concentration (c µc)for the PFPE COO --NH 4+surfactant,as has been done for oil -water inter-faces.24At concentrations above the c µc,the less negative slope is caused by the addition of surfactant primarily to adsorption at the pendant drop interface,the change in γis reduced.The adsorption obtained from the Gibbs’adsorption equationfor the PFPE COO -NH 4+surfactant was 1.77×10-10mol/cm 2,which corresponds to a surface coverage of ∼100Å2/molecule.Such a high surface coverage is sufficient for the formation of microemulsions.A comparable value of ∼140Å2/molecule was measured by Eastoe et al.48at 500bar and 25°C for the hybrid hydrocarbon -fluorocarbon C 7F 15CH(OSO 3-Na +)C 7H 15surfactant in CO 2.This value was determined by assuming that all the surfactant is adsorbed at the interface of spherical droplets of 25Å2radius,as measured by SANS,with a polydispersity of ∼0.2.The substantial reduction in γand relatively high surfactant adsorption explain why it was possible to form a w/c microemulsion with PFPE COO -NH 4+.The same surfactant had an absorption of 400Å2/molecule at the CO 2-PEG interface.16Phase behavior studies indicated that PEG-in-CO 2microemulsions are also formed with this surfactant,but the nature of the core has not been characterized.16Interfacial Tension:Fluoroether Sulfate and Sorbitol Surfactant.The phase behavior of fluoroether sulfates and fluoroether sorbitols was measured by Singley et al.38for various molecular weights of single-,twin-,and triple-tailed surfactants.The surfactants were soluble in CO 2at 33°C and moderate pressure (<300bar).The sorbitol surfactants were found to be more soluble in CO 2than the sulfate ones,as expected due to the low solubilities of ions in CO 2,because of its low dielectric constant.The results showed that branching depresses the cloud point curve of a surfactant until the solubility becomes domi-nated by the overall molecular weight.These surfactants were used to form CO 2-in-water and middle-phase emul-sions with excess CO 2and water.38The interfacial tension was measured at the water -CO 2interface for the single-tailed M w 2500sulfate and the triple-tailed (7500g/mol total)sorbitol surfactants.Our measured cloud point for the 1.4%(w/w)CO 2sorbitol surfactant was 215.6bar at 45°C.For 0.56%sulfate surfactant,it was 139.8bar at 45°C.The sulfate surfactant did not lower the interfacial tension significantly over the pressure range of 180-283bar 45°C at a concentration of 0.56%.The interfacial tension was difficult to determine accurately,because bubbles and possibly surfactant precipitate appeared on the surface of the pendant drop within 15min of drop formation.The interfacial tension was estimated to be ∼15mN/m by using manual edge detection of the pendant drop.For the sorbitol surfactant,the interfacial tension decreased to ∼5.5mN/m at 276bar and 45°C with a concentration of 1.4%.Relative to other surfactants reported in this study,these surfactants were less successful in lowering the interfacial tension.Interfacial Tension:PPO -PEO -PPO,PEO -PPO -PEO,and PBO -PEO Surfactants.Block co-polymers containing CO 2-philic and hydrophilic (CO 2-phobic)functional groups may be designed to be active at the CO 2-water interface.In this section,the CO 2-philic blocks are poly(propylene oxide)and poly(butylene oxide),while the CO 2-phobic block is poly(ethylene oxide).TheFigure 4.Interfacial tension for the PEG600-CO 2interface at varioustemperatures.Figure 5.Interfacial tension for the water -CO 2-PFPE COO -NH 4+system at 45°C and 276bar.The dotted line is used to determine the surfactant adsorption via the Gibbs adsorption equation.A discontinuity is present at the critical micromemulsion concentration.Γ2)-1RT (d γd ln c 2)T ,P(3)Surfactant Effect on Interfacial Tension Langmuir,Vol.15,No.2,1999423。

英文原文

Liang Guo Stephen L.Hodson Timothy S.FisherXianfan Xu1e-mail:xxu@ School of Mechanical Engineering and Birck Nanotechnology Center,Purdue University,West Lafayette,IN47907Heat Transfer AcrossMetal-Dielectric Interfaces During Ultrafast-Laser Heating Heat transfer across metal-dielectric interfaces involves transport of electrons and pho-nons accomplished either by coupling between phonons in metal and dielectric or by cou-pling between electrons in metal and phonons in dielectric.In this work,we investigate heat transfer across metal-dielectric interfaces during ultrafast-laser heating of thin metalﬁlms coated on dielectric substrates.By employing ultrafast-laser heating that cre-ates strong thermal nonequilibrium between electrons and phonons in metal,it is possible to isolate the effect of the direct electron–phonon coupling across the interface and thus facilitate its study.Transient thermo-reﬂectance measurements using femtosecond laser pulses are performed on Au–Si samples while the simulation results based on a two-temperature model are compared with the measured data.A contact resistance between electrons in Au and phonons in Si represents the coupling strength of the direct electron–phonon interactions at the interface.Our results reveal that this contact resist-ance can be sufﬁciently small to indicate strong direct coupling between electrons in metal and phonons in dielectric.[DOI:10.1115/1.4005255]Keywords:interface thermal resistance,ultrafast laser,thermo-reﬂectance,two-temper-ature model,electron–phonon coupling1IntroductionInterface heat transfer is one of the major concerns in the design of microscale and nanoscale devices.In metal,electrons,and pho-nons are both energy carriers while in dielectric phonons are the main energy carrier.Therefore,for metal-dielectric composite structures,heat can transfer across the interface by coupling between phonons in metal and dielectric or by coupling between electrons in metal and phonons in dielectric through electron-interface scattering.Phonon–phonon coupling has been simulated mainly by the acoustic mismatch model and the diffuse mismatch model[1].As for electron–phonon coupling,there are different viewpoints.Some studies have assumed that electron–phonon coupling across a metal-dielectric interface is negligible and heat transfer occurs as electron–phonon coupling within metal and then phonon–phonon coupling across the interface[2].Electron–phonon coupling between metal(Cr,Ti,Al,Ni,and Pt)and SiO2 has exhibited negligible apparent thermal resistance using a parallel-strip technique[3].On the other hand,comparison between simulations and transient thermal reﬂectance(TTR) measurements for Au-dielectric interfaces reveals that energy could be lost to the substrate by electron-interface scattering dur-ing ultrafast-laser heating,and this effect depends on electron temperature and substrate thermal properties[4–6].In this study,we employ TTR techniques to investigate inter-face heat transfer for thin goldﬁlms of varying thicknesses on sili-con substrates.(Here,we consider silicon as a dielectric since heat is carried by phonons in silicon.)Similar work has been reported [5].In our model,we consider two temperatures in metal and also the temperature in the dielectric substrate.This allows us to inves-tigate the effect of both the coupling between electrons in metal and phonons in the dielectric substrate,and the coupling between phonons in metal and phonons in the dielectric substrate,and allows us to isolate the effect of the electron–phonon coupling across the interface that can be determined from the TTR mea-surement.Experimentally,we employ pulse stretching to mini-mize the effect of nonequilibrium among the electrons.As a result,the experimental data can be well-explained using the com-putational model.The thermal resistance between electrons in Au and phonons in Si,which quantiﬁes the direct electron–phonon coupling strength,is calculated from the measured data.The results reveal that in the thermal nonequilibrium state,this electron–phonon coupling at the interface is strong enough to dominate the overall interface heat transfer.2TTR MeasurementAu–Si samples of varying Au thicknesses were prepared by thermal evaporation at a pressure of the order of10À7Torr.The thicknesses of the goldﬁlms are39,46,60,77,and250nm,meas-ured using an atomic force microscope.The pump-and-probe technique is used in a collinear scheme to measure the thermo-reﬂectance signal.The laser pulses are generated by a Spectra Physics Ti:Sapphire ampliﬁed femtosecond system with a central wavelength of800nm and a repetition rate of5kHz.The wave-length of the pump beam is then converted to400nm with a sec-ond harmonic crystal.The pump pulse has a pulse width(full width at half maximum-FWHM)of390fs measured by the sum-frequency cross-correlation method and is focused onto the sam-ple with a spot radius of20.3l m.The probe beam has a central wavelength of800nm and a pulse width of205fs measured by autocorrelation and is focused with a spot radius of16.9l m.This pump pulse width is intentionally stretched from the original pulse width of50fs to minimize the inﬂuence of thermal nonequili-brium among electrons since the electron thermalization time in Au can be of the order of100fs[7].This thermalization time is pump wavelength and pumpﬂuence dependent,and can be of the order of10fs if higher laserﬂuence is used[8,9].Our experiments did show the importance of pulse stretching.Figure1shows the TTR measurement results for the sample of thickness77nm with different pumpﬂuences before and after stretching the pulse.The plots show the normalized relative reﬂectance change(ÀD R/R)1Corresponding author.Contributed by the Heat Transfer Division of ASME for publication in the J OURNAL OF H EAT T RANSFER.Manuscript received May18,2011;ﬁnal manuscript received September30,2011;published online February13,2012.Assoc.Editor: Robert D.Tzou.with the delay time between the pump and the probe pulses to show the contrast in cooling rates.With a shorter pulse (Fig.1(a )),a steep initial drop is seen in the signal,which is attributed to the behavior of nonequilibrium among electrons.Since the TTM to be used for simulation assumes a well-deﬁned tempera-ture for electrons,i.e.,the electrons in gold have reached thermal equilibrium (not necessarily a uniform temperature),the model cannot predict the fast initial drop in the signals in Fig.1(a ).As will be shown later,the signals obtained by stretching the pulse can be predicted well using the TTM.3Two-Temperature Model for Thermal Reflectance MeasurementsUltrafast-laser heating induces thermal nonequilibrium between electrons and phonons in metal,which can be described by the TTM [10–13].We note that the heterogeneous interface consid-ered here involves three primary temperature variables (two in the metal and one in the dielectric).The “two-temperature”model is applied to the metal side.For investigating electron–phonon and phonon–phonon coupling at the interface,two thermal resistances are deﬁned:R es (its reciprocal)indicates the coupling strength between electrons in metal and phonons in dielectric,while R ps indicates the coupling strength between phonons in metal and phonons in dielectric.(Large thermal resistance corresponds to weak coupling.)The resulting governing equations,initial,and interface conditions areC e @T e @t ¼k e @2T e@x2ÀG ðT e ÀT p ÞþS (1a )C p @T p @t ¼k p @2T p @x 2þG ðT e ÀT p Þ(1b )C s @T s @t ¼k s @2T s@x(1c )T e ðt ¼0Þ¼T p ðt ¼0Þ¼T s ðt ¼0Þ¼T 0(2)Àk e@T e @xx ¼L ¼T e ÀT s R es x ¼L(3a )Àk p @T px ¼L ¼T p ÀT s ps x ¼L(3b )Àk s@T sx ¼L ¼T e ÀT s es x ¼L þT p ÀT s ps x ¼L(3c )The subscripts e ,p ,and s denote electrons in metal,phonons in metal,and phonons in the dielectric substrate,respectively.C is the volumetric heat capacity,k is the thermal conductivity,G is the electron–phonon coupling factor governing the rate of energy transfer from electrons to phonons in metal,and L is the thickness of the metal layer.At the front surface of the metal layer insula-tion boundary condition is used due to the much larger heat ﬂux caused by laser heating relative to the heat loss to air.At the rear surface of the substrate,since the thickness of the substrate used is large enough (1l m)so that there is no temperature rise during the time period of consideration,the insulation boundary condition is also applied.Thermal properties of phonons in both metal and dielectric are taken as temperature-independent due to the weak temperature dependence.The thermal conductivity of phonons in metal is much smaller than that of the electrons and is taken in this work as 0.001times the bulk thermal conductivity of gold (311W/(mK)).The volumetric heat capacity of the metal phonon is taken as that of the bulk gold.C e is taken as proportional to T e [14]with the proportion coefﬁcient being 70J/(m 3K 2)[15],and k e is calculated by the model and the data used in Ref.[13]which is valid from the room temperature to the Fermi temperature (6.39Â104K in Au,[14]).G can be obtained using the model derived in Ref.[16].In this work,the value of G at the room tem-perature is taken as 4.6Â1016W/(m 3K)[17],and its dependence on electron and phonon temperatures follows [16].The laser heat-ing source term S is represented by the model used in [13]asS ¼0:94ð1ÀR ÞJ t p ðd þd b Þ1Àexp ÀL d þd bexp Àx d þd b À2:77t t p2"#(4)which assumes all the absorbed laser energy is deposited in the metal layer.J is the ﬂuence of the pump laser,R is the surface re-ﬂectance to the pump,t p is the pulse width (FWHM),d is the opti-cal penetration depth,and d b is the electron ballistic length (around 100nm in Au,[18]).R es and R ps are treated as free pa-rameters for ﬁtting the experimental data.The wavelength of the probe laser in the experiment is centered at 800nm.For this wavelength,the incident photon energy is below the interband transition threshold in Au,which is around 2.47eV [18],and the Drude model can be used to relate the tem-peratures of electrons and phonons to the dielectric function and then the index of refraction,which is expressed as [19]e ¼e 1Àx 2px ðx þi x s Þ(5)x is the frequency of the probe laser and x p is the plasma fre-quency (1.37Â1016rad/s in Au evaluated using the data in Ref.[14]).x s is the electron collisional frequency,the inverse of the electron relaxation time.The temperature dependence ofelectricalFig.1TTR measurement results for the Au–Si sample of Authickness 77nm with different ﬂuences.(a )Results before pulse stretching;(b )results after pulse stretching.resistivity indicates that x s is approximately proportional to pho-non temperature at high temperature [14]and from the Fermi liq-uid theory,its variation with electron temperature is quadratic (T e 2)[20].Therefore,x s is related to T e and T p approximately asx s ¼A ee T 2e þB ep T p(6)A ee is estimated from the low-temperature measurement [21]andB ep is usually estimated from the thermal or electrical resistivity near the room temperature [14].In this work,A ee is taken as the lit-erature value 1.2Â107s À1K À2[6]while e 1and B ep are evaluated by ﬁtting the room-temperature value of the complex dielectric con-stant at 800nm wavelength provided in Ref.[22],which are found to be 9.7and 3.6Â1011s À1K À1,respectively.The complex index of refraction n 0þin 00is the square root of the dielectric ing Eqs.(5)and (6),n 0and n 00are evaluated as 0.16and 4.90,respectively,which agree with the empirical values [23].The re-ﬂectance is then calculated from n 0and n 00by the method of transfer matrix [24],which considers multiple reﬂections in thin ﬁlms.4Results and DiscussionThe results of TTR measurements with a pump ﬂuence of 147J/m 2are plotted in Fig.2.The fast decrease of the reﬂectance indicates that energy transfer between electrons and phonons in metal,followed by a relatively slow decrease after several ps which indicates electrons and phonons have reached thermal equi-librium.The initial cooling rates are smaller for samples with thicknesses less than the electron ballistic length since the electron temperature is almost uniform across the thin ﬁlm,and coupling with phonons within the metal ﬁlm and the dielectric substrate is the only cooling mechanism.For a thicker sample of thickness 250nm,the initial decrease is much faster due to thermal diffu-sion in the gold ﬁlm caused by a gradient of the electron tempera-ture in the ﬁlm.We investigate the effect of R es and R ps using the thermo-reﬂectance signal.Two values of R ps ,1Â10À10m 2K/W and 1Â10À7m 2K/W,are used,each with a parameterized range of values for R es .Figure 3shows the calculated results for the sample with a 39nm-thick gold ﬁlm.Little difference can be seen between Figs.3(a )and 3(b )while different cooling rates are obtained with varying R es in either plot,indicating that the cooling rate is not sensitive to the coupling strength between phonons in metal and dielectric.Note that an interface resistance of 1Â10À10m 2K/W is lower than any reported value,indicating a very high coupling strength between the phonons in metal and dielectric.Conversely,the results vary greatly with the coupling strength between electrons in metal and phonons in dielectric at the interface.This is because the lattice (phonon)temperature rise in metal is much smaller than the elec-tron temperature that the interface coupling between phonons in metal and dielectric does not inﬂuence the surface temperature,which directly determines the measured reﬂectance.On the other hand,the temperature rise of electrons is much higher,and conse-quently,the cooling rate is sensitive to R es .The relatively high sensitivity of R es to that of R ps demonstrates that the former can be isolated for the study of the coupling between electrons in metal and phonons in dielectric.We now use the measured TTR data to estimate R es ,the thermal resistance between electrons in metal and phonons in dielectric.R es is adjusted by the least square method to ﬁt the simulation results with the measured data,and the results are shown in Fig.4.We note that it is impossible to ﬁt the measured results using insu-lation interface condition (i.e.,no coupling or extremely large thermal resistance between electrons in metal and phonons in the dielectric substrate),which will signiﬁcantly underestimate the cooling rate.For thin samples,we ﬁnd that the value of R es is of the order of 10À10to 10À9m 2K/W.This value is below the ther-mal resistances of representative solid–solid interfaces measured in thermal equilibrium [25].This indicates that the direct coupling between electrons in metal and phonons in dielectric is strong.It is also noted that the resistance values increases with the thickness of the gold ﬁlm,indicating a decrease in the coupling strength between electrons in metal and the dielectric substrate.This could be due to the lower electron temperature obtained in thicker ﬁlms,and a decrease of the coupling strength with a decrease in the electron temperature [5].For the sample of thickness 250nm,R es has little effect on the simulation result since the interface is too far from the absorbing surface to inﬂuence the surface tempera-ture,and therefore it is not presented here.The agreement between the ﬁtted results and the measured data is generally good.The small discrepancy between the measured and the ﬁtted results can result from inaccuracy in computingtheFig.2TTR measurement results on Au–Si samples of varying AuthicknessesFig.3Simulation results with varying R es for the Au–Si sample of Au thickness 39nm.(a )R ps 51310210m 2K/W;(b )R ps 5131027m 2K/W.absorption or the temperature.Figure 1(b)shows the normalized TTR measurement results on the sample of thickness 77nm with three laser ﬂuences.It is seen that small variations in the shape of the TTR signals can be caused by different laser ﬂuences and thus the maximum temperature reached in the ﬁlm.Absorption in metal,multiple reﬂections between the metal surface and the Au–Si inter-face,and possible deviations of the properties of thin ﬁlms from those of bulk can all contribute to uncertainties in the temperature simulation;therefore affecting the calculated reﬂectance.With the values of R es shown in Fig.4,the calculation shows that the highest electron temperature,which is at the surface of 39nm–thick gold ﬁlm,is about 6700K.The highest temperature of electrons is roughly inversely proportional to the thickness of the ﬁlms for the four thinner ﬁlms.The highest temperature of elec-trons is much less than the Fermi temperature and thus ensures the validity of the linear dependence of C e on T e [14].The highest temperature for the lattice in metal is about 780K,also in the 39nm-thick gold ﬁlm.This large temperature difference between electrons and lattice indicates that the interface heat transfer is dominated by the coupling between electrons in metal and the phonons in the dielectric substrate.As shown in Fig.4,the meas-ured R es is very low,of the order of 10À10to 10À9m 2K/W.Even if R ps ,which is not determined in this study,is also that low (note that 10À10to 10À9m 2K/W is lower than any reported values),because of the large difference in temperatures between electrons and the phonons in metal,the interface heat transfer rate (Eqs.(3a )–(3c ))due to the coupling between electrons in metal and the substrate is much larger than that due to the coupling between phonons in metal and the substrate.5ConclusionsIn conclusion,TTR measurements using femtosecond laser pulses are performed on Au–Si samples and the results are analyzed using the TTM model.It is shown that due to the strong nonequilibrium between electrons and phonons during ultrafast-laser heating,it is possible to isolate the effect of the direct electron–phonon coupling across the interface,allowing investiga-tion of its ing stretched femtosecond pulses is shown to be able to minimize the nonequilibrium effect among electrons,and is thus more suitable for this study.The TTR measurement data can be well-represented using the TTM parison between the TTR data and the TTM results indicates that the direct coupling due to electron-interface scattering dominates the interface heat transfer during ultrafast-laser heating of thin ﬁlms.AcknowledgmentThis paper is based upon work supported by the Defense Advanced Research Projects Agency and SPAWAR Systems Cen-ter,Paciﬁc under Contract No.N66001-09-C-2013.The authors also thank C.Liebig,Y.Wang,and W.Wu for helpful discussions.NomenclatureA ee ¼coefﬁcient in Eq.(6),s À1K À2B ep ¼coefﬁcient in Eq.(6),s À1K À1C ¼volumetric heat capacity,J/(m 3K)G ¼electron–phonon coupling factor,W/(m 3K)i ¼unit of the imaginary number J ¼ﬂuence of the pump,J/m 2k ¼thermal conductivity,W/(mK)L ¼metal ﬁlm thickness,mn 0¼real part of the complex index of refractionn 00¼imaginary part of the complex index of refraction R ¼interface thermal resistance,m 2K/W;reﬂectance S ¼laser source term,W/m3Fig.4Comparison between the measurement and the simulation results for Au–Si samples of different Au thicknesses.The open circle represents the meas-ured data and the solid line represents the simulation results.(a )39nm ﬁtted by R es 55310210m 2K/W;(b )46nm ﬁtted by R es 56310210m 2K/W;(c )60nm ﬁtted by R es 51.231029m 2K/W;and (d )77nm ﬁtted by R es 51.831029m 2K/W.T¼temperature,Kt¼time,st p¼pulse width of the pump(FWHM),sx¼spatial coordinate,me¼complex dielectric constante1¼constant in the Drude modeld¼radiation penetration depth,md b¼electron ballistic depth,mx¼angular frequency of the probe,rad/sx p¼plasma frequency,rad/sx s¼electron collisional frequency,rad/sSubscripts0¼initial statee¼electron in metales¼electron in metal and phonon in dielectricp¼phonon in metalps¼phonon in metal and phonon in dielectrics¼phonon in dielectricReferences[1]Cahill,D.G.,Ford,W.K.,Goodson,K.E.,Mahan,G.D.,Majumdar,A.,Maris,H.J.,Merlin,R.,and Phillpot,S.R.,2003,“Nanoscale Thermal Trans-port,”J.Appl.Phys.,93(2),pp.793–818.[2]Majumdar,A.,and Reddy,P.,2004,“Role of Electron–Phonon Coupling inThermal Conductance of Metal–Nonmetal Interfaces,”Appl.Phys.Lett., 84(23),pp.4768–4770.[3]Chien,H.-C.,Yao,D.-J.,and Hsu,C.-T.,2008,“Measurement and Evaluationof the Interfacial Thermal Resistance Between a Metal and a Dielectric,”Appl.Phys.Lett.,93(23),p.231910.[4]Hopkins,P.E.,and Norris,P.M.,2007,“Substrate Inﬂuence in Electron–Phonon Coupling Measurements in Thin Au Films,”Appl.Surf.Sci.,253(15), pp.6289–6294.[5]Hopkins,P.E.,Kassebaum,J.L.,and Norris,P.M.,2009,“Effects of ElectronScattering at Metal–Nonmetal Interfaces on Electron-Phonon Equilibration in Gold Films,”J.Appl.Phys.,105(2),p.023710.[6]Hopkins,P.E.,2010,“Inﬂuence of Electron-Boundary Scattering on Thermore-ﬂectance Calculations After Intraband and Interband Transitions Induced by Short-Pulsed Laser Absorption,”Phys.Rev.B,81(3),p.035413.[7]Sun,C.-K.,Vallee,F.,Acioli,L.,Ippen,E.P.,and Fujimoto,J.G.,1993,“Femtosecond Investigation of Electron Thermalization in Gold,”Phys.Rev.B, 48(16),pp.12365–12368.[8]Fann,W.S.,Storz,R.,Tom,H.W.K.,and Bokor,J.,1992,“Electron Thermal-ization of Gold,”Phys.Rev.B,46(20),pp.13592–13595.[9]Fann,W.S.,Storz,R.,Tom,H.W.K.,and Bokor,J.,1992,“Direct Measure-ment of Nonequilibrium Electron-Energy Distributions in Subpicosecond Laser-Heated Gold Films,”Phys.Rev.Lett.,68(18),pp.2834–2837.[10]Kaganov,M.I.,Lifshitz,I.M.,and Tanatarov,L.V.,1957,“RelaxationBetween Electrons and the Crystalline Lattice,”Sov.Phys.JETP,4(2),pp.173–178.[11]Anisimov.S.I.,Kapeliovich,B.L.,and Perel’man,T.L.,1974,“ElectronEmission From Metal Surfaces Exposed to Ultrashort Laser Pulses,”Sov.Phys.JETP,39(2),pp.375–377.[12]Qiu,T.Q.,and Tien,C.L.,1993,“Heat Transfer Mechanisms During Short-Pulse Laser Heating of Metals,”ASME Trans.J.Heat Transfer,115(4),pp.835–841.[13]Chowdhury,I.H.,and Xu,X.,2003,“Heat Transfer in Femtosecond LaserProcessing of Metal,”Numer.Heat Transfer,Part A,44(3),pp.219–232. [14]Kittel,C.,1976,Introduction to Solid State Physics,John Wiley&Sons,Inc.,New York.[15]Smith,A.N.,and Norris,P.M.,2001,“Inﬂuence of Intraband Transitions onthe Electron Thermoreﬂectance Response of Metals,”Appl.Phys.Lett.,78(9), pp.1240–1242.[16]Chen,J.K.,Latham,W.P.,and Beraun,J.E.,2005,“The Role of Electron–Phonon Coupling in Ultrafast Laser Heating,”ser Appl.,17(1),pp.63–68.[17]Hostetler,J.L.,Smith,A.N.,Czajkowsky,D.M.,and Norris,P.M.,1999,“Measurement of the Electron-Phonon Coupling Factor Dependence on Film Thickness and Grain Size in Au,Cr,and Al,”Applied Optics,38(16),pp.3614–3620.[18]Hohlfeld,J.,Wellershoff,S.-S.,Gudde,J.,Conrad,U.,Jahnke,V.,and Mat-thias,E.,2000,“Electron and Lattice Dynamics Following Optical Excitation of Metals,”Chem.Phys.,251(1–3),pp.237–258.[19]Maier,S.A.,2007,Plasmonics:Fundamentals and Applications,SpringerScienceþBusiness Media,New York.[20]Ashcroft,N.W.,and Mermin,N.D.,(1976),Solid State Physics,W.B.Saun-ders,Philadelphia.[21]MacDonald,A.H.,1980,“Electron-Phonon Enhancement of Electron-ElectronScattering in Al,”Phys.Rev.Lett.,44(7),pp.489–493.[22]Johnson,P.B.,and Christy,R.W.,1972,“Optical Constants of the Noble Met-als,”Phys.Rev.B,6(12),pp.4370–4379.[23]Palik,E.D.,(1998),Handbook of Optical Constants of Solids,Academic,SanDiego.[24]Pedrotti,F.L.,Pedrotti,L.S.,and Pedrotti,L.M.,(2007),Introduction toOptics,Pearson Prentice Hall,Upper Saddle River,NJ.[25]Incropera,F.P.,Dewitt,D.P.,Bergman,T.L.,and Lavine,A.S.,2007,Funda-mentals of Heat and Mass Transfer,John Wiley&Sons,Inc.,Hoboken,NJ.。

摩擦纳米发电激发光动力学

摩擦纳米发电激发光动力学英文回答：Frictional nanogenerators (FNGs) are devices that can convert mechanical energy into electrical energy throughthe process of triboelectric effect. This technology has gained significant attention in recent years due to its potential applications in self-powered systems and wearable electronics. In this article, I will discuss the exciting field of optokinetics, which involves the use of FNGs to generate light.Optokinetics is the study of light-induced motion andits interaction with matter. It explores the principles of photophysics and photochemistry to understand how light can be used to control the movement of objects at the nanoscale. FNGs play a crucial role in optokinetics by providing the necessary electrical energy to drive light-emitting devices.The process of optokinetics begins with the generationof electrical energy through the triboelectric effect in FNGs. When two different materials come into contact and then separate, a charge imbalance is created on their surfaces. This charge imbalance can be harnessed togenerate an electric current. By integrating FNGs withlight-emitting devices, such as light-emitting diodes (LEDs), the electrical energy can be converted into light energy.One example of optokinetics in action is the development of self-powered nanoscale light sources.Imagine a scenario where you are in a dark room and need to find your way to the bathroom without turning on the lights. With optokinetics, you can wear a bracelet equipped with FNGs that generate electricity as you move your arm. This electrical energy can then be used to power tiny LEDs embedded in the bracelet, creating a small but sufficient amount of light to guide you in the dark.Another application of optokinetics is in the field of wearable electronics. For instance, researchers have developed smart clothing that can generate light patternsin response to specific gestures or movements. By incorporating FNGs into the fabric of the clothing, the mechanical energy produced during body movements can be converted into electrical energy, which in turn powers the light-emitting components. This technology has the potential to revolutionize fashion and entertainment industries by enabling interactive and visually appealing garments.In addition to self-powered light sources and wearable electronics, optokinetics can also be applied in other areas such as biomedical devices and environmental monitoring. For example, FNGs integrated with biosensors can generate light signals in response to specific biological markers, enabling real-time monitoring of disease progression or drug efficacy. Similarly, optokinetic sensors can be used to detect environmental pollutants by converting mechanical energy from air or water flow into light signals.中文回答：摩擦纳米发电器（FNG）是一种通过摩擦电效应将机械能转化为电能的设备。

巨磁电阻效应的英语

巨磁电阻效应的英语Giant magnetoresistance effect, huh? That's a mouthful! But let's break it down. Basically, it's this crazy phenomenon where the resistance of certain materials changes significantly when a magnetic field is applied.It's like they're super sensitive to magnets.Now, imagine this: you've got a material and you give it a little magnetic push. Suddenly, its resistance to electricity goes up or down by a huge amount. That's what we call giant magnetoresistance. And it's not just anylittle change; it's huge!One of the coolest things about this effect is how it's being used in tech. You know, like in those tiny sensors that can detect magnetic fields with incredible precision? They rely on this effect to work. It's like having a superpower to sense magnetic fields.And speaking of superpowers, imagine if we couldharness this effect for even more amazing things. Like, controlling robots with just our thoughts or something crazy like that. The possibilities are endless, really.So, in a nutshell, giant magnetoresistance is this fascinating effect where materials change their resistance a lot when you apply a magnetic field. It's not just a science experiment; it's shaping the future of technology in ways we can only imagine.。

水化热抑制剂对水泥-粉煤灰胶凝材料水化和混凝土性能的影响

第49卷第8期2021年8月硅酸盐学报Vol. 49，No. 8August，2021 JOURNAL OF THE CHINESE CERAMIC SOCIETY DOI：10.14062/j.issn.0454-5648.20200724 水化热抑制剂对水泥-粉煤灰胶凝材料水化和混凝土性能的影响陈炜一1，周予启1,2，李嵩2，阎培渝1(1. 清华大学土木工程系，北京 100084；2. 中建一局集团建设发展有限公司，北京 100102)摘要：探究了水化热抑制剂(TRI)对水泥-粉煤灰胶凝材料水化过程和混凝土性能的影响。

通过改变粉煤灰在胶凝材料中的占比和水化热抑制剂的掺量，观察了胶凝材料的水化过程以及混凝土的绝热温升、力学性能和干燥收缩特性。

胶凝材料的水化热测试结果表明，在含有粉煤灰的胶凝材料中，水化热抑制剂降低胶凝材料的放热速率峰值、延后放热峰出现时间的作用更加明显。

硬化浆体的相组成和微观结构测试表明，水化热抑制剂对胶凝材料水化程度的抑制主要发生在7d前。

混凝土试验结果表明，水化热抑制剂会放缓混凝土的绝热温升速率，降低粉煤灰混凝土的早期强度并增加干燥收缩。

关键词：水化热抑制剂；粉煤灰；胶凝材料；混凝土；水化；强度中图分类号：TU528.45 文献标志码：A 文章编号：0454–5648(2021)08–1609–10网络出版时间：2021–06–18Impact of Temperature Rising Inhibitor on Hydration of Cement-Fly Ash CementitiousMaterials and Performance of ConcreteCHEN Weiyi1, ZHOU Yuqi1,2, LI Song2, YAN Peiyu1(1. Department of Civil Engineering, Tsinghua University, Beijing 100084, China;2. China Construction First Division Group Construction & Development Co. Ltd, Beijing 100102, China) Abstract: Effect of temperature rising inhibitor (TRI) on the hydration process of cementitious materials containing fly ash and the performance of concrete was investigated. The hydration process of cementitious materials was examined as a function of the contents of fly ash and TRI. The adiabatic temperature rise, mechanical properties and drying shrinkage of concrete derived from the cementitious materials and TRI were also evaluated. According to the hydration heat of the binder pastes, it was revealed that the addition of TRI lowers and delays the exothermic peaks more significantly in the presence of fly ash. The phase composition and microstructure of the hardened paste indicate that TRI mainly inhibits the hydration degree of the cementitious materials in the first 7 days. The presence of TRI slows down the adiabatic temperature rising rate, reduces the early strength of the concrete and increases drying shrinkage of the concrete.Keywords: temperature rising inhibitor; fly ash; cementitious materials; concrete; hydration; strength温度裂缝是混凝土结构中最常出现的裂缝类型。

温度对半导体影响的书

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

摩擦纳米发电激发光动力学

摩擦纳米发电激发光动力学英文回答：Frictional nanogenerators (FNGs) are devices that can convert mechanical energy into electrical energy through the process of triboelectric effect. They work by utilizing the frictional forces between two different materials to generate a charge imbalance, which can then be harvested as electricity. FNGs have gained significant attention in recent years due to their potential applications in self-powered systems and wearable electronics.The study of the photodynamics of FNGs involves investigating the light emission properties that occur during the frictional process. When two materials rub against each other, they generate not only electrical energy but also light emissions. These light emissions can provide valuable information about the underlying mechanisms of FNGs and can be used to optimize their performance.One example of the photodynamics of FNGs is the generation of triboluminescence. Triboluminescence refers to the emission of light when certain materials are subjected to frictional forces. This phenomenon has been observed in various materials, such as sugar crystals, quartz, and certain types of plastics. When these materials are rubbed or crushed, they emit a brief burst of light. The exact mechanism behind triboluminescence is not yet fully understood, but it is believed to involve the breaking of chemical bonds, the release of stored energy, and the recombination of charged particles.Understanding the photodynamics of FNGs can have practical implications in the development of more efficient and reliable nanogenerators. By studying the light emissions during the frictional process, researchers can gain insights into the energy conversion mechanisms and identify ways to enhance the overall performance of FNGs. For example, by optimizing the materials used in FNGs, it may be possible to increase the intensity or duration of the light emissions, leading to higher energy output.中文回答：摩擦纳米发电激发光动力学是研究摩擦过程中发生的光发射特性的学科。

Nb-Ti低合金高强钢第二相析出及其对力学性能的影响

第40卷　第6期　上　海　金　属　Vol.40,No.612　2018年11月　SHANGHAI METALS November ,2018作者简介:张志建,男,博士,高级工程师,主要研究方向为汽车钢板开发及应用技术,E⁃mail:zhangzj⁃iris @Nb⁃Ti 低合金高强钢第二相析出及其对力学性能的影响张志建　陈　刚　刘志桥　李化龙(江苏省(沙钢)钢铁研究院,江苏张家港　215625) 【摘要】　采用光学显微镜㊁扫描电镜㊁透射电镜和拉伸试验机研究了Nb 含量和热轧加热温度对Nb⁃Ti 复合添加的低合金高强钢(HSLA )第二相析出行为,以及第二相析出对热轧及冷轧退火后钢板的显微组织和力学性能的影响㊂结果表明,在高的热轧加热温度下,含Nb 碳氮化物可以充分溶解并优先在富Ti 的(Ti ,Nb )(C ,N )粗大粒子上异质析出,阻止晶粒的长大;热轧后的第二相粒子特征可遗传到冷轧退火过程,对晶粒尺寸和第二相分布有重要影响㊂此外,0.053%Nb 钢在1250℃的加热温度下,热轧和冷轧退火钢板中有较多的粗大及细小析出相;每添加0.01%Nb 产生的热轧析出强化增量约为40MPa ,冷轧退火后的强度增量约为30MPa ㊂【关键词】　低合金高强钢　第二相析出　Nb⁃Ti 复合添加　退火Second Phase Precipitation and Its Effect on the MechanicalProperties of Nb⁃Ti Microalloyed HSLA SteelsZhang Zhijian　Chen Gang　Liu Zhiqiao　Li Hualong(Institute of Research of Iron and Steel ,Shasteel ,Zhangjiagang Jiangsu 215625,China ) 【Abstract 】　Effect of niobium contents and reheating temperatures on the second phase precipitation behavior of Nb⁃Ti microalloyed high strength low alloy (HSLA )steels was studied by optical ,scanning electron and transmission electron microscope ,and tensile tester ,and the effect of second phase precipitates on the microstructure and mechanical properties of HSLA steels during hot rolling and annealing process was also studied.The results showed that under high reheating temperature ,the Nb⁃containing carbonitrides could be fully dissolved and preferentially heterogeneous precipitated on large particles Ti (Ti ,Nb )(C ,N ),thus preventing the growth of grains during hotrolling.The characteristics of the second phase precipitates formed in hot rolling could be inherited to the cold rolling and annealing process ,which had an important effect on the grain size and the distribution of second phase precipitates.In addition ,the 0.053%Nb steel could obtain more coarse and fine precipitates in both hot⁃rolled and annealed steel plates at the reheating temperature of 1250℃.An addition of 0.01%Nb increased the tensile strength by about 40MPa after hot rolling and byabout 30MPa after annealing through precipitation hardening.【Key Words 】　high strength low alloy steel (HSLA ),second phase precipitation ,Nb⁃Ticomposite addition ,annealing 汽车工业安全减重的需求,促进了冷轧低合金高强钢(high strength low alloy steel,HSLA)的发展㊂HSLA 钢是在低碳的基础上,通过添加微量铌㊁钒㊁钛等合金元素,以通过细晶强化㊁析出强第6期　张志建等:Nb⁃Ti低合金高强钢第二相析出及其对力学性能的影响13化和固溶强化等机制,显著提高强度,并保持良好的成形性能㊂添加的微量合金在热轧及随后的冷轧退火过程中溶解和析出,形成的碳化物或碳氮化物等第二相粒子对微观组织有强烈的影响,从而决定了钢板的力学性能㊂微合金元素在控制轧制中的作用已有大量研究[1⁃3],如板坯加热时粗大析出物可阻止奥氏体晶粒长大,在随后轧制过程应变诱导析出的细小第二相粒子延迟再结晶形核,从而在卷取后得到细小的铁素体和珠光体组织㊂对于复合添加Nb㊁Ti的HSLA钢,少量Ti元素对抑制奥氏体晶粒的长大和提高再结晶温度有显著的影响[3],在热轧过程中析出的第二相粒子形态及分布也会影响后续的冷轧退火过程㊂因此,本文主要研究了不同成分HSLA钢在热轧及冷轧过程中第二相粒子的析出行为及其对显微组织㊁力学性能的影响,以期为冷轧HSLA钢的开发提供指导㊂1　试验材料与方法试验用HSLA钢复合添加Nb和Ti两种微合金元素,具体化学成分如表1所示,其中B钢的Nb含量较A钢略高㊂试验钢在工业生产线上浇铸成坯,然后采用控轧控冷(TMCP)工艺将板坯重新加热后再热轧至3.5mm厚,最后卷取,具体热轧工艺如表2所示,其中采用了两种加热温度(1200和1250℃)以研究Nb含量对第二相析出的影响㊂热轧钢板酸洗后在5机架轧机上冷轧至1.2mm厚,总压下量为65.7%㊂再将冷轧后的薄板加工成450mm×140mm方形试样,在多炉室带钢连续退火试验机上模拟带钢的连续退火过程㊂图1为连续退火过程温度控制曲线图,该曲线根据连续退火生产线退火炉的各段长度制定㊂为了研究连续退火温度对力学性能的影响,选择在730~850℃多个温度进行均热退火,退火时间为96s㊂退火在氮气保护下进行,钢板上的热电偶测量温度与设定温度的偏差小于5℃㊂退火后的钢板在Instron5585拉伸试验机上进行力学性　表1　试验钢的化学成分(质量分数)Table1　Chemical composition of theexperimental steels(mass fraction)%钢号C Si Mn Nb Ti P S A0.070.010.820.0330.014≤0.02≤0.01 B0.070.021.160.0530.014≤0.02≤0.01　表2　试验钢的热轧工艺参数Table2　Hot rolling parameters of theexperimental steels钢号成分加热温度/℃终轧温度/℃卷取温度/℃A1A1200870600B1B1200870600B2B1250870600 注:①预热,②加热,③均热退火,④缓冷,⑤快冷,⑥过时效,⑦终冷图1　连续退火过程温度控制曲线Fig.1　Temperature control curve of continuousannealing process能测试㊂采用光学显微镜㊁扫描电镜观察试样的显微组织,并采用透射电镜分析第二相的析出㊂2　试验结果与分析2.1　成分及热轧加热温度对组织及性能的影响图2为不同Nb含量和加热温度均热后轧制的试验钢的显微组织,可见3种试验钢的组织均为多边形铁素体和珠光体㊂A1㊁B1钢的热轧工艺相同,但随着Nb的质量分数从0.033%增加到0.053%,B1钢的晶粒尺寸减小(见图2a,2b);B1和B2钢的Nb含量相同,但当热轧加热温度从1200℃升高到1250℃后,B2钢的晶粒尺寸明显减小(见图2c)㊂通过截线法测量晶粒尺寸,获得A1㊁B1和B2钢的平均晶粒尺寸分别为5.95㊁5.11和3.53μm㊂表3列出了3种试验钢的力学性能,可见Nb 含量的增加和热轧加热温度的升高均显著提高了试验钢的强度,同时降低了断后伸长率㊂根据修正的Hall⁃Petch公式,热轧钢板的屈服强度由以下几种强化方式贡献:σy=σ0+σss+σppt+k y d-1/2(1)14 上　海　金　属　第40卷图2　不同Nb含量和加热温度热轧的试验钢的显微组织Fig.2　Microstructures of the tested steels of different Nb contents hot⁃rolled at different temperatures　表3　不同Nb含量和加热温度均热后轧制的试验钢的力学性能Table3　Mechanical properties of the tested steels of different Nb contents hot⁃rolled at different heatingtemperatures钢号屈服强度/MPa抗拉强度/MPa断后伸长率/%A138147139B148955334B252858629式中:σ0为晶格摩擦力;σss为固溶强化增量;σppt 为析出强化增量;k y d-1/2是晶粒细化增量;k y为晶界强化因子,碳锰钢为17.4MPa㊃mm1/2[4];d是晶粒直径㊂通过式(1)可以估算试验钢的强度增量㊂由于3种试验钢的热轧态组织基本相同,可认为晶格摩擦力相同㊂在固溶强化方面,相较于A钢,B 钢中Mn的质量分数增加了0.34%,按每添加0.1%Mn(质量分数,下同),强度增加3.7MPa计算[4],B钢的强度增量约13MPa;A1㊁B1和B2钢的晶粒强化增量分别为225㊁243和292MPa,据此可估算出相较于A1钢,B1钢的析出强化增量约77MPa,B2钢约85MPa㊂从以上结果可以看出,Nb的析出强化效果显著,每添加0.01%Nb,强度增加约40MPa;提高热轧加热温度,试验钢的析出强化增量并不明显,其强度的贡献主要来自于细晶强化,增量约49MPa㊂2.2　退火温度对冷轧组织及性能的影响对冷轧后的A1和B1钢在730~850℃进行连续退火试验㊂Chen等[5]采用接近A1钢成分的0.055C⁃1.32Mn⁃0.02Ti⁃0.032Nb钢,研究得出其在冷轧压下量为75%时670℃左右退火9min完成再结晶㊂图3为A1钢在730~830℃退火后的显微组织,可以看出,在所选择的4种退火温度下,再结晶过程都已经完成,组织为多边形铁素体和珠光体㊂随着退火温度的升高,晶粒逐渐长大㊂图4为A1钢在730~830℃退火后的晶粒尺寸,可见,低温退火时晶粒长大缓慢;780℃以上退火时,晶粒长大速度增快;约810℃及以上温度退火时,晶粒长大速度再次趋缓㊂在试验退火温度区间,A1钢的平均晶粒尺寸从730℃的4.36μm逐渐增加到850℃的7.15μm㊂图5为A1和B1钢在730~830℃退火后的力学性能变化,可见,随着退火温度的升高,试验钢的强度逐渐降低,断后伸长率逐渐增加㊂其中A1钢的强度在780℃以上时下降较快,810℃以上时下降速度减缓;当退火温度从730℃升高到850℃时,A1钢的强度约降低53MPa㊂根据式(1)计算得出,由晶粒长大而导致强度下降了约58MPa㊂由此可推算,晶粒长大是试验钢强度降低的主要原因㊂与A1钢不同,B1钢在730℃左右退火时强度就开始明显下降,790℃以上时下降速度减缓㊂观察显微组织发现,B1钢经730℃退火后还存在少量的纤维状组织[6],铁素体也未完成多边化,这可能与B1钢中Nb㊁Mn含量较高,推迟了再结晶完成有关㊂此外,在780℃左右退火时,A1钢与B1钢的屈服强度差值约36MPa,而试验测得在该温度退火的两种钢的晶粒尺寸基本相同,因此判定强度的变化主要是由第二相析出引起的㊂2.3　第二相析出及其对力学性能的影响2.3.1　热轧过程中第二相析出及其对力学性能的影响采用碳膜复型萃取制备试样,在透射电镜下观察热轧和冷轧退火后试验钢中第二相的析出㊂第6期　张志建等:Nb⁃Ti低合金高强钢第二相析出及其对力学性能的影响15图3　A1钢在不同温度退火后的显微组织Fig.3　Microstructures of A1steels after annealing at different temperatures图4　A1钢在不同温度退火后的晶粒尺寸Fig.4　Grain size of A1steels after annealing atdifferent temperatures图6是热轧试验钢中第二相粒子分布的TEM照片,可见试验钢的晶界均较规则,有正方体形的粗大颗粒析出,尺寸约80~150nm㊂A1钢中的大颗粒均为规则正方体(见图6a,6d);B1钢中大颗粒除少量仍为正方体外,大多数出现了球化趋势(见图6b,6e);B2钢中大颗粒多数仍为规则的正方体,但有少量大颗粒从单颗正方体向孪生体变化(见图6c,6d)㊂除粗大析出物外,试验钢的晶界及晶内还弥散分布着细小的球状第二相,尺寸主要为5~40nm,并有大量准10nm左右的第二相析出㊂对图6中箭头所指的大颗粒及典型的细图5　退火温度对A1和B1钢力学性能的影响Fig.5　Influence of annealing temperature on mechanical properties of A1and B1steels 小析出物进行能谱分析,获得的Nb㊁Ti的质量分数如表4所示㊂根据成分分析及文献[1,3],判断出形状规则的正方体颗粒应为复合析出的(Ti, Nb)(C,N)粒子,细小第二相为(Ti,Nb)C或NbC 粒子㊂低合金高强钢中的微合金元素以固溶和析出两种形式存在,第二相析出比固溶态对控制轧制过程的微观组织影响更为显著[2]㊂在板坯加热过程中,通常希望热轧前Nb元素能够在奥氏体中完全固溶,再在随后的控轧控冷过程中弥散析出㊂Ti的碳氮化物在1300℃以上开始溶解[3],在含16 上　海　金　属　第40卷图6　热轧试验钢中析出的第二相TEM 形貌Fig.6　TEM morphologies of second phases precipitated in the hot⁃rolled test steels　表4　热轧试验钢中析出的第二相化学成分(质量分数)Table 4　Chemical compositions of second phasesprecipitated in the hot⁃rolled teststeels (mass fraction )%第二相析出形貌及位置Ti Nb 图6(a)中粗大规则正方体70.7229.28图6(b)中粗大规则正方体41.7558.25图6(c)中粗大规则正方体63.1236.88图6(a)中细小圆球体0.00100.00图6(b)中细小圆球体3.7096.30图6(c)中细小圆球体3.4296.58图6(d)中规则正方体内部69.8630.14图6(e)中偏圆正方体内部65.7634.24图6(e)中偏圆正方体外缘5.3794.63图6(f)中孪生正方体内部69.0031.00图6(f)中孪生帽状体内部18.1081.90Nb 的HSLA 钢中添加Ti,可以在板坯加热过程形成稳定的富Ti 的(Ti,Nb)(C,N)氮化物或碳氮化物,从而有效地阻止晶粒长大;在随后的轧制变形过程,这些富Ti 第二相可以成为NbC 等粒子的优先形核位置㊂因此,Nb 的碳化物或碳氮化物在加热过程中的溶解程度对热轧过程Nb 作用的发挥有重要影响㊂目前,已有很多学者研究了Nb 的碳化物在奥氏体中的平衡溶解度计算公式,其中最为典型的为[7]:lg[Nb]㊃[C]=2.26-6770T ()K(2)式中:[Nb]㊁[C]分别为铌和碳的质量分数;T K 为加热温度,K㊂根据式(2)计算得出,0.033%Nb 和0.053%Nb 钢的平衡溶解度分别为1155和1220℃㊂据此分析,在1200℃加热时,0.033%Nb 钢中Nb 的碳化物可以充分溶解,而0.055%Nb 钢中Nb 的碳化物只有在1220℃以上才能充分溶解㊂表4的结果显示,图6中形状规则的粗大(Ti,Nb)(C,N)粒子均为富Ti 成分,A 1钢中Ti的相对质量分数达到70%左右;随着Nb 含量的升高,B 1钢中Ti 的相对质量分数降低到42%左右,这应该与加热温度不足㊁Nb 的溶解不完全有关;加热温度升高到1250℃后,B 2钢中Ti 的相对质量分数回升到63%左右,说明Nb 的溶解度有进一步提升㊂对粗大第二相的进一步观察发现,A 1钢中的第6期　张志建等:Nb⁃Ti低合金高强钢第二相析出及其对力学性能的影响17第二相均为规则的正方体,B1钢中的部分第二相出现了球化趋势,而B2钢中第二相的形貌除正方体外还有帽状㊂对析出物进行成分分析发现,B1钢的正方体外缘和B2钢孪生的帽状体均为富Nb 成分㊂Hong等[3]通过高分辨电镜在0.08C⁃0.043Nb⁃0.016Ti钢中也观察到了类似形状的析出物,并确定其为富Nb的(Nb,Ti)C碳化物,该碳化物在未完全溶解的富Ti的(Ti,Nb)(C,N)基体上优先形核,并与(Ti,Nb)(C,N)异质共格析出㊂综上可见,A1钢在1200℃加热时可保证Nb 充分溶解,但由于其Nb含量低于B1钢,因此B1钢的晶粒细化及第二相析出强化增量高于A1钢㊂在B1㊁B2钢中还观察到了Nb在未溶解第二相上的优先析出,但由于B1钢中粗大第二相大多呈球状,Nb的消耗较多,从而降低了Nb的固溶量,减少了细小NbC/(Nb,Ti)C在奥氏体晶内的析出㊂此外,由于B2钢的加热温度高,部分Ti的碳氮化物也开始溶解,在轧制过程析出的粗大第二相粒子较多,对晶粒细化的作用更为明显㊂因此,B2钢的晶粒细化和第二相析出对强度的贡献要大于B1钢㊂2.3.2　冷轧退火过程中第二相析出及其对力学性能的影响图7为3种试验钢冷轧后在780℃退火过程中析出的第二相,可见,析出物大致可分成为粗大析出和弥散析出两种类型㊂对于弥散细小的析出物,退火后其尺寸明显增加,呈球状在晶界及晶内弥散析出,尺寸以准10~50nm为主,分布不均匀;在透射电镜下仍可观察到10nm左右的第二相粒子,但更细小的析出物已难以区别;随着Nb 含量的增加及热轧加热温度的提高,细小析出物的数量整体呈增加趋势㊂相比较,粗大析出物的分布较均匀,尺寸为80~150nm,其形貌不同于热轧态的,均以球状为主,但B2钢中仍存在少量孪生帽状析出物(见图7f)㊂对第二相粒子进行能谱分析,得出细小析出物为富Nb的(Nb,Ti)C,在粗大正方体基体上生长或孪生状生长的也是富Nb的(Nb,Ti)C㊂图7　试验钢冷轧后在780℃退火过程中析出的第二相的TEM形貌Fig.7　TEM morphologies of the second phases precipitated in test steels after cold⁃rolling andthen annealing at780℃ 冷轧退火后的第二相粒子分布保留了热轧态的一些特征,这在粗大粒子的形态分布上更为明18 上　海　金　属　第40卷显㊂粗大析出物由于异性成核的界面能较低,退火时重新固溶析出的富Nb的(Nb,Ti)C碳化物优先在富Ti的(Ti,Nb)(C,N)核心上成长,因此A1㊁B1钢退火后的粗大第二相基本呈球状㊂而B2钢中粗大球状析出的数量虽增多,但少数仍为正方体或帽状㊂钢板冷轧后存储了大量的变形能,位错密度高㊂热轧析出的细小第二相在退火过程中逐渐粗化,将迫使位错从原来的切过或绕过机制向绕过机制转变㊂热轧初始细小第二相的数量一方面影响再结晶温度,另一方面也决定了冷轧后细小析出物的数量㊂3种试验钢在780℃退火后的力学性能见表5,相比A1钢,B1㊁B2钢的屈服强度分别提高了36和60MPa㊂由于B1钢的热轧加热温度与A1钢相同,退火过程中粗大析出物阻碍晶粒长大作用并不明显,因而其强度的贡献主要来源于细小析出物㊂B2钢热轧及退火后的晶粒尺寸均小于B1钢,且由于Nb的充分溶解,热轧过程中形成的细小析出物在退火后数量仍多于B1钢,因此,B2钢强度的贡献来源于晶粒细化和析出强化㊂　表5　试验钢在780℃退火后的力学性能Table5　Mechanical properties of the tested steels afterannealing at780℃钢号屈服强度/MPa抗拉强度/MPa断后伸长率/%A139545030B143147826B2455508233　结论(1)对于复合添加Nb⁃Ti的HSLA试验钢,热轧加热温度对钢中Nb的溶解及析出有重要影响㊂0.053%Nb钢在1250℃的加热温度下,热轧钢板中每添加0.01%Nb产生的析出强化增量约为40MPa;冷轧退火后每添加0.01%Nb产生的强度增量约为30MPa㊂(2)冷轧后的退火过程中,随着退火温度的升高,晶粒逐渐长大,导致试验钢的强度逐渐降低,断后伸长率逐渐增加㊂(3)在高的热轧加热温度下,含Nb碳氮化物可以充分溶解并优先在富Ti的(Ti,Nb)(C,N)粗大粒子上异质析出,阻止晶粒的长大;热轧第二相粒子特征遗传到冷轧后的退火过程,退火加热时重新固溶的Nb仍优先在富Ti的(Ti,Nb)(C,N)粗大粒子上异质析出,热轧初始细小第二相的数量决定了退火后细小析出物的数量㊂参考文献[1]GONG P,PALMIERE E J,RAINFORTH W M.Dissolution and precipitation behaviour in steels microalloyed with niobium during thermomechanical processing[J].Acta Materialia,2015,97: 392⁃403.[2]CITIC⁃CBMM中信微合金化技术中心.汽车用铌微合金化钢板[M].北京:冶金工业出版,2006.[3]HONG S G,KANG K B,PARK C G.Strain⁃induced precipitation of NbC in Nb and Nb⁃timicroalloyed HSLA steels [J].Scripta Materialia,2002,46(2):163⁃168. [4]曹建春,刘清友,雍岐龙,等.铌对高强度低合金钢的组织和强化机制的影响[J].钢铁,2006,41(8):60⁃63. [5]CHEN J,SHEN X J,JI F Q,et al.Effect of annealing time on microstructure and mechanical properties of cold⁃rolled niobium and titanium bearing micro⁃alloyed steel strips[J].Journal of Iron and Steel Research,2013,20(9):86⁃92.[6]刘志桥,张志建,陈刚,等.Nb含量及退火温度对冷轧低合金高强钢力学性能的影响[J].热加工工艺,2017,46(22): 225⁃227.[7]PALMIERE E J,GARCIA C I,DEARDO A positional and microstructural changes which attend reheating and grain coarsening in steels containing niobium[J].Metallurgical& Materials Transactions A,1994,25(2):277⁃286.收修改稿日期:2018⁃06⁃25。

大功率永磁同步发电机定子冷却系统优化分析

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

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

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

制备工艺对n型Bi_2Te_3基材料热电性能和抗压强度的影响

第25卷第6期无机材料学报Vol. 25No. 6 2010年6月Journal of Inorganic MaterialsJun. , 2010收稿日期: 2009-10-14, 收到修改稿日期: 2010-01-11 基金项目: 国家973计划项目(2007CB607501)作者简介: 王善禹(1984−), 男, 硕士研究生. 通讯联系人: 唐新峰, 教授. E-mail: tangxf@文章编号: 1000-324X(2010)06-0609-06 DOI: 10.3724/SP.J.1077.2010.00609制备工艺对n 型Bi 2Te 3基材料热电性能和抗压强度的影响王善禹, 谢文杰, 唐新峰(武汉理工大学材料复合新技术国家重点实验室, 武汉 430070)摘要: 以商用区熔(ZM)n 型Bi 2Te 3基材料为原料, 采用简单研磨结合放电等离子烧结技术(ZM+SPS)和熔体旋甩(MS)结合放电等离子烧结技术(MS+SPS)制备了n 型Bi 2Te 3基块体热电材料. 对三种不同工艺制备出样品的微结构、热电性能和力学性能进行了研究. FESEM 微结构表征结果表明: 区熔样品的晶粒粗大, 有较强的取向性; 经SPS 烧结后, 晶粒细化, 取向性大为降低; 而区熔样品经MS+SPS 后, 晶粒得到进一步细化, 且没有明显的取向性. 对三组样品进行的热电性能和抗压强度测试, 结果表明: 区熔原料最大ZT 值为0.72(430K), 抗压强度仅为40MPa; 经SPS 后, 样品的最大ZT 值为0.68(440K), 抗压强度为110MPa, 相比区熔样品提高了175%; MS+SPS 样品的最大ZT 值为0.96(320K), 其室温ZT 值相比区熔样品提高了64%, 抗压强度相比区熔样品提高了400%, 达到200MPa. 关键词: 碲化铋; 制备工艺; 热电性能; 抗压强度中图分类号: TB34 文献标识码: AEffects of Preparation Techniques on the Thermoelectric Properties and PressiveStrengths of n-type Bi 2Te 3 Based MaterialsWANG Shan-Yu, XIE Wen-Jie, TANG Xin-Feng(State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China)Abstract: The zone-melted n-type Bi 2Te 3 ingots were chosen as the starting material to prepare the bulk samplesby two different synthesis routes including hand grinding combined with spark plasma sintering process (ZM+SPS) and melt spinning (MS) technique combined with a subsequent spark plasma sintering process (MS+SPS). The mi-crostructures, thermoelectric properties and mechanical properties of three samples prepared by different techniques were studied. The ZM samples show rough grain size and strong grain orientations. After hand grinded and SPS process, the crystalline grains are refined and grain orientations are remarkably decreased. While the MS+SPS samples with fine grains have no distinct grain orientations. The results of thermoelectric properties and pressive strength measurement show that the maximum figure of merit ZT value reaches 0.72 at 430 K for ZM starting mate-rials and the pressive strength is only about 40MPa. The maximum figure of merit ZT value decreases to 0.68 at 440 K for the ZM+SPS samples but the pressive strength are increased to 110MPa, which is about 175% improve-ment compared with ZM samples. The maximum figure of merit ZT value and pressive strength are 0.96 at 320 K and 200MPa respectively for the MS+SPS samples, the room temperature ZT and pressive strength are about 64% and 400% improvement compared with ZM samples.Key words: bismuth tellurium; preparation technique; thermoelectric property; pressive strength热电制冷和热电发电是利用半导体材料本身的物理特性, 即Peltier 效应和Seebeck 效应来实现电和热之间相互转化的, 目前制约其实际应用的主要因素是材料的热电转换效率低. 材料的热电性能可用无量纲热电优值ZT 来表征, ZT=α2σT/κ , 其中α为Seebeck 系数, σ为电导率, κ为热导率, T 为绝对温610 无机材料学报第25卷度[1]. 好的热电材料必须具有好的电传输特性, 即高的α和σ, 同时必须具有较差的热传输特性, 即较低的κ. 但是α, σ和κ三者是相互关联的, 要提高ZT, 必须协同调控材料的电热传输特性[2].碲化铋合金(Bi2Te3)及其固溶体是室温段最好的热电材料, 属于斜方晶系, 空间群为R3m. 沿c 轴方向, Bi2Te3材料可视为六面体层状结构, 在同一层上具有相同的原子种类, 而原子间呈−Te(1)−Bi−Te(2)−Bi−Te(1)−的排布方式, 其中Te(1)−Te(1)之间则以较弱的范德华力相结合, 因此Bi2Te3晶体很容易在Te(1)原子面间发生解理[1, 3-4]. 传统区熔方法得到的材料的ZT值在1.0左右, 并且材料因为取向性较强容易发生解理, 力学性能差, 不利于机械加工和商业应用[1]. 因此探索新的制备工艺来获得热电性能和力学性能俱佳的块体Bi2Te3多晶材料显得非常重要.理论和实践都表明, 材料结构的纳米化能较大幅度地提高材料的热电性能, 一方面利用界面散射作用大幅降低晶格热导率; 另一方面可以利用量子限域效应提高费米面附近的态密度(DOS), 从而提高材料的Seebeck系数. 2008年Poudel等报道利用高能球磨结合热压烧结制备出p型BiSbTe, 其最大ZT值在100℃可达到1.4[5-7]; 同样2009年, Xie等报道利用熔体旋甩(MS)结合放电等离子烧结技术(SPS)制备出具有纳米结构的p型BiSbTe块体材料, 其最大ZT值在室温下可以达到1.56[8-10]. 2008年, Cao等利用水热合成纳米粉结合热压烧结制备出p 型(BiSb)2Te3块体材料, 其ZT值在450K左右达到1.47[11]. 近年来在Bi2Te3基材料方面取得的进展大都集中在p型材料, 而n型材料却鲜有报道, 但是热电器件需要性能良好的n型和p型材料来组成p-n 对, 因此制备出高热电性能和高机械性能的n型Bi2Te3材料尤为关键.本工作以商用区熔样品(ZM)为原料, 采用两种不同的制备工艺: 区熔样品经研磨结合放电等离子烧结技术(ZM＋SPS)和区熔样品经熔体旋甩(MS)结合放电等离子烧结技术(MS＋SPS)制备出块体n型Bi2Te3块体材料, 分别对区熔样品(ZM)、ZM＋SPS 和MS＋SPS进行了微结构分析及热电传输特性和抗压强度的测试.1实验区熔样品由上海申和热磁有限公司提供, 样品的组成为Bi2(Se0.07Te0.93)3+0.08wt%TeI4. 将区熔样品沿区熔生长方向切割, 测试其热电性能. 将区熔样品研磨过筛(~74μm), 再进行放电等离子烧结(SPS), 烧结温度和时间分别是450℃和180s. 另外将区熔样品直接熔体旋甩(Melt-Spinning : MS), 熔体旋甩的铜辊转速为10m/s, 喷气压力为0.02MPa, 再将得到的薄带样品研磨, 进行放电等离子烧结, 烧结温度和时间分别是450 ℃和180s.烧结后块体以及区熔样品的微观形貌通过场发射扫描电镜(FESEM)(Sirion 200 FESEM)进行表征; 电导率(σ)和Seebeck系数(α)是在ZEM-1型热电性能测试仪上同时测量的, 采用四电极法测量, α则根据在不同温差下测得的温差电势(△E)并用公式α=△E/△T计算得到; 热导率(κ)通过热扩散系数(D)、热容(C p)和密度(d)使用公式κ= DC p d 得到, D 采用激光热导仪(Netzsch LFA 457)测得, C p使用差式扫描量热仪(TA Instruments Q20)测得, 测试的温度范围为300~500K; 室温下霍尔系数R H, 载流子浓度n e及载流子迁移率μH用van der Pauw方法在霍尔效应测量系统Accent, HL5500PC上同时测量的; 块体材料的抗压强度测试使用InStron 5882电子万能材料试验机测试, 样品采用尺寸为6mm×3mm×3mm的条形柱体, 数据采用5个样品的平均值.2结果与讨论图1所示为三种不同制备工艺得到样品的场发射扫描照片(FESEM). 可以看出, 区熔样品的晶粒非常粗大, 而且取向性明显, 晶体沿晶面容易发生解理, 这是因为Te(1)—Te(1)原子层间是以弱的范德华力结合; 而ZM+SPS样品的晶粒得到了显著的细化, 晶粒排列的取向性大幅降低, 但样品同时也保持了区熔样品的层状结构, 层状结构的尺寸更为细小; MS+SPS样品的晶粒尺寸进一步降低, 晶粒随机排列, 无明显的取向性, 而且在样品中大量存在10～100nm的层状结构, 这些纳米层状结构会对样品的性能产生重要的影响.图2所示为三种不同制备工艺得到样品的电传输性质随温度的变化关系. 由图可知, 所有样品都表现为n型传导. 区熔样品经过SPS后, 其Seebeck 系数大大降低. 因为α=k B(γ +C−ln n e)/e, 其中k B为玻尔兹曼常数, e为电子电量, γ为散射因子, C为常数, n e为电子浓度[12]; 在SPS的过程中, Se和Te的挥发使Se和Te的空位V Se和V Te的浓度大量增加, 而V Se和V Te为n型传导, 大大地增加了载流子即电子的浓度, 使Seebeck系数降低. 对于MS+SPS处理第6期王善禹, 等: 制备工艺对n型Bi2Te3基材料热电性能和抗压强度的影响 611的样品, 一方面由于 MS和SPS过程中Se和Te的挥发, 产生了大量的V Se和V Te, 使电子浓度升高; 另一方面由于MS和研磨过程中产生了Bi原子占据Te或Se位置的反位缺陷Bi Te或Bi Se, 这种反位缺陷是p型传导的, 使电子浓度有所降低, 两种效应综合作用使载流子的浓度变化不大. 但是MS+SPS样品中大量存在的纳米结构和更多的晶界大大地增加了对载流子的散射, 使散射因子γ 增加, 从而使Seebeck系数增大[13]. 室温Hall测试的结果也证实了以上的解释, 表1所示为三种不同工艺制备样品的室温Hall测试的结果.由表1可知, ZM样品由于具有较高的载流子迁移率, 所以具有较高的电导率; 而ZM+SPS样品由于其具有较高的载流子浓度, 因而其电导率也较高, 图1 三种不同工艺制备样品的自由断面的FESEM照片Fig. 1 FESEM images of the samples prepared by different techniques(a) Zone melted sample; (b) ZM+SPS sample; (c) MS+SPS sample图2 三种不同工艺制备样品的电传输性质随温度的变化关系Fig. 2 Temperature dependences of electrical transport properties for three samples prepared by different techniques(a) Electrical conductivity; (b) Seebeck coefficient; (c) Power factor612 无机材料学报第25卷表1三种不同工艺制备样品的室温Hall系数R H、载流子浓度n e、迁移率μΗ和电导率σTable 1 The room temperature Hall coefficients R H, carrier concentrations n e, carrier motilities μΗ and electrical con-ductivity σof three samples prepared by different techniquesHall coefficients, R H/(×10−7, m3·C−1)Carrier concentrations, n e/(×1019, cm−3)Carrier motilities, μΗ/(cm2y V−1y s−1)Electricalconductivity, σ(×104, S y m−1)ZM −13.95 4.480 212.5 15.23 ZM+SPS −8.487 7.354 145.0 17.20 MS+SPS −13.39 4.661 113.4 8.45与ZM样品相当; 区熔样品经MS+SPS后, 由于载流子浓度和迁移率都有所降低, 因此其电导率相比区熔样品大幅降低. 由电导率和Seebeck系数可以计算出功率因子, ZM样品具有较高的功率因子, 这主要是其较高的电导率和较大的Seebeck系数; ZM+SPS和MS+SPS样品在室温附近具有大致相同的功率因子, MS+SPS样品由于随温度大于450K时Seebeck系数降低, 其功率因子随温度的升高降低较为显著.图3所示为三种不同制备工艺得到样品的热导率和晶格热导率随温度的变化关系. 晶格热导率是根据κL=κ−κe计算得出, κe由Wiedemann-Franz公式计算得出, κe=LσT, 其中L是Lorenz常数(L=2.0×10−8V2/K2), σ为电导率, T为绝对温度[12]. 可以看出, ZM样品具有很高的热导率, 在测试温度范围内其热导率均在2.0W/(m⋅K)以上; ZM+SPS样品的热导率相比ZM样品有了一定程度的降低, 这主要是大量晶界增加了对声子的散射从而降低了晶格热导率的缘故; MS+SPS样品的热导率最低, 在室温下其热导率不到1.0W/(m⋅K), 主要是由于晶格热导率和电子热导率都得到了降低. 三种不同工艺制备样品的热导率都是随温度的升高先稍有降低后显著增加, 而且MS+SPS样品随温度升高增加的尤为显著. 声子在传输过程中受到的散射机制主要包括声子−声子散射, 晶格缺陷散射和载流子对声子的散射. 声子−声子散射是晶格振动的固有特征, 而后两者为晶体结构不完整性的表现. 对处于本征激发区的半导体材料, 电子受到热激发从价带跃迁到导带, 从而形成价带空穴和导带电子同时导电, 且电子空穴对所形成的双极扩散对热导率也有较大贡献, 将此称为双极扩散热导率[12, 14]. 通常将这部分热导率计入晶格热导率, 可以看出晶格热导率随温度升高而急剧增加主要是双极扩散的贡献. 可以看出ZM样品具有很高的热导率, 这来源于其高的电导率和晶格热导率; 经过SPS烧结后, 样品的晶格热导率大幅降低, 研磨和SPS使烧结材料的晶粒细化, 增大了对声子的散射, 同时载流子对声子的散射也增加. 经MS+SPS处理的样品, 由于样品中存在大量纳米层状结构, 增加的界面大大增加了对声子的散射; 此外, 点缺陷即反位缺陷Bi Te或Bi Se等对声子尤其是短波声子的散射也大大加强, 所以在室温附近, 晶格热导率得到了大幅降低, 总热导率也随之大幅降低.由上述数据可以计算出三种不同工艺制备的样品的ZT值随温度变化的关系. 图4给出样品的ZT 值随温度变化的关系. ZM样品和ZM+SPS样品的图3 三种不同制备工艺得到样品的热导率随温度的变化关系Fig. 3 Temperature dependences of thermal conductivities for three samples prepared by different techniques(a) Thermal conductivity; (b) Lattice thermal conductivity第6期王善禹, 等: 制备工艺对n 型Bi 2Te 3基材料热电性能和抗压强度的影响 613最大ZT 值出现在420K 左右, 且ZM 样品比ZM+SPS 样品的ZT 值稍高. 经过MS+SPS 处理, 样品的室温ZT 值大幅提高, 在300K 时, ZT 值为0.94, 相比ZM 样品提高了近64%; 其最大的ZT 值为0.96(320K), 并且其ZT 值在300～400K 都在0.8以上. 但是MS+SPS 样品的ZT 值随温度升高减小较为显著, 其ZT 值在440K 以上低于ZM 样品, 这主要是热导率大幅升高的缘故.图5给出了三种不同工艺制备的样品的抗压强度值. 可以看出ZM 样品的抗压强度值很低, 仅为40MPa, 区熔样品沿垂直于c 轴方向容易理解, 样品难以加工, 由区熔样品制造的器件的使用可靠性不高; 经过SPS 后, 样品的抗压强度得到了较大幅度地提高, 可达到110MPa; 样品经MS+SPS 后, 抗压强度得到大幅提高, 可达200MPa, 相比ZM 样品提高了近400%. 由Orowan 关系式σ=kd −1/2可知(其中σ为材料的强度, k 为材料常数, d 为材料的晶粒尺寸): 脆性材料的强度与晶粒尺寸d 的开方成反比关系. 这是因为样品的晶粒尺寸越小, 大量存在的晶界对位错的滑移起到阻碍的作用, 从而提高材料的强度[15]. 从图1的FESEM 图片上也可以看出, 区熔(ZM)样品晶粒粗大, 而且容易沿层间解理, 所以其抗压强度很小; 而经过研磨SPS 后, 晶粒得到了细化, 而且晶粒排列的取向性也大为降低, 因此抗压强度有了较大幅度地提高; 经过MS+SPS 后, 样品的晶粒尺寸进一步降低, 而且存在大量的纳米结构, 晶粒排列无明显取向, 所以样品的抗压强度大幅提高.图4 三种不同工艺制备样品的ZT 值随温度的变化关系 Fig. 4 Temperature dependences of ZT values for three sam-ples prepared by different techniques图5 三种不同工艺制备样品的抗压强度值Fig. 5 Pressive strengths of three samples prepared by dif-ferent methods3 结论以商用区熔n 型碲化铋基材料为原料, 采用直接SPS 和MS+SPS 两种制备方法, 分别制备出块体n 型碲化铋基热电材料, 对区熔原料和烧结材料的微结构、热电传输特性和抗压强度进行了研究, 研究结果表明: MS+SPS 技术不仅大大地改善了材料的热电性能, 而且大幅提高了材料的抗压强度, 其最大ZT 值和抗压强度分别为0.96和200MPa, 相比区熔样品分别提高了64%和400%.参考文献:[1] Rowe D M. CRC Handbook of Thermoelectrics. Nashua USA,1995, 27: 1−18.[2] Yu Fengrong, Zhang Jianjun, Yu Dongli, et al . Enhanced ther-moelectric figure of merit in nanocrystalline Bi 2Te 3 bulk. J. Appl.. Phys., 2009, 105(9): 094303−1−5.[3] Seizo Nakajima. The crystal structure of Bi 2Te 3-x Se x . J. Phys. Chem.Solids , 1963, 24(3): 479−485.[4] Greenaway D L, Harbeke G.. Band structure of bismuth telluride,bismuth selenide and their respective alloys. J. Phys. Chem. Solids , 1965, 26(10): 1585−1604.[5] Ma Yi, Hao Qing, Poudel Bed, et al . Enhanced thermoelectricfigure-of-merit in p-type nanostructures bismuth antimony tellurium alloys made from elemental chunks. Nano Lett ., 2008, 8(8): 2580−2584.[6] Poudel B, Hao Q, Ma Y, et al . High-thermoelectric performance ofnanostructured bismuth antimony telluride bulk alloys. Science ,2008, 320(5876): 634−638.[7] Lan Yucheng, Poudel Bed, Ma Yi, et al . Structure study of bulknanograined thermoelectric bismuth antimony telluride. Nano Lett ., 2009, 9(4): 1419−1422.614 无机材料学报第25卷[8] Tang X F, Xie W J, Li H, et al. Preparation and thermoelectrictransport properties of high-performance p-type Bi2Te3 with layered nanostructure. Appl. Phys. Lett.,2007, 90(1): 012102−1−3.[9] Xie W J, Tang X F, Yan Y G, et al.Unique nanostructure and ther-moelectric performance of melt-spun BiSeTe alloys. Appl. Phys.Lett., 2009, 94(10): 102111−1−3.[10] Xie Wenjie, Tang Xinfeng, Yan Yonggao, et al. High thermoelectricperformance BiSbTe alloy with unique low-dimentional structure. J.Appl. Phys., 2009, 105(11): 113713−1−8.[11] Cao Y Q, Zhao X B, Zhu T J, et al. Syntheses and thermoelectricproperties of Bi2Te3/Sb2Te3 bulk nanocomposites with laminatednanostructure. Appl. Phys. Lett.,2008, 92(14): 143106−1−3. [12] Jiang Jun, Chen Lidong, Yao Qin, et al. Effect of TeI4 content onthe thermoelectric properties of n-type Bi-Te-Se crystals prepared by zone melting. Mater. Chem. Phys.,2005, 92(1): 39−42.[13] Liao Chien-Neng, Wu Li-Chieh. Enhancement of carrier transportproperties of Bi x Sb2-x Te3 compounds by electrical sintering process.Appl. Phys. Lett.,2009, 95(5): 052112−1−3.[14] Zhao Li-Dong, Zhang Bo-Ping, Liu Wei-Shu, et al. Effect ofmixed grain sizes on thermoelectric performance of Bi2Te3 com-pound. J. Appl. Phys., 2009, 105(2): 023704−1−6.[15] 关振铎, 张中太, 焦金生.无机材料物理性能. 北京: 清华大学出版社. 2004: 81−83.。

Effect of heat treatment on microstructure and

Effect of heat treatment on microstructure andtensile properties of A356 alloysPENG Ji-hua1, TANG Xiao-long1, HE Jian-ting1, XU De-ying21. School of Materials Science and Engineering, South China University of Technology,Guangzhou 510640, China;2. Institute of Nonferrous Metal, Guangzhou Jinbang Nonferrous Co. Ltd., Guangzhou 510340, ChinaReceived 17 June 2010; accepted 15 August 2010Abstract: Two heat treatments of A356 alloys with combined addition of rare earth and strontium were conducted. T6 treatment is a long time treatment (solution at 535 °C for 4 h + aging at 150 °C for 15 h). The other treatment is a short time treatment (solution at 550 °C for 2 h + aging at 170 °C for 2 h). The effects of heat treatment on microstructure and tensile properties of the Al-7%Si-0.3%Mg alloys were investigated by optical microscopy, scanning electronic microscopy and tension test. It is found that a 2 h solution at 550 °C is sufficient to make homogenization and saturation of magnesium and silicon in Į(Al) phase, spheroid of eutectic Si phase. Followed by solution, a 2 h artificial aging at 170 °C is almost enough to produce hardening precipitates. Those samples treated with T6 achieve the maximum tensile strength and fracture elongation. With short time treatment (ST), samples can reach 90% of the maximum yield strength, 95% of the maximum strength, and 80% of the maximum elongation.Key words: Al-Si casting alloys; heat treatment; tensile property; microstructural evolution1 IntroductionThe aging-hardenable cast aluminum alloys, such as A356, are being increasingly used in the automotive industry due to their relatively high specific strength and low cost, providing affordable improvements in fuel efficiency. Eutectic structure of A390 can be refined and its properties can be improved by optimized heat treatment [1]. T6 heat treatment is usually used to improve fracture toughness and yield strength. It is reported that those factors influencing the efficiency of heat treatment of Al-Si hypoeutectic alloys include not only the temperature and holding time [2], but also the as-cast microstructure [3í5] and alloying addition [6í8]. Some T6 treatment test method standards of A356 alloys are made in China, USA, and Japan, and they are well accepted. However, they need more than 4 h for solution at 540 °C, and more than 6 h for aging at 150 °C, thus cause substantial energy consumption and low production efficiency. It is beneficial to study a method to cut short the holding time of heat treatment.The T6 heat treatment of Al-7Si-0.3 Mg alloy includes two steps: solution and artificial aging; the solution step is to achieve Į(Al) saturated with Si and Mg and spheroidized Si in eutectic zone, while the artificial aging is to achieve strengthening phase Mg2Si. Recently, it is shown that the spheroidization time of Siis dependant on solution temperature and the original Si particle size [9í11]. A short solution treatment of 30 minat 540 or 550 °C is sufficient to achieve almost the same mechanical property level as that with a solution treatment time of 6 h [12]. From thermal diffusion calculation and test, it is suggested that the optimum solution soaking time at 540 °C is 2 h [13]. The maximum peak aging time was modeled in terms of aging temperature and activation energy [14í15]. According to this model, the peak yield strength of A356 alloy could be reached within 2í4 h when aging at 170 °C. However, few studies are on the effect of combined treatment with short solution and short aging.In our previous study, it was found that the microstructure of A356 alloy could be optimized by the combination of Ti, B, Sr and RE, and the eutecticFoundation item: Project (2008B80703001) supported by Guangdong Provincial Department of Science and Technology, China; Project (09A45031160) supported by Guangzhou Science and Technology Commission, China; Project (ZC2009015) supported by Zengcheng Science andTechnology Bureau, ChinaCorresponding author: PENG Ji-hua; Tel/Fax: +86-20-87113747; E-mail: jhpeng@DOI: 10.1016/S1003-6326(11)60955-2PENG Ji-hua, et al/Trans. Nonferrous Met. Soc. China 21(2011) 1950í1956 1951melting peak temperature was measured to be 574.4 °Cby differential scanning calorimetry (DSC) [16]. In this study, using this alloy modified together with Sr and RE, the effect of different heat treatments on the microstructure and its mechanical properties were investigated.2 ExperimentalCommercial pure aluminum and silicon were melted in a resistance furnace. The alloy was refinedusing Al5TiB master alloy, modified using Al-10Sr andAl-10RE master alloys. The chemical composition ofthis A356 alloy ingot (Table 1) was checked by readingspectrometer SPECTROLAB. Before casting, the hydrogen content of about 0.25 cm 3 per 100 g in the meltwas measured by ELH-III (made in China). Four bars of50 mm×70 mm×120 mm were machined from the sameingot and heat-treated according to Table 2. Followed thesolution, bars were quenched in hot water of 70 °C.Samples cut from the cast ingot and heat-treated barswere ground, polished and etched using 0.5% HF agent.Optical microscope Leica í430 and scanning electricmicroscope LEO 1530 VP with EDS (Inca 300) wereused to examine the microstructure and fractograph. Toquantify the eutectic Si morphology change of differentheat treatments, an image analyzer Image-Pro Plus 6.0 was used, and each measurement included 800í1200 particles. Table 1 Chemical composition of A356 modified with Ti, Sr and RE (mass fraction, %) Si Cu Fe Mn Mg Ti Zn RE Sr 6.85 <0.01 0.19 <0.01 0.370.23 0.03 0.250.012Table 2 Heat treatments in this study Solution Aging Treatment Temperature/ °C Holding time/h Temperature/°C Holdingtime/hST 550r 5 2 170 2T6 535r 5 4 150 15 Tensile specimens were machined from the heat treated bars. The tensile tests were performed using a screw driven Instron tensile testing machine in air at room temperature. The cross-head speed was 1 mm/min. The strain was measured by using an extensometer attached to the sample and with a measuring length of 50mm. The 0.2% proof stress was used as the yield stressof alloys. Three samples were tested for each heat treatment to calculate the mean value.3 Results and discussion3.1 Microstructural characterization of as-cast alloyThe microstructure of as-cast A356 alloy is shown in Fig. 1(a). It is shown that not only the primary Į(Al) dendrite cell is refined, but also the eutectic silicon is modified well. By means of the image analysis, microstructure parameters of as-cast A356 alloy were analyzed statistically as follows: Į(Al) dendrite cell sizeis 76.1 ȝm, silicon particle size is 2.2 ȝm×1.03 ȝm (length×width), and the ratio aspect of silicon is 2.13. The distributions of RE (mish metal rare earth, more than 65% La among them), Ti, Mg, and Sr in the area shown in Fig. 1(b) are presented in Figs. 1(c)í(f)respectively. It is shown that the eutectic silicon particle is usually covered with Sr, which plays a key role in Siparticle modification; Ti and RE present generallyuniform distribution over the area observed, although alittle segregation of RE is observed and shown by arrowin Fig. 1(d). It is suggested that because the refiner TiAl 3and TiB 2 are covered with RE, the refining efficiency isimproved significantly. In the as-cast alloy, some clustersof Mg probably indicate that coarser Mg 2Si phases exist(arrow in Fig. 1(d))).Ti solute can limit the growth of Į(Al) primarydendrite because of its high growth restriction factor [17].The impediment of formation of poisoning Ti-Si compound around TiAl 3 [18] and promotion of Ti(Al 1íx Si x )3 film covering TiB 2 [19] are very important in Al-Si alloy refining. For Al-Si alloys, the effect of RE on the refining efficiency of Ti and B can be contributed to the following causes [20]: preventing refiner phases from poisoning; retarding TiB 2 phase to amass and sink;promoting the Ti(Al, Si)3 compound growth to cover theTiB 2 phase. In this work, with suitable addition of Reand Sr, the microstructure of A356 alloy was optimized. Especially, eutectic Si is modified fully, which isbeneficial to promote Si to spheroidize further duringsolution treatment. 3.2 Microstructural evolution during heat treatmentThe microstructures of A356 alloys treated withsolution at 550 °C for 2 h and ST treatment are presented in Figs. 2(a) and (b) respectively, while those treatedwith solution at 535 °C for 4 h and T6 treatment are presented in Figs. 2(c) and (d), respectively. From Fig. 1 and Fig. 2, after different heat treatments, the primary Į(Al) has been to some extent and the eutectic silicon has been spheroidized further. Both ST and T6 treatmentsproduce almost the same microstructure. The eutectic Si particle distribution and statistical mean aspect ratio of eutectic Si particle are shown in Fig. 3. After onlysolution at 535 °C for 4 h and 550 °C for 2 h, the meanPENG Ji-hua, et al/Trans. Nonferrous Met. Soc. China 21(2011) 1950í19561952Fig. 1 SEM images (a, b), and EDS mapping from (b) for Ti (c), La (d), Mg (e) and Sr (f) in as-cast alloyFig. 2 Microstructure of A356 alloy with different heat treatments: (a) Solution at 550 °C for 2 h; (b) ST treatment; (c) Solution at 535 °C for 4 h; (d) T6 treatmentPENG Ji-hua, et al/Trans. Nonferrous Met. Soc. China 21(2011) 1950í1956 1953Fig. 3 Statistic analysis of eutectic Si in A356 alloy with different heat treatmentsaspect ratios of Si are 1.57 and 1.54 respectively. After being treated by ST and T6, those aspect ratios of Si do not vary greatly, and they are 1.49 and 1.48, respectively. After solution or solution + aging in this study, the friction of eutectic Si particles with aspect ratio of 1.5 is 50%.The eutectic melting onset temperature of Al-7Si-Mg was reported to be more than 560 °C [16, 19]. 550 °C is below the liquid +solid phase zone. During solution, two steps occur simultaneously, i.e., the formation of Al solution saturated with Si and Mg, and spheroidization of fibrous Si particle. The following model predicts that disintegration and spheroidization of eutectic silicon corals are finished at 540 °C after a few minutes (Ĳmax ) [9]:2maxs 32ʌ..ln 9kT D U UW JI I§· ¨¸©¹ (1) where I denotes the atomic diameter of silicon; Ȗ symbolizes the interfacial energy of the Al/Si interface; ȡ is the original radius of fibrous Si; D s is the inter-diffusion coefficient of Si in Al; and T is the solution temperature. When the D s variation at different temperatures is taken into account, it is plausible to suggest that Ĳmax at 550 °C is less than Ĳmax at 540 °C. From Fig. 2(a), it is actually proved that spheroidization of eutectic Si particle could be finished within 2 h when solution at 550 °C.In a selected area of A356 alloy treated with only solution at 550 °C for 2 h (Fig. 4(a)), the distribution of element Mg is presented in Fig. 4(b). Because there is no cluster of Mg in Fig. 4(b), it means a complete dissolution of Si, Mg into Al dendrite during this solution. From the microstructure of A356 alloy treated with T6 (Fig. 5(a)), the distribution of Mg is shown in Fig. 5(b).Fig. 4 SEM image (a) and EDS mapping (b) of Mg distribution in alloy after only solution at 550 °C for 2 hFig. 5 SEM image (a) and EDS mapping of Mg (b) in alloy after heat treatment with T6For A357 alloy with dendrite size of 240 ȝm, uniform diffusion and saturation of Mg in Al could be finished at 540 °C within 2 h [13]. In this study, the cellPENG Ji-hua, et al/Trans. Nonferrous Met. Soc. China 21(2011) 1950í1956 1954size of primary Į(Al) is less than 100 ȝm. It is reasonable that those solutions treated at 535 °C for 4 h and 550 °C for 2 h, can achieve Į(Al) solid solution saturated with Mg and Si because diffusion route is short, even at a higher solution temperature.During aging, Si and Mg2Si phase precipitation happened in the saturated solid solution of Į(Al) according to the sequence in the Al-Mg-Si alloys with excess Si [21]. The needle shaped Mg2Si precipitation was observed to be about 0.5 ȝm in length and less than 50 nm in width, and the silicon precipitates were mainly distributed in Į(Al) dendrites and few of them could be observed in the eutectic region [22]. Because of the small size, these precipitations could not be observed by SEM in this study. However, it is plausible to suggest that the distribution of Mg in dendrite Al cell zone and eutectic zone is uniform (Fig. 4(b) and 5(b)). According to the study by ROMETSCH and SCHAFFER [15], the time to reach peak yield is 2í4 h and 12í14 h at 170 °C and 150 °C, respectively. From 150 to 190 °C of aging temperature, the peak hardness varies between HB110 and HB120. Hence, it is believed that aging at 170 °C for 2 h produces almost the same precipitation hardening as aging at 150 °C for 15 h.3.3 Tensile properties of A356 alloysThe tensile mechanical properties of A356 alloys are given in Table 3. Due to the microstructure optimization of A356 alloy by means of combination of refining and modification, tensile strength and fracture elongation can reach about 210 MPa and 3.7% respectively. Using T6 treatment in this study, strengthand elongation can be improved significantly. For those samples with T6 treatment, the tensile strength and ductility present the maximum values. 90% of the maximum yield strength, 95% of the maximum ultimate strength, and 80% of the maximum elongation can be reached for samples treated by ST treatment. However,T6 treatment spends about 19 h, while ST treatment takes only about 4 h. Fractographs of samples treated with T6 are presented in Fig. 6. The dimple size is almost similar with different heat treatments, indicating that the size and spacing of eutectic silicon particle vary little with different heat treatments. Shrinkage pore, microcrack inside the silicon particle and crack linkage between eutectic silicon particles were observed on the fracture surfaces.Table 3 Tensile properties of A356 alloys with different heat treatmentsHear treatmentıb/MPa ı0.2/MPa į/% As-cast 210 í 3.7 ST 247 178 5.6T6 255 185 7.0Fig. 6 Fractographs of samples with different heat treatments: (a), (b) T6; (c), (d) STPENG Ji-hua, et al/Trans. Nonferrous Met. Soc. China 21(2011) 1950í1956 1955It is well known that shrinkage pores have a great effect on the tensile strength and ductility of A356 alloys. In-situ SEM fracture of A356 alloy indicates the fracture sequence as follows [4]: micro-crack initiation inside silicon particle; formation of slipping band in the Al dendrite; linkage between the macro-crack and micro-crack, and the growth of crack. During tensile strain, inhomogeneous deformation in the microstructure induces internal stresses in the eutectic silicon and Fe-bearing intermetallic particles. Although the full modification of eutectic Si particle was reached in this study, those samples treated with T6 treatment do not perform as well as expected. The main reason is probably due to the higher gas content (0.25 cm3 per 100 g Al). Our next step is to develop a new means to purify the Al-SI alloys to further improve their mechanical properties.4 Conclusions1) The solution at 535 °C for 4 h and the solution at 550 °C for 2 h can reach full spheroidization of Si particle, over saturation of Si and Mg in Į(Al). The heat treatments of T6 and ST produce almost the same microstructure of A356 alloy.2) After both T6 and ST treatments, the aspect ratio of eutectic Si particle will be reduced from 2.13 to less than 1.6, and the friction of eutectic Si particles with aspect ratio of 1.5 is 50%.3) The T6 treatment can make the maximum strength and fracture elongation for A356 alloy. After ST treatment, 90% of the maximum yield strength, 95% of the maximum ultimate strength, and 80% of the maximum elongation can be achieved.References[1]WAN Li, LUO Ji-rong, LAN Guo-dong, LIANG Qiong-hua.Mechanical properties and microstructures of squeezed and casthypereutectic A390 alloy [J]. Journal of Huazhong University ofScience and Technology: Natural Science Edition, 2008, 36(8):92í95. (in Chinese)[2]RAINCON E, LOPEZ H F, CINEROS H. Temperature effects on thetensile properties of cast and heat treated aluminum alloy A319 [J].Mater Sci Eng A, 2009, 519(1í2): 128í140.[3]MANDAL A, CHAKRABORTY M, MURTY B S. Ageingbehaviour of A356 alloy reinforced with in-situ formed TiB2particles [J]. Mater Sci Eng A, 2008, 489(1í2): 220í226.[4]LEE K, KWON Y N, LEE S. Effects of eutectic silicon particles ontensile properties and fracture toughness of A356 aluminum alloysfabricated by low-pressure-casting, casting-forging, and squeeze-casting processes [J]. J Alloys Compounds, 2008, 461(1í2):532í541. [5]VENCL A, BOBIC I, MISKOVIC Z. Effect of thixocasting and heattreatment on the tribological properties of hypoeutectic Al-Si alloy[J]. Wear, 2008, 264 (7í8): 616í623.[6]BIROL Y. Response to artificial ageing of dendritic and globularAl-7Si-Mg alloys [J]. J. Alloys Compounds, 2009, 484(1): 164í167. [7]TOKAJI K. Notch fatigue behaviour in a Sb-modifiedpermanent-mold cast A356-T6 aluminium alloy [J]. Mater Sci Eng A,2005, 396(1í2): 333í340.[8]KLIAUGA A M, VIEIRA E A, FERRANTE M. The influence ofimpurity level and tin addition on the ageing heat treatment of the356 class alloy [J]. Mater Sci Eng A, 2008, 480(1í2): 5í16.[9]OGRIS E, WAHLEN A, LUCHINGER H, UGGOWITZER P J.Onthe silicon spheroidization in Al-Si alloys [J]. J Light Metals, 2002,2(4): 263í269.[10]SJOLANDER E, SEIFEDDINE S. Optimisation of solutiontreatment of cast Al-Si-Cu alloys [J]. Mater Design, 2010, 31(s1):s44ís49.[11]LIU Bin-yi, XUE Ya-jun. Morphology transformation of eutectic Siin Al-Si alloy during solid solution treatment [J]. Special Casting &Nonferrous Alloys, 2006, 26 (12): 802í805. (in Chinese)[12]ZHANG D L, ZHENG L H, STJOHN D H. Effect of a short solutiontreatment time on microstructure and mechanical properties ofmodified Al-7wt.%Si-0.3wt.%Mg alloy [J]. J Light Metals, 2002,2(1): 27í36.[13]YU Z, ZHANG H , SUN B, SHAO G. Optimization of soaking timefor T6 treatment of aluminium alloy [J]. Heat Treatment, 2009, 24(5):17í20. (in Chinese)[14]ESTEY C M, COCKCROFT S L, MAIJER D M, HERMESMANNC. Constitutive behavior of A356 during the quenching operation [J].Mater Sci Eng A, 2004, 383(2): 245í251.[15]ROMETSCH P A, SCHAFFER G B. An age hardening model forAl-7Si-Mg casting alloys [J]. Mater Sci Eng A, 2002, 325(1í2):424í434.[16]TANG Xiao-long, PENG Ji-hua, HUANG Fang-liang, XU De-ying,DU Ri-sheng. Effect of mishmetal RE on microstructures of A356alloy [J]. The Chinese Journal of Nonferrous Metals, 2010, 20(11):2112í2117. (in Chinese)[17]EASTON M A, STJHON D H. A Model of grain refinementincorporation alloy constitution and potency of heterogeneous nucleant particles [J]. Acta Mater, 2001, 49(10): 1867í1878.[18]QIU D, TAYLOR J A, ZHANG M X, KELLY P M. A mechanismfor the poisoning effect of silicon on the grain refinement of Al-Sialloys [J]. Acta Mater, 2007, 55(4): 1447í1456.[19]JUNG H, MANGELINK-NOEL N, BERGMAN C, BILLIA B.Determination of the average nucleation undercooling of primaryAl-phase on refining particles from Al-5.0wt% Ti-1.0wt% B inAl-based alloys using DSC [J]. J Alloys Compounds, 2009, 477(1í2):622í627.[20]LAN Ye-feng, GUO Peng, ZHANG Ji-jun. The effect of rare earthon the refining property of the Al-Ti-B-RE intermediate alloy [J].Foundry Technology, 2005, 26(9): 774í778. (in Chinese)[21]EDWARDS G A, STILLER K, DUNLOP G L, COUPER M J. Theprecipitation sequence in Al-Mg-Si alloys [J]. Acta Mater, 1998,46(11): 3893í3904.[22]RAN G, ZHOU J E, WANG Q G. Precipitates and tensile fracturemechanism in a sand cast A356 aluminum alloy [J]. J Mater ProcessTechnol, 2008, 207(1): 46í52.PENG Ji-hua, et al/Trans. Nonferrous Met. Soc. China 21(2011) 1950í19561956⛁ ⧚ A356䪱䞥㒘㒛㒧㛑ⱘ1ē 1ē 1ē ԃ 21. ⧚ ⾥ Ϣ ⿟䰶ˈ 510640˗2. 䞥䙺㡆䞥䰤㡆䞥 ⷨお ˈ 510340㽕˖⫼ϸ⾡ϡ ⱘ⛁ ⧚ ⿔䬊㓐㒚䋼ⱘA356 䞥䖯㸠 ⧚ˈϔ⾡䭓䯈 ⧚ T6(535 °C ⒊4 h+150 °C 15 h)ˈ ϔ⾡ ⷁ 䯈ⱘ⛁ ⧚ ST(550 °C ⒊2 h+170 °C 2 h)Ǆ䞛⫼ 䬰ǃ ⬉䬰 ⏽ Ԍ 偠ㄝ ↉ ⛁ ⧚ A356 䞥㾖㒘㒛 Ԍ 㛑ⱘ Ǆ㒧㸼 ˖ 550 °Cϟ ⒊2 h ҹ㦋 MgǃSi䖛佅 Ϩ ⱘĮ(Al) ⒊ԧˈ Փ ⸙Ⳍ⧗ ˗ 㒣170 °CҎ 2 h ˈ ҹ䖒 Ӵ㒳T6 ⧚ⱘ Ǆ Ԍ 偠㒧㸼 ˈA356䪱䞥㒣Ӵ㒳T6 ⧚ њ 催ⱘ Ԍ 㺖Ԍ䭓⥛˗䗮䖛STⷁ ⛁ ⧚ ˈ Ԍ ǃ Ԍ䭓⥛ ҹ䖒 T6 ⧚ ⱘ90%ˈ95% 80%Ǆ䬂䆡˖Al-Si 䞥˗⛁ ⧚˗ Ԍ 㛑˗ 㾖㒘㒛ⓨ(Edited by LI Xiang-qun)。

PTFE复合材料高温摩擦磨损性能研究

2008年8月第33卷第8期润滑与密封LUBR I C A TI ON EN GI N EER I N GA ug .2008V ol 133No 18收稿日期作者简介范清,女,高级工程师,2f q _y @y 111PTFE 复合材料高温摩擦磨损性能研究邓联勇　范　清　彭　兵　王　勇(广州机械科学研究院　广东广州510700)摘要:研究了高温条件下不同填料填充的PTFE 复合材料的摩擦磨损性能,并与常温下的摩擦磨损性能进行了比较。

结果表明青铜粉、纤维填充的复合材料在高温下表现出与常温相反的摩擦磨损规律;碳类填充复合材料在不同温度下则表现出较为稳定的规律;特种塑料改性的PTFE 复合材料,具有极好的综合性能。

关键词:PTFE;复合材料;摩擦磨损中图分类号:T H11711　文献标识码:A 文章编号:0254-0150(2008)8-098-4Research on Tr ibologi ca l Behav i or s of PTFE C o m positesa t H i gh Tem pera tur eD e ng L ia ny o ng F a n Q ing P e ng B i ng W a ng Yong(Guangzh ou Mechanical Engi neering Resea rch Institute,Guangzhou Guangdong 510700,Chi na )A bstr ac t:The tribo logical behaviors of PTFE co mposites at high te mper ature was studied and c omp ar ed w ith those atno r mal te mp er ature .I t is indicated that the c ompo sites filled w ith b r onz e powder o r fibers show diff eren t fricti on and wear p r operties at no r mal and high te mp er atu r e,the co mposites filled w ith carbolic fillers have stab le tribo l ogical behavi o r when te mp er atu r e changes .The co mposites filled with special p lastic have best co mp rehensive perf or mance .Keyword s :PTFE;co mposites;friction and wear　聚四氟乙烯(PTFE )是一种性能优异的固体自润滑材料[1-2],具有极低的摩擦因数、良好的化学稳定性及热稳定性,广泛应用于各行各业。

金的等离子共振等综述

a b s t r a c t
This review describes the fundamental aspects of laser–gold nanoparticle (Au NP) interaction that leads to nanoscale energy deposition to the surroundings through light ampliﬁcation and heat generation. Besides the importance of the primary process in physics and chemistry, application of the light–NP interaction has attracted signiﬁcant interest from various areas ranging from analytical chemistry to material chemistry and biomedicine. Here we consider both mechanistic and application aspects. Our attention is focused on pulsed-laser-induced fast processes that revealed the heating–cooling dynamics of electrons, lattice (particle), and particle’s environment. On the application side, we focus on material fabrication and processing that beat diffraction-limited resolution. Together, we will shed a light on the essence of research activities carried out in the past 10 years. In addition to an abundance of latest information obtained from currently available literature, this review includes ﬁgures obtained by our own calculations to provide readers with a better understanding of the basics of the optical properties and energy and heat-transfer processes of Au NPs, which are not familiar to photochemists. © 2012 Elsevier B.V. All rights reserved.

应力对电化学的滞后作用英语

应力对电化学的滞后作用英语Electrochemical Lag Effects of Stress.Stress can have a significant impact on the electrochemical processes that occur in materials. These effects can be either positive or negative, depending on the specific material and the type of stress applied. In some cases, stress can lead to an increase in electrochemical activity, while in other cases it can lead to a decrease.One of the most common ways that stress affects electrochemical processes is by altering the microstructure of the material. When a material is subjected to stress,its atoms and molecules are forced to move and rearrange themselves. This can lead to changes in the material's grain size, crystal structure, and other microstructural features. These changes can, in turn, affect the material's electrochemical properties.For example, a study by the University of California, Berkeley found that stress can increase the corrosion rate of steel. The researchers found that when steel was subjected to tensile stress, its grain boundaries became more active and more susceptible to corrosion. This led to an increase in the overall corrosion rate of the steel.In other cases, stress can have the opposite effect and decrease electrochemical activity. A study by theUniversity of Tokyo found that stress can decrease the rate of hydrogen evolution from platinum. The researchers found that when platinum was subjected to compressive stress, its surface became less active and less likely to react with hydrogen ions. This led to a decrease in the rate of hydrogen evolution.The effects of stress on electrochemical processes can be complex and depend on a number of factors, including the type of material, the type of stress applied, and the environmental conditions. However, it is clear that stress can have a significant impact on the electrochemical properties of materials.Applications of Electrochemical Lag Effects of Stress.The electrochemical lag effects of stress can be usedin a variety of applications. One common application is in the field of corrosion control. By understanding how stress affects the corrosion rate of materials, engineers can design materials and structures that are more resistant to corrosion.Another application of the electrochemical lag effects of stress is in the field of energy storage. By understanding how stress affects the electrochemicalactivity of materials, scientists can develop new and more efficient energy storage devices.Conclusion.The electrochemical lag effects of stress are a complex and fascinating phenomenon. By understanding these effects, scientists and engineers can develop new materials and technologies that are more resistant to corrosion, moreefficient at energy storage, and more responsive to external stimuli.。

退火温度对BaTiO_3薄膜的结构和介电性能的影响_郑新芳

退火温度对BaTiO 3薄膜的结构和介电性能的影响郑新芳　李俊峰＊(河北师范大学化学与材料科学学院,河北石家庄050061;＊邯郸学院物理与电子工程系,河北邯郸056005)摘　要　采用溶胶-凝胶法制备Si (100)基片上的BaTiO 3陶瓷薄膜,并用红外光谱(IR )、x 射线衍射(XRD )、扫描探针(SPM )等技术分析了钛酸钡凝胶的热解过程,以及不同退火温度下薄膜的晶粒、晶相、表面形貌、介电性能等指标。

实验结果表明:高温有利于钛酸钡由立方相向四方相的转化;温度升高到1023K 时,钛酸钡薄膜的表面形貌平整、均匀并具有良好的介电性能。

关键词　钛酸钡薄膜　温度　溶胶-凝胶法　介电性收稿日期:2007-12-07作者简介:郑新芳(1976～),女,硕士生,研究方向:无机材料Effect of Anneal Temperature on Structure andDielectric Property of BaTiO 3Thin FilmsZheng Xinfang Li Junfeng＊(Hebei Nor mal University College of Chemistry &Material Science ,Hebei Shijiazhuang 050061;＊Handan College College of Physics &Electronic Engineering ,Hebei Handan 056005)A bstract BaTiO 3thin films were prepared on Silicon (100)Substrate using sol -gel method .The pyrogenation of Ba -TiO 3gel and crystal grain ,crystal character ,surface appearance ,dielectric property of the thin films at different anneal temperature were analyzed by IR ,XRD and SPM technology .The result showed that high temperature was propitious to phase transaction of Ba TiO 3form cube to square and when temperature rised to 1023K ,surface appearance of BaTiO 3thin films were smooth and even ,and with well dielectric property .Keywords BaTiO 3thin films temperature sol -gel method dielectric pr operty 制备薄膜的方法有射频溅射、有机化学气相沉积(MOCVD )、脉冲激光沉积(PLD )和溶胶-凝胶(sol -gel )技术等[3]。

化学机械抛光工艺中的抛光垫

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Effect of friction heat on tribological behavior of M2 steel against GCr15 steel in dry sliding

含氮硼酸酯添加剂的合成及其摩擦学性能研究

冰冻浓缩效应 绿色合成 英文

化学机械抛光工艺中的抛光垫

Effect of Surfactants on the Interfacial

英文原文

摩擦纳米发电激发光动力学

巨磁电阻效应的英语

水化热抑制剂对水泥-粉煤灰胶凝材料水化和混凝土性能的影响

温度对半导体影响的书

摩擦纳米发电激发光动力学

Nb-Ti低合金高强钢第二相析出及其对力学性能的影响

大功率永磁同步发电机定子冷却系统优化分析

制备工艺对n型Bi_2Te_3基材料热电性能和抗压强度的影响

Effect of heat treatment on microstructure and

PTFE复合材料高温摩擦磨损性能研究

金的等离子共振等综述

应力对电化学的滞后作用英语

退火温度对BaTiO_3薄膜的结构和介电性能的影响_郑新芳

化学机械抛光工艺中的抛光垫

冰冻浓缩效应绿色合成英文