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Regulation of Power Conversion in Fuel Cells

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Chemical Research in Chinese Universities 2004年第4期20卷 466-469页

作者： zhang j. K. Scott School of Chemical Engineering & Advanced Materials University of Newcastle upon Tyne Newcastle upon TyneSchool of Chemical Engineering & Advanced Materials University of Newcastle upon Tyne Newcastle upon Tyne NE1 7RU UK NE1 7RU UK

Here we report a regulation about power conversion in fuel cells. This regulation is expressed as that total power produced by fuel cells is always proportional to the square of the potential difference between the \{equilibrium\} potential and work potential. With this regulation we deduced fuel cell performance equation which can describe the potential *** current performance curves, namely, polarization curves of fuel cells with three power source parameters: equilibrium potential E_0; internal resistance R; and power conversion coefficient K. The concept of the power conversion coefficient is a new criterion to evaluate and compare the characteristics and capacity of different fuel cells. The calculated values obtained with this equation agree with practical performance of different types of fuel cells.

关键词： Fuel cell Power conversion coefficient Internal resistance Performance Potential

Design and optimization of the composition and mechanical properties for non-equiatomic CoCrNi medium-entropy alloys

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journal of Materials Science & Technology 2023年第8期139卷 232-244页

作者： j.X.Yan Z.j.zhang P.zhang j.H.Liu H.Yu Q.M.Hu j.B.Yang Z.F.zhang Shi-changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China School of Materials Science and Engineering Chongqing Jiaotong UniversityChongqing 400074China chool of Materials Science and Engineering University of Science and Technology of ChinaShenyang 110016China School of Materials Science and Engineering Northeastern UniversityShenyang 110819China School of Information Science and Engineering Shenyang University of TechnologyShenyang 111003China

The development of multi-principal element alloys(MPEAs,also called as high-or medium-entropy al-loys,HEAs/MEAs)provides tremendous possibilities for materials ***,designing MPEAs with desirable mechanical properties confronts great challenges due to their vast composition *** this work,we provide an essential criterion to efficiently screen the CoCrNi MEAs with outstanding strength-ductility *** negative Gibbs free energy difference△E_(FCC-BCC)between the face-centered cubic(FCC)and body-centered cubic(BCC)phases,the enhancement of shear modulus G and the decline of stacking fault energy(SFE)γ_(isf)are combined as three requisites to improve the FCC phase stability,yield strength,deformation mechanisms,work-hardening ability and ductility in the *** effects of chemical composition on△E_(FCC-BCC),G andγisf were investigated with the first principles calculations for Co_(x)Cr_(33)Ni_(67-x),Co_(33)Cr_(y)Ni_(67-y)and Co_(z)Cr_(66-z)Ni_(34)(0≤x,y≤67 and 0≤z≤66)*** on the essential criterion and the calculation results,the composition space that displays the neg-ative Gibbs free energy difference△E_(FCC-BCC),highest shear modulus G and lowest SFEγ_(isf)was screened with the target on the combination of high strength and excellent *** this context,the optimal composition space of Co-Cr-Ni alloys was predicted as 60 at.%-67 at.%Co,30 at.%-35 at.%Cr and 0 at.%-6 at.%Ni,which coincides well with the previous experimental evidence for Co_(55)Cr_(40)Ni_(5)*** valid-ity of essential criterion is further proved after systematic comparison with numerous experimental data,which demonstrates that the essential criterion can provide significant guidance for the quick exploitation of strong and ductile MEAs and promote the development and application of MPEAs.

关键词： Medium-entropy alloys First-principles calculations Phase stability Stacking-fault energy Strength Ductility

Mechanism transition of cross slip with stress and temperature in face-centered cubic metals

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journal of Materials Science & Technology 2020年第22期54卷 159-171页

作者： K.Q.Li Z.j.zhang j.X.Yan j.B.Yang Z.F.zhang Laboratory of Fatigue and Fracture for Materials Institute of Metal ResearchChinese Academy of SciencesShenyang110016China School of Materials Science and Engineering University of Science and Technology of ChinaShenyang 110016China

A/2 screw dislocation is commonly dissociated into two /6 Shockley partial dislocations on{111} planes in face-centered cubic *** the two partials are not purely screw,different mechanisms of cross-slip could take place,depending on the stacking fault energy,applied stress and tempe *** is crucial to classify the mechanisms of cross-slip because each mechanism possesses its own reaction path with a special activation *** this work,molecular dynamics simulations have been performed systematically to explore the cross-slip mechanism under different stresses and temperatures in three different metals Ag,Cu and Ni that have different stacking fault energies of 17.8,44.4 and 126.8 mj/m^2,re *** Ag and Cu with low stacking fault energy,it is observed that the cross-slip mechanism of screw dislocations changes from the Fleischer obtuse angle(FLOA),to the Friedel-Escaig(FE),and then to the FL acute angle(FLAA) at low temperatures,with increasing the applied ***,when the temperature increases,the FE mechanism gradually becomes dominant,while the FLAA only occurs at the high stress *** particular,the FLOA has not been observed in Ni because of its high stacking fault energy.

关键词： Cross-slip Molecular dynamics simulation Face-centered cubic metals Stacking fault energy

Nonlinear static and dynamic responses of an electrically actuated viscoelastic microbeam

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Acta Mechanica Sinica 2009年第2期25卷 211-218页

作者： Y.M.Fu j.zhang College of Mechanics and Aerospace Hunan University

On the basis of the Euler-Bernoulli hypothesis, nonlinear static and dynamic responses of a viscoelastic microbeam under two kinds of electric forces [a purely direct current （DC） and a combined current composed of a DC and an alternating current] are studied. By using Taylor series expansion, a governing equation of nonlinear integro-differential type is derived, and numerical analyses are performed. When a purely DC is applied, there exist an instantaneous pull-in voltage and a durable pull-in voltage of which the physical meanings are also given, whereas under an applied combined current, the effect of the element relaxation coefficient on the dynamic pull-in phenomenon is observed where the largest Lyapunov exponent is taken as a criterion for the dynamic pull-in instability of viscoelastic microbeams.

关键词： MEMS Viscoelastic microbeam Nonlineardynamics

A practical model for efficient anti-fatigue design and selection of metallic materials:Ⅰ.Model building and fatigue strength prediction

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journal of Materials Science & Technology 2021年第11期70卷 233-249页

作者： R.Liu P.zhang Z.j.zhang B.Wang Z.F.zhang Laboratory of Fatigue and Fracture for Materials Shi-changxu Innovation Center for Advanced MaterialsInstitute of Metal ResearchChinese Academy of Sciences72 Wenhua RoadShenyang 110016China

The high cost and low efficiency of fatigue tests are bottleneck problem for the anti-fatigue design of metallic *** this problem,a theoretical fatigue model is proposed in this study,the possible applications have also been *** results would be introduced in two serial papers,in which the first paper focuses on the model building and the applications on fatigue strength prediction;the second paper put emphasis on the influencing factors of the model parameters and the applications on fatigue strength *** this first paper,a theoretical model is proposed considering both the strength and plastic restrictions of fatigue *** the model builds up a brief relationship among yield strength(Y),tensile strength(T)and fatigue strength(F),it is named as the Y-T-F *** the verification with fatigue strength data covering various kinds of metallic materials and loading conditions,this Y-T-F model exhibits both generality and *** the Y-T-F model,the efficient fatigue strength prediction could be conducted by brief linear fitting and calculation,just through yield strength,tensile strength and several known fatigue strength ***,through its deduced Y-F model,the analytical formula of fatigue strength continuously changing with materials strengthening can be obtained,as well as the maximum value of fatigue strength and corresponding critical yield *** summary,the Y-T-F model would be useful for reducing the fatigue tests,thus providing new possibilities on the efficient anti-fatigue design and selection of metallic materials.

关键词： Yield strength Tensile strength Plasticity Fatigue strength Anti-fatigue design

Effect of organic modifiers on the capacity factor in micellar electrokinetic chromatography

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Chinese journal of Chemistry 1997年第2期15卷 144-153页

作者： Shi, W zhang, j Wang, L Zou, HF zhang, YK National Chromatographic R&A Center Dalian Institute of Chemical Physics Chinese Academy of Sciences Dalian Liaoning 116011 China

Organic modifiers were effective both to extend the migration time window and to improve the separation of very hydrophobic compounds in MEKC. An iteration method was used to determine the migration time of micelles. The quantitative relationship between the capacity factor k' and the concentration of organic modifiers was derived, which was investigated experimentally. The linear solvation energy relationships (LSER) methodology was applied to MEKC, and good linear relationships between lnk' and solvatochromic parameters of 15 solutes were obtained in the presence of organic modifier in different concentrations, which indicated a new access in MEKC to predict k' from the structural parameters of solutes. The effect of column temperature T on k' was also investigated.

关键词： micellar electrokinetic chromatography organic modifiers capacity factor migration time window

ELECTROCHEMICAL STUDY ON THE LOCALIZED CORROSION OF TWO DIFFERENT TEMPER LY12 ALLOYS

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Acta Metallurgica Sinica(English Letters) 2005年第5期18卷 609-619页

作者： F.H. Cao L. Guo L.j. zhang Z. zhang j. Q. zhang Department of Chemistry Yuquan Campus Zhejiang University Hangzhou 310027 China State Key Laboratory for Corrosion and Protection of Metals Institute of Metal Research The Chinese Academy of Sciences Shenyang 110016 China

The corrosion behavior of two different aged LY12 alloys in EXCO （234g/L NaCl, 50g/L KNO3 0.1M HNO3） and MIL-H-600 （35g/L NaCl, 5g/L （NH4）2SO4） solutions were studied using electrochemical impedance spectroscopy （EIS） in conjunction with SEM technique respectively, and the pH variation of the above accelerated corrosion solution during materials corroding was also measured to characterize the corrosion processes. At the beginning of corrosion, EIS plots exhibited two capacitive arcs in the high frequency range （Cd） and mediate frequency range （ Cf） originating from the original corroded surface and the newly formed interface respectively, and a low frequency inductive loop due to the relaxation phenomenon of reaction intermediates. In the EXCO,solution, the EIS results showed that once the exfoliation corrosion occurred, the inductive loop disappeared. The results also showed that the exfoliation corrosion susceptibility of state T6 is much higher than that of state T3, but the intergranular corrosion susceptibility has a reverse order. Based on the relationship of EIS results with SEM and metalloscopy morphologies of the corroding substrates and physic-chemical meaning of EIS parameters, an index （Cf/Cd） has been proposed to characterize the extent of the localized corrosion, which variation tallies with the real corrosion extent correctly. Meanwhile, good agreement was found between the experimental results and the electrochemical model proposed and, good coherence between the electrochemical features and the distribution type of constituent particles of corroding material was observed.

关键词： electrochemical impedance spectroscope LY12 alloy exfoliation corrosion intergranular corrosion

Microstructure and brazing mechanism of porous Si_3N_4/Invar joint brazed with Ag-Cu-Ti/Cu/Ag-Cu multi-layered filler

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journal of Materials Science & Technology 2018年第4期34卷 713-719页

作者： j.zhang j.Y.Liu T.P.Wang School of Materials Science and Engineering Harbin Institute of Technology

Porous Si3N4 was brazed to Invar alloy in this study, and Ag-Cu-Ti/Cu/Ag-Cu multi-layered filler was designed to inhibit the formation of Fe2Ti and Ni3Ti intermetallic compounds. The effects of the brazing temperature and the thickness of Cu interlayer on the microstructure and mechanical properties of brazed joints were investigated. The typical microstructure of the joint brazed with multi-layered filler was porous Si3N4/TiN ＋ Ti5Si3/Ag-Cu eutectic[Cu[Ag-Cu eutectic/Cu-rich layer ＋ diffusion layer/Invar. When the brazing temperature increased, the reaction layer at the ceramic/filler interface grew thicker and the Cu interlayer turned thinner. As the thickness of Cu interlayer increased from 50 to 150 μm, the joint strength first increased and then decreased. In this research, the maximum shear strength （73 MPa） was obtained when being brazed at 1173 K with a 100 μm Cu interlayer applied in the filler, which was 55% higher than that brazed with single Ag-Cu-Ti brazing alloy and had reached 86% of the ceramic. The release of residual stress and the barrier effect of Cu interlayer to inhibit the formation of Fe2Ti and Ni3Ti intermetallics played the major role in the improvement of joint strength.

关键词： Porous Si3N4 Invar alloy Brazing Microstructure Mechanical properties

Sub-high Rate Directional Solidification

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journal of Materials Science & Technology 1998年第1期14卷 9-14页

作者： Fu, HZ Geng, XG Li, jG zhang, j Northwestern Polytech Univ State Key Lab Solidificat Proc Xian 710072 Peoples R China

The main features of morphology evolution of crystal growth during near rapid directional solidification were reviewed and the concept of effective constitutional supercooling was proposed. On the basis of interface stability theory combined with experiments, the behaviour of transition from dendrites to fine cells was quantitatively described, and the transition from cells to plane front of absolute stability was also examined.

关键词： Rapid solidification