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Assessment of the apparent activation energies for gas/solid reactions—carbonate decomposition

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Journal of university of science and technology beijing 2003年第2期10卷 25-29页

作者： Jianhua Liu and Jiayun ZhangMetallurgical Engineering school, university of science and technology beijing,{2. Metall. Eng. Sch. Univ. of Sci. and Technol. Beijing Beijing 100083 China

The guidelines for assessing the apparent activation energies of gas/solidreactions have been proposed based on the experimental results from literatures. In CO_2.free inletgas flow, CaCO_3 decomposition between 950 and 12.0 K with thin sample layer could be controlled bythe interfacial chemical reaction with apparent activation energy E = (2.5+-10) KJ/mol and E=(2.0+-10) kJ/mol at T = 813 to 102. K, respectively. With relatively thick sample layer between 793and 12.3 K, the CaCO_3 decomposition could be controlled by one or more steps involvingself-cooling, nucleation, intrinsic diffusion and heat transfer of gases, and E could vary between147 and 190 kJ/mol. In CO_2.containing inlet gas flow (5 percent-100 percent of CO_2., E wasdetermined to be varied from 949 to 2.97 kJ/mol. For SrCO_3 and BaCO_3 decompositions controlled bythe interfacial chemical reaction, E was (2.3+-15) kJ/mol (1000-1350K) and (305+-15) kJ/mol(12.0-1400 K), respectively

关键词： assessment activation energy decomposition carbonate

Thermodynamic Properties of Mn-P and Fe-Mn-P Melts

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International Journal of Minerals,Metallurgy and materials 2000年第1期14卷 10-13页

作者： Jian Zhang Rong Zhu Metallurgy school, university of science and technology beijing,{2. Metallurgy school University of Science and Technology Beijing Beijing 100083 China

Based on the phase diagrams and the coexistence theory of metallic melts structure involving compound formation, the cal- culating models of mass action concentrations for Mn-P and Fe-Mn-P melts have been formulated. The calculated mass action concen- trations agree well with the corresponding measured activities, this in turn shows that the deduced models can reflect the structural char- acteristics of the melts concerned and there isn't any saturation of phosphorus in both melts.

关键词： activity dephosphorization the coexistence theory mass action concentration

Numerical Simulation on Irregular Shrinkage of Initial Shell in Continuous Casting of Steel

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International Journal of Minerals,Metallurgy and materials 1999年第2期13卷 103-106页

作者： Dejun Jing Kaike Cai(Metallurgy school, university of science and technology beijing,{2.) Metallurgy school University of Science and Technology Beijing Beijing 100083 China

Based on the microstructures of steel, a thermo-elasto-plastic stress model of continuously casting billets is established to study hailal solidifying process in molds. Results show that peritectic phase transformation contributes greatly to the irregular shrinkage ofinitial shell, which makes the billets vulnerable to surface defects.

关键词： thermo-elasto-plastic stress model peritectic phase transformation irregular shrinkage of initial shell

Calculating Model of Mass Action Concentrations for Fe-Cr-P Melts and Optimization of Thermodynamic Parameters

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International Journal of Minerals,Metallurgy and materials 1999年第1期13卷 11-14页

作者： Jian Zhang (Metallurgy school, university of {2. and technology Beliing, beijing 100083. china) Metallurgy school University of Science and Technology Beijing Beijing 100083 China

According to the results of research on the thermodynamic propelles of Fe-Cr, Fe-P and Cr-P melts, the measured achvihes of Fe-Cr-P melts from reference sources as well as the coexistence theory of metallic melts structure involving compound formation, a calculating model of the mass action concentrations for Fe-Cr-P melts has been formulated and some of its thermodynamic parameters have been optimized. The calculated mass action concentrations agree with the measured achvities, which shows that this model can reflect the structural reality of Fe-Cr-P melts.

关键词： activity dephosphorization of stainless steel, coexistence theory mass action concentration

Effects of silver powder particle size on the microstructure and properties of Ag-Yb_2._3 electrical contact materials prepared by spark plasma sintering

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Rare Metals 2010年第4期29卷 366-370页

作者： CHEN Xiaohua,JIA Chengchang,and LIU Xiangbing school of materials {2. and Engineering,university of {2. and technology beijing,beijing 100083.china school of materials {2. and Engineering University of Science and Technology Beijing Beijing China

mg-Yb2.3 electrical contact materials were fabricated by spark plasma sintefing （SPS）. The effects of silver powder particle size on the microstructure and properties of the samples were investigated. The surface morphologies of the sintered samples were examined by optical microscope （OM）, and the fracture morphologies were observed by scanning electron microscopy （SEM）. The physical and mechanical properties such as density, electrical resistivity, microhardness, and tensile strength were also tested. The results show that the silver powder particle size has evident effects on the sintered materials. Comparing with coarse silver powder （5 ktm）, homogeneous and fme microstmcture was obtained by fine silver powder （_〈0.5-1am）. At the same time, the electrical conductivity, microhardness, and tensile strength of the sin- tered samples with fine silver powder were higher than those of the samples with coarse silver powder. However, silver powder particle size has little influence on the relative densities, which of all samples （both by free and coarse silver powders） is more than 95%. The fracture characteristics are ductile.

关键词： composites electrical contact materials spark plasma sintering particle size microstructure physical properties mechanical properties

A Special TMCP Used to Develop a 800MPa Grade HSLA Steel

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Journal of university of science and technology beijing 2001年第3期8卷 224-228页

作者： Chengjia Shang,Xuemin Wang, Xinlai He, Shanwu Yang, Yi Yuan material science and Engineering {2., university of science and technology beijing, beijing, 100083. china material science and Eng. {2. Univ. of Sci. and Technol. Beijing Beijing 100083 China

The effect of relaxation after finished rolling on structures and properties of four microalloyed steel with different content of Nb and Ti was investigated. By alloy designing and control rolling + relaxation-precipitation-control phase trail storm ati on (RPC) process, a new 800 MPa grade HSLA plate steel could be obtained, the microstructure is composite ultra-fine lath bainite/martensite. The tempering process and mechanical properties of this kind of HSLA steel were investigated. The yield strength can achieve 800 MPa, and the ductility and impact toughness is satisfied.

关键词： HSLA steel microstructure and mechanical properties TMCP (thermomechanical control process) RPC

Relaxation of Deformed Austenite and Refinement of Bainite in a Nb-Containing Microalloyed Steel

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Journal of university of science and technology beijing 2001年第3期8卷 214-217页

作者： Shanwu Yang, Xuemin Wang, Chengjia Shang, Xinlai He, Yi Yuan material science and Engineering {2., university of science and technology beijing, beijing 100083. china material science and Eng. {2. Univ. of Sci. and Technol. Beijing Beijing 100083 China

By means of stress relaxation and strain-induced precipitation in deformed austenite, bainite with micron sheaves size was obtained in Nb-containing steel. Microstructures of deformed samples isothermally relaxed for various time followed by cooling in water were examined. Stress relaxation test and transmission electron microscopy (TEM) were employed to detect precipitation of microalloy elements, such as Nb, Ti, during isothermal holding after deformation. All the samples were constituted by lath-like bainite along with acicular ferrite, but the size of bainitic sheaves and the amount of acicular ferrite were changed with relaxation time. To achieve optimum refinement, relaxation should be confined in the stage when the precipitates have sufficiently grown and started to coarsen. The sample having not undergone relaxation does not exhibit obvious refinement despite of its higher dislocation density. These results indicate that relaxation promotes bainite to refine, which is because deformed austenitic grains are divided by dislocation walls formed during relaxation and acicular ferrite formed before bainitic transformation.

关键词： stress relaxation strain induced precipitation refinement

Numerical simulation of strain localization and damage evolution in large plastic deformation using mixed finite element method

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Journal of university of science and technology beijing 2004年第3期11卷 273-277页

作者： Zhanghua Chen Jiajian Jin Jiumei Xiao Applied science school,{2., beijing 100083. china Appl. Sci. Sch. Univ. of Sci. and Technol. Beijing Beijing 100083 China

An investigation of computer simulation is presented to analyze the effectsof strain localization and damage evolution in large plastic deformation. The simulation is carriedout by using an elastic-plastic-damage coupling finite element program that is developed based onthe concept of mixed interpolation of displacement/pressure. This program has been incorporated intoa damage mechanics model as well as the corresponding damage criterion. To illustrate theperformance of the proposed approach, a typical strain localization problem has been simulated. Theresults show that the proposed approach is of good capability to capture strain localization andpredict the damage evolution.

关键词： strain localization mixed element truesdell stress rate material damage

Reaction Sintering of Fe-Al Powder Mechanically Activated

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International Journal of Minerals,Metallurgy and materials 1998年第4期12卷 233-236页

作者： Chengchang jia Xiaosen Lu Jun Zhao Zizhang Xie(material science and Engineering {2., university of science and technology beijing, beijing 100083. china) (beijing Hard Metal Factory, beijing 100055, china) material science and Engineering {2. University of Science and Technology Beijing Beijing 100083 China beijing Hard Metal Factory Beijing 100055 China

The mixture of Fe and Al powder was mechanically activated and sintered to study a non-melting methodof producing the intermetallics Fe3Al. High-energy ball milling was used as an activation method, X-ray diffractionand SEM were chosen to analyze the materials variation before and after activation and sintering, and hot press ofFe-Al powder was inveshgated to compare mechanical activation with sintering. The results show that combiningmechanical activation with reaction sintering can complete the transformation from pure Fe and Al powder to intermetallics. It is difficult to do the transformation by either mechanical activation or hot press.

关键词： intermetallic compound sintering metal powder mechanical activation