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Anomalous magnetotransport in LaMn_(1-x)Te_xO_3

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science china(Physics,Mechanics & Astronomy) 2009年第7期52卷 987-992页

作者： TAN GuoTai1,2, CHEN ZhengHao3 & ZHANG XiaoZhong4,5 1 key laboratory of Beam Technology & materials Modification of the ministry of education, Institute of Low Energy Nuclear Physics, beijing Normal university, beijing 100875, china 2 beijing Radiation Center, beijing 100875, china 3 laboratory of Optical Physics, Institute of Physics, Chinese Academy of {13.s, beijing 100080, china 4 key laboratory of advanced materials of the ministry of education, Department of materials {13. and engineering, tsinghua university, beijing 100084, china 5 beijing National Center for Electron Microscopy, tsinghua university, beijing 100084, china 1. key laboratory of Beam Technology & materials Modification of the ministry of education Institute of Low Energy Nuclear Physics Beijing Normal University Beijing 100875 China 2. beijing Radiation Center Beijing 100875 China 3. laboratory of Optical Physics Institute of Physics Chinese Academy of Sciences Beijing 100080 China 4. key laboratory of advanced materials of the ministry of education Department of Materials Science and Engineering Tsinghua University Beijing 100084 China 5. beijing National Center for Electron Microscopy Tsinghua University Beijing 100084 China

The LaMn1-xTexO3+δ (x=0.1, 0.2, 0.3) were synthesized using solid-state reaction method for the first time. X-ray photoemission spectrum (XPS) shows that in the samples the Te ions have a valence of Te4+, and Mn3+ ions are partly converted into Mn2+ and Mn4+ due to the excess oxygen and Te doping. The magnetotransport associated with Mn2+, Mn3+ and Mn4+ was investigated. The experimental results show that the samples are insulator at 0 T when the amount of Mn3+ is much larger or less than the sum of Mn2+ and Mn4+; by contrast, the samples display metal to insulator transition with increasing temperature when the amount of Mn3+ is close to the sum of Mn2+ and Mn4+. These anomalous magnetotransport behaviors were analyzed in the frame of the double-exchange (DE) mechanism.

关键词： colossal magnetoresistance La-Te-Mn-O magnetotransport

Thermodynamic Functions and Phase Transformation of Metal Nanocrystals

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Journal of materials science & Technology 2005年第5期21卷 705-709页

作者： Jinping GAO, Xiaoyan SONG , Jiuxing ZHANG, keyong YANG and Xuemei LIUCollege of materials science and engineering, the key laboratory of advanced Functional materials of the education ministry,beijing university of Technology, beijing 100022,{13. College of materials science and engineering the Key Laboratory of Advanced Functional Materials of the Education Ministry Beijing University of Technology Beijing 100022 China

A model to calculate the thermodynamic functions of the pure metal nanocrystals has been developed, with the consideration of the effects of both the interfaces and the crystal in the nano-grain interior. As an example, the enthalpy, entropy and Gibbs free energy, as functions of the excess free volume at interfaces, temperature and grain size, are calculated for the Co nanocrystals. Furthermore, the characteristics of β-Co→α-Co phase transformation are studied, and the transformation temperatures at different levels of grain size, as well as the critical grain sizes at different temperatures, are predicted. The calculation results show that, the nano-grained β-Co （fcc） is thermodynamically stable at temperatures much lower than that for the conventional coarse-grained materials, and may also stably exist at room temperature when the grain size is reduced to be small enough. The present model is verified by comparisons between the experimental findings and the theoretical predictions.

关键词： Thermodynamic function Nanocrystal Phase transformation

A Time-saving Method for Assessing the Corrosion Inhibitor Efficiency

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Journal of Wuhan university of Technology(materials science) 2010年第5期25卷 856-861页

作者：耿春雷翁端 key laboratory of advanced materials Department of Materials Science and Engineering Tsinghua University

Corrosion inhibitor is one of the most important technologies to enhance the durability of steel reinforced concrete. A kind of time-saving method was developed to assess the inhibitor efficiency by using a 16 voltage electric field to accelerate the chloride ion diffusion in concrete and inducing corrosion. Both macrocell and microcell current measurements were used to confirm the corrosion initiation status of steel. The comprehensive efficiency of inhibitor shall be assessed in three aspects. The results clearly show the efficiency of different inhibitors, which indicate the reliability of this time-saving method.

关键词： inhibitors efficiency chloride ions diffusion steel reinforced concrete

Probing the hydration of composite cement pastes containing fly ash and silica fume by proton NMR spin-lattice relaxation

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science china(Technological sciences) 2010年第6期53卷 1471-1476页

作者： SHE AnMing & YAO Wu key laboratory of advanced Civil engineering materials (Tongji university),ministry of education,Shanghai 200092,china 1. key laboratory of advanced Civil engineering materials (Tongji university) Ministry of Education Shanghai 200092 China

Proton NMR spin-lattice relaxation (T1) was used as a prober for observing the hydration process of composite cement pastes blending fly ash and silica fume during the early *** distribution at initial time,evolution curves and signals intensity of T1 were shown in this *** demonstrate that the T1 distribution curves at initial time exhibit two peaks,which are regarded as two different water phases in the *** evolution curves of T1 are in good agreement with the hydration process of composite pastes and could be roughly divided into four stages:initial period,dormant period,acceleration period and steady *** hydration mechanism for each stage was *** hydration of the composite cement pastes was retarded by the addition of fly ash and silica fume when compared to that of pure ***,the hydration degree of the cement in the blends was promoted.

关键词： NMR relaxation cement fly ash silica fume hydration

Molecular dynamics simulations of non-Fourier heat conduction

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Progress in Natural science:materials International 2008年第8期18卷 999-1007页

作者： Qixin Liu, Peixue Jiang *, Heng Xiang key laboratory for Thermal science and Power engineering of ministry of education, Department of Thermal engineering, tsinghua university, beijing 100084, china key laboratory for Thermal science and Power engineering of ministry of education Department of Thermal Engineering Tsinghua University Beijing 100084 China

Unsteady heat conduction is known to deviate significantly from Fourier’s law when the system time and length scales are within certain temporal and spatial windows of relaxation. Classical molecular dynamics simulations were used to investigate unsteady heat conduction in argon thin films with a sudden temperature increase or heat flux at one surface to study the non-Fourier heat conduction effects in argon thin films. The studies were conducted with both pure argon films and films with vacancy defects. The temperature profiles in the argon films showed the existence of mechanical waves when the thin film was suddenly heated and the wave nature of the heat propagation. The flux phase relaxation time, sq, and the temperature phase relaxation time, st, were calculated from the temporal variations of the energy flux and temperature distribution in the film. Comparisons of the MD temperature profiles with temperature profiles predicted by Fourier’s law show that Fourier’s law is not able to predict the temperature variations with time. Different film thicknesses were also studied to illustrate the variation of the time needed for the films to reach steady-state temperature profiles after a sudden temperature rise at one surface and to illustrate the finite speed of the energy waves.

关键词： Molecular dynamics simulation Non-Fourier heat conduction Argon thin film

Analysis of residual stress distribution along interface asperity of thermal barrier coating system on macro curved surface

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Progress in Natural science:materials International 2011年第3期21卷 262-267页

作者： Ming SONG,Yue MA,Sheng-kai GONG key laboratory of Aerospace materials and Performance(ministry of education), School of materials science and engineering,Beihang university,beijing 100191,china key laboratory of Aerospace materials and Performance (ministry of education) School of Materials Science and Engineering Beihang University Beijing 100191 China

Based on the study of the radial residual stress distribution on the macro curved interfaces of thermal barrier coating system(TBCs) for the hollow curved substrate structures,the hollow four-concentric-circle model was *** the concentric-circle model with a fine scaled sinusoidal interface was proposed to describe the stresses distribution on the rough interface of TBCs with macro curved *** influences of the geometric and thermophysical parameters were discussed by the developed *** results showed that the radial stress on the rough interface can be separated into two sections:the overall level stress from macro surface curvature and the local stress from local asperity of the *** overall level stress was determined by the thicknesses and the thermophysical parameters of each *** has been found that the ratio of local stress and overall level stress was influenced by the interface asperity,the ratio of elastic modulus and the ratio of thermal expansion coefficients of the layers beside the rough ***,the convex macro curvature of the substrate can induce tensile stress onto the *** at the sharp corners of the substrate,the small curvature radius can cause high stress which should be taken more care about the occurrence of spalling cracking at interface

关键词： barrier coating system(TBC) residual stress interface asperity thermal grown oxide(TGO) concentric-circle model

Effects of solidification parameters on microstructure and mechanical properties of continuous columnar-grained Cu-Al-Ni alloy

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Progress in Natural science:materials International 2011年第5期21卷 368-374页

作者： Zhen WANG,Xue-feng LIU,Jian-xin XIE key laboratory for advanced materials Processing,ministry of education, university of science and Technology beijing,beijing 100083,china key laboratory for advanced materials Processing Ministry of Education University of Science and Technology Beijing Beijing 100083 China

Effects of melt temperature and casting speed on microstructure and mechanical properties of Cu-14%Al-3.8%Ni(mass fraction) alloy wires fabricated by continuous unidirectional solidification technology were *** was found that the average size of columnar grain in the alloy decreased and grain boundary turned clear and straight with increasing the casting speed at a given melt *** the melt temperature was up to 1 280℃,theβ1phase gradually transformed into lozenged and lanciformγ’1martensite,as well as parallel-sided plateβ’*** alloy with numerous coarsely dendriticγ2phase has poor mechanical properties due to the difficulty of stress-induced martensitic *** the amount of theγ2phase reduced and the coarse dendriteγ2phase evolved into the fine square particles,the elongation of the alloy increased gradually with a decrease in tensile ***,the plasticity of the alloy could also be improved by increasing the amount and size of martensites,particularly the lanciformγ’*** the alloy was almost composed of coarse lanciformγ’1martensite,the tensile strength and elongation of the alloy could be up to 772 MPa and 18.9%,respectively,and the tensile curve consisted of three transformation platforms.

关键词： shape memory alloy continuous unidirectional solidification columnar grain martensitic transformation

Development of New Type Mn-Series Bainitic Steels in china

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Journal of Iron and Steel Research International 2011年第S1期18卷 112-120页

作者： BAI Bing-zhe,GAO Gu-hui,ZHENG Yan-kang,YANG Zhi-gang (key laboratory of advanced materials of ministry of education,Department of Material science and engineering,tsinghua university,beijing 100084,china) tsinghua Univ Dept Mat Sci & Engn Minist Educ Key Lab Adv Mat Beijing 100084 Peoples R China

The alloying design idea,strengthening-toughening mechanism,microstructure,mechanical performances,development and application in china of new type Mn-series bainitic steels are ***-series air-cooling bainitic steels including granular bainitic steels,FGBA /BG duplex steels,CFB/M duplex steels,medium carbon bainite/martensite steels,cast bainitic steels are *** invented idea mechanical performances,development and application of second generation of Mn-series bainitic steels,*** quenching Mn-series bainitic steels invented by the authors newly are *** water quenching Mn-series bainitic steels cover severe series steels containing ultra-low carbon,low-low carbon,medium-low carbon,and high-low carbon content etc,which can reduce the amount of alloying content,increase hardening capability and improve *** should be pointed out that the application of both air cooling and water quenching Mn-series bainitic steels are complementary and mutually reinforcing,and the new type Mn-series bainitic steels can meet the performance requirements of most steels used in engineering *** newest technologies of Mn-series bainitic steels in china are discussed in this *** is suggested that the significance of the development of the Mn-series bainitic steels can be summarized as:significantly reducing costs of both raw materials and production;good combination of strength and toughness;excellent weldability;simple procedure;large savings in energy resources and reduced environmental pollution.

关键词： bainitic steels strengthening-toughening mechanism low cost,high performances air cooling bainitic steel water quenching bainitic steel

Advances in Thermionic Cathode of Tungsten and Molybdenum

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Rare Metals 2001年第3期20卷 137-141页

作者： Jinshu Wang,Meiling Zhou, Tieyong Zuo, Juan Liu, Jiuxing Zhang, Zuoren Nie The key laboratory of advanced Functional materials, ministry of education, School of materials Scence and engineering, beijing Polytechnic university, beijing 100022, china beijing Polytech Univ Sch Mat Sci & Engn Minist Educ Key Lab Adv Funct Mat Beijing 100022 Peoples R China

Several kinds of tungsten thermonic cathodes have been introduced. As a promising alternative for thoriated tungsten, rare earth doped molybdenum cathode has been studied. Compared with the traditional thoriated tungsten, La-Mo cathode has higher emission current density at lower temperature, but it has poor emission stability. In order to improve the emission stability, systematical study on the emission mechanism of La-Mo cathode has been carried out. The life of La-Mo cathode has been improved and has achieved 1400 It, which exceeds the minimum life for practical uses (1000 h). As another alternative for thoriated tungsten cathode, Y-Mo cathode has shown better performance. The thermionic emission capability of Y-Mo cathode is between that of La-Mo cathode and Th-W cathode.

关键词： tungsten molybdenum thermonic cathode emission