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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 & {2. Modification of the {2. 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 1. key laboratory of Beam Technology & {2. Modification of the {2. 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 {2. {2. 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

A Time-saving Method for Assessing the Corrosion Inhibitor Efficiency

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Journal of Wuhan university of Technology(materials{2.) 2010年第5期25卷 856-861页

作者：耿春雷翁端 key laboratory of {2. {2. 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

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 {2. and Power {2. of ministry of education, department of Thermal {2., tsinghua university, beijing 100084, China key laboratory for Thermal {2. and Power {2. 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

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 {2. and {2., the key laboratory of advanced Functional materials of the education ministry,beijing university of Technology, beijing 10002., China College of materials science and{2. 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

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 {2. {2. of ministry of education,department of Material science and engineering,tsinghua university,beijing {12.,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

Preparation of MWNTs/Al_2._3 composites and their mechanical and electrical properties

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science China(Technological sciences) 2005年第6期48卷 622-631页

作者： FAN Jinpeng1,2. ZHAO Daqing1,2. XU Zening1,2.& WU Minsheng1,2.1. department of Mechanical engineering,{2., beijing 100084, China 2. key laboratory for advanced Manufacturing by materials Processing Technology,{2., beijing 100084, China 1. department of Mechanical engineering Tsinghua University 100084 Beijing China 2. key laboratory for {2. Manufacturing by {2. Processing Technology Tsinghua University 100084 Beijing China

The mechanical and electrical properties of MWNTs/Al2.3 composite prepared fabricated by hot pressing are investigated. The relation between properties and microstructure of composites is also discussed. With 4wt% MWNTs as reinforcement, the fracture toughness of composite obtained reaches 5.55 MPa·m1/2. which is 80% higher than that of pure Al2.3 obtained in the same conditions. The main toughening mechanism is CNTs’ pinning alumina grain boundaries, and the pullout of CNTs takes effect also. Through adding 2.t% MWNTs and altering the mix method, the fracture toughness of the composite obtained is 3.97 MPa·m1/2. Furthermore, the electrical resistivity is as low as 8.4×10?3 ?·m, decreasing by 14 orders of magnitude compared with pure alumina ceramics. The function of CNTs in composite is related to the distribution state of CNTs in composite, and the distribution state of CNTs in matrix is dependent on preparation procedures.

关键词： MWNTs, alumina, composite, fracture toughness, electrical properties.

Improvement of water resistance of long afterglow SrAl_2._4: Dy, Eu phosphor by coating with SiO_2.film

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Rare Metals 2002年第2期21卷 152-155页

作者： ZHANG Junying, CHEN Qingming, LIN Yuanhua, and ZHANG ZhongtaiState key laboratory of New Ceramics and Fine Processing,{2., tsinghua university,beijing 100084, China department of materials{2. and engineering Tsinghua University State Key Laboratory of New Ceramics and Fine Processing 北京 100084

The long afterglow SrAl_2._4: Dy, Eu phosphor is liable tohydrolyze in water with deterioration of the lumin- escent ***_2._4: Dy, Eu phosphors were therefore heated at 60-90 deg. C inTEOS sol to form a surface gel and then heat-treated at 400 deg. C toobtain SiO_2.coated phosphors. Observation by ?Transmission ElectronMicroscope (TE) and X- ray photoelectron spectroscopy (XPS) showsthat a thin silica film forms on the surface of the phosphors. Thecoating procedure can be illustrated by a four-step process and thetransparent silica film can suppress the hydrolysis process, so thatthe luminescent properties of the phosphors are unimpaired or evenbetter.

关键词： phosphors coating luminescent materials SrAl_2._4

CO_2.Mitigation in Coal Gasification Cogeneration Systems with Integration of the Shift Reaction, CO_2.Absorption and Methanol Production

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Journal of Thermal science 2004年第3期13卷 193-198页

作者： Yuanyuan DUAN Jin ZHANG key laboratory of Thermal {2. and Power {2., department of Thermal {2., tsinghua university, beijing 100084, China key laboratory of Thermal {2. and Power {2. Department of Thermal Engineering Tsinghua University Beijing China

Cogeneration of electricity and liquid fuel can achieve higher efficiencies than electricity generation alone in Integrated Gasification Combined Cycle (IGCC), and cogeneration systems are also expected to mitigate CO2.emissions. A proposed methanol-electricity cogeneration system was analyzed in this paper using exergy method to evaluate the specified system. A simple cogeneration scheme and a complicated scheme including the shift reaction and CO2.removal were compared. The results show that the complicated scheme consumes more energy, but has a higher methanol synthesis ratio with partial capture of *** those methanol and electricity cogeneration systems, the CO2.mitigation is not merely an additional process that consumes energy and reduces the overall efficiency, but is integrated into the methanol production.

关键词： cogeneration system methanol synthesis CO2 mitigation exergy analysis

Numerical Simulation of Macrosegregation During Steel Ingot Solidification Using Continuum Model

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Journal of Shanghai Jiaotong university(science) 2011年第2期16卷 145-148页

作者：王励石伟 key laboratory for {2. {2. Processing Technology Ministry of Education department of Mechanical engineering Tsinghua University

A continuum model is adopted to study the macrosegregation phenomena during solidification of large steel *** of temperature,melt velocity,and compositional concentration field during a 2. t steel ingot solidification are illustrated by using the finite volume *** results of temperature distribution are validated by *** influence of local permeability relates to the friction that the melt experienced in mushy region is *** is shown that the continuum model is able to predict the temperature field,and the variation of permeability obviously affects the melt flowing behavior and the final compositional distribution.

关键词： continuum model steel ingot macrosegregation convection permeability