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Characterization of ZnO Based Varistor Derived from Nano ZnO Powders and Ultrafine Dopants

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Journal of materials science & Technology 2005年第2期21卷 183-186页

作者： Weizhong YANG, Dali ZHOU, Guangfu YIN, Runsheng WANG and Yun ZHANG College of material science and engineering, Sichuan University, Chengdu 610064, china Coll. of Mat. Sci. and Eng. Sichuan Univ. Chengdu 610064 China

Nanosized ZnO powders were prepared with a two-step precipitation method. The average size of ZnO particles was about 80 nm and their size distribution was narrow. Combining with ultrafine additive powders, ZnO base varistor was produced via an oxide mixing route. ZnO varistor derived from normal reagent grade starting materials was investigated for comparison purpose. Outstanding microstructure of the ZnO varistor derived from nanosize ZnO powders and ultrafine dopants was obtained: uniform distribution of fine ZnO grains (less than 3 microns), grain boundary and the dopant position. Higher varistor voltage (U=492 V/mm) and nonlinear coefficient (α=56.2) as well as lower leakage current (TL=1.5 μuA) were achieved. The better electrical properties were attributed to the uniform microstructure, which in turn led to stable and uniform potential barriers. Also this improved technique is more feasible for producing ZnO nanopowders and resulting varistor in large scales.

关键词： Zinc oxide (ZnO) Varistor Nanopowders Ultrafine dopants Two-step precipitation

Microstructure evolution of single crystal copper wires in cold drawing

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science china(Technological sciences) 2007年第6期50卷 736-748页

作者： CHEN Jian1,2, YAN Wen1,2, WANG XueYan2 & FAN XinHui2 1 Department of Applied Physics, Northwestern Polytechnical University, Xi’an 710072, china 2 School of material science and Chemical engineering, Xi’an Technological University, Xi’an 710032, china 1. Department of Applied Physics Northwestern Polytechnical University Xi’an 710072 China 2. School of material science and Chemical engineering Xi’an Technological University Xi’an 710032 China

The deformation microstructure evolution of single crystal copper wires produced by OCC method has been studied with the help of TEM, EBSD; OM. The results show that there are a small number of dendrites; twins in the undeformed single crystal copper wires. However, it is difficult to observe these dendrites in deformed single crystal copper wires. The structure evolution of deformed single crystal copper wires during drawing process can be divided into three stages. When the true strain is lower than 0.94, macroscopic subdivision of grains is not evident,; the microscopic evolution of deformed structure is that the cells are formed; elongated in drawn direction. When the true strain is between 0.94; 1.96, macroscopic subdivision of grains takes place,; the number of microbands located on {111}; cell blocks is much more than that with the true strain lower than 0.94. When the true strain is larger than 1.96, the macroscopic subdivision of grains becomes more evident than that with the true strain between 0.94; 1.96,; S-bands structure; lamellar boundaries will be formed. From EBSD analysis, it is found that part of 100 texture resulting from solidifying is transformed into 111; 112 due to shear deformation, but 100 texture component is still kept in majority. When the true strain is 0.94, the misorientation angle of dislocation boundaries resulting from deformation is lower than 14°. However, when the true strain arrives at 1.96, the misorientation angle of some boundaries will be greater than 50°,; the peak of misorientation angle distribution produced by texture evolution is located in the range between 25°; 30°.

关键词： single crystal copper wires, deformation structure, electron backscattering diffraction, transmission electron microscopy

Texture Evaluation of α_2 Phase in Ti-25Al-10Nb-3V-1Mo Alloy Sheet

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Journal of materials science & Technology 1996年第5期12卷 361-364页

作者： Weimin MAO Yongning YU Hong YANG and Bo SONG (dept. of materials science and engineering, University of science and Technology Beijing, Beijing 100083, china) dept. of materials science and engineering University of Science and Technology Beijing Beijing 100083 China

The texture evaluation of α2 phase in Ti-25Al-10Nb-3V-1Mo sheet during rolling and annealing has been investigated by means of microstructure observation and ODF analysis. From the weak initial {1010} (1210) and {0001}(1210) textures a {1210}(1010) texture and a {0001}(uvtw)fibre texture are formed after cold rolling. The {0001} (1210) texture is also strengthened simultaneously. The activation process of slip systems is discussed concerning formation of the rolling texture. Because of the disappearance of {0001} (nvtw) fibre texture the primary recrystallization process should occur and the {1210}(1010) texture forms during annealing

关键词： Al Phase in Ti-25Al-10Nb-3V-1Mo Alloy Sheet Ti Mo Texture Evaluation of

Dry Friction Characteristics of Ti-6Al-4V Alloy under High Sliding Velocity

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Journal of Wuhan University of Technology(materials science) 2007年第4期22卷 582-585页

作者：邱明 School of Mechatronic engineering Henan University of Science and Technology Theory of Lubrication and Bearing Institute Xi'an Jiaotong UniversityXi'an 710049China

Tribological behaviours of Ti-6Al-4V alloy pins sliding against GCr15 steel discs over a range of contact pressures （0.33-1.33 MPa） and sliding velocities （30-70 m/s） were investigated using a pin-on-disc tribometer under unlubricated conditions. The wear mechanisms and the wear transition were analyzed based on examinations of worn surfaces using SEM, EDS and XRD. When the velocity increases, the friction coefficient and the wear rate of the Ti-6Al-4V alloy show typical transition features, namely, the critical values of sliding velocities for 0.33 and 0.67 MPa are 60 and 40 m/s, respectively. The experimental results reveal that the tribological behaviours of Ti-6Al-4V alloys are controlled by the thermal-mechanical effects, which connects with the friction heat and hard particles of the pairs. A tribolayer containing mainly Ti oxides and V oxides is formed on the worn surface of Ti-6Al-4V alloy.

关键词： Ti alloy dry sliding friction behavior contact temperature wear mechanism

Special Orientation Relationships Observed at the Early Stages of Recrystallization in Pure AlMn Alloy

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International Journal of Minerals,Metallurgy and materials 1998年第3期12卷 140-146页

作者： Ping Yang(material science and engineering School, University of science and Technology Beijing, Beijing 100083, china)(Institute for Metal science and Metal Physics, Aachen University of Technology, D-52056, Aachen, Germany) material science and engineering School University of Science and Technology Beijing Beijing 100083 China Institute for Metal science and Metal Physics Aachen University of Technology D-52056 Aachen Germany

Electron Back Scattering Diffraction (EBSD) technique in a SEM was used to obtain local orientationalinformation on new grains and their surrounding deformed matrices at the early stages of recrystallization in pureA1-1 .3%Mn alloy. Results show that special orientation relationships including twin-relationship often exist betweennew grains, between new grains and deformed grains or between deformed grains. The occurrence of such specialorientation relationships is attributed to the special deformation behavior in the samples with large initial grain *** formation of recrystallization twins is discussed in a different way to those of traditional ones.

关键词： Orientation relationship recrystallization AlMn, EBSD

GTA Welds of Iron-Aluminide Based Alloys

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Journal of University of science and Technology Beijing 2001年第1期8卷 39-42页

作者： Dechun Gao, Wangyue Yang, Min Dong, Jihua Huang, Yuanding Huang, Zuqing Sun material science and engineering School, University of science and Technology Beijing, Beijing 100083, china Univ Sci & Technol Beijing Sch Mat Sci & Engn Beijing 100083 Peoples R China

The weldability of two Fe3Al-based intermetallic alloys and one Fe-16%Al-based (atom fraction) alloy has been investigated for gas tungsten are (GTA) welding on sheets with a thickness of 2 mm. The results indicated that pre-heating and post-annealing treatment were important procedures for retarding cold crack initiation and the propel selection of filler could effectively improve the weldability. For the same alloys with the same welding filler, it is better to choose lower welding current, in another word, lower heat input.

关键词： iron-aluminide gas tungsten arc welding weldability filler

MICROMECHANICAL MODELLING OF STRAIN SOFTENING IN MICROCRACK-WEAKENED QUASI-BRITTLE materialS

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Acta Mechanica Solida Sinica 1995年第2期8卷 121-132页

作者： Feng Xiqiao Yu Shouwen(dept.of engineering Mechanics,Tsinghua University,Beijing 100084,P.R.china) dept. of engineering Mechanics Tsinghua University Beijing 100084 China

By using the concept of domain of microcrack growth(DMG),the micromechanisms of damage in quasi-brittle materials subjected to triaxial either tensile or compressive loading are investigated and the complete strew-strain relation including four stages is obtained from micromechanical *** regime of pre-peak nonlinear hardening corresponds to the distributed damage,*** stable propagation of *** the attainment of the ultimate strength of load-bearing capacity, some microcracks experience the second unstable growth and the distributed damage is transmitted to the localization of *** analyses improve our understanding of the hardening and softening behaviors of quasi-brittle materials.

关键词： microcracks strain softening constitutive relation micromechanical damage mechanics brittle material

Oxygen Permeability of Polypropylene Containing Polyisobutene with Magnesium Acetate

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International Journal of Minerals,Metallurgy and materials 2000年第2期14卷 118-121页

作者： Wei Tian Raymond T. Woodhams(material science and engineering School, University of science and Technology Beijing, Beijing 100083, china)(dept. of Chemical engineering and Applied Chemistry, University of Toronto, Torono M5S IA4, Canada) Univ Sci & Technol Beijing Sch Mat Sci & Engn Beijing 100083 Peoples R China Univ Toronto Dept Chem Engn & Appl Chem Toronto ON M5S 1A4 Canada

The oxygen permeabilities of polypropylene films are reduced by adding a minor percentage of a polyisobutene ionomer. The polyisobutene ionomers were prepared by in situ salt exchange of magnesium acetate with maleated polyisobutenes of commercially available low relative molecular mass. The more polar magnesiurn salts aided phase separaion during crystallization from the molten polypropylene mixtusre. Scanning electron microscope photographs revealed that the polyisobotene ionomer is largely concentratd in the amorphous regions between the polypropylene spherulites, where the ionomer tends to concentrate during crystallization. The influence of the polyisobutene ionomer on the oxygen permeability of polypropylene was found to be slightly dependent upon the relative molecular mass of the polyisobutene precursor. Under optimum conditions, the oxygen permeability of polypropylene is reduced by 20%with only 1% additive.

关键词： oxygen permeability polypropylene polyisobutene

Analysis of variance for testing method of cement in determination of strength

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Progress in Natural science:materials International 2011年第4期21卷 341-346页

作者： Hong HUANG,Xiao-dong SHEN State Key Laboratory of materials-Oriented Chemical engineering,College of material science and engineering, Nanjing University of Technology,Nanjing 210009,china State Key Laboratory of materials-Oriented Chemical engineering College of Material Science and Engineering Nanjing University of Technology Nanjing 210009 China

The statistical tools such as descriptive statistics,full factorial design and analysis of source of variation were used to identify the potential factors that impact the validity of testing method for determining the strength of *** results showed that personal error impacted both accuracy and precision of test *** time associated with temperature fluctuation resulted in strength variation but did not impact the precision of test in all curing *** compactions did not impact the precision of test but resulted in the strength variation on 3 d and 28 d *** methods for the initial moist air curing significantly impacted the precision of testing method and resulted in the strength variation of cement on 1 d.

关键词： testing method of cement analysis of variance strength accuracy precision