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Low temperature synthesis of SiCN nanostructures

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Science China(Technological Sciences) 2009年第1期52卷 28-31页

作者： CHENG WenJuan ma xueming State Key Laboratory of Precision Spectroscopy East China Normal UniversityShanghai 200062China

Silicon carbon nitride (SiCN) nanowires, nanorods and nanotubes have gained much attention due to their excellent field emission and photoluminescence properties. These nanostructures were usually grown using catalysts at high temperature (800–1000 °C). In this paper, synthesis of SiCN nanostructures at a temperature less than 500°C is reported. Various kinds of SiCN nanostructures were synthesized using microwave plasma chemical vapor deposition method. Gas mixtures of CH4, H2 and N2 were used as precursors and Si chips were inserted in the sample holder at symmetrical positions around the specimen as additional Si sources. Metallic gallium was used as the liquid medium in a mechanism similar to vapor-liquid-solid. Morphologies of the resultant were characterized by field emission scanning electron microscopy. Energy dispersive spectrometry and X-ray photoelectron spectroscopy were used to characterize their compositions and bonding states.

关键词： SiCN gallium nanostructure low temperature

On U-ample ω-semigroups

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Frontiers of mathematics in China 2013年第6期8卷 1391-1405页

作者： Siyao ma xueming REN Ying YUAN Department of mathematics Xi'an University of Architecture and Technology Xi'an 710055China

The investigation of U-ample ω-semigroups is initiated. After obtaining some properties of such semigroups, a structure of U-ample ω-semigroups is established. It is proved that a semigroup is a U-ample ω-semigroup if and only if it can be expressed by WBR（T, 0）, namely, the weakly Bruck-Reilly extensions of a monoid T. This result not only extends and amplifies the structure theorem of bisimple inverse ω-semigroups given by N. R. Reilly, but also generalizes the structure theorem of ,-bisimple type A ω-semigroups given by U. Asibong-Ibe in 1985.

关键词： Bisimple inverse ω-semigroups weakly U-abundant semigroups,Ehresmann semigroups U-ample ω-semigroups

Amorphization of Co-Nb magnetic Alloys by Mechanical Alloying

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Chinese Physics Letters 1991年第8期8卷 436-438页

作者： ma xueming YUE Lanping DONG Yuanda Institute of Solid State Physics Academia SinicaHefei 230031

Formation of amorphous Co-Nb system by mechanical alloying(ma)in the composition range of Co_(25)Nb_(75)-Co_(70)Nb_(30) was studied by X-ray *** properties of the mechanically alloyed Co_(70)Nb_(30) powder were *** variation in H_(c) curve with milling time can be explained by two-stage mechanism involved in the milling *** results show that the amorphous powder prepared by ma is of good soft magnetic properties.

关键词： diffraction properties process

Microstructure and electrical properties of Y_2O_3-doped ZnO-based varistor ceramics prepared by high-energy ball milling

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Journal of University of Science and Technology Beijing 2007年第3期14卷 266-270页

作者： Hongyu Liu xueming ma Dongmei Jiang Wangzhou Shi College of Science Wuhan University of Science and Technology Wuhan 430081 China Department of Physics East China Normal University Shanghai 200062 China

Y2O3-doped ZnO-based varistor ceramics were prepared using high-energy ball milling （HEBM） and low-temperature sin- tering technique, with voltage-gradient of 1934-2197 V/mm, non-linear coefficients of 20.8-21.8, leakage currents of 0.59-1.04 μA, and densities of 5.46-5.57 g/cm3. With increasing Y2O3 content, the voltage-gradient increases because of the decrease of ZnO grain size; the non-linear coefficient and the leakage current improve but the density decreases because of more porosity; the donor con- centration and density of interface states decrease, whereas the barrier height and width increase because of the acceptor effect of Y2O3 in varistor ceramics.

关键词： inorganic materials electrical properties high-energy ball milling varistor microstructure low-temperature sintering zinc oxide yttrium oxide

Influence of Milling Conditions on the Mechanical Alloying of Fe-B Powders

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Journal of materials Science & Technology 1999年第2期15卷 137-142页

作者： Yang, Yuanzheng Li, Qiaoshen Zhu, Youlan ma, xueming Dong, Yuanda Guangdong Univ Technol Dept Mat Sci & Engn Guangzhou 510090 Peoples R China Shanghai Univ Dept Mat Sci & Engn Shanghai 200072 Peoples R China

Amorphous and nanostructural Fe-B alloys made by mechanical alloying of elemental Fe and amorphous B powders have been studied using X-ray diffraction, differential scanning calorimetry and Mossbauer spectroscopy. It has been shown that the milling conditions have a strong effect on the alloying. The single phase amorphous alloy, which is limited at nominal composition of Fe//6//0B//4//0, has been produced only by milling in Ar atmosphere and in other composition range the mixture of nanostructure Fe-like phase and Fe//2B compound with a little amorphous phase were obtained. While by milling in air atmosphere the introduction of oxygen in air may suppress the formation of amorphous phase, thus the compounds Fe//2B may be synthesized with no trace of amorphous phase. The crystallization temperatures of amorphous phase in the resultant products are higher than those of a single amorphous alloy Fe//6//0B//4//0, and hardly independent of the milling conditions and the composition. In addition, it is revealed that detectable B content in the final products is lower than the nominal composition of all the initial samples, which indicates that some B atoms may be located in the disordered interfacial regions of the nano-structural alloyed mixtures. (Edited author abstract) 12 Refs.

关键词： Iron alloys

Fabrication of ZnO-based thick film varistors with high potential gradient

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Rare Metals 2010年第4期29卷 390-395页

作者： KE Lei JIANG Dongmei ma xueming State Key Laboratory of Precision Spectroscopy Department of Physics East China Normal University Shanghai 200062 China

ZnO-based thick film varistors have been fabricated by Y203 doping and low-temperature sintering, of which the sample with the best electrical properties has a high potential gradient value of 3159.4 V/mm. The effects of Y2O3 doping concentration and sintering temperature on the potential gradient of the samples were systematically investigated. The results show that the sample with the best electrical properties can be obtained by doping 0.08 mol% Y2O3 and sintering at 725℃. Under these optimum preparation conditions, the leakage current and the nonlinear coefficient are found to be 36.4 gA and 13.1. The sample with the best electrical properties has a grain size of 1.290um, a single grain boundary voltage of 4.08 V, a barrier height of 0.81 eV, and a depletion layer width of 10.2 nm, which are determined by thermionic emission. Small grain size with good grain boundary characteristics is beneficial to improve the electrical properties of varistors and promote the potential gradient.

关键词： condensed matter physics thick film varistors low-temperature sintering doping potential gradient

Evaluation model for arc fluctuations of triple-electrode high speed fillet welding

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China Welding 2014年第2期23卷 17-21页

作者： ma Xiaoli Hua xueming Wang Fei Wu Yixiong School of materials Science and Engineering Shanghai Jiao Tong UniversityShanghai 200240

To improve the welding efficiency of conventional arc welding, triple-electrode fillet welding was proposed and developed. Stability of triple-electrode fillet welding process is the assurance for ideal joint. The evaluation model for arc fluctuations of triple-electrode fillet welding was established based on the characteristic parameters and their variation coefficients. This model indicated that variation coefficients could reflect arc voltage flnctuations of welding process, and its analysis result was consistent with the actual welding process.

关键词： process stability variation coefficient triple-electrode fillet welding

Investigation of Amorphization of Nb-Si Alloys by Mechanical Alloying

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Chinese Physics Letters 1994年第11期11卷 681-684页

作者： LI Bing ma xueming LIU Lin QI Zhenzhong DONG Yuanda Institute of Solid State Physics Academia SinicaHefei 230031 Department of Metallurgy and materials Shanghai University of TechnologyShanghai 200072

Amorphous Nb_(62.5)Si_(37.5) and Nb_(75)Si_(25) alloys were produced from mixtures of elemental Nb and Si powders by mechanical alloying(ma).The structural changes of mechanically alloyed powders were monitored by x-ray *** was found that NbSi_(2),intermetallic compound was formed in the initial stage of ma of or Nb_(62.5)Si_(37.5) or Nb_(75)Si_(25) *** continued milling,the mixtures of intermetallic NbSi_(2) and elemental Nb transformed into amorphous Nb-Si alloys(Nb_(62.5)Si_(37.5) or Nb_(75)Si_(25)).The slow interdiffusion of Nb and Si and the slower diffusion of silicon atoms to niobium matrix than that of niobium atoms to silicon matrix were suggested to be responsible for the formation of intermetallic NbSi_(2).The amorphization of 3NbSi_(2)+7Nb mixtures(or NbSi_(2)+5Nb mixtures)is believed to be controlled by material transfer,which moves composition of line intermetallic NbSi2 off stoichiometry,and causes the matrix of elemental Nb deformed.

关键词： intermetallic alloys alloying

Nb_2O_5-carbon core-shell nanocomposite as anode material for lithium ion battery

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Journal of Energy Chemistry 2013年第3期22卷 357-362页

作者： Ge Li Xiaolei Wang xueming ma Department of Physics East China Normal University Department of Chemical and Biomolecular Engineering University of CaliforniaLos AngelesCA 90095United States

Nb2O5-carbon nanocomposite is synthesized through a facile one-step hydrothermal reaction from sucrose as the carbon source, and stuclled as an anode material for high-performance lithium ion battery. The structural characterizations reveal that the nanocomposite possesses a core-shell structure with a thin layer of carbon shell homogeneously coated on the Nb2O5 nanocrystals. Such a unique structure enables the composite electrode with a long cycle life by preventing the Nb2O5 from volume change and pulverization during the charge-discharge process. In addition, the carbon shell efficiently improves the rate capability. Even at a current density of 500 ma.g-1, the composite electrode still exhibits a specific capacity of ~100 mah.g-1. These results suggest the possibility to utilize the Nb2O5-carbon core-shell composite as a high performance anode material in the practical application of lithium ion battery.

关键词： niobium pentoxide core-shell long cycle life high performance anode lithium ion battery