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Luo Q.,Yunnan University | Gan G.-Y.,Kunming University of Science and Technology | Gan G.-Y.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Gan G.-Y.,Key Laboratory of Advanced Materials of Yunnan Province
Dongbei Daxue Xuebao/Journal of Northeastern University | Year: 2012

The silver powder as a conductive phase in the silver paste mainly plays the role of conducting electricity. The composition, morphology, particle sizes and concentration of the conductive phase have relatively large influences on the electrical properties of the silver paste. The influences of the morphology, concentration and gradation of the different silver powders on the properties of the silver paste were studied and the conductivity mechanism of the silver film was also discussed. The results showed that the conductive properties of silver films were effectively increased by the addition of flake silver powder. When the content of the flake silver powder reached 80% (in mass) of the total sliver powders, square resistance reduced from 15.65 mΩ/□ with only spherical silver powder to 7.41 mΩ/□. When the mass percentage of the mixed silver powders as a conductive phase was 73% in the sliver paste, the conductive properties of the silver film was the best.


Liang Z.,Kunming University of Science and Technology | Liang Z.,Key Laboratory of Advance Materials of Yunnan Province | Liang Z.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Gan G.Y.,Kunming University of Science and Technology | And 17 more authors.
Advanced Materials Research | Year: 2014

Based on the density functional theory, the geometrical structure optimization and electronic structure of ZnO (1120) surfaces were calculated. ZnO (1120) surfaces in the structural relaxation, electron density difference, densities of states and the Ti adsorption were analyzed by using the first-principles and pseudopotential method. According to the computing result, the geometrical structures of the unabsorbed ZnO (1120) surfaces and the Ti-adsorbed ZnO (1120) surfaces are similar. When Ti adsorbs ZnO (1120) surfaces, the negative charge density is special high in the central region between Ti and O. Ti-O shows obviously better performance than Zn-O in covalent bond. The Ti-adsorbed ZnO (1120) surfaces have metallic characteristics because of the number of outer electron transferred from Ti to O is extremely limited and the area of negative charge of the surface is large. © (2014) Trans Tech Publications, Switzerland.


He X.X.,Kunming University of Science and Technology | He X.X.,Key Laboratory of Advanced Materials of Yunnan Province | He X.X.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Gan G.Y.,Kunming University of Science and Technology | And 20 more authors.
Advanced Materials Research | Year: 2014

The ZnO varistor ceramics were fabricated from ZnO powder and Ti-doped ZnO powder by microwave sintering process at 800 ~ 1150°C. The effects of milling time, sintering temperature and doping on microwave sintering technique have been studied. The results show that the powder is more homogeneously and smalle with the increasing of milling time, therefore the electric properties is improved. However the particle size and the electric properties tend towards stability after 20h milling time. The density and electric properties increase with the increasing of sintering temperature, but decrease sharply at 1100°C. So the better sintering temperature is 1100°C. TiO2 Doping improves the electric properties of ZnO, however the electric properties decrease with more than 2.5% doping. © (2014) Trans Tech Publications, Switzerland.


Fan M.Y.,Kunming University of Science and Technology | Fan M.Y.,Key Laboratory of Advance Materials of Yunnan Province | Fan M.Y.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Gan G.Y.,Kunming University of Science and Technology | And 20 more authors.
Advanced Materials Research | Year: 2014

The content and particle size of the Na - Ca System glass powder have significant effects on the properties of the silver paste. The effects of the sintering temperature, holding time, glass powder content and glass powder size on the adhesion and square resistance of the silver film were studied. The conductive network of the silver film was observed by SEM. The research results show that the silver paste with 6 wt.% content of the 2.47μm glass powder sintered at 680°C for 7 minutes have good properties. The adhesion strength and square resistance of the silver film are respectively 2.5 N/mm2 and 14 mΩ /. © (2014) Trans Tech Publications, Switzerland.


Zhang L.,Kunming University of Science and Technology | Zhang L.,Key Laboratory of Advance Materials of Yunnan Province | Zhang L.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Du J.,Kunming University of Science and Technology | And 11 more authors.
Advanced Materials Research | Year: 2012

Porous alumina insulation materials were prepared by the combination method of gelcasting and foaming. The effects of the amount of blowing agent, the solid volume, and the sintering temperature on porosity of aluminum oxide ceramic were studied. The result showed that, when the amount of blowing agent is 1wt %, the solid volume is 45 vol % and the sintering temperature is 1500°C, the porous alumina ceramics with high porosity, small pore diameters, evenly distributed, high bending strength and low heat conductance can prepared.


Feng J.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Feng J.,Kunming University of Science and Technology | Xiao B.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Xiao B.,Kunming University of Science and Technology | And 6 more authors.
Procedia Engineering | Year: 2012

White cast iron has been widely used as a wear resistance material for a long time in many industrial applications. It is well-known that the elastic properties of the alloy can be greatly affected by reinforced particles or precipitated phases. For white cast iron, the precipitated carbides usually refer to Fe 2C, Fe 3C, Fe 23C 7, etc. In practice, small amount of Cr and B is added into ordinary white cast iron in order to stabilize Fe xC-type carbides, as a result, the obtained carbides can be represented as (Fe, Cr) x C(B). When compared with the ordinary white cast iron, the elastic performance of Cr cast iron is enhanced. In recent years, first principles calculations based on density functional theory (DFT) have become a powerful tool to investigate the electronic, stability and mechanical properties of condensed matter. It is very suitable to study the equilibrium properties of compounds that cannot be synthesized on a large scale or are very difficult to obtain enough samples for mechanical tests. We have also used first principles calculations to compare the ground state properties of these compounds, but our main emphasis is on the mechanical aspect. The calculated mechanical properties of Cr 7C 3, Fe 2B and Fe 3C may be extremely useful for us to clearly understand the origin of such mechanical performance, because the mechanical response of solids, as we knew, is determined by chemical bonding among distinct atoms. © 2011 Published by Elsevier Ltd.


Yan F.C.,Kunming University of Science and Technology | Teng Y.,Kunming University of Science and Technology | Yan J.K.,Kunming University of Science and Technology | Du J.H.,Kunming University of Science and Technology | And 3 more authors.
Materials Science Forum | Year: 2016

In order to study the effects of composition ratio of silver paste and the sintering process on the properties of the silver film after sintering, the effects of different ratios of silver powders, glass powders and organic carrier in silver paste and different sintering temperatures and sintering time on the adhesion force and square resistance of the silver film were studied. The morphology of the sintered silver film was observed by SEM. The results showed that the silver film sintered at 760°C for 6 seconds had better properties after sintering when the ratio of silver powders, glass powders and organic carrier in silver paste was 80:5:15 and the silver powders was composed of spherical silver powders and flake silver powders at the ratio of 94:6. The adhesion force and square resistance of the silver film were 8.25 N and 3.47mΩ /□, respectively. © 2016 Trans Tech Publications, Switzerland.


Yang J.,Kunming University of Science and Technology | Yang J.,Key Laboratory of Advanced Materials of Yunnan Province | Yang J.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Yang J.,Kunming Key Laboratory of Advanced Materials of Precious Nonferrous Metals | And 24 more authors.
Materials Science Forum | Year: 2016

To lower the sintering temperature of ZnNb2O6 microwave dielectric ceramic, ZnNb2O6 doped with B2O3 were prepared by the traditional solid state reaction method. The effects of the amount of B2O3 (0.25-5.0wt.%) on the microstructure, density and electrical performances were investigated. The results show that a pure columbite ZnNb2O6 phase was obtained for all B2O3-doped ceramics. The microwave dielectric properties reached the maximum values of εr = 24.1, Q×f = 19502 GHz, τf = -52.19 ppm/℃ for 1wt% B2O3-doped ZnNb2O6 ceramic sintered at 1050 ℃ for 4 h. All of evidences suggest that the enhancement of microwave dielectric properties is due to the enhanced ions-energy and ionic diffusion with the increase of sintering temperature. Furthermore, B2O3 doping can generate liquid phase and reduce the activation energy of diffusion to promote the materials sintering. © 2016 Trans Tech Publications, Switzerland.


Kang K.,Kunming University of Science and Technology | Kang K.,Key Laboratory of Advanced Materials of Yunnan Province | Kang K.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Yan J.,Kunming University of Science and Technology | And 14 more authors.
Ceramics International | Year: 2016

The influence of doping with Ge on the nonlinear coefficient α and the breakdown electric field EB of TiO2-Ta2O5-CaCO3 varistor ceramics was investigated. In this study, TiO2-Ta2O5-CaCO3 varistor ceramics added with Ge was successfully prepared using the traditional method of ball milling-molding-sintering. The electrical performance, including the nonlinear coefficient α, the breakdown electric field EB, and the leakage current JL, are tested using a varistor direct current parameter instrument. The average barrier height ΦB of each sample is calculated using the relevant formula. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and scanning transmission electronic microscopy analyses demonstrated that Ge doping notably changed the microstructure of TiO2-Ta2O5-CaCO3 ceramics, thereby increasing α and decreasing EB. When the doping contents of Ta2O5 and CaCO3 were 0.2 and 0.4 mol%, respectively, the optimum doping content of 0.9 mol% Ge exhibited high α (10.2), low EB (14.1 V mm-1), and high ΦB (0.95 eV). These results are superior to previous findings. In addition, Ge as sintering aid reduced the sintering temperature caused by the low melting point. The optimal sintering temperature was 1300 °C for the TiO2-Ta2O5-CaCO3 ceramics doped with Ge. © 2015 Elsevier Ltd and Techna Group S.r.l.


Xiao B.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Xiao B.,Xi'an Jiaotong University | Feng J.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Zhou C.T.,Xi'an Jiaotong University | And 4 more authors.
Physica B: Condensed Matter | Year: 2010

The first principles calculations are performed to investigate the elastic constants and thermodynamic parameters of X2B compounds. The calculated elastic constants for these borides indicate that they are mechanically stable structures. The bulk modulus of them range from 230 to 310 GPa and the largest bulk modulus value is attributed to W2B. Furthermore, the scale relation between C44 and bulk modulus is observed in our case. Heat capacity is calculated based on Debye's quasi-harmonic approximation, and we decomposed the heat capacity into two contributions to find that electron excitations dominated the heat capacity at low temperatures. The hardness of X-B and B-B bonds is calculated using a semi empirical hardness theory. © 2009 Elsevier B.V.

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