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Key engineering materials
Trans Tech Publications Ltd.
Key engineering materials

Trans Tech Publications Ltd.

半月刊

1013-9826

Key engineering materials/Journal Key engineering materials
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    Effects of the Starting Powders on Microstructure and Properties of Porous Silica Ceramics

    Zhou LizhongWang Chang-AnHuang Yong
    674-677页
    查看更多>>摘要：Porous silica ceramics with above 70% porosity were fabricated by gelcasting process using tert-butyl alcohol (TBA) as solvent. Two types of starting powders, α-silica and fused silica, were chosen to fabricate porous silica ceramics. According to XRD analysis, only single α-cristobalite phase can be identified in the sintered samples. SEM observation showed that highly porous skeleton formed by the bonding of molten ceramic particles in porous silica ceramics. Comparing to the samples using α-silica as starting materials, a compressive strength of 6.30MPa was achieved at a porosity of 70.7% when using fused silica as starting materials. A relatively high specific surface area higher than 10m~2/g was obtained for both samples, which should be suitable for catalysis applications as catalyst supports.
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    Preparation and Grain Growth of Pb(Zr_(0.95)Ti_(0.05))O_3 Porous Ceramics Prepared by One-Step Pyrolysis Process Using Non-Aqueous Pechini Method

    Huiqing FanShaojun Qiu
    678-681页
    查看更多>>摘要：Pb(Zr_(0.95)Ti_(0.05))O_3 powders were prepared by one-step pyrolysis process from non-aqueous Pechini method. Porous Pb(Zr_(0.95)Ti_(0.05))O_3 ceramics were obtained by sintering the chemically prepared powders and the grain growth in the porous ceramics was investigated. For the powders calcined at 450℃ for 10 h by one-step pyrolysis process, the grain growth exponent value was observed to be 3.3 while the apparent activation energy was 193 kJ/mol.
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    Preparation of porous mullite ceramics Using Al as Foaming Agent

    Jiazhi YinJiachen LiuAnran GuoDi Song...
    682-683页
    查看更多>>摘要：Effects of Al in different added condition on pores shape and mullite configuration were investigated. Three sorts of hole were got by using Al as foaming agent in mullite composites. It was concluded that isolated holes could be formed by Al changing to Al_2Ol_3 with acidity condition in green state, open holes could be formed by Al changing to Al_2O_3 directly in sintering process, and mixed hole of isolated and open ones could be formed by Al changing to Al(OH)_3 with alkalescence condition in green state followed changing to Al_2O_3 in sintering process. These holes could supply a position for growth of mullite as well.
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    Preparation and Properties of Porous Diamond Preforms

    Yinghu DongXinbo HeRafi-ud-dinCaiyu Guo...
    684-688页
    查看更多>>摘要：A binder comprising of 60% PW (paraffin wax), 10% HDPE (high-density polyethylene), 12% PS (polystyrene), 13% PPR (random-polypropylene), and 5% SA (stearic acid) has been selected and successfully employed to fabricate the diamond preforms possessing high strength and well shape retention capability. Various effects of processing methods on the properties of the diamond preforms have been investigated. The results indicate that the binder consisting of PW-HDPE-PS-PPR-SA possesses excellent comprehensive rheological properties and is more appropriate as the organic vehicle for fabricating porous diamond preform. It has been evaluated that the mixing of 140μm size diamond particles with 20μm size diamond particles in the weight proportion of 3:1 provides the best particle size distribution for preparation of diamond preforms. It is also observed that impregnation of preform with 1.7wt (SiO2)% water glass and subsequently heat-treated in vacuum at 800℃ for 40min yields in high strength (with the strength of 7.1 MPa) diamond preform for infiltration. The strengthened preforms have been observed to possess an excellent shape maintaining capability. It is concluded that the diamond-copper composites fabricated by utilizing this high strength preform through hot-press infiltration method have high relative density of 96.4% and thermal conductivity of 300W.m~(-1).K~(-1).
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    Effects of Infrared Scattering Powders on the Thermal Properties of Porous SiO_2 Insulation Material

    Shi XingZhang ShichaoChen YufengLi Maoqiang...
    689-692页
    查看更多>>摘要：Porous SiO_2 insulation material was made by wet process. Fibrous xonotlite crystal and glass fiber were used as reinforced fibers, and graphite, zirconia and titania powders were added as infrared scattering materials into the porous SiO_2 insulation material. The density of the SiO_2 insulation material was about 0.3g/cm~3. The porosity was about 85%, and the pore size was mainly ranged from 20 to 60 nm in diameter. Heat transfer due to solid conduction and gas convection was reduced greatly because of the existence of larger amount of nano pores. Thermal radiation was partly blocked by the infrared scattering powders. Thermal conductivity of the porous SiO_2 insulation material added with graphite powder as infrared scattering powder can reach as low as 0.04W/m.K at 700℃. The type and amount of added infrared scattering powders had important influence on the thermal performances of insulation materials.
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    Mechanical Behaviors of Foam Nickel Ceramic

    Zhao RongguoChen ChaozhongLuo Xiyan
    693-696页
    查看更多>>摘要：The uniaxial tensions for foam nickel ceramic specimens with different relative densities are carried out on a CSS-44020 Universal Electronic Test Machine at ambient temperature, and the uniaxial tensile tests at various strain rates and temperatures are performed as well. The effects of relative density, strain rate and temperature on the elastic modulus are investigated. It is found that the elastic modulus of the foam nickel ceramic material increases with the density and stain rate, while decreases with the temperature. Simultaneously, the effects of relative density, strain rate and temperature on the yield strength of the foam nickel ceramic material are studied. It is shown that the yield stress increases with relative density and strain rate, but is reversed with increasing temperature. The comparison between the calculated result and experimental data demonstrates that the theoretical model can well predict the mechanical behavior of foam nickel ceramic material.
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    Effect of Hexagonal BN on the Microstructure and Mechanical Properties of Pressureless Sintered Porous Si_3N_4 Ceramics

    Yongfeng LiPing LiuXiangdong WangHaiyun Jin...
    697-700页
    查看更多>>摘要：Porous silicon nitride ceramics with various amounts (25, 35, and 45 vol %) of hexagonal boron nitride (h-BN) were fabricated at 1800℃ for 2h by the pressureless sintering process. With FESEM and TEM, the effects of h-BN on the microstructure and mechanical properties of Si_3N_4 ceramics were investigated. Results of the microstructure and mechanical properties of Si_3N_4/BN composites showed that the growth of the elongated β-Si_3N_4 were hindered by h-BN additive, which resulted in the decrease of fracture toughness of Si_3N_4/BN ceramics with increasing h-BN content. The morphologies of the fracture surfaces by FESEM revealed the fracture mode for Si_3N_4/BN composites to be intergranular. However, phase analysis by XRD indicated that the effect of h-BN on the α- to β-Si_3N_4 phase transformation of Si_3N_4/BN composites was negligible.
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    Dielectric Properties of Porous Si_3N_4 Ceramics Prepared by In situ Cordierite Bonding

    Yongfeng XiaYu-Ping ZengDongliang Jiang
    701-704页
    查看更多>>摘要：In situ bonding porous silicon nitride (Si_3N_4) ceramics were fabricated in air using a conventional ceramic process using Si_3N_4, Al_2O_3 and MgO as the starting materials. The effects of additives content, sintering temperature and holding time on phase composition, microstructure, dielectric properties and porosity were studied. The porous Si_3N_4 ceramics were composed of α- Si_3N_4, SiO_2 (cristobalite) and cordierite. Porous Si_3N_4 ceramics with porosities of 34.12～-50.22%, dielectric constant of 2.95～4.45 and dielectric loss of～0.0025 were obtained.
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    Fabrication and Characterizations of YSZ Electrolyte Films for SOFC

    Min-Fang HanZhibin YangZe LiuHui-Rong Le...
    705-709页
    查看更多>>摘要：Yttria stabilized zirconia (YSZ) has been widely used as electrolyte in solid oxide fuel cell (SOFC). The effect of fabrication process on the properties of YSZ electrolyte thick film is discussed in the paper. With YSZ nano-powders of about 20-60nm as raw material, YSZ green adobe was fabricated by tape calendering process. Three-step sintering process was performed firstly holding at 1000℃ for 2h, then raising to 1300～1400℃, then decreasing to 1200～1300℃ within 30 minutes, and finally calcining at 1200～1300℃ for 5～20 hrs. Dense YSZs with relative density of 96-99% are obtained; the grain size of YSZ was reduced to 0.5～3 μm. During the process of grain growth, there are both grain boundary diffusion and grain boundary migration. The feasibility of densification without grain growth relies on the suppression of grain boundary migration while keeping grain boundary diffusion active at a temperature as low as 1200～1300℃. Whereas the electric conductivities of the YSZs are even higher than that obtained in conventional single step sintering process. The process is applied to the anode-supported SOFCs co-fired at 1250～1300℃, and the cathode-supported SOFCs co-fired at 1200～1250℃.
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    Influence of Thickness on Oxide Ionic Conductivity in Sm~(3+) and Nd~(3+) Co-Doped CeO_2 Electrolyte

    Wei LiuBin LiWei Pan
    710-713页
    查看更多>>摘要：Sm~(3+) and Nd~(3+) co-doped CeO_2 solid electrolytes with various thicknesses were prepared by citric-nitrate combustion process. The electrical conductivity as a function of electrolyte thickness was determined by ac impedance spectroscopy. The results showed that the ionic conductivity increases with the decrease of the electrolyte thickness approximately and it was estimated that the conductivity enhancement was due to the increased grain boundary conductivity.
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