Wang Xiaogang

Thermo-physical Properties and Reaction Process of SiCp/Al-7Si-5Mg Aluminum Matrix Composites Fabricated by Pressureless Infiltration

Abstract SiCp/Al composites of 55%∼70% (volume fraction) were prepared by pressureless infiltration to investigate the reaction mechanism, morphology and the thermo-physical properties of the prepared composites. X-ray diffraction (XRD) and thermodynamic analyses show that the main interface reaction may be SiO2(s)+Al(l)+MgO(s)→MgAl2O4(s)+Si(s) in the preparation process of the composites. The enhancing of Si activity can obviously suppresses the formation of harmful interface reaction product Al4C3. Metallographic observation shows that the microstructures of the composites are homogenous and dense, infiltration defects are liable to occur in the preparation process. The thermo-physical tests show that the best thermal conductivity (TC) and the coefficient of thermal expansion (CTE) for the prepared SiCp/Al composites with less infiltration defects and dense structure are 170.2 W/(m·K) and 6.64×10−6 K−1, respectively.

Process and Performance of β-SiCp/Al Prepared by Bottom-Vacuum Pressureless Infiltration

Abstract A composite material β -SiC p /Al was fabricated by a novel manufacturing process of bottom-vacuum pressureless infiltration. The β -SiC perform was oxidized at 1373 K and the infiltration in molten Al with the addition of Si and Mg. To evaluate the microstructure and the fractograph of the prepared composites, metallographic and scanning electron microscopes (SEM) were applied. The results reveal that SiC particles can be distributed in the aluminum matrix uniformly, the SiC preform can be completely infiltrated by the molten aluminum. X-ray diffraction (XRD) shows that the main crystalline phases in the composites are β -SiC and Al. There exist Mg 2 Si, MgAl 2 O 4 interface products, brittle phases such as Al 4 C 3 are not formed within the interface zone. Mechanical properties of the β -SiC p /Al composites were investigated by the wear and friction, Brinell hardness tests. The results prove that the wear mechanisms of the composites are abrasive and adhesive wear. With the increased of SiC volume fraction the wear rate of the composite decreases while the hardness increases.

New anti-corona material for large-scale electric machine

The non-linear electrical conduction property of /spl beta/-SiC micro-powder/epoxy ester lacquer composite was investigated. The /spl beta/-SiC micro-powder was synthesized under different temperature and has different particle size. Experiment shows that the non-linear electrical conduction becomes greater by increasing the /spl beta/-SiC powder particle size or synthesizing temperature. Under the same particle size conditions, the non-linear electrical conduction coefficient /spl beta/ and corona voltage rising with the /spl beta/-SiC content increased. The /spl beta/-SiC micro-powder is used to regulate the non-linear electrical conduction property of /spl alpha/-SiC, showing that it is possible to replace /spl alpha/-SiC with /spl beta/-SiC for anti-corona material to increase greatly the anti-corona property.

Preparation of silicon nitride nanowires by using carbon nanotubes as the precursors

Solid silicon nitride nanowires were produced by using carbon nanotubes as precursors. The reaction was carried out in ammonia atmosphere, Si and SiO2 were used as starting materials. The structure, phase composition, dielectric properties and oxidation resistance of the sample were investigated. The results showed that the sizes of the nanorods are 60–80 nm in diameter and up to several microns in length. In the products α-Si3N4 is the main component; due to nano-materials quantum size effects, the FTIR spectra of the silicon nitride nanowires have blue shift phenomena; the sample shows good oxidation resistance in high temperature. The dielectric constants decrease with the increasing measuring frequency. The dielectric constants reduced from 9(10KHz) to 6.9(100MHz) at room temperature.