Preparation and thermal conductivities of diamond/SiC composites

Abstract

Diamond/SiC composites have been prepared by Si vapor reactive infiltration in vacuum at 1650 °C using phenolic resin, graphite, and diamond to generate SiC by the Si–C reaction. Dense composites with low porosity were obtained. The SiC grain size changes with the type of carbon. For pyrolyzed resin and graphite, the grain size is 2 µm, but for diamond it is 0.5 µm. Moreover, the thermal conductivity (TC) and densification of the composites were simultaneously investigated. The TC increases with increasing diamond particle size, surface roughness of diamond, and SiC content. The TC is highest (518 W/mK) for a diamond particle size of 110 µm, 50% volume fraction crushed diamond, 35% SiC, and 1650 °C. It also increases with increasing infiltration temperature from 1550 to 1650 °C. However, for an infiltration temperature of 1700 °C, it significantly decreases because the high infiltration temperature causes significant graphitization of diamond and increases the interfacial thermal resistance. For diamond volume fraction of less than 30%, the measured TC values agree with those predicted by the Hasselman–Johnson (HJ) model. However, when the volume fraction of the diamond is above 30%, it agrees with the combined action of the HJ and Agari models. Densification of the diamond/SiC composite is a mass transport process that includes two stages: formation of SiC and deposition of silicon vapor.