Effect of preforms on the synthesis of micro beta-SiC from phenol resin and silicon

The aim of present study is to investigate the effect of preforms on the synthesis of micro beta-SiC. For this purpose, preforms were prepared from commercially available phenol resin and silicon powders by pyrolysing at 650 deg C and 750 deg C in vacuum. Then, preforms were hot isostatically pressed (HIPed) at 1400 deg C for 10 min in an argon atmosphere of 50 MPa to synthesize micro beta-SiC. X-ray diffraction analyses showed that the formation of beta-SiC was enhanced in the specimens prepared by HIP-ing the preforms pyrolyzed at 750 deg C, which might be due the more carbonization and the development of porous structure in the range 600-800 deg C. Scanning electron microscopy observations revealed the formation of micro-crystals (up to 8 mum in size) with facets in the HIPed specimens. In addition, the degree of crystallites in the specimen obtained from the preforms pyrolyzed at 750 deg C was higher than the preforms pyrolyzed at 650 deg C. The energy dispersive spectroscopy showed that crystals were of SiC because the atomic ratio of silicon and carbon atoms in the crystals was almost 1 : 1. The density of the specimens obtained by HIPing the preforms pyrolyzed at 750 deg C was (3.11 g/cm3) more than the specimens obtained by HIPing preforms pyrolyzed at 650 deg C (2.95 g/cm3). The HIPing process, in addition to densification, led to the formation and growth of beta-SiC.