SYNTHESIS OF ALPHA-SILICON NITRIDE POWDER FROM A POLYMERIC PRECURSOR

Methylcyclosiloxanes and methylcyclosilazanes prepared using dichlorom ethylsilane have been reacted together to prepare a copolymer which wa s pyrolysed to give a ceramic powder. The copolymer was characterized using proton nuclear magnetic resonance spectroscopy (H-1 NMR) and Fou rier transform infra-red spectroscopy (FT-IR). Thermogravimetric analy sis of the pyrolysis process and reactions which could occur during co nversion of the copolymer to the ceramic are discussed. The product, w hich was found to be amorphous, was also studied using FT-IR, crystall ized by re-heating and characterized using FT-IR, X-ray techniques and scanning electron microscopy. It was identified as alpha-silicon nitr ide and its characteristics are compared with a conventionally prepare d, widely used, commercially available grade of silicon nitride. The a lpha-silicon nitride synthesised in the present work contains a wide r ange of particle morphologies, varying from needles (500 nm in length and 100 nm in width) to equiaxed agglomerates (200-500 nm in size with a substructure in the size range 50-120 nm).