SYNTHESIS OF ALPHA-SILICON NITRIDE POWDER FROM A POLYMERIC PRECURSOR

Methylcyclosiloxanes and methylcyclosilazanes prepared using dichloromethylsilane have been reacted together to prepare a copolymer which was pyrolysed to give a ceramic powder. The copolymer was characterized using proton nuclear magnetic resonance spectroscopy (H-1 NMR) and Fourier transform infra-red spectroscopy (FT-IR). Thermogravimetric analysis of the pyrolysis process and reactions which could occur during conversion of the copolymer to the ceramic are discussed. The product, which was found to be amorphous, was also studied using FT-IR, crystallized by re-heating and characterized using FT-IR, X-ray techniques and scanning electron microscopy. It was identified as alpha-silicon nitride and its characteristics are compared with a conventionally prepared, widely used, commercially available grade of silicon nitride. The alpha-silicon nitride synthesised in the present work contains a wide range 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).