Possibility of Methylpolysilazanes as a Precursor to Ceramics

Abstract

Recently many authors have much interested in making ceramics from a variety of organometallic compounds by pyrolysis. We report some experimenta l conditions for making suitable precursors easy to form ceramics by use of silazanes as starting materials and describe the following factors: i )kinds of methylchlorosilanes, ii) their combinations and molar ratios, iii) molecular weight increase and gelation-time of the polysilazane precursor, and iv) thermal properties of the precursors analysed by thermogravimetry. Methyltrichlorosilane or dimethyldichlorosilane was allowed to react with gaseous ammonia in benzene at room temperature or in diethyl ether-liquid ammonia mixture at -50--40°C. Binary mixtures of methyltrichlorosilane/dimethyldichlorosilane or methyltrichlorosil ane/silicon tetrachloride with different molar ratios also underwent co-ammonolysis in diethyl ether-liquid ammonia mixture. The liquid products having low molecular weight initially obtained were either viscous and opaque or viscous and transparent. Their molecular weight was found to be increased by being kept at a constant temperature and they finally transformed into gel. Thus, the most suitable precursors for ceramics via polysilazane were obtained_ by the combination of methyltrichloroisilaneklimethyldichlorosilane with an appropriate molar ratios.