MODEL STUDIES ON THE DISPOSAL OF WASTE PRODUCTS RESULTING FROM THE PYROLYSIS OF CH3SICL3 IN CVD PROCESS

Analysis of the process of pyrolysis of CH3SiCl3 in hydrogen is presented. Because of the high toxicity of both CH3SiCl3 and its waste products, careful disposal is necessary. Due to the great variety of chloromethylosilane compounds that can be found in the waste products, the best method of disposal is to burn them in pure oxygen or in air. During burning of the examined mixtures in air, the yield of the reaction is about 70% and depends to a very small degree on the rate of gas flow. Much greater yields can be obtained if pure oxygen is used. For low gas flow rates the yield is around 92%. For high gas flow rates it reaches 99%. As could be expected, SiO2, CO2, HCl, H2O and traces of Cl2 have been found in the combustion products. The silicon dioxide was amorphous and contained less than 0·001% impurities. The tendency of the silica phase to deposit in the reactor depended to a large on the conditions of the burning process. The conditions of the deposition processes have been analysed and a coalescent mechanism of rapid growth of the large grains of silica dust has been proposed. Theoretical and experimental explanations have been given for the considerable decrease in the critical Reynolds number of gas flow in the system investigated. This has a pronounced effect on the process of fast coalescence of particulates. © 1990.