Silicon carbonitride materials derived from the distillation residue of methylchlorosilane synthesis

During the industrial-scale preparation of methylchlorosilanes from silicon and methyl chloride (Muller-Rochow synthesis), distillation residue, consisting of a mixture of differently substituted methylchlorodisilanes and higher silanes, is produced as a byproduct. Conversion of this disilane mix with gaseous ammonia in a non-polar organic solvent leads to the formation of a polysilazane mixture that is soluble in the solvent used. When subjected to thermal treatment at around 1200°C, the synthesized polysilazane mixtures gradually cross-link and pyrolyse to form Si-C-N materials with an N/C ratio of between 1:1 and 1:1,5. The ceramic yield varies between 60 and 70 mass%. These synthesized polysilazanes can be used to produce Si-C-N materials, such as composite materials, fibre composites, infiltrated materials and joining materials. To minimize shrinkage of the material during pyrolysis, applications with a large surface-to-volume ratio have proven optimum. The use of distillation residue presents a cost-efficient method for the production of Si-C-N materials, and beyond this it reduces the quantity of residue which would otherwise have to be disposed of.