Process for preparing finely divided chloride-free silicon carbonitride powders

摘要

The invention relates to the fields of inorganic chemistry and ceramics, and the powders prepared according to the invention can, for example, be processed into nanoscale ceramic Si3N4/SiC materials. The object of the invention, to prepare a powder which can be used for producing Si3N4-SiC composite materials having improved high-temperature properties, is achieved by preparing a mixture of vaporisable polysilazanes having a C:Si ratio of from 1.5 to 4 from dialkyldichlorosilanes and/or alkylmonochlorosilanes by reaction with nitrogen carriers and subsequent separation of ammonium chloride and/or alkylammonium chloride and a solvent, which polysilazane mixture is vaporised at a temperature below the sublimation temperature of ammonium chloride and/or alkylammonium chloride in a protective gas or reactive gas stream of N2 or Ar or He and H2 and/or NH3 and is subsequently pyrolysed in the reactive gas stream at from 600 to 1400@C for at least 1 s.