NANOSIZED Si3N4/SiC-POWDERS BY POLYSILAZANE /POLYCARBOSILANE-PYROLYSIS

The preparation of the nanosized powders was realised by gas phase pyrolysis of volatile precursor compounds at temperatures between 600 and 1200 C. Silicon carbonitride powders were created from polysilazanes, which were synthesised by ammonolysis of alkylchlorosilanes. Silicon carbide powders were prepared from 1,1,3,3-tetramethyl-1,3-disilacyclobutane, gained by the dechlorination- and coupling reaction of chloromethyldimethylchlorosilane with magnesium. The ball-like powder particles have a diameter between 100 and 500 nm and a surface of 10 to 50 m2/g. They are X-ray amorphous and can be crystallised upper 1400 C to alpha-Si3N4 and beta-SiC respectively. 12 refs.