Silicon nitride ceramics from isocyanate- and isothiocyanate-modified polysilazanes

Claim 1

A process for preparing a silicon nitride-containing ceramic material comprising (1) preparing a silazane ammonolysis product by reacting ammonia with a halogenated silicon compound selected from the group consisting of RSiX 3 , RR'SiX 2 and mixtures thereof, wherein X is selected from the group consisting of Cl, Br and I; and R and R' are the same or different and are selected from the group consisting of H, substituted or unsubstituted 1-6 carbon alkyl, aryl, 1-6 carbon alkenyl and 1-6 carbon alkynyl groups, at least one of the halogenated silicon compounds containing a Si--H bond, (2) reacting the silazane ammonolysis product with from about 0.1% to about 30% by weight, based on the weight of the ammonolysis product, of a compound selected from the group consisting of isocyanates, isothiocyanates, ketenes, thioketenes, and carbodiimides to form a polysilazane addition polymer, (3) heating to a temperature not exceeding 300° C. for a time sufficient to partially cross-link the addition polymer and increase the viscosity to a value suitable for the desired end use of the polymer, and (4) heating to a temperature of at least 800° C. in an inert or ammonia-containing atmosphere.