Silicon nitride ceramics, from polysilazanes

Borazine-Modified Hydridopolysilazanes. Polysilazanes have been shown to be excellent polymeric precursors to silicon nitride or SiNC ceramic materials. Chemical modification of polysilazanes has also been proposed as a means of modifying and enhancing e properties of the polymer and/or the final ceramic materials. For example, the incorporation of boron in the polysilazane has been claimed to decrease the crystallinity of the silicon nitride deriv from these polymers and thereby extend the effective use-temperature of these ceramics. Given the potential importance of SiNCB ceramics, investigations of the generation of new classes of hybrid polymers that might serve as processable precursors to such composites were initiate. 

Tris transaminates readily with ammonia or primary amines when catalyzed by carbon dioxide or strong organic acids. The polysilazane products range from discrete solid disilazanes, to liquid distillable oligomers, and to highly cross-linked infusible polymers. Some of these polysilazanes can be pyro-lyzed to amorphous silicon nitride or mixtures of silicon nitride and silicon carbide below 1550 or to crystalline ceramics above that temperature. 

Another special type of silicone containing polymers is polysilazanes. These materials are used in for the preparation of high performance ceramics, silicon nitride, etc. Polysilazane can be prepared from substituted methylchlorodisilanes and gaseous ammonia in the following reaction [4] ... 

---