Further capability of silazane dehydrocoupling polymerization catalyzed by ruthenium carbonyl (20–200 ppm) is demonstrated in a series of reactions. Ammonia and monomethylamine are used as reactants to bridge oligomers and polymers containing Si-H bonds to provide higher molecular weight polymers with higher latent reactivity and to increase the ceramic yields and the nitrogen-to-carbon ratio in the final ceramic compositions. New types of tractable polymers containing cyclomers having [MeSiHNH] units with molecular weights over 2000 d are formed. Various polymeric properties (e.g., viscosities, softening and melting points) and ceramic yields up to 80–85 wt% are obtained by controlling the catalytic reaction conditions.

Compression molded bodies fabricated from commercial Si3N4 powder using a polysilazane precursor to Si3N4 as a preceramic binder have been characterized. The process has been partially optimized and can produce green bodies with densities approaching 75% theoretical and considerable mechanical strength. Microstructural development during binder pyrolysis and high-temperature treatment indicate significant interactions and bonding between the commercial powder and the polymer-derived material.

Characterization of the pyrolysis products of preceramic polysilazanes synthesized by reactions of the oligomer-[H2SiNMe]x in the presence of Ru3 (CO)12 catalyst has demonstrated that these polymers have great potential as precursors of Si3N4 for several applications. The polysilazanes studied are viscous liquids that can be converted to ceramic material with a yield of >65 wt %. The vitreous product contains regions of fully dense material and large cavities that indicate of considerable gas evolution. A preliminary pyrolysis sequence has been constructed based on a combination of TGA of the polymer, SEM investigation of the product, and mass spectroscopic analysis of the gases and heavy fragments released during conversion of the polysilazanes to ceramic material. This understanding of pyrolysis mechanisms will aid in developing even more effective polymeric precursors to Si3N4 and in optimizing pyrolysis procedures for a variety of useful appl ications.

A transition metal (e.g., Ru3 (CO)12, Pt/C) catalyzed process for Si-N bond formation is discussed that provides a new route to mono-, oligo-, and polysilazanes. The catalysts function by activating Si-H bonds in the pres-ence of ammonia. Polymeric silazanes can also be produced from oligomers in the presence of ammonia at low temperatures. This method allows us to control or modify the composition of the polysilazane during or after the polymeriza-tion. A variety of polysilazanes were prepared and converted to Si3 N4 with ceramic yields ranging from 55%-85%. By varying the monomers and reaction conditions, we can control the nitrogen and carbon content in the preceramic polymers, which enables us to obtain ceramic products that are primarily Si3N4and simultaneously minimizes the coproduction of SiC and C.