Polymer-derived ceramics synthesis

Riedel R, Mera G, Hauser R, Klonczynski A (2006) Silicon-based polymer-derived ceramics synthesis properties and applications a review. J Ceram Soc Jpn 114 425 44... 

Riedel, R., Mera, G., Hauser, R., Klonc-zynski, A. (2006). SDicon-hased polymer-derived ceramics Synthesis properties and appUcations - A review. Journal of the Ceramic Society of Japan, 114(1330), 425-444. doi 10.2109/jcersj. 114.425. 

Summary Precursor-derived quaternary Si-B-C-N ceramics frequently possess an enhanced thermal stability compared to SiC, SisN4 or Si-C-N ceramics. The stability of the materials towards crystallization and/or decomposition is directly coimected to the molecular structure and the elemental composition of the polymeric precursors. This paper highlights recent investigations on the synthesis of boron-modified polysilazanes and polysilylcarbodiimides. Hydroboration of polyvinylsilazanes and dehydrocoupling reactions of boron-modified silanes with ammonia or amines as well as cyanamide are described. It is shown that simple organosilicon chemistry provides a means to efficiently optimize ceramic yields and tune elemental composition as well as thermal properties of the polymer-derived ceramics. 

Borazine and its derivatives are also possible educts to synthesize precursors for Si-B-N-C ceramics. Sneddon and co-workers prepared Si-B-N-C preceramic precursors via the thermal dehydrocoupling of polysilazanes and borazines [7]. A further synthesis route is the hydroboration of borazines. The work group of Sneddon found that definite transition metal reagents catalyze hydroboration reactions with olefins and alkynes to give 5-substituted borazines [8]. Recently, Jeon et al. reported the synthesis of polymer-derived Si-B-N-C ceramics even by uncatalyzed hydroboration reactions from borazines and dimethyldivinylsilane [9]. 

DAVID WILSON is a research specialist with 3M and has more than 10 years of research and development experience in the synthesis of new ceramic fibers using sol-gel techniques and is the inventor of the Nextel 610 and Nextel 720 ceramic fibers. His experience includes the development of novel fiber precursor formulations, continuous fiber processing, and characterization of ceramic fibers at room and elevated temperatures. Current research activities include preceramic polymer-derived SiC fibers and MOCVD coating and composite fabrication for the Mullite Matrix Composite Consortium Program. Mr. Wilson holds four patents and is the author of several publications. 

Because of their ease of synthesis and processability, as well as the increased thermal stabilities and reduced crystallinity of their derived ceramics, these new hybrid borazine-modified hydridopolysilazanes polymers may prove to be reasonable... 

Few fibers have the excellent mechanical properties reported for the UF-HM fibers however, if the synthesis parallels the original one (see above), the expected drawbacks for the process include (1) the use of an autoclave, not desirable for large-scale production and (2) low ceramic yields of SiC, given that the fiber is derived from a polymer precursor containing a 1 2 Si C ratio. 

The following discussion covers the chemical synthesis of ceramics derived from organometallic polymers BN, AIN, TiN, TiC, and TiBa. It should be emphasized here that some of the syntheses involve starting materials, monomers, and intermediates, as well as polymers, that are oxidatively unstable and/or susceptible to hydrolysis. These syntheses therefore generally require inert atmospheres and the extensive use of vacuum (Schlenk type) line or dry-box techniques. This makes it obvious that collaborations between synthetic chemists and materials and ceramic scientists and engineers is important. Here we outline a selected number of synthetic routes to preceramic polymers. 

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