Nitride Ceramics from Polymeric Precursors

More complex (ternary and quaternary) nitride ceramics can also be formed from polymeric precursors. Thermal decomposition of [CH3Si(N = C = N)i.5]n has been shown by N NMR to form NSi3 units when the protons are lost from the system during heating at 600-800°C (Gabriel et al. 1999). The product is an amorphous mixture of Si3N4 and carbon which reacts to form an amorphous Si-C-N ceramic phase. Similar studies have been carried out on the formation of Si-B-N ceramics from single phase 

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Is the sample free of hydrogen Sol-gel-prepared ceramics easily retain a few wt% of protons up to 1000°C or more, and these protons drive the sintering and crystallization mechanisms. - Rather similar amounts of hydrogen are retained in carbides/nitrides derived from polymeric precursors (e.g., in SiC fibers thermally treated at approximately 1200°C). This hydrogen can generate unwanted gas departure. 

Renewed interest in borazine derivatives has resulted from their possible application as precursors to boron nitride ceramics. For example, the inorganic analogue of styrene, (H->C=CH)B3NjH5i has been polymerized and decomposed to produce BN.72... 

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. 

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