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Silicon Nitride Ceramic Fibers from Preceramic Polymers.
SRI INTERNATIONAL MENLO PARK CA
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The program objectives are to develop 1 Transition metal catalyzed synthetic routes to designed, tractable silicon nitride Si3N4 preceramic polymers polysilazanes based on SRI developed technology 2 Methods of spinning the resultant polysilazanes into continuous preceramic fibers and, 3 Pyrolysis techniques for transforming the preceramic fibers into high strength Si3N4 and silicon carbide nitride SiCN fibers. In the past year, we have learned to prepare polysilazanes driven from precursors of the type-H2SiNMe whose viscoelastic properties can be carefully controlled by type of catalyst andor reaction conditions. This control has permitted us to draw preceramic fibers of diameters as small as 10 um as seen in the attached photographs. Furthermore, we have developed pyrolysis methodology that permits us to obtain ceramic yields of 50-70 with Si3N4 purities ranging from 80-99. We have discovered that polymer molecular weight greatly influences the ceramic yield but only monomer design or pyrolysis under a reactive atmosphere seems to influence selectivity to specific ceramic products as shown in the attached Table.
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