Processible precursor for boron nitride coatings and matrixes

An organic solvent soluble borazinyl oligomer, 1, was formed by a reaction of B,B',B"-trichloroborazine with HN(SiMe3)2 at low temperatures in nonpolar solvents. High-purity BN powders, characterized by IR and X-ray diffraction spectra, were produced by bulk pyrolysis of 1 to 1000-degrees-C in NH3. Thin approximately 0.02-mu-m BN coatings were successfully applied to Al2O3/ZrO2 and carbon fibers by dip coating fiber bundles in 5-10% (w/w) solutions of 1 followed by pyrolysis of the coated fibers in an ammonia atmosphere. The BN-coated carbon fibers were subjected to oxidation in air at 800-degrees-C; scanning electron microscopy of the coated fibers and the BN sheaths remaining after oxidation confirmed the formation of BN coatings.