Dibromoborane-Dimethyl Sulfide: A Simple Molecular Precursor for the Formation of Bulk Powders and Fiber Coatings of Boron Nitride

The Lewis base-borane adduct (CH3)(2)S center dot BHBr2 has been found to be an effective molecular precursor for the formation of high-purity bulk powders and ceramic fiber coatings of boron nitride. Bulk pyrolyses of (CH3)(2)S center dot BHBr2 under ammonia carried out at various temperatures between 650 and 1500 degrees C resulted in the formation of BN powders, as characterized by diffuse-reflectance IR and X-ray diffraction spectra, density measurements, and elemental analysis. Thermogravimetric analysis studies in air demonstrated that BN powders prepared at temperatures as low as 650 degrees C exhibit oxidative stability to 820 degrees C. Materials of increased purity, crystallinity, and oxidative stability were prepared at higher temperatures. Boron nitride fiber coatings were achieved on Al2O3/ZrO2 and SiC fibers by dip coating either single fibers or fiber bundles in 2-18% (w/w) solutions of (CH3)(2)S center dot BHBr2 followed by pyrolysis of the coated fibers under an ammonia atmosphere to a maximum temperature of 1000 degrees C. Scanning electron microscopy and Auger electron spectroscopy studies confirmed the formation of BN coatings.