NANO-CRYSTALLINE ULTRA HIGH TEMPERATURE HfB2 AND HfC POWDERS AND COATINGS USING A SOL-GEL APPROACH

Nano-crystalline HfB2 and HfC powders have been synthesized through a simple sol-gel route by using inorganic precursors like hafnium (IV) chloride (HfCl4), boric acid (H3BO3) and phenolic resin as a source of hafnium, boron and carbon respectively. The resulting HfB2 powders had an average crystallite size of similar to 35 nm whilst the HfC powders were similar to 75 nm in diameter. The precursor gels of HfC and HfB2 were also used to dip coat SiC fibre bundles, on heat treatment, a continuous coating of HfC and HfB2 was obtained. The wettability of the gels was determined using contact angle measurements. The continuity of the coatings on the SiC fibre bundles were characterized using optical and scanning electron microscopy.