Hafnium boride - Hafnium diboride HfB2 Melting point: ~3250°C - A light grey metallic powder, chemically attacked very little by cold HCl, more rapidly by HNO3, and is dissolved by aqua regia. It reacts with H2SO4 and is readily attacked by fused alkali hydroxides, carbonates and disulfides. Produced by various processes. Useful in nuclear applications because of the presence of Boron-10. Other applications include use of its relatively high conductivity, especially for a ceramic.