H 8919 (OTTO) Hafnium boride powder, 5-10 μm, 99.5% Cas 12007-23-7 - used in wear resistant coatings. It is also employed as a nuclear reactor control rod. H 8919 (OTTO) Hafnium boride powder, 5-10 μm, 99.5% Cas 12007-23-7 - used in hypervelocity re-entry vehicles like ICBM heat shields or aerodynamic leading-edges. It is useful in the preparation of high temperature composites in conjunction with silicon carbide (SiC).