Silicothermic synthesis of phase‐pure HfB2 fine powder

Phase pure and nano‐sized hafnium diboride (HfB2) fine powder was prepared via a novel sustainable silicothermic route at 1100°C from inexpensive raw materials HfO2, Na2B4O7 and Si. By introducing sodium oxysalts as source of Na2O into the batch mixtures, the SiO2/ Na2O modulus in the melt were reduced from 5:1 to 2:1, and the original water‐insoluble byproduct SiO2 was taken by the melt at test temperature and converted into water soluble sodium silicate (Na2Si2O5) which was easily removed from the reacted mass via simple hot water washing. Consequently, the aqua sodium silicate could be readily recycled and used as a precursor for preparing many other valuable materials due to absence of foreign salts (eg halides, especially in the molten salt‐assisted synthesis process) in the synthesis process, and the relevant environmental concerns could be alleviated. Using excessive amount of 20 wt% Si and 15 wt% Na2B4O7 as compensation for the evaporation loss of silicon, in the form of SiO (g), and B2O3 in the reduction process, a high reaction extent was achieved and HfO2 and Na2B4O7 were completely converted into HfB2 at 1100°C.