Molten salt synthesis, formation mechanism, and oxidation behavior of nanocrystalline HfB2 powders

Nanocrystalline Hf B2 powders were successfully synthesized by molten salt synthesis technique at 1373 K using B and Hf Oas precursors within KCl/Na Cl molten salts. The results showed that the as-synthesized powders exhibited an irregular polyhedral morphology with the average particle size of 155 nm and possessed a single-crystalline structure. From a fundamental aspect, we demonstrated the molten-salt assisted formation mechanism that the molten salts could accelerate the diffusion rate of the reactants and improve the chemical reaction rate of the reactants in the system to induce the synthesis of the high-purity nanocrystalline powders. Thermogravimetric analysis showed that the oxidation of the as-synthesized Hf B2 powders at 773–1073 K in air was the weight gain process and the corresponding oxidation behavior followed parabolic kinetics governed by the diffusion of oxygen in the oxide layer.