Nanocrystalline HfB2 powders were successfully synthesized by molten salt synthesis technique at 1373 K using B and HfO2 as precursors within KCl/NaCl 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 HfB2 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.
We acknowledge financial support from the National Key R&D Program of China (No. 2017YFB0703200), National Natural Science Foundation of China (Nos. 51802100 and 51972116), Young Elite Scientists Sponsorship Program by CAST (No. 2017QNRC001), and the fund of the State Key Laboratory of Solidification Processing in NWPU (No. SKLSP201820).
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