Low-temperature synthesis of calcium hexaboride nanoparticles via magnesiothermic reduction in molten salt

Abstract

Calcium hexaboride (CaB₆) nanoparticles were prepared via low temperature magnesiothermic reduction of CaO and B₂O₃ in molten NaCl, KCl or CaCl₂. The effects of salt type, Mg amount, and firing temperature and time on the reaction extents were examined, and the responsible reaction mechanisms were discussed. Under an identical firing condition, CaCl₂ facilitated the overall synthesis more effectively than the other two salts. In the case of using 20 mol % excessive Mg, phase-pure CaB₆ nanoparticles of ∼50 nm were formed in CaCl₂ after 6 h at 800°C. The “dissolution-precipitation” mechanism is believed to be responsible for the molten salt synthesis of high quality nanosized CaB₆ particles at such a low temperature.