One-Pot Synthesis of Alumina-Titanium Diboride Composite Powder at Low Temperature

Alumina-titanium diboride (Al₂O₃-TiB₂) composite powders were synthesised via aluminothermic reduction of TiO₂ and B₂O₃, mediated by a molten chloride salt (NaCl, KCl, or MgCl₂). The effects of salt type, initial batch composition, and firing temperature/time on the phase formation and overall reaction extent were examined. Based on the results and equilibrium thermodynamic calculations, the mechanisms underpinning the reaction/synthesis processes were clarified. Given their evaporation losses at test temperatures, appropriately excessive amounts of Al and B₂O₃ are needed to complete the synthesis reaction. Following this, phase-pure Al₂O₃-TiB₂ composite powders composed of 0.3-0.6 μm Al₂O₃ and 30-60 nm TiB₂ particles were successfully fabricated in NaCl after 5 h at 1050 °C. By increasing the firing temperature to 1150 °C, the time required to complete the synthesis reaction could be reduced to 4 h, although the sizes of Al₂O₃ and TiB₂ particles in the resultant phase pure composite powder increased slightly to 1-2 μm and 100-200 nm, respectively.