| Summary: | Alumina-titanium diboride (Al<sub>2</sub>O<sub>3</sub>-TiB<sub>2</sub>) composite powders were synthesised via aluminothermic reduction of TiO<sub>2</sub> and B<sub>2</sub>O<sub>3</sub>, mediated by a molten chloride salt (NaCl, KCl, or MgCl<sub>2</sub>). 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 B<sub>2</sub>O<sub>3</sub> are needed to complete the synthesis reaction. Following this, phase-pure Al<sub>2</sub>O<sub>3</sub>-TiB<sub>2</sub> composite powders composed of 0.3–0.6 μm Al<sub>2</sub>O<sub>3</sub> and 30–60 nm TiB<sub>2</sub> 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 Al<sub>2</sub>O<sub>3</sub> and TiB<sub>2</sub> particles in the resultant phase pure composite powder increased slightly to 1–2 μm and 100–200 nm, respectively.
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