Abstract
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.
Highlights
Alumina (Al2 O3 ) is a representative high performance ceramic material possessing numerous superior properties
Previous studies found that incorporation of TiB2 particles into Al2 O3 conferred much improved hardness, strength, fracture toughness and electrical conductivity on the resultant Al2 O3 -TiB2 composite materials [11,12,13,14,15,16], making them suitable for a variety of demanding applications, e.g., in electrodes, cutting tools, wear parts, lightweight armors, high-temperature/glow-plug heaters, and heat exchangers [14,17,18]
After firing in KCl, α-Al2 O3 and TiB2 were identified as the primary phases
Summary
Alumina (Al2 O3 ) is a representative high performance ceramic material possessing numerous superior properties. Titanium diboride (TiB2 ) stood out as one of the reinforcement phases, owing to its good structural and thermodynamic compatibility with Al2 O3 [8,9] and its excellent properties such as high melting point, high hardness/elastic modulus, relatively low density, and good thermal/electrical conductivities [10]. Previous studies found that incorporation of TiB2 particles into Al2 O3 conferred much improved hardness, strength, fracture toughness and electrical conductivity on the resultant Al2 O3 -TiB2 composite materials [11,12,13,14,15,16], making them suitable for a variety of demanding applications, e.g., in electrodes, cutting tools, wear parts, lightweight armors, high-temperature/glow-plug heaters, and heat exchangers [14,17,18]
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