Effect of carbon source and reaction atmosphere on the synthesis of TiB ₂ via microwave‐assisted boro/carbothermal reduction

Abstract Thermodynamics evaluations of the TiO ₂ –B ₄ C–C system at 1 and 0.1 atm were conducted, respectively. Subsequently, the effect of carbon sources (i.e., graphite, carbon black, and activated carbon) and reaction atmosphere (Ar and vacuum) on the phase composition, microstructure, and particle size of the synthesized TiB ₂ products were comparatively investigated. The powder samples synthesized with graphite and activated carbon contained Ti ₂ O ₃ and C, Ti ₂ O ₃ as impurities, respectively, in addition to TiB ₂ product. Nevertheless, high‐purity TiB ₂ with 0.18 wt% residual C was acquired with carbon black. Moreover, TiB ₂ synthesized at 1450°C for 20 min using carbon black had an irregular plate‐like structure, with an average grain size of approximately 0.25 µm, which was finer than that of TiB ₂ derived from other carbon sources, due to its large specific surface area, higher chemical reactivity, and higher microwave heat absorption capacity. In addition, irregular TiB ₂ plate‐like grains with fine quasi‐spheroidal‐shaped TiB ₂ /TiC grains were synthesized in the Ar atmosphere. The vacuum atmosphere was conducive to reducing the partial pressure of CO gas in the reaction system, resulting in lowering the reaction temperature and facilitating the complete reaction without the presence of TiC impurities.