Effect of initial compositions on boron carbide synthesis and corresponding growth mechanism

The yield of boron carbide (B4C) synthesised by carbothermal reduction (CTR) is low (40-50%) owing to the inappropriate initial composition. In this paper, thermodynamic equilibrium simulations for effects of initial compositions on B4C synthesis were performed, while initial compositions on the quality and yield of B4C synthesised by CTR from B2O3-C mixture at atmospheric pressure were systemically investigated. The reaction mechanisms for B4C synthesis process were thermodynamically analysed. Moreover, growth mechanisms for B4C particles were speculated based on the thermodynamic and experimental results. The results show that the simulations agree well with experimental results, and optimal initial composition is 1.906 (B2O3/C weight ratio). Under optimal condition, B4C powder prepared at 1973 K is high-quality with well crystallinity, purity of 93.58% and yield of 90.05%. Additionally, the prepared B4C particles show two types of morphologies, aggregate of small equiaxed particles and needle-like particle, which are formed through different reaction mechanisms, respectively.