Effect of B4C particle size on TiB2 synthesis via microwave-assisted boro/carbothermal reduction

Abstract

Understanding the reaction behavior of B₄C feedstocks with varying particle sizes is crucial for the synthesis of fine high-purity TiB₂ via microwave-assisted boro/carbothermal reduction in the TiO₂‒B₄C‒C system. The influence of three particle sizes of B₄C, that is, 15.8, 2.8, and 0.6 µm on the microstructure, particle size, and purity of synthesized TiB₂ was investigated. It was found that the morphology and size of TiB₂ product synthesized with coarse (15.8 µm) and medium (2.8 µm) B₄C were independent of the feedstock size. Whereas the resultant TiB₂ size (0.56 µm) closely matched the initial fine B₄C size (0.6 µm). The reduction of B₄C particle size significantly enhanced TiB₂ purity, lowering residual C and O impurities from 0.42% and 1.24% (with 15.8 µm B₄C) to 0.23% and 0.48% (with 0.6 µm B₄C), respectively. Furthermore, thermodynamic analysis and differential scanning calorimetry revealed distinct reaction pathways: coarse B₄C resulted in incomplete contact between TiO₂ and B₄C raw materials led to the formation of TiBO₃ and Ti₂O₃ intermediates, whereas fine B₄C facilitated direct TiB₂ formation without intermediates. Based on the thermodynamic evaluation and experimental results, the reaction mechanism for synthesis of TiB₂ from coarse- and fine-grained B₄C was also systematically explored and established, respectively.