Insights into the reduction pathway of TiB2 powder synthesized with TiO2-B4C-C system by boro/carbothermal reduction

Abstract

Understanding the reaction mechanism is crucial for precisely controlling the synthesis of high-quality TiB₂ powders with tailored particle characteristics. The microwave-assisted boro/carbothermal reduction reaction pathway of TiO₂-B₄C-C system was systematically investigated by stepwise heating method and thermogravimetric-differential scanning calorimetry (TG-DSC) analysis and the reaction process showed an obvious two-stage feature: in Stage Ⅰ (750–1100 °C), TiBO₃ acted as the main intermediate phase, coexisting with the substable Ti₂O₃ and TiC, prompting the TiB₂ nuclei began to nucleate initially at the interface of the feedstock B₄C and TiBO₃. Stage II (1100–1450 °C) featured progressive solid-state diffusion process that eliminated residual B₂O₃ and TiC, resulting in the formation of phase-pure TiB₂ with optimized grain morphology. By systematically tracing the phase transition process and combining it with microstructural characterization, it was confirmed that the generation and transformation of intermediate phases, especially the formation and decomposition of the TiBO₃ phase, played an important role in regulating the particle size and morphology distribution of the final products. Eventually, finer TiB₂ powders (D50 = 330 nm) with carbon and oxygen contents of 0.36 wt% and 0.53 wt%, respectively, were prepared using a smaller (D50 = 0.44 μm) B₄C precursor.