Low-temperature synthesis of high-purity TiB2 via carbothermal reduction of metatitanic acid and H3BO3

Abstract

The purity of TiB2 is unsatisfactory (<97%) even when synthesized at a high reaction temperature (∼1800 °C) using the carbothermal method. In this work, a thermodynamic investigation with an experimental approach was conducted to optimize the reaction parameters to improve TiB2 purity and confirm the carbothermal reaction mechanism utilizing H3BO3, C, and highly-reactive metatitanic acid as raw materials. High-purity TiB2 a with low level of impurities (0.27% C and 0.56% O) was successfully synthesized at 1550 °C for 60 min with carbon black as the optimal reductant at a molar ratio of 1:2.5:5.25 (Ti:B:C). Based on the thermodynamic and experimental results, the TiB2-synthesis mechanism was confirmed to involve TiC as the precursor for TiB2 formation, which then reacted with liquid B2O3 and C to form TiB2. Additionally, the as-synthesized TiB2 powders were spark-plasma sintered to a relative density of 96.5% with fine grains at 1800 °C for 10 min under a pressure of 50 MPa without additives, mainly owing to the lower O content. This study provides a feasible route for large-scale production of high-purity TiB2.