Thermodynamic investigation and reaction mechanism of B4C synthesis based on carbothermal reduction

The reaction mechanism of B4C synthesis as yet remains unclear due to the lack of sufficient thermodynamic investigation, which limits the large-scale controllable production of B4C ceramic material. In this paper, thermodynamic investigation of B4C synthesized by carbothermal reduction was calculated at atmospheric pressure over a wide temperature range (1500-2500 K) coupled with the effects of pressure on B4C synthesis. Besides, predominance diagrams for B-C-O system at different temperatures and pressures were further established. Upon thermodynamic results, reaction mechanism was proposed and then verified by the synthesis experiment of B4C at desired temperatures. The thermodynamic investigation indicates that B4C may be synthesized by the reactions of C with liquid B2O3 (LS mechanism) or gaseous B2O2 (VS mechanism). At low temperature (~1823 K), B4C is polyhedral shape via LS mechanism, while two-dimensional flake-like B4C is synthesized by VS mechanism at high temperature (2123 K~). The obtained two types of B4C verify the accuracy of thermodynamic results. This study is instructive for the optimization of temperature, pressure for large-scale controllable production of B4C ceramic material.