Growth mechanism of bimodal-sized TiB2 particles synthesis via a NaCl additive-microwave-assisted carbothermal reduction

Abstract

A NaCl additive synergized with microwave co-assisted carbothermal reduction methodology was innovatively developed for the low-temperature synthesis of submicron TiB2 powders. The effect of synthesis temperature (1350−1500 °C) and amount of NaCl additive (2−6 wt%) on the phase composition, purity and morphology of the as-obtained products were systemically investigated. Pure-phase TiB2 powders with particle size of 0.2 μm were successfully synthesized at 1400 °C for 30 min utilizing TiO2, B4C, and carbon black with 2 wt% NaCl additive. B2O3 was identified as a possible intermediate reaction product and induced the coarsening of TiB2 particles. Besides, the addition of 2 wt% NaCl exhibited a significant positive influence on enhancing the TiB2 purity by approximately 3.12 % and concurrently refining the grain size from 0.9 μm to 0.2 μm, leading to a higher densification of TiB2 ceramic after spark-plasma sintering. More importantly, the bimodal-sized TiB2 particles were innovatively discovered and differed significantly in grain size and morphology as follows: quasi-spherical-shaped grains (0.2 μm) and hexagonal-shaped particles (4.0 μm). The corresponding growth mechanisms of the bimodal-sized TiB2 grains were discussed in detail.