Studies on the formation of TiB2 through carbothermal reduction of TiO2 and B2O3

Formation of titanium di-boride (TiB2) whiskers through carbothermal reduction of TiO2 and B2O3 has been studied from 900 to 1600 °C in 1 atm argon. K2CO3, which forms a low melting liquid by reacting with TiO2, and NiCl2, which catalyses the carbon gasification, were used to aid the whisker formation by a vapor–liquid–solid (VLS) growth mechanism. TiO2, NiCl2, K2CO3, carbon black and B2O3 were reacted in a molar ratio (TiO2:NiCl2:K2CO3:C:B2O3=x:0.15:0.144:4:1), where x=1/0.5/0.25. Irrespective of TiO2 content, TiB2 was formed as the major phase. Small quantities of TiC were also formed in the system containing 1 mol of TiO2. Whiskers of TiB2 were observed at 940–1200 °C. Above 1400 °C, the formation of particulate was the dominant process. Upon decreasing the TiO2 content to 0.5 mol, a single phase TiB2 was formed. Further decrease in the TiO2 content to 0.25 mol, resulted in the formation of B4C apart from TiB2. The B4C had appeared mainly as platelets. A vapour–liquid–solid growth mechanism was identified for TiB2 whisker formation.