Effect of temperature and Ar flow rate on Ti3SiC2 formation from TiSiO4 powders coated with pyrolytic carbon

Abstract

In this study, equilibrium thermodynamic analysis was initially carried out for TiO2:SiO2:C molar ratio of 1:1:4 at 1600 K, 1700 K and 1800 K as a function of Ar/solid reactant ratio. It was predicted that single phase Ti3SiC2 is formed when a critical Ar/solid reactant ratio is exceeded. This behavior is ascribed to the reduction of partial pressures of gaseous reaction products of SiO and CO. Subsequently, formation of Ti3SiC2 phase from carbon coated TiSiO4 powders by carbothermal reduction was investigated as a function temperature, isothermal holding time and Ar flow rate. Carbothermal reduction experiments at 1800 K and at a Ar flow rate of 250 cm(3)/min for 60 min showed that the optimal C content was determined to be 27.47 wt.%. The ternary carbide compound was not detected within 120 min at 1600 K and 1700 K, but a major TiOC phase along with a minor SiC phase. Whereas at 1800 K, the ternary carbide phase was observed and its amount increased from 6.80 wt.% at 0 min to 38.91 wt.% at 75 mm above which it gradually decomposed into the binary carbides. The experiments carried out for various Ar flow rate at 1800 K for 75 mm revealed that the highest ternary carbide content (47.84 wt.%) was obtained at a Ar flow rate of 425 cm(3)/min. The thermodynamic and experimental results indicate that Ti3SiC2 formation takes place via the reaction of pre-formed TiC and SiC phases with the remaining SiO2. (C) 2013 Elsevier Ltd. All rights reserved.