Synthesis and reaction mechanism of Ti3SiC2 ternary compound by carbothermal reduction of TiO2 and SiO2 powder mixtures
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The present study aims to investigate synthesis of Ti3SiC2 from TiO2 and SiO2 powder mixtures by carbothenrial reduction method. Equilibrium TiO2-SiO2-C ternary phase diagram was used to predict the conditions for the formation of Ti3SiC2 at 1800 K under Ar atmosphere. A reactant mixture with a TiO2:SiO2 molar ratio of 1.5 and a C content of 68.75 mol% (26.86 wt%) was initially selected among the thermodynamically favorable reactant compositions for the experimental studies. Two different C sources, graphite flakes and pyrolytic C coating, were used to synthesize Ti3SiC2 at 1800 K under Ar atmosphere. When graphite flakes were used, the products contained a trace amount of Ti3SiC2 phase along with major TiC and minor SiC phases. Whereas, pyrolytic C coating on the oxide particles resulted in the products with much higher Ti3SiC2 contents owing to the close contact between the reactants. Optimal C concentration for the C coated oxide mixtures with a TiO2:SiO2 molar ratio of 1.5 was determined to be 30.05 wt% under the experimental conditions studied. Ti3SiC2 content of the products obtained from this reactant was observed to increase with reaction time to 31 wt% at 75 min beyond which it gradually decreased. XRD studies indicated that the product with the highest ternary carbide content also contained TiC and a trace amount of SiC. SEM-EDS analyses showed that this sample essentially consisted of spherical fine TiC particles and Ti3SiC2 nanolaminates. Equilibrium thermodynamic analysis of the TiO2-SiO2-C system suggested that the reaction of solid Ti2O3 with SiO and CO gases may play a dominant role in the formation of Ti3SiC2. (c) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
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