International Journal Of Refractory Metals Materials, cilt.29, sa.5, ss.566-572, 2011 (SCI Expanded İndekslerine Giren Dergi)
This study investigates chemical vapor deposition of C from CH4 on particulate SiO2 and subsequent carbothermal conversion of the resultant composite particles to SiC powders. Mass measurements, HR-TEM, SEM and XRD were used to characterize the products at various stages of the processes. It was found that oxide particles gained mass rapidly at 1300 K under CH4 atmosphere owing to enhanced C uptake. Pyrolytic carbon layers 5–8 nm thick were deposited on SiO2 particles. The coated powders with high C loadings (40–42.6 wt.% C) were converted to SiC under Ar flow in a temperature range of 1700–1800 K. Almost pure SiC powders containing a mixture of particles and whiskers of ~ 100 nm were synthesized at 1750 K for 45 min and at 1800 K for 30 min using the starting powder with 40 wt.% C. Whisker diameter increased with the C content of the coated powder. It was proposed that SiC whisker was grown by a vapor–solid mechanism. Equilibrium thermodynamic analysis by the method of minimization of Gibbs’ free energy predicted the reaction pathways to SiC and to the product species in the Si–O–C–Ar system. This study demonstrated that either C shell-SiO2 core powders or SiC powders could be synthesized rapidly in the same reactor.