Formation mechanism of Al4SiC4 in Al–SiC composite under flowing nitrogen at 1300 °C

Abstract

Resin-bonded Al–SiC composite was sintered in an electric heating shuttle kiln to prepare aluminum-carbon sliding gates at 1300 °C with nitrogen gas, which synthesized ternary carbide Al4SiC4 in situ and a three-dimensional space interlocking structure of Al4SiC4rods/SiCparticles grown on the surface of SiC particles. The phase composition and microstructure of sintered sample were characterized by XRD and SEM, combined with thermodynamics to investigate the formation mechanism of Al4SiC4. It was found that as temperature increases, trace O2(g) in N2(g) causes active oxidation of carbon, with the composition of gas in environment as N2(g)+CO(g) +trace O2(g). A dense layer (Al4C3+Al2OC-AlNss) was formed on the outer layer of sample preventing the diffusion of ambient gas into inner. Under high temperature and low oxygen partial pressure conditions, the oxygen partial pressure inside the sample was lowered again by the active oxidation of Al(l), and the low oxygen partial pressure induced the active oxidation of SiC(s) so that N2(g)+CO(g)+trace O2(g) outside the sample was transformed to Al2O(g)+SiO(g)+CO(g) inside. Subsequently, Al4SiC4 nuclei were formed on the highly reactive surface of SiC particles by gas-gas reactions as well as releasing trace amounts of O2(g); surrounding SiC(s) and Al(l) rapidly convert O2(g) into reactive gas to participate a second time in the growth process of Al4SiC4 nuclei. A self-circulating system with O2(g) as a catalytic medium has been established to "catalyze" the nucleation and growth of Al4SiC4, which realizes a refined modification of Al4SiC4 morphology at the micro-scale.