MECHANISM AND KINETICS OF THE CHEMICAL INTERACTION BETWEEN LIQUID ALUMINUM AND SILICON-CARBIDE SINGLE-CRYSTALS

Previous investigations of phase equilibria in the ternary system Al-C-Si have shown that silicon carbide is attacked by pure aluminium at temperatures higher or equal to 923 +/- 3 K and up to about 1 600 K, according to the chemical reaction: 4Al + 3SiC <-> Al4C3 + 3Si In the present work, a study has been carried out to obtain more detailed information on the mechanism and kinetics of this reaction. For that purpose, 6H silicon carbide platelets with broad Si (0001) and C (0001BAR) faces were isothermally heated at 1000 K in a large excess of liquid aluminium. Characterization of the resulting samples by Auger electron spectroscopy (AES) and scanning electron microscopy (SEM) revealed that the reaction proceeds in both faces via a dissolution precipitation mechanism. However, the polarity of the substrate surface strikingly influences the rate at which silicon carbide decomposes. dissolution starts much more rapidly on the Si face than on the C face, but, while a barrier layer of aluminium carbide is formed on the Si face protecting it against further attack, the major part of the C face remains directly exposed to liquid aluminium and thus may continue to dissolve at a low but constant rate up to complete decomposition of the alpha-SiC crystal.