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 t emperatures higher or equal to 923 +/- 3 K and up to about 1 600 K, ac cording to the chemical reaction: 4Al + 3SiC <-> Al4C3 + 3Si In the pr esent work, a study has been carried out to obtain more detailed infor mation on the mechanism and kinetics of this reaction. For that purpos e, 6H silicon carbide platelets with broad Si (0001) and C (0001BAR) f aces were isothermally heated at 1000 K in a large excess of liquid al uminium. Characterization of the resulting samples by Auger electron s pectroscopy (AES) and scanning electron microscopy (SEM) revealed that the reaction proceeds in both faces via a dissolution precipitation m echanism. However, the polarity of the substrate surface strikingly in fluences the rate at which silicon carbide decomposes. dissolution sta rts 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 direc tly exposed to liquid aluminium and thus may continue to dissolve at a low but constant rate up to complete decomposition of the alpha-SiC c rystal.