Influence of SiC surface polarity on the wettability and reactivity in an Al/SiC system

Abstract

The wetting of (0001) 6H-SiC single crystals by molten Al was investigated using a dispensed sessile drop method in a high vacuum at 973–1173K. The wettability and reactivity in this system are sensitive to the surface polarity of SiC. The interfacial reaction on the Si-terminated surface is rapid. The formation of a continuous Al4C3 product layer at the interface leads to an equilibrium contact angle of 56±1° at 1173K. In comparison, the interfacial reaction on the C-terminated surface is sluggish. The interface is only partially covered by discrete Al4C3 platelets even after dwelling at 1173K for 2h. The final wettability, however, is much better (θF=41±1°) than that of the Si-terminated surface which was covered by a dense Al4C3 layer, suggesting that the formation of Al4C3 should not always contribute to the wetting in the Al/SiC system. A plausible explanation is that the clean (i.e., deoxidized) C-terminated surface should be well wetted by molten Al in nature, owing to the strong chemical interactions between liquid Al and the surface atoms of the C-terminated SiC. It is likely that the presence of the oxide film at the surface of the molten Al drop or the SiC substrate and the rapid formation of Al4C3, which prevent the establishment of a real Al/SiC interface, conceal the intrinsic wettability of this system.