Oxygen induced interfacial phenomena during wetting of alumina by liquid aluminium

Abstract Sessile drop experiments of liquid Al on sapphire (α-Al2O3) were conducted under a low pressure (10−3 Torr) controlled Ar atmosphere as a function of oxygen partial pressure, temperature and/or time. Microstructural investigations of the samples from the experiments indicated that two different dominant processes occur at the liquid Al-sapphire interface: epitaxial growth of new α-Al2O3 layers on the sapphire substrate at temperatures below ≈1100°C and dissolution of the sapphire substrate at temperatures above ≈1100°C. Possible mechanisms by which oxygen affects wetting and adhesion of liquid Al on sapphire are examined. The non-wetting to wetting transition in this system may be explained by formation of an oxygen-rich interphase at the liquid Al-sapphire interface. It is concluded that dissolution of sapphire under Al oxidation conditions is capillary driven.