Oxygen induced interfacial phenomena during wetting of alumina by liquid aluminium

Sessile drop experiments of liquid Al on sapphire (alpha-Al(2)O(3)) 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 alpha-Al(2)O(3) layers on the sapphire substrate at temperatures below approximate to1100degreesC and dissolution of the sapphire substrate at temperatures above approximate to1100degreesC. 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 oxyen-rich interphase at the liquid Al-sapphire interface. It is concluded that dissolution of sapphire under Al oxidation conditions is capillary driven. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.