Some Observations on the Wetting of Al 2 O 3 , by Aluminum

The contact angle of liquid aluminum with recrystallized alumina and with sapphire, respectively, was measured using the sessile‐drop technique, The variation in contact angle with time was determined at temperatures of the order of 1200°C. in vacuo at 10‐ 4 mm. Hg. A significant difference in spreading behavior was observed for aluminum on the respective aluminas. In the case of aluminum on recrystallized Al 2 O 3 the contact angle attained a steady value, whereas on sapphire the drop was observed to spread and contract repeatedly. The contact angle assumed after each contraction was essentially constant. The observations are discussed and an explanation is proposed for the effect in terms of changes in the interfacial geometry between liquid aluminum and the alumina due to dissolution.