Wetting of pure aluminium on graphite, SiC and Al2O3 in aluminium filtration

The wettability of pure aluminium on filter materials and on inclusions is believed to be an important factor affecting the filtration of aluminium. The contact angles of molten aluminium on alumina, SiC and graphite were measured under 10(-8) bar high vacuum in the temperature range of 1000-1300 degrees C. To describe the wetting behaviour of the Al on ceramic at lower temperatures used in filtration and casting aluminium, a semi-empirical calculation was employed. The calculated contact angles at 700 degrees C were around 97 degrees for alumina, 92 degrees for vitreous graphite, 126 degrees for single- and poly-crystal graphite, and 79 degrees for single crystal SiC, respectively. This indicates that aluminium does not wet alumina or graphite (or Al4C3) around the casting temperature, but wets SiC at this temperature. Thus a priming height is required for aluminium to infiltrate an alumina filter. Increasing temperature can also improve the wettability of Al on ceramic.