INFLUENCE OF SURFACE-MORPHOLOGY ON WETTABILITY OF SINTERED AL2O3 WITH MOLTEN METALS

The influences of surface morphology and porosity on the wettability of sintered Al2O3 powder or fiber substrates by molten Al, Ag, Pb-Sn alloy and cast iron were investigated by the sessile drop method under a vacuum of 2 x 10(-3) Pa. The apparent contact angles (theta) of molten aluminium on the sintered fiber and lustrous sintered powder substrates were larger than that (theta-1) on the transparent Al2O3 substrate with a smooth surface. The measured theta-values were almost equal to those calculated by Cassie's equation from theta-1 and the surface porosity (f(vs)) which was evaluated from the bulk porosity (f(v)) of the substrate by a simple surface structure model. theta on the lusterless sintered powder substrate was much larger than that estimated from the above simple structure model, because the surface of the substrate was very rough. The surface porosity (f(vs)) of the lusterless substrate was correctly estimated by using an image processing system. theta of molten Ag and Pb-Sn alloy to the sintered powder substrates with a lustrous or lusterless surface were almost equal to the angles estimated by Cassie's equation from f(vs). theta of molten cast iron to the sintered substrates was also estimated from f(vs) of the original unreacted substrate during the first 30 s of wetting time, though the molten iron reacted with Al2O3 occurred and theta-changed with time.