Reactive-Wetting of Alumina by Molten Aluminum Alloys

摘要

Sessile drop experiments of molten Al, Al-2.5 at. %La and Al-3 at. %Y alloys on alumina were conducted in vacuum (10~(-4) to 10~(-5) Pa) at 1300℃ to obtain the time-dependent contact angles as a function of time. In all cases, it was found that the magnitude of the contact angle decreased with time. With the addition of lanthanum or yttrium, the final contact angle reached 57 and 69 degrees, respectively, at times longer than 4500 seconds, whereas for pure Al the final contact angle for the same conditions was 82 degrees. After removal of the metallic droplet from the substrate, observations of the interfacial region by scanning electron microscopy revealed a series of rings formed on the surface of the alumina substrate. Considering the high negative values of the free energy of formation of lanthanum and yttrium oxides, the presence of these rings suggests reactive-wetting taking place between the aluminum alloys and alumina.