Variation of contact angles with temperature and time in the Al-Al2O3 system

Abstract

The contact angles of liquid Al on polycrystalline Al2O3 determined by the conventional sessile drop method were obtuse (similar to 120 deg) up to 900 degrees C but decreased rapidly at 1000 degrees C. When the molten Al was squeezed through a narrow orifice and dropped onto-the substrate, the contact angle at 900 degrees C was 77 deg and decreased linearly with temperature. At 1000 degrees C and 1100 degrees C, the contact angles decreased slowly with holding times up to 50 and 6 hours, respectively. At 1200 degrees C, the contact angle also decreased with holding time up to 40 minutes, after which it oscillated, resulting in a ring pattern on the substrate. The structural change of the Al2O3 substrate surface is suggested to be an important variable that determines the wetting behavior of the Al-Al2O3 system.