INTERFACIAL REACTION WETTING IN THE BORON-NITRIDE MOLTEN ALUMINUM SYSTEM

An improved sessile drop technique which prevented the oxidation of aluminum was used to measure the changes in contact angle between boron nitride and molten aluminum in a purified He-3% H-2 between 1173 and 1373 K. The contact angle progressed through the four wetting phases similar to other ceramics when the results were plotted on a logarithmic time scale. However, at and above 1273 K the equilibrium contact angle was 0-degrees which is much less than those of typical ceramics. Using the value in phase II, the original contact angle between boron nitride and aluminum (contact angle between non-reacted boron nitride and aluminum) was estimated to be 133-degrees at 1373 K. The wetting progressed by producing another non-wetting material, AlN, in this non-wetting system. The detailed mechanism of the solid/liquid/vapor interfacial advance during wetting in such a system was also explained using Cassie's equation.