The influence of surface structure on wetting of α-Al2O3 by aluminum in a reduced atmosphere

Abstract An improved sessile-drop wetting experiment was performed in this study to investigate the wettability and adhesion of molten Al on three different oriented α-Al2O3 single crystals, R ( 01 1 2 ), A (11 2 0 ) and C(0001), over a wide temperature range from 800–1500 °C in a reduced Ar-3%H2 atmosphere. It is found that the wettability and adhesion between molten Al and α-Al2O3 are quite sensitive to the crystallographic orientation. The adhesion is much stronger for the molten Al on the R and A surfaces than that on the C surface. On the other hand, the adhesion on the reconstructed C- ( 31 × 31 ) R±9 ∘ surface is weaker than that on the relaxed yet unreconstructed C-(1×1) surface. The results suggest that in the reduced Ar-3%H2 atmosphere, the top layers of the R and A α-Al2O3 surfaces are oxygen-terminated while that of the C surface is aluminum-terminated, and the reconstructed C- ( 31 × 31 ) R±9 o surface is an oxygen-deficient structure based on the results of the work of adhesion.