An improved sessile-drop wetting experiment was performed in this study to investigated the wettability and adhesion of molten Al on three different oriented α-Al_2O_3 single crystals, R (011-bar2), A(112-bar0) and C(0001), over a wide temperature range from 800-1500 ℃ in a reduced Ar-3%H_2 atmoshpere. It is found that the wettability and adhesion between molten Al and α-Al_2O_3 are quite sensitive to they 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~(1/2) * 31~(1/2) 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%H_2 atmosphere, the top layers of the R and A α-Al_2O_3 surfaces are oxygen-terminated while that of the C surface is aluminum-terminated, and the reconstructed C-(31~(1/2) * 31~(1/2))R±9° surface is an oxygen-deficient structure based on the results of the work of adhesion.
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