The influence of surface orientation on the wetting and reaction at the Al/MgAl2O4 interfaces.

The wetting of (100), (110) and (111) MgAl 2 O 4 single crystals by molten Al at 1073–1273 K in vacuum was investigated using a dispensed sessile drop method to determine the effect of the substrate orientation on the wettability and reaction in this system. This system is non-wetting in nature. The initial contact angles are generally in the range of 96–106°, slightly decreasing with increasing temperature but without significant dependence on the MgAl 2 O 4 surface orientation. However, the interfacial reaction is sensitive to the MgAl 2 O 4 surface orientation and temperature. No reaction product was observed at 1073 K while the thickness of the Al 2 O 3 product layer was in the order of (100) > (110) > (111) at 1173 K and 1273 K. During the reactive wetting process, significant reconstruction and "whisker growth" occurred at the periphery of the triple line due to the stress created at the substrate surface as a result of volume change between the reactant and product, and the morphology of the "whiskers" was closely related to the MgAl 2 O 4 crystal orientation. The formation of these "whiskers" not only affected the wetting behavior but also weakened the dependence of the wettability on the MgAl 2 O 4 surface orientation. [ABSTRACT FROM AUTHOR]