Role of Surface Hydroxyl Groups on Zinc Adsorption Characteristics on α-Al2O3(0001) Surfaces: First-Principles Study

Adhesion at zinc/alumina interface is a key issue in the field of steelmaking industry, where selective Al oxidation, followed by surface segregation of alumina islands, efficiently impedes wetting of anticorrosive Zn coating on the high strength steel grades. Relying on ab initio total energy calculations, we have examined adsorption of Zn adatoms on different terminations of alpha-Al2O3(0001) surface under both vacuum conditions and in the presence of surface hydroxyls. Surface configurations with strongly bound Zn and thermodynamic conditions necessary for their stability have been identified. We have shown the existence of a wide range of nonextreme oxygen-rich conditions under which Zn tends to spill over the alumina substrate as an array of strongly adsorbed adatoms, rather than to form metallic clusters weakly bound to the substrate. This effect has been assigned to surface non-neutrality, such as due to surface polarity, or to an excess of surface hydroxyls. Moreover, compared to its direct neighbors in the periodic table (Cu, Ag), we have shown that surface structures with strongly bound adatoms can be stabilized already in much more oxygen-poor conditions.