Relationship between the contact angle of pure Cu and its alloys owing to liquid Na and electronic states at the interface

Saito, Junichi  ; Monbernier, M.*

Contact angle is an indicator of the wettability between liquid Na and pure metals. This has been evaluated using the atomic interactions obtained from the calculations of the electronic structure of the interface. This study aims to investigate the applicability of the atomic interactions of the interface to the alloys. An interface model between Cu and Na with an alloying element was constructed, and the electronic states of the interface were calculated by the molecular orbital calculation. The bond order, which indicates the strength of the covalent bonding at the interface, and ionicity, which indicates the amount of charge transfer, were obtained as theoretical parameters from the calculation. The contact angles between the Cu or Cu alloys and liquid Na were measured using a droplet of liquid Na at 423 K in a high-purity Ar atmosphere. The contact angles of the Cu alloys were evaluated using these theoretical parameters. As a result, a correlation was obtained between the ratio of the bond order between the substrate metal atoms to the bond order between the Na atom and the substrate metal atoms and the contact angle, which is consistent with previous studies. Furthermore, for the first time, the correlation between the ionicity or difference in the ionicity and contact angle was clarified. The difference in ionicity is the difference between the ionicity of Na atoms and that of the alloying element, indicating the strength of the ionic bonding. It was suggested that Cu and Cu alloys should consider covalent and ionic bonding when evaluating wettability, because Cu has an intermediate electronic state between transition and nontransition metals. Further, it became clear that the evaluation of the contact angle using the atomic interactions at the interface are applicable not only to pure metals but also to alloys.