Oxygen influence on ceramics wettability by liquid metals: Ag/α-Al2O3—Experiments and modelling

A renewed interest in the effects of oxygen on the wetting of solid oxides has recently risen in connection to the development of the technique of “air brazing” which makes use of the strong effect of oxygen to increase the wettability of oxides by means of processes running in air or in atmospheres with high oxygen content. Adsorption of oxygen not only at the liquid–vapour surface but also at the solid–liquid interface has been postulated by many previous researches, mainly on the basis of thermodynamic considerations. Along the same line, new results of the wetting behaviour in the system Ag/α-Al₂O₃ as a function of oxygen partial pressure are presented, with the simultaneous measurement of the liquid surface tension. These results are compared with the existing ones, and discussed on the basis of thermodynamic principles. The resulting work of adhesion is compared with the “work of separation” computed by the density functional theory (DFT) approach. DFT calculations are also employed, at variance with previous models, to investigate the structures that are formed at the interface upon addition of oxygen in different sites energetics, atomic and electronic properties of this oxygen-rich interface are discussed together with the connection with experiments.