INTERFACIAL BONDING, WETTABILITY AND REACTIVITY IN METAL-OXIDE SYSTEMS

Pure non-reactive metals develop weak interactions with iono-covalent oxides (insulators) which can be both physical (van der Waals) and chemical (low density interfacial electronic states). As a result, non-wetting is generally observed, the contact angle being larger than 90 degrees. Improvement of wetting can be obtained by alloying the metal with a reactive solute B capable of modifying in a favourable sense the metal/oxide interface. This can be achieved via two mechanisms depending on the strength of the interactions between solute B and dissolved oxygen. For moderate O-B interactions, the solute B can modify the liquid-side of the interface by adsorption of OB clusters, the oxygen coming from the dissolution of the oxide substrate. This mechanism can lead to a decrease of theta down to almost-equal-to 60-degrees. For strong O-B interactions, the solute B can also lead to the precipitation at the solid-side of the interface of a new phase. When this new phase features metallic bonding, wetting can be strongly improved and nearly perfect wetting can be obtained.