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 che mical (low density interfacial electronic states). As a result, non-we tting is generally observed, the contact angle being larger than 90 de grees. Improvement of wetting can be obtained by alloying the metal wi th a reactive solute B capable of modifying in a favourable sense the metal/oxide interface. This can be achieved via two mechanisms dependi ng on the strength of the interactions between solute B and dissolved oxygen. For moderate O-B interactions, the solute B can modify the liq uid-side of the interface by adsorption of OB clusters, the oxygen com ing from the dissolution of the oxide substrate. This mechanism can le ad to a decrease of theta down to almost-equal-to 60-degrees. For stro ng O-B interactions, the solute B can also lead to the precipitation a t 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.