Mechanism of interface interactions between thermodynamically stable oxides and Al containing melts

Scandia, yttria and erbia are thermodynamically stable oxides and could be used as a structural material for crucibles, in order to avoid contamination of the melt. These oxides have similar wetting behaviour in contact with aluminium containing melts, but different interaction characteristics and different interfacial products. When yttria and erbia substrates are exposed to Al containing melts, the substrate decomposes, large amounts of Y or Er are released into the melt and a thick interaction layer consisting of a new YAlO₃ or ErAlO₃ phase is formed beneath the drop. These results were not obtained in the Sc₂O₃/Al system where only a slight amount of Sc was dissolved in the melt and a thin interfacial layer consisting of Al₂O₃ was formed. The differences in the mechanism and in the nature of the reaction products of the studied systems are attributed to the thermodynamic properties of the ternary Al-Me-O systems. These properties dictate the sequence of dissolution-precipitation reactions during the wetting experiment and the final equilibrium state for each system.