THE ROLE OF STOICHIOMETRY IN CONTACT INTERACTION OF ZIRCONIA WITH METAL MELTS

As a transition metal compound, zirconia can lose oxygen with the formation of nonstoichiometric phases. The stoichiometry affects the properties of material, therefore, the wetting of nonstoichiometric zirconia with inert metals (Cu, Ni, Sn, Ge, Ag, Pt) and alloys (Cu–Ga, Cu–Ge, Cu–Ni) is studied under conditions when the high oxygen deficit in zirconia is caused by the contact interaction with metal melts (such as Cu–Ti, Ni–Ti, Ti). It is established that the melts of inert metals can wet nonstoichiometric zirconia. This effect is explained as follows: the oxygen deficit may be considered as the zirconium surplus; this surplus of zirconium dissolves in the metal melt and, when the melt composition changes, then, the surface properties of the melt change too. Since zirconium is an active metal, the adhesion of the melt to the oxide substrate increases. In case of nickel, the microstructural study reveals nickel–zirconium intermetallide on the metal–oxide interface indicating the interaction of the nickel melt with zirconium from the substrate. Thermodynamic calculations show that such process is quite possible. Thin films are also considered. It is found out that Pt, Pd, and Ni films on stoichiometric zirconia are congregated in the islands at the temperatures significantly lower than the melting temperatures of corresponding metals, while they remain continuous on nonstoichiometric zirconia. Also, it can be explained by the chemical interaction of the metal film with the substrate.