Vanadia reactions with yttria stabilized zirconia

The reaction of vanadia films with yttria stabilized single-crystal cubic and polycrystalline cubic-tetragonal zirconias was studied using Rutherford backscattering (RBS) and x-ray diffraction, with some selected depth profiling studies. Vandium on zirconia readily oxidizes at 500 0C to form vanadia films. With increasing temperature, small amounts of vanadia diffuse into the zirconia. Near 650 0C the vanadia forms a eutectic solution at the surface and massive diffusion into the ZrO2 occurs. With rapid heating much of the vanadia volatilizes; with slow heating the vanadia diffuses large distances into the zirconia. Near 800 0C the vanadia principally reacts with yttria to form yttrium vanadate. At 980 0C and above, vanadia is completely reacted. Zirconia coated with materials which do not form a eutectic mixture (tantala, tantalum, vanadium) showed little reaction or diffusion at 900--1000 0C, but massive dissolution when a eutectic is formed (vanadia, chromia+vanadia). Yttria preferentially diffuses toward the surface when a reaction takes place to form YVO4 . When yttria is sequestered as the vanadate, the zirconia changes phase from cubic to monoclinic. Little difference in reactivity is observed between single-crystal and polycrystalline zirconia due to eutectic solution formation, which, with the phase separation, produces a very corroded surface