Transformation of Yttria‐Doped Tetragonal ZrO₂ Poly crystals by Annealing under Controlled Humidity Conditions

Phase changes on the surface resulting from low‐temperature annealing of yttria‐doped tetragonal ZrO₂ polycrystals under controlled humidity conditions were investigated at 0.1 to 7350 Pa of water vapor pressure and 100° to 600°C for 1 to 50 h. The tetragonal‐to‐monoclinic phase transformation was greatly accelerated by increasing water vapor pressure; the transformation rate was first order with respect to the concentration of tetragonal ZrO₂ on the surface of the sample.