The Effects of High-Temperature- and High-Pressure-Water on the Low Temperature Degradation Behavior of Y-TZP

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Abstract
The effects of high-temperature (200°-800°C)-and high-pressure (5 or 100MPa)-water on the low temperature degradation behavior of Y-TZP were investigated. Tetragonal (t) to monoclinic (m) transformation is markedly accelerated by the existence of water, under the hydrothermal condition at 200°-300°C, the surface of the specimen is spalled by the stress accompanied by the expansion of t→m transformation. The spalled layers and the surfaces of the unspalled bulk specimen consist of almost m-phase (≈90vol%). From SEM observation on these specimens, large cracks occurred from the corner of the specimen by the stress concentration, and then they propagated parallelly to the surface of the specimen and caused the spalling. An Arrhenius plot of the reaction rate estimated from the degraded thickness (spalled plus remained transformed thickness) gives the activation energy of about 16-17kcal/mol regardless the pressure or hydrothermal treatments. This value which seems to be the activation energy for the diffusion of OH- in Y-TZP lattice, suggests that the degradation of Y-TZP under hydrothermal conditions seems to be controlled by the OH- diffusion.

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