Abstract
The author shows two examples of phase transformation in some oxide ceramics, which is caused by the reaction of oxide ceramics and a vapor phase. The first example is a tetragonal-to-monoclinic transformation in ZrO2-Y2O3 ceramics which takes place isothermally during low temperature aging in air, accompanying an weight increase. An absorption band at 3340 cm-1 appears in FT-IR DRIFT spectrum in association with the appearance of monoclinic phase in ZrO2-Y2O3 ceramics. The reaction between ZrO2-Y2O3 ceramics and H2O in air, and the diffusion of OH- ions in the powders must be essential for this phase transformation to take place. The second case is an oxidation and reduction of powdered ceramic superconductor YBa2Cu3Oy In the case of isothermal reduction using orthorhombic powders, the reduction is controlled by the removing rate of oxygen from the particle surface. On the other hand, in a case of isothermal oxidation of tetragonal powders, the orthorhombic phase exists as a skin surrounding the unreacted core of the tetragonal phase. The oxidation is recognized to be controlled by the moving rate of the interface between the tetragonal and orthorhombic phases.
