INFLUENCE OF OXYGEN PARTIAL-PRESSURE ON THE METASTABILITY OF UNDOPED ZIRCONIA DISPERSED IN ALUMINA MATRIX

The influence of oxygen content in the sintering atmosphere on, zircon ia phases in alumina-zirconia ceramics was studied. As was demonstrate d, in the case of samples sintered in art atmosphere with oxygen parti al pressure between 2.80 +/- 10(-5) Pa and 2.80 X 10(-2) Pa, 100% of z irconia was found to be in the cubic form. The appearance of transform able cubic zirconia is a result of oxygen vacancy concentration in zir conia. The increase of oxygen pal tial pressure and decrease of oxygen vacancy concentration leads to a breakdown of the cubic phase which t ransforms to the t- and/or m-phases. Critical values of oxygen vacancy concentration responsible for the metastability of cubic and tetragon al zirconia were estimated.