INFLUENCE OF PH ON THE STABILITY OF LOW-TEMPERATURE T-ZRO2

The influence of the conditions of the chemical synthesis on stability of metastable t-ZrO2 was studied. Zirconia samples were crystallized from zirconium hydroxide precipitated at pH 13, 7 and 2.5. In all the samples, t-ZrO2 was the dominant phase but the m-ZrO2 phase was also p resent as a minor component. The samples obtained were subjected to th e influence of temperature (500 and 700 degrees C), pressure (500, 100 0 and 1350 MPa) and gamma-irradiation (10 MGy). The results of phase a nalysis showed that the change in the pH of zirconium hydroxide precip itation significantly changed the sensitivity of the metastable t-ZrO2 to temperature and pressure. The metastable t-ZrO2 was the most stabl e in the sample obtained from zirconium hydroxide precipitated at pH 2 .5 (a decrease of 2% of the starting t-ZrO2 phase after heating at 700 degrees C and a decrease of 35% after the application of a pressure o f 1350 MPa) and the most unstable in the sample obtained from zirconiu m hydroxide precipitated at pH 7 (a decrease of 97% of the starting t- ZrO2 phase after heating at 700 degrees C, and a decrease of 65% after application of a pressure of 1350 MPa). The effects of the factors me ntioned were monitored by X-ray powder diffraction and laser Raman spe ctroscopy. The results of laser Raman spectroscopy indicated that, wit hout regard to the precipitation pH, gamma-irradiation had very little influence on the metastable t-ZrO2. (C) 1998 Elsevier Science Ltd. Al l rights reserved.