Phase Transformation of Zirconium Oxide. Influence of Pressure and Temperature.

Abstract

IVToNOCLINIC ZIRCONIA received from Wah Chang Corp. (99.9+U with 82 p.p.m. hafnium and < 100 p.p.m. iron as the major impurities) was prepressed at room temperature at 1500 atm., placed in a cylindrical high pressure device, and pressed to about 20,000 atm. at > 1800°C ., using a Pt, Pt-10U Rh thermocouple which failed at the maximum temperature. The device was then rapidly quenched to room temperature by the cutoff of the DC power supply and by water cooling the die. The high pressure cell consisted of a cylindrical silicon carbidecarbon heating element, boron nitride insulation, Pyrophvllite top and bottom pieces, and a platinum foil sample

Reactive hot pressing of ZrB2-based composites with changes in ZrO2/SiC ratio and sintering conditions. Part I: Densification behavior

“…This comparison verified that in the hot pressing of ZrB 2 composites reinforced by SiC and ZrO 2 , the applied pressure has more influence on the densification, may be due to the phase transformation of ZrO 2 during the hot pressing process [10][11]. Vahldiek et al [26] reported that the applied pressure can decrease the transition of the tetragonal ZrO 2 to the monoclinic phase (during cooling).…”

Electrical Resistivity and Diffusionless Phase Transformations of Zirconia at High Temperatures and Ultrahigh Pressures

“…In spite of the voluminous literature on zirconia, the influence of hydrostatic pressure, along with high temperatures on the course of the monoclinic-tetragonal transformation has received relatively little attention, although the fusion of ZrOe at 65,000 arm in a carbon tube has been reported (12). Vahldiek, Robinson, and Lynch have investigated the influence of pressure and temperature on the phase transformation of zirconia (13). They found that samples of chemically pure monoclinic zirconia after hot pressing at approximately 20,000 atm at temperatures of 1800~ and then rapidly quenched to room temperature, followed by decompression, subsequently exhibited a lower monoclinic-tetragonal phase transformation temperature on reheating.…”