Time-resolved high and low temperature phase transitions of the nanocrystalline cubic phase in the Y2O3-ZrO2 and Fe2O3-ZrO2 system

The nanocrystalline cubic Phase of zirconia was found to be thermally stabilized by the addition of 2.56 to 17.65 mol % Y2O3 (5.0 to 30.0 mol % Y, 95.0 to 70.0 mol % Zr cation content). The cubic phase of yttria stabilized zirconia was prepared by thermal decomposition of the hydroxides at 400 degreesC for 1 hr. 2.56 mol % Y2O3-ZrO2 was stable up to 800 degreesC in an argon atmosphere. The samples with 4.17 to 17.65 mol % Y2O3 were stable to 1200 degreesC and higher. All samples at temperatures between 1450 degreesC to 1700 degreesC were cubic except the sample with 2.56 mol % Y2O3 which was tetragonal. The crystallite sizes observed for the cubic phase ranged from 50 to 150 Angstrom at temperatures below 900 degreesC and varied from 600 to 800 Mn between 1450 degreesC and 1700 degreesC. Control of furnace atmosphere is the main factor for obtaining the cubic phase of Y-SZ at higher temperature. Nanocrystalline cubic Fe-SZ (Iron Stabilized Zirconia) with crystallite sizes from 70 to 137 Angstrom was also prepared at 400 degreesC. It transformed isothermally at temperatures above 800 degreesC to the tetragonal Fe-SZ and ultimately to the monoclinic phase at 900 degreesC. The addition of up to 30 mol % Fe(III) thermally stabilized the cubic phase above 800 degreesC in argon. Higher mol % resulted in a separation of Fe2O3. The nanocrystalline cubic Fe-SZ containing a minimum 20 mol % Fe (III) was found to have the greatest thermal stability. The particle size was a primary factor in determining cubic or tetragonal formation. The oxidation state of Fe in zirconia remained Fe3+. Fe-SZ lattice parameters and rate of particle growth were observed to decrease with higher iran content. The thermal stability of Fe-SZ is comparable with that of Ca-SZ, Mg-SZ and Mn-SZ prepared by this method.