Time-Resolved High and Low Temperature Phase Transitions of the Nanocrystalline Cubic Phase in the Y_2O_3-ZrO_2 and Fe_2O_3-ZrO_2 System

摘要

The nanocrystalline cubic phase of zirconia was found to be thermally stabilized by addition of 2.56 to 17.65 mol% Y_2O_3 (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 400degC for hr.2.56 mol% Y_2O_3-ZrO_2 was stable up to 800degC in an argon atmosphere.The samples with 4.17 to 17.65 mol% Y_2O_3 were stable to 1200degC and higher.All samples at temperatures between 1450degC to 1700degC were cubic except the sample with 2.56 mol% Y_2O_3 which was tetragonal.The crystallite sizes observed for the cubic phase ranged from 50 to 150 A at temperatures below 900degC and varied from 600 to 800 nm between 1450degC and 1700degC.Control of urnace 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 A was also prepared at 400degC.It transformed isothermally at temperatures above 800degC to the tetragonal Fe-SZ and ultimately to the monoclinic phase at 900degC.The addition of up to 30 mol% Fe(III)thermally stabilized the cubic phase above 800degC in argon.Higher mol% resulted in a separation of Fe_2O_3.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 Fe~(3+).Fe-SZ lattice parameters and rate of particle growth were observed ot decrease with higher iron content.The thermal stability of Fe-SZ is comparable with that of Ca-SZ,Mg-SZ and Mn-SZ prepared by htis mehtod.