Phase transformation kinetics of 3 mol% yttria partially stabilized zirconia (3Y-PSZ) nanopowders prepared by a non-isothermal process

摘要

A crystalline nanopowder of 3 mol% yttria-partially stabilized zirconia (3 Y-PSZ) has been synthesized using ZrOCl_2 and Y(NO_3)_3 as raw materials throughout a co-precipitation process in an alcohol-water solution. The phase transformation kinetics of the 3 Y-PSZ freeze dried precursor powders have been investigated by nonisothermal methods. Differential thermal and thermogravimetric analyses (DTA/TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) have been utilized to characterize the 3 Y-PSZ nanocrystallites. When the 3Y-PSZ freeze dried powders are calcined in the range of 703-1073 K for 2 h, the crystal structure is composed of tetragonal and monoclinic ZrO_2. The BET specific surface area of the 3 Y-PSZ freeze dried precursor powders calcined at 703 K for 2 his 118.42 m~2/ g, which is equivalent to a crystallite size of 8.14 nm. The activation energy from tetragonal ZrO_2 converted to monoclinic ZrO_2 in the 3Y-PSZ freeze dried precursor powders was determined as 401.89 kJ/mol. The tetragonal (T) and monoclinic (M) ZrO_2 phases coexist with a spherical morphology, and based on TEM examination have a size distribution between 10 and 20 nm. When sintering green compacts of the 3 Y-PSZ, a significant linear shrinkage of 8 % is observed at about 1283 K. On sintering the densification cycle is complete at approximately 1623 K when a total shrinkage of 32% is observed and a final density above 99% of theoretical was achieved.