Phase Transformation Charactheristic of Nano-Sized Zirconia-Alumina Composite Powder

Abstract

A series of highly homogeneous ZrO2-Al2O3 composite powder was prepared by the spray-drying and calcination of mixed oxalate solution with any desired component ratio. The homogeneity extent(the separation range between ZrO2 and Al2O3) is below 10Å as determined experimentally. The homogeneous mixing between ZrO2-Al20O3 leads to a postponed crystallization of the tetragonal zirconia phase from amorphous phase at elevated temperatures. The grain growth of zirconia is greatly restrained by Al203 present in the composite powder as soon as ZrO2 particles appear as an isolated phase surrounded by Al203 matrix. For pure zirconia, 50mol%alumina doped and 80mol%alumina doped composite powders calcined at 1000°C-25min the average grain sizes are 100nm, 30nm and 13nm(by XRD-Line Broadening) respectively. In the mean time, with grain growth restraining, the phase transformation of zirconia particles from tetragonal to monoclinic is obviously repressed by the A12O3 surroundings. Higher temperature and larger critical grain size are needed for the phase transformation of composite powders with higher Al203 contents. For pure zirconia powder calcined at 800°C, the monoclinic content is higher than 95%(its critical grain size of transformation is equal to about 30nm at 600 C); but the monoclinic content of 80mol%alumina doped composite powder is less than 5% at 1300°C and 35% at 1550°C-3h.