THE PROPERTIES OF ZIRCONIA POWDERS PRODUCED BY HOMOGENEOUS PRECIPITATION

Spherical particles of zirconia were obtained by the calcination of monodisperse oxy-basic zirconium carbonate particles produced by homogeneous precipitation from zirconium sulphate solutions. By varying the salt concentration, monodisperse powders with diameters of 0.2-3 microns were obtained. The evolution of the structural characteristics of these powders during the calcination process was studied in some detail. The most interesting findings were the development of fully crystalline tetragonal zirconia at temperatures as low as 300 degrees C and the existence of the metastable zirconia in domains of up to 100 nm in diameter. These domains appeared to exhibit a sub-structure of closely oriented nanocrystallites. By comparing powders calcined in air and nitrogen it appeared that the stability of the metastable tetragonal phase with respect to monoclinic zirconia was enhanced in sub-stoichiometric material. The interpretation of measurements of crystallite size and microstrain by X-ray diffraction is also discussed.