INFLUENCE OF SOME VARIABLES OF THE PRECIPITATION PROCESS ON THE STRUCTURAL CHARACTERISTICS OF FINE ZIRCONIA POWDERS

Zirconia gels precipitated at pH 6, 10.4 and 13.5 from zirconyl chloride solutions have been investigated by thermogravitry and differential thermal analysis techniques. The total mass loss is 20% but increases for the lower pH studied. Oxide crystallization occurred at 447 degrees C, and no clear relation appears between processing conditions and thermal effects. The calcined powders were investigated by X-ray diffraction and nitrogen adsorption techniques. X-ray powder patterns only exhibited the tetragonal reflections after precipitation performed at pH 13.5 at room temperature. However, for a slight increase in the precipitant temperature the diffraction profile shows a mixture of monoclinic and tetragonal phases. The order of addition of solutions during the precipitation process produces some differences concerning crystallite sizes. Specific surface area values are found to be independent of the pH of precipitation, but strongly affected by the washing media.