Preparation of crystalline zirconia powders. Characterization of the bulk phase and interfacial behaviour

Calcinations, in oxygen, of ZrCl4, and Zr(OH)4, prepared hydrothermally, have been performed over a wide temperature range (200-850°C). The product of the reaction was (except for the 850°C sample) a phase mixture composed, at lower temperatures, of the stable monoclinic and the metastable cubic and tetragonal forms and, at higher temperatures, of the monoclinic and tetragonal polymorphs. Subjecting the powders to a severe mechanical grinding resulted, at any temperature, in the transformation of the phase mixture into a pure monoclinic phase. Some of the controversial aspects both of occurrence and of "stabilization" at low temperatures of ZrO2 polymorphs are discussed. Results concerning the dependence on the temperature of preparation and the features of the pure monoclinic phases (crystallites sizes, surface area, porosity) are presented. The paper also reports surface charge versus pH curves obtained on suspensions of the powders in KNO3. The effects induced by the temperature of preparation on the surface electrification behaviour are discussed. © 1990.