INFLUENCE OF ETHANOL WASHING OF THE HYDROUS PRECURSOR ON THE TEXTURAL AND STRUCTURAL-PROPERTIES OF ZIRCONIA

The influence of post-precipitation washing with ethanol on the evolution of the porous texture and structure of ZrO2 upon calcination in air has been investigated. Washing of the hydrogel of zirconia with ethanol was found to exert little influence on the process of crystallization of the hydrous zirconia: neither the temperature of crystallization nor the enthalpy change associated with the transition of the amorphous to the metastable tetragonal phase of zirconia was influenced significantly. On the other hand, the thermal stability of the tetragonal phase formed was found to be drastically reduced by effects imparted by the nature of the solvent used for washing the hydrogel; the process of phase-transformation to the thermodynamically more stable monoclinic modification was promoted strongly as a consequence of the washing with ethanol. This influence of ethanol washing appears to arise from a promotional effect of carbonaceous residues; these carbonaceous impurities are thought to facilitate the nucleation of the monoclinic phase. Washing the precipitate with ethanol was also found to have a profound effect on the textural properties of the (calcined) zirconia: the specific surface area, total pore volume and most frequent pore radius were all increased significantly. These effects of ethanol washing are believed to be due to an inhibition of polycondensation reactions of the surface hydroxyl groups located on adjacent particles which would have yielded new Zr-O-Zr bonds; this is probably associated with the presence of surface ethoxide species, the formation of which has been shown.