Preparation and anion exchange properties of zirconia Original Research Article

Zirconia samples were obtained from zirconyl chloride or nitrate following two procedures. The gel precipitation is performed either at a non steady pH, starting at a value lower than 0.5 up to a final value between 4 and 12, or at constant pH. In the first procedure the specific area increases with the final pH. The water content of the amorphous gels thus obtained maximizes at pH 10, reflecting an evolution of the textural properties. Precipitation at constant pH, using zirconyl chloride yield samples with specific areas higher than 300 m2 g−1. Upon calcination, structural and textural evolutions of the amorphous gel take place with a progressive decrease of the specific area and crystallization into a tetragonal phase. The crystallization temperatures were determined in situ by XRD measurements using a high temperature cell. The successive transformations of the amorphous gel into a tetragonal and the monoclinic phase are controlled by the size of the crystals and the excess energy. The exchange capacities of a sample calcined at increasing temperatures were followed by a titration method. Anion exchange capacities of 0.25 meq g−1 were found for amorphous zirconia. A decrease of 65% is noticed when the material becomes tetragonal. The monoclinic phase has nearly no exchange capacity.