An investigation into the preparation of high surface area zirconia

Hydrous zirconia was digested in solutions containing different cations at constant ionic strength. The influences of the cations, Na+, K+, and NH4+, on the hydrous zirconia and the resulting zirconia were studied. The anions of the digestion medium, Cl- and OH-, were the same in all series. At a constant pH, zirconia formed from the Na-series had the highest surface area, followed by the K-series and the NH3-series. This was explained by a more effective neutralization of the charged gel by the Na ions so that agglomeration of the primary particles to a porous but stabilized framework resulted. The surface area of the zirconia formed increases with pH. Above pH 11, lower surface area was obtained for samples that had been digested for long times. Digestion between pH 8 and 11 resulted in a preferential crystallization of the tetragonal phase. However, at pH 12, faster Ostwald ripening leads to the stable monoclinic phase for samples subjected to more than 96 h of digestion. The adsorption of cations on the hydrous zirconia is small for pH 8-11 but increased significantly from pH 12. These adsorbed ions affect the crystal phase of zirconia. (C) 1999 Elsevier Science B.V. All rights reserved.