The preparation of high surface area zirconia — Influence of precipitating agent and digestion Original Research Article

High surface area zirconia was produced by digestion of the hydrous oxide at 100°C for various lengths of time. Precipitation of the hydrous zirconia was effected by potassium hydroxide and sodium hydroxide, the pH during precipitation being maintained at 14. The zirconia obtained after calcination of the undigested hydrous precursors at 500°C for 12 h had a surface area of ∼40–50 m2/g. With digestion, surface areas as high as 250 m2/g could be obtained. NaOH-digested samples were found to have higher surface areas than KOH-digested ones. An optimum digestion time of 12–24 h was found for both precipitants. The zirconia was thermally stable up to 800°C with a surface area of 170 m2/g. Longer-digested samples were more thermally stable than shorter-digested ones. The effect of digestion on the surface area was attributed to the aggregation of particles followed by strengthening of inter-particle contacts. Hence, the high surface area of the hydrous oxides was retained in the zirconia formed after calcination. The crystal phase of zirconia depends on digestion and the precipitating agent. Zirconia prepared from the undigested precursors comprised of both monoclinic and tetragonal phases. NaOH-digested samples crystallize only in the tetragonal phase while KOH-digested zirconia was a mixture of monoclinic and tetragonal phase (∼20 : 80). These observations were explained by the incorporation of sodium and potassium ions in the lattice. In all digested samples, the tetragonal phase was observed up to 1000°C; a sudden change to the monoclinic structure occurred above this temperature.