COMPOSITE OXIDES OR HYDROXIDES COMPRISING ALUMINA, ZIRCONIA AND OPTIONALLY CERIA AND/OR RARE EARTH

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An improved method for the formation of composite hydroxides or oxides comprising, on an oxide basis, A1203 and Zr02, and optionally Ce02, La203, Nd203, Pr6011, Sm203, Y203, and other rare earth oxides, comprising the steps of preparing an aqueous metal salt solution and forming a hydroxide precipitate slurry by combining the aqueous metal salt solution with an aqueous solution of a caustic alkali at a pH greater than 8.5 to precipitate out all the metal species. The variation in pH during the precipitation reaction is +/- 1. The invention also relates to composites formed by this method comprising 20-70wt% A1203, 10-77wt% Zr02, 0-34wt% Ce02 and 0-22wt% REOs other than Ce02, and to composites per se comprising, on an oxide basis, 42-70wt% A1203, 10-48wt% Zr02, 2-34wt% Ce02 and 0-9wt% REOs other than Ce02 and having the following properties after heating to 850 °C over four hours and holding at 850 °C for four hours then allowing to cool to ambient temperature : - a surface area after aging at 950 °C for 2 hours equal to or greater than 60 m2/g, and - a surface area after aging at 1100 °C for 2 hours equal to or greater than 30 m2/g.