Process for preparing zirconium oxides and zirconium-based mixed oxides

1. A process for preparing a zirconium oxide in the absence of a cerium salt which comprises forming an aqueous solution of a zirconium salt and sulfate anions in a ratio of SO 4 2− /Zr 4+ ions of from 0.3/1 to 1.5/1, cerium salt being absent in said aqueous solution, maintaining said aqueous solution at a temperature not greater than 50° C. and precipitating only a single precipitate from said aqueous solution, said single precipitate being a zirconium hydroxide formed by reaction of said aqueous solution with an alkali at said temperature and then calcining said single precipitate of said zirconium hydroxide to form zirconium oxide, whereby the zirconium oxide thus formed is essentially sulfate free.

2. A process as claimed in claim 1 wherein the SO 4 2− concentration of the zirconium oxide formed is 0.1% by weight or less.

3. A process as claimed in claim 2 wherein the SO 4 2− concentration of the zirconium oxide formed is 0.07% by weight or less.

4. A process as claimed in claim 3 wherein the SO 4 2− concentration of the zirconium oxide formed is 0.05% by weight or less.

5. A process as claimed in claim 1 when the alkali is added dropwise with stirring over time to raise the pH up to about pH 13.

6. A process as claimed in claim 1 wherein the alkali is sodium hydroxide.

7. A process as claimed in claim 1 wherein the aqueous solution includes a salt of a metal selected from the group consisting of alkaline earths, rare earths, the first row transition metals, silicon, aluminum, tin, lead and combinations thereof.

8. A process as claimed in claim 7 wherein the transition metal is yttrium or lanthanum.

9. A process as claimed in claim 1 wherein the aqueous solution contains a salt which does not react with any other component.

10. A process as claimed in claim 9 wherein said salt is sodium chloride.

11. A process as claimed in claim 1 wherein the amount of zirconia in the product oxide is in the range of 30 to 100% by weight.

12. A process as claimed in claim 1 in which the total concentration of zirconium and any of said metals present in the aqueous solution measured as their respective oxides is at least 5 weight %.

13. A process as claimed in claim 12 wherein said concentration is 10 to 20 weight %.

14. A process as claimed in claim 13 wherein said concentration is 15 weight %.

15. A process as claimed in claim 1 wherein said temperature of said aqueous solution is less than 15° C.

16. A process as claimed in claim 1 wherein said temperature of said aqueous solution is less than 5° C.

17. A process as claimed in claim 1 wherein the ratio of ions SO 4 2− /Zr 4+ is 0.45/1 to 1.25/1.

18. A process as claimed in claim 1 including the step of adding hydrogen peroxide during or at the end of the precipitation step.

19. A process as claimed in claim 1 wherein the zirconium oxide produced has a surface area after sintering at 1000° C. of at least 40 m 2 /g and a surface area after sintering at 1100° C. of at least 10 m 2 /g.

20. A process as claimed in claim 1 wherein the zirconium oxide produced is sinterable at not more than 1450° C. within 8 hours.

21. A process as claimed in claim 20 wherein the zirconium oxide product is sinterable at not more than 1350° C. within 8 hours.

22. A process as claimed in claim 1 including the step of a hydrothermal treatment of the zirconium hydroxide before calcination.

23. A process as claimed in claim 1 including the step of drying the zirconium hydroxide before calcination.

24. A process as claimed in claim 23 when the drying is effected by spray drying.

25. A process as claimed in claim 1 wherein no gelatinous precipitate is formed during formation of said zirconium hydroxide.