Method for producing zirconia colloids

1. A method for producing a colloidal suspension of zirconia particles, comprising the following successive steps:

a) subjecting a mixture of zirconium oxychloride (ZrOCl 2 ) and an alkali metal halide in an aqueous solvent to hydrothermal treatment at a temperature above 150° C.,

b) separating a slurry obtained from a supernatant in step (a), and

c) peptizing said slurry by adding a strong acid thereto, and

d) desalting said slurry, so as to form the colloidal suspension of zirconia particles.

2. The method according to claim 1 , wherein the alkali metal halide is potassium chloride.

3. The method according to claim 1 , wherein the zirconium oxychloride and the alkali metal halide are mixed in a molar ratio of the alkali metal halide/ZrOCl 2 from 1/10 to 1/1.

4. The method according to claim 3 , wherein the molar ratio of alkali metal halide/ZrOC 1 2 is from 1/4 to 1/2.

5. The method according to claim 1 , wherein the zirconium oxychloride concentration in said mixture ranges from 0.5 to 4 mol/l.

6. The method according to claim 5 , wherein the zirconium oxychloride concentration in said mixture ranges from 1 to 2 mol/ 1 .

7. The method according to claim 1 , wherein the hydrothermal treatment is conducted at a temperature from 150 to 220° C. during at least one day.

8. The method according to claim 7 , wherein the hydrothermal treatment is conducted at a temperature from 160 to 200° C. during at least one day.

9. The method according to claim 8 , wherein the hydrothermal treatment is conducted at a temperature from 170 to 190° C. during at least one day.

10. The method according to claim 1 , wherein peptizing is conducted by means of hydrochloric acid.

11. The method according to claim 1 , wherein the method further includes a step of pH modification by addition of an inorganic or organic base.

12. The method according to claim 1 , wherein the method further includes a step of improving zirconia dispersion, either by adding a dispersant, or by surface modification of the zirconia particles.

13. The method according to claim 1 , wherein it further includes a step of dialysis so as to substitute at least one alcoholic solvent for the aqueous solvent.

14. A transparent colloidal suspension of zirconia particles obtainable by the method according to claim 1 , wherein the zirconia particles are provided in the form of single monoclinic rod-like crystallites, the dimensions of which range from 1 to 15 nm along their short axis and from 3 to 30 nm along their long axis.

15. The transparent colloidal suspension according to claim 14 , wherein the transparent colloidal suspension has a zeta potential of at least 30 mV in absolute value.

16. The transparent colloidal suspension according to claim 14 , wherein the transparent colloidal suspension has a solid content of at least 15 wt. %.

17. The transparent colloidal suspension according to claim 16 , wherein the transparent colloidal suspension has a solid content of at least 20 wt. %.

18. The transparent colloidal suspension according to claim 14 , wherein the zirconia particles have a refractive index of at least 1.8.

19. The transparent colloidal suspension according to claim 14 , wherein a pH is under 6 and the transparent colloidal suspension is free of stabilizer.

20. An optical article comprising a transparent polymer substrate and at least one coating prepared from a composition comprising a colloidal suspension according to claim 14 .