Particulate metal oxide

1. A particulate metal oxide comprising primary particles and secondary particles wherein the mean length of the primary particles is in the range from 50 to 90 nm, the mean width of the primary particles is in the range from 5 to 20 nm, and the median particle volume diameter of the secondary particles is less than 45 nm.

2. A metal oxide according to claim 1 wherein the primary particles have a mean length in the range from 55 to 85 nm and a mean width in the range from 8 to 19 nm.

3. A metal oxide according to claims 1 wherein at least 70% of the particles have a length in the range from 55 to 85 nm.

4. A metal oxide according to claim 3 wherein at least 70% of the particles have a length in the range from 60 to 80 nm.

5. A metal oxide according to claim 1 wherein the median particle volume diameter of the primary particles is in the range from 28 to 32 nm.

6. A metal oxide according to claim 1 wherein the median particle volume diameter of the secondary particles is in the range from 32 to 38 nm.

7. A metal oxide according to claim 1 wherein no more than 16% by volume of the secondary particles have a volume diameter of less than 24 nm.

8. A metal oxide according to claim 1 wherein more than 84% by volume of the secondary particles have a volume diameter of less than 60 nm.

9. A metal oxide according to claim 8 wherein more than 84% by volume of the secondary particles have a volume diameter of less than 50 nm.

10. A metal oxide according to claim 1 wherein the mean number of primary particles present in the secondary particles is in the range from 1.3 to 3.

11. A metal oxide according to claim 1 wherein the particles are hydrophobic.

12. A metal oxide according to claim 11 wherein the particles comprise an organic water repellant coating.

13. A metal oxide according to claim 1 wherein the particles comprise (i) in the range from 65% to 95% by weight of titanium dioxide, (ii) in the range from 2% to 12% by weight of inorganic coating, preferably alumina, and (iii) in the range from 4% to 18% by weight of organic coating, preferably fatty acid and/or salt thereof, all with respect to the total weight of the particles.

14. A sunscreen product comprising a metal oxide as defined in claim 1 .

15. A sunscreen product according to claim 14 which is transparent when applied to the skin and has a change in whiteness ΔL in the range from 0.5 to 2.5.

16. A sunscreen product according to claim 14 having a whiteness index in the range from 10% to 80%.

17. A method of forming a sunscreen product comprising introducing a metal oxide as defined in claim 1 into said product.

18. A particulate metal oxide comprising primary particles and secondary particles wherein the mean length of the primary particles is in the range from 55 to 85 nm, the mean width of the primary particles is in the range from 8 to 19 nm, and at least 70% of the primary particles have a length in the range from 55 to 85 nm.

19. A dispersion comprising primary particles and secondary particles of metal oxide in a dispersing medium wherein the mean length of the primary particles is in the range from 50 to 90 nm, the mean width of the primary particles is in the range from 5 to 20 nm, and the median particle volume diameter of the secondary particles is less than 45 nm.

20. A dispersion according to claim 19 comprising an organic medium and at least 45% by weight of metal oxide particles.

21. A dispersion according to claim 19 comprising an aqueous medium and at least 35% by weight of metal oxide particles.

22. A dispersion according to claim 19 wherein the primary particles have a mean length in the range from 55 to 85 nm and a mean width in the range from 8 to 19 nm.

23. A dispersion according to claim 19 wherein at least 70% of the particles have a length in the range from 55 to 85 nm.

24. A dispersion according to claim 23 wherein at least 70% of the particles have a length in the range from 60 to 80 nm.

25. A dispersion according to claim 19 wherein the median particle volume diameter of the primary particles is in the range from 28 to 32 nm.

26. A dispersion according to claim 19 wherein the median particle volume diameter of the secondary particles is in the range from 32 to 38 nm.

27. A dispersion according to claim 19 wherein no more than 16% by volume of the secondary particles have a volume diameter of less than 24 nm.

28. A dispersion according to claim 19 wherein more than 84% by volume of the secondary particles have a volume diameter of less than 60 nm.

29. A dispersion according to claim 28 wherein more than 84% by volume of the secondary particles have a volume diameter of less than 50 nm.

30. A dispersion according to claim 19 wherein the mean number of primary particles present in the secondary particles is in the range from 1.3 to 3.

31. A dispersion according to claim 19 wherein the particles are hydrophobic.

32. A dispersion according to claim 31 wherein the particles comprise an organic water repellant coating.

33. A dispersion according to claim 19 wherein the particles comprise (i) in the range from 65% to 95% by weight of titanium dioxide, (ii) in the range from 2% to 12% by weight of inorganic coating, preferably alumina, and (iii) in the range from 4% to 18% by weight of organic coating, preferably fatty acid and/or salt thereof, all with respect to the total weight of the particles.

34. A sunscreen product comprising a dispersion as defined in claim 19 .

35. A sunscreen product according to claim 34 which is transparent when applied to the skin and has a change in whiteness ΔL in the range from 0.5 to 3.5.

36. A sunscreen product according to claim 34 whiteness index in the range from 10% to 80%.

37. A method of forming a sunscreen product comprising introducing a dispersion as defined in claim 19 into said product.