Silica-based sols

1. An aqueous sol containing silica-based particles wherein the sol has a specific surface area of at least 115 m 2 /g aqueous sol, thereby representing the specific surface area that is available per gram of aqueous silica-based sol, said silica-based particles have a specific surface area within the range of from 550 m 2 /g SiO 2 and less than about 1200 m 2 /g SiO 2 , thereby representing the average specific surface area of the silica-based particles present in the sol, wherein the specific surface area is determined by means of titration with NaOH after removal of or adjustment for any compounds present that may disturb the titration, wherein the sol has a pH of at least 10.5, and wherein the sol is substantially free from aluminium.

2. The aqueous sol according to claim 1 wherein the sol has a molar ratio of SiO 2 to M 2 O, where M is alkali metal or ammonium, within the range of from 15:1 to 40:1.

3. The aqueous sol according to claim 1 wherein the sol has an S-value within the range of from 25 to 35%.

4. The aqueous sol according to claim 3 wherein the sol has a specific surface area of at least 120 m 2 /g aqueous sol.

5. The aqueous sol according to claim 1 wherein the sol has a specific surface area of at least 120 m 2 /g aqueous sol.

6. The aqueous sol according to claim 1 wherein the sol has a silica content within the range of from 10 to 30% by weight.

7. The aqueous sol according to claim 1 wherein the sol has a viscosity within the range of from 5 to 40 cP.

8. The aqueous sol according to claim 1 wherein the sol is a stable silica sol.

9. An aqueous sol containing silica-based particles wherein the sol has a specific surface area of at least 115 m 2 /g aqueous sol, thereby representing the specific surface area that is available per gram of aqueous silica-based sol, and an S-value within the range of from 10 to 45%, wherein the specific surface area is determined by means of titration with NaOH after removal of or adjustment for any compounds present that may disturb the titration, wherein the sol has a pH of at least 10.5, and wherein the sol is substantially free from aluminium.

10. The aqueous sol according to claim 9 wherein the sol has a molar ratio of SiO 2 to M 2 O, where M is alkali metal or ammonium, within the range of from 15:1 to 40:1.

11. The aqueous sol according to claim 9 wherein the silica-based particles have a specific surface area of at least 550 m 2 /g SiO 2 .

12. The aqueous sol according to claim 9 wherein the sol has a specific surface area of at least 120 m 2 /g aqueous sol.

13. The aqueous sol according to claim 9 wherein the silica- based particles have a specific surface area of at least 300 m 2 /g SiO 2 and less than 1200 m 2 /g SiO 2 .

14. The aqueous sol according to claim 9 wherein the sol has a pH of at least 10.6.

15. The aqueous sol according to claim 9 wherein the sol is a stable silica-based sol.

16. An aqueous sol having

(a) a specific surface area of at least 115 m 2 /g aqueous sol, thereby representing the specific surface area that is available per gram of aqueous silica-based sol;

(b) an S-value within the range of from 10 to 45%;

(c) a molar ratio of SiO 2 to M 2 O, where M is alkali metal or ammonium, within the range of from 15:1to 40:1; and

(d) a pH of at least 10.5;

and containing

(e) silica-based particles which have a specific surface area of at least 550 m 2 /g SiO 2 and less than about 1200 m 2 /g SiO 2 , thereby representing the average specific surface area of the silica-based particles present in the sol,

wherein the specific surface area is determined by means of titration with NaOH after removal of or adjustment for any compounds present that may disturb the titration, and

wherein the sol is substantially free from aluminium.

17. The aqueous sol according to claim 16 wherein the sol is a stable silica-based sol.