Method of making silica-glass granule from pyrogenic silica powder
View Patent ↗Silica glass granule having the following features: Area: 100 to 5000 μm 2 , ECD: 5 to 100 μm, Circumference: 20 to 400 μm, Maximum diameter: 10 to 140 μm, Minimum diameter: 5 to 80 μm, where all values are medium values, Specific BET surface area: <1 m 2 /g Impurities: <50 ppm It is prepared by a) compacting pyrogenic silicon dioxide powder with a tamped density of 15 to 190 g/l to slugs, b) subsequently crushing them and removing slug fragments with a diameter of <100 μm and >800 μm, c) the slug fragments having a tamped density of 300 to 600 g/l, and d) subsequently treating them at 600 to 1100° C. in an atmosphere which comprises one or more compounds which are suitable for removing hydroxyl groups, and e) then sintering them at 1200° C. to 1400° C.
1. A process for preparing a silica glass granule, the process comprising:
a) mechanically compacting pyrogenic silicon dioxide powder having a tamped density of 15 to 190g/l, to obtain slugs;
b) crushing the slugs, to obtain slug fragments having a tamped density of 300 to 600g/l;
c) removing the slug fragments having a diameter of <100 μm and >800 μm, to obtain classified fragments;
d) heating the classified fragments at a temperature in a range from 600 to 1100° C. in an atmosphere comprising a compound which removes hydroxyl groups, to obtain treated fragments; and
e) sintering the treated fragments at a temperature in range from 1200° C. to 1400° C., to obtain silica glass granules having:
a median area in a range from 100 to 5000 μm 2 ;
a median ECD in a range from 5 to 100 μm,
a median circumference in a range from 20 to 400 μm;
a median maximum diameter in a range from 10 to 140 μm.
a median minimum diameter in a range from 5 to 80 μm,
a specific BET surface area of <1 m 2 /g; and
a total impurity content of <50 ppm.
2. The process of claim 1 , wherein the pyrogenic silicon dioxide powder has a tamped density of 30 to 150 g/l.
3. The process of claim 1 , wherein the slug fragments have a tamped density of 400 to 500g/l.
4. The process of claim 1 , wherein the compound, during (d), is at least one selected from the group consisting of chlorine, hydrochloric acid, a sulphur halide, and a sulphur oxide halide.
5. The process of claim 4 , wherein the compound, during (d), is hydrochloric acid.
6. The process of claim 4 , wherein the compound, during (d), is a sulphur halide.
7. The process of claim 6 , wherein the compound, during (d), is disulphur dichloride.
8. The process of claim 4 , wherein, during (d), a content of the compound in the atmosphere is in a range from 0.5 to 20% by volume.
9. The process of claim 1 , wherein the silica glass granule has a bimodal distribution.
10. The process of claim 9 , wherein the bimodal distribution has a first maximum at 100 to 200 μm and a second maximum at 250 to 450 μm.
11. The process of claim 1 , wherein a surface of a silica granule grain has elevations with irregular spacings.
12. The process of to claim 11 , wherein a height of the elevations is in a range from 0.5 μm to 35 μm.
13. The process of claim 1 , wherein the silica glass granule has a median area in a range from 500 to 1500 μm median ECD in a range from 10 to 50 μm, a median circumference in a range from 50 to 150 μm, a median maximum diameter in a range from 30 to 70 μm, and a median minimum diameter in a range from 20 to 50 μm.
14. The process of claim 13 , wherein the silica glass granule has a bimodal distribution with a first maximum at 100 to 200 μM and a second maximum at 250 to 450 μm.
15. The process of claim 13 , wherein a surface of a silica granule grain has elevations with irregular spacings and a height of the elevations is in a range from 0.5 μm to 35 μm.
16. The process of claim 15 , wherein the compound, during (d), is hydrochloric acid.
17. The process of claim 13 , wherein the compound, during (d), is at least one selected from the group consisting of chlorine, hydrochloric acid, a sulphur halide, and a sulphur oxide halide.
18. The process of claim 13 , wherein the compound, during (d), is chlorine.
19. The process of claim 13 , wherein the compound, during (d), is a sulphur halide.
20. The process of claim 13 , wherein the compound, during (d), is disulphur dichloride.