METHOD FOR GRINDING SILICON-CONTAINING SOLIDS

Abstract

The object of the invention are methods for the production of silicon particles by grinding silicon-containing solids in a jet mill using a grinding fluid containing water vapor.

Claims

1. A process for producing silicon particles by milling silicon-containing solids in a jet mill using a milling fluid, which contains 20% by volume of steam, based on a total volume of the milling fluid.

2. The process for producing silicon particles as claimed in claim 1, where the milling fluid has a temperature of from 160 to 800 C.

3. The process for producing silicon particles as claimed in claim 1, wherein the milling fluid has a pressure of from 5 to 220 bar.

4. The process for producing silicon particles as claimed in claim 1, wherein the milling fluid contains 50% by volume of steam, based on the total volume of the milling fluid.

5. The process for producing silicon particles as claimed in claim 1, wherein the milling fluid contains 50% by volume of nitrogen, noble gases and other inert gases, based on the total volume of the milling fluid.

6. The process for producing silicon particles as claimed in claim 1, wherein the milling fluid is introduced into a milling chamber at a speed of sound of >343 m/s.

7. The process for producing silicon particles as claimed in claim 1, wherein a temperature of the steam is 2 C. above a dew point of water.

8. The process for producing silicon particles as claimed in claim 1, wherein the milling fluid contains superheated steam.

9. The process for producing silicon particles as claimed in claim 8, wherein the superheated steam is obtainable by heating water to a boiling point, subsequently introducing a heat of vaporization to form saturated steam and finally introducing further heat.

10. The process for producing silicon particles as claimed in claim 8, wherein at a given pressure, a temperature of the milling fluid flowing into the jet mill is greater than a temperature which corresponds to a saturated steam curve of water at the given pressure, where the saturated steam curve in a phase diagram of water is a dividing line between wet steam and superheated steam.

11. The process for producing silicon particles according to claim 1, wherein a median of a volume-weighted diameter size distribution d.sub.50 of the silicon particles so obtained is in a range from 0.3 m to 100 m.

12. The process for producing silicon particles as claimed in claim 1, wherein the silicon particles so obtained have an oxygen content of 10 mg, based on 1 m.sup.2 of surface area of the silicon particles.

13. The process for producing silicon particles as claimed in claim 2, wherein the milling fluid has a pressure of from 5 to 220 bar.

14. The process for producing silicon particles as claimed in claim 13, wherein the milling fluid contains 50% by volume of steam, based on the total volume of the milling fluid.

15. The process for producing silicon particles as claimed in claim 14, wherein the milling fluid contains 50% by volume of nitrogen, noble gases and other inert gases, based on the total volume of the milling fluid.

16. The process for producing silicon particles as claimed in claim 15, wherein the milling fluid is introduced into a milling chamber at a speed of sound of >343 m/s.

17. The process for producing silicon particles as claimed in claim 16, wherein a temperature of the steam is 2 C. above a dew point of water.

18. The process for producing silicon particles as claimed in claim 17, wherein the milling fluid contains superheated steam.

19. The process for producing silicon particles as claimed in claim 18, wherein the superheated steam is obtainable by heating water to a boiling point, subsequently introducing a heat of vaporization to form saturated steam and finally introducing further heat.

20. The process for producing silicon particles as claimed in claim 19, wherein at a given pressure, a temperature of the milling fluid flowing into the jet mill is greater than a temperature which corresponds to a saturated steam curve of water at the given pressure, where the saturated steam curve in a phase diagram of water is a dividing line between wet steam and superheated steam.

21. The process for producing silicon particles according to claim 20, wherein a median of a volume-weighted diameter size distribution d.sub.50 of the silicon particles so obtained is in a range from 0.5 m to 10 m.

22. The process for producing silicon particles as claimed in claim 22, wherein the silicon particles so obtained have an oxygen content of 10 mg, based on 1 m.sup.2 of surface area of the silicon particles.

Description

EXAMPLE 1

[0068] 600 g of high-purity polycrystalline silicon powder composed of solar silicon (Wacker BGF (sg) type PCL-NCS-F, d.sub.10=100 m, d.sub.50=240 m, d.sub.90=440 m) were introduced into the reservoir of a steam jet mill s-Jet 25 (manufacturer: Netzsch Trockenmahltechnik GmbH). The mill was operated using 15 kg/h of steam at 190 C. and a gauge pressure of 10 bar. The steam jet mill had previously been heated by means of nitrogen having a temperature of 120 C. The speed of rotation of the classifier wheel was 13 000 rpm. After 140 minutes, the steam jet mill was stopped and the collection vessel on the particle filter was opened. The particles were subsequently stored at room temperature in air under ambient pressure.

[0069] The collection vessel contained 230 g of silicon powder having d.sub.10=0.37 m, d.sub.50=0.83 m and d.sub.90=1.9 m (determined using the measuring instrument Horiba LA950).

[0070] The surface area calculated from the particle size distribution assuming spherical particles was 4 m.sup.2/g.

[0071] The oxygen content (determined using the oxygen analyzer Leco TCH 600) was 2.1% by weight and 5.2 mg/m.sup.2, based on the calculated particle surface area.

EXAMPLE 2

[0072] Example 2 was carried out in the same way as Example 1, with the following differences:

[0073] The speed of rotation of the classifier wheel was 4000 rpm and the steam jet mill was stopped after 20 minutes.

[0074] The collection vessel contained 350 g of silicon powder having d.sub.10=2 m, d.sub.50=4.3 m and d.sub.90=7.4 m (determined using the measuring instrument Horiba LA950).

[0075] The surface area calculated from the particle size distribution assuming spherical particles was 0.82 m.sup.2/g. The oxygen content (determined using the oxygen analyzer Leco TCH 600) was 0.44% by weight and 5.4 mg/m.sup.2, based on the calculated particle surface area.

COMPARATIVE EXAMPLE 3

[0076] 5 kg of high-purity polycrystalline silicon powder composed of solar silicon (Wacker BGF (sg) type PCL-NCS-F, d.sub.10=100 m, d.sub.50=240 m, d.sub.90=440 m) were introduced into the reservoir of a fluidized-bed jet mill CGS 16 (manufacturer: Netzsch Trockenmahltechnik GmbH). The fluidized-bed jet mill was operated using 93 m.sup.3/h of nitrogen at 20 C. and a gauge pressure of 7 bar. The speed of rotation of the classifier wheel was 6000 rpm. After 60 minutes, the fluidized-bed jet mill was stopped and the collection vessel on the particle filter was opened. The particles were subsequently stored at room temperature in air under ambient pressure.

[0077] The collection vessel contained 3.4 kg of silicon powder having d.sub.10=3.1 m, d.sub.50=4.8 m and d.sub.90=7.1 m (determined using the measuring instrument Horiba LA950).

[0078] The surface area calculated from the particle size distribution assuming spherical particles was 0.57 m.sup.2/g. The oxygen content (determined using the oxygen analyzer Leco TCH 600) was 0.27% by weight and 4.7 mg/m.sup.2, based on the calculated particle surface area.