Claims
- 1. A process for producing alpha alumina particles having crystallite size below about 1 micron, said process comprising:
- (a) providing particles of alumina having less than about 25 wt % alpha alumina content and an average particle size of about 1-20 microns,
- (b) fluidizing the alumina particles in a reactor with a fluidizing gas comprising principally steam having a pH of about 3-6, and
- (c) maintaining the alumina particles in said reactor at a temperature of about 380.degree.-600.degree. C. and a steam pressure of at least about 1000 psig for a sufficient time to obtain particles comprising predominantly alpha alumina and having an average crystallite size of less than about 1 micron.
- 2. The process of claim 1 wherein the pH of the fluidizing gas is about 3-5.
- 3. The process of claim 1 wherein the average crystallite size of the alpha alumina is less than about 0.5 micron.
- 4. The process of claim 1 wherein the average crystallite size of the alpha alumina is less than about 0.2 micron.
- 5. The process of claim 1 wherein the alumina particles provided in step (a) comprise alumina hydrate particles having average particle size of about 1-10 microns.
- 6. The process of claim 1 further comprising:
- (d) boiling water to obtain steam for the fluidizing gas in step (b), and
- (e) adding a water-soluble acid to the water.
- 7. The process of claim 6 wherein said acid is selected from the group consisting of hydrochloric acid, hydrofluoric acid, acetic acid, nitric acid, sulfuric acid, and carbonic acid.
- 8. The process of claim 6 wherein said acid is nitric acid.
- 9. The process of claim 1 wherein the temperature in the reactor is about 425.degree.-550.degree. C.
- 10. The process of claim 1 wherein the temperature in the reactor is about 425.degree.-500.degree. C.
- 11. The process of claim 1 wherein step (c) is performed for approximately 4-100 hours.
- 12. The process of claim 1 wherein the reactor pressure is about 1000-6000 psig.
- 13. In a process for producing alpha alumina particles of average crystallite size of less than about 1 micron, said process comprising the steps of:
- (a) sizing particles of alumina having less than about 25 wt % alpha alumina content to obtain an average particle size of about 1-2 microns,
- (b) fluidizing the sized alumina particles in a fluidized bed reactor with a fluidizing gas comprising principally steam, and
- (c) maintaining the sized alumina particles in said reactor at a temperature of about 380.degree.-500.degree. C. and a steam pressure of about 1000-6000 psig for a sufficient time to obtain particles comprising predominantly alpha alumina;
- the improvement comprising controlling the pH of the fluidizing gas to a value of about 3-6.
- 14. The process of claim 13 wherein the pH of the fluidizing gas is about 3-5.
- 15. The process of claim 13 further comprising:
- (d) boiling water to obtain steam for the fluidizing gas in step (b), and
- (e) adding to the water of step (d) a water-soluble acid selected from the group consisting of nitric acid, hydrochloric acid, hydrofluoric acid, acetic acid, sulfuric acid, and carbonic acid.
- 16. The process of claim 13 wherein the average crystallite size of the alpha alumina is less than about 0.5 micron.
- 17. The process of claim 13 wherein the average crystallite size of the alpha alumina is less than about 0.2 micron.
- 18. The process of claim 13 wherein the average crystallite size of the alpha alumina is about 0.1 micron.
PENDING RELATED PATENT APPLICATION
This application is a continuation of U.S. Ser. No. 011,247 filed Feb. 5, 1987, now abandoned.
US Referenced Citations (3)
Number |
Name |
Date |
Kind |
2642337 |
Newsome |
Jun 1953 |
|
4019914 |
Esper et al. |
Apr 1977 |
|
4477427 |
Matyasi et al. |
Oct 1984 |
|
Foreign Referenced Citations (1)
Number |
Date |
Country |
802731 |
Oct 1958 |
GBX |
Non-Patent Literature Citations (1)
Entry |
The Condensed Chemical Dictionary, Eigth Ed. Van Nostrand Reinhold Company NY p. 246, 1971. |
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
11247 |
Feb 1987 |
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