Producing alpha alumina particles with pressurized acidic steam
AssigneeAluminum Company of America
InventorChanakya Misra
Life of this patent
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Abstract
Alumina particles having average particle size of about 1-20 microns are converted to alpha alumina in a steam-fluidized bed maintained at about 380.degree.-600.degree. C. and a pressure greater than about 1000 psig. Acidifying the steam reduces average crystallite size of the product and lowers content of some impurities. A preferred product is alpha alumina having an average crystallite size of less than about 0.2 micron.
Claims18
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.
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.
Dependencies are inferred from the claim text.