US3838980A
Expired / Lapsed
US
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Precipitation of bayer alumina trihydrate suitable for the manufacture of ceramic grade alumina of improved grindability
Assignee: Alcan Research and Development Ltd
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Filing: 1972-01-12
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Granted: 1974-10-01
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Expires: 1992-01-12
Abstract
Abstract Alpha alumina characterized by monocrystals of a small size, e.g. smaller than 5 microns, is produced from alumina trihydrate precipitated from pregnant Bayer solution by adding thereto alumina trihydrate seed crystals having a particle size such that at least 80-90 percent by weight of the seed crystals have a particle size smaller than 325 mesh. The seed crystals are added to the pregnant Bayer solution in a relatively large amount, such as an amount greater than 70 grams per liter. Desirably, the precipitation of the alumina trihydrate from the Bayer solution is carried out at a relatively high temperature, such as at a temperature in the range 165* -175* F. The resulting precipitated alumina trihydrate, characterized by a relatively low fluorine and residual soda (Na2O) content, is separated and calcined, such as at a temperature of about 1,250* C. to produce an alpha alumina product characterized by monocrystals having a size smaller than about 5 microns. The resulting produced alpha alumina is readily reduced in size by grinding, such as by impact grinding or by ball milling, to produce a superior ceramic grade alumina.
Inventors
- 👤 B Gnyra
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 07:08
CPC Classifications
C; C30; C30B; C30B7/00; C30B7/14; C01; C01F; C01F7/00; C01F7/02; C01F7/04; C01F7/14; C01F7/144; C04; C04B; C04B35/00; C04B35/01; C04B35/10; C04B35/111; C04B35/1115; C01P; C01P2004/00; C01P2004/60; C01P2004/61; C01P2006/00; C01P2006/12
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
193 words
THE METHOD OF PRODUCING CALCINED ALPHA ALUMINA OF CONTROLLED SMALL PARTICLE SIZE, THE ALPHA ALUMINA BEING CHARACTERIZED BY RELATIVELY SMALL MONOCRYSTALS, WITH COMPRISES ADDING SEED ALUMINA TRIHYDRATE CRYSTALS TO PREGNANT BAYER SOLUTION HAVING A CAUSTIC CONCENTRATION BETWEEN ABOUT 160 AND ABOUT 190 GRAMS PER LITER CAUSTIC MEASURED AS NA2CO3 TO PRECIPITATE ALUMINA TRIHYDRATE FROM SAID BAYER SOLUTION, THE AMOUNT OF SAID ALUMINA TRIHYDRATE ADDED TO SAID BAYER SOLUTION BEING IN THE RANGE FROM ABOUT 70 TO ABOUT 100 GRAMS PER LITER BASED ON SAID BAYER SOLUTION, SAID SEED ALUMINA TRIHYDRATE CRYSTALS HAVING A PARTICLE SIZE SUCH THAT AT LE WEIGHT IS SMALLER THAN 325 MESH, THE ADDITION OF SAID ALUMINA TRIHYDRATE CRYSTALS AND THE PRECIPITATION OF SAID ALUMINA TRIHYDRATE FROM SAID BAYER SOLUTION BEING CARRIED OUT AT A TEMPERATURE IN THE RANGE FROMF ABOUT 160*F, TO ABOUT 175*F, SEPARATING THE RESULTING PRECIPITATED ALUMINA TRIHYDRATE AND CALCINING THE SEPARATED ALUMINA TRIHYDRATE TO PRODUCE AN ALPHA ALUMINA PRODUCT MADE UP OF AGGREATES OF ALPHA ALUMINA MONOCRYSTALS SUCH THAT THE RESULTING CALCINED ALPHA ALUMINA PRODUCT IS MADE UP OF AT LEAST ABOUT 50 PERCENT BY WEIGHT ALPHA ALUMINA HAVING A MONOCRYSTAL SIZE LESS THAN 5 MICRONS.
Claim 2
Independent Claim
193 words
THE METHOD OF PRODUCING CALCINED ALPHA ALUMINA OF CONTROLLED SMALL PARTICLE SIZE, THE ALPHA ALUMINA BEING CHARACTERIZED BY RELATIVELY SMALL MONOCRYSTALS, WITH COMPRISES ADDING SEED ALUMINA TRIHYDRATE CRYSTALS TO PREGNANT BAYER SOLUTION HAVING A CAUSTIC CONCENTRATION BETWEEN ABOUT 160 AND ABOUT 190 GRAMS PER LITER CAUSTIC MEASURED AS NA2CO3 TO PRECIPITATE ALUMINA TRIHYDRATE FROM SAID BAYER SOLUTION, THE AMOUNT OF SAID ALUMINA TRIHYDRATE ADDED TO SAID BAYER SOLUTION BEING IN THE RANGE FROM ABOUT 70 TO ABOUT 100 GRAMS PER LITER BASED ON SAID BAYER SOLUTION, SAID SEED ALUMINA TRIHYDRATE CRYSTALS HAVING A PARTICLE SIZE SUCH THAT AT LE WEIGHT IS SMALLER THAN 325 MESH, THE ADDITION OF SAID ALUMINA TRIHYDRATE CRYSTALS AND THE PRECIPITATION OF SAID ALUMINA TRIHYDRATE FROM SAID BAYER SOLUTION BEING CARRIED OUT AT A TEMPERATURE IN THE RANGE FROMF ABOUT 160*F, TO ABOUT 175*F, SEPARATING THE RESULTING PRECIPITATED ALUMINA TRIHYDRATE AND CALCINING THE SEPARATED ALUMINA TRIHYDRATE TO PRODUCE AN ALPHA ALUMINA PRODUCT MADE UP OF AGGREATES OF ALPHA ALUMINA MONOCRYSTALS SUCH THAT THE RESULTING CALCINED ALPHA ALUMINA PRODUCT IS MADE UP OF AT LEAST ABOUT 50 PERCENT BY WEIGHT ALPHA ALUMINA HAVING A MONOCRYSTAL SIZE LESS THAN 5 MICRONS.
Claim 3
Dependent Claim
24 words
In the operation in accordance with claim 1 wherein the precipitated and separated alumina trihydrate is calcined at an elevated temperature above about 1,100*-1,300*C.
Claim 4
Dependent Claim
48 words
In the operation in accordance with claim 1 wherein the calcining of said precipitated and separated alumina trihydrate is carried out in the presence of about 0.1 percent by weight aluminum trifluoride (AlF3) added as mineralizer, said percent by weight being based on the weight of alumina trihydrate.
Claim 5
Dependent Claim
46 words
In the operation in accordance with claim 1 wherein said pregnant Bayer solution has a ratio measured as the ratio of the grams per liter alumina measured as Al2O3 in solution to the grams per liter caustic soda measured as Na2CO3 in solution below about 0.640.
Claim 6
Independent Claim
264 words
The method of producing alpha alumina of controlled small particle size, the alpha alumina being characterized by relatively small monocrystals, which comprises adding seed alumina trihydrate crystals to pregnant Bayer solution having a caustic concentration between about 160 and about 190 grams per liter caustic measured as Na2CO3 to precipitate alumina trihydrate from said Bayer solution, the amount of said alumina trihydrate crystals added to said Bayer solution being in the range from about 70 to about 100 grams per liter based on said Bayer solution, said seed alumina trihydrate crystals having a particle size such that at least 80 percent by weight is smaller than 325 mesh, the addition of said seed alumina trihydrate crystals and the precipitation of said alumina trihydrate from said Bayer solution being carried out at a temperature in the range from about 160*F. to about 175*F. and for a period of time of at least about 20 hours, said Bayer solution to which said seed alumina trihydrate crystals are added having a ratio measured as the ratio of the grams per liter alumina measured as Al2O3 in solution to the grams per liter caustic soda measured as Na2CO3 in solution below about 0.640, separating the resulting precipitated alumina trihydrate, calcining the resulting separated alumina trihydrate at a temperature above about 1, 200*C. for at least one hour to produce an alpha alumina product made up of aggregates of alpha alumina monocrystals such that at least 50 percent by weight of the alpha alumina product is made up of alpa alumina having a monocrystal size less than 5 microns.
Claim 7
Independent Claim
264 words
The method of producing alpha alumina of controlled small particle size, the alpha alumina being characterized by relatively small monocrystals, which comprises adding seed alumina trihydrate crystals to pregnant Bayer solution having a caustic concentration between about 160 and about 190 grams per liter caustic measured as Na2CO3 to precipitate alumina trihydrate from said Bayer solution, the amount of said alumina trihydrate crystals added to said Bayer solution being in the range from about 70 to about 100 grams per liter based on said Bayer solution, said seed alumina trihydrate crystals having a particle size such that at least 80 percent by weight is smaller than 325 mesh, the addition of said seed alumina trihydrate crystals and the precipitation of said alumina trihydrate from said Bayer solution being carried out at a temperature in the range from about 160*F. to about 175*F. and for a period of time of at least about 20 hours, said Bayer solution to which said seed alumina trihydrate crystals are added having a ratio measured as the ratio of the grams per liter alumina measured as Al2O3 in solution to the grams per liter caustic soda measured as Na2CO3 in solution below about 0.640, separating the resulting precipitated alumina trihydrate, calcining the resulting separated alumina trihydrate at a temperature above about 1, 200*C. for at least one hour to produce an alpha alumina product made up of aggregates of alpha alumina monocrystals such that at least 50 percent by weight of the alpha alumina product is made up of alpa alumina having a monocrystal size less than 5 microns.
Claim 8
Dependent Claim
52 words
The method in accordance with claim 5 wherein said aggregates of alpha alumina monocrystals are subjected to size reduction to produce an alpha alumina product having a particle size such that not more than 5 percent by weight of the resulting produced alpha alumina has a particle size greater than 10 microns.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-09-30 | 1978-04-01 | 1978-10-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-09-30 | 1982-04-01 | 1982-10-01 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-09-30 | 1986-04-01 | 1986-10-01 | $7700.00 | Window Closed / Lapsed |