US4487756A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Process for manufacturing crystalline alumina
Assignee: SWISS ALUMINIUM Ltd A CORP OF SWITZERLAND
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Filing: 1983-08-12
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Granted: 1984-12-11
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Expires: 2003-08-12
Abstract
Abstract The invention relates to a process for manufacturing crystalline alumina from aluminum hydroxide which after further conventional treatment is advantageously suitable for ceramic and refractory purposes or as a lapping and polishing agent. The process is such that aluminum hydroxide with a Na2O content of </=0.1 wt. % with respect to Al2O3 is subjected either directly or after prior partial dehydration to a thermal treatment above the temperature for transformation to alpha -Al2O3. The aluminum hydroxide has an addition of an ammonium containing mineralizer made to it, simultaneously in the presence of boron and/or fluorine, in particular an addition of NH4BF4. The product is characterized by way of the essentially isometric shape of the single crystals.
Inventors
- 👤 Tiberiu Mizrah
- 👤 Bernhard Schepers
- 👤 Bernd Schr/o/ der
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 14:17
CPC Classifications
C; C01; C01F; C01F7/00; C01F7/02; C01F7/44; C01F7/441; C01F7/442; C09; C09K; C09K3/00; C09K3/14; C09K3/1409; C01P; C01P2002/00; C01P2002/01; C01P2004/00; C01P2004/54
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
120 words
Process for manufacturing crystalline alumina α--Al 2 O 3 from aluminum hydroxide including a Na 2 O concentration of ≦0.1 wt.% with respect to Al 2 O 3 , adding to the aluminum hydroxide a mineralizer selected from the group consisting of boron-containing compounds, fluorine-containing compounds and mixtures thereof, wherein said mineralizer has added to it a mineralizer containing ammonium, and calcining said aluminum hydroxide at a temperature from 700° C. up to a temperature above that required for the transformation to α--Al 2 O 3 in the presence of said mineralizers to produce said alumina wherein at least 80% of the crystals are 1-10 μm in size and exhibit at most a diameter to height ratio D/H of 2.
Claim 2
Dependent Claim
120 words
Process for manufacturing crystalline alumina α--Al 2 O 3 from aluminum hydroxide including a Na 2 O concentration of ≦0.1 wt.% with respect to Al 2 O 3 , adding to the aluminum hydroxide a mineralizer selected from the group consisting of boron-containing compounds, fluorine-containing compounds and mixtures thereof, wherein said mineralizer has added to it a mineralizer containing ammonium, and calcining said aluminum hydroxide at a temperature from 700° C. up to a temperature above that required for the transformation to α--Al 2 O 3 in the presence of said mineralizers to produce said alumina wherein at least 80% of the crystals are 1-10 μm in size and exhibit at most a diameter to height ratio D/H of 2.
Claim 3
Dependent Claim
23 words
Process according to claim 1 wherein said aluminum hydroxide includes a Na 2 O concentration of equal to or less than 0.05 wt.%.
Claim 4
Dependent Claim
22 words
Process for manufacturing crystalline alumina according to claim 1 wherein at least one of the boron and fluorine containing compounds contains ammonium.
Claim 5
Dependent Claim
22 words
Process for manufacturing crystalline alumina according to claim 3 wherein the boron and fluorine containing compound is NH 4 BF 4 .
Claim 6
Dependent Claim
36 words
Process for manufacturing crystalline alumina according to claim 1 wherein the aluminum hydroxide is pre-dried in a first stage and is subjected to the calcination treatment in a second stage after the addition of the mineralizer.
Claim 7
Dependent Claim
23 words
Process for manufacturing crystalline alumina according to claim 5 wherein the first stage is carried out in a temperature range of ≧200°-550° C.
Claim 8
Dependent Claim
23 words
Process for manufacturing crystalline alumina according to claim 6 wherein the first stage is carried out in a temperature range of 400°-550° C.
Claim 9
Dependent Claim
25 words
Process for manufacturing crystalline alumina according to claim 5 wherein the calcination treatment time in the second stage of the process is about 1.5-4.5 hours.
Claim 10
Dependent Claim
20 words
Process according to claim 1 wherein said calcining step is at a temperature of from about 700° to 1400° C.
Claim 11
Dependent Claim
44 words
Process according to claim 1 wherein the aluminum hydroxide is pre-dried in a first stage, the mineralizer is added to the drier along with the aluminum hydroxide and the dried aluminum hydroxide with mineralizer is subjected to the calcination treatment in a second stage.
Claim 12
Dependent Claim
25 words
Process according to claim 1 wherein said aluminum hydroxide includes a Na 2 O concentration of 0.1-0.03% with respect to Al 2 O 3 .
Claim 13
Dependent Claim
55 words
Process according to claim 1 wherein said boron and fluorine-containing mineralizers are selected from the group consisting of NaF, CaF 2 , AlF 3 , Na 3 AlF 6 and x(BF 4 ) n , wherein x stands for metallic elements with a valence of 1 or 2 and n is the valence of x.
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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) | 1987-12-11 | 1988-06-11 | 1988-12-11 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-12-11 | 1992-06-11 | 1992-12-11 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-12-11 | 1996-06-11 | 1996-12-11 | $7700.00 | Window Closed / Lapsed |