US4374119A
Expired / Lapsed
US
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Process for the production of coarse crystalline alumina
Assignee: Schweizerische Aluminium AG
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Filing: 1981-09-16
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Granted: 1983-02-15
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Expires: 2001-09-16
Abstract
Abstract The invention describes a process for the production of coarse crystalline alumina from aluminum hydroxide, which after preparation by known methods is advantageously useful for abrasives, lapping and polishing purposes or for refractory materials. The process is characterized by aluminum hydroxide, either directly or after previous partial dehydration in the range 200 DEG -550 DEG C., being added with a mineralizer of compound type x(BF4)n, wherein x stands for NH4 and metallic elements and n is for the formal valence of x, and subsequently is subjected to an elevated temperature treatment between 750 DEG C. and a value higher than the phase change temperature to alpha -Al2O3.
Inventors
- 👤 Bernhard Schepers
- 👤 Volker Nobbe
- 👤 Bernd Schroder
- 👤 Werner Borer
- 👤 Manfred Kullack
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 00:18
CPC Classifications
C; C01; C01F; C01F7/00; C01F7/02; C01F7/44; C01F7/441; C01F7/442; C09; C09K; C09K3/00; C09K3/14; C09K3/1409; C01P; C01P2004/00; C01P2004/50; C01P2004/54; C01P2004/60; C01P2004/61
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
104 words
Process for the production from aluminum hydroxide of coarse crystalline alumina, α-Al 2 O 3 , with a mean crystallite diameter of >10μ, which comprises mixing aluminum hydroxide and a mineralizer of compound type x(BF 4 ) n , wherein x stands for NH 4 and metallic elements with a valence of 1 or 2, and n for the formal valence level of x, and subjecting said mixture to an elevated temperature treatment between 750° C. and a value lying above that required for the phase change to α-Al 2 O 3 to convert said aluminum hydroxide to the α-Al 2 O 3 .
Claim 2
Dependent Claim
104 words
Process for the production from aluminum hydroxide of coarse crystalline alumina, α-Al 2 O 3 , with a mean crystallite diameter of >10μ, which comprises mixing aluminum hydroxide and a mineralizer of compound type x(BF 4 ) n , wherein x stands for NH 4 and metallic elements with a valence of 1 or 2, and n for the formal valence level of x, and subjecting said mixture to an elevated temperature treatment between 750° C. and a value lying above that required for the phase change to α-Al 2 O 3 to convert said aluminum hydroxide to the α-Al 2 O 3 .
Claim 3
Dependent Claim
33 words
Process for the production of coarse crystalline alumina according to claim 1 wherein the maximum temperature is about 1350° C. and the residence time between 750° and 1350° C. is about 2.5-4.5 hours.
Claim 4
Dependent Claim
9 words
Process according to claim 1 wherein x is sodium.
Claim 5
Dependent Claim
9 words
Process according to claim 1 wherein x is potassium.
Claim 6
Dependent Claim
24 words
Process for the production of coarse crystalline alumina according to claim 1 wherein from 0.1 to 0.4 weight percent of the mineralizer is added.
Claim 7
Dependent Claim
40 words
Process for the production of coarse crystalline alumina according to claim 1 wherein aluminum hydroxide is used with an agglomerate size of <60μ and a Na 2 O content based on Al 2 O 3 of preferably 0.4-0.8 weight percent.
Claim 8
Dependent Claim
20 words
Process according to claim 1 which comprises a two-stage process wherein in the first stage the aluminum hydroxide is predried.
Claim 9
Dependent Claim
26 words
Process for the production of coarse crystalline alumina according to claim 7 wherein the first process stage is conducted at a temperature range from ≧200°-550° C.
Claim 10
Dependent Claim
26 words
Process for the production of coarse crystalline alumina according to claim 7 wherein the first process stage is conducted at a temperature range from ≧400°-550° C.
Claim 11
Dependent Claim
16 words
Process according to claim 7 wherein the aluminum hydroxide is substantially dehydrated in the predrying step.
Claim 12
Dependent Claim
25 words
Process according to claim 7 wherein the aluminum hydroxide starting material has an alkali content based on Al 2 O 3 in the range 0.2-1.4%.
Claim 13
Dependent Claim
41 words
Process for the production of coarse crystalline alumina according to claim 7 wherein the maximum temperature in the second stage is about 1350° C. and the residence time about 2.5-4.5 hours, of which for about 1 hour 1200° C. is exceeded.
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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) | 1986-02-14 | 1986-08-16 | 1987-02-15 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1990-02-14 | 1990-08-16 | 1991-02-15 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1994-02-14 | 1994-08-16 | 1995-02-15 | $7700.00 | Window Closed / Lapsed |