Patent US3645677A successfully refreshed from Google Patents.
US3645677A
Expired / Lapsed
US
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Production of gypsum
Assignee: Taki Chemical Co Ltd
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Filing: 1969-09-24
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Granted: 1972-02-29
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Expires: 1989-09-24
Abstract
Abstract Production of calcium sulfate dihydrate (gypsum) by hydrating calcium sulfate hemihydrate in admixture with a surface active agent, sulfuric acid and phosphoric acid, the mole ratio H2SO4/H3PO4 being greater than 0.4.
Inventors
- 👤 Hakuichi Akazawa
- 👤 Shigeaki Washio
- 👤 Keiji Kaji
- 👤 Shisao Fujita
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 15:38
CPC Classifications
C; C01; C01F; C01F11/00; C01F11/46; C01F11/466
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
20 words
A process according to claim 1 wherein the total concentration of the mixture of acids is 20 to 40 percent.
Claim 2
Dependent Claim
25 words
A process according to claim 1 wherein the surface active agent is selected from the group consisting of alkylarylsulfonic acids and alkali metal salts thereof.
Claim 3
Dependent Claim
15 words
A process according to claim 1 wherein the mol ratio H2SO4/H3PO4 is 0.5 to 5.0:1.
Claim 4
Dependent Claim
31 words
A process according to claim 1 wherein the calcium sulfate hemihydrate is obtained by decomposing a calcium phosphate-containing material in sulfuric acid or in a mixture of sulfuric and phosphoric acid.
Claim 5
Dependent Claim
49 words
A process according to claim 1 wherein phosphoric acid and calcium sulfate hemihydrate are produced by decomposing a calcium phosphate-containing material in sulfuric acid or in a mixture of sulfuric and phosphoric acid in the presence of said surface active agent, and the hemihydrate is subjected to said hydration.
Claim 6
Dependent Claim
14 words
A process according to claim 6 wherein the calcium phosphate-containing material is phosphate rock.
Claim 7
Dependent Claim
32 words
A process according to claim 6 wherein the surface active agent is present in an amount of 0.1 to 1.2 percent based on the calcium phosphate-containing material in the acid-decomposition reaction system.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-02-28 | 1975-08-30 | 1976-02-29 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-02-28 | 1979-08-30 | 1980-02-29 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-02-28 | 1983-08-30 | 1984-02-29 | $7700.00 | Window Closed / Lapsed |