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Patent US4540439A successfully refreshed from Google Patents.
US4540439A
Expired / Lapsed
US
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Process for preparation of gypsum shapes
Assignee: Ruhr Stickstoff AG
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Filing: 1982-05-06
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Granted: 1985-09-10
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Expires: 2002-05-06
Abstract
Abstract A process for preparing shaped articles from waste gypsum from wet-process phosphoric acid production comprises: (1) mixing wet calcium sulfate hemihydrate with 0.5-20% by wt. of calcium hydroxide or calcium oxide, (2) adjusting the total water content of said mixture to 20-40% by wt., if necessary, and (3) molding shaped articles from said mixture by compression molding. The shaped objects so prepared have a low density and relatively high compressive strength.
Inventors
- 👤 Hans-Friedrich Kurandt
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-05 17:48
CPC Classifications
C; C04; C04B; C04B28/00; C04B28/14; C04B28/142; C04B28/143
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
120 words
A shaped gypsum article prepared by a process which comprises: (a) controlling the water content of a moist α-calcium sulfate hemihydrate obtained by filtration from the production of phosphoric acid without preliminary purification, drying, or calcining to be in the range of from 20 to 40% by weight, (b) mixing the hemihydrate from step (a) with 0.5 to 20% by weight calcium hydroxide or calcium oxide, and (c) compression molding the mixture from step (b) without adding any additional binding agent within 8 hours of said mixing, wherein said article has a density of from 1.61 to 1.8 kg/dm 3 and a compression strength of 200 to 285 kp/cm 2 when measured by DIN 106 for the size NF=240×115×71 mm.
Claim 2
Dependent Claim
120 words
A shaped gypsum article prepared by a process which comprises: (a) controlling the water content of a moist α-calcium sulfate hemihydrate obtained by filtration from the production of phosphoric acid without preliminary purification, drying, or calcining to be in the range of from 20 to 40% by weight, (b) mixing the hemihydrate from step (a) with 0.5 to 20% by weight calcium hydroxide or calcium oxide, and (c) compression molding the mixture from step (b) without adding any additional binding agent within 8 hours of said mixing, wherein said article has a density of from 1.61 to 1.8 kg/dm 3 and a compression strength of 200 to 285 kp/cm 2 when measured by DIN 106 for the size NF=240×115×71 mm.
Claim 3
Dependent Claim
18 words
The article of claim 1, wherein the weight of calcium hydroxide or calcium oxide is at least 3%.
Claim 4
Dependent Claim
18 words
The article of claim 1, wherein the weight of calcium hydroxide or calcium oxide is at least 5%.
Claim 5
Dependent Claim
18 words
The article of claim 1, wherein the weight of calcium hydroxide or calcium oxide is at least 8%.
Claim 6
Dependent Claim
16 words
The article of claim 1 wherein the water content of said mixture is 21-29% by wt.
Claim 7
Dependent Claim
20 words
The article of claim 1 wherein the amount of said calcium hydroxide or calcium oxide used is 1-10% by wt.
Claim 8
Dependent Claim
20 words
The article of claim 1 wherein said molded articles are allowed to cure for at least 4 hours after molding.
Claim 9
Dependent Claim
31 words
The article of claim 1 wherein additional ingredients selected from the group consisting of water-repellants, biocidal agents, conventional fillers, and conventional additives are additionally incorporated into the mixture of step (b).
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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) | 1988-09-09 | 1989-03-11 | 1989-09-10 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1992-09-09 | 1993-03-11 | 1993-09-10 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1996-09-09 | 1997-03-11 | 1997-09-10 | $7700.00 | Window Closed / Lapsed |