US4029512A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method for the preparation of fibrous insoluble calcium sulfate anhydrite
Assignee: Johns Manville Corp
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Filing: 1974-08-05
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Granted: 1977-06-14
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Expires: 1994-08-05
Abstract
Abstract A process is described for the formation of fibrous insoluble calcium sulfate anhydrite, the fibers thereof having specified dimensions. A dilute aqueous suspension of gypsum and, if desired, a crystal habit modifier suitable for the formation of fibrous calcium sulfate hemihydrate, is first formed. The gypsum in this suspension is then converted to the fibrous hemihydrate by reaction in the presence of saturated steam at 120° C to 155° C for 0.5 to 2.5 hours, thereby forming fibrous calcium sulfate hemihydrate of the desired dimensions. The fibrous hemihydrate is thereafter calcined at 500° C to 750° C for 0.5 to 3.0 hours to convert the fibrous hemihydrate to fibrous insoluble calcium sulfate anhydrite having substantially the same crystalline shape and dimensions.
Inventors
- 👤 Karlis L. Jaunarajs
- 👤 Julie C. Yang
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 08:29
CPC Classifications
C; C01; C01B; C01B25/00; C01B25/16; C01B25/26; C01B25/38; C01B25/40; C01B25/41; C01F; C01F11/00; C01F11/46; C01F11/466; C04; C04B; C04B14/00; C04B14/38; C01P; C01P2004/00; C01P2004/10; C01P2004/54; C01P2004/60; C01P2004/61
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
200 words
A process for the formation of fibrous water insoluble calcium sulfate anhydrite, the fibers thereof having an overall average length in the range of from 30 to 70 microns, individual maximum lengths not exceeding 180 microns, and aspect ratios in the range of from 10:1 to 100:1; which comprises: a. forming an aqueous suspension of gypsum, said suspension being not greater than 0.30 molar in gypsum, and said gypsum prior to dispersion being in the form of particles at least 90% of which are minus 4 mesh in size; and b. converting the gypsum in said suspension to said fibrous calcium sulfate hemihydrate by reaction in a pressure vessel in the presence of saturated steam at a temperature in the range of from 120° C to 155° C for a period of 0.5 to 2.5 hours, thereby forming fibers of calcium sulfate hemihydrate having the aforesaid dimensions; and c. thereafter calcining said fibers of calcium sulfate hemihydrate at a temperature in the range of 500° C to 750° C for a period of 0.5 to 3.0 hours to convert said fibers of calcium sulfate hemihydrate to fibers of water insoluble calcium anhydrite having substantially the same crystalline shape and dimensions.
Claim 2
Dependent Claim
200 words
A process for the formation of fibrous water insoluble calcium sulfate anhydrite, the fibers thereof having an overall average length in the range of from 30 to 70 microns, individual maximum lengths not exceeding 180 microns, and aspect ratios in the range of from 10:1 to 100:1; which comprises: a. forming an aqueous suspension of gypsum, said suspension being not greater than 0.30 molar in gypsum, and said gypsum prior to dispersion being in the form of particles at least 90% of which are minus 4 mesh in size; and b. converting the gypsum in said suspension to said fibrous calcium sulfate hemihydrate by reaction in a pressure vessel in the presence of saturated steam at a temperature in the range of from 120° C to 155° C for a period of 0.5 to 2.5 hours, thereby forming fibers of calcium sulfate hemihydrate having the aforesaid dimensions; and c. thereafter calcining said fibers of calcium sulfate hemihydrate at a temperature in the range of 500° C to 750° C for a period of 0.5 to 3.0 hours to convert said fibers of calcium sulfate hemihydrate to fibers of water insoluble calcium anhydrite having substantially the same crystalline shape and dimensions.
Claim 3
Dependent Claim
27 words
The process of claim 1 wherein said temperature of formation of the fibrous calcium sulfate hemihydrate is in the range of from 125° C to 140° C.
Claim 4
Dependent Claim
18 words
The process of claim 1 wherein said calcining is at a temperature of 550° C to 650° C.
Claim 5
Dependent Claim
21 words
The process of claim 1 wherein the reaction time in step (b) is a period of from 0.75 to 2.0 hours.
Claim 6
Dependent Claim
47 words
The process of claim 1 wherein said aqueous suspension also contains a crystal habit modifier suitable for formation of said fibrous hemihydrate and selected from the group consisting of boric, succinic, adipic, malonic and sebacic acids and salts thereof; sodium, aluminum and zinc sulfates and sodium chloride.
Claim 7
Dependent Claim
26 words
The process of claim 5 wherein said crystal habit modifier is present in a concentration of from 0.1 to 5 weight percent of said aqueous suspension.
Claim 8
Dependent Claim
13 words
The process of claim 6 wherein said crystal habit modifier is boric acid.
Claim 9
Dependent Claim
21 words
The process of claim 1 wherein said calcining in step (c) is for a period of from 0.75 to 2.0 hours.
Claim 10
Dependent Claim
19 words
The process of claim 1 wherein said aqueous suspension has a concentration not greater than 0.26 molar in gypsum.
Claim 11
Dependent Claim
26 words
A reinforced composite article comprising an inorganic matrix reinforced with the fibrous water insoluble calcium sulfate anhydrite produced in accordance with the process of claim 1.
Claim 12
Dependent Claim
28 words
A reinforced composite article comprising an organic polymeric resin matrix reinforced with the fibrous water insoluble calcium sulfate anhydrite produced in accordance with the process of claim 1.
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) | 1980-06-13 | 1980-12-13 | 1981-06-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1984-06-13 | 1984-12-13 | 1985-06-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1988-06-13 | 1988-12-13 | 1989-06-14 | $7700.00 | Window Closed / Lapsed |