US3974079A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Production of gamma iron oxide
Assignee: Bayer AG
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Filing: 1973-11-02
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Granted: 1976-08-10
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Expires: 1993-11-02
Abstract
Abstract Process for producing ferromagnetic iron oxides whereby a solution of a ferrous salt is oxidized in the presence of α-FeO(OH) seed, a basic precipitant, and phosphoric acid or a water soluble salt thereof to form α-FeO(OH), which can be dehydrated, optionally tempered, reduced and re-oxidized to needle-shaped γ-Fe 2 O 3 . The resulting product has high coercive force values which make it especially useful for magnetic impulse recording and reproduction.
Inventors
- 👤 Peter Woditsch
- 👤 Kurt Hill
- 👤 Franz Hund
- 👤 Fritz Rodi
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 23:02
CPC Classifications
H; H01; H01F; H01F1/00; H01F1/01; H01F1/03; H01F1/032; H01F1/10; H01F1/11; H01F1/113; C; C01; C01G; C01G49/00; C01G49/02; C01G49/06; C09; C09C; C09C1/00; C09C1/22; C09C1/24; G; G11; G11B; G11B5/00; G11B5/62; G11B5/68; G11B5/70; G11B5/706; G11B5/70626; G11B5/70642; G11B5/70647; G11B5/70652; G11B5/70663; C01P; C01P2004/00; C01P2004/10; C01P2004/54; C01P2004/60; C01P2004/62; C01P2006/00; C01P2006/42; C01P2006/80
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
142 words
In the process of producing ferromagnetic iron oxides by the steps comprising oxidizing a solution of a ferrous salt in the presence of α-FeO(OH) seed and a basic precipitant which acts as a proton acceptor thereby to form α-FeO(OH) pigment, dehydrating said α-FeO(OH) pigment to α-Fe 2 O 3 , reducing said α-Fe 2 O 3 to Fe 3 O 4 and re-oxidizing said Fe 3 O 4 to γ-Fe 2 O 3 having a needle length-to-width ratio of from 2:1 to 20:1, the improvement which comprises adding to said solution at the beginning of or during pigment formation phosphoric acid or a water soluble salt thereof in an amount, calculated as P 2 O 5 , of about 0.1 to 4% by weight of the α-FeO(OH) pigment produced, whereby the γ-Fe 2 O 3 ultimately produced is of high coercive force.
Claim 2
Dependent Claim
142 words
In the process of producing ferromagnetic iron oxides by the steps comprising oxidizing a solution of a ferrous salt in the presence of α-FeO(OH) seed and a basic precipitant which acts as a proton acceptor thereby to form α-FeO(OH) pigment, dehydrating said α-FeO(OH) pigment to α-Fe 2 O 3 , reducing said α-Fe 2 O 3 to Fe 3 O 4 and re-oxidizing said Fe 3 O 4 to γ-Fe 2 O 3 having a needle length-to-width ratio of from 2:1 to 20:1, the improvement which comprises adding to said solution at the beginning of or during pigment formation phosphoric acid or a water soluble salt thereof in an amount, calculated as P 2 O 5 , of about 0.1 to 4% by weight of the α-FeO(OH) pigment produced, whereby the γ-Fe 2 O 3 ultimately produced is of high coercive force.
Claim 3
Dependent Claim
43 words
The process of claim 1 wherein said solution is maintained at a pH of about 2 to 7 and at a temperature of about 40° to 95°C, oxidizing of said ferrous salt being performed at a rate of about 0.5 to 15 g/l/hour.
Claim 4
Dependent Claim
18 words
The process of claim 2, wherein oxidizing is performed at a rate of about 3 to 8 g/l/hour.
Claim 5
Dependent Claim
31 words
The process of claim 1 wherein said phosphoric acid or water-soluble salt thereof is first dissolved in the basic precipitant and the mixture thereof is added to said ferrous salt solution.
Claim 6
Dependent Claim
31 words
The process of claim 1 wherein said α-Fe 2 O 3 is tempered at a temperature of about 400° to 900°C prior to said reduction to Fe 3 O 4 .
Claim 7
Dependent Claim
31 words
The process of claim 1 wherein said α-Fe 2 O 3 is tempered at a temperature of about 600° to 830°C prior to said reduction to Fe 3 O 4 .
Claim 8
Dependent Claim
17 words
The process of claim 1 wherein said α-FeO(OH) seed was produced in the presence of phosphate ions.
Claim 9
Dependent Claim
33 words
The process of claim 1 wherein the phosphoric acid or water-soluble salt thereof calculated as P 2 O 5 is added in about 0.2 to 2% by weight of the α-FeO(OH) pigment produced.
Claim 10
Dependent Claim
127 words
The process of claim 1 wherein said α-FeO(OH) seed was produced in the presence of phosphate ions, the phosphoric acid or water-soluble salt thereof is first dissolved in the basic precipitant and the mixture thereof is added to said ferrous salt solution in an amount to provide about 0.2 to 2% of P 2 O 5 by weight of the α-FeO(OH) pigment ultimately produced, said solution is maintained at a pH of about 2 to 7 and at a temperature of about 40° to 95°C, oxidizing of said ferrous salt being performed at a rate of about 3 to 8 g/l/hour, and the α-Fe 2 O 3 is tempered at a temperature of about 600° to 830°C prior to said reduction to Fe 3 O 4 .
References Cited (Backward Citations)
US2694656A
Cited
DE1138750B
Cited
DE1176111B
Cited
US3382174A
Cited
DE1592398A1
Cited
US3652334A
Cited
BE783021A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1979-08-10 | 1980-02-09 | 1980-08-10 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1983-08-10 | 1984-02-09 | 1984-08-10 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1987-08-10 | 1988-02-09 | 1988-08-10 | $7700.00 | Window Closed / Lapsed |