US4290799A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Ferromagnetic metal pigment essentially consisting of iron and a process for its production
Assignee: Bayer AG
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Filing: 1980-02-25
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Granted: 1981-09-22
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Expires: 2000-02-25
Abstract
Abstract A metal powder, suitable for magnetic recording, consisting essentially of iron, the individual particles being acicular and containing on average no more then 5 pores and consisting on average of no more than 2 metal cores is produced by precipitating and oxidizing an aqueous iron-(II)-salt solution to produce finely divided acicular iron-(III)-oxide-hydroxide, stabilizing it as by treatment with cadmium, lead, calcium, magnesium, zinc, aluminum, chromium, tungsten, a phosphorus oxide and/or a boron oxide, converting it into ferromagnetic iron oxide of low pore content, and reducing it to metallic iron with a gaseous reducing agent at about 300° to 600° C.
Inventors
- 👤 Gerhard Schroeder
- 👤 Gunter Buxbaum
- 👤 Franz Hund
- 👤 Heinrich-Christian Schopper
- 👤 Rolf Naumann
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 21:13
CPC Classifications
H; H01; H01F; H01F1/00; H01F1/01; H01F1/03; H01F1/032; H01F1/04; H01F1/06; H01F1/065; G; G11; G11B; G11B5/00; G11B5/62; G11B5/68; G11B5/70; G11B5/706; G11B5/70605; G11B5/70615
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
36 words
A metal powder, suitable for magnetic recording, consisting essentially of iron, the individual particles being acicular and containing on average no more than 5 pores and consisting on average of no more than 2 metal cores.
Claim 2
Dependent Claim
36 words
A metal powder, suitable for magnetic recording, consisting essentially of iron, the individual particles being acicular and containing on average no more than 5 pores and consisting on average of no more than 2 metal cores.
Claim 3
Dependent Claim
32 words
A metal powder as claimed in claim 1, in which the individual particles contain on average no more than 1 pore and consist on average of no more than 1 metal core.
Claim 4
Dependent Claim
45 words
A metal powder as claimed in claim 1, containing about 0.1 to 7% by weight of at least one of cadmium, lead, calcium, zinc, magnesium, aluminum, chromium, tungsten, phosphorus (expressed as P 2 O 5 ) and/or boron (expressed as B 2 O 3 ).
Claim 5
Dependent Claim
33 words
A metal powder as claimed in claim 1, containing about 0.1 to 4% by weight of phosphorus (expressed as P 2 O 5 ) and about 0.1 to 4% by weight of zinc.
Claim 6
Dependent Claim
29 words
A metal powder as claimed in claim 1, having a squareness ratio Br/4πI s of greater than about 0.55, preferably greater than 0.6, for a field of 3500 Oe.
Claim 7
Dependent Claim
117 words
In the production of a metal powder according to claim 1, wherein an aqueous iron-(II)-salt solution is precipitated and oxidized to produce finely divided acicular iron-(III)-oxide-hydroxide, the iron-(III)-oxide-hydroxide is dehydrated and then reduced to the metal, the improvement which comprises tempering the dehydrated iron-(III)-oxide-hydroxide in an inert gas at a temperature of about 600° to 900° C. to form ferromagnetic iron oxide of low pore content, subsequently reducing it to Fe 3 O 4 with moist hydrogen at about 300° to 600° C., stabilizing the low pore iron oxide by tempering at about 600° to 800° C., and reducing it to the metal with a gaseous reducing agent at a temperature from about 300° to 600° C.
Claim 8
Dependent Claim
51 words
A process as claimed in claim 6, wherein precipitation and oxidation to form the iron-(III)-oxide hydroxide are carried out at a pH-value below about 7, oxidation is terminated on reaching a pH-value lower than about 4 and the FeOOH obtained is protected against sintering by chemical stabilization prior to dehydration. PG,22
Claim 9
Dependent Claim
50 words
A process as claimed in claim 6, wherein to the suspension of iron-(III)-oxide-hydroxide precipitate at least one soluble compound of at least one of the elements cadmium, lead, calcium, magnesium, zinc, aluminum, chromium, tungsten, and/or an oxygen compound of phosphorus or boron is added for stabilizing the FeOOH against sintering.
Claim 10
Dependent Claim
25 words
A process as claimed in claim 8, wherein the stabilizing substances are added to the precipitation suspension before termination of the precipitation and oxidation reaction.
Claim 11
Dependent Claim
17 words
A process as claimed in claim 8, wherein a water-soluble phosphorus-oxygen compound is used for chemical stabilization.
Claim 12
Dependent Claim
20 words
A process as claimed in claim 8, wherein a zinc compound and a phosphorus-oxygen compound are used for chemical stabilization.
Claim 13
Dependent Claim
25 words
A process as claimed in claim 6, wherein the α-FeOOH has a mean particle size of about 12 to 32 nm, determined from X-ray-diffractometric data.
Claim 14
Dependent Claim
24 words
A process as claimed in claim 6, wherein the stabilization as ferromagnetic oxide includes at least partial reoxidation to γ-Fe 2 O 3 .
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) | 1984-09-21 | 1985-03-23 | 1985-09-22 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1988-09-21 | 1989-03-23 | 1989-09-22 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1992-09-21 | 1993-03-23 | 1993-09-22 | $7700.00 | Window Closed / Lapsed |