Patent US3932293A successfully refreshed from Google Patents.
US3932293A
Expired / Lapsed
US
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Metallic ferromagnetic particles for use in environmentally stable magnetic recording media
Assignee: 3M Co
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Filing: 1974-08-28
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Granted: 1976-01-13
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Expires: 1994-08-28
Abstract
Abstract Environmentally stable magnetic recording composition comprising fine metal particles based on iron, cobalt, or nickel, the particles having a chromium-based outer layer formed by exposing the particles to a solution containing dichromate or chromate ions under high-shear mixing conditions.
Inventors
- 👤 John S. Roden
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 16:00
CPC Classifications
H; H01; H01F; H01F1/00; H01F1/01; H01F1/03; H01F1/032; H01F1/04; H01F1/06; H01F1/061; G; G11; G11B; G11B5/00; G11B5/62; G11B5/68; G11B5/70; G11B5/706; G11B5/70605; G11B5/70615; G11B5/712; Y; Y10; Y10S; Y10S428/00; Y10S428/90; Y10T; Y10T428/00; Y10T428/29; Y10T428/2982; Y10T428/2991
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
104 words
Fine magnetizable particles useful in the magnetizable layer of a magnetic recording medium to provide magnetic recording characteristics of improved environmental stability, said particles comprising at least 75 weight-percent metal, at least a majority of which is iron, cobalt, or nickel, and having a thin outer layer that comprises a chromium- and oxygen-containing compound and is formed by exposing the particles under high-shear mixing conditions to a solution containing dichromate or chromate ions and having a pH of up to 7.0, the amount of chromium in said thin outer layer comprising between about 1 and 10 percent of the total weight of the particles.
Claim 2
Dependent Claim
104 words
Fine magnetizable particles useful in the magnetizable layer of a magnetic recording medium to provide magnetic recording characteristics of improved environmental stability, said particles comprising at least 75 weight-percent metal, at least a majority of which is iron, cobalt, or nickel, and having a thin outer layer that comprises a chromium- and oxygen-containing compound and is formed by exposing the particles under high-shear mixing conditions to a solution containing dichromate or chromate ions and having a pH of up to 7.0, the amount of chromium in said thin outer layer comprising between about 1 and 10 percent of the total weight of the particles.
Claim 3
Dependent Claim
30 words
Magnetizable particles of claim 1 in which the amount of chromium in said thin outer layer comprises between about 3 and 5 percent of the total weight of the particles.
Claim 4
Dependent Claim
26 words
Magnetizable particles of claim 1 in which at least a majority of the metal is iron and 0.1 to 10 weight-percent of the metal is cobalt.
Claim 5
Dependent Claim
19 words
Magnetizable particles of claim 1 in which the particles have an average diameter of less than about 800 angstroms.
Claim 6
Dependent Claim
8 words
A slurry containing magnetizable particles of claim 1.
Claim 7
Dependent Claim
109 words
Fine magnetizable particles useful in the magnetizable layer of a magnetic recording medium to provide magnetic recording characteristics of improved environmental stability, said particles having an average diameter less than about 800 angstroms, comprising at least 75 weight-percent metal, at least 75 percent of which is iron, and having a thin outer layer that comprises a chromium- and oxygen-containing compound and that is formed by exposing the particles under high-shear mixing conditions to a solution containing dichromate or chromate ions and having a pH of up to 7.0, the amount of chromium in said outer layer averaging between about 3 and 5 percent of the weight of the particles.
Claim 8
Dependent Claim
109 words
Fine magnetizable particles useful in the magnetizable layer of a magnetic recording medium to provide magnetic recording characteristics of improved environmental stability, said particles having an average diameter less than about 800 angstroms, comprising at least 75 weight-percent metal, at least 75 percent of which is iron, and having a thin outer layer that comprises a chromium- and oxygen-containing compound and that is formed by exposing the particles under high-shear mixing conditions to a solution containing dichromate or chromate ions and having a pH of up to 7.0, the amount of chromium in said outer layer averaging between about 3 and 5 percent of the weight of the particles.
Claim 9
Dependent Claim
8 words
A slurry containing magnetizable particles of claim 6.
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) | 1979-01-12 | 1979-07-14 | 1980-01-13 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1983-01-12 | 1983-07-14 | 1984-01-13 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1987-01-12 | 1987-07-14 | 1988-01-13 | $7700.00 | Window Closed / Lapsed |