US3720618A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method of producing a powder of cobalt-containing needle-like shaped gamma-ferric oxide particles as magnetic recording material
Assignee: Toda Kogyo Corp
•
Filing: 1971-02-25
•
Granted: 1973-03-13
•
Expires: 1991-02-25
Abstract
Abstract Procedure is described for producing a powder of cobaltcontaining, needle-like shaped gamma-ferric oxide, gamma -Fe2O3 particles useful for magnetic recording and the making of magnetic tape, magnetic sheet and magnetic disk with the powder which has high coercive force, high remanence and good dispersibility, uniform chemical composition, the cobalt uniformly dispersed on each particle, no twin particle structure, a particle length of 0.2-0.5 micron, a specific surface area of 15-25 m2/g and a content of anion such as SO42 less than 0.1 percent. Alkali is added to a mixture of a ferrous salt solution and a cobalt salt solution until the pH exceeds 11, an oxidizing gas of constant oxygen partial pressure is blown into the solution as uniformly fine air bubbles, also causing agitation while maintaining the solution at 30*-50*C, whereupon alpha-Fe2O3 hydrate particles precipitate with the cobalt ions in solid solution, and by washing, dehydrating, reducing and oxidizing conversion into the desired gamma -Fe2O3 particles results.
Inventors
- 👤 H Toda
- 👤 S Shimizu
- 👤 H Ihara
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 18:19
CPC Classifications
G; G11; G11B; G11B5/00; G11B5/62; G11B5/68; G11B5/70; G11B5/706; G11B5/70626; G11B5/70642; G11B5/70652; G11B5/70668; G11B5/70673; B; B82; B82Y; B82Y30/00; C; C01; C01G; C01G49/00; C01G49/02; C01G49/06; C01P; C01P2004/00; C01P2004/01; C01P2004/03; C01P2004/10; C01P2004/54; C01P2004/60; C01P2004/62; C01P2004/64; C01P2006/00; C01P2006/12; C01P2006/42; Y; Y10; Y10S; Y10S264/00; Y10S264/58
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
228 words
In the method of preparing cobalt-containing magnetic gamma -ferric oxide in which cobalt-containing Alpha -ferric oxide is precipitated as the hydrate through the passage of air through an aqueous solution of a ferrous salt and a cobalt salt, the cobalt-containing Alpha -ferric oxide is dehydrated and reduced, and the reduced product is then reoxidized, the improvements resulting in the precipitation of Alpha -ferric oxide hydrate particles containing cobalt in solid solution form, said particles having length of 0.2 to 0.5 microns, a length width ratio of at least 10:1 and a specific surface area of 25 to 70 m2/g., which in turn upon said dehydration, reduction and reoxidation will produce uniform cobalt-containing gamma -ferric oxide needles of a length of from 0.2 to 0.5 microns, a specific surface area of 15 to 25 m2/g. and a sulfate ion content of less than 1 percent, which comprise (a) adding to an aqueous solution of from 0.3 to 0.7 mol/L of ferrous salt containing sufficient cobalt salt to supply 0.5 to 10 atomic percent of cobalt ion to ferrous ion, an excess of caustic alkali sufficient to produce a pH of not less than 11, (b) maintaining said solution at a temperature of 30* to 50*C, and (c) introducing said air as uniformly dispersed fine bubbles at a constant pressure at a rate of 0.25 to 2.5 L/min/L of solution.
Claim 2
Dependent Claim
228 words
In the method of preparing cobalt-containing magnetic gamma -ferric oxide in which cobalt-containing Alpha -ferric oxide is precipitated as the hydrate through the passage of air through an aqueous solution of a ferrous salt and a cobalt salt, the cobalt-containing Alpha -ferric oxide is dehydrated and reduced, and the reduced product is then reoxidized, the improvements resulting in the precipitation of Alpha -ferric oxide hydrate particles containing cobalt in solid solution form, said particles having length of 0.2 to 0.5 microns, a length width ratio of at least 10:1 and a specific surface area of 25 to 70 m2/g., which in turn upon said dehydration, reduction and reoxidation will produce uniform cobalt-containing gamma -ferric oxide needles of a length of from 0.2 to 0.5 microns, a specific surface area of 15 to 25 m2/g. and a sulfate ion content of less than 1 percent, which comprise (a) adding to an aqueous solution of from 0.3 to 0.7 mol/L of ferrous salt containing sufficient cobalt salt to supply 0.5 to 10 atomic percent of cobalt ion to ferrous ion, an excess of caustic alkali sufficient to produce a pH of not less than 11, (b) maintaining said solution at a temperature of 30* to 50*C, and (c) introducing said air as uniformly dispersed fine bubbles at a constant pressure at a rate of 0.25 to 2.5 L/min/L of solution.
Claim 3
Dependent Claim
19 words
The method as defined in claim 1 in which mechanical stirring means are employed for stirring the aqueous solution.
Claim 4
Dependent Claim
20 words
The method as defined in claim 1 in which the pH of the aqueous solution is not less than 12.
Claim 5
Dependent Claim
227 words
In the method of preparing cobalt-containing magnetic gamma -ferric oxide in which cobalt-containing Alpha -ferric oxide is precipitated as the hydrate through the passage of air through an aqueous solution of a ferrous salt and a cobalt salt, the cobalt-containing Alpha -ferric oxide is dehydrated and reduced, and the reduced product is then reoxidized, the improvements resulting in the precipitation of Alpha -ferric oxide hydrate particles containing cobalt in solid solution form, said particles having length of 0.26 to 0.49 microns, a length width raTio of at least 10:1 and a specific surface area of 37 to 67 m2/g., which in turn upon said dehydration, reduction and reoxidation will produce uniform cobalt-containing gamma -ferric oxide needles of a length of from 0.2 to 0.4 microns, a specific surface area of 15 to 24 m2/g. and a sulfate ion content of less than 0.1 percent, which comprise (a) adding to an aqueous solution of about 0.5 mol/L of ferrous salt containing sufficient cobalt salt to supply about 2 atomic percent of cobalt ion to ferrous ion, more than 1.5 equivalents of caustic alkali so as to produce a pH of not less than 12, (b) maintaining said solution at a temperature of about 40*C, and (c) introducing said air as uniformly dispersed fine bubbles at a constant pressure at a rate of 1 to 2.5 L/min/L of solution.
Claim 6
Dependent Claim
227 words
In the method of preparing cobalt-containing magnetic gamma -ferric oxide in which cobalt-containing Alpha -ferric oxide is precipitated as the hydrate through the passage of air through an aqueous solution of a ferrous salt and a cobalt salt, the cobalt-containing Alpha -ferric oxide is dehydrated and reduced, and the reduced product is then reoxidized, the improvements resulting in the precipitation of Alpha -ferric oxide hydrate particles containing cobalt in solid solution form, said particles having length of 0.26 to 0.49 microns, a length width raTio of at least 10:1 and a specific surface area of 37 to 67 m2/g., which in turn upon said dehydration, reduction and reoxidation will produce uniform cobalt-containing gamma -ferric oxide needles of a length of from 0.2 to 0.4 microns, a specific surface area of 15 to 24 m2/g. and a sulfate ion content of less than 0.1 percent, which comprise (a) adding to an aqueous solution of about 0.5 mol/L of ferrous salt containing sufficient cobalt salt to supply about 2 atomic percent of cobalt ion to ferrous ion, more than 1.5 equivalents of caustic alkali so as to produce a pH of not less than 12, (b) maintaining said solution at a temperature of about 40*C, and (c) introducing said air as uniformly dispersed fine bubbles at a constant pressure at a rate of 1 to 2.5 L/min/L of solution.
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) | 1976-03-12 | 1976-09-11 | 1977-03-13 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-03-12 | 1980-09-11 | 1981-03-13 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-03-12 | 1984-09-11 | 1985-03-13 | $7700.00 | Window Closed / Lapsed |