US4394160A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Making magnetic powders
Assignee: Unisys Corp
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Filing: 1979-12-03
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Granted: 1983-07-19
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Expires: 1999-12-03
Abstract
Abstract Magnetic powders for use in the manufacture of magnetic recording media are produced by a borohydride process in which aqueous solutions of ferrous sulfate and sodium borohydride are mixed in a magnetic field. The coercive force of the magnetic powder produced as a result of this method is controlled by controlling the temperature of the reactant solutions prior to mixing thereof.
Inventors
- 👤 Walter O. Freitag
- 👤 Victor V. Suchodolski
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 10:23
CPC Classifications
H; H01; H01F; H01F1/00; H01F1/01; H01F1/03; H01F1/032; H01F1/04; H01F1/06; H01F1/065; B; B22; B22F; B22F9/00; B22F9/16; B22F9/18; B22F9/24; Y; Y10; Y10S; Y10S428/00; Y10S428/90
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
198 words
A method of producing magnetic powders having a coercive force in the range of from about 300 Oe to 700 Oe for use in the manufacture of magnetic recording media which comprises: (a) pre-determining the desired coercive force of said magnetic powders, (b) preparing a solution of metal salt capable of forming a ferromagnetic material, (c) maintaining the solution of Step (b) at a pre-selected temperature which is functionally determinate of the desired coercive force, said pre-selected temperature being within a range of from about 0° C. to 50° C., (d) preparing a solution of a borohydride reducing agent, (e) maintaining the solution of Step (d) at a pre-selected temperature which is functionally determinate of the desired coercive force, said pre-selected temperature being within a range of from about 0° C. to 50° C., (f) mixing the solutions of Steps (c) and (e) together while applying a magnetic field of a selected magnitude to said mixture during the reducing reaction between said solutions, the temperatures of said reactant solutions of Steps (c) and (e) prior to the mixing being pre-selected so as to control the coercive force of the magnetic powder produced from the mixture of Step (f).
Claim 2
Independent Claim
198 words
A method of producing magnetic powders having a coercive force in the range of from about 300 Oe to 700 Oe for use in the manufacture of magnetic recording media which comprises: (a) pre-determining the desired coercive force of said magnetic powders, (b) preparing a solution of metal salt capable of forming a ferromagnetic material, (c) maintaining the solution of Step (b) at a pre-selected temperature which is functionally determinate of the desired coercive force, said pre-selected temperature being within a range of from about 0° C. to 50° C., (d) preparing a solution of a borohydride reducing agent, (e) maintaining the solution of Step (d) at a pre-selected temperature which is functionally determinate of the desired coercive force, said pre-selected temperature being within a range of from about 0° C. to 50° C., (f) mixing the solutions of Steps (c) and (e) together while applying a magnetic field of a selected magnitude to said mixture during the reducing reaction between said solutions, the temperatures of said reactant solutions of Steps (c) and (e) prior to the mixing being pre-selected so as to control the coercive force of the magnetic powder produced from the mixture of Step (f).
Claim 3
Dependent Claim
21 words
The method of claim 1 wherein the temperature is maintained within a range of from about 5° C. to 40° C.
Claim 4
Dependent Claim
17 words
The method of claim 1 wherein solution of Step (b) is an aqueous solution of ferrous sulfate.
Claim 5
Dependent Claim
18 words
The method of claim 1 wherein said solution of Step (d) is an aqueous solution of sodium borohydride.
Claim 6
Dependent Claim
18 words
The method of claim 4 wherein said solution of Step (d) is an aqueous solution of sodium borohydride.
Claim 7
Dependent Claim
48 words
The method of claim 1 wherein said mixture of Step (f) is a powder slurry and includes the steps of dewatering said powder slurry with a water miscible organic solvent to remove the water therefrom to produce a magnetic powder suitable for use as a magnetic recording medium.
Claim 8
Dependent Claim
36 words
The method according to claim 6 wherein said coercive force of said powder is directly and functionally dependent on the preselected temperatures of Steps (c) and (e), as set forth in FIG. 1 at curve 12.
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) | 1986-07-18 | 1987-01-17 | 1987-07-19 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1990-07-18 | 1991-01-17 | 1991-07-19 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1994-07-18 | 1995-01-17 | 1995-07-19 | $7700.00 | Window Closed / Lapsed |