# US 4,394,160 A · Making magnetic powders

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 4,394,160 A
- Document ID: US4394160A
- Status: Granted
- Kind: A
- Application number: 06/099,365
- Filed: 1979-12-03
- Granted: 1983-07-19
- Earliest claimed: 1979-12-03
- Assignees: Sperry Corporation
- Inventors: Walter O. Freitag; Victor V. Suchodolski
- Web page: https://patentgrep.com/patent/US4394160A

## CPC

- H01F 1/065: {obtained by a reduction}
- B22F 9/24: starting from liquid metal compounds, e.g. solutions
- Y10S 428/90: Magnetic feature
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- B22F: WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER (making alloys by powder metallurgy C22C); APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

## 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.

## Claims

### Claim 1

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.degree. C. to 50.degree. 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.degree. C. to 50.degree. 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 (depends on 1)

The method of claim 1 wherein the temperature is maintained within a range of from about 5.degree. C. to 40.degree. C.

### Claim 3 (depends on 1)

The method of claim 1 wherein solution of Step (b) is an aqueous solution of ferrous sulfate.

### Claim 4 (depends on 1)

The method of claim 1 wherein said solution of Step (d) is an aqueous solution of sodium borohydride.

### Claim 5 (depends on 4)

The method of claim 4 wherein said solution of Step (d) is an aqueous solution of sodium borohydride.

### Claim 6 (depends on 1)

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 7 (depends on 6)

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.