# US 4,396,596 A · Method of preparing gamma ferric hydroxyoxide powder

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- Number: US 4,396,596 A
- Document ID: US4396596A
- Status: Granted
- Kind: A
- Application number: 06/312,797
- Filed: 1981-10-19
- Granted: 1983-08-02
- Earliest claimed: 1980-10-24
- Assignees: Sony Corporation
- Inventors: Kenji Ogisu; Makoto Inoue; Kenji Yazawa; Haruko Masuya
- Web page: https://patentgrep.com/patent/US4396596A

## CPC

- C01G 49/06: Ferric oxide [Fe2O3]
- G11B 5/70652: {gamma - Fe2 O3}
- C01P 2004/03: obtained by SEM
- C01P 2004/10: extending in one dimension, e.g. needle-like
- C01P 2004/20: extending in two dimensions, e.g. plate-like
- C01P 2006/42: Magnetic properties
- C01G: COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F (metal hydrides {monoborane, diborane or addition complexes thereof} C01B6/00; salts of oxyacids of halogens C01B11/00; peroxides, salts or peroxyacids C01B15/00; thiosulfates, dithionites, polythionates C01B17/64; compounds containing selenium, or tellurium C01B19/00; binary compounds of nitrogen with metals C01B21/06; azides C01B21/08; {compounds containing nitrogen, other non-metals and metal C01B21/082}; metal amides C01B21/092; nitrites C01B21/50; {compounds of noble gases C01B23/0005}; phosphides C01B25/08; salts of oxyacids of phosphorus C01B25/16; carbides C01B32/90; compounds containing silicon C01B33/00; compounds containing boron C01B35/00; compounds having molecular sieve properties but not having base-exchange properties C01B37/00; compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites, C01B39/00; cyanides C01C3/08; salts of cyanamide C01C3/16; thiocyanates C01C3/20)
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)
- C01P: INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS

## Abstract

A method of preparing gamma ferric hydroxyoxide in which ferrous ions are reacted in an alkaline solution to produce a suspension of ferric hydroxide, the resulting suspension is treated with an oxidizing gas in a first oxidizing step at a relatively high oxidation rate, sufficient to cause nucleation of gamma ferric hydroxyoxide to occur, and then the oxidation rate is reduced in a second oxidizing step to cause crystal growth to occur on the nuclei formed in the first oxidizing step. The resulting product has magnetic and physical characteristics making it extremely suitable for use in the manufacture of magnetic recording media.

## Claims

### Claim 1

A method of preparing gamma ferric hydroxyoxide which consists essentially of:
reacting ferrous ions in an alkaline solution to produce a suspension of ferrous hydroxide,
passing an oxidizing gas into said suspension in a first oxidizing step to an extent sufficient to cause nucleation of gamma ferric hydroxyoxide to occur, and until the ratio of ferric ions to the total amount of iron in solution is in the range from 0.3 to 0.48, and the ratio of hydroxyl ions to ferrous ions is less than one and
reducing the oxidation rate of said gas after such nucleation occurs and said ratios are effected to a value of 1/5 to 1/50 of the rate in said first oxidizing step in a second oxidizing step to cause crystal growth to occur on the nuclei formed in said first oxidizing step without significantly increasing the amount of new nuclei formed, with the resultant crystals exhibiting a central rectangular shape without any significant vein shape.

### Claim 2 (depends on 1)

A method according to claim 1 in which:
said first oxidizing step is continued until the ratio of ferric ions to the total amount of iron in solution is in the range from 0.35 to 0.47.

### Claim 3 (depends on 1)

A method according to claim 1 which includes the steps of:
adding a solution containing green rust to the crystals growing in said second oxidizing step and
continuing the oxidation at the reduced oxidation rate.

### Claim 4 (depends on 1)

A method according to claim 1 which includes the step of:
reducing said rate of oxidation by decreasing the proportion of oxygen in the oxygen-containing gas.

### Claim 5 (depends on 1)

A method according to claim 1 which includes the steps of:
reducing said rate of oxidation both by decreasing the proportion of oxygen in the oxygen-containing gas and also decreasing the flow rate of said oxygen-containing gas into said suspension.