Improving the magnetic properties of gamma-iron (III) oxide

• US 4,212,903 A
• Filed: 02/22/1977
• Issued: 07/15/1980
• Est. Priority Date: 11/09/1972
• Status: Expired due to Term

• Current Assignee: BASF AG (BASF SE)
• Original Assignee: BASF AG (BASF SE)
• Inventors: Ohlinger, Manfred, Hammon, Fritz, Schnell, Georg
• Primary Examiner(s): Pianalto, Bernard D.
• Application Number:
  US05/770,989
• Time in Patent Office: 1,239 Days
• Field of Search: 427/48, 427/127-132, 428/900
• US Class Current: 427/127
• CPC Class Codes: G11B 5/70647 with a skin G11B5/70657 takes precedence
• CPC Class Codes: G11B 5/70652 gamma - Fe2 O3
• CPC Class Codes: G11B 5/70657 with a skin
• CPC Class Codes: Y10S 428/90 Magnetic feature

Abstract

The invention relates to a process for improving the magnetic properties, especially the remanent magnetization, of gamma-iron(III) oxide which can be used advantageously as the magnetic component in magnetic recording media exhibiting reduced print-through. For this purpose, a gamma-iron(III) oxide manufactured according to known processes is heated at temperatures of from 400° to 700° C., the magnetic pigment having basic compounds on the crystal surface during this heat treatment and retaining a pH value above 8 until heating is over. Gamma-iron(III) oxide magnetic pigments treated in this way are particularly suitable for the manufacture of low-noise magnetic recording media with high remanent magnetization and particularly low print-through.

Claims

1. A process for improving the magnetic properties of gamma-iron(III) oxide pigments which comprises:

applying to said gamma-iron(III) oxide pigments a basic compound selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides to provide a pigment crystal surface having a pH above 8, which basic compounds can be removed by elution of the said pigments after they have been heated at a temperature of from 400°

to 700°

C., and

heating said pigments at a temperature of from 400°

to 700°

C., said surface crystal pH remaining above 8 throughout said heating step, whereby the magnetic properties of said pigments are improved.

2. A process as claimed in claim 1, wherein the pigment is heated at 450°

to 550°

C.

3. A process as set forth in claim 1 wherein said basic compound is sodium hydroxide.

4. A process as claimed in claim 1, wherein cobalt-modified gamma-iron(III) oxides are heated.

5. A process as set forth in claim 1 wherein the surface crystal pH of the pigments remains above 9 during the heating step.