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High Temperature Stable Gamma Iron Oxide

IP.com Disclosure Number: IPCOM000079840D
Original Publication Date: 1973-Sep-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Adams, GM: AUTHOR [+3]

Abstract

Gamma iron oxide which is brown and ferromagnetic up to its curie point and has a cubic structure, normally transforms to alpha iron oxide, which is red, nonmagnetic and has a rhombohedral structure when heated to 400 degrees centigrade.

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High Temperature Stable Gamma Iron Oxide

Gamma iron oxide which is brown and ferromagnetic up to its curie point and has a cubic structure, normally transforms to alpha iron oxide, which is red, nonmagnetic and has a rhombohedral structure when heated to 400 degrees centigrade.

The temperature of transformation may be increased to above 600 degrees centigrade. Gamma iron oxide particles are mixed in a solution with a material containing between 0.08 and 5% by weight based on the weight of iron oxide of a cation, chosen from the group having a cation size at least substantially that of the Na/+/ ion and less than the Cs/+/ ion, and evaporating the solvent from the solution. The chosen cation must be capable of entering the iron oxide lattice in cationic form from the solution. Typical cations are calcium, sodium, and potassium, in the form of a hydroxide, phosphate, or anionic phosphate ester.

In another approach, an anionic phosphate ester is added to a fundamental solution of a ferric salt and a hydroxide to coprecipitate a basic iron hydroxide, from which subsequent gamma iron oxide having improved temperature stability is formed. The anionic phosphate ester is present in a range between 0.08 to 5% by weight based on the weight of iron oxide to be formed, and of a cation chosen from the group having a cation size at least that of Na/+/ and less than that of Cs/+/. This latter approach is preferred where iron oxide particles greater than 15 microns are used.

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