Process for producing single phase magnetite powder

Details Process for producing single phase magnetite powder Process for producing single phase magnetite powder

1994-10-03

1996-04-30

Bonner, Melissa

Compositions

Magnetic

Iron-oxygen compound containing

423632, C01G 4908, C01G 4906

Patent

active

055121950

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a process for producing single phase magnetite powder suitable for use in a wide range of technical fields, e.g., those of toners and carriers for electrophotography, electric resistance elements and magnetic fluids.
In the above process of the present invention, the single phase magnetite powder is produced by adding an organic substance, etc., to hematite powder and heating the mixture in an inert gas.


BACKGROUND ART

The following three general methods are known for producing magnetite, and it is known that they have respective drawbacks as described below. alkaline and coprecipitated. production, although fine particles each having a relatively high purity are readily obtained by coprecipitation. or steam to thereby be reduced. atmosphere, e.g., either high pressure steam or hydrogen and carbon monoxide, so that danger accompanies the mass production, and large scale equipment is required. difficult to stably produce high quality powder for a prolonged period of time.
Taking into account the advantages and disadvantages of the above processes, various proposals have been made with respect to the production of magnetite powder for use in magnetic toners and carriers for electrophotography, etc.
For example, Japanese Patent Publication Nos. 238,580/1987, 39,498/1990 and 51,505/1990 disclose processes for producing magnetite useful as a carrier component of an electrophotographic developer, especially a two-component developer composed of a toner and a carrier. Each of these processes comprises providing magnetite powder (or globular magnetite particles) as a starting material, granulating the same into globular grains through, for example, mixing with a binder, followed by heating (sintering), and applying a resin coating to the resultant globular magnetite particles according to the conventional technique.
The use of a material called soft ferrite as carrier particles is known (U.S. Pat. No. 3,929,657, etc.). In this connection, it is known that the carrier particles each composed of the above ferrite not only are excellent in magnetic properties but also do not require a resin coating layer, so that their durability is excellent. Noting that ferrite particles have resistance variations depending on the control of sintering atmosphere, even with the same composition, attempts have been made to enlarge resistance variation ranges by changing the sintering atmosphere. As an example thereof, there can be mentioned an attempt described in Japanese Patent Publication No. 37782/1987. This comprises providing an Mg ferrite as a starting material and increasing the amount of ferric oxide (Fe.sub.2 O.sub.3) to more than 53% by mole so as to enlarge its resistance variation range.
On the basis of the above prior art, the inventors have found a novel process for producing single phase magnetite as an oxidic magnetic material.


DISCLOSURE OF THE INVENTION

A primary object of the present invention is to provide a novel process for producing single phase magnetite as an oxidic magnetic material on the basis of the above prior art.
Another object of the present invention is to provide a process for producing single phase magnetite powder of high quality in a large amount, with less cost and safely by simple equipment and operation, as compared with the above conventional processes.
A further object of the present invention is to provide a process for mass-producing single phase magnetite powder of high quality and a desired electric resistance.
A still further object of the present invention is to provide a process for producing an oxidic magnetic material (magnetic oxide) having a desired electric resistance while retaining the properties characteristic of magnetite powder and arbitrarily regulating the conductivity of the base material of magnetite powder per se.
The present invention provides a process for producing single phase magnetite powder by adding an organic substance, etc., to hematite powder and heating the mixture in an inert gas. The thus produced si

REFERENCES:
patent: 3929657 (1975-12-01), Jones
patent: 4305921 (1981-12-01), Umeki
patent: 4311684 (1982-01-01), Umeki

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