Specialized metallurgical processes – compositions for use therei – Processes – Producing or purifying free metal powder or producing or...
Patent
1989-02-02
1990-08-14
Sheehan, John P.
Specialized metallurgical processes, compositions for use therei
Processes
Producing or purifying free metal powder or producing or...
B22F 928
Patent
active
049484222
DESCRIPTION:
BRIEF SUMMARY
Technical Field
The present invention relates to a method of efficiently manufacturing a superfine magnetic metal powder used as a high density magnetic recording medium.
Background Art
Presently, a superfine magnetic metal powder for magnetic recording is manufactured industrially as follows. In the first step, a needle-like iron oxide is prepared by a wet precipitation method, followed by applying a treatment to prevent sintering to the needle-like iron oxide. Further, dehydration, reduction and deoxidation treatments are applied to the needle-like iron oxide so as to obtain the desired superfine magnetic metal powder. Clearly, the conventional method involves many treating steps, leading to a high manufacturing cost of the superfine magnetic metal powder.
As an alternative to the conventional method outlined above, a gaseous phase evaporation method, a melt reducing method, a gaseous phase chemical reaction method, etc. are now under study. However, any of these methods is still incapable of sufficiently reducing the manufacturing cost of the superfine magnetic metal powder, leaving room for further improvement before the industrial application.
The gaseous phase chemical reaction method utilizes in principle a gaseous phase chemical reaction between a metal halide vapor and hydrogen gas to produce a superfine magnetic metal powder. Some improvements are being proposed with respect to the gaseous phase chemical reaction method as follows: vapor stream and a hydrogen gas stream are introduced at different flowing speeds to form an unstable region at the interface between the two. It is taught that the formation of the unstable region permits promoting the growth of nuclei, leading to an improved yield of the fine magnetic metal powder.
However, it is difficult to obtain a superfine powder having a particle size of 100 to 300 .ANG., which can be used for high density magnetic recording. The particle size of the powder obtained by this prior art is in general about 400 to 6000 .ANG.. art 1 given above. It is taught that the gaseous reaction mixture is rapidly cooled immediately after the reaction between the metal halide vapor and hydrogen gas in the unstable region at the interface. In this prior art 2, a magnetic field is applied in some cases to the unstable region at the interface.
Prior art 2 is superior to prior art 1 in that it is possible to suppress the growth of the powder particles. In order to increase the yield of the superfine powder, however, prior art 2 requires a large amount of hydrogen gas, leading to a high manufacturing cost of the superfine magnetic metal powder.
The present inventors have studied in detail prior arts 1 and 2 outlined above. It has been found that the reactivity between the metal halide vapor and hydrogen gas is low, resulting in an insufficient nuclei formation. It has also been found that nonuniform nuclei formation brings about an abnormal particle growth. In each of prior arts 1 and 2, it is necessary to use a large amount of hydrogen gas in order to form superfine nuclei sufficiently by promoting a uniform nuclei formation. However, the increase in the amount of hydrogen gas boosts the manufacturing cost of the superfine magnetic metal powder.
Disclosure of the Invention
An object of the present invention is to provide a method of manufacturing a superfine magnetic metal powder which permits minimizing the amount of hydrogen gas used and also permits efficiently manufacturing a superfine magnetic metal powder having satisfactory properties.
The method of the present invention is characterized in that at least one kind of metal halide vapor is reacted with hydrogen gas while supplying to the reacting region an active gas whose reactivity with the metal halide vapor is higher than the reactivity of hydrogen gas with the metal halide vapor so as to manufacture a desired superfine magnetic metal powder.
The metal halides used in the present invention include, for example, metal chlorides such as FeCl.sub.2, CoCl.sub.2 and NiCl.sub.2.
The active gas which is in
REFERENCES:
patent: 4383852 (1983-05-01), Yoshizawa et al.
patent: 4526611 (1985-07-01), Yoshizawa et al.
Maeda Tomoo
Yamato Masayuki
Yoshizawa Akinori
Nippon Kokan Kabushiki Kaisha
Sheehan John P.
Yoshizawa Akinori
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