Compositions – Magnetic – Iron-oxygen compound containing
Patent
1994-06-29
1996-05-21
Bonner, Melissa
Compositions
Magnetic
Iron-oxygen compound containing
252 6262, 423594, C04B 3530
Patent
active
055186416
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a magnetic material used for various kinds of electronic parts, and a method of manufacturing the same.
BACKGROUND ART
A conventional magnetic material has been manufactured in the following manner.
First, ferrite raw powder is previously sintered, thereafter, the sintered mass is crushed. Particles obtained by the crushing operation are thereafter compressed in metallic dies. The compact removed from the metallic dies is sintered. Thus, the magnetic material is obtained. However, it is a well-known fact that the magnetic material manufactured in the above-described manner inevitably shrinks during the sintering process, and consequently, the magnetic material is designed considering this shrinkage so that it will have a slightly larger size than a desired size when it is sintered. Therefore, after the sintering process, the magnetic material must be cut to have the desired size and shape. However, since the magnetic material after sintered is extremely hard, a cutting blade wears considerably, and it must be replaced with a new one frequently. As a result, the manufacturing cost increase.
Consequently, there was suggested a magnetic material whose shrinkage during sintering was substantially prevented so that the above-mentioned cutting operation would not be required (cf. JP-A-1-264959). This magnetic material is manufactured by mixing magnetic powder with filling powder which is one kind selected from silicon, titanium and aluminum, compressing this mixture by metallic dies, and thereafter sintering the compact, which has been removed from the metallic dies, in an oxygen atmosphere or in a nitrogen atmosphere. In the case of this conventional magnetic material, oxidization expansion or nitrogenization expansion of the above-mentioned filling powder can decrease shrinkage of the magnetic material during sintering to an extremely small degree. However, silicon, titanium, aluminum or the like which is a non-magnetic material is mixed in the magnetic powder, and consequently, there arises a problem that the magnetic property as the magnetic material is deteriorated.
Thus, an objective of the invention resides in providing a magnetic material whose dimensional change due to sintering is small and whose magnetic property is not deteriorated.
DISCLOSURE OF THE INVENTION
In order to achieve the objective, a magnetic material of the invention comprises a great number of ferrite grains which are formed by sintering ferrite raw powder, and shrinkage preventing grains which are interposed among these plural ferrite grains and which are sintered with the ferrite grains in contact with the outer peripheries thereof and are also oxidized with oxygen so as to change into ferrite when the grains are sintered.
With the above-described structure, a rate of dimensional change of the magnetic material due to sintering is low, and deterioration in the magnetic property does not occur. The reason is that the shrinkage preventing grains are interposed among the ferrite grains and sintered with the ferrite grains in contact with their outer peripheries, thereby preventing shrinkage which is caused by ferrite grains approaching to one another to be bound, as in the case of the conventional magnetic material. Further, the shrinkage preventing grains are oxidized with oxygen and change into ferrite when they are sintered with the ferrite grains, so that a non-magnetic material observed in the conventional magnetic material will not be mixed, and that the magnetic property will not be deteriorated.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an enlarged view showing an internal structure of a magnetic material according to one embodiment of the present invention;
FIG. 2 is an enlarged view showing one condition of the magnetic material in a manufacturing process; and
FIG. 3 is a characteristic graph showing a dimensional change rate.
BEST MODE FOR CARRYING OUT THE INVENTION
Example 1
A first embodiment of the present invention will be hereinafter described with refere
REFERENCES:
patent: 2700023 (1955-01-01), Albers-Schonberg
patent: 4490268 (1984-12-01), Tchernev
Database WPI Week 9425, Derwent Publications Ltd., London, GB; AN 94-208000 & SU-A-1 809 931 (USSR Structural Makrokinetics Inst.) 15 Apr. 1993.
Database WPI Week 9435, Derwent Publications Ltd., London, GB; AN 94-284689 & SU-C-2 009 561 (USSR Structural Makrokinetics Inst.) 15 Mar. 1994.
Database WPI Week 8031, Derwent Publications Ltd., London, GB; AN 80-54382C & JP-A-55 080 727 (Mitsubishi) Jun. 19, 1980.
Database Week 9206, Derwent Publications Ltd., London, GB; AN 92-046159 & JP-A-3 291 901 (TDK) 24 Dec. 1991.
Fujii Hiroshi
Harada Shinji
Inuzuka Tsutomu
Ohba Michio
Bonner Melissa
Matsushita Electric - Industrial Co., Ltd.
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