Compositions – Magnetic – Iron-oxygen compound containing
Reexamination Certificate
2001-07-05
2002-11-12
Wood, Elizabeth D. (Department: 1755)
Compositions
Magnetic
Iron-oxygen compound containing
C252S06251C, C252S062560, C252S06251C, C252S062620, C423S021100, C423S138000, C423S155000, C501S152000
Reexamination Certificate
active
06478982
ABSTRACT:
TECHNICAL FIELD
The present invention relates to ferrite magnet powder, a magnet using the ferrite magnet powder, and methods for manufacturing the same.
BACKGROUND ART
The ferrite is a generic name for compounds produced from oxides of divalent cationic metals and trivalent iron. Ferrite magnets have found various applications in motors, generators, and the like. As materials for the ferrite magnets, widely used are magnetoplumbite hexagonal-structured Sr ferrites (SrFe
12
O
19
) and Ba ferrites (BaFe
12
O
19
). These ferrites are produced at comparatively low cost by a powder metallurgical method using iron oxides and carbonates of strontium (Sr), barium (Ba), and the like.
The basic composition of the magnetoplumbite ferrites is generally represented by a chemical formula “MO.nFe
2
O
3
” where element M is a metal that is to serve as divalent cations, selected from Sr, Ba, Pb, Ni, and the like. Iron ions (Fe
3+
) at respective sites of the ferrite, which have a spin magnetic moment, are coupled by superexchange interaction via intermediate oxygen ions (O
2−
). The magnetic moment of Fe
3+
ions at their sites are oriented “upward” or “downward” along the c axis. Because the number of sites having an “upward” magnetic moment is different from the number of sites having a “downward” magnetic moment, the ferrite exhibits ferromagnetism (as a ferrimagnet) as the entire crystal.
It is known that, among the magnetic performance of the magnetoplumbite ferrite magnets, the residual magnetic flux density (B
r
) can be enhanced by improving the Is of crystals and increasing the density of a sintered body and the degree of orientation of the crystals. Also known is that the coercive force (H
cj
) can be enhanced by increasing the rate of existence of single-domain crystals. However, an attempt of by increasing the density of the sintered body to enhance the residual flux density (B
r
) will facilitate crystal growth, resulting in reducing the coercive force (H
cj
). In reverse, an attempt of enhancing the coercive force by controlling the size of crystal grains by addition of Al
2
O
3
and the like will reduce the density of the sintered body, resulting in reducing the residual flux density. Various studies were made on the compositions, additives, and production conditions of ferrites for the purpose of enhancing the magnetic properties of the ferrite magnets. However, it was found difficult to develop a ferrite magnet enhanced both in residual flux density and coercive force.
The applicant of the present invention developed a ferrite magnet of which the coercive force was enhanced without reduction in residual flux density by adding Co to a raw material (Japanese Patent Examined Publication Nos. 4-40843 and 5-42128).
After the above development, there was proposed a ferrite magnet of which the saturation magnetization (&sgr;
s
) was enhanced by substituting Zn and La for Fe and Sr, respectively (Japanese Laid-Open Publication Nos. 9-115715 and 10-149910). A ferrite magnet has relatively low saturation magnetization because it is a ferrimagnet in which the magnetic moments of Fe
3+
ions orient in opposite directions depending on the sites as described above. According to the above publications, however, the “downward” magnetic moments can be reduced by placing ions having a magnetic moment smaller than the magnetic moment of Fe in specific sites of Fe ions, to thereby enhance the saturation magnetization &sgr;
s
. The publications also describe examples using Nd and Pr in place of La, and Mn, Co, and Ni in place of Zn.
The Abstracts of the Magnetics Society of Japan Annual Meeting (distributed on Sep. 20, 1998) discloses ferrite magnets of which both the coercive force (Hcj) and the saturation magnetization (&sgr;
s
) are enhanced by use of La- and Co-added compounds Sr
1−x
La
x
Co
x
.Fe
12−x
O
19
.
The above ferrite magnets are still insufficient in improvement of both the coercive force and the saturation magnetization.
The above-mentioned abstracts (distributed on Sep. 20, 1998) report that the coercive force can be improved to some extent by substituting Co, in place of Zn, for Fe, but fail to describe the cause of this improvement. In addition, the degrees of the improvement of the coercive force and the residual flux density are considered insufficient.
DISCLOSURE OF THE INVENTION
In view of the above, the main object of the present invention is providing ferrite magnet powder enhanced both in saturation magnetization and coercive force, and magnet using such magnet powder. The magnet powder of the present invention is magnet powder having a ferrite major phase represented by (1−x)AO.(x/2)R
2
O
3
.(n−y/2)Fe
2
O
3
.yMO (where A denotes one or two kinds of metal selected from Sr and Ba, R denotes a rare earth element necessarily including La, and M denotes a divalent metal necessarily including Co), wherein x, y, and n represent mole ratios and satisfy 0.22−0.02≦x≦0.22+0.02, 0.18−0.02≦y≦0.18+0.02, and 5.2≦n≦6.0, where x>y.
The bond magnet of the present invention includes the magnet powder described above, and the sintered magnet of the present invention is made of the magnet powder described above.
The method for manufacturing magnet powder of the present invention includes the steps of: preparing raw material mixed powder of SrCO
3
powder and Fe
2
O
3
powder with addition of powder of oxides of La and Co; calcinating the raw material mixed powder to form a ferrite calcinated product as magnet powder having a ferrite major phase represented by (1−x)AO.(x/2)R
2
O
3
.(n−y/2)Fe
2
O
3
.yMO (where A denotes one or two kinds of metal selected from Sr and Ba, R denotes a rare earth element necessarily including La, and M denotes a divalent metal necessarily including Co), wherein x, y, and n represent mole ratios and satisfy 0.22−0.02≦x≦0.22+0.02, 0.18−0.02≦y≦0.18+0.02, and 5.2≦n≦6.0, where x>y; and pulverizing the calcinated product.
The method for manufacturing a magnet of the present invention includes the steps of: preparing raw material mixed powder of SrCO
3
powder and Fe
2
O
3
powder with addition of powder of oxides of La and Co; calcinating the raw material mixed powder to form a ferrite calcinated product as magnet powder having a ferrite major phase represented by (1−x)AO.(x/2)R
2
O
3
.(n−y/2)Fe
2
O
3
.yMO (where A denotes one or two kinds of metal selected from Sr and Ba, R denotes a rare earth element necessarily including La, and M denotes a divalent metal necessarily including Co), wherein x, y, and n represent mole ratios and satisfy 0.22−0.02≦x≦0.22+0.02, 0.18−0.02≦y≦0.18+0.02, and 5.2≦n≦6.0, where x>y; pulverizing the calcinated product to form ferrite magnet powder; and compacting and sintering the ferrite magnet powder.
The method for manufacturing a magnet of the present invention includes the steps of: preparing raw material mixed powder of SrCO
3
powder and Fe
2
O
3
powder with addition of powder of oxides of La and Co; calcinating the raw material mixed powder to form a ferrite calcinated product as magnet powder having a ferrite major phase represented by (1−x)AO.(x/2)R
2
O
3
.(n−y/2)Fe
2
O
3
.yMO (where A denotes one or two kinds of metal selected from Sr and Ba, R denotes a rare earth element necessarily including La, and M denotes a divalent metal necessarily including Co), wherein x, y, and n represent mole ratios and satisfy 0.22−0.02≦x≦0.22+0.02, 0.18−0.02≦y≦0.18+0.02, and 5.2≦n≦6.0, where x>y; pulverizing the calcinated product to form ferrite magnet powder; and forming a bond magnet from the ferrite magnet powder.
The value of n is preferably in the range of 5.4≦n≦5.7, and x/y is preferably in the range of 1.1 to 1.3.
REFERENCES:
patent: 5846449 (1998-12-01), Taguchi et al.
patent: 5951937 (1999-09-01), Taguchi et al.
patent: 5958284 (1999-09-01), Takami et al.
patent: 6086781 (2000-07-01)
Anamoto Shuji
Furuchi Isamu
Costellia Jeffrey L.
Nixon & Peabody LLP
Sumitomo Special Metals Co. Ltd.
Wood Elizabeth D.
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