Compositions – Magnetic – Chromium or chromium compound containing
Reexamination Certificate
2000-05-25
2002-05-07
Mai, Ngoclan (Department: 1742)
Compositions
Magnetic
Chromium or chromium compound containing
C148S100000
Reexamination Certificate
active
06383406
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to the field of methods for producing magnetic material based on a substance system comprising a rare-earth element, iron, nitrogen and carbon, and optionally hydrogen. More particularly, the present invention relates to the field of methods for processing high T
c
Sm—Fe—N and Sm—Fe—C, N magnetic materials. In particular, the present invention relates to the field of methods for synthesis of magnetic materials by polymerizing, pyrolyzing and sintering amide precursor in an inert or reduced atmosphere.
2. Description of the Prior Art
Ferromagnetic materials and permanent magnets are important materials widely used in electrical and electronic products. The well-established Nd
2
Fe
14
B based magnets have a high saturation magnetization, m
o
M
S
of 1.6 T, high anisotropy field, m
o
H
A
of 6.7 T and high energy product, (BH)
max
, of 360 kJ/m
3
at room temperature. However, the low Curie temperature, T
c
, of 310° C. seriously reduces the performance above room temperature.
In recent years, many studies have been conducted on the nitrides and carbides of rare earth iron compounds, and two compounds, Sm
2
Fe
17
N
2.3
and Sm
2
Fe
17
C
2
, have been formed with characteristics superior to Nd
2
Fe
14
B. For example, the parameters for Sm
2
Fe
17
N
2.3
are T
c
=485° C., m
o
M
s
=1.5 T, m
o
H
A
=15 T and for Sm
2
Fe
17
C
2
are T
c
=407° C., m
o
M
s
=1.4 T, m
o
H
A
=13.9 T. These parameters imply that magnets made from these alloys could have an energy product as high as 470 kJ/m
3
, with a superior T
c
.
However, the a-Fe precipitated during the nitridation of Sm—Fe alloy is found to reduce the performance of hard magnets. Furthermore, stability of Sm—Fe—N hard magnetic materials is limited at temperature above 300° C. A significant enhancement of coercivity of Sm—Fe—N is observed with a refinement of the material's microstructure, including homogeneity both in composition and grain size distribution, as well as second phase effect.
The state-of-the-art of the process for rare earth iron nitride, or rare earth iron carbide, or rare earth iron hydride is to form rare earth iron alloy first followed by nitridation, carbonation and hydridation. The lattice constants increase about 6% percent after nitridation from Sm
2
Fe
17
to Sm
2
Fe
17
N
2+&dgr;
.
One way to fabrication of nitride materials is to use metal amides and derivatives. High purity and homogeneous nitride and carbonitride materials, such as aluminum nitride, titanium nitride, molybdenum carbonitride, have been synthesized by decomposition of polymerized amide precursors, such as (R
2
N)
3
Al, R(H)AlN(H)R, Ti(NR
2
)
n
, where R stands for alkyl groups.
The following seven (7) prior art references are found to be pertinent to the field of the present invention:
1. U.S. Pat. No. 5,137,587 issued to Schultz et al. on Aug. 11, 1992 for “Process For The Production Of Shaped Body From An Anisotropic Magnetic Material Based On The SM—FE—N System” (hereafter the “Schultz Patent”);
2. U.S. Pat. No. 5,137,588 issued to Wecker et al. on Aug. 11, 1992 for “Process For The Production Of An Anisotropic Magnetic Material Based Upon The SM—FE—N System” (hereafter the “Wecker Patent”);
3. U.S. Pat. No. 5,288,339 issued to Schnitzke et al. on Feb. 22, 1994 for “Process For The Production Of Magnetic Material Based On The SM—FE—N System” (hereafter the “Schnitzke Patent”);
4. U.S. Pat. No. 5,665,177 issued to Fukuno et al. on Sep. 9, 1997 for “Method For Preparing Permanent Magnet Material, Chill Roll, Permanent Magnet Material, And Permanent Magnet Material Powder” (hereafter the “Fukuno Patent”);
5. U.S. Pat. No. 5,720,828 issued to Strom-Olsen on Feb. 24, 1998 for “Permanent Magnet Material Containing A Rare-Earth Element, Iron, Nitrogen And Carbon” (hereafter the “Strom-Olsen Patent”);
6. U.S. Pat. No. 5,788,782 issued to Kaneko et al. on Aug. 4, 1998 for “R—FE—B Permanent Magnet Materials And Process Of Producing The Same” (hereafter the “Kaneko Patent”); and
7. Journal Of Organometallic Chemistry 87 (1975) 301-309 (hereafter the “Journal”).
The Schultz Patent discloses a process for the production of shaped body from an anisotropic magnetic material based on the Sm—Fe—N system. The system includes a crystalline, hard magnetic phase with a Th
2
Zn
17
crystal structure, wherein N atoms are incorporated in the crystal lattice, is produced by compacting a powder Sm—Fe preliminary product with a Sm—Fe phase having a magnetically isotropic structure, followed by hot-shaping to provide an intermediate product with a Sm—Fe phase having a magnetically anisotropic structure, followed by heat treating the intermediate product in a nitrogen atmosphere to provide a Sm—Fe—N hard magnetic phase.
The Wecker Patent discloses a process for the production of an anisotropic magnetic material based upon the Sm—Fe—N system. The magnetic material of the Sm—Fe—N system includes a crystalline, hard magnetic phase with a Th
2
Zn
17
crystal structure, wherein N atoms are incorporated in the crystal lattice, is produced. First a preliminary product is formed by sintering a Sm—Fe powder which is oriented in a magnetic field to provide a sintered body having a two-component Sm—Fe phase. The sintered body is heat treated in a nitrogen atmosphere to form the Sm—Fe—N hard magnetic phase.
The Schnitzke Patent discloses a process for the production of magnetic material based on the Sm—Fe—N system of elements. The magnetic material of the Sm—Fe—N system exhibits a crystalline hard magnetic phase with a Th
2
Zn
17
crystal structure, wherein N atoms are incorporated in the crystal lattice. A preliminary product has a dual component Sm
2
Fe
17
phase is produced by mechanical alloying followed by thermal treatment to achieve the desired microstructure. The preliminary product may also be obtained by a rapid-quenching technique.
The Fukuno Patent discloses a method for preparing permanent magnet material, chill roll, permanent magnet material, and permanent magnet material powder. A permanent magnet material is prepared by cooling with a chill roll a molten alloy containing R wherein R is at least one rare earth element inclusive of Y, Fe or Fe and Co, and B. The chill roll has a plurality of circumferentially extending grooves in a circumferential surface, the distance between two adjacent ones of the grooves at least in a region with which the molten alloy comes in contact being 100 to 300 &mgr;m average in an arbitrary cross section containing a roll axis. Permanent magnet material of stable performance is obtained since the variation of cooling rate caused by a change in the circumferential speed of the chill roll is small. The variation of cooling rate is small even when it is desired to change the thickness of the magnet by altering the circumferential speed. The equalized groove pitch results in a minimized variation in crystal grain diameter.
The Strom-Olsen Patent discloses a permanent magnet material containing a rare-earth element, iron, nitrogen and carbon. They are produced by gas absorbing nitrogen and carbon sequentially into a parent intermetallic compound. The resulting magnetic materials have high T
C
, &mgr;
o
M
s
and &mgr;
o
H
A
, are essentially free of &agr;-Fe, and have a coercivity at 300° K. of at least 1.5 T. Anisotropic magnetic materials are produced by pretreating the intermetallic compound, which contains carbon, by powder sintering or oriented hot shaping, followed by nitriding and/or carbiding.
The Kaneko Patent discloses R—Fe—B permanent magnet materials having a good oxidation resistance and magnetic characteristics, and process of producing the same capable of pulverizing efficiently, whereby an R—Fe—B molten alloy having a specific composition is cast into a cast piece having a specific plate thickness and a structure, in which an R-rich phase is finely separated below 5 &mgr;m, by a strip casting process.
The Journal discloses a Ti(—NMe—SiMe
2
—SiMe
2
—MeN—)
2
(I) has been obtained fro
Huang Yuhong
Wei Qiang
Zheng Haixing
Chemat Technology Inc.
Chen Tony D.
Fong Jerry
Mai Ngoclan
Rozsa Thomas I.
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