U.S. patent application number 15/867143 was filed with the patent office on 2018-05-17 for method for manufacturing magnetic particles, magnetic particles, and magnetic body.
The applicant listed for this patent is NISSHIN ENGINEERING INC., NISSHIN SEIFUN GROUP INC.. Invention is credited to Akihiro KINOSHITA, Keitaroh NAKAMURA, Naohito UEMURA.
Application Number | 20180137960 15/867143 |
Document ID | / |
Family ID | 53777750 |
Filed Date | 2018-05-17 |
United States Patent
Application |
20180137960 |
Kind Code |
A1 |
NAKAMURA; Keitaroh ; et
al. |
May 17, 2018 |
METHOD FOR MANUFACTURING MAGNETIC PARTICLES, MAGNETIC PARTICLES,
AND MAGNETIC BODY
Abstract
Provided is a method for manufacturing magnetic particles, in
which an oxidation treatment, a reduction treatment, and a
nitriding treatment are performed in that order on raw material
particles with a core-shell structure in which a silicon oxide
layer is formed on the surfaces of iron microparticles, thereby
nitriding the iron microparticles while maintaining the core-shell
structure. Due to this configuration, granular magnetic particles
with a core-shell structure in which a silicon oxide layer is
formed on the surfaces of iron nitride microparticles can be
obtained.
Inventors: |
NAKAMURA; Keitaroh;
(Fujimino-city, JP) ; KINOSHITA; Akihiro;
(Fujimino-city, JP) ; UEMURA; Naohito;
(Fujimino-city, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NISSHIN SEIFUN GROUP INC.
NISSHIN ENGINEERING INC. |
Tokyo
Tokyo |
|
JP
JP |
|
|
Family ID: |
53777750 |
Appl. No.: |
15/867143 |
Filed: |
January 10, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
15116103 |
Aug 2, 2016 |
|
|
|
PCT/JP2015/051403 |
Jan 20, 2015 |
|
|
|
15867143 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 33/02 20130101;
H01F 7/02 20130101; B22F 1/0048 20130101; B22F 7/062 20130101; H01F
1/061 20130101; B22F 2998/10 20130101; B22F 1/02 20130101; B22F
2999/00 20130101; B22F 2999/00 20130101; B22F 1/02 20130101; B22F
1/0088 20130101; B22F 2201/02 20130101; B22F 1/0088 20130101; B22F
2201/01 20130101; B22F 1/0088 20130101; B22F 1/0018 20130101; B22F
1/0088 20130101; C22C 2202/02 20130101; B22F 2998/10 20130101; B22F
1/0088 20130101; B22F 2999/00 20130101 |
International
Class: |
H01F 7/02 20060101
H01F007/02; C22C 33/02 20060101 C22C033/02; B22F 1/00 20060101
B22F001/00; B22F 1/02 20060101 B22F001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 10, 2014 |
JP |
2014-023851 |
Claims
1. Magnetic particles being spherical particles each having a
core-shell structure in which a silicon oxide layer is formed on a
surface of an iron nitride fine particle, wherein the iron nitride
fine particle is composed of Fe.sub.16N.sub.2.
2. A magnetic body formed using spherical particles each having a
core-shell structure in which a silicon oxide layer is formed on a
surface of an iron nitride fine particle, wherein the iron nitride
fine particle is composed of Fe.sub.16N.sub.2.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional of co-pending application
Ser. No. 15/116,103, filed on 2 Aug. 2016, for which priority is
claimed under 35 U.S.C. .sctn. 120; which claims priority of PCT
Application No. PCT/JP2015/051403 filed on 20 Jan. 2015 under 35
U.S.C. .sctn. 119(e) and this application claims priority of
Application No. JP 2014-023851 filed in JAPAN on 10 Feb. 2014 under
35 U.S.C. .sctn. 119; the entire contents of all of which are
hereby incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to spherical magnetic
particles each having a core-shell structure in which a silicon
oxide layer is formed on the surface of an iron nitride fine
particle, a method for manufacturing such spherical magnetic
particles, and a magnetic body using such spherical magnetic
particles.
BACKGROUND ART
[0003] Today, motors for hybrid vehicles, electric vehicles, home
electric appliances such as air conditioners and washing machines,
industrial machinery and the like are required to have
energy-saving, high efficiency and high performance
characteristics. Accordingly, magnets used for such motors are
required to have a higher magnetic force (coercive force,
saturation magnetic flux density). At present, iron nitride-based
magnetic particles are attracting attention as magnetic particles
used to form a magnet, and various proposals have been made on such
iron nitride-based magnetic particles (see Patent Literatures 1 to
3).
[0004] Patent Literature 1 describes ferromagnetic particles which
comprise an Fe.sub.16N.sub.2 single phase, have surfaces coated
with an Si compound and/or an Al compound and have a BH.sub.max
value of not less than 5 MGOe. The ferromagnetic particles can be
obtained by coating the surfaces of iron compound particles with
the Si compound and/or the Al compound, followed by reduction
treatment and then nitridation treatment. The iron compound
particles used as a starting material are composed of iron oxide or
iron oxyhydroxide.
[0005] Patent Literature 2 describes ferromagnetic particles which
comprise an Fe.sub.16N.sub.2 compound phase in an amount of not
less than 70% as measured by Mossbauer spectrum, contain a metal
element X in such an amount that a molar ratio of the metal element
X to Fe is 0.04 to 25%, have surfaces coated with an Si compound
and/or an Al compound and have a BH.sub.max value of not less than
5 MGOe. The metal element X is at least one element selected from
the group consisting of Mn, Ni, Ti, Ga, Al, Ge, Zn, Pt and Si.
[0006] The ferromagnetic particles are obtained by subjecting iron
compound particles previously passed through a mesh having a size
of not more than 250 .mu.m to reduction treatment and then to
nitridation treatment, the iron compound particles used as a
starting material being formed of iron oxide or iron oxyhydroxide
which has a BET specific surface area of 50 to 250 m.sup.2/g, an
average major axis diameter of 50 to 450 nm and an aspect ratio
(major axis diameter/minor axis diameter) of 3 to 25 and comprises
a metal element X (wherein X is at least one element selected from
the group consisting of Mn, Ni, Ti, Ga, Al, Ge, Zn, Pt and Si) in
such an amount that a molar ratio of the metal element X to Fe is
0.04 to 25%.
[0007] Patent Literature 3 describes ferromagnetic particles
comprising an Fe.sub.16N.sub.2 compound phase in an amount of not
less than 80% as measured by Mossbauer spectrum, and each having an
outer shell in which FeO is present in the form of a film having a
thickness of not more than 5 nm.
[0008] The ferromagnetic particles are obtained by subjecting iron
oxide or iron oxyhydroxide having an average major axis diameter of
40 to 5000 nm and an aspect ratio (major axis diameter/minor axis
diameter) of 1 to 200 as a starting material to dispersing
treatment to prepare aggregated particles having D50 of not more
than 40 .mu.m and D90 of not more than 150 allowing the obtained
aggregated particles to pass through a mesh having a size of not
more than 250 subjecting the iron compound particles passed through
the mesh to hydrogen reduction treatment at a temperature of 160 to
420.degree. C. and then subjecting the resulting particles to
nitridation treatment at a temperature of 130 to 170.degree. C.
CITATION LIST
Patent Literature
[0009] Patent Literature 1: JP 2011-91215 A [0010] Patent
Literature 2: JP 2012-69811 A [0011] Patent Literature 3: JP
2012-149326 A
SUMMARY OF INVENTION
Technical Problems
[0012] In Patent Literatures 1 to 3 above, while the magnetic
particles with a minor axis diameter and a major axis diameter
differing in length are obtained, spherical magnetic particles
cannot be obtained. The magnetic particles with a minor axis
diameter and a major axis diameter differing in length have
anisotropy in terms of magnetic properties. Furthermore, the
magnetic particles obtained in Patent Literatures 1 to 3 tend to be
fused during reduction treatment at high temperature and are poor
in dispersibility.
[0013] An object of the present invention is to solve the above
problems inherent in the prior art and to provide a method for
manufacturing magnetic particles that enables the manufacture of
spherical magnetic particles each having a core-shell structure in
which a silicon oxide layer is formed on the surface of an iron
nitride fine particle, as well as such spherical magnetic particles
and a magnetic body using such spherical magnetic particles.
Solution to Problems
[0014] In order to attain the above object, the present invention
provides as its first aspect a magnetic particle manufacturing
method, comprising: an oxidation treatment step of subjecting raw
particles each having a core-shell structure in which a silicon
oxide layer is formed on a surface of an iron fine particle to
oxidation treatment; a reduction treatment step of subjecting the
raw particles having undergone the oxidation treatment to reduction
treatment; and a nitridation treatment step of subjecting the raw
particles having undergone the reduction treatment to nitridation
treatment to nitride iron fine particles with the core-shell
structure being maintained.
[0015] Preferably, the oxidation treatment is performed on the raw
particles in air at 100.degree. C. to 500.degree. C. for 1 to 20
hours. More preferably, the oxidation treatment is performed at
200.degree. C. to 400.degree. C. for 1 to 10 hours.
[0016] Preferably, the reduction treatment is performed at
200.degree. C. to 500.degree. C. for 1 to 50 hours as mixed gas of
hydrogen gas and nitrogen gas is supplied to the raw particles.
More preferably, the reduction treatment is performed at
200.degree. C. to 400.degree. C. for 1 to 30 hours.
[0017] Preferably, the nitridation treatment is performed at
140.degree. C. to 200.degree. C. for 3 to 50 hours as nitrogen
element-containing gas is supplied to the raw particles. More
preferably, the nitridation treatment is performed at 140.degree.
C. to 160.degree. C. for 3 to 20 hours.
[0018] Preferably, the raw particles take on a spherical shape and
have a particle size of less than 200 nm and more preferably of 5
to 50 nm.
[0019] The present invention provides as its second aspect magnetic
particles being spherical particles each having a core-shell
structure in which a silicon oxide layer is formed on a surface of
an iron nitride fine particle.
[0020] The present invention provides as its third aspect a
magnetic body formed using spherical particles each having a
core-shell structure in which a silicon oxide layer is formed on a
surface of an iron nitride fine particle.
Advantageous Effects of Invention
[0021] According to the present invention, it is possible to obtain
spherical magnetic particles each having a core-shell structure in
which a silicon oxide layer is formed on the surface of an iron
nitride fine particle. The obtained spherical magnetic particles
each have the surface constituted by the silicon oxide layer and
therefore, the iron nitride fine particles do not come into direct
contact with each other. Furthermore, owing to the silicon oxide
layer that is an insulator, each iron nitride fine particle is
electrically isolated from another particle, and this can prevent
electric current from flowing between adjacent magnetic particles.
As a result, damage caused by electric current can be reduced or
prevented.
[0022] Since fine particles are composed of iron nitride, magnetic
particles of the invention and a magnetic body produced using such
magnetic particles have a high coercive force and excellent
magnetic properties.
BRIEF DESCRIPTION OF DRAWINGS
[0023] FIG. 1 (a) is a schematic cross-sectional view showing a
magnetic particle of the invention, and (b) is a schematic
cross-sectional view showing a raw particle.
[0024] FIG. 2 is a flow chart showing a method of manufacturing
magnetic particles of the invention.
[0025] FIG. 3 is a graph showing an example of magnetic hysteresis
curves (B-H curves) of magnetic particles and raw particles.
[0026] FIG. 4 (a) is a graph showing a result of crystal structure
analysis by X-ray diffractometry made on raw particles having yet
to undergo treatment; (b) is a graph showing a result of crystal
structure analysis by X-ray diffractometry made on the raw
particles having undergone oxidation treatment; and (c) is a graph
showing a result of crystal structure analysis by X-ray
diffractometry made on magnetic particles obtained through, after
the oxidation treatment, reduction treatment and then nitridation
treatment.
[0027] FIG. 5 includes images corresponding to FIG. 4(a) to FIG.
4(c). (a) is a schematic view showing a TEM image of the raw
particles having yet to undergo treatment; (b) is an enlarged view
of FIG. 5(a); (c) is a schematic view showing a TEM image of the
raw particles having undergone oxidation treatment; (d) is an
enlarged view of FIG. 5(c); (e) is a schematic view showing a TEM
image of the magnetic particles; and (f) is an enlarged view of
FIG. 5(e).
[0028] FIG. 6 (a) and (b) are graphs showing results of crystal
structure analysis by X-ray diffractometry made on raw particles
having undergone nitridation treatment; (c) is a graph showing a
result of crystal structure analysis by X-ray diffractometry made
on Fe16N2 serving as a reference; (d) is a graph showing a result
of crystal structure analysis by X-ray diffractometry made on the
raw particles having yet to undergo nitridation treatment; and (e)
is an enlarged view of an important portion of FIG. 6(b).
DESCRIPTION OF EMBODIMENTS
[0029] A method for manufacturing magnetic particles, magnetic
particles and magnetic body according to the invention are
described below in detail with reference to preferred embodiments
shown in the accompanying drawings.
[0030] FIG. 1(a) is a schematic cross-sectional view showing a
magnetic particle of the invention, and FIG. 1(b) is a schematic
cross-sectional view showing a raw particle. FIG. 2 is a flow chart
showing a method of manufacturing magnetic particles of the
invention. FIG. 3 is a graph showing an example of magnetic
hysteresis curves (B-H curves) of magnetic particles and raw
particles.
[0031] As shown in FIG. 1(a), a magnetic particle 10 of this
embodiment is a spherical particle having a core-shell structure in
which a silicon oxide layer (SiO.sub.2 layer) 14 (shell) is formed
on the surface of an iron nitride fine particle 12 (core).
[0032] The magnetic particle 10 is a spherical particle having a
particle size of about 50 nm and preferably of 5 to 50 nm. The
particle size is obtained by converting a measurement value of the
specific surface area.
[0033] In the magnetic particle 10, the iron nitride fine particle
12 exerts magnetic properties. Among iron nitrides,
Fe.sub.16N.sub.2 having excellent magnetic properties is most
preferred in terms of magnetic properties such as coercive force.
Therefore, it is most preferable that the fine particle 12 be
constituted by an Fe.sub.16N.sub.2 single phase. When the fine
particle 12 is constituted by the Fe.sub.16N.sub.2 single phase,
the magnetic particle 10 is also referred to as
"Fe.sub.16N.sub.2/SiO.sub.2 composite fine particle."
[0034] The fine particle 12 is not limited to the Fe.sub.16N.sub.2
single phase and may have the composition having another iron
nitride included therein.
[0035] The silicon oxide layer 14 serves to electrically insulate
the fine particle 12, prevent the fine particle 12 from coming into
contact with another magnetic particle or the like and inhibit
oxidation or the like of the iron nitride fine particle 12. The
silicon oxide layer 14 is an insulator.
[0036] Owing to the iron nitride fine particle 12, the magnetic
particle 10 has a high coercive force and excellent magnetic
properties. As will be described in detail later, when the fine
particle 12 is composed of the Fe.sub.16N.sub.2 single phase, the
coercive force is to be, for instance, 1700 Oe (about 135.3 kA/m).
The magnetic particle 10 also has excellent dispersibility.
[0037] In the magnetic particle 10, the silicon oxide layer 14,
which is an insulator, serves to prevent electric current from
flowing between magnetic particles 10, thereby reducing or
preventing damage caused by electric current.
[0038] A magnetic body formed using such magnetic particles 10 has
a high coercive force and excellent magnetic properties. One
example of the magnetic body is a bonded magnet.
[0039] Next, a method for manufacturing the magnetic particles 10
is described.
[0040] To manufacture the magnetic particles 10, raw particles 20,
one of which is shown in FIG. 1(b), are prepared.
[0041] Next, as shown in FIG. 2, the raw particles 20 are subjected
to oxidation treatment to oxidize iron (Fe) fine particles 22 (Step
S10). Subsequently, the raw particles 20 are subjected to reduction
treatment to reduce the oxidized iron (Fe) fine particles 22 (Step
S12). Thereafter, the raw particles 20 are subjected to nitridation
treatment to nitride the reduced iron (Fe) fine particles 22 (Step
S14). The magnetic particles 10 having the iron nitride fine
particles 12 can be thus manufactured.
[0042] The raw particles 20 each have a core-shell structure in
which a silicon oxide layer 24 is formed on the surface of the iron
(Fe) fine particle 22. The raw particle 20 is also referred to as
"Fe/SiO.sub.2 particle."
[0043] The raw particle 20 is a spherical particle having a
particle size of about 50 nm and preferably 5 to 50 nm. The
particle size is obtained by converting a measurement value of the
specific surface area.
[0044] As described above, the iron fine particles 22 are oxidized
in the oxidation treatment step (Step S10), subsequently the
oxidized iron fine particles 22 are reduced in the reduction
treatment step (Step S12), and then the iron fine particles 22 are
nitrided in the nitridation treatment step (Step S14), thereby
obtaining fine particles composed of iron nitride and most
preferably of Fe.sub.16N.sub.2. In this regard, the silicon oxide
layer 24 is a stable substance which does not change through
oxidation treatment, reduction treatment or nitridation treatment.
Thus, the iron fine particles 22, which are cores, are oxidized,
reduced and nitrided to be changed into the iron nitride fine
particles 12 with the core-shell structure being maintained, to
thereby obtain the magnetic particles 10 of FIG. 1(a).
[0045] As described later, the magnetic particles 10 thus
manufactured are free from aggregation and have high
dispersibility.
[0046] In the present invention, the magnetic particles 10 can be
manufactured by subjecting the raw particles 20 to oxidation
treatment, reduction treatment and nitridation treatment.
[0047] Methods of oxidation treatment include a method in which:
the raw particles 20 are put into, for example, a glass container;
air is supplied into this container; and the raw particles 20 are
subjected to oxidation treatment in air at 100.degree. C. to
500.degree. C. for 1 to 20 hours. More preferably, oxidation
treatment is performed at 200.degree. C. to 400.degree. C. for 1 to
10 hours.
[0048] At an oxidation treatment temperature of less than
100.degree. C., the degree of oxidation is not sufficient. At an
oxidation treatment temperature in excess of 500.degree. C., the
raw particles are fused. In addition, the oxidation reaction is
saturated so that the oxidation does not progress any more.
[0049] With an oxidation treatment time of less than 1 hour, the
degree of oxidation is not sufficient. With an oxidation treatment
time in excess of 20 hours, the raw particles are fused. In
addition, the oxidation reaction is saturated so that the oxidation
does not progress any more.
[0050] Methods of reduction treatment include a method in which:
the raw particles 20 having undergone the oxidation treatment are
put into, for example, a glass container; mixed gas of H.sub.2 gas
(hydrogen gas) and N.sub.2 gas (nitrogen gas) is supplied into this
container; and the raw particles 20 are subjected to reduction
treatment in the atmosphere of the mixed gas at 200.degree. C. to
500.degree. C. for 1 to 50 hours. More preferably, reduction
treatment is performed at 200.degree. C. to 400.degree. C. for 1 to
30 hours.
[0051] The upper-limit concentration of the hydrogen gas in the
mixed gas is about 4 vol % (that is, lower than the flammability
limit).
[0052] Methods of reduction treatment also include a method using
H.sub.2 gas (hydrogen gas) alone, other than the foregoing method
using the mixed gas. In other words, reduction treatment may be
carried out with a hydrogen gas concentration of 100 vol %. A lower
hydrogen gas concentration is preferred for ease of handling.
[0053] At a reduction treatment temperature of less than
200.degree. C., the degree of reduction is not sufficient. At a
reduction treatment temperature in excess of 500.degree. C., the
raw particles are fused while the reduction reaction is saturated
so that the reduction does not progress any more.
[0054] With a reduction treatment time of less than 1 hour, the
degree of reduction is not sufficient. With a reduction treatment
time in excess of 50 hours, the raw particles are fused while the
reduction reaction is saturated so that the reduction does not
progress any more.
[0055] Methods of nitridation treatment include a method in which:
the raw particles 20 are put into, for example, a glass container;
nitrogen element-containing gas such as NH.sub.3 gas (ammonia gas)
is supplied as a nitrogen source into this container; and the raw
particles 20 are subjected to nitridation treatment in the presence
of the NH.sub.3 gas (ammonia gas) at 140.degree. C. to 200.degree.
C. for 3 to 50 hours. More preferably, nitridation treatment is
performed at 140.degree. C. to 160.degree. C. for 3 to 20
hours.
[0056] At a nitridation treatment temperature of less than
140.degree. C., the degree of nitridation is not sufficient. At a
nitridation treatment temperature in excess of 200.degree. C., the
raw particles are fused while the nitridation is saturated.
[0057] The nitridation treatment time is preferably 3 to 50 hours.
At a nitridation treatment time of less than 3 hours, the degree of
nitridation is not sufficient. At a nitridation treatment time in
excess of 50 hours, the raw particles are fused while the
nitridation is saturated.
[0058] While the raw particles 20 of FIG. 1(b) are used as a raw
material as described above, the invention is not limited thereto.
The raw material may be a mixture of the raw particles 20 and
another type of particles. Another type of particles have a size
substantially the same as that of the raw particles 20 and each
have a core-shell structure in which an iron oxide layer is formed
on the surface of an iron (Fe) fine particle. The iron oxide is not
particularly limited, and examples thereof include Fe.sub.2O.sub.3
and Fe.sub.3O.sub.4.
[0059] It has been confirmed that when the above-described
oxidation treatment step, reduction treatment step and nitridation
treatment step are performed with the use of the mixture of the raw
particles 20 and another type of particles as a raw material, with
the proportion of the other type of particles being about 50 vol %,
the magnetic particles 10 of FIG. 1(a) are of course manufacture,
and in addition, magnetic particles each having a core-shell
structure in which an iron oxide layer (shell) is formed on the
surface of an iron nitride fine particle (core) are manufactured.
It has been also confirmed that the foregoing magnetic particles
having the iron oxide layers have a size substantially the same as
that of the magnetic particles 10 of FIG. 1(a). Furthermore, the
magnetic particles 10 and the foregoing magnetic particles having
the iron oxide layers do not adhere to each other but disperse.
[0060] It has been confirmed that even when the mixture of the raw
particles 20 and the other type of particles as above is used as a
raw material, with the proportion of the other type of particles
being about 50 vol %, and merely subjected to nitridation
treatment, the magnetic particles 10 and the foregoing magnetic
particles having the iron oxide layers can be manufactured with
substantially the same particle sizes and do not adhere to each
other but disperse. Thus, even when the mixture of the raw
particles 20 and the other type of particles is used as a raw
material, the magnetic particles 10 can be obtained and in
addition, the magnetic particles having the iron oxide layers as
above can be obtained.
[0061] In the present invention, none of oxidation, reduction and
nitridation treatment methods is limited to the foregoing
illustrative methods as long as the iron fine particles 22, which
are cores, can be oxidized, reduced and nitrided and thereby
changed into the iron nitride fine particles 12 with the core-shell
structure of the raw particles 20 as a raw material being
maintained.
[0062] The raw particles 20 (Fe/SiO.sub.2 particles) of FIG. 1(b)
can be produced by a method of producing superfine particles using
thermal plasma as disclosed by, for example, JP 4004675 B (a method
of producing oxide-coated metallic fine particles), and therefore,
a detailed explanation thereof will not be made. It should be noted
that a method of producing the raw particles 20 is not limited to
methods using thermal plasma as long as the raw particles 20
(Fe/SiO.sub.2 particles) can be produced.
[0063] The raw particles 20 used as a raw material and the magnetic
particles 10 were measured for magnetic properties. The results are
shown in FIG. 3.
[0064] As shown in FIG. 3, magnetic hysteresis curves (B-H curves)
denoted by A were obtained with the material particles 20, while
magnetic hysteresis curves (B-H curves) denoted by B were obtained
with the magnetic particles 10. As can be seen from the magnetic
hysteresis curves A and B, the magnetic particles 10 have more
excellent magnetic properties. Having the iron nitride fine
particles 12 as cores, the magnetic particles 10 can have a
coercive force of, for instance, 1700 Oe (about 135.3 kA/m) which
is higher than that of the raw particles 20 having iron cores. In
addition, the magnetic particles 10 can have a saturation magnetic
flux density of 93.5 emu/g (about 1.15.times.10.sup.-4 Wbm/kg).
[0065] The present applicants used raw particles (Fe/SiO.sub.2
particles) with an average particle size of 10 nm as a raw material
and subjected the raw particles (Fe/SiO.sub.2 particles) to
oxidation treatment, reduction treatment and nitridation treatment
in this order, thereby manufacturing magnetic particles. The raw
particles in the manufacturing process and the manufactured
magnetic particles were analyzed for their crystal structures by
X-ray diffractometry, and their states were observed with TEM
(transmission electron microscope). Results were obtained as shown
in FIGS. 4(a) to 4(c) and FIGS. 5(a) to 5(f).
[0066] FIG. 4(a) is a graph showing a result of crystal structure
analysis by X-ray diffractometry made on raw particles having yet
to undergo treatment; FIG. 4(b) is a graph showing a result of
crystal structure analysis by X-ray diffractometry made on the raw
particles having undergone oxidation treatment; and FIG. 4(c) is a
graph showing a result of crystal structure analysis by X-ray
diffractometry made on magnetic particles obtained through, after
the oxidation treatment, reduction treatment and then nitridation
treatment.
[0067] FIGS. 5(a) to 5(f) are corresponding to FIGS. 4(a) to 4(c).
FIG. 5(a) is a schematic view showing a TEM image of the raw
particles having yet to undergo treatment; FIG. 5(b) is an enlarged
view of FIG. 5(a); FIG. 5(c) is a schematic view showing a TEM
image of the raw particles having undergone oxidation treatment;
FIG. 5(d) is an enlarged view of FIG. 5(c); FIG. 5(e) is a
schematic view showing a TEM image of the magnetic particles; and
FIG. 5(f) is an enlarged view of FIG. 5(e).
[0068] The oxidation treatment was performed in air at 300.degree.
C. for 4 hours.
[0069] The reduction treatment was performed in an atmosphere in
which hydrogen is present, at 300.degree. C. for 10 hours. To form
the atmosphere in which hydrogen is present, H.sub.2 gas (hydrogen
gas) was used with an H.sub.2 gas concentration of 100 vol %.
[0070] The nitridation treatment was performed in an ammonia gas
atmosphere at 145.degree. C. for 10 hours.
[0071] FIG. 4(a) shows a result of crystal structure analysis made
on the raw particles, FIG. 5(a) is a TEM image of the raw
particles, and FIG. 5(b) is an enlarged view of FIG. 5(a). The raw
particles had the composition of Fe/SiO.sub.2 as shown in FIG.
4(a), and had a core-shell structure as shown in FIGS. 5(a) and
5(b).
[0072] FIG. 4(b) shows a result of crystal structure analysis made
on the raw particles having undergone oxidation treatment, FIG.
5(c) is a TEM image of the raw particles having undergone oxidation
treatment, and FIG. 5(d) is an enlarged view of FIG. 5(c).
Diffraction peaks of iron oxides are exhibited as shown in FIG.
4(b), and this means that iron (Fe) fine particles were oxidized.
As shown in FIGS. 5(c) and 5(d), the raw particles having undergone
oxidation treatment have a core-shell structure.
[0073] FIG. 4(c) shows a result of crystal structure analysis made
on the obtained magnetic particles, FIG. 5(e) is a TEM image of the
magnetic particles, and FIG. 5(f) is an enlarged view of FIG. 5(e).
The cores of the raw particles were changed into iron nitride
(Fe.sub.16N.sub.2) as shown in FIG. 4(c), and the magnetic
particles have a core-shell structure as shown in FIGS. 5(e) and
5(f). In addition, the magnetic particles did not aggregate but
disperse.
[0074] For comparison, raw particles (Fe/SiO.sub.2 particles) with
an average particle size of 33 nm, as a raw material, were
subjected to reduction treatment and nitridation treatment in this
order, without undergoing oxidation treatment. The raw particles
having undergone reduction treatment and nitridation treatment,
without undergoing oxidation treatment, were analyzed for their
crystal structures by X-ray diffractometry, and the results were
obtained as shown in FIGS. 6(a) and 6(b).
[0075] FIG. 6(a) shows a result of crystal structure analysis made
on the raw particles that have been subjected to reduction
treatment in a hydrogen gas (100 vol %) atmosphere at 300.degree.
C. for 3 hours and then nitridation treatment at 175.degree. C. for
5 hours, without undergoing oxidation treatment. FIG. 6(b) shows a
result of crystal structure analysis made on the raw particles that
have been subjected to reduction treatment in a hydrogen gas (100
vol %) atmosphere at 300.degree. C. for 3 hours and then
nitridation treatment at 185.degree. C. for 5 hours, without
undergoing oxidation treatment. FIG. 6(c) shows a result of crystal
structure analysis by X-ray diffractometry made on Fe.sub.16N.sub.2
serving as a reference. FIG. 6(d) shows a result of crystal
structure analysis made on the raw particles. FIG. 6(e) is an
enlarged view of a region D of FIG. 6(b).
[0076] Comparing FIGS. 6(a), 6(b) and 6(d) in which reduction
treatment and nitridation treatment were performed whereas no
oxidation treatment was performed, with FIG. 6(c) showing the
reference, this reveals that in cases where reduction treatment and
nitridation treatment were performed whereas no oxidation treatment
was performed, in addition to Fe.sub.16N.sub.2, Fe.sub.4N was also
generated. In other words, an Fe.sub.16N.sub.2 single phase cannot
be obtained without oxidation treatment.
[0077] The present invention is basically configured as above.
While the method for manufacturing magnetic particles, the magnetic
particles and the magnetic body according to the invention have
been described above in detail, the invention is by no means
limited to the foregoing embodiments and it should be understood
that various improvements and modifications are possible without
departing from the scope and spirit of the invention.
REFERENCE SIGNS LIST
[0078] 10 magnetic particle [0079] 12, 22 fine particle [0080] 14,
24 silicon oxide layer [0081] 20 raw particle
* * * * *