Composite soft magnetic sintered material having high density and high magnetic permeability and method for preparation thereof

Abstract

An object of the present invention is to provide a composite soft magnetic sintered material that has high density, high mechanical strength and high relative magnetic permeability at high frequencies and, in order to achieve this object, the present invention provides a method of producing the composite soft magnetic sintered material, which comprises mixing a composite soft magnetic powder, that consists of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder (hereinafter these powders are referred to as soft magnetic metal powder) of which particles arc coated with a ferrite layer which has a spinel structure, with 0.05 to 1.0% by weight of silicon dioxide powder having a mean powder particle size of 100 nm or less and sintering the mixed powder after compression molding, or processing two or more kinds of the composite soft magnetic powders, of which particles are coated with ferrite layer having a spinel structure of a different compositions, by compression molding and sintering.

Description

TECHNICAL FIELD

[0001] The present invention relates to a composite soft magnetic sintered material having high density and high magnetic permeability, and a method of producing the same.

BACKGROUND ART

[0002] Soft magnetic sintered materials are used in magnetic cores for such devices as low-loss yoke, transformer and choke coil used in motors, actuators or the like. And it is known that the soft magnetic sintered materials can be obtained by sintering a soft magnetic metal powder such as:

[0003] iron powder such as pure iron powder;

[0004] Fe—Si based soft magnetic iron alloy powder containing 0.1 to 10% by weight of Si with the rest consisting of Fe and inevitable impurities (for example, iron alloy powder of Fe-3% Si);

[0005] Fe—Si—Al based soft magnetic iron alloy powder containing 0.1 to 10% by weight of Si and 0.1 to 20% by weight of Al with the rest consisting of Fe and inevitable impurities (for example, Sendust iron alloy powder having a composition of Fe-9% Si-5% Al);

[0006] Fe—Al based soft magnetic iron alloy powder containing 0.1 to 20% by weight of Al with the rest consisting of Fe and inevitable impurities (for example, Alperm iron alloy powder having a composition of Fe-15% Al);

[0007] Fe—Cr based soft magnetic iron alloy powder containing 1 to 20% by weight of Cr and, as required, one or two of 5% or less Al and 5% or less Si with the rest consisting of Fe and inevitable impurities; or

[0008] nickel-based soft magnetic alloy powder containing 35 to 85% of Ni and, as required, one or more of 5% or less Mo, 5% or less Cu, 2% or less Cr and 0.5% or less Mn with the rest consisting of Fe and inevitable impurities (for example, powder of Fe-79% Ni) (hereinabove percentages are by weight). It is also known that soft magnetic sintered materials can be obtained by sintering a powder of a metal oxide such as ferrite that has a spinel structure. The ferrite having a spinel structure is generally represented by formula (MeFe)3O4 (where Me represents Mn, Zn, Ni, Mg, Cu, Fe or Co, or a mixture of some of these elements).

[0009] However, although the soft magnetic sintered metals have high saturation magnetic flux densities, they are inferior in high frequency characteristics. The soft magnetic sintered metal oxides that are made by sintering powder of a metal oxide such as ferrite having a spinel structure, on the other hand, have good high frequency characteristics and relatively high initial magnetic permeability, but have low saturation magnetic flux densities. In order to overcome these drawbacks, a composite soft magnetic sintered material has been proposed that is obtained by sintering a composite soft magnetic powder formed from a soft magnetic metal powder of which particles are coated with layers of ferrite having a spinel structure on the surface thereof (refer to Unexamined Japanese Patent Application, First Publication No. Sho 56-38402).

[0010] However, in the composite soft magnetic sintered material that is obtained by sintering the composite soft magnetic powder formed from the soft magnetic metal powder of which particles are coated with layers of ferrite having a spinel structure on the surface thereof, the ferrite layer having a spinel structure is made of an oxide and it is therefore difficult to sinter, thus resulting in a problem that the composite soft magnetic sintered material that has a sufficient density cannot be obtained. Thus there is a demand for a composite soft magnetic sintered material having further improved magnetic characteristics.

DISCLOSURE OF THE INVENTION

[0011] The present inventors have intensively studied the problem described above and found the following:

[0012] (A) A mixed powder having improved sintering characteristics can be obtained by preparing a composite soft magnetic powder by forming a ferrite layer which has a spinel structure on the surfaces of particles of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, and mixing the composite soft magnetic powder with 0.05 to 1.0% by weight of silicon dioxide powder having a mean powder particle size of 100 nm or less. A composite soft magnetic sintered material, that is made from the mixed powder containing the silicon dioxide powder by compression molding, high-pressure molding, warm compaction or cold isostatic pressing followed by sintering, or by hot isostatic pressing or hot pressing, has higher density and hence higher mechanical strength, and has higher magnetic characteristics and, particularly, improved relative magnetic permeability at high frequencies;

[0013] (B) A mixed powder, that is obtained by mixing two or wore kinds of composite soft magnetic powders made by forming ferrite layer which has a spinel structure of a different composition on the surfaces of particles of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, and sintering the mixed powder after compression molding, high-pressure molding, warm compaction or cold isostatic pressing, or processing the mixed powder by hot isostatic pressing or hot pressing, is easier to sinter than in such a case as the composite soft magnetic powder coated with ferrite layer of the same type is processed by compression molding, high-pressure molding, warm compaction or cold isostatic pressing followed by sintering, or by hot isostatic pressing or hot pressing. As a result, the composite soft magnetic sintered material thus obtained has higher density and hence higher mechanical strength, while the magnetic characteristics are improved and, in particular, relative magnetic permeability at high frequencies is improved;

[0014] (C) A mixed powder, that is obtained by mixing two or more kinds of composite soft magnetic powders made by forming ferrite layer of a spinel structure that has a different composition on the surfaces of particles of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, with the mixture being further mixed with 0.05 to 1.0% by weight of silicon dioxide powder having a mean powder particle size of 100 nm or less, has further improved sintering characteristics. A composite soft magnetic sintered material, that is made from the mixed powder containing silicon dioxide powder by compression molding, high-pressure molding, warm compaction or cold isostatic pressing followed by sintering, or by hot isostatic pressing or hot pressing, has higher density and hence higher mechanical strength, while the magnetic characteristics are improved further and, in particular, the relative magnetic permeability at high frequencies is improved further,

[0015] (D) In the composite soft magnetic sintered material obtained by the method (A) described above, the iron particles, Fe—Si based soft magnetic iron alloy particles, Fe—Al based soft magnetic iron alloy particles, Fe—Si—Al based soft magnetic iron alloy particles, Fe—Cr based soft magnetic iron alloy particles or nickel-based soft magnetic alloy particles that are coated with a ferrite phase having a spinel structure on the surface thereof are dispersed and the silicon dioxide powder having a mean powder particle size of 100 nm or less that is added thereto does not form a solid solution with the ferrite phase even when sintered and therefore remains dispersed in the ferrite phase. As a result, the composite soft magnetic sintered material has such a structure as the silicon dioxide particles having a mean powder particle size of 100 nm or less are dispersed in the ferrite phase, and the proportion of the silicon dioxide particles dispersed in the ferrite phase is from 0.05 to 1.0% by weight, the same as that of the silicon dioxide powder that was added;

[0016] (E) The composite soft magnetic sintered material obtained by the method (B) described above has such a structure as the iron particles, Fe—Si based soft magnetic iron alloy particles, Fe—Al based soft magnetic iron alloy particles, Fe—Si—Al based soft magnetic iron alloy particles, Fe—Cr based soft magnetic iron alloy particles or nickel-based soft magnetic alloy particles that are coated with a ferrite phase which has a spinel structure and has a different composition formed on the surface thereof are dispersed;

[0017] (F) The composite soft magnetic sintered material obtained by the method (C) described above comprises the iron particles, Fe—Si based soft magnetic iron alloy particles, Fe—Al based soft magnetic iron alloy particles, Fe—Si—Al based soft magnetic iron alloy particles, Fe—Cr based soft magnetic iron alloy particles or nickel-based soft magnetic alloy particles that are coated with a ferrite phase which has a spinel structure and has a different composition formed on the surface thereof being dispersed therein, wherein the silicon dioxide powder, having a mean powder particle size of 100 nm or less, that has been added thereto does not form a solid solution with the a ferrite phase even when sintered and therefore remains dispersed in the ferrite phase of a different composition, and the composite soft magnetic sintered material has such a structure as the silicon dioxide particles having a wean powder particle size of 100 nm or less are dispersed in the ferrite phase that has a different composition, and the proportion of the silicon dioxide particles dispersed in the ferrite phase of a different composition is from 0.05 to 1.0% by weight, the same as that of the silicon dioxide powder that was added; and

[0018] (G) The ferrite layer having a spinel structure formed on the particles of the iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder can be formed by a chemical plating process, high-speed impact agitation coating process where the coating layer is formed mechanically by high speed agitation, or binder coating process where the coating layer is formed by bonding with resin.

[0019] The present invention has been completed on the basis of the findings obtained from the research described above, and is characterized by the following features:

[0020] (1) A composite soft magnetic sintered material having high density and high magnetic permeability with such a structure as iron particles, Fe—Si based soft magnetic iron alloy particles, Fe—Al based soft magnetic iron alloy particles, Fe—Si—Al based soft magnetic iron alloy particles, Fe—Cr based soft magnetic iron alloy particles or nickel-based soft magnetic alloy particles, coated with a ferrite phase that has a spinel structure are dispersed, and silicon dioxide particles having a mean powder particle size of 100 nm or less are dispersed in said ferrite phase, wherein the content of silicon dioxide is from 0.05 to 1.0% by weight;

[0021] (2) A composite soft magnetic sintered material having high density and high magnetic permeability with such a structure as iron particles, Fe—Si based soft magnetic iron alloy particles, Fe—Al based soft magnetic iron alloy particles, Fe—Si—Al based soft magnetic iron alloy particles, Fe—Cr based soft magnetic iron alloy particles or nickel-based soft magnetic alloy particles, coated with a ferrite phase that has a spinel structure of a different composition are dispersed;

[0022] (3) A composite soft magnetic sintered material having high density and high magnetic permeability with such a structure as iron particles, Fe—Si based soft magnetic iron alloy particles, Fe—Al based soft magnetic iron alloy particles, Fe—Si—Al based soft magnetic iron alloy particles, Fe—Cr based soft magnetic iron alloy particles or nickel-based soft magnetic alloy particles, coated with a ferrite that has a spinel structure of a different composition are dispersed, and silicon dioxide particles having a mean powder particle size of 100 nm or less are dispersed among said ferrite phase, wherein the content of silicon dioxide is from 0.05 to 1.0% by weight;

[0023] (4) A method of producing the composite soft magnetic sintered material having high density and high magnetic permeability described in (1), wherein the composite soft magnetic powder, that is made by forming a ferrite layer that has a spinel structure on the surfaces of particles of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, is mixed with 0.05 to 1.0% by weight of silicon dioxide powder having a mean powder particle size in a range from 1 to 100 nm, and the mixed powder is sintered after compression molding, high-pressure molding, warm compaction or cold isostatic pressing;

[0024] (5) A method of producing the composite soft magnetic sintered material having high density and high magnetic permeability described in (1), wherein the composite soft magnetic powder, that is made by forming ferrite layer which has a spinel structure on the surfaces of particles of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy-powder, is mixed with 0.05 to 1.0% by weight of silicon dioxide powder having a mean powder particle size in a rage from 1 to 100 nm, and the mixed powder is subjected to hot isostatic pressing or hot pressing;

[0025] (6) A method of producing the composite soft magnetic sintered material having high density and high magnetic permeability described in (2), which comprises preparing two or more kinds of composite soft magnetic powders that are made by forming ferrite layer which has a spinel structure of a different composition on the surfaces of particles of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, mixing and sintering two or more kinds of composite soft magnetic powders after compression molding, high-pressure molding, warm compaction or cold isostatic pressing;

[0026] (7) A method of producing the composite soft magnetic sintered material having high density and high magnetic permeability described in (2), which comprises preparing two or more kinds of composite soft magnetic powders, that are made by forming ferrite layer having a spinel structure of a different composition on the surfaces of particles of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, mixing two or more kinds of the composite soft magnetic powders, and subjecting them to hot isostatic pressing or hot pressing;

[0027] (8) A method of producing the composite soft magnetic sintered material having high density and high magnetic permeability described in (3), which comprises preparing two or more kinds of composite soft magnetic powders, that are made by forming ferrite layer having a spinel structure of a different composition on the surfaces of particles of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, mixing two or more kinds of the composite soft magnetic powders with 0.05 to 1.0% by weight of silicon dioxide powder having a mean powder particle size in a range from 1 to 100 nm, sintering the mixed powder after compression molding, high-pressure molding, warm compaction or cold isostatic pressing;

[0028] (9) A method of producing the composite soft magnetic sintered material having high density and high magnetic permeability described in (3), which comprises preparing two or more kinds of composite soft magnetic powders, that are made by forming a ferrite layer having a spinel structure of a different composition on the surfaces of particles of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, mixing two or more kinds of the composite soft magnetic powders with 0.05 to 1.0% by weight of silicon dioxide powder having a mean powder particle size in a range from 1 to 100 nm, and subjecting the mixed powder to hot isostatic pressing or hot pressing; and

[0029] (10) A method of producing the composite soft magnetic sintered material having high density and high magnetic permeability described in any one of (4), (5), (6), (7), (8) and (9), wherein the composite soft magnetic powder, that is made by forming ferrite layer having a spinel structure on the surface of the particles of the iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, is made by forming the ferrite layer on the particles of the iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder by a chemical plating process, a high-speed impact agitation coating process or a binder coating process.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a photograph of a secondary electron image taken by an Auger spectrometer showing grain boundaries in sintered material No. 61 of the present invention.

[0031] FIG. 2 is a photograph of an Auger electron image of Si showing the distribution of SiO2 in the grain boundaries shown in FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

[0032] The iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder used in the method of producing the composite soft magnetic sintered material of the present invention having high density and high magnetic permeability is a soft magnetic alloy powder that has been known to the public, for which the soft magnetic metal powder such as iron powder, Fe—Si based soft magnetic iron alloy powder containing 0.1 to 10% by weight of Si with the rest consisting of Fe and inevitable impurities, Fe—Si—Al based soft magnetic iron alloy powder containing 0.1 to 10% by weight of Si and 0.1 to 20% by weight of Al with the rest consisting of Fe and inevitable impurities, Fe—Al based soft magnetic iron alloy powder containing 0.1 to 20% by weight of Al with the rest consisting of Fe and inevitable impurities, Fe—Cr based soft magnetic iron alloy powder containing 1 to 20% by weight of Cr and, as required, one or two of 5% or less Al and 5% or less Si with the rest consisting of Fe and inevitable impurities; or nickel-based soft magnetic alloy powder containing 35 to 85% of Ni and, as required, one or more of 5% or less Mo, 5% or less Cu, 2% or less Cr and 0.5% or less Mn with the rest consisting of Fe and inevitable impurities, that has been described in conjunction with the prior art may be used.

[0033] Therefore, the iron particles, Fe—Si based soft magnetic iron alloy particles, Fe—Al based soft magnetic iron alloy particles, Fe—Si—Al based soft magnetic iron alloy particles, Fe—Cr based soft magnetic iron alloy particles or nickel-based soft magnetic alloy particles included in the composite soft magnetic sintered material of the present invention having high density and high magnetic permeability are made of the soft magnetic metal particles of the same composition as that of the soft magnetic metal powder described above, and the ferrite phase having a spinel structure that covers the soft magnetic metal particles and separates the particles is a ferrite phase represented by the general formula (MeFe)3O4 (where Me represents Mn, Zn, Ni, Mg, Cu, Fe or Co, or a mixture of some of these elements).

[0034] The iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, of which particles are coated with layers of ferrite having a spinel structure on the surface thereof, that are used as the feed stock powder in producing the composite soft magnetic sintered material of the present invention having high density and high magnetic permeability can be made by forming the ferrite layer by a chemical plating process, high-speed impact agitation coating process or binder coating process.

[0035] The composite soft magnetic sintered material of the present invention having high density and high magnetic permeability can be produced by any of the methods (4) to (9) described above using the composite soft magnetic powder made as described above.

[0036] The compression molding process and the high-pressure molding process employed in the methods of (4), (6) and (8) described above are different only in the molding pressure. The high-pressure molding process molds powder with a pressure higher than in the ordinary compression molding process, and has the merit that the compressed body made by the high-pressure molding process can be sintered at a somewhat lower temperature.

[0037] The term “sintering” used in the method of producing the composite soft magnetic sintered material of the present invention having high density and high magnetic permeability includes liquid phase sintering as well as solid phase sintering. Therefore, sintering carried out in the methods of (4), (6) and (8) described above includes liquid phase sintering as well as solid phase sintering.

[0038] The reason for limiting the mean powder particle size of the silicon dioxide powder included in the composite soft magnetic sintered material of the present invention having high density and high magnetic permeability to 100 nm or less is that the effect of improving the sintering characteristic decreases and the relative magnetic permeability decreases when the mean powder particle size of the silicon dioxide powder is larger than 100 nm. The lower limit of the mean powder particle size of the silicon dioxide powder is preferably 1 nm or larger for reasons of the production cost.

[0039] The reason for setting the content of the silicon dioxide powder of a mean powder particle size within 100 nm to 0.05% by weight or more is that the sintering characteristics are not significantly affected and relative magnetic permeability decreases when less than 0.05% by weight of the silicon dioxide powder of a mean powder particle size within 100 nm is included, while the content exceeding 1.0% by weight has undesirable effects such as increasing the proportion of nonmagnetic phase and decreasing the relative magnetic permeability. The content of the silicon dioxide powder is most preferably in a range from 0.1 to 0.5% by weight.

EXAMPLE 1

[0040] An alloy material was melted by induction melting, with the resultant molten metal being subjected to water atomization so as to make an atomized powder, and the atomized powder was classified to prepare atomized feed stock powder. The atomized feed stock powder was classified further with an air classifier thereby to make a soft magnetic powder such as pure iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder and nickel-based soft magnetic alloy powder that had compositions and a mean powder particle sizes shown in Tables 1 and 2 (hereinafter these soft magnetic powders are referred to as soft magnetic metal powder). These soft magnetic metal powders were immersed in ion exchange water, stirred well and were fully deoxidized with nitrogen.

[0041] Aqueous solutions of metal chlorides having the oxide composition shown in Tables 1 and 2 were prepared by dissolving metal chlorides (MCl2, where M represents Fe, Ni, Zn, Cu, Mn or Mg) in ion exchange water that bad been fully deoxidized with nitrogen. The aqueous solutions of metal chlorides were gently poured onto the soft magnetic metal powders, and the pH value was adjusted to 7.0 by means of an aqueous solution of NaOH. This mixed liquid was held at a constant temperature of 70° C., and was stirred mildly while blowing air therein for a period of 0.3 to 3 hours, thereby to form a ferrite coating layer on the surfaces of the particles of the soft magnetic metal powder. Then the soft magnetic metal powder coated with ferrite layer was filtered, washed in water and dried thereby to obtain the composite soft magnetic powder.

[0042] SiO2 powder having the mean powder particle size shown in Tables 1 and 2 was mixed in the composite soft magnetic powder obtained as described above, with the mixture being pressed with a pressure of 6 tons/cm2 to mold ring-shaped green compacts measuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm in height. The ring-shaped green compact was sintered in an inert gas atmosphere with a controlled partial pressure of oxygen at temperature from 600 to 1200° C., thereby making composite soft magnetic sintered materials of the present invention 1 to 16, comparative composite soft magnetic sintered materials 1 to 3 and composite soft magnetic sintered material of the prior art, all having a ring shape. TEM observation of the structures of ring-shaped sintered bodies showed SiO2 powder dispersed in the ferrite phase in all the composite soft magnetic sintered materials of the present invention 1 to 16 and the comparative composite soft magnetic sintered materials 1 to 3. The relative density was measured on the composite soft magnetic sintered materials of the present invention 1 to 16, the comparative composite soft magnetic sintered materials 1 to 3 and the composite soft magnetic sintered material of the prior art, with the results shown in Tables 3 and 4. The relative magnetic permeability at high frequencies was measured at frequencies shown in Tables 3 and 4 with an impedance analyzer on the composite soft magnetic sintered materials of the present invention 1 to 16, the comparative composite soft magnetic sintered materials 1 to 3 and the composite soft magnetic sintered material of the prior art, with the results shown in Tables 3 and 4.

	TABLE 1
	Composite soft magnetic powder
	Soft magnetic metal powder	Ferrite coating layer	SiO2 powder
Composite soft		Mean powder		Mean	Mean powder
magnetic sintered	Composition	particle size	Composition	thickness	particle size	Content (% by
materials	(% by weight)	(μm)	(atomic %)	(μm)	(nm)	weight)
Composite	1	Fe: 100	52	(Mn33Fe67)3O4	0.2	10	0.6
soft magnetic	2	Fe: 100	78	(Mn17Zn16Fe67)3O4	1.4	30	0.8
sintered	3	Fe: 100	88	(Ni10Zn19Fe71)3O4	1.2	80	0.3
materials of	4	Fe: 99, Si: 1	69	(Cu5Mg5Zn23Fe67)3O4	2.4	30	0.2
present	5	Fe: 97, Si: 3	90	(Mn16Mg5Zn14Fe71)3O4	0.8	80	0.9
invention	6	Fe: 90, Al: 10	76	(Mn10Cu5Zn18Fe67)3O4	1.7	30	0.15
	7	Fe: 85, Si: 10, Al: 5	85	(Mn25Fe75)3O4	2.0	80	0.7
	8	Fe: 51, Ni: 49	49	(Mn17Zn12Fe71)3O4	0.4	10	0.07
	9	Fe: 21, Ni: 79	55	(Mn10Cu5Zn14Fe71)3O4	1.9	10	0.4
	10	Fe: 16, Ni: 79, Mo: 5	63	(Ni10Zn23Fe67)3O4	0.5	30	0.5
	11	Fe: 95, Cr: 5	48	(Ni10Zn15Fe75)3O4	2.3	30	0.2

[0043]

	TABLE 2
	Composite soft magnetic powder	SiO2 powder
	Soft magnetic metal powder		Mean
Composite soft		Mean powder	Ferrite coating layer	powder
magnetic sintered	Composition (% by	particle size	Composition	Mean	particle size	Content (%
materials	weight)	(μm)	(atomic %)	thickness (μm)	(nm)	by weight)
Composite soft	12	Fe: 91, Cr: 9	76	(Ni10Cu5Zn15Fe70)3O4	1.7	80	0.5
magnetic	13	Fe: 87, Cr: 13	61	(Mn25Fe75)3O4	2.2	80	0.3
sintered	14	Fe: 83, Cr17	78	(Ni5Zn20Fe75)3O4	1.4	10	0.5
materials of	15	Fe: 93, Cr: 3, Al: 2	52	(Ni10Cu5Mn18Fe67)3O4	0.1	30	0.1
present	16	Fe: 90, Cr: 9, Si: 1	84	(Ni10Zn23Fe67)3O4	0.7	30	0.8
invention
Comparative	1	Fe: 100	78	(Mn15Mg5Zn9Fe71)3O4	1.5	120*	0.2
composite soft	2	Fe: 97, Si: 3	90	(Mn29Fe71)3O4	0.3	30	0.02*
magnetic	3	Fe: 21, Ni: 79	55	(Ni6Zn23Fe71)3O4	0.9	30	1.2a
sintered
materials
Composite soft	Fe: 100	78	(Ni10Zn23Fe67)3O4	1.5	—	—
magnetic sintered
material of the prior
art
Figures marked with * are out of the scope of the present invention.

[0044]

TABLE 3
Composite soft magnetic	Relative	Relative magnetic permeability at various frequencies
sintered materials	density (%)	1 KHz	3 KHz	10 KHz	30 KHz	100 KHz	300 KHz	1 MHz
Composite soft	1	95	312	313	313	311	312	301	232
magnetic sintered	2	94	301	299	298	300	301	299	273
materials of present	3	94	291	277	279	278	277	275	251
invention	4	95	279	277	279	278	277	275	251
	5	93	292	291	292	292	294	265	189
	6	93	288	288	289	288	289	285	276
	7	96	286	284	285	285	281	264	203
	8	93	304	304	305	304	301	286	207
	9	94	290	289	290	290	289	289	280
	10	94	321	321	321	320	321	319	296
	11	92	289	290	290	288	266	241	212

[0045]

TABLE 4
Composite soft magnetic	Relative	Relative magnetic permeability at various frequencies
sintered materials	density (%)	1 KHz	3 KHz	10 KHz	30 KHz	100 KHz	300 KHz	1 MHz
Composite soft magnetic	12	95	300	299	300	300	299	296	279
sintered materials of present	13	95	296	295	296	296	287	262	207
invention	14	94	290	290	291	290	276	254	204
	15	96	307	307	307	305	305	300	292
	16	94	301	300	300	300	297	291	274
Comparative composite soft	1	90	224	224	222	223	221	206	147
magnetic sintered materials	2	89	231	230	230	231	228	210	122
	3	88	206	206	207	206	207	205	172
Composite soft magnetic	85	212	211	212	212	212	210	181
sintered material of
the prior art

[0046] From the results shown in Tables 1 to 4, it can be seen that the composite soft magnetic sintered materials of the present invention 1 to 16, that were made by compression molding and sintering of the mixture of composite soft magnetic powder consisting of soft magnetic metal powder coated with layers of ferrite having a spinel structure on the surface thereof and 0.05 to 1.0% by weight of SiO2 powder, have higher density than the composite soft magnetic sintered material of the prior art and excellent relative magnetic permeability at high frequencies, although the comparative composite soft magnetic sintered materials of 1 to 3 are inferior in at least one of density and relative magnetic permeability.

EXAMPLE 2

[0047] Molten metal was subjected to water atomization so as to make atomized powder, and the atomized powder was classified to prepare atomized feed stock powder. The atomized feed stock powder was classified further with an air classifier thereby to make the soft magnetic metal powders having compositions and the mean powder particle sizes shown in Tables 5. These soft magnetic metal powders were immersed in ion exchange water, stirred well and were fully deoxidized with nitrogen.

[0048] Aqueous solutions of metal chlorides having the oxide compositions shown in Tables 5 were prepared by dissolving metal chlorides (MCl2, where M represents Fe, Zn, Cu, Mn or Mg) in ion exchange water that had been fully deoxidized with nitrogen. The aqueous solutions of metal chlorides were gently poured onto the soft magnetic metal powders, with the pH value thereof being adjusted to 7.0 by means of an aqueous solution of NaOH. This mixed liquid was held at a constant temperature of 70° C., and was stirred mildly while blowing air therein for a period of 0.3 to 3 hours, thereby to form a ferrite coating layer on the surfaces of the particles of the soft magnetic metal powder. Then the soft magnetic metal powder coated with the ferrite coating layer was filtered, washed in water and dried thereby to obtain composite soft magnetic powders A to G having ferrite coating layer formed on the particles thereof shown as in Table 5.

[0049] The composite soft magnetic powders A to G obtained as described above were mixed in the proportions shown in Tables 6 and 7 and were pressed with a pressure of 6 tons/cm2 to mold a ring-shaped green compacts measuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm in height. The ring-shaped green compacts were sintered in an inert gas atmosphere with controlled partial pressure of oxygen at temperature from 600 to 1200° C., thereby making composite soft magnetic sintered materials of the present invention 17 to 30 and the composite soft magnetic sintered materials of the prior art 1 to 7, all having a ring shape. The relative density was measured on the composite soft magnetic sintered materials of the present invention 17 to 30 and the composite soft magnetic sintered materials of the prior art 1 to 7, with the results shown in Tables 6 and 7. The relative magnetic permeability at high frequencies was measured with an impedance analyzer at the frequencies shown in Tables 6 and 7 on the composite soft magnetic sintered materials of the present invention 17 to 30, and the composite soft magnetic sintered material of the prior art 1 to 7, with the results shown in Tables 6 and 7.

	TABLE 5
	Soft magnetic metal powder	Ferrite coating layer
	Composition	Mean powder particle	Composition	Mean
Type	(% by weight)	size (μm)	(atomic %)	thickness (μm)
Composite soft	A	Fe: 100	52	(Mn33Fe67)3O4	0.2
magnetic powders	B	Fe: 100	78	(Mn17Zn16Fe67)3O4	1.4
	C	Fe: 99, Si: 1	69	(Cu5Mg5Zn23Fe67)3O4	2.4
	D	Fe: 97, Si: 3	90	(Mn10Mg5Zn14Fe71)3O4	0.8
	E	Fe: 90, Al: 10	76	(Mn10Cu5Zn18Fe67)3O4	1.7
	F	Fe: 21, Ni: 79	66	(Mn10Cu5Zn15Fe70)3O4	0.5
	G	Fe: 87, Cr: 13	61	(Mn25Fe75)3O4	2.2

[0050]

	TABLE 6
	Proportions of composite
Composite	soft magnetic powders shown	Relative	Relative magnetic permeability
soft magnetic	in Table 5 (% by weight)	density	at various frequencies
sintered materials	A	B	C	D	E	F	G	(%)	1 KHz	3 KHz	10 KHz	30 KHz	100 KHz	300 KHz	1 MHz
Composite soft	19	50	—	50	—	—	—	—	96	286	286	287	286	287	281	255
magnetic sintered	20	—	70	—	—	30	—	—	94	293	292	293	293	293	276	234
materials of	21	—	—	40	60	—	—	—	94	288	286	286	287	286	270	217
present invention	22	40	—	—	30	30	—	—	95	305	305	305	304	305	294	264
	23	—	80	10	10	—	—	—	93	307	306	306	307	306	300	266
	24	20	20	—	—	60	—	—	94	278	278	279	279	278	272	259
	25	30	—	20	30	20	—	—	93	291	290	290	290	290	276	251
	26	—	20	20	30	30	—	—	93	287	288	287	287	288	273	254
	27	10	50	10	10	20	—	—	96	302	302	303	302	302	282	267
	28	20	10	20	30	10	—	—	95	294	295	294	295	295	291	269
	29	40	—	—	—	—	60	—	96	293	291	292	291	290	272	244
	30	—	20	30	—	—	—	50	94	290	290	291	290	287	271	237
	31	20	—	—	10	20	20	30	93	298	298	297	298	297	287	268
	32	10	20	10	10	20	20	10	94	301	303	303	302	300	284	270

[0051]

	TABLE 7
	Proportion of composite soft magnetic
Composite soft	powders shown in Table 5	Relative	Relative magnetic permeability
magnetic sintered	(% by weight)	density	at various frequencies
materials	A	B	C	D	E	F	G	(%)	1 KHz	3 KHz	10 KHz	30 KHz	100 KHz	300 KHz	1 MHz
Composite	1	100	—	—	—	—	—	—	88	230	230	229	230	216	298	106
soft	2	—	100	—	—	—	—	—	89	225	225	225	222	204	161	95
magnetic	3	—	—	100	—	—	—	—	89	212	211	211	211	212	204	143
sintered	4	—	—	—	100	—	—	—	90	219	218	218	217	218	202	135
materials	5	—	—	—	—	100	—	—	89	227	227	226	227	226	211	174
of the	6	—	—	—	—	—	100	—	87	222	223	223	222	218	203	181
prior art	7	—	—	—	—	—	—	100	89	206	206	205	205	198	195	149

[0052] From the results shown in Tables 5 to 7, it can be seen that the composite soft magnetic sintered materials of the present invention 17 to 30, that were made by mixing and sintering the composite soft magnetic powders consisting of the soft magnetic metal powders coated with ferrite coating layers of a different composition and having a spinel structure on the surface thereof, have higher density than the composite soft magnetic sintered material of the prior art 1 to 7 and excellent relative magnetic permeability at high frequencies.

EXAMPLE 3

[0053] The composite soft magnetic powders A to G made in Example 2 were mixed further with SiO2 powder in the proportions shown in Table 8 and were pressed with pressure of 6 tons/cm2 to mold a ring-shaped green compacts measuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm in height. The ring-shaped green compacts were sintered in an inert gas atmosphere with a controlled partial pressure of oxygen at a temperature from 600 to 1200° C., thereby making the composite soft magnetic sintered materials of the present invention 31 to 36. The relative density was measured on the composite soft magnetic sintered materials of the present invention 31 to 36, with the results shown in Table 8. The relative magnetic permeability at high frequencies was measured with an impedance analyzer at the frequencies shown in Table 8 on the composite soft magnetic sintered materials of the present invention 31 to 36, with the results shown in Table 8.

	TABLE 8
	Proportion (% by weight)
	SiO2
	powder
	of mean
Composite		powder	Rela-
soft	Composite soft	particle	tive
magnetic	magnetic powder	size	den-	Relative magnetic permeability
sintered	shown in Table 5	shown	sity	at various frequencies
materials	A	B	C	C	E	F	G	in ()	(%)	1 KHz	3 KHz	10 KHz	30 KHz	100 KHz	300 KHz	1 MHz
Composite	31	—	40	—	—	20	39.6	—	0.4	97	304	305	304	305	305	292	254
soft									(30 nm)
magnetic	32	29.1	—	—	20	20	—	30	0.9	97	308	309	309	308	308	305	296
sintered									(80 nm)
materials	33	10	10	20	—	—	30	29.1	0.1	96	299	299	298	298	295	278	244
of									(10 nm)
present	34	40	—	—	20	—	39.4	—	0.6	96	302	302	300	301	300	292	277
invention									(10 nm)
	35	—	59.5	—	—	—	40	—	0.5	98	316	314	314	315	313	303	291
									(30 nm)
	36	—	—	39.3	—	20	—	40	0.7	96	302	302	303	302	302	300	286
									(80 nm)

[0054] It can be seen that the composite soft magnetic sintered materials of the present invention 31 to 36 shown in Table 8, that were made by mixing the composite soft magnetic powders consisting of the soft magnetic metal powder coated with the ferrite coating layer having a spinel structure and a different composition on the surfaces of the particles thereof with SiO2 powder in the proportions shown in Table 8 and sintering the mixture, have higher density than the composite soft magnetic sintered material of the prior art 1 to 7 shown in Table 7 that were made in Example 2 and excellent relative magnetic permeability at high frequencies.

EXAMPLE 4

[0055] The soft magnetic metal powder shown in Table 9 and ferrite powder were mixed in proportions of soft magnetic metal powder: ferrite powder=98:2. The mixed powder was processed for two minutes in a high-speed impact mixer with an impeller rotating at a speed of 6000 rpm, thereby making the composite soft magnetic powders AS, BS, CS, DS, ES, FS and GS having a ferrite coating layer on the particles thereof shown in Table 9.

[0056] SiO2 powder having a mean powder particle size of 50 nm was mixed with the composite soft magnetic powders AS, BS, CS, DS, Es, FS and GS obtained as described above in the proportions shown in Table 10, with the mixture being hot-pressed with a pressure of 2 tons/cm2 at 800° C. so as to mold the composite soft magnetic sintered materials of the present invention 37 to 43 having a ring shape measuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm in height. TEM observation of the structures of ring-shaped sintered bodies showed SiO2 powder dispersed in the ferrite phase in all the composite soft magnetic sintered materials of the present invention 37 to 43. The relative density was measured on the composite soft magnetic sintered materials of the present invention 37 to 43, with the results shown in Table 10. The relative magnetic permeability at high frequencies was measured with an impedance analyzer at the frequencies shown in Table 10 on the composite soft magnetic sintered materials of the present invention 37 to 43, with the results shown in Table 10.

	TABLE 9
	Soft magnetic metal powder	Ferrite coating layer
	Composition	Mean powder particle		Mean
Type	(% by weight)	size (μm)	Composition (atomic %)	thickness (μm)
Composite	AS	Fe: 100	52	(Mn33Fe67)3O4	1.7
soft	BS	Fe: 100	78	(Mn17Zn16Fe67)3O4	1.5
magnetic	CS	Fe: 99, Si: 1	69	(Cu5Mg5Zn23Fe67)3O4	2.1
sintered	DS	Fe: 97, Si: 3	90	(Mn10Mg5Zn14Fe71)3O4	1.9
materials	ES	Fe: 90, Al: 10	76	(Mn10Cu5Zn18Fe67)3O4	2.4
	FS	Fe: 21, Ni: 79	66	(Mn10Cu5Zn15Fe70)3O4	2.0
	GS	Fe: 87, Cr: 13	61	(Mn25Fe75)3O4	1.2

[0057]

TABLE 10
	Proportion (% by weight)
Composite soft	Composite	SiO2 powder	Relative	Relative magnetic permeability
magnetic sintered	soft magnetic powder	having mean powder	density	at various frequencies
materials	shown in Table 9	particle size of 50 nm	(%)	1 KHz	3 KHz	10 KHz	30 KHz	100 KHz	300 KHz	1 MHz
Composite	37	AS: 99.6	0.4	93	310	311	310	310	309	288	221
soft magnetic	38	BS: 99.1	0.9	92	275	276	276	277	276	274	209
sintered	39	CS: 99.9	0.1	94	308	308	309	309	308	286	222
materials of	40	DS: 99.4	0.6	93	298	299	298	297	297	280	215
present	41	ES: 99.5	0.5	93	299	299	299	298	297	278	210
invention	42	FS: 99.3	0.7	92	285	286	285	286	285	272	203
	43	GS: 99.7	0.3	94	291	292	292	291	291	283	218

[0058] From the results shown in Tables 9 and 10, it can be seen that the composite soft magnetic sintered materials of the present invention 37 to 43, that were made by mixing 0.05 to 1.0% by weight of SiO2 powder with the composite soft magnetic powders AS, BS, CS, DS, ES, FS and GS consisting of the soft magnetic metal powder of which particles are coated with a ferrite layer having a spinel structure by a high-speed impact stirring coating method and processing the mixture by a hot pressing process, have higher density than the composite soft magnetic sintered material of the prior art 1 to 7 shown in Table 7 and excellent relative magnetic permeability at high frequencies.

EXAMPLE 5

[0059] The composite soft magnetic powders AS, BS, CS, DS, ES, FS and GS shown in Table 9 made in Example 4 were mixed in the proportions shown in Table 11. The mixed powders were hot-pressed with a pressure of 2 tons/cm2 at 800° C. so as to make the composite soft magnetic sintered materials of the present invention 44 to 53 having a ring shape measuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm in height. The relative density was measured on the composite soft magnetic sintered materials of the present invention 44 to 53, with the results shown in Table 11. The relative magnetic permeability at high frequencies was measured with an impedance analyzer at the frequencies shown in Table 11 on the composite soft magnetic sintered materials of the present invention 44 to 53, with the results shown in Table 11.

TABLE 11
	Proportion of composite
Composite	soft magnetic powder	Relative	Relative magnetic permeability
soft magnetic	shown in Table 9 (% by weight)	density	at various frequencies
sintered materials	AS	BS	CS	DS	ES	FS	GS	(%)	1 KHz	3 KHz	10 KHz	30 KHz	100 KHz	300 KHz	1 MHz
Composite soft	44	50	—	50	—	—	—	—	95	295	296	295	295	295	282	253
magnetic sintered	45	—	70	—	—	30	—	—	96	299	301	300	300	300	290	260
materials of	46	—	—	40	60	—	—	—	96	296	296	295	296	296	284	257
present invention	47	40	—	—	30	—	—	30	93	286	286	285	285	284	265	235
	48	—	80	10	10	—	—	—	94	293	293	293	292	293	276	256
	49	—	20	—	—	60	20	—	95	303	303	302	302	303	294	268
	50	30	—	20	30	20	—	—	96	297	299	298	299	298	293	266
	51	—	20	20	30	30	—	—	95	291	290	290	291	290	287	260
	52	10	—	10	10	20	—	50	94	290	290	290	289	288	280	252
	53	20	10	20	—	10	30	—	95	301	302	301	302	300	298	271

[0060] From the results shown in Table 11, it can be seen that the composite soft magnetic sintered materials of the present invention 44 to 53, that were made by mixing the composite soft magnetic powders consisting of the soft magnetic metal powders of which particles are coated with ferrite layer of a different composition having a spinel structure and sintering the mixed powder, have higher density than the composite soft magnetic sintered materials of the prior art 1 to 7 shown in Table 7 and excellent relative magnetic permeability at high frequencies.

EXAMPLE 6

[0061] Two or more kinds of the composite soft magnetic powders AS to GS shown in table 9 made in Example 4 were mixed and the mixture was further mixed with SiO2 powder having a mean powder particle size of 50 nm in the proportions shown in Table 12. The mixtures were hot-pressed with a pressure of 2 tons/cm2 at 800° C. so as to make composite soft magnetic sintered materials of the present invention 54 to 59 having a ring shape measuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm in height. The relative density was measured on the composite soft magnetic sintered materials of the present invention 54 to 59, with the results shown in Table 12. The relative magnetic permeability at high frequencies was measured with an impedance analyzer at the frequencies shown in Table 12 on the composite soft magnetic sintered materials of the present invention 54 to 59, with the results shown in Table 12.

TABLE 12
Composite	Proportion	Rela-
soft	(% by weight)	tive
magnetic	Composite soft magnetic		den-	Relative magnetic permeability
sintered	powder shown in Table 9	SiO2	sity	at various frequencies
materials	AS	BS	CS	DS	ES	FS	GS	powder	(%)	1 KHz	3 KHz	10 KHz	30 KHz	100 KHz	300 KHz	1 MHz
Composite	54	—	40	—	—	20	39.6	—	0.4	96	302	303	303	303	303	292	250
soft	55	29.1	—	—	20	20	—	30	0.9	97	307	307	308	308	307	304	293
magnetic	56	10	10	20	—	—	30	29.1	0.1	96	299	299	300	300	299	270	238
sintered	57	40	—	—	20	—	39.4	—	0.6	97	305	305	304	304	303	300	282
materials	58	—	59.5	—	—	—	40	—	0.5	98	309	310	310	309	309	305	288
of present	59	—	—	39.3	—	20	—	40	0.7	97	300	301	300	299	299	298	280
invention

[0062] It can be seen that the composite soft magnetic sintered materials of the present invention 54 to 59 shown in Table 12, that were made by mixing the composite soft magnetic powders consisting of the soft magnetic metal powder of which particles were coated with ferrite layer having a spinel structure of a different composition with SiO2 powder in the proportions shown in Table 12 and sintering the mixed powder, have a higher density than the composite soft magnetic sintered material of the prior art 1 to 7 shown in Table 7 that were made in Example 2 and excellent relative magnetic permeability at high frequencies.

EXAMPLE 7

[0063] The soft magnetic metal powders having the compositions shown in Table 13 were charged into a rolling agitation granulating apparatus to which 200 ml of polyvinyl alcohol solution 3% in concentration and ferrite powder in a proportion of 2% by weight to the soft magnetic metal powder were added so as to mix for 30 minutes while running the apparatus at a speed of 1000 rpm, thereby making composite soft magnetic powders AB, BB, CB, DB, EB, FB and GB shown in Table 13 by a binder coating process.

[0064] A SiO2 powder having a mean powder particle size of 50 nm was mixed with the composite soft magnetic powders AB, BB, CB, DB, EB, FB and GB obtained as described above in the proportions shown in Table 14, with the mixed powder being subjected to high-pressure molding with a pressure of 10 tons/cm2 so as to mold ring-shaped green compacts measuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm in height. The ring-shaped green compacts were sintered at a temperature from 500 to 1200° C., thereby making the composite soft magnetic sintered materials of the present invention 60 to 66 having a ring shape. TEM observation of the structures of the ring-shaped sintered bodies thus obtained showed SiO2 powder dispersed in the ferrite phase in all the composite soft magnetic sintered materials of the present invention 60 to 66. Results of analysis of the SiO2 included in the grain boundary of the composite soft magnetic sintered material 61, in particular, with a surface analysis apparatus (Auger electron analyzer (AES), product name Physical Electronics 670xi produced by Perkin Elmer) are shown in FIGS. 1 and 2. FIG. 1 is a secondary electron image of the grain boundary and FIG. 2 is Auger electron image of Si in the grain boundary, which shows the distribution of SiO2. From FIGS. 1 and 2, it can be seen that SiO2 is dispersed substantially uniformly in the ferrite phase in the grain boundary. The relative density was measured on the composite soft magnetic sintered materials of the present invention 60 to 66, with the results shown in Table 14. The relative magnetic permeability at high frequencies was measured with an impedance analyzer at the frequencies shown in Table 14 on the composite soft magnetic sintered materials of the present invention 60 to 66, with the results shown in Table 14.

	TABLE 13
	Soft magnetic metal powder	Ferrite coating layer
	Composition	Mean powder	Composition	Mean
Type	(% by weight)	particle size (μm)	(atomic %)	thickness (μm)
Composite soft	AB	Fe: 100	52	(Mn33Fe67)3O4	2.1
magnetic	BB	Fe: 100	78	(Mn17Zn16Fe67)3O4	2.8
sintered	CB	Fe: 99, Si: 1	69	(Cu3Mg3Zn23Fe67)3O4	1.4
materials	DB	Fe: 97, Si: 3	90	(Mn10Mg5Zn14Fe71)3O4	2.0
	EB	Fe: 90, Al: 10	76	(Mn10Cu5Zn18Fe67)3O4	2.9
	FB	Fe: 21, Ni: 79	66	(Mn10Cu5Zn15Fe70)3O4	2.8
	GB	Fe: 87, Cr: 13	61	(Mn25Fe75)3O4	1.4

[0065]

	TABLE 14
	Proportion (% by weight)
Composite soft	Composite soft	SiO2 powder having	Relative	Relative magnetic permeability
magnetic sintered	magnetic powder	mean powder particle	density	at various frequencies
materials	shown in Table 13	size of 50 nm	(%)	1 KHz	3 KHz	10 KHz	30 KHz	100 KHz	300 KHz	1 MHz
Composite soft	60	AB: 99.6	0.4	93	309	310	310	309	309	287	223
magnetic	61	BB: 99.1	0.9	92	276	276	275	276	276	273	210
sintered	62	CB: 99.9	0.1	94	305	306	305	306	304	300	218
materials of	63	DB: 99.4	0.6	92	290	290	289	288	288	279	213
present	64	EB: 99.5	0.5	92	289	290	291	290	289	277	208
invention	65	FB: 99.3	0.7	91	275	274	275	274	273	255	212
	66	GB: 99.7	0.3	93	301	301	300	300	300	280	211

[0066] From the results shown in Tables 13 and 14, it can be seen that the composite soft magnetic sintered materials of the present invention 60 to 66, that were made by mixing 0.05 to 1.0% by weight of SiO2 powder with the composite soft magnetic powders AB, BB, CB, DB, EB, FB and GB consisting of the soft magnetic metal powders of which particles were coated with ferrite layer having a spinel structure by a binder coating method and hot pressing the mixed powder, have a higher density than the composite soft magnetic sintered material of the prior art 1 to 7 shown in Table 7 and excellent relative magnetic permeability at high frequencies.

EXAMPLE 8

[0067] The composite soft magnetic powders AB, BB, CB, DB, EB, FB and GB shown in Table 13 made in Example 7 were mixed in proportions shown in Table 15. The mixed powders were subjected to high-pressure molding with a pressure of 10 tons/cm2 so as to make composite soft magnetic sintered materials of the present invention 67 to 76 having a ring shape measuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm in height. The relative density was measured on the composite soft magnetic sintered materials of the present invention 67 to 76, with the results shown in Table 15. The relative magnetic permeability at high frequencies was measured with an impedance analyzer at frequencies shown in Table 15 on the composite soft magnetic sintered materials of the present invention 67 to 76, with the results shown in Table 15.

TABLE 15
	Proportion of composite soft
Composite	magnetic powder shown in	Relative	Relative magnetic permeability
soft magnetic	Table 13 (% by weight)	density	at various frequencies
sintered materials	AB	BB	CB	DB	EB	FB	GB	(%)	1 KHz	3 KHz	10 KHz	30 KHz	100 KHz	300 KHz	1 MHz
Composite soft	67	50	—	50	—	—	—	—	95	293	294	293	294	293	285	261
magnetic sintered	68	—	70	—	—	30	—	—	95	290	290	291	290	290	278	262
materials of	69	—	—	40	60	—	—	—	96	295	295	294	295	294	284	260
present invention	70	40	—	—	30	—	—	30	94	281	282	282	281	280	261	240
	71	—	80	10	10	—	—	—	94	290	290	289	289	287	276	257
	72	—	20	—	—	60	20	—	95	300	301	301	300	299	295	268
	73	30	—	20	30	20	—	—	95	291	290	290	290	290	292	257
	74	—	20	20	30	30	—	—	94	286	285	286	285	285	280	255
	75	10	—	10	10	20	—	50	94	288	288	289	288	287	275	254
	76	20	10	20	—	10	30	—	96	300	302	301	300	301	297	270

[0068] From the results shown in Tables 15, it can be seen that the composite soft magnetic sintered materials of the present invention 67 to 76, that were made by mixing the composite soft magnetic powders consisting of the soft magnetic metal powders of which particles were coated with layers of ferrite having a spinel structure of a different composition and sintering the mixed powder, have higher density than the composite soft magnetic sintered material of the prior art 1 to 7 shown in Table 7, and excellent relative magnetic permeability at high frequencies.

EXAMPLE 9

[0069] Two or more kinds of the composite soft magnetic powders AB to GB shown in Table 13 made in Example 7 were mixed and the mixture was further mixed with SiO2 powder having a mean powder particle size of 50 nm in proportion shown in Table 16. The mixed powder was hot-pressed with a pressure of 2 tons/cm2 at 800° C. so as to make composite soft magnetic sintered materials of the present invention 77 to 82 having a ring shape measuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm in height. The relative density was measured on the composite soft magnetic sintered materials of the present invention 77 to 82, with the results shown in Table 16. The relative magnetic permeability at high frequencies was measured with an impedance analyzer at frequencies shown in Table 16 on the composite soft magnetic sintered materials of the present invention 77 to 82, with the results shown in Table 16.

TABLE 16
Composite		Rela-
soft	Proportion (% by weight)	tive
magnetic	Composite soft magnetic		den-	Relative magnetic permeability
sintered	powder shown in Table 13	SiO2	sity	at various frequencies
materials	AB	BB	CB	DB	EB	FB	GB	powder	(%)	1 KHz	3 KHz	10 KHz	30 KHz	100 KHz	300 KHz	1 MHz
Composite	77	—	40	—	—	20	39.6	—	0.4	96	300	300	301	299	299	291	251
soft	78	29.1	—	—	20	20	—	30	0.9	97	304	304	303	304	304	300	290
magnetic	79	10	10	20	—	—	30	29.1	0.1	97	298	299	299	298	297	272	240
sintered	80	40	—	—	20	—	39.4	—	0.6	96	301	301	300	300	300	291	273
materials	81	—	59.5	—	—	—	40	—	0.5	97	299	300	300	300	299	294	278
of present	82	—	—	39.3	—	20	—	40	0.7	96	297	297	297	296	295	290	270
invention

[0070] It can be seen that the composite soft magnetic sintered materials of the present invention 77 to 82, that were made by mixing the composite soft magnetic powders consisting of the soft magnetic metal powder of which particles were coated with ferrite layer having a spinel structure of a different composition with SiO2 powder in proportion shown in Table 16 and sintering the mixed powder, have a higher density than the composite soft magnetic sintered material of the prior art 1 to 7 shown in Table 7 that were made in Example 2 and excellent relative magnetic permeability at high frequencies.

[0071] As will be understood from the foregoing detailed description, the present invention provides the composite soft magnetic sintered material having high industrial applicability, offering remarkable effects in the electrical and electronics industries.

Claims

1. A composite soft magnetic sintered material having high density and high magnetic permeability with such a structure as iron particles, Fe—Si based soft magnetic iron alloy particles, Fe—Al based soft magnetic iron alloy particles, Fe—Si—Al based soft magnetic iron alloy particles, Fe—Cr based soft magnetic iron alloy particles or nickel-based soft magnetic alloy particles, coated with a ferrite phase that has a spinel structure arc dispersed, and silicon dioxide particles having a mean powder particle size of 100 nm or less are dispersed in said ferrite phase, wherein the content of silicon dioxide is from 0.05 to 1.0% by weight.

2. A composite soft magnetic sintered material having high density and high magnetic permeability with such a structure as iron particles, Fe—Si based soft magnetic iron alloy particles, Fe—Al based soft magnetic iron alloy particles, Fe—Si—Al based soft magnetic iron alloy particles, Fe—Cr based soft magnetic iron alloy particles or nickel-based soft magnetic alloy particles, coated with a ferrite phase that has a spinel structure of a different composition are dispersed.

3. A composite soft magnetic sintered material having high density and high magnetic permeability with such a structure as iron particles, Fe—Si based soft magnetic iron alloy particles, Fe—Al based soft magnetic iron alloy particles, Fe—Si—Al based soft magnetic iron alloy particles, Fe—Cr based soft magnetic iron alloy particles or nickel-based soft magnetic alloy particles, coated with a ferrite that has a spinel structure of a different composition are dispersed, and silicon dioxide particles having a mean powder particle size of 100 nm or less are dispersed among said ferrite phase, wherein the content of silicon dioxide is from 0.05 to 1.0% by weight.

4. A method of producing the composite soft magnetic sintered material having high density and high magnetic permeability of claim 1, wherein the composite soft magnetic powder, that is made by forming a ferrite layer that has a spinel structure on the surfaces of particles of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, is mixed with 0.05 to 1.0% by weight of silicon dioxide powder having a mean powder particle size in a range from 1 to 100 nm, and the mixed powder is sintered after compression molding, high-pressure molding, warm compaction or cold isostatic pressing.

5. A method of producing the composite soft magnetic sintered material having high density and high magnetic permeability of claim 1, wherein the composite soft magnetic powder, that is made by forming a ferrite layer which has a spinel structure on the surfaces of particles of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, is mixed with 0.05 to 1.0% by weight of silicon dioxide powder having a mean powder particle size in a rage from 1 to 100 nm, and the mixed powder is subjected to hot isostatic pressing or hot pressing.

6. A method of producing the composite soft magnetic sintered material having high density and high magnetic permeability of claim 2, which comprises preparing two or more kinds of composite soft magnetic powders that are made by forming a ferrite layer which has a spinel structure of a different composition on the surfaces of particles of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, mixing and sintering two or more kinds of composite soft magnetic powders after compression molding, high-pressure molding, warm compaction or cold isostatic pressing.

7. A method of producing the composite soft magnetic sintered material having high density and high magnetic permeability of claim 2, which comprises preparing two or more kinds of composite soft magnetic powders, that are made by forming a ferrite layer having a spinel structure of a different composition on the surfaces of particles of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, mixing two or more kinds of the composite soft magnetic powders, and subjecting them to hot isostatic pressing or hot pressing.

8. A method of producing the composite soft magnetic sintered material having high density and high magnetic permeability of claim 3, which comprises preparing two or more kinds of composite soft magnetic powders, that are made by forming a ferrite layer having a spinel structure of a different composition on the surfaces of particles of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, mixing two or more kinds of the composite soft magnetic powders with 0.05 to 1.0% by weight of silicon dioxide powder having a mean powder particle size in a range from 1 to 100 nm, sintering the mixed powder after compression molding, high-pressure molding, warm compaction or cold isostatic pressing.

9. A method of producing the composite soft magnetic sintered material having high density and high magnetic permeability of claim 3, which comprises preparing two or more kinds of composite soft magnetic powders, that are made by forming ferrite layer having a spinel structure of a different composition on the surfaces of particles of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, mixing two or more kinds of the composite soft magnetic powders with 0.05 to 1.0% by weight of silicon dioxide powder having a mean powder particle size in a range from 1 to 100 nm, and subjecting the mixed powder to hot isostatic pressing or hot pressing.

10. A method of producing the composite soft magnetic sintered material having high density and high magnetic permeability of any one of claims 4, 5, 6, 7, 8 and 9, wherein the composite soft magnetic powder, that is made by forming a ferrite layer having a spinel structure on the surface of the particles of the iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder, is made by forming the ferrite layer on the particles of the iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder by a chemical plating process, a high-speed impact agitation coating process or a binder coating process.