JP3345941B2 - Magnetic ceramics and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic ceramic having silicon nitride as a matrix and a method for producing the same.

[0002]

_2. Description of the Related Art Conventionally, FeO, Fe ₂ O
₃ , silicon nitride Si to which iron oxide of Fe ₃ O ₄ is added
₃ N _4, for example, JP 58-64268, JP-Sho 59-88374, JP-Sho 61-72685
And U.S. Pat. No. 4,332,909.

Further, Japanese Patent Application Laid-Open No. 2-293380 discloses a sintered silicon nitride ceramic containing a sintering aid. The silicon nitride sintered ceramic is obtained by adding iron oxide to silicon nitride and converting it to iron silicide, cold-formed and fired in a nitrogen atmosphere.

[0004] Japanese Patent Application Laid-Open No. 2-132711 discloses a method for manufacturing an oxide superconducting wire. The method for producing an oxide superconducting wire comprises, when filling an oxide-based superconducting wire powder or a melt into a sheath material pipe, adding the electrolytic or magnetic flux or both to the filling. Is what you do.

[0005]

However, silicon nitride ceramics having magnetic properties are desired. In general, when silicon carbide, boron nitride, or oxide particles are dispersed in Si ₃ N ₄ , the reactivity at the bonding interface is poor, and the strength of the material itself is reduced. Further, in a material in which boron nitride is compounded, the portion is oxidized at a high temperature, the crystal structure is changed, and the friction coefficient may be increased. As disclosed in the above publication, in the case where a metal oxide such as Fe ₃ O ₄ is added as a sintering aid, the amount of addition is small, and it cannot exhibit magnetism or increase strength.

Further, iron oxides of FeO, Fe ₂ O ₃ , and Fe ₃ O ₄ function as a sintering aid for silicon nitride (Si ₃ N ₄ ) and act to improve the strength. Becomes an impurity with respect to silicon nitride (Si ₃ N ₄ ), and the strength is deteriorated. For silicon nitride, FeO, Fe ₂ O ₃ ,
When the amount of Fe ₃ O ₄ iron oxide is increased, the magnetic properties are improved, but the strength is reduced. For engine parts and the like, materials capable of securing strength, for example, strength of 300 MPa or more, are desired. If silicon nitride ceramics having such strength and improved magnetic properties can be manufactured, the material may be used. The fields of application will grow and become useful as materials.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to disperse an Fe-Si compound in a matrix containing Si ₃ N ₄ or SiC as a main component to form an engine part or the like. Another object of the present invention is to provide a magnetic ceramic having improved strength and a magnetic ceramic having an effective strength, and a method for producing the same.

[0008]

According to the present invention, an Fe--Si compound is dispersed in the matrix using silicon nitride as a matrix, and the size of the Fe--Si compound is 10 .mu.m or less. And a magnetic ceramic characterized by being sintered by pressing under pressure.

In this magnetic ceramic, the pressure molding in the magnetic field is performed in the magnetic field of 10 kOe or more.

This magnetic ceramic is CIP-molded in the atmosphere after the pressure molding in the magnetic field.

This magnetic ceramic is made of the Fe-Si
When the compound is converted into FeO, Fe ₂ O ₃ , Fe ₃ O ₄ ,
1 wt% or more and 50 wt% or less are contained.

Further, according to the present invention, there is provided a semiconductor device according to the present invention, wherein the Fe-Si compound is dispersed in the mother phase using silicon nitride as a mother phase, and the size of the Fe-Si compound is 10 μm or less.
Pressure molding is performed in a magnetic field of 0 kOe or more. After the pressure molding in the magnetic field, CIP molding is performed in the air to form a molded body. Then, the molded body is fired in a nitrogen atmosphere to obtain a sintered body. The present invention relates to a method for producing a magnetic ceramic characterized by being made.

Since the magnetic ceramic according to the present invention is constituted as described above, it exhibits magnetism and has high strength. In order to secure sufficient strength as a magnetic material, the above-mentioned Fe--Si The compound is FeO, Fe
1 wt% or more in terms of ₂ O ₃ and Fe ₃ O ₄ and 50
wt% or less. When the amount of the Fe—Si compound added to silicon nitride is limited to the above range, even if the strength of the conventional magnet is large, it is 300 MPa.
Although the degree was limited, a strength of 300 MPa or more can be secured.

Further, Fe—S such as FeSi and FeSi ₂
The i-compound exhibits magnetism, but a large size Fe-Si compound is a starting point of destruction, so a smaller size is more effective for increasing strength. According to the theory of graphics, it is preferable that the thickness is 10 μm or less to prevent a fracture, for example, a starting point of pores, cracks, and the like.
The size of the compound is limited to 10 μm or less.

Further, since this method for producing a magnetic ceramic is constituted as described above, the directions of spins in the compact are uniformed by press-forming in a magnetic field.
It has an advantageous effect on the magnetic properties after firing and can improve the magnetic properties. In particular, by forming a mixture of iron oxide and silicon nitride by CIP, the density of the green body is improved, and the strength of the green body is improved. Can be improved.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a magnetic ceramics and a method of manufacturing the same according to the present invention will be described with reference to the drawings. This magnetic ceramic is characterized in that an Fe—Si compound is dispersed in the matrix using silicon nitride as a matrix. In this magnetic ceramic, the size of the Fe—Si compound is selected to be as small as 10 μm or less in order to prevent the size of the Fe—Si compound from becoming a starting point of breaking such as cracks, cracks, and pores. In addition, this magnetic ceramic is made of Fe-S with respect to silicon nitride in order to secure a sufficient strength of 300 MPa or more as a magnetic material.
The amount of i compounds FeO, Fe ₂ O _3, Fe is and selected to 50wt% or less in ₃ O ₄ in terms of 1 wt% or more.

In the method for producing a magnetic ceramic according to the present invention, the Fe--Si compound is mainly dispersed in the matrix with silicon nitride as the matrix, and the Fe--Si compound is dispersed in the matrix.
The size of the Si compound is 10 μm or less and 10 kOe
Press forming in the above magnetic field, press forming in the magnetic field, and then perform CIP forming in the air to form a formed body, and then fire the formed body in a nitrogen atmosphere to form a sintered body. It is characterized by the following. In this method for producing magnetic ceramics, the pressure molding in a magnetic field is performed at 10 kOe or more.
This is performed by IP (cold isostatic pressing).

Embodiment 1 of the embodiment of the method for producing a magnetic ceramic according to the present invention will be described. In this method for producing magnetic ceramics, Si ₃ N ₄ , Al ₂ O ₃ and Y ₂ O ₃ are blended in the following ratio. Si ₃ N ₄ : Al ₂
O ₃ : Y ₂ O ₃ = 90: 5: 5. Based on this total weight, three types of oxides of Fe, ie, FeO, Fe
Predetermined amounts of ₂ O ₃ and Fe ₃ O ₄ are added, mixed with distilled water and a binder for about 24 hours in a ball mill to form a mixture, and the mixture is subjected to granulation by a spray dryer to form a granular material. Was.

Next, these granulated granules were used as forming raw materials in a magnetic field of 15 kOe under a pressure of 1000 kgf.
After being preformed by a press pressure of / cm ² , it was pressed by a CIP at a pressure of about 2000 kgf / cm ² to obtain various rectangular solids. After degreased these compacts, these degreased compacts were heated and fired to a maximum temperature of 1850 ° C. in a 9.3 MPa N ₂ atmosphere to obtain a large number of dense sintered compacts. These sintered bodies were processed into 3 × 3 × 4 mm to prepare rectangular test pieces, and the magnetic properties of these test pieces such as residual magnetic flux density, coercive force and initial permeability were measured.

[0020] FeO, for measuring the magnetic characteristic corresponding to the amount of change of the _{Fe 2 O 3, Fe 3 O} 4 iron oxide (Fe _m O _n), changing the amount of various iron oxides Si ₃
The results of the magnetic properties of the test piece of N ₄ are shown in FIGS. 1, 2 and 3. The addition amount of 1 iron oxide (Fe _m O _n) amount of residual magnetic flux density for (wt%) graph illustrating the (Gaussian G), Fig. 2 is iron oxide (Fe _m O _n) (wt
The addition amount of the coercive force with respect to%) (oersted Oe) graph showing, and FIG. 3 is iron oxide (Fe _m O _n) (wt
%) Is a graph showing initial magnetic permeability with respect to%. In each figure, the amount of Fe _m O _n is the place of 0, a silicon nitride itself, shows a comparative example.

FIG. 1 shows the residual magnetic flux density with respect to the added amount of FeO, the residual magnetic flux density with respect to the added amount of Fe ₂ O ₃ , and the residual magnetic flux density with respect to the added amount of Fe ₃ O ₄ , respectively. In FIG. 2, the coercive force with respect to the added amount of FeO, the coercive force with respect to the added amount of Fe ₂ O ₃ , and Fe ₃
The coercive force with respect to the added amount of O ₄ is shown.
Further, in FIG. 3, the initial magnetic permeability, F
The initial permeability with respect to the added amount of e ₂ O ₃ and the initial permeability with respect to the added amount of Fe ₃ O ₄ are shown. From the above chart, by the Si ₃ N ₄ is added iron oxide (Fe _m O _n), a soft magnetic be granted to Si ₃ N ₄ which did not have magnetism, The amount of Fe _m O _n It can be seen that as the value increases, the magnetic characteristics improve.

Further, the addition amount of Fe _m O _n is a tissue of 10 wt% of the sliding test pieces, SEM (Scanning Electron Micr
was observed with oscopy), the addition amount of Fe _m O _n is 10
In the wt% sliding test piece, the iron-containing portion was not solid-dissolved at a size of 10 μm or less, and was present in a state where iron was uniformly dispersed in the Si ₃ N ₄ crystal grain boundaries. It could be confirmed. FIG. 5 shows the result of analysis of the identification of this phase using X-ray microanalysis. As can be seen from FIG. 5, the above phase was found to be a Fe—Si compound. It was presumed that the presence of this Fe—Si compound in Si ₃ N _{4 provided} magnetism.

From the sintered body produced by this method for producing a magnetic ceramic, a test piece for a four-point bending strength test of 3 × 4 × 40 mm was produced. The result is shown in FIG. Figure 4 is an iron oxide addition amount of _{(Fe m O n) (wt} %)
4 is a graph showing a four-point bending average strength (MPa) with respect to FIG. As can be seen from this graph, the intensity in accordance with gradually increasing the amount of iron oxide to _{Si 3 N 4 (Fe m O} n) is decreased, the amount of Fe _m O _n is 10~20wt
% In the test piece in Comparative Example (FIG. 4 not added, Fe _m O
The point _where the addition amount of _n is 0), that is, the strength is equal to or higher than that of ordinary Si ₃ N ₄ .

FIG. 4 shows the four-point bending average strength with respect to the added amount of FeO, the four-point bending average strength with respect to the added amount of Fe ₂ O ₃ , and the four-point bending average strength with respect to the added amount of Fe ₃ O _4. I have. Moreover, was observed by SEM, the inside organization of the Fe _m O _n 10wt% of the added amount of the magnetic ceramic, pores not be substantially recognized, Si ₃ N ₄
It was found that the growth of the crystal grains was suppressed by the presence of the iron oxide, resulting in fine and uniform crystal grains. Such a tissue is considered to be advantageous for high strength in view of the Griffith relation.

Further, when the test piece of the Fe _m O _n magnetic ceramics were added amount further increased, the strength is lowered, they were tissue observed in the same manner as described above, Fe
_m O _n aggregation of was observed, pores were present in the place where was the aggregation. That is, it is considered that as a result of the pores remaining in the test piece, the pores serve as a starting point of destruction, so that the strength of the test piece has decreased.

In the above method for producing a magnetic ceramic, a magnetic ceramic was similarly produced by changing the magnetic force at the time of forming in a magnetic field with respect to a mixture of Si ₃ N ₄ and 30 wt% of Fe ₃ O ₄ . When the residual magnetic flux density of these magnetic ceramics was measured, the following results were obtained. That is, when the magnetic force is 0 kOe, the residual magnetic flux density is 82 G,
When the magnetic force is 5 kOe, the residual magnetic flux density is 105 G and the magnetic force is 10 k.
In Oe, the residual magnetic flux density was 215 G, when the magnetic force was 15 kOe, the residual magnetic flux density was 223 G, when the magnetic force was 20 kOe, the residual magnetic flux density was 220 G, and when the magnetic force was 25 kOe, the residual magnetic flux density was 231 G. From the above results, it is understood that the pressure molding in a magnetic field is preferably performed at 10 kOe or more. Then, Si ₃ N ₄ and Fe _m O _n the mixed powder by press molding in a magnetic field of, Fe _m in the compact
O _n the spin direction is aligned in, now favors the magnetic properties after firing, thereby improving the magnetic properties.

In the above-described method for producing a magnetic ceramic, a mixture obtained by adding 10 wt% of Fe ₃ O ₄ to Si ₃ N ₄ is preformed by working under a magnetic field,
A test piece fired without performing IP was prepared, and its four-point bending strength was measured to be 820 MPa. That is, C
The strength of the magnetic ceramic without IP was about 160 MPa compared to the magnetic ceramic with CIP.
It was found that the degree had decreased. This indicates that when CIP molding is performed after pressure molding in a magnetic field, the density of the molded body is increased and the strength is improved.

The magnetic ceramic according to the present invention, since the magnetic properties will be improved as increasing the amount of Fe _m O _n, strength decreases, the securing strength of more than 300MPa as a magnetic body, Fe _m O _n 1-50 wt%
Must be within the range. The strength is 3
By securing 00 MPa or more, it can be used, for example, as an engine component such as a permanent magnet of a turbocharger having a generator / motor. Further, Fe _m O _n is Si ₃ N
_It also functions as a sintering aid and works to improve strength.
Si becomes an impurity and its strength deteriorates. Therefore, manufactured by blending the Fe _m O _n mixture of silicon nitride powder mixture, Fe-Si compound to produce a magnetic ceramic dispersed silicon nitride in the matrix phase.

[0029]

The magnetic ceramics and the method of manufacturing the same according to the present invention have the following effects because they are configured as described above. In this magnetic ceramic, the Fe-Si compound is dispersed in the matrix of silicon nitride.
A silicon nitride having magnetism and high strength can be provided. And to secure the strength of 300MPa or more,
The size of the Fe—Si compound was controlled to be 10 μm or less, and the Fe—Si compound was FeO, F
In terms of e ₂ O ₃ and Fe ₃ O ₄ , the content is controlled so as to be contained at 1 wt% or more and 50 wt% or less.

In this method for producing magnetic ceramics, it is preferable to carry out pressure molding in a magnetic field of 10 kOe or more in order to improve the magnetic properties, and to carry out CIP in order to improve the strength of the fired body. It is preferred to increase body density.

[Brief description of the drawings]

FIG. 1 shows an iron oxide Fe for this magnetic ceramic.
is a graph showing the residual magnetic flux density measurement results for the addition amount of _m O _n.

FIG. 2 shows an iron oxide Fe for this magnetic ceramic.
is a graph showing measurement results of coercive force relative to the addition amount of _m O _n.

FIG. 3 shows an iron oxide Fe for this magnetic ceramic.
It is a graph showing the measurement results of the initial permeability to the addition amount of _m O _n.

FIG. 4 shows an iron oxide Fe for this magnetic ceramic.
It is a graph showing the measurement results of the four-point bending average intensity for the addition amount of _m O _n.

FIG. 5 is a graph showing a result of analyzing the magnetic ceramics using an X-ray microanalysis method.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C04B 35/584-35/596

Claims (5)

(57) [Claims] 1. A are dispersed is Fe-Si compound, silicon nitride in said matrix as a matrix phase, the Fe-Si compound
The size of the object is 10μm or less,
A magnetic ceramic characterized by being sintered . Claim 2. A pressure forming in a said magnetic field is characterized by being carried out in the magnetic field of more than 10 kOe 1
The magnetic ceramic according to 1. 3. The method according to claim 1, wherein after the pressure molding in the magnetic field, C.
2. The magnetic ceramic according to claim 1, wherein the magnetic ceramic is IP-molded . 4. The method according to claim 1, wherein the Fe—Si compound is FeO, Fe ₂
In terms of O ₃ and Fe ₃ O ₄ , not less than 1 wt% and 50
2. The magnetic ceramic according to claim 1, wherein the magnetic ceramic is contained in an amount of not more than wt%. 5. A method according to claim 1 , wherein silicon nitride is used as a mother phase.
The Fe-Si compound is dispersed, and the Fe-Si compound
The size of the object is 10 μm or less and the magnetic
Pressing in a magnetic field, and after pressing in the magnetic field,
CIP molding inside to make a molded body, then
Characterized by firing the body in a nitrogen atmosphere to make a sintered body
Method of manufacturing a magnetic ceramics.