JPH06227864A - Magnetic ceramic and their production - Google Patents

Abstract

PURPOSE:To obtain magnetic ceramics dispersing a Fe-Si compound in Si3N4 mother phase, capable of exhibiting magnetism and having high strength by forming an iron oxide and Si3N4 mixed powder in magnetic field and then, in the air under pressure and burning the resultant formed body in nitrogen atmosphere. CONSTITUTION:An iron oxide and Si3N4 mixed powder are formed in magnetic field under pressure and then formed in the air under pressure and the resultant formed body is burned in nitrogen atmosphere to provide the objective magnetic ceramics dispersing A Fe-Si compound in a mother phase consisting essentially of Si3N4. These magnetic ceramics contains the Fe-Si compound in an amount limited to 1-50wt.%, expressed in terms of FeO, Fe2O3 and Fe3O4 in order to secure strength sufficient as the magnetic material. Although a Fe-Si compound such as FeSi or FeSi2 exhibits magnetism, but becomes starting point of breakage, size thereof is limited to <=10mum. Forming under pressure in the magnetic field is carried out in >=10kOe and forming under pressure in the air is carried out by CIP.

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 mother phase and a method for producing the same.

[0002]

_2. Description of the Related Art Conventionally, FeO and Fe ₂ O have been used as sintering aids.
Silicon nitride Si with the addition of iron oxides such as ₃ , Fe ₃ O _4
3 N ₄ is, for example, JP-A-58-64268, JP-A-59-88374, and JP-A-61-72685.
Japanese Patent Publication No. 4332909 and the like.

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

Further, 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 is such that when an oxide-based superconducting wire powder or a melt is filled in a sheath material pipe, the filling is performed while adding electrolysis or magnetic flux or both to the filling material. It is something to do.

[0005]

By the way, it is desired that silicon nitride ceramics have magnetism. In general, when particles of silicon carbide, boron nitride or oxide are dispersed in Si ₃ N ₄ , the reactivity at the bonding interface is poor and the strength of the material itself is lowered. Further, in a material containing boron nitride, that portion may be oxidized at a high temperature to change the crystal structure and increase the friction coefficient. As disclosed in the above-mentioned publication, when a metal oxide such as Fe ₃ O ₄ is added as a sintering aid, the addition amount is too small to show magnetism or improve strength.

Further, iron oxides such as 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 strength, but FeSi is nitrided. It becomes an impurity with respect to silicon Si ₃ N ₄ and its strength deteriorates. FeO, Fe ₂ O ₃ , Fe _{3 with} respect to silicon nitride
When the amount of O ₄ iron oxide added is increased, the magnetic properties are improved, but the strength is decreased. Further, in engine parts and the like, a material capable of securing strength, for example, strength of 300 MPa or more is desired, and if a material of silicon nitride ceramics that secures such strength and improves magnetic characteristics can be manufactured, The field of application will be large and will be useful as a material.

Therefore, an object of the present invention is to solve the above-mentioned problems, and an Fe-Si compound is dispersed in a mother phase of Si ₃ N ₄ or SiC containing Si as a main component to obtain an engine. It is an object of the present invention to provide a magnetic ceramic and a method for manufacturing the same, which secures effective strength for parts and the like and has improved magnetic characteristics.

[0008]

In order to achieve the above object, the present invention is configured as follows. That is,
This invention uses silicon nitride as a mother phase, and F
The present invention relates to a magnetic ceramic in which an e-Si compound is dispersed.

In this magnetic ceramic, the size of the Fe-Si compound is 10 μm or less.

In this magnetic ceramic, the Fe--Si compound is FeO, Fe ₂ O ₃ , Fe ₃ O ₄
It is contained in an amount of 1 wt% or more and 50 wt% or less.

Alternatively, according to the present invention, a step of press-molding a mixed powder of iron oxide and silicon nitride in a magnetic field, a step of press-molding the powder in the atmosphere to form a molded body, and then the molding The present invention relates to a method for producing magnetic ceramics, which comprises a step of firing a body in a nitrogen atmosphere to produce a fired body.

Further, in this method for producing magnetic ceramics, the pressure molding in the magnetic field is performed at 10 kOe or more.

Further, in this method for producing magnetic ceramics, the pressure molding in the atmosphere is carried out by CIP.

[0014]

The magnetic ceramics and the method for producing the same according to the present invention are configured as described above and operate as follows. That is, this magnetic ceramic exhibits magnetism and high strength because the Fe-Si compound is dispersed in the mother phase with silicon nitride as the mother phase.
Further, as a magnetic material, in order to ensure sufficient strength, FeO said Fe-Si _{compound, Fe 2 O 3, Fe 3} O 4
It is limited to 1 wt% or more and 50 wt% or less. When the amount of the Fe-Si compound added to silicon nitride was limited to the above range, the conventional magnet had a maximum strength of about 300 MPa, but a strength of 300 MPa or more could be secured.

Further, Fe--S such as FeSi and FeSi ₂
The i compound exhibits magnetism, but the large size of the Fe—Si compound serves as the starting point of fracture, so a smaller size is more effective for increasing strength. According to the theory of graphics, it is desirable that 10 μm or less is desirable to prevent fracture, for example, the starting point of pores and cracks. Therefore, in order to secure the strength of silicon nitride, the size of the Fe—Si compound should be Is limited to 10 μm or less.

Further, in the method for producing magnetic ceramics, by performing pressure molding in a magnetic field, the spin directions in the molded body are aligned, which has an advantageous effect on the magnetic properties after firing,
The magnetic characteristics can be improved. Furthermore, by molding a mixture of iron oxide and silicon nitride by CIP, the density of the molded body can be improved and the strength of the fired body can be improved.

[0017]

Embodiments of the magnetic ceramics and the method for producing the same according to the present invention will be described below with reference to the drawings. This magnetic ceramic is characterized in that silicon nitride is used as a mother phase and an Fe-Si compound is dispersed in the mother phase. In this magnetic ceramic, Fe
The size of the Si compound is selected to be a small size of 10 μm or less in order to prevent the starting point of fracture such as cracks, cracks, and pores. Further, in the magnetic ceramic, in order to ensure sufficient strength of at least 300MPa as magnetic, 1 wt% in terms of the amount of Fe-Si compound to silicon nitride FeO, to _{Fe 2 O 3, Fe 3 O} 4 The above is selected and 50 wt% or less is selected.

The method for producing magnetic ceramics according to the present invention mainly comprises a step of press-molding a mixed powder of iron oxide and silicon nitride in a magnetic field, and press-molding it in the atmosphere to form a molded body. The method is characterized by including a step of producing and then firing the molded body in a nitrogen atmosphere to produce a fired body. In this method for producing magnetic ceramics, the pressure molding in the magnetic field is performed at 10 kOe or more, and the pressure molding in the atmosphere is C
It is performed by IP (cold isotropic working press).

An embodiment of the method for producing magnetic ceramics according to the present invention will be described as Embodiment 1. In this method for producing magnetic ceramics, Si ₃ N ₄ , Al ₂ O ₃
And Y ₂ O ₃ in the following proportions. Si ₃ N ₄ : Al
₂ O ₃ : Y ₂ O ₃ = 90: 5: 5. Three kinds of Fe oxides, namely FeO and F, based on this total weight
A predetermined amount of e ₂ O ₃ and Fe ₃ O ₄ was added and mixed with distilled water and a binder in a ball mill for about 24 hours to prepare a mixture, and then the mixture was granulated by a spray dryer to form granules. Had made.

Next, these granulated granules were used as a forming raw material in a magnetic field of 15 kOe and 1000 kgf.
After preforming by press pressure of / cm ^2, and pressed at a pressure of about 2,000 kgf / cm ² by CIP, to obtain a variety of molded bodies of a rectangular parallelepiped. After degreasing these shaped bodies, these degreased shaped bodies were heated and fired to a maximum temperature of 1850 ° C. in a N ₂ atmosphere of 9.3 MPa to obtain many dense sintered bodies. These sintered bodies were processed into 3 × 3 × 4 mm to prepare rectangular parallelepiped test pieces, and the magnetic characteristics of the residual magnetic flux density, coercive force, and initial permeability of these test pieces were measured.

In order to measure the magnetic characteristics corresponding to the change in the added amount of the iron oxide Fe _m O _n of FeO, Fe ₂ O ₃ and Fe ₃ O ₄ , the Si ₃ with various added amounts of the iron oxide was measured. N ₄
The results of the magnetic characteristics of the test piece of No. 1 are shown in FIGS. 1, 2 and 3. Figure 1 shows the addition amount of iron oxide Fe _m O _n (wt
%) Graph showing the residual magnetic flux density (Gauss G),
Figure 2 is a graph showing amount of iron oxide Fe _m O _n the coercivity for (wt%) (oersted Oe), and 3 initial permeability to the addition amount of iron oxide Fe _m O _n (wt%) It is a graph which shows. In each figure, the place where the amount of Fe _m O _n added is 0 is the silicon nitride itself, and shows a comparative example.

Further, 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 . 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 the Fe ₃
The coercive force for each added amount of O ₄ is shown.
Further, in FIG. 3, the initial magnetic permeability, F
The initial magnetic permeability with respect to the added amount of e ₂ O ₃ and the initial magnetic permeability with respect to the added amount of Fe ₃ O ₄ are shown. From the above chart, the addition of iron oxide Fe _m O _n in Si ₃ N _4, the Si ₃ N ₄ which did not have magnetism can impart soft, also increase the addition amount of Fe _m O _n It can be seen that the magnetic characteristics are improved as the temperature is increased.

Further, the structure of the sliding test piece in which the amount of Fe _m O _n added was 10 wt% was changed to SEM (Scanning Electron Micr
oscopy) showed that the addition amount of Fe _m O _n was 10
In the wt% sliding test piece, the iron-containing portion had a size of 10 μm or less, did not form a solid solution, and existed in a state in which iron was uniformly dispersed in the Si ₃ N ₄ grain boundaries. It could be confirmed. Further, the result of analysis using the X-ray microanalysis method for identifying this phase is shown in FIG. As can be seen from FIG. 5, the above phase was found to be a Fe—Si compound. By this Fe-Si compound is present in Si ₃ N _4, was assumed magnetic was granted.

A test piece for 4-point bending strength test of 3 × 4 × 40 mm was produced from the sintered body produced by this method for producing magnetic ceramics. The result is shown in FIG. FIG. 4 is a graph showing the 4-point bending average strength (MPa) with respect to the addition amount (wt%) of the iron oxide Fe _m O _n .
As can be seen from this graph, iron oxide F is added to Si ₃ N _4.
strength is lowered as will increase the amount of e _m O _n, the addition amount 10-20 wt% of the specimen of Fe _m O _n, addition of the comparative example (FIG. 4 without the addition Fe _m O _n It can be seen that the strength is equal to or higher than that of ordinary Si ₃ N ₄ when the amount is 0).

FIG. 4 shows the 4-point bending average strength with respect to the added amount of FeO, the 4-point bending average strength with respect to the added amount of Fe ₂ O ₃ , and the 4-point bending average strength with respect to the added amount of Fe ₃ O _4. There is. Moreover, when observed by SEM, almost no pores were observed in the structure of the magnetic ceramics containing 10 wt% of Fe _m O _n , and Si ₃ N ₄
It was found that the growth of crystal grains was suppressed by the presence of iron oxide, resulting in fine and uniform crystal grains. Such a structure is considered to be advantageous for strengthening, considering the Griffith's relational expression.

Further, the strength of the magnetic ceramics test pieces in which the amount of Fe _m O _n added was further increased, but the strength was decreased.
_m O _n aggregation of was observed, pores were present in the place where was the aggregation. That is, it is considered that the strength of the test piece is lowered because the pores become the starting points of the fracture as a result of the remaining pores in the test piece.

In the above-described method for producing magnetic ceramics, a magnetic ceramic was similarly produced by changing the magnetic force during processing and molding in a magnetic field with respect to a mixture obtained by adding 30 wt% of Fe ₃ O ₄ to Si ₃ N 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.
Oe had a residual magnetic flux density of 215 G, magnetic force of 15 kOe had a residual magnetic flux density of 223 G, magnetic force of 20 kOe had a residual magnetic flux density of 220 G, and magnetic force of 25 kOe had a residual magnetic flux density of 231 G. From the above results, it is understood that pressure molding in a magnetic field is preferably performed at 10 kOe or more. Then, the mixed powder of Si ₃ N ₄ and Fe _m O _n is pressure-molded in a magnetic field to obtain Fe _m O in the molded body.
The spin directions of _n are aligned, and the magnetic properties after firing become advantageous, and the magnetic properties can be improved.

[0028] In the manufacturing method of the magnetic ceramic, after preformed processed molded in a magnetic field with respect to mixtures of Fe ₃ O ₄ was added 10 wt% in Si ₃ N _4, CI
When a test piece that was fired without P was prepared and the 4-point bending strength was measured, it was 820 MPa. That is, CI
It was found that the strength of the magnetic ceramics not subjected to P was about 160 MPa lower than that of the magnetic ceramics subjected to CIP. It can be understood that this is because, when the CIP molding is performed after the pressure molding in the magnetic field, the density of the molded body is increased and the strength is improved.

Regarding the magnetic ceramics according to the present invention, the magnetic characteristics are improved as the amount of Fe _m O _n added is increased, but the strength is lowered.
To secure the strength of a or more, the addition amount of Fe _m O _n is 1
It is necessary to be in the range of ˜50 wt%. Also, by ensuring a strength of 300 MPa or more,
For example, it can be used as an engine component such as a permanent magnet of a turbocharger having a generator / motor. In addition, Fe _m O
_{Although n} also functions as a sintering aid for Si ₃ N ₄ and serves to improve strength, FeSi becomes an impurity and deteriorates in strength. Therefore, a magnetic ceramic in which an Fe-Si compound is dispersed in a matrix of silicon nitride is prepared by mixing a Fe _m O _n mixture with silicon nitride mixed powder.

[0030]

The magnetic ceramics and the method for producing the same according to the present invention are configured as described above and have the following effects. That is, in the magnetic ceramic according to the present invention, since the Fe-Si compound is dispersed in the mother phase of silicon nitride, it is possible to provide silicon nitride exhibiting magnetism and having high strength. Then, in order to secure a strength of 300 MPa or more, the size of the Fe—Si compound is controlled to be 10 μm or less, and the Fe—Si compound is converted into FeO, Fe ₂ O ₃ , and Fe ₃ O ₄ , 1 wt
% And 50 wt% or less.

Further, 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 magnetic properties, and to improve the strength of the fired body, CIP is carried out. It is preferable to improve the body density.

[Brief description of drawings]

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

FIG. 2 Iron oxide Fe of this magnetic ceramics
is a graph showing measurement results of coercive force relative to the addition amount of _m O _n.

FIG. 3 Iron oxide Fe of this magnetic ceramics
It is a graph showing the measurement results of the initial permeability to the addition amount of _m O _n.

FIG. 4 Iron oxide Fe for this magnetic ceramics
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 the results of analysis of this magnetic ceramics using an X-ray microanalysis method.

Claims (6)

[Claims] 1. A magnetic ceramic comprising silicon nitride as a mother phase and an Fe-Si compound dispersed in the mother phase. 2. The size of the Fe—Si compound is 10 μm.
The magnetic ceramics according to claim 1, which is less than or equal to m. 3. The Fe—Si compound is FeO, Fe ₂
Converted to O ₃ and Fe ₃ O ₄ , 1 wt% or more and 50
The magnetic ceramics according to claim 1, which is contained in an amount of not more than wt%. 4. A step of press-molding a mixed powder of iron oxide and silicon nitride in a magnetic field, a step of press-molding the mixed powder in the atmosphere to form a molded body, and then the molded body in a nitrogen atmosphere. A method for producing magnetic ceramics, comprising the step of firing in the inside to produce a fired body. 5. The method for producing magnetic ceramics according to claim 4, wherein the pressure molding in the magnetic field is performed at 10 kOe or more. 6. The method for producing magnetic ceramics according to claim 4, wherein the pressure molding in the atmosphere is performed by CIP.