JPH03180434A - Manufacture of cermet type ferrite - Google Patents

Abstract

PURPOSE:To manufacture a composite body having good magnetic characteristics by mixing ferrite powder with magnetic powder, filling the mixture into a die and simultaneously executing compacting and electric discharge- conduction bonding by voltage impression. CONSTITUTION:Ferrite powder having an almost single phase and metallic (alloy) magnetic powder are mixed, and the mixture is filled into a die. The die is a combination of a cell 10 and an electrode 12 serving also as a pressure punch, and its internal space is filled with sample powder 14. Desired pressurizing force is applied to the electrode 12 by a pressurizing mechanism 16, and a power source 18 for heating supplies an electric current of which DC is overlapped with AC. They are controlled by a control device 20. By voltage impression, compacting and electric discharge-conduction bonding are almost simultaneously executed while intergranular electric discharge is generated, by which a cermet type composite body in which grains are directly bonded each other can be formed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method of discharging and discharging ferrite powder and metallic magnetic powder.
The present invention relates to a method for manufacturing a composite (cermet-type ferrite) in which particles are directly bonded to each other by electrically bonding.

[Prior Art] Cermet, which is a composite material of metal and oxide, has been widely put into practical use as a structural material. However, there are few research reports on composite materials of magnetic materials such as metals or alloys and ferrite, which is a ferromagnetic oxide (this is called "cermet-type ferrite"). As described above, there is a method in which boric anhydride (B*Os) is added in an amount of 1 to 10% by weight to a mixture of ferrite vJl powder and magnetic metal powder or magnetic alloy powder, and the mixture is fired at a temperature of 600 to 800°C.

[Problems to be Solved by the Invention] The reason why there are few examples of cermet-type ferrite being put into practical use is that the difference between the high vacuum atmosphere that creates magnetic materials such as metals and alloys and the oxidizing atmosphere that creates ferrite is extremely large.
This is because it is difficult to combine them. When mixing ferrite powder with magnetic powder of metal or alloy and firing it,
Sufficient sintering cannot be achieved unless the temperature is heated to at least 900°C. However, when sintered under such conditions, oxidation of the metal layer and significant reaction with the ferrite phase occur, resulting in a ferrite phase that is close to a single phase. This results in inferior characteristics.

On the other hand, if the treatment is performed at low temperatures to prevent metal oxidation, the reaction of the ferrite phase will be insufficient, resulting in properties close to, but inferior to, metallic single-phase. For these reasons, even if materials are composited, conventional sintering methods will not produce positive effects.

Therefore, in the prior art, a method was adopted in which a low melting point oxide called BzOi was mixed and bonded at a low temperature. In other words, B2
O3 entered between the magnetic powder of metal or alloy and the ferrite powder, indirectly bonding the particles to each other and creating a composite. In other words, in the prior art, the presence of a non-magnetic binder (B, Off) was essential for effective compositing. Therefore, it was inevitable that the mechanical properties and mechanical strength would deteriorate.

An object of the present invention is to provide a method for manufacturing a composite magnetic material having good magnetic properties that combines the advantages of both materials by directly bonding ferrite powder and metallic magnetic powder without using a binder. There is a particular thing.

[Means for Solving the Problems] The present invention can solve the above technical problems. Ferrite powder exhibiting almost a single phase and metallic (metal or alloy) Mi magnetic powder are mixed and filled into a mold for forming and joining,
This is a method for producing a composite (cermet-type ferrite) in which particles are directly bonded to each other by performing pressure molding and discharge/current bonding almost simultaneously while causing interparticle discharge by applying a voltage.

Here, "exhibiting a single phase" refers to a material that is a single phase to the extent that no different phases are detected by powder X-ray diffraction. In order to produce such a ferrite powder exhibiting an almost single phase, there are methods using a solid phase reaction (dry method), a method using a reaction in a solution (e.g. coprecipitation method), and a method using a gas phase reaction (e.g. spray heat method). Any method such as the decomposition method may be used.In the case of a dry method, it is produced through the steps of mixing, drying, calcination, and pulverization of solid powder raw materials.

Ferrites other than Mn-Zn-based ferrites basically become a single phase when subjected to a certain firing temperature (approximately 800°C or higher, depending on the relationship with time).

In the case of Mn-Zn ferrite, methods include calcination under reduced pressure or vacuum, methods to forcibly remove oxygen using a reducing agent such as hydrogen or water vapor, and methods to determine the stoichiometric composition in a nitrogen atmosphere. There is also a method of firing, adding Fe and 04, and pulverizing the mixture.

In the coprecipitation method, a strong alkali is added to the raw material 14, and the raw material 14 is produced through the steps of dissolution, precipitation, air oxidation, filtration, and drying. In the case of the spray pyrolysis method, it is produced through the steps of dissolving raw materials, spray pyrolysis, and crushing.

For discharge/current bonding, a device at the bottom of the tank as shown in Fig. 1 is used. The mold for molded joining is made of carbon, tungsten carbide,
It is a combination of a cell 10 made of silicon carbide, metal, etc., and an electrode 12 made of carbon, etc., which also serves as a pressurizing punch. Fill. The electrode 12 is
The desired pressing force can be applied by the E machine side 16, and it can also be used for heating. ii source 18. The heating power source 18 is capable of supplying a current in which alternating current is superimposed on direct current, and these are controlled by a control device 20 . others,
Although not shown, the temperature inside the cell and the amount of deformation under pressure can be monitored.

The ferrite powder used in the present invention has an average particle size of 0.0
A thickness of about 5 to 3 μm is desirable.

Further, it is desirable to use metal-based magnetic powder with a diameter of 10 μm or less. The reason for this is that if the average particle diameter is too coarse, banking between particles will be difficult to achieve even if pressure is applied during discharge/current bonding. On the other hand, even if the average particle size is small, it becomes difficult to pack properly due to cross-linking, and the reaction rate becomes too high, making it difficult to control the microstructure, and contamination is more likely to occur. Moisture and impurities adhere to it, making it difficult to handle.
This is because reactions with cells are likely to occur.

As the ferrite powder, Mn-Zn type, Mg-
The metal-based magnetic powder may be of any type such as Zn-based, Ni-7, n-based, etc. In addition to metal magnetic powder, alloy magnetic powder may also be used; for example, carbonyl iron powder, sendust powder, etc. may be used. can. The mixing ratio of ferrite powder and metallic magnetic powder can be varied over a wide range depending on the magnetic properties of the final composite.

The actual bonding process is performed in an inert atmosphere such as a nitrogen or argon atmosphere, or in a vacuum or reduced pressure to prevent oxidation of the metal magnetic powder.

[Operation 1] Cermet-type ferrite, which is a composite of ferrite and metallic magnetic material, can be produced in a short time by the method of the present invention. When a high voltage is applied to the ferrite powder and metallic magnetic powder filled in the mold, the powder causes dielectric breakdown and discharges.

This discharge energy activates the particle surface, removes dirt, etc., and cleans it. When pressurizing force is applied in this state, the powders come into close contact with each other, and electricity is generated directly in the powder network around the contact points, generating Joule heat. At the same time, discharge energy due to plasma impact pressure is added, and if the cell is electrically conductive, indirect current heating is also added. Pressurized and heated by these.

In the method of the present invention, the reaction time is very short, on the order of minutes, so that the reaction occurs only near the interface between the powders, resulting in bonding. An ion diffusion reaction that reaches the inside of the powder between the ferrite and the metallic magnetic material does not occur. The cermet type ferrite obtained by the present invention is schematically shown in FIGS. 2A and 2B. The composition of the matrix 7 when finally composited varies depending on the mixing ratio of ferrite and metallic magnetic material, particle size, etc. In the same figure, A shows a case where there is little ferrite, and B shows a case where there is a lot of ferrite. In the present invention, the particles are only directly bonded to each other on the surface, so the properties of ferrite and metallic magnetic materials are not lost.
Therefore, it is possible to obtain a high-frequency high-magnetic-flux-density material that has both the characteristics of high resistivity (ferrite) and high magnetic flux density (metallic magnetic material $4), which have not been previously available.

The material obtained by the present invention is suitable for use in magnetic helmets, high-frequency power sources, flybank transformers, chishniks, and the like.

[Example 1] Mn-Zn ferrite with an average particle diameter of 0.1 cm was used as ferrite powder, which was produced by a coprecipitation method.

Its composition is 52.5 mol% of Fe-Ol, 31.5 mol% of MnO, and 16.0 mol% of ZnO. This ferrite powder has a single phase in terms of X41 diffraction. As the metallic magnetic powder, spherical carbonyl iron powder with an average particle diameter of 1 μm was used.

The above M n -Z n ferrite and carbonyl iron powder were mixed at a weight ratio of 1:1 using a crusher for 30 minutes. Then, using a device with a configuration not shown in Fig. 1, the outer diameter is 25--φ and the inner diameter is 1.
A toroidal sample measuring 5 m+mφ and 5 cm in height was prepared. The processing conditions are as follows.

・Maximum pressurizing force...500 kg/cm"・Pressing speed・
...250 kg/cm" ・Minutes ・Atmosphere: In nitrogen gas ・Temperature rising time: 2 minutes ・Bonding processing time: 1 minute Bonding processing temperature (top temperature in heat treatment): 300-9
Table 1 shows the properties of the samples obtained by varying the temperature in the range of 00°C.The temperature was measured by forming a through hole in the cell from the side and inserting a thermocouple in contact with the sample.

Table 1 As can be seen from Table 1, even when the bonding temperature is as low as 500° C., the density can be considerably increased, and at a bonding temperature higher than that, a composite with a high density, that is, a high magnetic flux density can be obtained. If the treatment is performed at a temperature of 800° C. or higher, an oxidation-reduction reaction occurs between the ferrite and the metal, resulting in deterioration of the magnetic properties. For these reasons, the optimum range is 500 to 800°C under the conditions of this example. However, this varies depending on the materials used, mixing ratio, particle size, etc. This example proves that the present invention can complete bonding at low temperatures and in a short time and yield a good composite.

[Example 2] 1n-phase Mg-Zn-based ferrite produced by a normal dry method was used as ferrite powder.

Its average particle diameter is 0.5 μm. The composition is FezO,
is 46 mol%, MgO is 30 mol%, MnO is 3 mol%,
CuO is 1 mol% and ZnO is 20 mol%. As the metallic magnetic powder, spherical carbonyl iron powder with an average particle diameter of 3 μm was used.

The above ferrite powder and spherical carbonyl iron powder were mixed at different blending ratios and processed at a bonding temperature of 600°C.

Other processing conditions are the same as in Example 1. The experimental results are shown in Table 2.

Table 2 It can be seen from Table 2 that a material with high resistivity and high magnetic flux density, which cannot be obtained with ferrite or metallic magnetic materials alone, can be obtained. The saturation magnetic flux density increases monotonically as the weight ratio of carbonyl iron powder increases, but in the case of this example, in order to maintain high resistivity, the carbonyl iron powder is preferably 50% by weight or less. In this way, it has been demonstrated that a material with high resistivity and high magnetic flux density can be obtained by bonding a mixture of MgZn-based ferrite, which has the highest resistivity among ferrite materials, and carbonyl iron powder.

[Example 31 Mn-Zn ferrite powder of Example 1 and average particle size of 2μ
m Sendust powder was mixed at a weight ratio of 6:4, and a bonding process was performed at 600°C. The processing conditions were basically the same as in Example 1, but the temperature increase time was 1 minute and the bonding time was varied. The experimental results are shown in Table 3.

Table 3 Table 3 shows that it is possible to use a material f4 other than carbonyl iron powder as the metallic magnetic powder, and that it is possible to bond within extremely short distances y and ¥. Since the characteristics hardly change with respect to the bonding time, it can be seen that the bonding is almost completed during the temperature rise.

[Effects of the Invention] As described above, the present invention mixes ferrite powder exhibiting a substantially single phase and metallic magnetic powder, and performs pressure molding and discharge/current bonding almost simultaneously while causing electric discharge between the powders. Since the process of the present invention is short, the reaction occurs only near the interface between the ferrite and the metal, resulting in a bonding process. However, almost no ion diffusion reaction that reaches the interior occurs between the ferrite powder and the metal-based magnetic powder, and therefore conventional materials that have both the characteristics of high resistivity (ferrite) and high magnetic flux density (metallic magnetic materials) A high magnetic flux density material for high frequencies, which cannot be obtained by other technologies, can be obtained.

Furthermore, since the present invention does not use any binding materials, problems such as reduction in magnetic properties and mwt strength due to such materials do not occur.

In addition, in the present invention, since molding and bonding are performed simultaneously, a near net shape (near net 5 shape) can be obtained.
Processing costs can be reduced because there is less machining allowance, and the processing time is very short, on the order of minutes, improving manufacturing efficiency and reducing manufacturing costs.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of a molding and joining device used in the present invention, and FIGS. 2A and 2B are explanatory diagrams of a composite obtained by the present invention. DESCRIPTION OF SYMBOLS 10... Cell, 12... Electrode, 14... Sample powder, 16... Pressure mechanism, 18... Heating power supply, 20...
...control device, 22...ferrite, 24...metallic magnetic material.

Claims (1)

[Claims] 1. A ferrite powder exhibiting a nearly single phase and a metallic magnetic powder are mixed and filled into a mold for forming and bonding, and pressure forming and discharge/current bonding are performed almost simultaneously while applying a voltage to cause interparticle discharge. A method for producing cermet-type ferrite, characterized by obtaining a composite in which particles are directly bonded to each other.