JP2833722B2 - Manufacturing method of soft ferrite - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a soft ferrite containing zinc as one main component, such as a Mn-Zn or Ni-Zn type, used as a high frequency soft magnetic material.

[0002]

2. Description of the Related Art In general, soft ferrites such as Mn-Zn and Ni-Zn are formed into a desired shape after mixing, calcining, pulverizing and granulating raw material oxides. It is manufactured by firing under appropriate temperature and atmospheric conditions. The firing is generally performed in a pusher-type continuous furnace or a roller hearth-type continuous furnace. In firing, the ferrite molded body is loaded on a ceramic plate having high strength at high temperature. At this time, alumina or mullite ceramics are used in most cases from the viewpoints of economy, service life, etc., and zirconia may be used in special cases.

[0003] Further, if necessary, Al ₂ O ₃ granules or ZrO ₂ granules may be sprayed between the ferrite molded body and the ceramic base plate and used as an underlay.

[0004]

However, in the case of using an alumina or mullite flooring, there is a problem that the portion in contact with the ferrite flooring changes during firing and the final magnetic properties are deteriorated. Incidentally, an experiment by the present inventor who clarified the degree of this deterioration will be introduced below.

The molar ratio of Fe ₂ O ₃ : MnO: ZnO is 53:35:12
And added as minor additives SiO ₂ , CaCO ₃ and Nb ₂ O ₅
After the material added with was mixed, calcined, pulverized, and granulated, it was processed into a toroidal shape (outer diameter: 36 mm) by press molding. These molded cores are stacked in two-tiered form on alumina and mullite flooring plates and placed in nitrogen with controlled oxygen partial pressure.
Fired at 1350 ° C, the obtained core is 100kHz, 200m
The iron loss value at T and 80 ° C. was measured. Table 1 shows the results.

[0006]

[Table 1]

In Table 1, the core loading position means the upper stage and the lower stage of the two-stage stacking. The bottom of the core of the lower stage is in direct contact with the bottom plate, whereas the core of the upper stage has the bottom. There is a difference that it is in contact with the lower core. As is clear from Table 1, it is clear that the core loss value of the core in contact with the sintering plate is deteriorated by about 70 to 100 mW / cm ^{3 as} compared with the upper core.

[0008] An attempt was also made to spray alumina granules between the molding core and the floor plate, but no improvement was found in the iron loss value of the lower core. By the way, one method for solving this problem has been proposed in Japanese Patent Application Laid-Open No. Sho 62-65970. This method is a method of using fired granules having the same composition as the Mn-Zn-based ferrite to be fired as an underlay of the ferrite molded body at the time of firing. The molded body is Al ₂ O ₃ granules,
Al, Zr, etc. penetrate into ferrite as impurities because they are arranged underneath ZrO ₂ granules, Al ₂ O ₃ plates, ZrO ₂ plates, etc.

[0009] However, this method involves firing Mn-Zn
Granules having the same composition as the base ferrite must be manufactured by firing in advance, which is troublesome, and there is a problem that they adhere to the bottom of the fired ferrite, and improvement in magnetic properties is also improved. It was small. In view of the above problems, the present inventor has already proposed a method for producing soft ferrite using a modified ceramic flooring plate in Japanese Patent Application No. 3-70783, but the present invention further relates to this method. In addition, the purpose of the present invention is to investigate the powder material sprayed between the molded body core and the ceramic base plate, solve the above-mentioned problems, and propose a method of manufacturing a soft ferrite having excellent magnetic properties. .

[0010]

SUMMARY OF THE INVENTION According to the present invention, when a soft ferrite molded article containing zinc as one of the constituent components is placed on a ceramic flooring plate and fired, zinc oxide is formed between the molded body and a floor plate surface in contact with the molded body. Is a method of producing soft ferrite characterized by spraying and using a powder containing zinc as a main component such as zinc carbonate or the like, and the ceramic base plate is made of Al ₂ O ₃ or Al ₂ O ₃ -SiO ₂ system. A bottom plate or a bottom plate in which zinc is contained in the surface of the bottom plate in contact with the molded product is advantageously used.

[0011]

[Work] The present inventors have conducted basic research on the above-described characteristic deterioration, clarified the cause thereof, and completed the present invention based on the knowledge. FIG. 1 shows the results of measuring the Zn concentration by EPMA in the direction from the bottom surface, which was in contact with the bottom plate of the lower core, fired on the alumina bottom plate shown in Table 1 to the inside of the core. As is clear from the figure, about 2
The Zn concentration is lower than the level inside the core over the depth range of 00 μm, and it is found that the Zn concentration at the bottom portion, which is the outermost layer, is significantly lower than the bulk composition by about 2% by weight. To be observed.

On the other hand, the Al concentration was not particularly increased at the bottom surface of the core. The lattice constant and residual stress of this bottom were further measured by X-ray diffraction. As a result, the lattice constant of the spinel phase shrunk by about 0.02 to 0.03% and the tensile residual of about 3 kg / mm ² compared to the inside of the core, which was not affected by the base plate. It was found that stress remained. On the other hand, the EPMA of the alumina sole plate that was in contact with the ferrite core during firing
From the measurement, a remarkable increase in Zn concentration was observed, contrary to ferrite. The same tendency was observed in the case of using a mullite floor plate.

After removing a layer of about 250 μm from the bottom surface of the sintered core by mechanical polishing and chemical polishing, the iron loss was measured to be 332 mW / cm ³ , which was improved to the same level as that of the upper stacked core. From the above results, the cause of the deterioration of the magnetic properties when the ferrite is fired on the alumina or mullite base plate depends on the penetration of Al into the ferrite as described in JP-A-62-65970. Instead, the Zn content in the ferrite surface layer moves into the alumina or mullite slab, causing the lattice constant of the spinel in the ferrite surface layer to shrink, which results in the generation of tensile residual stress in the core and the magnetic properties. It can be seen that this is caused by the deterioration of

On the basis of the above findings, the present inventor has proposed, as described above, an Al ₂ O ₃ or Al ₂ O ₃ —SiO ₂ ceramic or the like in which the zinc concentration of the base plate portion in contact with the ferrite molded body during firing is increased. A method using a slab is proposed. By this method,
Was it possible to use as compared to the ZrO ₂ decking such inexpensive as Al ₂ O ₃ and Al ₂ O ₃ -SiO ₂ -based decking without deteriorating the magnetic properties of the sintered core, prolonged use of decking In some cases, the magnetic properties of the fired core may change due to deterioration and the like. It has been found that a soft ferrite core having excellent magnetic properties can be stably produced even when a ceramic flooring is used for a long period of time by spraying and using powders such as zinc and zinc carbonate.

As described above, according to the present invention, it is possible to suppress the movement of zinc from the ferrite core to the floor plate during firing. In this case, the effect is further enhanced by using a flooring plate which has already been proposed by the present inventors and has a higher zinc concentration in a portion in contact with the ferrite molded body during firing. Further, as will be described in detail in Examples, a method for spraying ZrO ₂ powder or fired granules of the same quality as the fired core proposed in JP-A-62-65970 between an alumina or mullite base plate and a ferrite molded body. Attempts were made but the improvement in properties was not sufficient. In particular, when applying the latter method, fired granules of the same material must be prepared in advance for each ferrite material. In some cases, the result of removal was needed.

On the other hand, when zinc oxide or zinc carbonate powder was used, a phenomenon that a part of the powder migrated to the floor plate during firing was observed, but it was necessary to adhere to the core and grind and remove it in a later step. Was not seen at all. It should be noted that the sole plate with an increased zinc concentration that can be used in the present invention is a ZnO substrate for a long time at a high temperature.
It can be made by annealing a ceramic base plate of Al ₂ O ₃ or Al ₂ O ₃ -20% SiO ₂ or the like in powder, but the method of manufacturing the base plate is not limited to this method.

The ferrite to which the method of the present invention is applied includes all ferrites containing ZnO as one of the constituent components. As the powder containing zinc, zinc oxide or zinc carbonate which is easily converted to zinc oxide by heating is desirable.

[0018]

EXAMPLE An Al ₂ O ₃ plate having a thickness of 5 mm and a size of 100 mm × 100 mm and an Al ₂ O ₃ -22% SiO ₂ plate were embedded in ZnO powder and annealed in air at 1350 ° C. for 10 hours. After this treatment, X-ray diffraction measurements were performed on the surfaces of these flooring plates, and the surface layer was ZnA
l ₂ O ₄ had a single phase. After that, these treated soleplates are (A)
Al ₂ O ₃ plate, (B) Al ₂ O ₃ —SiO ₂ plate. Also especially ZnO
The untreated Al ₂ O ₃ plate not impregnated with is referred to as (C).

On the other hand, SiO ₂ , CaO, Nb ₂ O ₅ and TiO ₂ are added to raw materials having a basic composition of a final composition of 52.3 mol% of Fe ₂ O ₃ , 36.1 mol% of MnO, and 11.6 mol% of ZnO.
The material with the addition of
It was formed into a 36 mm toroidal core. These compacts were scattered with the zinc oxide powder on the above-mentioned base plates (A), (B) and (C), loaded and fired at 1320 ° C. for 3 hours.

Further, as comparative examples, (1) the molded body is directly mounted on (A), (B), (C) the base plate, and (2) ZrO ₂ or (3)
Baking was performed under the condition that sintered granules of the same material as the compact were sprayed. Table 2 shows the measurement results of the iron loss values of the obtained sintered core at 100 kHz, 200 mT, and 80 ° C.

[0021]

[Table 2]

From Table 2, the improvement of the magnetic properties by the method of the present invention is remarkable, especially when combined with an Al ₂ O ₃ or Al ₂ O ₃ —SiO ₂ base plate in which the zinc concentration in the portion in contact with the compact during firing is increased. It can be seen that excellent magnetic properties can be obtained by the above.

[0023]

According to the present invention, the characteristic degradation caused when using an alumina plate which is generally used as a floor plate during firing of a ferrite molded article is caused by the Zn component in the ferrite moving to the floor plate during firing. When firing a ferrite molded body based on the newly discovered finding that a powder containing zinc as a main component such as zinc oxide or zinc carbonate is sprayed between the molded body and the ceramic floorboard As a result, the dezincification reaction from the ferrite described above could be prevented, and as a result, the property deterioration of the fired ferrite core could be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in Zn concentration of a Mn-Zn ferrite core mounted on an alumina base plate and fired from a contact surface of the base plate to the inside.

Claims (3)

(57) [Claims] When a soft ferrite compact containing zinc as one of its constituents is placed on a ceramic soleplate and fired, a powder containing zinc as a main component is interposed between the compact and a soleplate surface in contact with the compact. A method for producing soft ferrite, which is used by spraying. 2. A method according to claim 1, wherein the ceramic base plate is an Al ₂ O ₃ or Al ₂ O ₃ —SiO ₂ based base plate, or a base plate containing zinc on the surface of the base plate in contact with the molded body. Item 4. A method for producing a soft ferrite according to Item 1. 3. A powder comprising zinc oxide or zinc carbonate as a powder containing zinc as a main component.
Or a method for producing a soft ferrite according to 2.