JP2862692B2 - Manufacturing method of single crystal 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 single crystal ferrite for growing a single crystal ferrite by hot isostatic pressure treatment utilizing a solid phase reaction.

[0002]

2. Description of the Related Art Conventionally, there have been various methods for producing a single crystal ferrite in which a polycrystal ferrite and a seed single crystal ferrite are brought into contact with each other and heated to grow the single crystal ferrite into the polycrystal ferrite by a solid phase reaction. Things are known.

[0003] Among them, in Japanese Patent Publication No. Sho 62-15518, single crystal ferrite is grown from seed single crystal ferrite in hot pressing and / or hot isostatic pressing (hereinafter also referred to as HIP). A technique for performing this is disclosed. Further, in JP 64 over 4003 JP, temperatures T ₁ a primary firing: 1100 <T ₁ <conducted at 1350 ° C., secondary firing temperature T _2: T ₁ over 100 ℃ <T ₂ <T inhibit densification and grain growth is performed in a HIP in ₁ over 50 ° C., a temperature T ₃ of the third primary firing: T ₂
A method is disclosed for producing polycrystalline ferrite that grows in HIP at higher temperatures by grain growth. Furthermore, Japanese Patent Application Laid-Open No. 55-43833 discloses a technique of growing a polycrystal by annealing after HIP treatment.

[0004]

However, of the above-mentioned technologies, Japanese Patent Publication No. Sho 62-15518 discloses that the pressure bonding is required or the holding force H of the obtained single crystal ferrite is high.
There was a problem that c was as large as 0.05 Oe and affected by magnetizing noise. In addition, there was a problem that the single crystal growing distance was as short as about 12 mm and was not suitable for mass production. Furthermore, Japanese Patent Application Laid-Open Nos. 64-4003 and 55-43833 disclose that strain is released by grain growth using HIP, but the target is limited to polycrystalline ferrite. there were.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a method for producing a single crystal ferrite which can lengthen a single crystal growing distance by using IP processing and is suitable for mass production.

[0006]

According to the method for producing single crystal ferrite of the present invention, a compact is produced from a ferrite raw material mainly using iron oxide having a spinel structure or having a history as iron oxide. For molded objects
After firing under reduced pressure in a temperature range of 1100 ° C to 1280 ° C, firing in a helium atmosphere containing 0.1 to 3% oxygen,
By performing primary baking further cooling in nitrogen,
A sintered polycrystalline ferrite having an average particle diameter of 10 μm or less is produced, and the sintered polycrystalline ferrite is temporarily bonded to a seed single crystal ferrite, and the temporary bonded body is heated to a temperature of 1300 ° C. or more and less than 1560 ° C. under hot isostatic pressure. The treatment is carried out at the following temperature.

[0007]

In the above-described structure, the primary sintering of the ferrite molded body is performed in a predetermined low temperature and low oxygen atmosphere to increase the amount of oxygen vacancies to produce a polycrystal, and the seed single crystal ferrite is formed. The contact temperature is increased by increasing the processing temperature from the first baking under the condition using a predetermined HIP treatment. Further, by performing single crystallization by a solid phase reaction, a single crystal having a small number of pores and a long crystal growth distance can be obtained.

In the present invention, since the single crystal is produced in the HIP, the pores remaining in the first firing are compressed with respect to the external pressure, so that the magnetic properties may be degraded. However, in the first half of the HIP treatment of the polycrystalline ferrite, the HIP is baked at a temperature equal to or higher than the primary calcination temperature. By increasing the amount of oxygen vacancies and selecting a low oxygen concentration, the pores are partially diffused into the bulk and eliminated outside the sample, so that there is no deterioration in magnetic properties and there is almost no pores. Crystal ferrite has been obtained.

The reason why the oxygen concentration is specified in the present invention is that if the oxygen concentration is less than 0.1% in a He atmosphere, the workability deteriorates. On the other hand, if the oxygen concentration exceeds 3% in a He atmosphere, vacancies generated by firing under reduced pressure are coordinated by oxygen, and the pore diffusion effect decreases and single crystallization deteriorates.

[0010] That is, the spinel lattice has an unstable state due to the presence of a vacancy, and the subsequent heating facilitates the movement of the interface, whereby a single crystal can be easily formed.
Further, when the pore diffusion effect is reduced as described above, compressive stress due to the HIP process is applied to a small number of pores present in the sample, and not only does the residual strain remain and good magnetic properties cannot be obtained. The single crystal growing distance is also reduced.

[0011] Further, the reason why the temperature and the pressure are defined as the conditions of the HIP treatment is that this range is a temperature at which grain growth can substantially occur and a pressure at which pores can be reduced by the HIP treatment. It is. Even when the pressure was increased to 2000 kg / cm ² within the temperature range of the present invention, there was no generation of FeO 2 as a liquid phase substance that would hinder single crystallization. In addition, as an iron oxide raw material used for producing a ferrite molded body, as is conventionally known, it is essential to have a spinel structure or to have a history of the spinel structure to produce a single crystal ferrite. But it specifies the raw materials.

[0012]

An actual example will be described below. Roasting the magnetite synthesized by wet process as iron oxide raw material,
MnO 31.0mol%, after ZnO 16.4mol%, formulated into Fe ₂ O ₃ 52.6mol% of the composition, mixing, via the calcined, pulverized at 1050 ° C., 3500
Molded at 0 psi.

The obtained molded body is heated to 800 ° C. at a rate of 150 ° C./h using a rotary pump, and then heated to 40 ° C./h
And the temperature was raised to 1000 ° C. After maintaining at this temperature for 8 hours, the temperature was raised to 1100 ° C. at a rate of 10 ° C./h, and maintained at this temperature for 8 hours. Further, it was fired at a heating rate of 10 ° C./h to a primary firing temperature within and outside the range of the present invention shown in Table 1 below, and kept at this temperature in a vacuum atmosphere for 8 hours. Thereafter, as shown in Table 1, the sample was kept in a He atmosphere or a He atmosphere containing low-concentration oxygen for 4 hours, and then switched to a nitrogen atmosphere and cooled. One example of the obtained polycrystal had a porosity of 0.5% and a crystal particle diameter of 6.7 μm.

The obtained polycrystalline ferrite was cut and polished under the conventional ferrite processing conditions by 20 × 8 × 20 m.
polycrystalline ferrite m shape and a seed single crystal ferrite 20x8x1mm shape, temporarily bonded with nitric acid, placed inside an alumina sagger was covered with ferrite was used N ₂ gas Gr-H
The temperature was raised at a heating rate of 300 ° C./h by IP, a single crystal ferrite was grown at a temperature and pressure within and outside the range of the present invention shown in Table 1, and then cooled in the same atmosphere.

As an example of the obtained single-crystal ferrite, there was a single-crystal ferrite having a single crystallization of 20 mm, in which no sub-grains and pores of 1 μm or more were found. Also, the presence of FeO due to the reduction was not observed. At a temperature lower than 1300 ° C. in HIP, single crystallization did not occur.
Table 1 shows the results. In Table 1, the single crystal growth distance was determined as the distance at which the single crystal ferrite was grown from the joint interface between the seed single crystal ferrite and the polycrystalline ferrite. Also,
The number of pores was determined by visually observing pores of 1 μm or more in a 1000-fold scale visual field on a surface finished with a high-speed lapping machine using an optical microscope. Observed subgrain size is 10 ~
It was 20 μm.

[0016]

[Table 1]

From the results in Table 1, the primary firing conditions and HIP
Test Nos. 1 to 15 within the scope of the present invention that satisfy both of the processing conditions
Is a comparative example test No. 16 which does not satisfy the present invention in any point
It can be seen that the single crystal growth distance is longer and the number of pores and the number of sub-grains in the single crystal are smaller than those of Nos. To 23. In the case of not firing under reduced pressure before the primary firing, the single crystal growth distance was short and the number of pores was large. Furthermore, when there was no oxygen as a condition for the primary firing, cracks occurred in the sample during the cutting process, which was not practical.

Incidentally, for example, the AC characteristics of the obtained single-crystal ferrite of Test No. 2 of the present invention were 5 φ × 3 φ × 1.5 tmm
0.1 μm = 4800, 1 MHz = 1100 in μ of the shape, and 0.1 MHz = 1800, 1 MHz = 1100 in Comparative Example Test No. 17, which shows that the magnetic properties of the present invention example are significantly improved as compared with the comparative example. Recognize. In addition, as a DC characteristic, within the scope of the present invention
5 φx3 φx1.5tmm H _c1 shape was 0.01 to 0.02 Oe.

[0019]

As is apparent from the above description, according to the method for producing single crystal ferrite of the present invention, the first firing at a predetermined temperature and atmosphere is performed for a predetermined ferrite molded body.
By performing the heat treatment for the solid phase reaction by the HIP treatment at a predetermined temperature and pressure after the subsequent bonding of the seed single crystal and the polycrystal, the number of pores in the grown single crystal can be reduced and the single crystal can be grown. Since the distance can be increased, single crystal ferrite having good magnetic characteristics can be mass-produced.

Further, the single crystal ferrite obtained by the present invention does not require embedded powder for its production, and there is no problem that the mechanical strength is reduced by reduction. In addition, some sub-grains have disappeared during production. Further, there is no need to perform annealing after the HIP treatment, and H _c1 that contributes to the magnetizing noise is less than 0.05 Oe, which is the upper limit.
It was 0.01 to 0.02 Oe. When iron oxide other than the spinel structure is used as the iron oxide raw material, the crystal particle diameter is
It grew to more than μm, the single crystal growth distance was as small as 1 mm, and there were many pores in the single crystal.

As described above, the obtained single-crystal ferrite has much less pores than the single-crystal ferrite obtained by the conventional solid-phase reaction, so that it can be used as an RDD substrate or a VTR substrate having strict dimensional specifications. Suitable for use.

Continuation of the front page (56) References JP-A-55-43833 (JP, A) JP-A-64-4003 (JP, A) JP-B-61-3313 (JP, B2) JP-B-61-10438 (JP) , B2) JP-B 62-15518 (JP, B2) JP-B 62-49647 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) C30B 28/00-35/00 H01F 1/34

Claims (3)

(57) [Claims] Claims: 1. An iron oxide having a spinel structure,
Alternatively, a molded body is manufactured from a ferrite raw material mainly using iron oxide having its history, and 1100
After firing under reduced pressure in the temperature range from ℃ to 1280 ℃,
Firing in a helium atmosphere containing 0.1 to 3% oxygen, and further performing primary firing by cooling in nitrogen, thereby producing a polycrystalline ferrite sintered body having an average particle diameter of 10 μm or less,
This polycrystalline ferrite sintered body is temporarily joined to a seed single crystal ferrite, and this temporarily joined body is heated to a temperature of 1300 ° C. or more under hot isostatic pressure.
A method for producing a single crystal ferrite, wherein the method is performed at a temperature of less than 60 ° C. 2. The method for producing single crystal ferrite according to claim 1, wherein the temperature of the hot isostatic pressure treatment is 1450 ° C. or higher. 3. The single crystal ferrite according to claim 1, wherein the temperature of the hot isostatic pressure treatment is equal to or higher than the temperature of the first firing, and the pressure of the hot isostatic pressure treatment is equal to or greater than 60 kg / cm ² . Production method.