JPS6224379B2 - - Google Patents

Description

[Detailed description of the invention]

Field of Application This invention relates to a method for manufacturing high-density ferrite for magnetic heads. BACKGROUND ART If pores exist in ferrite, which is a material for a magnetic head, when a magnetic tape runs on the head surface,
These pores are undesirable because they cause damage to the head, deteriorate the characteristics of the magnetic head, and damage the magnetic tape. For this reason, ferrite for magnetic heads is required to have high density and few pores. Methods for obtaining such high-density ferrite include the vacuum sintering method (Japanese Patent Publication No. 15194-1971), the hot pressing method (Japanese Patent Publication No. 128296-1972), and the hot isostatic pressing method (Japanese Patent Publication No. 128296-1972). No.) etc. are known. Among these, the hot isostatic pressing method is superior to other methods in eliminating pores, and also has good productivity. This hot isostatic pressing method requires primary sintering as a preliminary step when a container is not used, and the resulting sintered body is treated in a high temperature, high pressure inert gas atmosphere. However, in order to prevent oxidation of the high-pressure container and the heating element, this method is treated in an inert gas such as nitrogen or argon, which creates a reducing atmosphere for Mn-Zn ferrite and Ni-Zn ferrite. The amount of oxygen deviates from the stoichiometric amount, and the magnetic properties deteriorate significantly. In order to deal with this, Japanese Patent Application Laid-Open No. 73299/1983 proposes that after primary sintering of a ferrite material for a magnetic head, this sintered material is added to a ferrite powder that has the same composition and the same treatment as the raw material for the sintered body. A technique has been proposed in which the body is implanted and hot isostatically pressed. However, even with this method, the sintered body undergoes partial reduction due to the atmosphere during hot isostatic pressing, causing variations in magnetic properties, making it difficult to stably mass-produce high-density ferrite with good quality. It was hot. OBJECTS OF THE INVENTION The object of the present invention is to provide a method for producing high-density ferrite that eliminates the above-mentioned problems and does not require annealing after hot isostatic pressing. Structure of the Invention That is, in this invention, after primary sintering of a ferrite molded body,
At least one powder selected from Al ₂ O ₃ powder, ZrO ₂ powder, and MgO powder is embedded in a container tightly packed, a ZnO plate is placed on top of the filled powder, and a lid is placed,
This is a method for producing high-density ferrite, the gist of which is hot isostatic pressing in an inert gas atmosphere at high temperature and high pressure. Preferred Embodiment of the Invention In the present invention, when a ferrite material press-molded into a predetermined shape is primarily sintered, a mixed gas of oxygen and an inert gas such as nitrogen is used.
For Zn-based ferrite molded bodies, oxygen 0.1 to 10
%, the balance being an inert gas.Also, for Ni-Zn ferrite molded bodies, magnetic permeability and porosity cannot be improved in an atmosphere containing an inert gas, and 100% It is most effective to use oxygen gas at 1 to 2 atmospheres. In addition, in the hot isostatic pressing of the present invention, the primary sintered body is formed into a single powder of Al ₂ O ₃ powder, ZrO ₂ powder, or MgO powder, or a mixed powder of two or more of them, which is densely packed in a container. The reason for embedding the powder in is reduced and generates oxygen gas, which has the effect of preventing reduction of the primary sintered body. The particle size of the above powder used is 50 μm to 3000 μm.
If it is less than 50 μm, the powder will easily scatter during handling, and it will be difficult to replace the atmospheric air with inert gas during the preparation stage for hot isostatic pressure treatment. If it exceeds 3000 μm, the container will not be packed tightly. However, since the porosity in the powder is large and reduction of the primary sintered body is likely to occur, a particle size of 50 μm to 3000 μm is preferable. In addition, in this invention, after embedding the primary sintered body in a single powder of Al ₂ O ₃ powder, ZrO ₂ powder, and MgO powder, or a mixed powder of two or more types, which is densely packed in a container, the powder is molded into a specified shape on top
The reason for placing the ZnO plate is that the ZnO on the plate is reduced by hot isostatic pressure treatment, but together with the powder, it reduces the O ₂ concentration in the processing atmosphere of the primary sintered body of ferrite in the container. This is because the concentration can be maintained at equilibrium. Furthermore, the ZnO plate can prevent reduction during hot isostatic pressure treatment of ferrite even after repeated use several times, and mass-produces high-density ferrite with excellent magnetic properties at low cost and with high quality. There are advantages to being able to do so. It is preferable that the gap between the ZnO plate and the container be as small as possible to allow the inert gas of the pressure medium to pass through.
The thickness of the plate is preferably as thick as possible, and may be appropriately selected in consideration of the production volume such as the size and number of primary ferrite sintered bodies. Examples Example 1 Iron oxide 52.0 mol%, manganese carbonate 26.8 mol%,
21.2 mol% of zinc oxide was stirred and mixed in a ball mill using water as a dispersion medium, dried, and then calcined in air. This was wet-milled again in a ball mill for 20 hours to obtain a powder with a particle size of approximately 1 μm. Next, this raw material powder is 36mmφ×24mmφ×6
It was press-molded to a size of 1.5 mm, and primary sintered at 1200° C. for 3 hours in N ₂ gas containing 0.1 to 21.0% oxygen.
Cooling was done in pure _N2 gas. This primary sintered body was embedded in a container filled with -28 mesh ZrO ₂ powder, and the top was 75 mmφ x 5 mm thick.
After placing a ZnO disk of mm in size, the lid was placed and heated to 1100℃.
Hot isostatic pressure treatment was carried out under the conditions of argon gas at a pressure of 1000 Kg/cm ² for 1 hour. For comparison, the same primary sintered body was embedded in a container filled with -14 mesh ferrite powder of the same composition and same treatment as the sintered body, and hot isostatically treated under the same conditions as above. . Table 1 shows the results of measuring the magnetic permeability and porosity of each sample obtained. Note that sample 7 of the comparative example in Table 1 shows the results when hot isostatic pressure treatment was performed in a state filled with ZrO ₂ powder without placing a ZnO disk. Example 2 Iron oxide 49.5 mol%, nickel oxide 13.5 mol%,
32.0 mol% of zinc oxide and water as a dispersion medium were stirred and mixed in a ball mill, dried, and then calcined in air. After calcining, the powder was wet-pulverized for 20 hours in a ball mill to obtain a powder with a particle size of approximately 1 μm. Next, this raw material powder is 36mmφ×24mmφ×6mm
Press molded into
Primary sintering was performed at 1200°C for 3 hours. Cooling was done in air. This primary sintered body was embedded in a container filled with -28 mesh ZrO ₂ powder, and the top was 75 mmφ x 5 mm thick.
After placing a ZnO disk of mm in size, place the lid on and heat at 1200℃.
Hot isostatic pressure treatment was carried out under the conditions of argon gas at a pressure of 1000 Kg/cm ² for 1 hour. For comparison, the same primary sintered body was embedded in a container filled with -14 mesh ferrite powder of the same composition and same treatment as the sintered body, and hot isostatically treated under the same conditions as above. . Table 2 shows the results of measuring the magnetic permeability and porosity of each sample obtained. In addition, Sample 5 of the comparative example in Table 2 shows the results when hot isostatic pressure treatment was performed in a state filled with ZrO ₂ powder without placing a ZnO disk.

【table】

[Table] Effect of the invention As is clear from the results in Tables 1 and 2,
According to the method of this invention, better magnetic properties were obtained than the conventional method of embedding in ferrite powder and the case of not placing a ZnO disk, and the sample was reduced during hot isostatic pressure treatment. less often,
In particular, the oxygen concentration of Example 1 (Table 1) is 2 to 10%,
The density of the primary sintering in a gas with a balance of N ₂ and the primary sintering of Example 2 (Table 2) at 100% oxygen concentration and 1 atm is approximately 100% of the theoretical density. It can be seen that the magnetic properties significantly improve as the temperature increases. In addition, since ZrO ₂ powder is used, there is no seizure of the sintered body during hot isostatic pressure treatment, and the ZrO ₂ powder after use is stable at temperatures above 1000℃.
It can be used repeatedly by heat treatment in the atmosphere for 3 to 3 hours, making it highly suitable for mass production. Furthermore, annealing after hot isostatic pressure treatment is no longer necessary, significantly improving mass productivity.

Claims (1)

[Claims] 1 After primary sintering of the ferrite molded body,
At least one powder selected from Al ₂ O ₃ powder, ZrO ₂ powder, and MgO powder is embedded in a container tightly packed, a ZnO plate is placed on top of the filled powder, and a lid is placed,
A method for producing high-density ferrite, which is characterized by hot isostatic pressing in an inert gas atmosphere at high temperature and high pressure.