JPH0217517B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention is a method for producing a ferrite single crystal, in which polycrystalline ferrite and single-crystal ferrite are contacted and heated, and single-crystal ferrite is grown in the direction of polycrystalline ferrite to grow single-crystal ferrite. More specifically, it relates to a method for producing a ferrite single crystal containing few pores in the single crystal. (Prior Art) Conventionally, as a method for producing single crystal ferrite, the Bridgeman method is known in which a single crystal is grown from a liquid phase obtained by melting raw materials at a high temperature equal to or higher than the melting point. However, the Bridgman method requires large-scale manufacturing equipment, is not suitable for mass production, and has the disadvantage that the resulting single-crystal ferrite products are expensive. In order to eliminate the above-mentioned drawbacks, the applicant disclosed in Japanese Patent Application Laid-Open No. 155100/1983 that polycrystalline ferrite and single-crystal ferrite are brought into contact with each other, and by heating the single-crystal ferrite is grown in the direction of the polycrystalline ferrite. When producing single crystal ferrite, especially iron oxide and/or iron oxide having a spinel structure are used as polycrystalline ferrite.
Or iron oxide with a history of spinel structure as Fe ₂ O ₃
Production of single-crystal ferrite using polycrystalline ferrite produced using iron oxide containing 60% by weight or more in terms of iron oxide, and further heating it to a temperature below the temperature at which discontinuous crystal grain growth of polycrystalline ferrite occurs. Discloses the law. (Problems to be solved by the invention) In the above-mentioned method for producing temperature ferrite,
Although it is true that single crystal products can be obtained cheaply and in large quantities,
Large pores of 5 to 10 μm may remain in single crystal ferrite, and the large pores are
The drawback was that it could not be used in VTR magnetic heads and the yield was extremely low. The purpose of the present invention is to eliminate the above-mentioned drawbacks, suppress the appearance of relatively large pores of 5 μm or more that occur in ferrite single crystals, improve product yield, and obtain ferrite single crystals at low cost. The aim is to provide a manufacturing method that can. (Means for Solving the Problems) The method for producing a ferrite single crystal of the present invention includes contact heating of polycrystalline ferrite and single crystal ferrite,
In the manufacturing method of single crystal ferrite, which grows single crystal ferrite by growing single crystal ferrite in the direction of polycrystalline ferrite, Fe ₂ O ₃ , MnO, ZnO
After calcining the polycrystalline ferrite-forming mixture consisting of the following, the sulfur content in the ferrite powder after calcining was adjusted to 40 ppm or less, and the average particle size of the polycrystalline ferrite powder was adjusted to 1.0 to 2.0 μm, and then molded. It is characterized by using polycrystalline ferrite obtained by firing. (Function) FIG. 1 is a flowchart for explaining the manufacturing method of the present invention. Fe ₂ O ₃ and MnO with an S content of 1.5% or less, which have a history of magnetite (Fe ₃ O ₄ ),
ZnO and the like are mixed in a predetermined ratio, and this mixture is calcined and wet-pulverized. The average particle diameter of the obtained finely ground ferrite is 1.0 to 2.0 μm, preferably 1.2 to 2.0 μm.
In addition to adjusting the diameter to 1.8 μm, S contained in Fe ₂ O ₃
Reduce the residual content to 1.5% or less by adjusting cleaning and firing conditions, etc., and reduce the residual sulfur content in the ferrite powder to 400ppm or less. The finely ground ferrite prepared as described above is molded and then fired to obtain a polycrystalline ferrite molded body. Next, after mirror-polishing the joint surfaces of the polycrystalline ferrite molded body and the seed single crystal ferrite prepared in advance, the joint surfaces are preferably joined with HNO ₃ interposed between them and heated. This heating is carried out below the temperature at which discontinuous grain growth of the polycrystalline ferrite occurs. As a result, the single crystal ferrite grows from the joint surface in the direction of the polycrystalline ferrite, converting the polycrystalline ferrite into a single crystal, thereby obtaining single crystal ferrite. The present invention shows that the cause of relatively large pores is closely related to the particle size of the ferrite powder, and that the S or S contained in the raw material ferrite powder is closely related to the particle size of the ferrite powder.
This was done after discovering that compounds are also related. In other words, as shown in Figure 2, which shows the relationship between the average particle diameter and S content in ferrite powder and the number of pores of 5 μm or more in a ferrite single crystal, the larger the average particle diameter becomes, the fewer the large pores of 5 μm or more decrease. However, it was found that the number of pores caused by poor filling during molding increases when the diameter is 1.8 μm or more, and that the amount of S in the ferrite powder and the number of large pores show a positive correlation. Considering the above-mentioned economic effects, the average particle diameter was limited to 1.0 to 2.0 μm, and the content of S or S compound in the ferrite powder was limited to 40 ppm or less as S. In addition, the content of S or S compounds in ferrite powder depends on the S compound contained as an impurity in the raw material, so it is used as a raw material within a range that can reduce the amount of S in ferrite powder to 40 ppm or less. do
Residual S content in Fe ₂ O ₃ . It was limited to 5% or less. In addition, outside the above-mentioned numerical limitation range, it was difficult to reduce the average value of large pores of 5 μm or more to one or less. (Example) Iron oxide (Fe ₂ O ₃ 98.5%) produced by a wet method and containing 0.9% sulfur as an impurity was washed with hot water,
Three types with different sulfur content (0.3%, 0.5%, 0.9
%) iron oxide, 99.9% pure manganese oxide, and 99.9% pure zinc oxide as raw materials.
A mixture of 52.5 mol % Fe ₂ O ₃ , 28 mol % MnO, and 19.5 mol % ZnO was calcined to obtain three types of calcined products with different sulfur contents. After coarsely crushing these three types of calcined products, each was further divided into three equal parts, and finely pulverized in a ball mill of 5 for 10H, 15H, and 20H to create a total of nine types of ferrite powders. After molding, equilibrium oxygen Nine types of mother polycrystalline ferrites were obtained by sintering at 1320°C for 4 hours under partial pressure. On the other hand, single-crystal ferrite produced by the high-pressure Bridgeman method and having almost the same composition as these three types of polycrystal ferrite was prepared. These mother polycrystalline ferrite and single crystalline ferrite are each 10×
Cut into blocks of 30 x 5 mm and 10 x 30 x 0.5 mm,
After mirror-polishing the joint surfaces with diamond abrasive grains, 6N HNO ₃ was applied, and the joints were bonded by adhesion and drying. The bonded mother polycrystalline ferrite and single-crystalline ferrite were heated at 1340° C. for 3 hours in a controlled atmosphere to cause crystal growth of the single-crystalline ferrite in the direction of the polycrystalline ferrite, thereby obtaining single-crystalline ferrite. In order to investigate the number of pores of 5 μm or more, which is the objective of the present invention, 5 × 10
A small piece of 5 mm in size was cut out, one side of the piece was mirror-polished with diamond abrasive grains, and then pores of 5 μm or more present within a 1 mm ² area were visually counted and observed using an optical microscope at 1000x magnification. The results are shown in Table 1. Note that the average particle diameter is the result of measurement by a known air permeation method.

[Table] (Effects of the invention) As is clear from the detailed explanation above, according to the method for producing a ferrite single crystal of the present invention, the average particle diameter of the finely ground ferrite is 1.0 to 1.
By finely pulverizing the ferrite to a size in the range of 2.0 μm and preferably adjusting the S content in the pulverized material to 40 ppm or less, high-quality single crystal ferrite with suppressed appearance of large pores of 5 μm or more can be produced in a high yield. Obtainable. Furthermore, since inspection of the number of pores, etc., which were conventionally necessary, can be omitted, the number of steps and process period can be reduced. According to the present invention, high quality Fe ₂ O ₃ -MnO-
Since ZnO-based single crystal ferrite can be obtained,
Since a single crystal ferrite which can be used in magnetic heads for VTRs and has low noise can be obtained, it can be effectively used in various magnetic heads.

[Brief explanation of drawings]

Figure 1 is a flowchart for explaining the manufacturing method of the present invention, and Figure 2 shows the average particle diameter and S content in ferrite powder and the ferrite single crystal.
It is a graph showing the relationship between the number of pores of 5 μm or more.

Claims (1)

[Scope of Claims] 1. A method for producing a ferrite single crystal in which polycrystalline ferrite and single-crystal ferrite are contacted and heated, and single-crystal ferrite is grown in the direction of polycrystalline ferrite to grow single-crystal ferrite, _comprising : _3. A polycrystalline ferrite-forming mixture consisting of MnO, ZnO, etc. was calcined, and the sulfur content in the ferrite powder after calcining was reduced to 40 ppm or less, and the average particle size was adjusted to 1.0 to 2.0 μm in the pulverization process. A method for producing a ferrite single crystal, characterized in that a polycrystalline ferrite obtained by molding and firing is used. 2. Production of a ferrite single crystal according to claim 1, characterized in that Fe ₂ O ₃ with a history of magnetite (Fe ₃ O ₄ ) and a residual sulfur content of 1.5% or less is used as a ferrite raw material. Law.