JPH0122228B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing high-density Mn--Zn ferrite. High-density magnetic recording head materials for computers, VTRs, etc. not only have excellent electromagnetic properties, but also have the ability to withstand precision machining and have low wear due to contact with magnetic disks, magnetic tapes, etc. required. Single-crystal ferrite is excellent in terms of precision machinability and wear resistance and is used for heads and the like, but it has drawbacks such as large variations in magnetic properties, large sliding noise, and high cost. On the other hand, although sintered ferrite has advantages such as low variation in properties, low sliding noise, and low cost, it has problems with precision machinability, wear resistance, etc. due to the presence of pores. However, if hot pressing or static isostatic pressing is used, the porosity can be reduced to around 0.2%, creating a high-density ferrite that has precision workability comparable to single crystal, wear resistance, and the advantages of polycrystal. Obtainable. Among these, methods using hot isostatic pressing can apply pressure up to several thousand atmospheres, making it easier to obtain high-density sintered bodies and mass-produce them than the hot pressing method, which is limited by the strength of the mold material (several hundred atmospheres). Also suitable for In order to achieve high density using hot isostatic pressing, primary sintering is performed before hot isostatic pressing to eliminate open pores in the sintered body, leaving only closed pores. You must do so. Even in the case of closed pores, if the amount thereof is large, the sintered body is likely to crack because the pores once compressed by hot isostatic pressing expand when the pressure is removed. Therefore, in primary sintering, the pores are not only closed, but also the amount of pores is adjusted to a density of 90% or more, more preferably 95% or more, as described in JP-A-49-128296.
It must be reduced so that the density is around 96%. The present invention has been made to solve the above problems, and the present invention has been made in order to solve the above problems, and in ferrite having a composition of 25 to 40 mol% MnO, 5 to 25 mol% ZnO, and 52 to 60 mol% Fe ₂ O ₃ , the average particle size is 0.8 After primary sintering using a raw material mixed powder with a particle size of 1000 to 1300℃ and 400 to 2000℃ using a raw material mixture powder or calcined and pulverized powder with a diameter of 1000 to 1300℃ and 400 to 2000℃.
It is characterized by hot isostatic pressing at atmospheric pressure. The reason why the present invention is limited to the above composition is as follows. In other words, in order to increase magnetic permeability, saturation magnetic flux density, etc., Mn-Zn ferrite generally has an _iron excess of 50 _mol % compared to the stoichiometric composition.
The above compositions are often used. in this case,
Sintering partially reduces Fe ³⁺ ions and turns them into Fe ²⁺ ions, but surplus oxygen is generated at this time. A part of this oxygen is released to the outside of the sintered body by diffusion, but the other part remains as pores inside the sintered body. When sintered under the same conditions, the greater the degree of iron excess, the greater the amount of Fe ²⁺ ions produced;
More oxygen tends to remain within the pores. Therefore, in order to increase the density of Mn-Zn ferrite with an iron-rich composition, it is necessary to release as much oxygen as possible to the outside of the sintered body before the pores become closed due to sintering and the diffusion rate of oxygen ions slows down. There is a need to. In the sintering of powder, generally the smaller the particle size of the powder, the higher the activity and the faster the sintering progresses. For this reason, the present inventors have noticed that when manufacturing Mn--Zn ferrite having an iron-excessive composition, the particle size of the raw material mixed powder or the pulverized powder after calcination often poses a problem. In other words, if the particle size is too small (less than 0.8 μm), sintering progresses rapidly, and as the pores become more closed, oxygen ions become less active, and as described above, the inside of the sintered body becomes inactive. It is easy for pores to remain and sintering cracks to occur. On the other hand, if the particle size is too large, exceeding 2 μm, the activity of the powder is too low and sintering does not proceed sufficiently, leaving a large amount of pores. As described above, if the particle size is too small or too large, a primary sintered body suitable for hot isostatic pressing cannot be obtained. Therefore, in order to obtain a good primary sintered body, it is necessary to use a raw material mixed powder or pulverized powder having an appropriate particle size. The method of the present invention will be explained below using Examples. Example 1 MnCO ₃ 26 mol%, ZnO2 2 mol% and
After molding a raw material mixed powder with a blending ratio of 52 mol% Fe ₂ O _{3 and} an average particle size of 0.8μ, primary sintering was performed at 1250°C, and hot isostatic pressing was performed at 1250°C and 500 atm. . Example 2 After molding a raw material mixed powder having the same composition as in Example 1 and an average particle size of 0.6μ, primary sintering and hot isostatic pressing were performed under the same conditions as in Example 1. Example 3 MnCO ₃ 32 mol%, ZnO 10 mol% and
A raw material mixed powder with a blending ratio of 58 mol % Fe ₂ O ₃ was calcined at 1100°C and then pulverized to obtain a pulverized powder with an average particle size of 2 μm.
After shaping the pulverized powder, primary sintering was performed at 1300°C, and hot isostatic pressing was performed at 1300°C and 1000 atm. Example 4 The same calcined powder as in Example 3 was pulverized to an average particle size of 2.5μ.
A pulverized powder was obtained, molded, and then subjected to primary sintering and hot isostatic pressing under the same conditions as in Example 3. The results obtained for the above four examples are summarized in the following table.

[Table] In the above table, μ _(100KHz) is the value of magnetic permeability μ when measured at 100KHz alternating current, and B ₁₀ is the value of magnetic flux density B in a magnetic field of 10 Oe. As can be seen from the table, Mn-Zn obtained by the method of the present invention was obtained by hot isostatic pressing under specific conditions using raw material powder with an average particle size within the range of 0.8 to 2 μm.
The ferrites (Example 1 and Example 3) have excellent magnetic properties, have few pores, and do not generate cracks. The Mn-Zn ferrite thus obtained is a material excellent in precision workability, wear resistance, and electromagnetic conversion characteristics, and the industrial contribution of the present invention is significant.

Claims (1)

[Claims] 1 MnO25-40 mol%, ZnO5-25 mol% and
In Mn-Zn ferrite with a composition of 52 to 60 mol% Fe ₂ O ₃ , after primary sintering using a raw material mixed powder or calcined and crushed powder with an average particle size of 0.8 μ or more and 2 μ or less, 1000 A method for producing high-density ferrite, characterized by hot isostatic pressing at ~1300°C and 400-2000 atm.