JPS6319447B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to non-magnetic zinc ferrite used, for example, as a gap spacer of a magnetic head, and to improvements in a method for manufacturing the same. In recent years, as ferrite for magnetic heads, small, dense ferrite with few pores and uniform particle diameter has been required in order to avoid inconveniences such as head damage and tape damage. In order to meet these requirements, manufacturing methods such as vacuum firing, rubber pressing, hot pressing, and hot isostatic pressing are known, but among them, the pore elimination effect is large;
The hot isostatic pressing method, which also has good productivity, is superior to other methods. Incidentally, the gap spacer that provides the gap in the magnetic head is similarly required to be made of a dense material with low porosity and small, uniform particle size. Non-magnetic zinc ferrite is used as a conventional gear spacer material. Generally, non-magnetic zinc ferrite contains 49.0~52.0 mol% ZnO and 48.0
It is manufactured by calcining and finely pulverizing a powder containing ~51.0 mol% of Fe ₂ O ₃ , followed by press molding and firing in the atmosphere. however,
In the case of such a manufacturing method, in order to obtain a high-density material, it is necessary to sinter at a relatively high temperature of 1250° C. or higher, and the average particle size grows to be 15 μm or higher. As a result, the mechanical strength of the material decreases, and Zn decomposes and precipitates at grain boundaries.
Zn, which is dense with small particle size, is the cause of grain shedding.
The situation has become difficult to manufacture ferrite. SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a dense non-magnetic ferrite having a small particle size and good workability. The present invention focuses on oxides that are easily dissolved in Zn-Fe ₂ O ₄ and relatively easy to concentrate at grain _boundaries , _and
By adding CaO or Al ₂ O ₃ and MgO in combination as subcomponents, precipitation of Zn is suppressed and a grain growth suppressing effect is produced. Table 1 shows that when Al ₂ O ₃ is added to ZnFe ₂ O ₄ , 1200
The figure shows the grain growth state and the Zn precipitation state when fired at ℃ for 2 hours in the air. Al ₂ O ₃
When 0.5wt% or more is added, no Zn precipitation is observed. This is because the Zn produced by the separation reacts with Al ₂ O ₃ .
This is thought to be due to the formation of ZnAl ₂ O ₄ and good solid solution in Zn.Fe ₂ O ₄ . However, addition of 2.0 wt% or more causes grain growth and the generation of huge intragranular pores, which is not preferable.

[Table] Figure 1 shows the particles obtained when 0.5, 1.0 and 2.0wt% of Al ₂ O ₃ and 0.05 to 1.0wt% of CaO or MgO were added and fired at 1200℃ for 2 hours in the air. This shows the change in diameter. It was found that both CaO and MgO have a grain growth inhibiting effect at 0.5 wt% or less. This reacts with SiO ₂ , which is unavoidably present in trace amounts in the raw material,
Forms grain boundary phases such as CaO-SiO ₂ or MgO-SiO ₂ ,
This is thought to be to control grain growth. Therefore,
Add 0.2 to 2.0 wt% of Al ₂ O ₃ and at the same time add CaO or
By adding 0.5wt% or less of either MgO, it is possible to suppress the precipitation of Zn and to reduce the
It has become clear that ferrite can be produced. In addition, by subjecting the Zn/ferrite of the present invention to hot isostatic pressing after primary firing, the porosity can be significantly reduced without Zn precipitation while keeping the average particle size small. The present invention will be explained below based on examples. Example 1 0.5 wt% of Al ₂ O ₃ and 0.2 wt% of CaCO ₃ in terms of CaO were added to a raw material powder consisting of 50.2 mol% of ZnO and 49.8 mol% of Fe ₂ O ₃ , and the mixture was placed in a ball mill. The mixture was wet mixed for 40 hours, filtered and dried, and then calcined for 2 hours at a temperature of 900°C. Furthermore, in a ball mill
After grinding for 24 hours to obtain a powder with an average particle size of 1 μm, a binder was added and the powder was pulverized 60×20× at a pressure of 2000 Kg/cm ^2.
A 10 mm green compact was produced, and primary firing was performed in the air at a temperature of 1150°C for 2 hours. obtained at this time
The average particle size of Zn-ferrite was 3.4 μm, and no Zn precipitation was observed. However, the porosity is
It was 3.5%. This is done at a temperature of 1100℃ and a pressure of 1000Kg/
As a result of hot isostatic pressing in cm ² of Ar gas for 1 hour, the magnetic permeability at 100 KHz was 1, and while maintaining the average particle size of 3.6 μm, the particle size of the primary firing,
Dense and small particle size with significantly reduced porosity of 0.03%.
Zn-ferrite was obtained. Of course, no Zn precipitation was observed. Example 2 1.0 wt% of Al ₂ O ₃ and 0.5 wt% of MgO were added to a raw material powder consisting of 50.0 mol% of ZnO and 50 mol% of Fe ₂ O ₃ ,
A green compact was produced in the same manner as in Example-1, and 1200
Primary firing was performed in the air at a temperature of 0.degree. C. for 2 hours. The average particle diameter of the Zn-ferrite obtained at this time was 5.1 μm, and no Zn precipitation was observed, but the porosity was 4%. This temperature is 1150
As a result of hot isostatic pressing for 1 hour in Ar gas at a temperature of 800 kg/cm ² and a pressure of 800 Kg/cm 2,
Magnetic permeability at 100KHz is 1, average particle size
Zn-ferrite with a compact particle size of 5.5 μm and a porosity of 0.03% was obtained. Further, no precipitation of Zn was observed. FIGS. 2 and 3 show 2000x electron micrographs of the fractured surfaces of the product of the present invention and the conventional product, respectively. In both figures, 2 cm on the figure corresponds to 10 μm.
From both figures, it can be seen that the product of the present invention is denser than the conventional product, has greater grain boundary strength, and exhibits intragranular fracture. As explained above, the present invention has the effect of suppressing the precipitation of Zn, which is a major cause of grain shedding, etc., and the porosity can be extremely reduced by hot isostatic pressing, resulting in good specularity. It is possible to obtain non-magnetic ferrite with excellent workability, and it is extremely useful as a gear spacer material for magnetic heads.

[Brief explanation of the drawing]

Figure 1 shows Zn-ferrite with Al ₂ O ₃ and CaO or
This figure shows the change in average particle size when varying amounts of MgO are added. Figures 2 and 3 are
2000x electron micrographs of the fractured surfaces of the product of the present invention and the conventional product are shown, respectively.

Claims (1)

[Claims] 1 ZnO 49.0 to 52.0 mol% and Fe ₂ O ₃ 48.0 to 51.0
Non-magnetic zinc ferrite whose main component is mol%,
As accessory components, 0.5wt% or less of any one of CaO and MgO (not including 0) and 0.5 to 2.0wt of Al ₂ O ₃
Non-magnetic zinc ferrite characterized by adding %. 2 ZnO 49.0-52.0 mol% and Fe ₂ O ₃ 48.0-51.0
The main component consisting of mol% is 0.5wt% or less (not including 0) of either CaO or MgO.
A non-magnetic zinc ferrite characterized in that raw material powder adjusted to have a composition containing 0.3 to 2.0 wt% of Al ₂ O ₃ as a subcomponent is processed by hot isostatic pressing after primary firing. Production method.