JPS6117787B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high-density ferrite suitable for use in magnetic heads and the like.

High-density ferrite is widely used in audio and video magnetic heads, etc., but the high-density ferrite used in video magnetic heads in particular has a grain size of ferrite in order to minimize sliding noise. ) is preferably small. However, in general, when the grain size is reduced, the density of ferrite decreases, the number of pores increases, and it becomes mechanically weak.
For example, when used in a magnetic head, there are drawbacks such as chipping on the tape running surface.

As a conventionally proposed method for producing high-density ferrite, a so-called hot press method is known, in which a ferrite material is fired by heating while pressurizing it from one axis. In this hot pressing method as well, the grain size is grown to 50μ or more, taking into account the drop-off of crystal grains. In order to obtain ferrite with a small grain size of 50μ or less by the hot pressing method, the firing temperature must be lowered, and the firing temperature must be lowered to avoid an increase in pores (i.e., a decrease in density) due to the lower firing temperature. It is conceivable to increase the pressure. however,
In reality, the pressure is determined by the mechanical strength of the mold.
The limit is 500Kg/ ^cm2 . Furthermore, even if the pressurizing force is increased, the frictional force between the wall of the mold containing the ferrite material and the ferrite material does not apply uniform pressure to the inside of the ferrite material, resulting in small grain size and pores. Almost no high-density ferrite can be obtained.

On the other hand, there is a hot static press method as a method of pressurized firing under high pressure. This method involves applying high pressure from the surroundings to the pressure-fired product in a high-pressure gas atmosphere, and the pressure ranges from several thousand kg/cm ² to 10,000 kg/cm ² . It is said that high pressure is possible. Therefore, such a hot isostatic pressing method can be used to produce high-density ferrite, but in this case, the ferrite material must be vacuum sealed in a platinum or nickel container, and this vacuum sealing process is extremely time-consuming. It takes. It is also possible to use a glass container as the enclosure, but
In addition to the complexity of sealing, gases such as H ₂ O or O ₂ are released from the glass container during heating and pressurization. Therefore, α-FE ₂ O ₃ is generated depending on the condition of the sample before hot isostatic pressing and the conditions of hot isostatic pressing.
Some parts may not be turned into spinel.

In order to eliminate the above-mentioned defects, the applicant has
We have already proposed a new method for producing ferrite in Japanese Patent Application No. 48-41727. This method consists of a primary sintering process in which the ferrite material is sintered to a density of 90% or more, a process in which the ferrite material after this primary sintering is hot isostatically pressed, and after this hot isostatic pressing. ferrite material and an annealing process at a temperature higher than that of hot isostatic pressing.

This makes it possible to obtain a ferrite that is easy to manufacture, has almost no pores, and does not have many crystal grains falling off (so-called chipping) from the sliding surface during mechanical sliding such as by running a tape. . However, while this method has many advantages, there are still problems that need to be overcome.
That is, on the other hand, the sintering temperature is low and the grains are grown to a predetermined size by annealing after hot isostatic pressing, but the grains tend to become irregular and it is difficult to control the grain size. It is difficult to reduce the sliding noise. However, in the obtained ferrite, small grains existing in the vicinity of large grains tend to peel off when the tape runs.

The present invention was invented to correct the above-mentioned defects, and the present invention is made by sintering ferrite material at a temperature T ₁ higher than the growth temperature at which grain growth occurs (T ₁ ≧1250°C) to achieve a density of 90. % or more, and a temperature T ₂ lower than the above-mentioned growth temperature at which grain growth does not substantially occur (however, 1000℃≦T ₂ ≦1250
℃, T ₁ ≧ T ₂ + 100℃) on the ferrite sintered body to make the density of the ferrite sintered body 99% or more. This is related to. By this method, the grain size can be made small and uniform without annealing, and it is possible to provide ferrite with excellent wear resistance and magnetic properties with little peeling.

In the present invention, a temperature higher than the above-mentioned growth temperature is used.
By sintering at T ₁ (T ₁ ≧1250℃), the grains can be grown to the desired average size to adjust the grain size, and the density can be increased to 90% or more for the next hot isostatic pressing. Prepare for. This hot static pressure pressing is performed at a temperature T ₂ lower than the above-mentioned growth temperature and at which grain growth does not substantially occur (however, at 1000°C
≦T ₂ ≦1250°C, T ₁ ≧T ₂ +100°C), and the ferrite sintered body is further densified to a density of 99% or more while maintaining a uniform grain size.

Therefore, since the grain size is small and uniform by sintering at a temperature of _T1 , when a magnetic head is constructed from the obtained ferrite, the sliding noise during tape running is greatly reduced. , grain peeling can be reduced. In addition, the density of the ferrite sintered body is made to be 90% or more (X-ray density or the ratio of the measured density to the theoretical density) through sintering, so even if there are pores, the ferrite sintered body is almost closed. It is in a hole state. For this reason, even if this ferrite sintered body is directly placed in high-pressure gas, atmospheric gas will not enter from the surface, and it can be heated without being sealed in a vacuum in a platinum, nickel, or glass container as in the past. Can be placed directly into the high pressure container of an interstatic press.

When carrying out the present invention, the sintering temperature T ₁ satisfies the following condition (a), and the temperature during hot isostatic pressing is
T ₂ must satisfy the condition (c) below, and the atmosphere during sintering at temperature T ₁ and the pressure during hot isostatic pressing must satisfy the conditions (b) and (d) below, respectively. It is desirable that you do so.

(a), Sintering temperature T ₁ The above sintering temperature T ₁ must actually be 1250℃ or higher, otherwise the grain growth will be small and 90%
It is not possible to obtain a ferrite sintered body with a density higher than that. This sintering temperature can be varied depending on the desired grain size.

(b) Atmosphere during sintering The oxygen partial pressure of the atmosphere during sintering at temperature T ₁ must be appropriately selected. This is because if the oxygen partial pressure is too high than necessary, α-Fe ₂ O ₃ phase will precipitate during sintering, and if the oxygen partial pressure is too low than necessary, the oxygen in the ferrite sintered body after sintering will This is because if the amount is small, cracks will easily form in the ferrite after the next hot isostatic pressing step.

(c), Temperature T ₂ during hot isostatic pressing The above-mentioned temperature T ₂ during hot isostatic pressing is actually 1000℃≦T ₂ ≦1250℃, and its relationship with the sintering temperature T ₁ is Then, T ₁ ≧T ₂ +100℃. That is, by lowering the temperature T ₂ below 1250°C, grain growth does not substantially occur, and it is possible to maintain the grain size due to sintering at the temperature T ₁ and obtain a predetermined density by pressing. can. Also the temperature T ₂
By lowering the temperature by more than 100° C. from the temperature T ₁ , grain growth can be completely suppressed and, therefore, strain accumulation due to grain growth can be completely prevented, and there is no need to perform annealing after processing. If the grains grow using this hot static pressure pressing, it is not appropriate because the grains will peel off during tape running.

(d) Pressure during hot isostatic pressing This pressure is preferably 300 atmospheres or more.
That is, by increasing the pressure to 300 atmospheres or more, the density of the ferrite sintered body can be increased to 99% or more, and it is possible to prevent chips from occurring on the tape running surface of the magnetic head. In this case, there is a certain relationship between the pressure and time during pressing; at a pressure of 300 atm, it takes 10 hours, at a pressure of 500 atm, it takes 4 hours, and at a pressure of 2000 atm, it takes 30 minutes.

Next, an embodiment in which the present invention is applied to Mn--Zn ferrite will be described with reference to the drawings.

After weighing 52 moles of Fe ₂ O ₃ , 20 moles of ZnO, and 28 moles of MnO, they were mixed in a ball mill, dried, and then press-molded into blocks of a predetermined size. Next, this block was sintered at 1350°C to obtain a ferrite sintered body with a grain size of 10 to 30 μm (average 20 μm). Further, this sintered body was placed in a high-pressure inert gas (for example, N ₂ or Ar gas) and subjected to hot isostatic pressing at 1150° C. and 500 atm for 4 hours. After this treatment, the pressure was gradually released, and the pressure was suddenly returned from around 800°C and 100 atm to atmospheric pressure, and the temperature was lowered at a rate of 100°C/hr.

The grain size of the resulting ferrite was the same as that before hot isostatic pressing, but the pores were significantly reduced.

FIG. 1 shows a microscopic photograph of the ferrite sintered body after sintering (before hot isostatic pressing), and it can be seen that the ferrite grains have grown to a predetermined size and that the grain sizes are almost uniform.

Figure 2 shows a micrograph of ferrite after hot isostatic pressing under the above conditions, and shows that although the ferrite has become more dense, the grain size is still the same as shown in Figure 1. It turns out that not much has changed.

Figure 3 shows that the primary sintering conditions are the same as those described above, and the hot isostatic pressing conditions are 1150℃ and 2000℃.
A micrograph of ferrite obtained at atmospheric pressure for 1 hour is shown, and the grain size is still 10~
It can be seen that the pores are significantly reduced at 30μ (average 20μ).

When magnetic heads were made using the ferrite shown in FIGS. 1 to 3 and the tape was run for 1000 hours, no grain separation was observed. Moreover, the density (theoretical density) of this ferrite was 99.6% when the cotton density was taken as 100%.

The magnetic properties of this magnetic head are B _S =4800gauss, H _C without annealing after hot isostatic pressing.
= 0.06 Oe, μ = 7000 to 8000, which was sufficient for head use.

Note that the present invention is not limited to Mn-Zn ferrite, but also applies to Ni
It is preferable to apply it to particularly soft materials such as -Zn ferrite, Cu-Zn ferrite, etc., but it is not limited thereto.

[Brief explanation of the drawing]

The drawings show an example in which the present invention is applied to Mn-Zn ferrite. Figure 1 is a micrograph of the ferrite before hot isostatic pressing, and Figure 2 is a micrograph of the ferrite after hot isostatic pressing. Fig. 3 is a micrograph of ferrite after hot isostatic pressing under different conditions.

Claims (1)

[Claims] 1. Sintering the ferrite material at a temperature T ₁ higher than the growth temperature at which grain growth occurs (T ₁ ≧1250°C) to obtain a ferrite sintered body with a density of 90% or more;
A temperature T ₂ lower than the growth temperature above and at which grain growth does not substantially occur (however, 1000℃≦T ₂ ≦1250℃, T ₁ ≧
The density of the ferrite sintered body was reduced by subjecting the ferrite sintered body to hot isostatic pressing at T ₂ +100°C).
A method for producing high-density ferrite, comprising the steps of increasing the density of ferrite to 99% or more.