JPS605045B2 - Manufacturing method of high-density ferrite - Google Patents

Description

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

Ferrite has a much higher specific resistance than metal magnetic materials such as permalloy, so when used as a material for magnetic heads, eddy current loss is greatly reduced, allowing good recording and reproduction in the high frequency range, and it also has excellent durability. Abrasion resistance is also improved.

Therefore, ferrite is currently widely used as a material for magnetic heads for audio and video applications. However, since ferrite is used as a sintered body, grain boundaries exist, and pores are likely to be formed along these grain boundaries. For this reason, the bonding force between the crystal particles (grains) at the grain boundary becomes weak, and when the magnetic head is actually installed in a tape recorder and the tape is run, there is a risk that the grains on the ferrite surface will peel off and fall off. expensive. In addition, in order to reduce the sliding noise as much as possible, the crystal grain size of the ferrite (
Although it is desirable that the grain size (grain size) is small, in general,
When the grain size is reduced, the density of the ferrite decreases, the number of pores increases, and the tape becomes mechanically weak, resulting in drawbacks such as chipping on the tape running surface when a magnetic head is used. Conventionally proposed methods for manufacturing high-density ferrite in order to reduce pores and grain separation include, for example, firing the ferrite material by applying pressure from the Ichito direction and heating it at a temperature close to the firing temperature. A so-called hot press method is known.

Also in this hot press method, the grain size is grown to 50 W or more in consideration of grain dropout. In order to obtain ferrite with a small grain size of 5 capes or less by the hot pressing method, the firing temperature must be lowered, and processing must be performed 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 pressurizing force is at most several hundred atmospheres (for example, 50
0 kg/) is the limit. 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. It is not possible to obtain dense ferrite. However, this method has the disadvantage that the running cost is high because it requires consumables, and because it is a uniaxial press, residual stress remains in the material and annealing is required after hot pressing. On the other hand, there is a hot isostatic press method as a method of pressure firing under high pressure. This method applies high pressure from the gas pressure to the pressure-fired product from the surroundings in a high-pressure gas atmosphere, and presses it isotropically. k9
It is said that it is possible to apply pressures as high as the enemy. 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 very time-consuming. It takes. It is also conceivable to use a glass container as the enclosure, but in addition to the complexity of the enclosure, gases such as 20 or 02 will come out of the glass container during heating and pressurization. Therefore, depending on the condition of the sample before hot isostatic pressing and the hot isostatic pressing conditions, Q-Fe
203 may be generated and a portion may not be spinelized. However, cracks on the ferrite surface cannot be sufficiently prevented. In order to eliminate the above-mentioned defects, the present applicant developed a completely new method for manufacturing ferrite (hereinafter referred to as the "Sakihan's method") dated October 22, 1976.

) has already been proposed. This method consists of a step of sintering (primary competitive sintering) ferrite material at a temperature higher than the growth temperature at which grain growth occurs (for example, 1250°C or higher) to obtain a ferrite sintered body with a density of 90% or higher, and a step lower than the growth temperature mentioned above. temperature (e.g. 10
The present invention relates to a method for producing high-density ferrite, comprising the steps of subjecting the ferrite compact to hot static pressing (for example, at a pressure of 30 pia or more) at a temperature of 0 to 1250°C. By this method, the grain size can be easily controlled to be small and uniform without annealing, and ferrite with less peeling and excellent wear resistance and magnetic properties can be provided.
Since hot isostatic pressing is performed in an inert gas (mainly -gas) atmosphere, this inert gas also acts as a kind of reducing atmosphere. Therefore, the amount of oxygen corresponding to the equilibrium oxygen partial pressure of the ferrite is insufficient on the surface of the ferrite.
To compensate for this, oxygen in the ferrite becomes easier to move to the surface. In this case, since high pressure is applied, the oxygen that has moved to the surface does not escape completely to the outside, and therefore small pores are likely to be formed on the surface. As a result, vacancies or small holes are likely to occur in the ferrite, and it is necessary to control the oxygen pressure in the atmosphere at high temperatures, which is particularly important in Mn-Zn ferrite. In conventional hot isostatic pressing, since metal is used as the heating element, it is difficult to control the oxygen pressure, and the magnetic and mechanical properties of the surface of the pressed material deteriorate.

The present invention is an invention that takes advantage of the features of the method of the prior application and further improves it. The present invention relates to a method for producing high-density ferrite, which includes the steps of subjecting the ferrite pseudo-supply body to hot static pressure pressing while the surface thereof is covered with oxide powder containing ferrite powder. By this method, a product with high density and less grain separation can be obtained very simply and easily, and reliability can be improved. Explaining the principle of the method according to the present invention, when a ferrite compact is wrapped in an oxide powder containing ferrite powder and subjected to hot static pressing, the ferrite powder in the oxide powder is in equilibrium with the atmosphere. It contributes to the formation of oxygen pressure, making it easier to obtain an equilibrium oxygen partial pressure, and therefore effectively preventing oxygen from coming out of the ferrite crystals to the surface.

That is, the ferrite powder in the oxide powder acts as a combined source of oxygen, and the oxygen released from the ferrite powder forms an equilibrium oxygen partial pressure in the vicinity of the ferrite burnt stripes. For this reason, the ferrite dovetail stripes are pressed to a high density without generating pores, so a high density and uniform material can be obtained without controlling the oxygen pressure of the atmosphere.
Moreover, in the pressing process, there is no need to wrap the ferrite scale bodies in platinum foil or vacuum seal them in a glass ampoule, making the operation easy and reducing costs. In the present invention, it is desirable to use the same type of ferrite powder as the ferrite sintered silk body. For example, it is preferable to wrap a Mn-Zn ferrite competitive body with Mn-Zn ferrite powder.

That is, two types of ferrite compacts are made, one of them is crushed, and the ferrite powder can be used as is.Furthermore, depending on the characteristics of the material, the ferrite powder can be prepared in advance to obtain the desired equilibrium oxygen pressure. In addition, if you mix other oxide powders such as high melting point powders such as alumina and zirconia with ferrite powder and wrap the surface of the ferrite light body with this mixture,
It is possible to prevent the solid phase reaction between the ferrite compact and the powder during hot static pressing. Generally, in the present invention, it is necessary to remove the powder portion on the surface of the ferrite mound compact after hot isostatic pressing treatment, but when the above-mentioned solid phase reaction occurs, the oxide powder becomes sintered and difficult to remove. If left as is, the part of the powder that has solidified will become porous and cause deterioration of the properties. Further, the oxide powder preferably has a particle size of 1 mm or less in order to increase the surface area and facilitate obtaining equilibrium oxygen pressure, but it may have an average particle size of about 100 mm.

The oxide powder may be present at a density of 30 to 91% so as to sufficiently cover the surface of the ferrite compact (actually, one leg or more). Further, the effect is greater when this density is set to 50% or more. Moreover, if the density is about 20%, it will be in a state as if it was sprinkled with powder, resulting in poor stability. Further, a density of 91% is a packing density at which atmospheric gas can theoretically penetrate during hot static pressure pressing, and if it exceeds 91%, it becomes difficult for gas to penetrate and there is a possibility that desired pressing cannot be performed. Further, the oxide powder may be pressed and solidified to a desired density. Note that the "filling rate" here is expressed as a percentage when the case of single crystal is taken as 100%. Next, when carrying out the method according to the present invention, it is desirable to adopt the method of the earlier application.

That is, first, a ferrite material is sintered at a temperature higher than the growth temperature at which grain growth occurs to obtain a ferrite fringe body with a density of 90% or more,
Next, hot static pressing is performed at a temperature lower than the growth temperature while the surface of the ferrite aggregate is covered with the oxide powder. In this case, by condensing at the above-mentioned growth temperature or higher, the grains are grown to a desired average size, the grain size is adjusted, and the density is set to 90% or more in preparation for the next hot isostatic pressing.

This hot static pressing is performed at a temperature that does not cause grain growth, thereby further increasing the density of the ferrite competitive body while maintaining a uniform grain size. Therefore, since the grain size is small and uniform through sintering, when a magnetic head is constructed using the obtained ferrite, the sliding/distortion during tape running is greatly reduced, further preventing grain separation. It can be reduced. Furthermore, since the density of the ferrite scale body is set to 90% (Yoshisuki Kirifurikaku XIOO) by dawning, even if there are pores, the ferrite scale body is almost in a closed pore state. For this reason, even if this ferrite sintered body is placed directly into high-pressure gas, atmospheric gas will not enter from the surface, and unlike conventional platinum,
It can be placed directly into the high-pressure container of a hot isostatic press without having to be vacuum sealed in a nickel or glass container. When carrying out the present invention, it is desirable that the following conditions a to d be satisfied.

{a}, Competitive temperature T, The above-mentioned competitive bonding temperature T must actually be 1250° C. or higher, otherwise grain growth will be reduced and a ferrite sintered body with a density of 90% or higher cannot be obtained.

This condensation temperature can be varied depending on the desired grain size. [b), Sintering atmosphere The oxygen partial pressure of the sintering atmosphere must be appropriately selected.

This is because if the oxygen partial pressure is too high than necessary, the -Fe203 phase will precipitate during competitive bonding, and if the oxygen partial pressure is too low than necessary, the amount of oxygen in the ferrite leech aggregate after dawn silk will be small. This is because cracks are likely to form in the ferrite after the next hot isostatic pressing step. Therefore, it is desirable to carry out dawning at about equilibrium oxygen pressure. [c}, temperature L during hot isostatic pressing The temperature T2 during hot isostatic pressing mentioned above is actually 100
and OST2SI250q○, and in relation to the condensation temperature T, it is preferable that T,2T2100q0.

That is, by lowering the temperature T2 to less than 1250 qo, grain growth does not substantially occur, and a predetermined density can be achieved by pressing while maintaining the grain size due to competitive coalescence. However, if the temperature exceeds 125 pi, a solid phase reaction occurs between the ferrite compact and the oxide powder, causing the two to coagulate, making it difficult to remove them after treatment. Further, by lowering the temperature T2 by 100 qo or more lower than the temperature T, it is possible to completely suppress grain growth, thereby completely preventing the accumulation of strain due to grain growth, and there is no need to perform annealing after processing. If grains grow during hot static pressure pressing, the grains will peel off during tape running, which is not desirable. [d}, Pressure during hot isostatic pressing This pressure is preferably 20 pica or more, and preferably 30 or more hydrophobic pressure.

That is, if the pressure is set to 30 degrees 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 30 pia, it takes one feeding hour, at a pressure of 50 pia, it takes 4 hours, and at a pressure of 200 p, it takes 3 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 20352 mol of Fe, 20 mol of Zn, and 28 mol of Mn, they were mixed in a ball mill, dried, and then press-molded into a block of a predetermined size.

Next, this block was subjected to primary sintering (oxygen partial pressure 20%) at 1300 qo for 1 hour to obtain a ferrite burnt striped body with a grain size of 10 to 30 grains and an average grain size of 20 grains. The density of this Akatsuki compact was 98%. Next, as shown in FIG. 1, a ferrite powder layer 2 having an average particle size of about 100 mm was made to exist on the surface of the ferrite sintered body block.

In order to produce this ferrite powder, the ferrite sintered silk body block obtained in the above-mentioned sintering process is crushed into powder, and this powder is used as it is. Note that the ferrite powder does not have to be of the same type as the competitive silk body block 1, and may have a different composition. Next, in the state shown in FIG. 1, the ferrite sintered body block was subjected to hot isostatic pressure while applying a pressure of 1000 atm for 1 hour at 1150 pm in a high-pressure inert gas (for example, N2 or Ar gas). Pressed. After this treatment, the pressure was gradually released, and from around 80,000 to 80, the pressure was suddenly returned to atmospheric pressure, and flooding occurred at a rate of 100° C./hr. As a result, high-density ferrite having a density of 99.5% or more of the theoretical density was obtained.

The grain size of this ferrite was the same as before hot isostatic pressing, but the pores were significantly reduced. Further, no annealing was required to adjust the grain size. Figure 2 shows a microscopic photograph of the polished surface of a ferrite compact that has been hot isostatically pressed using a conventional method. I know it's in there.

Figure 3 shows a microscopic photograph of the polished surface of a ferrite aya body that has been subjected to hot isostatic pressing using the method of the present invention. Regardless, it can be seen that the grain size is uniform and no peeling or cracking of the grains occurs.

When magnetic heads were manufactured using the ferrite obtained by the method of the present invention and subjected to a tape running test for 100 feeding hours, almost no grain separation was observed.

Also, the density of this ferrite (actually measured density) is 1
00%, it was 99.6%. The magnetic properties of this magnetic head without annealing after hot isostatic pressing were Bs = 480 female auss, Hc = 0.060e, and French = 7000 to 8000, which were sufficient for use as a head.

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

[Brief explanation of the drawing]

The drawings are for explaining the present invention, and FIG. 1 is a schematic cross-sectional view showing the state when hot isostatic pressing is applied to a ferrite compact, and FIG. 2 is a cross-sectional view of a ferrite compact obtained by a conventional method. FIG. 3 is a micrograph of the polished surface of a high-density ferrite obtained by the method of the present invention. In the symbols used in the drawings, 1 is a ferrite sintered block and 2 is a ferrite powder layer. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 A step of sintering a ferrite material to obtain a ferrite sintered body, and applying hot static pressure to the ferrite sintered body with the surface of the ferrite sintered body wrapped in oxide powder containing ferrite powder. A method for producing high-density ferrite, comprising the steps of: