JPH0696931A - High-density polycrystalline ferrite - Google Patents

Abstract

PURPOSE:To suitably use ferrite for forming magnetic heads used for magnetic recording media having high coercive forces and, at the same time, to prevent the deterioration of sliding characteristics of the magnetic heads. CONSTITUTION:This ferrite is composed of 60-68mol% ferric oxide, 10-20mol% zinc oxide, and 30-12mol% manganese oxide and has a >=5,800-G saturation magnetic flux density (B10) and <=0.01% porosity. In addition, the ferrite has such a composition that the porosity does not substantially increase even when the ferrite is heat-treated at >=1,000 deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to high density polycrystalline ferrite,
Especially metal tape for VTR, FDD, RDD, etc.
The present invention relates to a Mn-Zn-based ferrite material which has a small magnetic flux variation with respect to frequency and can be suitably used for a recording / reproducing head for a high coercive force magnetic recording medium such as a vapor deposition tape and has a high magnetic flux density.

[0002]

BACKGROUND ART Conventionally, a ferrite material represented by Mn-Zn ferrite has been used as a material for a magnetic recording / reproducing head such as a VTR, but such a ferrite material (sintered body) is generally used. , A ferrite raw material powder mixture having a composition containing ferric oxide in a molar ratio of 50 to 54% is calcinated to have a ferritization rate of about 80% or more, and then the calcinated product is crushed and The molded body obtained by molding into a predetermined shape is first subjected to 12
After firing at a temperature of 00 ° C. or lower, it is sintered at a temperature of 1250 ° C. or higher under approximately equilibrium oxygen partial pressure (0.1 to 100% as oxygen concentration) to control the ferrite particle size and magnetic properties. It is manufactured by the so-called vacuum firing method.
In the firing step under vacuum, the ferrite rate of the molded body is set to about 100% at around 900 ° C., and the gas inside the molded body is evacuated so that the pores in the molded body are reduced to 1200 ° C. It is designed to have closed pores.

However, the ferrite having the iron oxide composition as described above has a saturation magnetic flux density (B ₁₀ ) of 560.
Since it is 0 G (gauss) or less, it cannot be used as a ferrite material for a recording / reproducing head of a high coercive force magnetic recording medium such as a metal tape.

Further, as one of the methods for densifying polycrystalline ferrite, a method of firing the above-mentioned molded body under pressure by hot isostatic pressing (HIP) method or hot pressing (HP) method is also studied. And by this,
It has been recognized that a fired ferrite body having a porosity of 0.01% or less can be obtained. However, in the high density polycrystalline ferrite body having the reduced porosity, it is possible to obtain a temperature of 1000 ° C or higher. When the ferrite body is reheated to a temperature, the phenomenon in which the pores are revived in the ferrite body to become a ferrite body having a high porosity again is caused. Therefore, such a ferrite body is converted into a single crystal by solid phase reaction. It was a problem to single crystallize in.

On the other hand, in JP-A-59-64599, the molar ratio of ferric oxide is 61.5 to 65%, zinc oxide is 10 to 20%, and manganese oxide is 28.5 to 15%. A single crystal ferrite by a so-called Bridgman method, which has a composition and grows from a melt (liquid phase), has been proposed. With such a ferrite composition, the saturation magnetic flux density (B ₁₀ ) is 5
It has been clarified that it is possible to obtain ferrite of 500 G or more.

However, in order to obtain a ferrite body having a ferric oxide content of more than 60 mol%, when a ferrite raw material powder mixture having a high ferric oxide content is calcinated in air, The ferritization rate is about 40 to 60%, and a calcined product having such a ferritization rate is crushed and further subjected to predetermined molding to obtain a molded body, which is fired by the above-mentioned firing method under vacuum. Then, the ferritic rate becomes about 100% at a temperature of around 1000 ° C., that is, the hematite in the fired body disappears completely, and therefore the densification does not occur sufficiently even after the sintering operation at a temperature of 1250 ° C. or higher. It was extremely difficult to control the porosity of the obtained sintered body to 0.01% or less. Moreover, since the obtained ferrite body has many pores, even if it is attempted to be single-crystallized by the solid-state reaction single-crystalization method, the temperature becomes considerably high, and it is difficult to control the single-crystalization. In addition to the above, there is a problem that the crystal grains are coarsened, or differently oriented crystals are generated, and a large amount of pores remain in the obtained single crystal.

[0007]

The present invention has been made in view of such circumstances, and a problem to be solved by the present invention is that the change of magnetic permeability with respect to frequency is small and the saturation magnetic flux density (B ₁₀ ) is small. Another object of the present invention is to provide a high-density polycrystalline ferrite having a coercive force of 5800 G or more and which can be suitably used as a magnetic head material for a high coercive force magnetic recording medium. The following is to provide a high-density polycrystalline ferrite that does not impair the sliding characteristics of the magnetic head, and yet another problem to be solved is that the single crystallization temperature in the single crystallization method by solid-state reaction is low, Another object of the present invention is to provide a high-density polycrystalline ferrite, which has less generation of heterogeneous crystals and solves the problem of pore revival due to heating.

[0008]

In order to solve such a problem, the high density polycrystalline ferrite according to the present invention has a molar ratio of 60 to 68% ferric oxide, 10 to 20% zinc oxide, and 30 to 30%. It has a composition of 12% manganese oxide, a saturation magnetic flux density (B ₁₀ ) of 5800 G or more, a porosity (P) of 0.01% or less, which will be defined later, and 1000 ° C. or more. It is characterized in that the porosity does not substantially increase in the heat treatment at the temperature.

[0009]

DETAILED DESCRIPTION OF THE INVENTION In order to obtain the high-density polycrystalline ferrite according to the present invention, a raw material powder mixture of Mn-Zn ferrite giving a predetermined composition is calcined by a conventional method and then pulverized. Then, a molded body formed into a suitable shape such as a block is used as a ferrite material. Incidentally, such a molded body is generally composed of about 40 to 60% by weight of a ferrite phase, and the remaining 60 to 40% by weight of an unreacted material phase mainly composed of a hematite phase.

The composition of such a ferrite material is the composition of the high-density polycrystalline ferrite obtained by firing it as it is, but the composition of the high saturation magnetic flux density (B ₁₀ ) of the present invention is as follows. The high-density polycrystalline ferrite has a molar ratio of 60 to 68% ferric oxide (Fe ₂ O ₃ ), 1
It is obtained by using a ferrite material having a composition of 0 to 20% zinc oxide (ZnO) and 30 to 12% manganese oxide (MnO). Among them, ferric oxide is 63 to 6 in particular.
A ferrite material having a composition of 5 mol%, 10 to 15 mol% of zinc oxide, and 27 to 20 mol% of manganese oxide is preferably used, whereby the saturation magnetic flux density is 5800 G or more,
A high density polycrystalline ferrite of 6000 G or more is preferably obtained.

The ferrite material (calcined body) having a hematite phase together with the above ferrite phase is first prepared by using He, Ar or N _{2 having} an oxygen concentration of 0.01 to 50%.
And the like, the hematite phase in the ferrite material is gradually reduced, and 1
The hematite phase is made to substantially disappear in the temperature range of 100 to 1250 ° C (first firing step). In other words, in this first firing step, 110
The temperature and the oxygen partial pressure (concentration) are adjusted according to the ferric oxide composition of the ferrite material so that the hematite phase substantially disappears in the temperature range of 0 to 1250 ° C.

It should be noted that the oxygen concentration in the firing atmosphere is 0.
When it is lower than 01%, the ferrite material progresses to become ferrite rapidly and the hematite phase is substantially eliminated in the low temperature region, so that there is a problem that the porosity of the ferrite material cannot be sufficiently reduced. 50% oxygen concentration
If it exceeds, the progress of ferritic formation is slow and the disappearance of the hematite phase is delayed in the second firing step, so that there is a problem that coarse air holes remain inside the sintered body.

Further, if the hematite phase substantially disappears at a temperature of less than 1100 ° C., the ferrite material cannot be sufficiently densified in the second firing step, and the porosity of the final fired body will be sufficient. It becomes difficult to reduce Furthermore, when the disappearance of the hematite phase is performed at a temperature of 1250 ° C. or higher, there is a problem that coarse air holes are generated in the subsequent second firing step.

Further, as the firing temperature of the ferrite material in the first firing step, a temperature of 800 ° C. or higher is generally used. However, if the temperature is lower than 800 ° C., the progress of ferritization proceeds slowly, and an effective reduction reaction of the hematite phase cannot be induced. Then, in such a first firing step, a method of firing the ferrite material by using a temperature raising operation of raising the temperature stepwise or continuously is adopted, but generally, a plurality of The firing temperature is increased stepwise according to the stepwise temperature raising step, and the final temperature raising step heats the ferrite material to a temperature of 1100 to 1250 ° C. so that the hematite phase in the ferrite material disappears. It will be done.

More specifically, the preferred stepwise temperature raising operation in the first firing step is a first temperature raising step of gradually raising the temperature from about 800 ° C. to reach a temperature lower than 1200 ° C., The first holding step consisting of the subsequent holding at the ultimate temperature for a predetermined time and the subsequent 1100 to 125
It includes a second temperature raising step of raising the temperature to a predetermined temperature in the region of 0 ° C., and a second holding step of holding at that temperature for a predetermined time to substantially eliminate the hematite phase. And the temperature rising speed at that time is usually 800 ° C.
Up to about 150 to 200 ° C./hr, and in both the first and second temperature raising steps, about 30 to 40 ° C./hr.

Next, the ferrite material in which the hematite phase has been eliminated in the first firing step is further fired in the second firing step to be further densified. As the firing atmosphere in the second firing step, an atmosphere having an oxygen concentration of 0.1 to 100% is used, and such an oxygen concentration finally has a porosity of 0.01% or less. It is necessary to control the crystal grain size and magnetic characteristics of ferrite. The components other than oxygen in the firing atmosphere are inert gas components such as He, Ar and N ₂ . Further, it is necessary to use a temperature higher than 1250 ° C. as a firing temperature, which allows effective sintering to proceed, thereby obtaining a dense ferrite sintered body in which the porosity is effectively reduced. You can do it.

The ferrite sintered body obtained through the first firing step and the second firing step is a high density polycrystalline ferrite having a porosity of 0.01% or less, and has a high recording / reproducing head height. It has excellent workability as a density ferrite material, and does not cause problems such as head chipping and noise due to clogging of magnetic powder pores when sliding with a magnetic tape. Compared with large conventional polycrystalline ferrite and single crystal ferrite, it has excellent characteristics that the change in magnetic permeability with frequency is small.

Further, since it is an atmospheric pressure sintering method, it is less expensive than the HIP method and the hot pressing method in terms of cost, does not require a large apparatus, and is simple in the process. Furthermore, the resuscitation of the pores is effectively suppressed even by the heat treatment at 1000 ° C. or higher, and the porosity does not substantially increase.
Even if such high-density ferrite (polycrystalline ferrite) is made into a single crystal, the porosity does not increase, and the porosity of the obtained single crystal can be 0.01% or less. Here, the fact that the porosity does not substantially increase means that the porosities before and after reheating are within the measurement error range and hardly change. The measurement error range in this case can be considered to be a change within a range of about ± 50% of the measured value in view of the accuracy of the porosity measurement.

Furthermore, the composition of the high-density polycrystalline ferrite of the present invention is 60-68 mol% ferric oxide and 10-2.
By using a Mn-Zn-based ferrite having a composition of 0 mol% zinc oxide and 30 to 12 mol% manganese oxide, the saturation magnetic flux density (B ₁₀ ) is 5800 G or more, preferably 6000 G or more. Crystalline ferrite can be obtained, which can be advantageously used as a recording / reproducing head material such as a metal tape or a vapor deposition tape which is a magnetic recording medium having a high coercive force.

The porosity in the present invention is a percentage of the area occupied by the pores on any cut surface of the sample, and is specifically determined as follows. That is, an arbitrary cut surface of a predetermined sample is polished, and the polished surface is inspected with a metallurgical microscope at a magnification of 1000.
Then, the number: n is measured, the porosity is measured from the porosity area with respect to the total visual field area, and the porosity: P% is obtained according to the following formula.

[0021]

[Equation 1]

The term "ferritization rate" refers to the weight percentage of the ferrite phase. The weight of the hematite phase at the time of preparation and the weight of the hematite phase after calcination are measured, and all the disappeared hematite is ferrite. It is calculated as a phase. Furthermore, the saturation magnetic flux density (B ₁₀ ) is
It shows a saturation magnetic flux density in a magnetic field of 10 Oe.

[0023]

EXAMPLES In order to more specifically clarify the present invention, some examples of the present invention will be shown below, but the present invention should be construed to be limited by the description of such examples. Not to mention that.

The present invention can be carried out in various modes other than the specific description of the present invention and the following examples, and those skilled in the art can carry out the invention without departing from the spirit of the present invention. It is to be understood that all of the various aspects that can be implemented based on the knowledge of are within the scope of the present invention.

Example 1 A composition having a molar ratio of ferric oxide: 61.0%, manganese carbonate: 27.0%, and zinc oxide: 12.0% obtained by roasting hydrothermally synthesized magnetite. The ferrite raw material powder mixture was calcined in the air at a temperature of about 1000 ° C. for 2 hours, and then the calcined product was crushed and molded into a predetermined shape.

Then, the obtained molded body (ferrite material) was fired as follows. That is, first, from room temperature to 800 ° C., at a heating rate of 150 ° C./hr, and
From 00 ° C to 1000 ° C, the temperature is raised at a heating rate of 40 ° C / hr, and then 4 times at a temperature of 1000 ° C.
Held for hours. During this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 0.1%. Then 40 ° C
The temperature was raised at a heating rate of / hr, and the temperature was maintained at 1200 ° C. for 2 hours to continue the first firing operation to eliminate the hematite phase in the molded body. Incidentally, when the fired body immediately after being heated to 1100 ° C. and the fired body after being kept at 1200 ° C. for 2 hours were taken out and the cross section inside the fired body was examined by an X-ray diffraction method, a hematite phase remained in the former case. On the other hand, it was confirmed that the latter had a 100% ferrite phase and the hematite phase disappeared during this period. During this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 1%.

After that, the second firing operation was carried out by raising the temperature to 1300 ° C. at a temperature rising rate of 150 ° C./hr and maintaining the temperature for 8 hours. Also, during this firing, the firing temperature was a nitrogen atmosphere with an oxygen concentration of 5%. Then, after such firing, a cooling step at 1100 ° C. or lower was performed in a nitrogen atmosphere to obtain a desired ferrite fired body (polycrystalline body). The obtained polycrystal had an average particle size of 9.
8 μm, porosity: 0.01%, discontinuous grain growth temperature: 13
It was 40 ° C.

Further, the obtained polycrystal was made into 5 mm × 5
The pieces were cut into a size of mm × 10 mm, and heat treatment was performed as follows, and changes in porosity after the heat treatment were examined. First, the temperature was raised from room temperature to 1100 ° C. at 300 ° C./hr, and the atmosphere during this period was nitrogen. After that, further 300 ℃ / h
The temperature was raised to 1300 ° C. with r and held for 2 hours. The atmosphere during this period was a nitrogen atmosphere with an oxygen concentration of 5%. Then, the temperature was lowered at 300 ° C./hr, and the temperature was lowered from 1100 ° C. in a nitrogen atmosphere to obtain a heat-treated ferrite fired body.

EXAMPLE 2 Ferric oxide obtained by roasting hydrothermally synthesized magnetite in a molar ratio of 62.5%, manganese carbonate: 26.5%, zinc oxide: 11.0%. The ferrite raw material powder mixture was calcined in the air at a temperature of about 1000 ° C. for 2 hours, and then the calcined product was crushed and molded into a predetermined shape.

Then, the obtained molded body was fired as follows. That is, from room temperature to 800 ° C, 150 ° C /
The temperature is raised at a heating rate of hr and further from 800 ° C. to 1000 ° C. at a heating rate of 40 ° C./hr, and 1
It was kept at a temperature of 000 ° C. for 4 hours. During this firing, a nitrogen atmosphere having an oxygen concentration of 0.5% was used as a firing atmosphere. Then, after that, the temperature was raised at a temperature rising rate of 40 ° C./hr, and the temperature was further held at 1220 ° C. for 2 hours to eliminate the hematite phase in the molded body. Incidentally, when the fired body immediately after being heated to 1100 ° C. and the fired body after being held at 1220 ° C. for 2 hours were taken out and the cross section inside the fired body was examined by an X-ray diffraction method, a hematite phase remained in the former case. On the other hand, it was confirmed that the latter had a 100% ferrite phase and the hematite phase disappeared during this period. During that time, the atmosphere was a nitrogen atmosphere with an oxygen concentration of 1%.

Next, at a temperature rising rate of 150 ° C./hr, 13
The final firing operation was carried out by raising the temperature to 00 ° C. and holding at that temperature for 8 hours. Further, during this firing, the firing atmosphere was a nitrogen atmosphere having an oxygen concentration of 3%. Then, after firing, a cooling step at 1100 ° C. or lower was performed in a nitrogen atmosphere to obtain a desired ferrite fired body (polycrystalline body). The obtained polycrystal had an average particle size of 8.
9 μm, porosity: 0.008%, discontinuous grain growth temperature: 1
It was 350 ° C.

Further, the polycrystal thus obtained was cut into a size of 5 mm × 5 mm × 10 mm, and the heat treatment was carried out by the same method as in Example 1 to change the porosity after the heat treatment. I checked.

Example 3 A composition of ferric oxide: 63.5%, manganese carbonate: 22.5%, zinc oxide: 14.0% obtained by roasting hydrothermally synthesized magnetite in a molar ratio. The ferrite raw material powder mixture was calcined in the air at a temperature of about 1000 ° C. for 2 hours, and then the calcined product was crushed and molded into a predetermined shape.

Then, the obtained molded body was fired as follows. That is, from room temperature to 800 ° C, 150 ° C /
The temperature is raised at a temperature of hr and further at a temperature of 800 ° C. to 1000 ° C. at a temperature of 40 ° C./hr.
It was kept at a temperature of 000 ° C. for 4 hours. During this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 1%. After that, 1200 ° C at a temperature rising rate of 40 ° C / hr.
The heating operation was continued by raising the temperature to 1,200 ° C. for 2 hours and extinguishing the hematite phase in the molded body. Incidentally, when the fired body immediately after being heated to 1100 ° C. and the fired body after being kept at 1200 ° C. for 2 hours were taken out and the cross section inside the fired body was examined by an X-ray diffraction method, a hematite phase remained in the former case. On the other hand, it was confirmed that the latter had a 100% ferrite phase and the hematite phase disappeared during this period. Meanwhile, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 1%.

Then, at a temperature rising rate of 150 ° C./hr, 13
The final firing operation was performed by raising the temperature to 50 ° C. and holding it there for 8 hours. Further, during this firing, the firing atmosphere was a nitrogen atmosphere having an oxygen concentration of 1%. Then, after such firing, a cooling step at 1100 ° C. or lower was performed in a nitrogen atmosphere to obtain a desired ferrite fired body (polycrystalline body). This polycrystal had an average grain size of 10.2 μm, a porosity of 0.008%, and a discontinuous grain growth temperature of 1420 ° C.

Further, the polycrystal thus obtained was cut into a size of 5 mm × 5 mm × 10 mm, and the heat treatment was carried out by the same method as in Example 1 to change the porosity after the heat treatment. Examined.

Example 4 Ferric oxide obtained by roasting hydrothermally synthesized magnetite in a molar ratio of 65.0%, manganese carbonate: 25.0%, zinc oxide: 10.0% The ferrite raw material powder mixture was calcined in the air at a temperature of about 1000 ° C. for 2 hours, and then the calcined product was crushed and molded into a predetermined shape.

Then, the obtained molded body was fired as follows. That is, from room temperature to 800 ° C, 150 ° C /
The temperature is raised at a heating rate of hr, and further from 800 ° C. to 1050 ° C. at a heating rate of 40 ° C./hr.
The temperature of 050 ° C was maintained for 4 hours. During this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 3.0%. After that, the temperature was raised at a heating rate of 40 ° C./hr, and the temperature was held at 1220 ° C. for 2 hours to eliminate the hematite phase in the molded body. 1100 ° C
When the fired body immediately after heating and the fired body after being held at 1220 ° C. for 2 hours were taken out and the cross section inside the fired body was examined by an X-ray diffraction method, the former showed that the hematite phase remained. In the latter case, it was confirmed that the ferrite phase was 100%, and the hematite phase disappeared during this period. Meanwhile, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 1.0%.

Then, at a temperature rising rate of 150 ° C./hr, 13
The final firing operation was carried out by raising the temperature to 50 ° C. and holding it there for 8 hours. Further, during this firing, the firing atmosphere was a nitrogen atmosphere having an oxygen concentration of 1.0%. Then, after such firing, a cooling step at 1100 ° C. or lower was performed in a nitrogen atmosphere to obtain a desired ferrite fired body (polycrystalline body). This polycrystal had an average grain size of 9.2 μm, a porosity of 0.009%, and a discontinuous grain growth temperature of 1380 ° C.

Further, the polycrystal thus obtained was cut into a size of 5 mm × 5 mm × 10 mm, and the heat treatment was carried out by the same method as in Example 1 to change the porosity after the heat treatment. Examined.

EXAMPLE 5 Ferric oxide obtained by roasting hydrothermally synthesized magnetite in a molar ratio of 66.5%, manganese carbonate: 17.0%, zinc oxide: 16.5%. The ferrite raw material powder mixture was calcined in the air at a temperature of about 1000 ° C. for 2 hours, and then the calcined product was crushed and molded into a predetermined shape.

Then, the obtained molded body was fired as follows. That is, from room temperature to 800 ° C, 150 ° C /
The temperature is raised at a heating rate of hr and further from 800 ° C. to 1000 ° C. at a heating rate of 40 ° C./hr, and 1
It was kept at a temperature of 000 ° C. for 4 hours. During the firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 10%. After that, the temperature was raised at a heating rate of 40 ° C./hr, and the temperature was kept at 1200 ° C. for 2 hours to eliminate the hematite phase in the molded body. 1100 ° C
When the fired body immediately after heating and the fired body after being held at 1200 ° C. for 2 hours were taken out in the middle and the cross section inside the fired body was examined by X-ray diffraction method, the former had a hematite phase, whereas In the latter case, it was confirmed that the ferrite phase was 100%, and the hematite phase disappeared during this period. Meanwhile, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 3%.

Next, at a temperature rising rate of 150 ° C./hr, 13
The final firing operation was carried out by raising the temperature to 50 ° C. and holding at that temperature for 8 hours. Also, during this firing
The firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 0.5%. Then, after such firing, a cooling step at 1100 ° C. or less was performed in a nitrogen atmosphere to obtain a desired ferrite fired body (polycrystalline body). This polycrystal has an average particle size of 1
It was 0.5 μm, porosity: 0.008%, discontinuous grain growth temperature: 1410 ° C.

Further, the polycrystal thus obtained was cut into a size of 5 mm × 5 mm × 10 mm, and the heat treatment was carried out by the same method as in Example 1 to change the porosity after the heat treatment. Examined.

Example 6 Ferric oxide obtained by roasting hydrothermally synthesized magnetite in a molar ratio of 67.5%, manganese carbonate: 20.5%, zinc oxide: 12.0%. The ferrite raw material powder mixture was calcined in the air at a temperature of about 1000 ° C. for 2 hours, and then the calcined product was crushed and molded into a predetermined shape.

Then, the obtained molded body was fired as follows. That is, from room temperature to 800 ° C, 150 ° C /
The temperature is raised at a heating rate of hr, and further from 800 ° C. to 1100 ° C. at a heating rate of 35 ° C./hr.
Hold at a temperature of 100 ° C. for 4 hours. The firing atmosphere during this firing was a nitrogen atmosphere with an oxygen concentration of 20%. After that, the temperature is raised at a heating rate of 35 ° C./hr, and 1
By holding at a temperature of 250 ° C. for 2 hours, the hematite phase in the molded body was extinguished. Incidentally, when the fired body immediately after being heated to 1100 ° C. and the fired body after being held at 1250 ° C. for 2 hours were taken out halfway and the cut surface inside the fired body was examined by an X-ray diffraction method, the hematite phase remained in the former case. In contrast, the latter is 100% ferrite phase,
During this period, it was confirmed that the hematite phase had disappeared.
Meanwhile, the firing atmosphere is a nitrogen atmosphere having an oxygen concentration of 5%.

Then, at a temperature rising rate of 150 ° C./hr, 13
The final firing operation was carried out by raising the temperature to 70 ° C. and holding at that temperature for 8 hours. Further, during this firing, the firing atmosphere was a nitrogen atmosphere having an oxygen concentration of 0.3%. Then, after such firing, a cooling step at 1100 ° C. or lower was performed in a nitrogen atmosphere to obtain a desired ferrite fired body (polycrystalline body). This polycrystal had an average grain size of 10.3 μm, a porosity of 0.01%, and a discontinuous grain growth temperature of 1430 ° C.

Further, the polycrystal thus obtained was cut into a size of 5 mm × 5 mm × 10 mm, and the heat treatment was carried out in the same manner as in Example 1 to change the porosity after the heat treatment. Examined.

Comparative Example 1 Ferric oxide obtained by roasting hydrothermally synthesized magnetite in a molar ratio of 58.0%, manganese carbonate: 24.0%, zinc oxide: 18.0%. The ferrite raw material powder mixture was calcined in the air at a temperature of about 1000 ° C. for 2 hours, and then the calcined product was crushed and molded into a predetermined shape.

Then, the obtained molded body was fired as follows. That is, from room temperature to 800 ° C, 150 ° C /
The temperature is raised at a heating rate of hr, and further from 800 ° C. to 1000 ° C. at a heating rate of 40 ° C./hr, and then 1
It was kept at a temperature of 000 ° C. for 4 hours. During this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 0.05%. After that, the temperature was raised at a heating rate of 40 ° C./hr and the temperature was held at 1200 ° C. for 2 hours. In addition,
Immediately after raising the temperature to 1100 ° C., the fired body was taken out in the middle, and the cross section inside the fired body was examined by X-ray diffraction.
It was confirmed that it was a 0% ferrite phase and the hematite phase had already disappeared. Meanwhile, the firing atmosphere is
A nitrogen atmosphere having an oxygen concentration of 0.5% was used.

Then, at a temperature rising rate of 150 ° C./hr, 13
The final firing operation was carried out by raising the temperature to 50 ° C. and holding at that temperature for 8 hours. During the firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 10%. Then, after such firing, a cooling step at 1100 ° C. or lower was performed in a nitrogen atmosphere to obtain a desired ferrite fired body (polycrystalline body). This polycrystal had an average grain size of 10.5 μm, a porosity of 0.03%, and a discontinuous grain growth temperature of 1470 ° C.

Further, the polycrystal thus obtained was cut into a size of 5 mm × 5 mm × 10 mm, and the heat treatment was carried out by the same method as in Example 1 to change the porosity after the heat treatment. Examined.

COMPARATIVE EXAMPLE 2 Ferric oxide obtained by roasting hydrothermally synthesized magnetite in a molar ratio of 70.0%, manganese carbonate: 15.0%, zinc oxide: 15.0%. The ferrite raw material powder mixture was calcined in the air at a temperature of about 1000 ° C. for 2 hours, and then the calcined product was crushed and molded into a predetermined shape.

Then, the obtained molded body was fired as follows. That is, from room temperature to 800 ° C, 150 ° C /
The temperature is raised at a heating rate of hr, and further from 800 ° C. to 1000 ° C. at a heating rate of 40 ° C./hr, and then 1
It was kept at a temperature of 000 ° C. for 4 hours. During this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 30%. After that, the temperature was raised at a heating rate of 40 ° C./hr and the temperature was held at 1200 ° C. for 2 hours. Note that 120
When the fired body held at 0 ° C. for 2 hours was taken out in the middle and the cross-section inside the fired body was examined by X-ray diffraction, it was confirmed that the hematite phase remained and during this period, the ferrite formation was not completed. Meanwhile, the atmosphere has an oxygen concentration of 1%.
And a nitrogen atmosphere.

Next, at a temperature rising rate of 150 ° C./hr, 13
The final firing operation was carried out by raising the temperature to 50 ° C. and holding at that temperature for 8 hours. During this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 0.1%. Then, after such firing, a cooling step at 1100 ° C. or lower was performed in a nitrogen atmosphere to obtain a desired ferrite fired body (polycrystalline body). This polycrystal had an average grain size of 10.3 μm, a porosity of 0.05%, and a discontinuous grain growth temperature of 1460 ° C.

Further, the polycrystal thus obtained was cut into a size of 5 mm × 5 mm × 10 mm, and the heat treatment was carried out in the same manner as in Example 1 to change the porosity after the heat treatment. Examined.

Comparative Example 3 Ferric oxide obtained by roasting hydrothermally synthesized magnetite in a molar ratio of 52.5%, manganese carbonate: 31.0%, zinc oxide: 16.5%. The ferrite raw material powder mixture was calcined in the air at a temperature of about 1000 ° C. for 2 hours, and then the calcined product was crushed and molded into a predetermined shape.

Then, the obtained molded body was fired as follows. That is, from room temperature to 800 ° C, 150 ° C /
The temperature is raised at a heating rate of hr and further from 800 ° C. to 1000 ° C. at a heating rate of 40 ° C./hr, and 1
It was kept at a temperature of 000 ° C. for 4 hours. During this time, 10 ^-3 torr
The following vacuum atmosphere was used. Incidentally, when the fired body held at 1000 ° C. for 4 hours was taken out in the middle and the cross-section inside the fired body was examined by X-ray diffraction method, it was found to be 100% ferrite phase, and the hematite phase had already disappeared. It was confirmed. After that, the temperature was raised at a heating rate of 40 ° C./hr and the temperature was held at 1200 ° C. for 2 hours.
During this period, a vacuum atmosphere of 10 ⁻³ torr or less was set.

Next, at a temperature rising rate of 150 ° C./hr, 13
The final firing operation was performed by raising the temperature to 50 ° C. and maintaining the temperature for 8 hours. During this firing, the atmosphere was a nitrogen atmosphere with an oxygen concentration of 1%.
Then, after such firing, a cooling step at 1100 ° C. or lower was performed in a nitrogen atmosphere to obtain a desired ferrite fired body (polycrystalline body). This polycrystal has an average grain size of 8.
5 μm, porosity: 0.008%, discontinuous grain growth temperature: 1
It was 420 ° C.

The polycrystal thus obtained was cut into a size of 5 mm × 5 mm × 10 mm, and the heat treatment was carried out in the same manner as in Example 1 to change the porosity after the heat treatment. Examined.

Comparative Example 4 A composition of ferric oxide: 63.5%, manganese carbonate: 22.5%, zinc oxide: 14.0% obtained by roasting hydrothermally synthesized magnetite in a molar ratio. The ferrite raw material powder mixture was calcined in the air at a temperature of about 1000 ° C. for 2 hours, and then the calcined product was crushed and molded into a predetermined shape.

Then, the obtained molded body was fired as follows. That is, from room temperature to 800 ° C, 150 ° C /
The temperature is raised at a heating rate of hr, and further from 800 ° C. to 1000 ° C. at a heating rate of 40 ° C./hr, and then 1
It was kept at a temperature of 000 ° C. for 4 hours. And during that time, 1
The vacuum atmosphere was set to 0 ^-3 torr or less. After that, 40 ℃
The temperature was raised at a heating rate of / hr and the temperature was kept at 1200 ° C for 2 hours. During this period, a vacuum atmosphere of 10 ⁻³ torr or less was set. The fired body immediately after being heated to 1100 ° C. was taken out on the way and the cross section inside the fired body was examined by an X-ray diffraction method to find that the ferrite phase was 100% and the hematite phase had already disappeared. It was confirmed.

Then, at a temperature rising rate of 150 ° C./hr, 13
The final firing operation was performed by raising the temperature to 50 ° C. and maintaining the temperature for 8 hours. The firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 1%. After the firing, a cooling step at 1100 ° C. or less is performed in a nitrogen atmosphere to obtain a desired ferrite fired body (polycrystalline body).
Got This polycrystal had an average grain size of 9.8 μm, a porosity of 0.06%, and a discontinuous grain growth temperature of 1500 ° C.

Further, the polycrystal thus obtained was cut into a size of 5 mm × 5 mm × 10 mm, and the heat treatment was carried out in the same manner as in Example 1 to change the porosity after the heat treatment. Examined.

Comparative Example 5 Ferric oxide obtained by roasting hydrothermally synthesized magnetite in a molar ratio of 63.5%, manganese carbonate: 22.5%, zinc oxide: 14.0%. The ferrite raw material powder mixture was calcined in the air at a temperature of about 1000 ° C. for 2 hours, and then the calcined product was crushed and molded into a predetermined shape.

Then, the obtained molded body is
Pre-baking was performed at a temperature of ° C for 2 hours in a nitrogen atmosphere having an oxygen concentration of 10%. The temperature rise and fall at this time is 300 ° C
/ Hr and a nitrogen atmosphere was used at 1100 ° C or lower.

Then, the following HIP process was performed. In order to prevent reduction, Mn-Zn ferrite powder having substantially the same composition was filled around the pre-fired body and Ar
Firing was performed as follows using gas as a pressure medium. The pressure was 1000 kg / cm ² , the temperature was 1300 ° C., and the treatment was performed for 2 hours. The temperature was raised and lowered at 300 ° C./hr, and the pressure was raised and lowered at about 1000 ° C. After the HIP, an annealing treatment was performed under the same conditions as the preliminary firing to obtain a target ferrite sintered body.

-Performance Comparison-Characteristics of various ferrite sintered bodies obtained in Examples 1 to 6 and Comparative Examples 1 to 5, that is, porosity, 10 Oe.
The saturated magnetic flux density and the porosity after the heat treatment were examined, and the results are shown in Table 1 below.

[0069]

[Table 1]

As is clear from the results shown in Table 1, in the ferrite sintered bodies of Examples 1 to 6 according to the present invention,
Saturation magnetic flux density is extremely high and porosity is 0.0
It is 1% or less, and further, such a porosity does not change even after the heat treatment, and it is recognized that there is no resuscitation of the pores.

In contrast, the ferrite sintered bodies of Comparative Examples 1 and 3 having a low iron oxide mol% have a low saturation magnetic flux density, and when the iron oxide mol% is high, Comparative Examples 2, 4 and 5 It is recognized that the porosity increases as the ferrite sintered body has a high porosity or the pores are revived by heating.

[0072]

As is clear from the above description, the high-density polycrystalline ferrite according to the present invention has a high saturation magnetic flux density (B ₁₀ ) of 5800 G or more and a small change in magnetic permeability with respect to frequency. , Which can be suitably used as a magnetic head material for a high coercive force magnetic recording medium,
Further, when the porosity is 0.01% or less, it can be suitably used as a ferrite material that does not impair the sliding characteristics of the magnetic head. Further, since the high-density polycrystalline ferrite according to the present invention does not substantially increase in porosity even after heat treatment at 1000 ° C. or higher, it is advantageously used as a single crystallizing material by solid-state reaction, In particular, it is a material that solves the problem of pore revival due to heating, which has a low single crystallization temperature in the single crystal crystallization method by solid-state reaction, produces few heterogeneous crystals.

Claims (1)

[Claims] 1. A composition having a molar ratio of 60 to 68% ferric oxide, 10 to 20% zinc oxide and 30 to 12% manganese oxide, and a saturation magnetic flux density (B ₁₀ ). Is 5
The porosity (P) defined in the text is 800.
A high density polycrystalline ferrite characterized in that the porosity does not substantially increase in a heat treatment at a temperature of 01% or less and 1000 ° C. or more.