JPH0796475B2 - Method for producing single crystal ferrite - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a single crystal ferrite in which a polycrystal and a single crystal are brought into contact with each other and heated, and a single crystal is grown and grown by a solid phase reaction.

[0002]

2. Description of the Related Art Conventionally, a method for producing Mn-Zn ferrite by a solid-phase reaction method in which a polycrystal and a single crystal are brought into contact with each other and heated, and a single crystal is grown and grown by the solid-state reaction, is disclosed in, for example, Japanese Patent Publication No. It is known in Japanese Patent Publication No. 61-10438 and Japanese Patent Publication No. 61-3313.

However, the above-mentioned manufacturing method has a problem that a large number of pores are generated in the grown and grown single crystal ferrite, and the material cannot be a suitable material depending on the conditions.

[0004]

With respect to this point, it is considered that if the porosity in the polycrystal used for the solid phase reaction is reduced, the porosity in the grown single crystal will be reduced. It is known to reduce the porosity of the.

However, even if the porosity in the polycrystal is reduced, the porosity in the single crystal grown by subsequent high temperature heating for growing the single crystal increases, which is preferable as a product, that is, 1 μm or more. It was not possible to obtain a product with less than 20 pores per 0.54 mm ² and less than 0.01% in terms of porosity.

This is because the single crystal growth by the solid-phase reaction method is usually processed at a temperature higher than a general annealing temperature, that is, at a high temperature of about 1300 ° C. to 1560 ° C., so that apparently disappeared pores are revived. It was because of it.

Further, Japanese Patent Laid-Open No. 62-41797 by the present applicant discloses a technique of growing a single crystal ferrite and then subjecting the obtained single crystal ferrite to a pressure heat treatment by a hot isostatic pressing method. .

However, in this method, when a magnetic head is used, the magnetizing noise is large, that is, the coercive force Hc contributing to the magnetizing noise is 0.05 Oe or less, which exceeds the condition required for the magnetic head and deteriorates to about 0.1 Oe. There was a problem.

The object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a method for producing a single crystal ferrite, which has few pores in the single crystal ferrite grown by the solid-state reaction method and has a long single crystal growth distance, which is suitable for mass production.

[0010]

The method for producing a single crystal ferrite according to the present invention comprises producing a compact from a ferrite raw material mainly using iron oxide having a spinel structure as iron oxide or having a history thereof. The molded body is vacuum-treated in the temperature range of 1100 ° C to 1280 ° C and then fired in a helium atmosphere or a helium atmosphere containing oxygen of 3% or less and cooled in nitrogen, or immediately after the vacuum treatment, cooled in nitrogen. Primary calcination, average particle size 10μm
The following sintered body is produced, and the sintered body is fired in a temperature range of 1150 ° C to 1350 ° C at a temperature equal to or higher than the primary firing temperature under a hydrostatic pressure of 60 kg / cm ² or more. After firing, a polycrystalline ferrite sintered body is produced that has grown to a grain size larger than the average particle diameter of the sintered body after the primary firing, and this polycrystalline ferrite sintered body is bonded to a seed single crystal, and this bonding is performed. It is characterized in that the body is heat-treated in a nitrogen atmosphere containing nitrogen or 3% or less of oxygen in the temperature range of 1300 ° C to 1560 ° C above the temperature of the second firing.

[0011]

In the above-mentioned structure, first, the ferrite molded body is subjected to a predetermined primary firing in a low oxygen atmosphere to increase the amount of oxygen vacancies, and then subjected to a predetermined HIP treatment (hydrostatic pressing treatment). In the secondary calcination used, the treatment temperature was raised from the primary calcination, the grains were grown from the primary calcination, the grain boundaries were shifted, the polycrystalline ferrite with pores diffused in the bulk was brought into contact with the seed single crystal ferrite, and the prescribed heating was performed. Since the solid-phase reaction is carried out by the treatment, it is possible to obtain a single crystal having a long crystal growth distance with few pores in the grown single crystal ferrite.

Here, since the temperature for carrying out the solid-phase reaction after HIP treatment is 1300 ° C. to 1560 ° C., which is higher than the treatment temperature before that, it seems that stomatal resuscitation occurs as in the conventional case, but in the present invention, Focusing on the movement of grain boundaries along with the grain growth of HIP treatment of polycrystalline ferrite, by increasing the amount of oxygen vacancies produced and selecting a low oxygen concentration, there is little pore resuscitation and virtually no pores. A suitable single crystal ferrite close to is obtained.

The temperature and pressure are defined as the conditions for HIP firing because this range is the temperature at which grain growth substantially occurs, and the pressure is such that HIP treatment can reduce pores. In addition, the pressure is 2000 in the temperature range of the present invention.
Even if the weight is increased up to kg / cm ^{2, the} liquid phase substance
FeO was not generated.

The firing atmosphere and the temperature are defined as the single crystal growth conditions in the solid-state reaction, because the pore revival is small within this range.

The reason why the single crystal growth distance is long in the present invention is as follows. First, the first reason is that in the spinel unit lattice that constitutes ferrite, if the presence of oxygen is small, the lattice unit becomes unstable and the driving force required for single crystallization becomes small. For this reason, the force for maintaining the polycrystal is weak, the single crystal growth temperature is slightly lowered, or the abnormal growth start temperature and the single crystal growth temperature are separated from each other, and single crystal formation from a heterogeneous crystal is suppressed.

The second reason is that the polycrystal has a large amount of oxygen vacancies, the spinel lattice is distorted by the pressure applied to the ferrite during the HIP treatment, and the HIP treatment itself acts as a reducing action on the ferrite. This is because the driving force is easily increased by the subsequent heating from the outside, and the single crystal growing distance can be lengthened. In fact, in the case of single crystallization, the growth distance of the single crystal was increased because the outside of the sample was rapidly expanded and the polycrystal was covered with the single crystal grown before the generation of the heterogeneous crystal.

It is essential for the production of single crystal ferrite that the iron oxide raw material used for producing the ferrite molded body has a spinel structure or a history thereof, as conventionally known. Therefore, the raw material is specified also in the present invention.

[0018]

[Examples] Wet-synthesized magnetite as an iron oxide raw material was roasted, and MnO 31.0mol%, ZnO 16.4mol%, Fe ₂ O ₃
The mixture was compounded to a composition of 52.6 mol%, mixed, calcined at 1050 ° C., ground, and molded at 35000 psi.

This molded body was prepared by using a rotary pump.
After raising the temperature to 800 ° C. at a temperature rising rate of 0 ° C./h, the temperature was changed to 40 ° C./h and the temperature was raised to 1000 ° C. After holding at this temperature for 8 hours, the temperature was raised to 1060 ° C at a heating rate of 10 ° C / h,
Hold at this temperature for 8 hours. Further, the temperature was raised at a heating rate of 10 ° C./h to the primary firing temperature within and outside the scope of the present invention shown in Table 1 below, and this temperature was maintained for 8 hours.

After this, the firing atmosphere was changed to H as shown in Table 1.
e atmosphere (displayed as 0% oxygen concentration) or O _{2 at} 3% or less
After holding in a He atmosphere containing He for 4 hours, switch to an N ₂ atmosphere and cool, or immediately switch to nitrogen as shown in Table 2 and then cool to 950 ° C at a temperature lowering rate of 300 ° C / h, and then stop and seal nitrogen. . An example of the obtained polycrystalline ferrite had a porosity of 0.5% and a crystal grain size of 7.1 μm.

The obtained polycrystalline ferrite was set in an alumina crucible without using any embedded powder under the use of Gr-HIP N ₂ gas, and the temperature was raised at a heating rate of 300 ° C./h. 60 kg / cm ² at a temperature within and outside the range of the present invention shown in 2 for 3 hours.
After that, HIP treatment was carried out, and then cooling was performed. An example of the obtained polycrystalline ferrite has 2 pores / 0.54 mm ² ,
The crystal particle size was 8.2 μm. Further, in the polycrystalline ferrite according to the conditions within the scope of the present invention, precipitation of FeO 2 accompanying reduction was not observed.

The obtained polycrystalline ferrite is cut and polished under the conventional processing conditions of ferrite, and the polished polycrystalline ferrite and the seed single crystal are temporarily joined with nitric acid,
It is placed in an alumina bowl with the inside covered with ferrite, heated in a nitrogen atmosphere at a heating rate of 300 ° C / h, and heated to 1150 ° C in Table 1.
The atmosphere was switched to a nitrogen atmosphere having oxygen concentrations within and outside the range of the present invention as shown in FIG.

After that, the temperature was further raised at a heating rate of 300 ° C./h to reach 1340 ° C., and then the temperature was switched to a heating rate of 15 ° C./h to grow a single crystal. Further, the same atmosphere was maintained up to 1480 ° C., and thereafter, the temperature was raised to 300 ° C./h, the atmosphere was changed to nitrogen-only atmosphere, the temperature was kept at 1500 ° C. for 0.5 h to eliminate subgrains, and then cooled in a nitrogen atmosphere.

For each bonded body, there was no subgrain of the single crystal ferrite obtained by growing. The growth distance is
The distance was calculated as the grown distance of the single crystal ferrite from the joint surface between the seed single crystal ferrite and the polycrystalline ferrite. Also, the number of pores is 1000 on the surface finished with a high-speed lapping machine.
The pores of 1 μm or more in the double scale visual field were determined by visual observation with an optical microscope. The results are also shown in Table 1. The porosity is calculated by the following formula 1.

[Formula 1] However, d _i: pore diameter (major axis), n _i: was determined from the number of the pore diameter d _i.

[0025]

[Table 1]

[0026]

[Table 2]

From the results of Tables 1 and 2, the test Nos. 1 to 11 and Nos. 19 to 22 within the scope of the present invention have few pores in the single crystal grown and have a large single crystal growth distance. It can be seen that in Test Nos. 12 to 18 and Nos. 23 to 25, which are outside the scope of the present invention, the single crystal has many pores and the single crystal growth distance is small. In addition, μ of the magnetic characteristics of the single crystal ferrite of the present invention test No.
The characteristics are 0.1MHz = 4800, 1MHz = 2400, and in the comparative example test No. 14 outside the scope of the present invention, 0.1MHz = 1800, 1MHz = 1100, and in the present invention example, the magnetic characteristics are significantly improved compared to the comparative example. You can see that it is done.

[0028]

As is apparent from the above description, according to the method for producing a single crystal ferrite of the present invention, a predetermined ferrite compact is subjected to primary firing at a predetermined temperature and atmosphere,
The number of pores in the grown single crystal is reduced by performing secondary calcination by HIP treatment at a predetermined temperature and pressure after that, and heat treatment for solid phase reaction at a predetermined temperature and atmosphere after joining with the seed single crystal. Since it is possible to increase the single crystal growth distance, it is possible to mass-produce single crystal ferrite having good magnetic characteristics.

The single crystal ferrite obtained according to the present invention does not require any embedded powder in its production,
-HIP N ₂ gas treatment did not cause any problems such as precipitation of FeO due to reduction, or reduction in grain boundary strength and poor machining. The single crystal thus obtained has a significantly improved porosity as compared with the single crystal obtained by the conventional solid-phase reaction, so it becomes a substrate for RDDs or VTRs with strict size specifications and excellent head characteristics. Became.

Claims (1)

[Claims] 1. An iron oxide having a spinel structure,
Alternatively, a molded body is produced from a ferrite raw material mainly using iron oxide having that history, and
After vacuum treatment in the temperature range of 00 ° C to 1280 ° C, switch to a helium atmosphere or a helium atmosphere containing 3% or less of oxygen and bake and cool in nitrogen, or immediately after the vacuum treatment, cool in nitrogen. Calcinated, average particle size 10
We made a sintered body of μm or less, and weighed 60kg / c for this sintered body.
A m ² or more under hydrostatic pressure primary firing temperature above 1150
Perform the secondary firing to fire in the temperature range of ℃ to 1350 ℃,
A polycrystalline ferrite sintered body was produced by grain growth larger than the average particle diameter of the sintered body after the primary firing, and this polycrystalline ferrite sintered body was bonded to a seed single crystal, and this bonded body was 1. A method for producing a single crystal ferrite, which comprises heat-treating in a nitrogen atmosphere containing nitrogen or 3% or less of oxygen in a temperature range of 1300 ° C. to 1560 ° C. which is higher than a temperature of the subsequent firing.