JPH04240195A - Production of single-crystalline ferrite - Google Patents

Abstract

PURPOSE:To obtain single-crystalline ferrite nearly free from pores and grown over a long range by joining polycrystalline ferrite to single-crystalline ferrite as a seed, heating them and growing the single-crystalline ferrite by a solid phase reaction. CONSTITUTION:A prescribed ferrite sintered body is successively subjected to primary firing by treatment at 1,100-1,280 deg.C in vacuum, calcining in an He atmosphere or an He atmosphere contg. <=3% oxygen and cooling in N2 or by the treatment and cooling and to secondary calcining by hot isostatic pressing at 1,150-1,350 deg.C above the primary calcining temp. under >=60kg/cm<2> pressure to obtain polycrystalline ferrite. This ferrite is joined to single-crystalline ferrite as a seed and they are heated at 1,300-1,560 deg.C in nitrogen or a nitrogen atmosphere contg. <=3% oxygen to produce single-crystalline ferrite by a solid phase reaction.

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 single crystal ferrite in which a polycrystal and a single crystal are brought into contact with each other and heated to grow a single crystal through a solid phase reaction.

0002

[Prior Art] Conventionally, a method for manufacturing Mn-Zn ferrite using a solid phase reaction method in which a polycrystalline body and a single crystalline body are brought into contact with each other and heated to grow and grow a single crystal through the solid phase reaction has been described, for example, by Publication No. 61-10438 and Special Publication No. 61
It is known from the publication No. 3313.

However, in the above-mentioned manufacturing method, there is a problem that many pores are generated in the grown single crystal ferrite, and the material is not suitable depending on the conditions.

0004

[Problem to be solved by the invention] Regarding this point, it is thought that if the pores in the polycrystalline material used for the solid phase reaction are reduced, the pores in the grown single crystal will also be reduced. is known to reduce pores.

However, even if the pores in the polycrystal are reduced, the number of pores in the single crystal grown by high-temperature heating for subsequent single crystal growth increases. The pore size is 0.54
It was not possible to obtain a product with 20 particles or less per mm2, or 0.01% or less in terms of porosity.

[0006] This means that single crystal growth using the solid phase reaction method is performed at a temperature higher than the general annealing temperature, that is, from 1300°C to 15°C.
This is because the treatment is carried out at a high temperature of about 60° C., which causes the stomata that had seemingly disappeared to be revived.

[0007] Also, Japanese Patent Application Laid-Open No. 62-4179 by the applicant
No. 7 discloses a technique of growing single crystal ferrite and then subjecting the obtained single crystal ferrite to pressure heat treatment using a hot isostatic pressing method.

However, with this method, when a magnetic head is used, the magnetization noise is large, that is, the coercive force Hc contributing to the magnetization noise exceeds the necessary condition for a magnetic head of 0.05 Oe or less, and deteriorates to about 0.1 Oe. There was a problem sometimes.

[0009] The purpose of the present invention is to solve the above-mentioned problems,
The present invention aims to provide a method for producing single crystal ferrite grown by a solid-phase reaction method, which has fewer pores, a longer single crystal growth distance, and is suitable for mass production.

0010

[Means for Solving the Problems] The method for producing single-crystal ferrite of the present invention involves producing a molded body from a ferrite raw material mainly using iron oxide having a spinel structure or a history of spinel structure as iron oxide. For the molded body,
After vacuum treatment in a temperature range of 1100°C to 1280°C, firing is performed in a helium atmosphere or a helium atmosphere containing 3% or less oxygen and cooling in nitrogen, or primary firing is performed by cooling in nitrogen immediately after the vacuum treatment. and average particle size 1
A sintered body with a diameter of 0 μm or less is produced, and a
A second firing is performed under a hydrostatic pressure of 0 kg/cm2 or more at a temperature higher than the first firing temperature and in a temperature range of 1150°C to 1350°C, and the average particle diameter of the sintered body after the first firing is A polycrystalline ferrite sintered body with larger grain growth is produced, this polycrystalline ferrite sintered body is joined to a seed single crystal, and this joined body is heated at a temperature higher than the second firing temperature to 130°C.
It is characterized by heat treatment in a temperature range of 0° C. to 1560° C. in nitrogen or a nitrogen atmosphere containing 3% or less oxygen.

[0011]

[Operation] In the above-described structure, first, the ferrite molded body is subjected to a prescribed primary firing in a low oxygen atmosphere to increase the amount of oxygen vacancies, and then subjected to a prescribed HIP treatment (hydrostatic pressing treatment). In the secondary firing used, the treatment temperature was higher than that in the primary firing, and the polycrystalline ferrite, which had been made to grow grains by shifting the grain boundaries and diffusing pores into the bulk, was brought into contact with the seed single-crystal ferrite, and heated to a predetermined temperature. Since a solid phase reaction is carried out during the treatment, there are few pores in the grown single crystal ferrite, and a single crystal with a long crystal growth distance can be obtained.

[0012] Here, since the temperature at which the solid phase reaction is carried out after the HIP treatment is 1300°C to 1560°C, which is higher than the previous treatment temperature, stomatal resuscitation seems to occur as in the conventional case, but in the present invention, Focusing on the movement of grain boundaries as grains grow during HIP treatment of polycrystalline ferrite, by increasing the amount of oxygen vacancies generated and selecting a low oxygen concentration, pore regeneration is minimal and there are virtually no pores. A suitable single-crystal ferrite close to the above was obtained.

[0013] The reason why the temperature and pressure were specified as the conditions for HIP firing is that this range is the temperature at which grain growth substantially occurs, and the pressure is such that the HIP treatment can reduce pores. Note that the pressure is 20% within the temperature range of the present invention.
Even when the weight was increased to 0.00 kg/cm2, FeO 2 , a liquid phase substance that would be an obstacle to single crystallization, was not generated.

The reason why the firing atmosphere and temperature are specified as the single crystal growth conditions in the solid phase reaction is that within these ranges, pore regeneration is less likely to occur.

Furthermore, the reason why the single crystal growth distance is long in the present invention is as follows. The first reason is that in the spinel unit lattice that constitutes ferrite, if there is little oxygen, the lattice unit becomes unstable and the driving force required for single crystallization becomes small. For this reason, the power to maintain polycrystals is weak, and the single crystal growth temperature is slightly lowered, or the abnormal growth start temperature and the single crystal growth temperature are different, and the formation of a single crystal from a different type of crystal is suppressed.

The second reason is that the amount of oxygen vacancies in the polycrystal is large, and the spinel lattice is distorted due to the pressure applied to the ferrite during the HIP process, and the HIP process itself acts as a reducing effect on the ferrite. This is because when the crystal becomes unstable, the driving force can be easily increased by subsequent external heating, and the single crystal growth distance can be increased. In fact, during single crystallization, the outer side of the sample expanded quickly and was covered by the single crystal grown by polycrystals before the generation of foreign crystals, resulting in a longer single crystal growth distance.

[0017] As is conventionally known, it is essential for the production of single crystal ferrite that the iron oxide raw material used to produce the ferrite molded body has a spinel structure or a history thereof. Therefore, the present invention also specifies the raw materials.

[0018]

[Example] Wet-synthesized magnetite was roasted as a raw material for iron oxide, and mixed with 31.0 mol% of MnO and ZnO.
16.4 mol%, Fe2O3 52.6 mol%
After mixing, calcining at 1,050°C, and crushing, it was molded at 35,000 psi.

[0019] This molded body was pumped using a rotary pump.
After heating up to 800°C at a heating rate of 50°C/h,
The temperature was increased to 1000°C by changing the heating rate to 0°C/h. After holding at this temperature for 8 hours, the temperature was raised to 1060°C at a heating rate of 10°C/h and held at this temperature for 8 hours. Furthermore, the temperature was raised at a heating rate of 10° C./h to the primary firing temperature within and outside the range of the present invention shown in Table 1 below, and held at this temperature for 8 hours.

After that, the firing atmosphere was changed to H as shown in Table 1.
e atmosphere (displayed as 0% oxygen concentration) or 3% or less O2
After being maintained in a He atmosphere containing He for 4 hours, the atmosphere was changed to N2 for cooling, or as shown in Table 2, the atmosphere was immediately changed to nitrogen, and thereafter, the atmosphere was cooled to 950° C. at a rate of 300° C./h, and the nitrogen gas was stopped and sealed. The porosity of an example of the obtained polycrystalline ferrite was 0.5%, and the crystal grain size was 7.1%.
It was μm.

[0021] The obtained polycrystalline ferrite was subjected to Gr-HIP
The crucible was placed in an alumina crucible without powder using N2 gas, and the temperature was raised at a rate of 300 °C/h. Table 1
and 3 at temperatures within and outside the invention range shown in Table 2.
After performing HIP treatment while maintaining the pressure at 60 kg/cm2 for an hour, the sample was cooled. The number of pores in an example of the obtained polycrystalline ferrite is 2/0.54 mm2, and the crystal grain size is 8.2.
It was μm. Further, in polycrystalline ferrite under conditions within the scope of the present invention, precipitation of FeO 2 due to reduction was not observed.

The obtained polycrystalline ferrite was cut and polished under conventional ferrite processing conditions, and the polished polycrystalline ferrite and seed single crystal were temporarily joined with nitric acid.
It was placed in an alumina sagger whose inside was covered with ferrite, and the temperature was raised at a rate of 300 °C/h in a nitrogen atmosphere to 115 °C.
At 0°C, the atmosphere was changed to a nitrogen atmosphere with an oxygen concentration within and outside the range of the present invention shown in Table 1, and maintained for 15 minutes.

Thereafter, the temperature was further increased at a rate of 300° C./h until reaching 1340° C., and then the rate was changed to 15° C./h to grow a single crystal. Furthermore, 1480℃
The same atmosphere was maintained until then, and thereafter the temperature was increased at a rate of 300° C./h, and the atmosphere was switched to a nitrogen-only atmosphere, and the temperature was maintained at 1500° C. for 0.5 h to eliminate subgrains, and thereafter, it was cooled in a nitrogen atmosphere.

[0024] For each bonded body, there were no single-crystal ferrite subgrains grown. The growth distance is
It was determined as the distance that the single crystal ferrite grew from the joint surface between the seed single crystal ferrite and the polycrystalline ferrite. In addition, the number of pores is 10
Pores of 1 μm or more within a 00x scale field of view were determined by visual observation using an optical microscope. The results are also listed in Table 1. In addition, the porosity is calculated using the following formula 1

[Formula 1] where di: pore diameter (longer diameter), ni: pore diameter di
It was calculated from the number of pieces.

[0025]

[Table 1]

[0026]

[Table 2]

From the results in Tables 1 and 2, it can be seen that in tests Nos. 1 to 11 and Nos. 19 to 22 within the scope of the present invention, the pores in the grown single crystals were small and the single crystal growth distance was large; Tests No. 12 to 18 and No. outside the scope of the present invention
It can be seen that samples Nos. 23 to 25 have many pores in the single crystal and the single crystal growth distance is short. In addition, the μ characteristic of the magnetic property of the single crystal ferrite of the present invention test No. 4 is 0.1 MHz = 48
00.1MHz=2400, and in comparative example test No. 14 outside the scope of the present invention, 0.1MHz=1800.1M
Hz=1100, and it can be seen that the magnetic properties of the inventive example are significantly improved compared to the comparative example.

[0028]

Effects of the Invention As is clear from the above explanation, according to the method for producing single crystal ferrite of the present invention, a predetermined ferrite molded body is subjected to primary firing at a predetermined temperature and atmosphere.
After that, the number of pores in the grown single crystal is reduced by performing secondary firing by HIP treatment at a predetermined temperature and pressure, and heat treatment for solid phase reaction at a predetermined temperature and atmosphere after joining with the seed single crystal. In addition, since the single crystal growth distance can be increased, single crystal ferrite having good magnetic properties can be mass-produced.

Furthermore, the single crystal ferrite obtained according to the present invention does not require powder in its production, and
Even in the treatment of r-HIP N2 gas, FeO is generated due to reduction.
There were no problems such as precipitation of grains or reduction in grain boundary strength resulting in poor machining. The single crystal thus obtained has significantly improved porosity compared to single crystals obtained by conventional solid-phase reactions, so it can be used as a substrate for RDDs or VTRs with strict dimensional specifications, and has excellent head characteristics. It became.

Claims (1)

[Claims] Claim 1: A molded body is produced from a ferrite raw material mainly using iron oxide that has a spinel structure or a history of spinel structure, and for this molded body,
After vacuum treatment in a temperature range of 1100°C to 1280°C, the first step is to switch to a helium atmosphere or a helium atmosphere containing 3% or less oxygen and then sinter it and cool it in nitrogen, or to cool it in nitrogen immediately after the vacuum treatment. Firing is performed to produce a sintered body with an average particle size of 10 μm or less, and the sintered body is heated at a temperature of 1150°C to 1350°C, which is higher than the temperature of the primary firing, under a hydrostatic pressure of 60 kg/cm2 or more. A polycrystalline ferrite sintered body is produced by performing a second firing in which the grains are grown to be larger than the average particle diameter of the sintered body after the first firing, and this polycrystalline ferrite sintered body is seeded as a single seed. A single crystal that is bonded to a crystal, and the bonded body is heat-treated in a temperature range of 1300°C to 1560°C above the temperature of the secondary firing in nitrogen or a nitrogen atmosphere containing 3% or less oxygen. Ferrite manufacturing method.