JPH0321498B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for producing high-density ferrite, and in particular to a method for producing high-density ferrite, which is highly densified, has few pores, and has excellent workability, and is suitable for use in magnetic heads. The present invention relates to a method for producing ferrite having a similar structure.

(Prior Art) High-density ferrite is widely used in magnetic heads for audio and magnetic disks, as well as substrates for thin film heads, and several methods have been proposed for its production.

In other words, as a method for manufacturing high-density ferrite, for example, the hot press method is known, in which uniaxial pressure is applied while heating and firing is performed ^. However, even if the pressurizing force is increased, the friction between the mold and the ferrite material does not apply a uniform force to the inside of the ferrite, so there is a disadvantage that it is difficult to obtain high-density ferrite with small particle size and few bubbles. In addition, regarding the production of high-density ferrite by high-pressure treatment, a method of hot isostatic pressing of ferrite material is also known, and according to this method, high pressures of several thousand kg/cm ² or more are possible. This requires the ferrite material to be temporarily sintered under normal pressure, which is a complicated process, and also has the disadvantage that part of the material may not be converted into spinel depending on the conditions. The process is complicated because it requires multiple heat treatment steps, such as the need for heat treatment in an equilibrium oxygen atmosphere, and there are disadvantages in that large-scale and expensive equipment is required.

(Structure of the Invention) The present invention relates to a method for producing high-density ferrite that solves these disadvantages. The product is characterized in that it is formed into a molded product having a weight of 3.0 g/cm ² or more, then degassed, then vacuum sintered and atmosphere sintered.

To explain this, the present inventors have conducted various studies on methods for manufacturing high-density ferrite, which has a dense structure with few pores and has excellent workability.
This starting material, ferrite material, is made into a reduced form with a lower oxygen content than the stoichiometric composition, and is molded to a density of 3.0 g/cm ² or more, then heated in a vacuum and degassed. However, they discovered that the desired high-density ferrite could be mass-produced at low cost by vacuum sintering and then atmosphere sintering. The present invention was completed by conducting research on methods and other matters.

The ferrite material used as the starting material in the method of the present invention may be any known sintered mixture of oxides such as iron oxide, manganese oxide, nickel oxide, zinc oxide, etc., but this material can be sintered in a vacuum. Since bubbles, crevasses, etc. are sometimes generated in the sintered body due to the release of oxygen due to the reduction action, it is necessary to make the sintered body have a slightly reduced oxygen content, which has a lower oxygen content than the stoichiometric composition. This may be, for example, 5 to 20% less oxygen than the stoichiometric composition. The reduced ferrite material can be obtained, for example, by calcining a mixture of metal oxides as a material at 1300 DEG C. to 1400 DEG C. for 5 to 10 hours in a nitrogen gas atmosphere. This calcined body is then crushed in a ball mill or the like to obtain a powder with a particle size of approximately 1 to 3 μm, and is made into a molded body for sintering. It is necessary to have a density of 3.0 g/cm ² or more, and for this purpose, it is preferable to mold the powder raw material using an impact molding machine or the like at a pressure of 5 tons/cm ^{2 or} more.

The ferrite material molded body obtained as described above is then sintered to produce sintered ferrite, but in order to obtain ferrite with fewer pores, it is necessary to degas the air between the particles of the molded body. There is. This is because the density of the molded body is increased, which improves the sinterability of the particles, traps gas between particles within the sintered body, and increases the number of pores. For effective degassing, 10 ^-4 ~
Temperature just before sintering begins in a vacuum of 10 ^-5 Torr
It is preferable to hold the temperature at 800 to 950°C for 10 hours, preferably for 20 hours or more. After sufficient degassing in this way, the temperature is raised while maintaining the vacuum and vacuum sintering is performed, but the speed of temperature rise at this time is
When sintering is carried out in a vacuum at an appropriate rate of 0.5 to 2°C/min, ferrite is in a state in which oxygen is deficient compared to its stoichiometric composition. Since it is necessary to have a theoretical composition, it is necessary to combine vacuum sintering and atmosphere sintering. This vacuum sintering may be performed under a vacuum of 10 ^-4 to 10 ^-5 torr at 1100° C. to 1350° C. for 0.5 to 5 hours, followed by normal pressure sintering in an equilibrium oxygen atmosphere. In this atmosphere sintering, the equilibrium oxygen atmosphere may be an oxygen-nitrogen mixed gas containing 0 to 5% oxygen. 5 at 1100-1350℃ in this atmosphere
Sintering can be performed for ~20 hours. The composition of this atmospheric gas is described in IEEE Transactions on Magnetics, vol.
It may be determined arbitrarily by referring to Mag-11, no. 5 (1975) P1312-1314, etc.

According to the method of the present invention, the oxygen-deficient and slightly reduced ferrite material used as the starting material is converted into a complete oxide by atmospheric sintering in the presence of oxygen;
In addition, since the compact is said to have a density of 30 g/cm ³ or more, high-density ferrite can be easily obtained with a single heating process without the need for equipment such as hot pressing or hot isostatic pressing. According to this method, the density is 5.1 g/cc or more, there are few pores, the magnetic flux density _B10 is 4000 to 6000 Gauss, and the coercive force Hc is 0.02 to 6000 Gauss.
Permeability at 0.10 oersted, 5MHz frequency
It is advantageous that a high-density polycrystalline ferrite having a characteristic of 500 to 1000 can be obtained industrially and at low cost with good mass production.

Next, examples of the present invention will be given.

Example High purity iron oxide and zinc oxide with a purity of 99.6% or more,
The final composition ratio is manganese carbonate with a purity of 93% or more.
53 mol% Fe ₂ O ₃ , 29 mol% MnO and 18 mol% ZnO were mixed in a steel ball mill pot containing pure water, and the slurry obtained by stirring and mixing for 15 hours was heated under pressure. The mixture was shaped into a cake and dried at 150°C for 48 hours.

Next, this was calcined at 1350℃ for 10 hours in a nitrogen gas atmosphere, and then heated to 70℃ in a steel ball mill using pure water as a dispersion medium.
The powder was ground for hours and dried at 100°C for 24 hours to obtain ferrite powder with a particle size of D ₅₀ =2 μm.

Next, add 1% PVA as a binder to this powder.
5% by weight of an aqueous solution was added and molded using an impact molding machine at a pressure of 5 tons/cm ³ to obtain a molded product of 15 mmφ×10 mm. This was dried in air at 100℃ for 168 hours to reduce the density.
A molded article weighing 3.2 g/cm ³ was obtained. Put this in a vacuum,
The temperature was raised to 900°C at a heating rate of 5°C/min under a vacuum of 1×10 ^-4 Torr, heated at 900°C for 24 hours, and then raised to 1250°C at a heating rate of 1°C/min. After that, the temperature was maintained for 30 minutes, 1% O ₂ -N ₂ gas was introduced as an atmospheric gas, and the temperature was maintained at 1250° C. for 2 hours. Thereafter, the atmosphere gas was changed and heated at 0.5% O ₂ - N ₂ for 1 hour, 0.3% O ₂ - N ₂ for 1 hour, 0.1% O ₂ - N ₂ for 1 hour, and then lowered at 10 °C/min. Raise the temperature at a high speed, from 1250℃ to 1000℃,
A ferrite polycrystal was obtained using a 0.06% O ₂ -N ₂ atmosphere and a 100% N ₂ atmosphere below 1000°C.

This polycrystalline ferrite has a density of 5.11 g/cm ³ and has very few pores.

Experimental example 1 (When raw material powder is not subjected to reduction treatment) High purity iron oxide with a purity of 99.6% or more and manganese carbonate with a zinc oxide purity of 93% or more are combined in a final composition ratio of 53
The slurry obtained by mixing in a steel ball mill pot containing pure water with mol% Fe ₂ O ₃ , 29 mol% MnO, and 18 mol% ZnO was pressurized and mixed for 15 hours. It was shaped into a cake and dried at 150°C for 48 hours.

Next, this was calcined in air at 1250° C. for 5 hours, pulverized in a steel ball mill using pure water as a dispersion medium for 100 hours, and dried at 100° C. for 24 hours to obtain ferrite powder with D ₅₀ =1.8 μm.

Next, add 1% PVA as a binder to this powder.
5% by weight of an aqueous solution was added and molded using an impact molding machine at a pressure of 5 tons/cm ² to obtain a molded product of 15 mmφ×10 mm. This was dried in air at 100℃ for 168 hours to reduce the density.
After making a 3.2g/ ^cm3 molded product, it was placed in a vacuum furnace.
The temperature was raised to 900°C at a heating rate of 5°C/min under a vacuum of ×10 ^-4 Torr, heated at 900°C for 24 hours, and then raised to 1250°C at a heating rate of 1°C/min. It was then held for 30 minutes. The subsequent atmosphere sintering was carried out under the same conditions as in Example 1, and the resulting ferrite polycrystalline body had a density of 5.05 g/cm ³ .

Experimental example 2 (without degassing step) Highly purified iron oxide and zinc oxide with a purity of 99.6% or more,
The final composition ratio is manganese carbonate with a purity of 93% or more.
The resulting slurry was mixed in a steel ball mill pot with pure water in an amount of 53 mol% Fe ₂ O ₃ , 29 mol% MnO, and 18 mol% ZnO, and then stirred and mixed for 15 hours. The mixture was shaped into a cake and dried at 150°C for 48 hours.

Next, this was calcined at 1350℃ for 10 hours in a nitrogen gas atmosphere, and then placed in a steel ball mill using pure water as a dispersion medium.
Grind for 70 hours and dry at 100℃ for 24 hours D ₅₀ = 2μm
ferrite powder was obtained.

Next, add 1% PVA as a binder to this powder.
5% by weight of an aqueous solution was added and molded using an impact molding machine at a pressure of 5 tons/cm ² to obtain a molded product of 15 mmφ×10 mm. This was dried in air at 100℃ for 168 hours, and the density
After forming a 3.2g/cm ² molded product, it was placed in a vacuum furnace.
The temperature was raised to 1250°C at a heating rate of 5°C/min under a vacuum of 1 × 10 ^-4 Torr and held for 30 minutes, and the subsequent atmosphere sintering was performed under the same conditions as in Example 1. , the density of the obtained ferrite polycrystal is
It was 5.07g/ ^cm3 .

Experimental example 3 (When molded to low density using a hydraulic molding machine) High purity iron oxide and zinc oxide with a purity of 99.6% or more,
The final composition ratio is manganese carbonate with a purity of 93% or more.
The slurry obtained by mixing pure water in a steel ball mill pot with pure water in an amount of 53 mol% Fe ₂ O ₃ , 29 mol% MnO, and 18 mol% ZnO was pressurized and mixed for 15 hours. It was shaped into a cake and dried at 150°C for 48 hours.

Next, this was calcined at 1350℃ for 10 hours in a nitrogen gas atmosphere, and then placed in a steel ball mill using pure water as a dispersion medium.
Grind for 70 hours and dry at 100℃ for 24 hours D ₅₀ = 2μm
ferrite powder was obtained.

Next, add 1% PVA as a binder to this powder.
5% by weight of an aqueous solution was added and molded using an impact molding machine at a pressure of 1 ton/cm ² to obtain a molded product of 15 mmφ×13 mm. This was dried in air at 100℃ for 168 hours, and the density
After forming a molded body of 2.5 g/cm ³ , a degassing step, vacuum sintering, and atmosphere sintering were performed under the same conditions as in Example 1 to obtain a ferrite polycrystalline body.

The thus obtained polycrystalline ferrite had a density of 5.0 g/cm ³ .

Experimental example 4 (when reduction treatment and deaeration process are omitted) High purity iron oxide and zinc oxide with a purity of 99.6% or more,
The final composition ratio is manganese carbonate with a purity of 93% or more.
53 mol% Fe ₂ O ₃ , 29 mol% MnO and 18 mol% ZnO were mixed in a steel ball mill pot with pure water, and the slurry obtained by stirring and mixing for 15 hours was filtered under pressure. The mixture was shaped into a cake and dried at 150°C for 48 hours.

Next, this was calcined in air at 1250° C. for 5 hours, pulverized in a steel ball mill using pure water as a dispersion medium for 100 hours, and dried at 100° C. for 24 hours to obtain ferrite powder with D ₅₀ =1.8 μm.

Next, add 1% PVA as a binder to this powder.
5% by weight of an aqueous solution was added and molded using an impact molding machine at a pressure of 5 tons/cm ² to obtain a molded product of 15 mmφ×10 mm. This was dried in air at 100℃ for 168 hours to reduce the density.
A molded article weighing 3.2 g/cm ² was obtained. This was placed in a vacuum furnace and heated to 1250°C at a rate of 5°C/min under a vacuum of 1×10 ^-4 Torr and held for 30 minutes, followed by atmosphere sintering under the same conditions as in Example 1. The density of the obtained ferrite polycrystal was 4.9.
g/ ^cm3 .

Claims (1)

[Claims] 1. A reduced ferrite material powder that is deficient in oxygen compared to the stoichiometric composition is made into a compact with a density of 3.0 g/cm ³ or more, degassed, and then vacuum sintered and atmosphere sintered. A method for producing high-density ferrite characterized by: