JP2000226606A - PRODUCTION OF SPINDLELIKE ALLOY MAGNETIC GRAIN POWDER ESSENTIALLY CONSISTING OF Fe AND Co FOR MAGNETIC RECORDING - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing spindlelike alloy magnetic grain powder essentially consisting of Fe and Co for magnetic recording which has high coercive force and high saturation magnetization value in spite of the small size of crystallites advantageously from the industrial and economical phases. SOLUTION: Spindlelike goethite grains of 0.05 to 0.15 μm major axis size contg. cobalt of 20 to 45 atomic % expressed in terms of Co to the whole Fe or spindlelike hematite grains obtd. by subjecting the goethite grains to dehydration under heating are used as a starting raw material, this starting raw material is charged into a fixed layer reducing device to form a fixed layer of <=30 cm layer height, thereafter, its temp. is raised to the temp. range of 400 to 700 deg.C in an inert gas atmosphere, next, it is changed over to a reducing gas atmosphere, and, after that, the starting raw material is reduced in the temp. range of 400 to 700 deg.C by reducing gas in which gas superficial velocity is 40 to 150 cm/s.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high coercive force, in particular a high saturation magnetization of 167.1 kA / m (2100 Oe) or more, in particular a small crystallite size, in particular of less than 160 °, in particular 135 Am ² / kg (135 em
The present invention relates to a method for producing a spindle-shaped alloy magnetic particle powder mainly composed of Fe and Co for magnetic recording, which has at least u / g) or more, in an industrially and economically advantageous manner.

[0002]

2. Description of the Related Art In recent years, devices for magnetic recording / reproducing for audio, video, and computers have been significantly reduced in size and weight, long-time recording, high-density recording, or an increase in storage capacity. Demands for higher performance and higher density recording of magnetic tapes and magnetic disks as magnetic recording media are increasing more and more.

That is, high image quality and high output characteristics of magnetic recording media, particularly, improvement of frequency characteristics, storage characteristics, and durability are required. For that purpose, reduction of noise due to the magnetic recording media, It is required that the coercive force Hc, the coercive force distribution SFD, and the weather resistance ΔBm be excellent.

[0004] These characteristics of the magnetic recording medium are closely related to the magnetic particle powder used in the magnetic recording medium, and in recent years, the coercive force is higher than that of the conventional iron oxide magnetic particle powder. And magnetic metal particles containing iron as a main component and having a large saturation magnetization σs are attracting attention, such as digital audio tape (DAT), 8 mm video tape, Hi-
8 tapes, and W-VHS tapes for HDTV,
Used for digital recording type DVC tapes and the like. For computers, it is used for removable disks such as Zip and Super Disk. Recently, large capacity Hi-FD is used.
And is currently in the commercialization stage.

[0005] Therefore, it is strongly desired to further improve the characteristics of the magnetic metal particles containing iron as a main component.

That is, in order to obtain a magnetic recording medium having a higher coercive force, an excellent coercive force distribution SFD, and an excellent weather resistance ΔBm, the magnetic metal particles containing iron as a main component require a higher coercive force. It has a large saturation magnetization and
It is strongly required that the distribution of the particle size be as narrow as possible, the dispersibility be excellent, and the oxidation stability Δσs be excellent.

Further, Japanese Patent Application Laid-Open No. 7-126704 discloses that
As described in "... It is also effective to reduce the X-ray particle size of the metal magnetic particles as much as possible in order to reduce the noise level caused by the magnetic recording medium ..." to obtain a magnetic recording medium, the magnetic metal particles containing iron as a main component has a smaller crystallite size D ₁₁₀ is strongly demanded.

However, it is very difficult to obtain metal magnetic particles having a small crystallite size and satisfying both a high coercive force and a large saturation magnetization value due to the production method.

Hereinafter, this fact will be described in detail.

That is, generally, iron-based metal magnetic particle powder is passed through an aqueous solution containing an iron-containing precipitate obtained by reacting an aqueous ferrous salt solution and an aqueous alkaline solution with an oxygen-containing gas such as air. Spindle-like goethite particle powder obtained by performing an oxidation reaction by heating, spindle-like hematite particle powder obtained by heating and dehydrating the goethite particle powder, or spindle-like particle powder containing a heterogeneous element other than iron in these particle powders Is used as a starting material, and the starting material is reduced by heating under a reducing gas atmosphere.

First, regarding the relationship between the coercive force and the saturation magnetization value of the metal magnetic particle powder, since the conditions such as atmosphere and temperature in the heating and reducing step are very severe, the spindle-shaped metal magnetic particle powder And sintering is likely to occur between particles. In particular, in order to obtain a large saturation magnetization value, which is an advantage of metal magnetic particle powder, it is necessary to increase the heating reduction temperature as much as possible and sufficiently promote reduction.
On the other hand, when the heating and reducing temperature is increased, the starting material is liable to cause shape breakage, resulting in a decrease in coercive force.

Next, regarding the relationship between the crystallite size and the coercive force, Japanese Unexamined Patent Publication No. Hei 4-61302 states that "... the coercive force tends to decrease as the crystallite size decreases. There is a strong demand for magnetic particles having a small crystallite size while maintaining the coercive force of the particle powder as high as possible. " The coercive force has an inverse correlation, and as described above, it is very difficult to reduce both the crystallite size of the metal magnetic particle powder and have a high coercive force.

Further, as a heating reduction device used in the heating reduction step, a fluidized bed reduction device for heating and reducing the starting material while flowing it in a powder form, or a starting material is granulated into granules to form a fixed bed. 2. Description of the Related Art A fixed-bed reduction device for performing heat reduction is known.

[0014] As the demand for mass-production technology increases along with the increase in the demand for metal magnetic particle powder, even if the flow rate of a reducing gas such as hydrogen is increased, there is no scattering of particles and mass production is possible. The device is industrially and economically advantageous.

However, when heat reduction is performed in a hydrogen gas atmosphere using a fixed bed reduction apparatus, the partial pressure of water vapor increases due to rapid reduction occurring in the lower part of the fixed bed, and the particles in the upper part of the bed are reduced with respect to the lower part of the bed. A large amount of shape destruction and short-axis growth occur, and the characteristics of the particles at the lower layer and the upper layer tend to be different.

In recent years, in order to obtain metal magnetic particles having a high coercive force, the particle size has been increasingly reduced, and the starting materials thereof have also been reduced. 0.15μ starting material
When the particle size is less than m, the destruction of the particle shape in the heat reduction step tends to be more remarkable. The shape-destructed metal magnetic particle powder cannot obtain a high coercive force due to a decrease in shape anisotropy, and the particle size distribution decreases. In addition, even in the production of a magnetic recording medium, dispersibility decreases due to kneading with a binder in a vehicle, an increase in interparticle force in a dispersion process, or an increase in magnetic cohesion, and the magnetic coating film The squareness ratio at the time of the
A magnetic recording medium having D cannot be obtained.

Therefore, there is a strong demand for a heating and reducing method which can prevent the destruction of the particle shape as much as possible and in which the characteristics of the metal magnetic particle powder in the lower part and the upper part of the layer in the fixed bed reducing apparatus are uniform.

By the way, the fine particles, especially the major axis diameter is 0.12
When the metal magnetic particle powder containing iron of less than μm as a main component is taken out into the air after the heat-reduction step, the oxidation reaction proceeds rapidly due to oxygen in the air, resulting in a significant decrease in magnetic properties.
In particular, the saturation magnetization value is lowered, so that it is impossible to obtain a metal magnetic particle powder having a desired large saturation magnetization value, and furthermore, the magnetic coating film is inferior in weather resistance ΔBm.

In order to obtain metal magnetic particle powder having a large saturation magnetization immediately after reduction and excellent oxidation stability, a method of containing Co in a large amount of 20 to 45 atomic% is known. ing. According to this method, metal magnetic particles having improved oxidation stability can be obtained, but excessive particle growth is likely to occur during heat treatment and shape destruction is induced. Due to the reduced anisotropy, a high coercive force cannot be obtained, and the size distribution is reduced and the dispersibility is reduced.

Conventionally, as a method for obtaining metal magnetic particle powder containing iron as a main component and having a high coercive force and uniform characteristics of the metal magnetic particle powder using a fixed bed reduction apparatus, a gas superficial velocity of hydrogen gas has been used. (JP-A-54-62915), a method of continuously transferring an object to be reduced on a gas-flowable belt provided in a gas-flow reactor, and removing hydrogen gas. A method of performing heat reduction while flowing in a vertical direction (JP-A-6-93312) is known.

[0021]

SUMMARY OF THE INVENTION Small crystallite size,
High coercive force, especially below 160 °,
In particular, a saturation magnetization value as large as 167.1 kA / m (2100 Oe) or more, especially 135 Am ² / kg (135 emu /
g) It is the most demanded at present that the spindle-shaped alloy magnetic particles mainly composed of Fe and Co having both of the above are industrially and economically advantageously produced using a reduction apparatus having a fixed layer. However, spindle-shaped alloy magnetic particles that sufficiently satisfy the above-mentioned properties have not been provided yet.

That is, in the method described in the above-mentioned Japanese Patent Application Laid-Open No. 54-62915, since the Co content is low and the gas superficial velocity is low, the obtained magnetic metal particles have a coercive force of 9%.
It is as small as about 5.5 kA / m (1200 Oe).
As shown in a comparative example described later, the coercive force is extremely low and the crystallite size is very large, so that it is not sufficient.

In the method described in the above-mentioned Japanese Patent Application Laid-Open No. 6-93312, no Co is contained, and as shown in a comparative example, a reducing gas is used as the atmosphere at the time of temperature rise. Means that the coercive force of the obtained metal magnetic particle powder is 127.3.
It is about kA / m (1600 Oe), and the coercive force is low and the saturation magnetization value is low at the same crystallite size as in later examples of the present invention.

Thus, the present invention uses a reduction device with a fixed layer formed thereon to achieve a high coercive force, especially 167.1 k, despite having a small crystallite size, especially less than 160 °.
It is a technical object of the present invention to obtain a spindle-shaped alloy magnetic particle powder containing Fe and Co as a main component which satisfies both a large saturation magnetization value of at least A / m (2100 Oe) and at least 135 Am ² / kg (135 emu / g). And

[0025]

The above technical objects can be achieved by the present invention as described below.

That is, the present invention relates to a spindle-shaped goethite particle powder containing 20 to 45 atomic% of cobalt in terms of Co with respect to all Fe and having an average major axis diameter of 0.05 to 0.15 μm or the goethite particle powder. Is used as a starting material, and the starting material is charged into a fixed bed reduction device to form a fixed bed having a bed height of 30 cm or less. At 400-700
After the temperature was raised to a temperature range of 400 ° C. and the atmosphere was switched to a reducing gas atmosphere, the starting material was reduced by a reducing gas having a superficial gas velocity of 40 to 150 cm / s in a temperature range of 400 to 700 ° C. A method for producing spindle-shaped alloy magnetic particle powder mainly containing Fe and Co for magnetic recording, wherein the spindle-shaped alloy magnetic particle powder mainly containing Fe and Co is used.

Next, conditions for implementing the present invention will be described.

The starting material in the present invention contains 20 to 45 atomic% of cobalt in terms of Co with respect to all Fe,
Spindle-shaped goethite particles having an average major axis diameter of 0.05 to 0.15 μm or contain 20 to 45 atomic% of cobalt in terms of Co with respect to all Fe obtained by heating and dehydrating the goethite particles. And the average major axis diameter is 0.05-0.
Spindle-shaped hematite particle powder having a size of 13 μm is used.

The starting material in the present invention is spindle-shaped particle powder. The spindle-shaped particle powder does not contain dendritic particles and has an excellent size distribution.

When the content of cobalt as a starting material in the present invention is less than 20 atomic% based on the total Fe, the obtained spindle-shaped alloy magnetic particles containing Fe and Co as main components have oxidation stability. It cannot be sufficiently improved, and it is difficult to obtain a large saturation magnetization value. If the content exceeds 45 atomic%, it becomes extremely difficult to control the reduction rate, and shape destruction and sintering occur between the particles during heat reduction, making it difficult to obtain a high coercive force.

When the average major axis diameter of the starting material in the present invention is less than 0.05 μm, the obtained spindle-shaped alloy magnetic particles become superparamagnetic, so that a large saturation magnetization cannot be obtained, and at the same time, a high coercive force cannot be obtained. It is difficult to obtain. 0.15
If it exceeds μm, the desired high coercive force cannot be obtained.

The spindle-shaped goethite particles according to the present invention have an average minor axis diameter of 0.010 to 0.023 μm in consideration of the effect of preventing sintering and controlling the reduction rate. It is preferable that the alloy contains atomic% of aluminum, has an axial ratio (average major axis diameter / average minor axis diameter) of 4 to 8, and a BET specific surface area of 100 to 250 m ² / g.

The spindle-shaped goethite particles in the present invention may be coated on the particle surface with a compound of Co element, a compound of Al element and a sintering inhibitor.

As the sintering inhibitor, compounds of rare earth elements can be used, and one or more of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium and the like are preferable. Particularly, yttrium and neodymium are preferable.

In order to improve the effect of preventing sintering, or if necessary, other elements such as Si, B, Ca, M
One, two or more compounds of elements selected from g, Ba, Sr and the like may be used. These compounds not only have the effect of preventing sintering but also have the function of controlling the reduction rate, and thus may be used in combination as necessary.

The spindle-shaped hematite particles according to the present invention have an average minor axis diameter of 0.010 to 0.022 μm and a total Fe content in consideration of the effect of preventing sintering and controlling the reduction rate.
Contains 5 to 15 atomic% of aluminum in terms of Al and 5 to 15 atomic% of rare earth in terms of rare earth element,
It is preferable that the axial ratio (average major axis diameter / average minor axis diameter) is 4 to 8, and the BET specific surface area value is 50 to 120 m ² / g.

The spindle-shaped hematite particles can be prepared by subjecting the spindle-shaped goethite particles to 150-35 under an oxidizing atmosphere.
Dehydrate by heating in the temperature range of 0 ° C.
It is preferable to obtain by performing heat treatment in a temperature range of more than 0 ° C and less than 700 ° C.

Further, the spindle-shaped hematite particles after the heat treatment may be washed in order to remove impurity salts such as Na ₂ SO ₄ contained from the reaction for producing the spindle-shaped goethite particles. In this case, by washing under the condition that the coated sintering inhibitor does not elute,
It is preferable to remove unnecessary impurities.

In the present invention, when the starting particles are charged into a fixed reduction apparatus, it is preferable that the starting particle powder is granulated by a conventional method and used as granules having an average diameter of 1 to 5 mm.

The reduction device using a fixed bed in the present invention may be a stationary reduction device (batch type) or a mobile reduction device (a continuous type) in which a fixed layer is formed on a belt and reduced while transferring the belt. Is preferred.

In the present invention, the starting material has a layer height of 30 c
m or less. If it exceeds 30 cm, a large amount of Co
At the same time as the effect of promoting reduction is remarkable,
An increase in the partial pressure of water vapor due to rapid reduction of the lower part of the fixed layer causes problems such as a decrease in the coercive force of the upper part of the fixed layer, and the characteristics are deteriorated as a whole. In consideration of industrial productivity, 3 to 30 cm is preferable. Incidentally, a batch method (Japanese Patent Application Laid-Open No. 54-62915, Japanese Patent Application Laid-Open No.
Publication), continuous type (JP-A-6-93312, etc.)
Therefore, in a batch-type fixed-bed reducing device, the thickness is preferably more than 8 cm and not more than 30 cm.

In the production method according to the present invention, 400 to 7
The atmosphere during which the temperature is raised to the reduction temperature of 00 ° C. is an inert gas atmosphere. As the inert gas atmosphere, nitrogen gas, helium gas, argon gas and the like are preferable, and nitrogen gas is particularly preferable. In an atmosphere other than an inert gas, reduction occurs when the temperature rises over time, and the reduction temperature during the formation of metal magnetic particles cannot be constant, so uniform particle growth is unlikely to occur and a high coercive force is obtained. Absent.

Although the heating rate is not particularly specified,
100 ° C./min is preferred.

In addition, the gas superficial velocity of the inert gas at the time of raising the temperature is not particularly limited, but may be a velocity at which the starting material granular material is not scattered or destroyed. ~ 50 cm / s is preferred.

The switching from the inert gas atmosphere at the time of temperature increase to the reducing gas atmosphere in the heating and reducing step differs depending on the type of the reducing apparatus. In the case of a batch system, the pressure in the reducing apparatus is industrially increased. A method in which the temperature is controlled stepwise while controlling is preferable, and in the case of a continuous system, a method in which a heating zone and a reduction zone are divided is preferable. In any case, it is preferable to perform the switching in a short time, and it is preferable to perform the switching within at least 10 minutes.

The atmosphere in the heating and reducing step in the present invention is a reducing gas, and hydrogen is preferably used as the reducing gas.

The heat reduction temperature in the heat reduction step in the present invention is 400 to 700 ° C. It is preferable that the reduction temperature is appropriately selected from the above temperature range according to the type and amount of the compound used for the coating treatment of the starting material. Heat reduction temperature is 4
When the temperature is lower than 00 ° C., the progress of the reduction is very slow and not industrial, and the saturation magnetization value of the obtained spindle-shaped alloy magnetic powder becomes low. If the temperature exceeds 700 ° C., the reduction reaction proceeds rapidly, causing shape destruction of the particles and sintering between the particles and between the particles, and the coercive force decreases.

The gas superficial velocity of the reducing gas in the heat reduction step in the present invention is 40 to 150 cm / s. If the gas superficial velocity is less than 40 cm / s, the speed at which the steam generated by the reduction of the starting material is carried out of the system becomes very slow, so that the coercive force and SFD at the upper part of the layer are reduced, and the overall coercive force is high. Can not be obtained. If it exceeds 150 cm / s,
Although the desired spindle-shaped alloy magnetic particle powder can be obtained, it is not preferable because problems such as a high reduction temperature being required, or a granulated material being scattered and broken are likely to occur.

The spindle-shaped alloy magnetic particles containing Fe and Co as the main components after the heat-reduction step in the present invention can be obtained by a known method, for example, a method of dipping in an organic solvent such as toluene, a method of reducing Fe and Co after reduction. After once replacing the atmosphere of the spindle-shaped alloy magnetic particles powder containing as a main component with an inert gas,
Stable by forming an oxide film on the particle surface by a method of finally producing air while gradually increasing the oxygen content in the inert gas, or a method of gradually oxidizing using a mixed gas of oxygen and water vapor And can be taken out into the air.

Next, the spindle-shaped alloy magnetic particles containing Fe and Co as main components in the present invention will be described.

The spindle-shaped alloy magnetic particles containing Fe and Co as main components in the present invention contain Co in an amount of 2 to all Fe.
0 to 45 at%, preferably 20 to 40 at%, more preferably 20 to 35 at%. The average major axis diameter is 0.05 to 0.12 μm, and the crystallite size D ₁₁₀
Is 135 to 160 °.

The spindle-shaped alloy magnetic particles containing Fe and Co as main components in the present invention have a coercive force of 167.1 to 1
98.9 kA / m (2100 to 2500 Oe),
More preferably, 175.1 to 198.9 kA / m (22
00 to 2500 Oe). When the saturation magnetization value is 13
^{5~160Am 2 / kg (135~160emu / g} )
It is.

[0053]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention is as follows.

The average major axis diameter, average minor axis diameter and axial ratio of the spindle-shaped goethite particle powder, the spindle-shaped hematite particle powder, and the spindle-shaped alloy magnetic particle powder containing Fe and Co as main components in the present invention are all The average value of the numerical values measured from the electron micrograph was shown.

Content of Co, Al, Rare Earth Element and Other Metal Elements of Spindle-Shaped Goethite Particle Powder, Spindle-Shaped Hematite Particle Powder, and Spindle-Shaped Alloy Magnetic Particle Powder Mainly Containing Fe and Co in the Present Invention The amount was measured using "Inductively Coupled Plasma Emission Spectrometer SPS4000" (manufactured by Seiko Instruments Inc.).

The specific surface area of the particle powder is “Monosorb MS”.
-11 "(Cantachrome Co., Ltd.)
It was shown by the value measured by the method.

The crystallite size D ₁₁₀ (the X-ray crystal particle size of the spindle-shaped alloy magnetic particles) was measured using an “X-ray diffractometer” (Rigak
u) (Measurement conditions: target Cu, tube voltage 40 kV,
Using a tube current of 40 mA), the size of the crystal particles measured by the X-ray diffraction method was determined using the (110)
It represents the thickness of a crystal grain in a direction perpendicular to each of the crystal planes, and is represented by a value calculated from the diffraction peak curve for each crystal plane using the following Scherrer equation.

D ₁₁₀ = Kλ / βcosθ

Here, β = half value width (in radians) of a true diffraction peak corrected for the mechanical width caused by the apparatus.

K = Scherrer constant (= 0.9), λ = wavelength of X-ray (0.1542 nm of Cu Kα ray), θ = diffraction angle (corresponding to diffraction peak on (110) plane)

The magnetic properties of the spindle-shaped alloy magnetic particles containing Fe and Co as main components are described in “Vibration sample magnetometer VSM-3.
S-15 "(manufactured by Toei Kogyo Co., Ltd.) with an external magnetic field of 795.8 kA / m (10 kOe).

The magnetic properties of the magnetic coating film pieces were as follows:
A magnetic paint prepared by mixing and dispersing for 8 hours in a paint shaker (manufactured by Red Devil Co., Ltd.) in a 00 cc polybin at the following ratio was applied to a polyethylene terephthalate film having a thickness of 25 μm by using an applicator. And then dried in a magnetic field of 5 kGauss to measure the magnetic properties of the magnetic coating pieces obtained. 3 mmφ steel ball: 800 parts by weight, spindle-shaped alloy magnetic particles mainly composed of Fe and Co: 100 parts by weight, polyurethane resin having sodium sulfonate group: 20 parts by weight, cyclohexanone: 83.3 parts by weight, methyl ethyl ketone: 83.3 parts by weight, toluene: 83.3 parts by weight.

Δσs, which is an evaluation of the oxidation stability of the saturation magnetization value of the powder, and ΔBm, which is an evaluation of the weather resistance of the saturation magnetic flux density Bm of the magnetic coating film, are obtained by placing the powder in a thermostat at a temperature of 60 ° C. and a relative humidity of 90%. After an accelerated aging test in which the body or the magnetic coating film piece is allowed to stand for one week, the saturation magnetization value of the powder and the saturation magnetic flux density of the magnetic coating film were measured, respectively, with σs and Bm measured before the start of the test. Values obtained by dividing the difference (absolute value) between σs ′ and Bm ′ one week after the accelerated aging test by σs and Bm before the start of the test, respectively, were calculated as Δσs and ΔBm. Δσs, ΔB
The closer m is to 0%, the better the oxidation stability.

<Production of Spindle-Shaped Goethite Particle Powder> 25 mol of sodium carbonate and an aqueous sodium hydroxide solution
30 l of a mixed alkali aqueous solution containing 0 mol (sodium hydroxide corresponds to 28.6 mol% in terms of a prescribed conversion with respect to the mixed alkali) is charged into the bubble column, and nitrogen gas is introduced at a gas superficial velocity of 2.21 cm / s. Adjust to 47 ° C with ventilation. Then, 20 l of an aqueous ferrous sulfate solution containing 20 mol as Fe ²⁺ (a mixed alkali aqueous solution with respect to ferrous sulfate corresponds to 1.75 equivalents in terms of a prescribed conversion) was charged into a bubble column and aged for 20 minutes. 4.2 mol of Co ²⁺
4 l of an aqueous solution of cobalt sulfate (corresponding to 21 atomic% in terms of Co with respect to the total Fe) is added for 4 hours.
After aging for 0 minutes, the air was released at a gas superficial velocity of 1.32 cm /
The gas was passed through s to carry out an oxidation reaction until the oxidation rate of Fe ²⁺ reached 40%, thereby producing goethite seed crystal particles.

Next, the air flow rate was determined by changing the gas superficial velocity to 3.
After increasing to 31 cm / s, Al ³⁺2.4 mol
1 liter of aqueous aluminum sulfate solution
This corresponds to 12 atomic% by calculation. ) Of 3 ml / sec or less
After adding at a high speed to perform the oxidation reaction, filter press
With water until the electric conductivity reaches 60μS and press cake
did.

A spindle-shaped goethite particle powder obtained by drying and pulverizing a part of the cake by a conventional method has an average major axis diameter of 0.131 μm and an average minor axis diameter of 0.0175 μm.
m, axial ratio 7.5, σ (standard deviation) 0.0250μ
m, size distribution (standard deviation / major axis diameter) 0.191, B
ET specific surface area is 179.2 m ² / g, and C
The o content was 21 atomic% based on the total Fe, and the Al content was 12 atomic% based on the total Fe.

<Production of Spindle-Shaped Hematite Particle Powder> Then, 1000 g of the spindle-shaped goethite particle powder obtained here was obtained.
After sufficiently dispersing the press cake containing (7.8 mol as Fe) in 40 l of water, 2 l of an yttrium nitrate aqueous solution containing 243 g of yttrium nitrate hexahydrate (as Y with respect to all Fe in the spindle-shaped goethite particles powder) 2 liters of a cobalt sulfate solution containing 197 g of cobalt sulfate heptahydrate (corresponding to 9 atomic% as Co with respect to all Fe in the spindle-shaped goethite particles), and sufficiently stirred. did. Then, with stirring, the concentration 2
A 5.0% by weight aqueous sodium carbonate solution was added as a precipitant to adjust the pH to 9.5, and then filtered and washed with a filter press to obtain a press cake. The obtained press cake was extruded using a molding plate having a hole diameter of 3 mm using an extruder, and then dried at 120 ° C. to obtain a molded product of spindle-shaped goethite particles coated with a Y and Co compound. The content of Co in the obtained spindle-shaped goethite particles was 30 atomic% with respect to all Fe, and the content of Al was
And the content of Y was 8 atomic% based on the total Fe.

The molded product of the spindle-shaped goethite particles coated with the Y and Co compounds is dehydrated by heating at 300 ° C. in the air, and then heat-treated at 600 ° C. in the same atmosphere to form the molded product of the spindle-shaped hematite particles. I got The obtained spindle-shaped hematite particle powder molded product is granular and has an average diameter of 2.6.
mm.

The obtained spindle-shaped hematite particles had an average major axis diameter of 0.122 μm and an average minor axis diameter of 0.0168.
μm, axial ratio 7.3, σ (standard deviation) 0.0218μ
m, size distribution 0.179, BET specific surface area 95.
7 m ² / g, the content of Co in the particles was 30 atomic% based on the total Fe, and the content of Al was 12 atomic% based on the total Fe.
Atomic% and the content of Y were 8 atomic% with respect to all Fe.

<Manufacture of Spindle-Shaped Alloy Magnetic Particle Powder> Next, 500 g (average diameter: 2.6 mm) of the obtained granulated spindle-shaped hematite particle powder was put into a batch-type fixed bed reduction apparatus having an inner diameter of 72 mm. (This corresponds to a layer height of 27 cm.) While heating and raising the temperature to 600 ° C. while passing nitrogen gas at 600 ° C. and a gas superficial velocity of 20 cm / s, switching to hydrogen gas and a gas superficial velocity of 50 cm / s. The mixture was heated and reduced at 600 ° C. until the dew point of exhaust gas reached −30 ° C. while passing hydrogen gas. After that, switching to nitrogen gas again and cooling to 80 ° C., then mixing water vapor with nitrogen gas, further mixing air and gradually increasing the oxygen partial pressure to form a stable oxide film on the particle surface, A molded product of the spindle-shaped alloy magnetic particles was obtained.

From the obtained spindle-shaped alloy magnetic particle powder molded product, about 10 g of a part of the molded product from the lower portion (portion having a layer height of 3 cm or less) and the upper layer portion (portion having a layer height of 25 cm or more) was obtained.
, And magnetic properties and crystallite size were measured separately from the remaining molded products.

The obtained spindle-shaped alloy magnetic powder has an average major axis diameter of 0.104 μm, a standard deviation of 0.0165 μm, a size distribution (standard deviation / average major axis diameter) of 0.159, and an average minor axis diameter of 0.159 μm. 0.0153 μm, average axis ratio 6.8, BET
The particles consisted of particles having a specific surface area of 52.4 m ² / g and a crystallite size D ₁₁₀ of 153 °, and had a spindle shape, a uniform particle size, and no dendritic particles. Further, the Co content in the particles was 30 atomic% based on the total Fe, the Al content was 12 atomic% based on the total Fe, and the Y content was 8 atomic%.

The magnetic properties of the spindle-shaped alloy magnetic particles are as follows. The coercive force Hc is 184.7 kA / m (2321O).
e), the saturation magnetization value σs is 146.8 Am ² / kg (14
6.5 emu / g) and squareness ratio (σr / σs) of 0.54
0, the oxidation stability Δσs of the saturation magnetization is 9.
3% (actual measurement value: -9.3%), and the magnetic coating film properties were as follows: coercive force Hc: 188.6 kA / m (2370 Oe), squareness ratio (Br / Bm): 0.875, SFD: 0.380 ,
The oxidation stability ΔBm is 7.1% as an absolute value (actual measurement value−
7.1%).

The spindle-shaped alloy magnetic particles extracted from the lower layer have a coercive force Hc of 185.8 kA / m (2335).
Oe), and the saturation magnetization value s is 145.9 Am ² / kg (1
45.9 emu / g) and squareness ratio (σr / σs) of 0.5
41, the crystallite size D ₁₁₀ was 152 °. Spindle-shaped alloy magnetic particles extracted from the upper portion, the coercive force Hc 183.9kA / m (2311Oe), a saturation magnetization value σs is 146.8Am ² /kg(146.8emu/
g), squareness ratio (σr / σs) is 0.538, a crystallite size _{D 110} was 155A.

[0075]

In the manufacturing method according to the present invention, the present inventor considers the reason why a spindle-shaped alloy magnetic powder having a small crystallite size, a high coercive force and a large saturation magnetization value with respect to the crystallite size can be obtained. By increasing the temperature of the fixed layer to 30 cm or less and raising the temperature in an inert gas atmosphere, the partial pressure of water vapor rapidly increases in the initial stage of reduction, and magnetite, or the like so that shape destruction or short-axis growth does not occur. Has the effect of increasing the crystallite size of wustite, reducing the specific surface area, and reducing the rate of subsequent reduction to pure iron, thus enabling control of the growth of particles and minimizing the shape destruction of particles. It is believed that the crystallite size can be reduced.

Further, by reducing the layer height of the starting material to 30 cm or less and raising the temperature in an inert gas atmosphere, reduction does not occur at the time of temperature change when the temperature changes with time, and reduction starts in a homogeneous state. And switching to reducing gas, the gas superficial velocity is 40 to 150 cm / in a certain temperature range.
By setting s, even if the water vapor partial pressure increases rapidly in the initial stage of reduction, shape destruction or short-axis growth of magnetite or wustite is not induced, and reduction proceeds uniformly in the entire layer. It is believed that spindle-shaped alloy magnetic particles having a high coercive force and a large saturation magnetization can be obtained.

[0077]

Next, examples and comparative examples will be described.

Spindle-shaped goethite particles 1 and 2 Spindle-shaped goethite particles having the properties shown in Table 1 were prepared as starting material particles.

[0079]

[Table 1]

Spindle-shaped hematite particle powders 1 to 4 Except for changing the type of spindle-shaped goethite, the type and amount of coating used for sintering prevention treatment, and the heating / dehydrating temperature,
Spindle-shaped hematite particles were obtained in the same manner as in the embodiment of the invention. Tables 2 and 3 show the conditions and various properties of the obtained spindle-shaped hematite particles.

[0081]

[Table 2]

[0082]

[Table 3]

Examples 1-5, Comparative Examples 1-7 Types of spindle-shaped hematite particles, layer height, type of heating gas,
A spindle-shaped alloy magnetic powder was obtained in the same manner as in the embodiment of the invention except that the type of the reducing gas, the gas superficial velocity, and the reduction temperature were changed. The production conditions at that time are shown in Table 4, and various characteristics of the obtained spindle-shaped alloy magnetic particles are shown in Tables 5 and 6.
It was shown to. In Example 5, in the method for producing the hematite particles 1, goethite particles which had been subjected to only the sintering prevention treatment and had not been subjected to dehydration and heat treatment were used as starting materials.

[0084]

[Table 4]

[0085]

[Table 5]

[0086]

[Table 6]

In Example 1 and Comparative Example 1, as in the embodiment of the present invention, a part of the spindle-shaped alloy magnetic particles was extracted from the upper layer and the lower layer of the fixed layer. Table 7 shows properties of the extracted spindle-shaped alloy magnetic particles.

[0088]

[Table 7]

Using each of the spindle-shaped alloy magnetic particle powders shown in Table 5, magnetic coating pieces were obtained in the same manner as in the embodiment of the present invention. Table 8 shows properties of the obtained magnetic coating film pieces.

[0090]

[Table 8]

[0091]

According to the method for producing spindle-shaped alloy magnetic particles containing Fe and Co as the main components according to the present invention, shape destruction at the time of heat reduction can be prevented as much as possible. Since the lower portion of the layer can be uniformly reduced, spindle-shaped alloy magnetic particles having a small crystallite size, a high coercive force, and a large saturation magnetization can be obtained.

The magnetic recording medium obtained by using the spindle-shaped alloy magnetic particles containing Fe and Co as the main components produced by the production method according to the present invention has a high coercive force and excellent S
FD and excellent weather resistance, so high density recording,
It is suitable as a spindle-shaped alloy magnetic particle powder mainly composed of Fe and Co for a high-output magnetic recording medium.

Claims (1)

[Claims] 1. An average major axis diameter containing 20 to 45 atomic% of cobalt in terms of Co with respect to all Fe and having an average major axis diameter of 0.05 to 0.1%.
A spindle-shaped goethite particle powder having a diameter of 15 μm or a spindle-shaped hematite particle powder obtained by heating and dehydrating the goethite particle powder is used as a starting material, and the starting material is charged into a fixed bed reduction device to have a bed height of 30 cm or less. After forming the fixed layer, the temperature is raised to a temperature range of 400 to 700 ° C. in an inert gas atmosphere, and then the atmosphere is switched to a reducing gas atmosphere.
In a temperature range of 400 to 700 ° C., the starting material is reduced by a reducing gas having a superficial gas velocity of 40 to 150 cm / s to obtain spindle-shaped alloy magnetic particles containing Fe and Co as main components. Of producing spindle-shaped alloy magnetic particles containing Fe and Co as main components for magnetic recording.