JPH0340485B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing ferromagnetic metal iron particles having a fine particle shape. More specifically, the present invention relates to a method for producing acicular iron oxyhydroxide fine particles having good suitability as a raw material for ferromagnetic metal (α-Fe) fine particles for magnetic recording.

[Conventional technology]

Magnetic materials for magnetic recording have high coercive force (Hc), saturation magnetization (σs), and residual magnetization (σr).
Magnetic properties such as a high squareness ratio (R=σr/σs) and a high squareness ratio (R=σr/σs) are required. In the case of ferromagnetic metal iron,
Since it is advantageous to provide fine acicular particle morphology, many methods for producing acicular iron oxyhydroxide particles and acicular iron oxide particles have been reported. For example, patent
No. 166146 (August 4, 1952) describes a method for producing acicular iron oxyhydroxide particles using FeSO4.7H2O as an iron raw material, applying air oxidation and seeded crystallization after neutralization reaction with NaOH. ing.

[Problem to be solved by the invention]

A drawback of these conventional methods for producing acicular iron metal particles is that when forming metal iron particles from fine acicular iron oxyhydroxide particles through a catalytic reaction with a reducing gas, the iron oxyhydroxide particles used as raw materials Even if most of the particles have a fine needle-like morphology, the contact reaction with the reducing gas inevitably causes particle breakage, destruction, and even sintering.

As a result, significant deterioration of the magnetic properties of the fine particles,
That is, this results in a decrease in coercive force, saturation magnetization, residual magnetization, and squareness ratio, which greatly impairs the properties required of ferromagnetic metal iron particles for magnetic recording.

[Means to solve the problem]

The purpose of the present invention is to provide a method for producing ferromagnetic metallic iron (α-Fe) fine particles with good performance using special iron oxyhydroxide fine particles that can prevent such particle destruction. .

The present invention has been developed by chemically modifying the surface of fine acicular iron oxyhydroxide particles by adhering a metal phosphate compound to the surface layer of fine acicular iron oxyhydroxide particles. The purpose of this method is to produce fine particles and process them by a known reduction reaction to obtain α-Fe without damage, destruction, or even sintering of the particle shape.

The amount of metal phosphate compound deposited in the method of the present invention is 0.05/100 to 0.05/100 in atomic weight ratio of P to Fe.
Must be 5/100, preferably
0.1/100~3/100, more preferably 0.5/100~
It is within the range of 1/100. If the deposition amount is less than this, the effect of deposition of the metal phosphate compound will not be noticeable, and if the amount is more than this, peeling from the surface of the metal iron particles will occur in the subsequent reduction reaction. The chemical modification of the surface layer of metal iron particles, which is the main objective of the present invention, does not become noticeable.

The metal phosphate compounds used in the present invention include potassium salts such as K ₃ PO ₄ , K ₂ HPO ₄ KH ₂ PO ₄ , chromium phosphate salts such as CrPO ₄ .6H ₂ O, and
Cobalt phosphate salt of Co ₃ (PO ₄ ) ₂ can be suitably used. However, there are no restrictions on the form of these compounds.

Generally, alkali metal salts are water-soluble, but surprisingly, metal phosphate compounds that are almost insoluble in water are used in wet neutralization and modification of fine acicular iron oxyhydroxide particles through oxidation reactions. The remarkable effects of the present invention can also be recognized.

In the method of the present invention, the time when the metal phosphate compound is deposited on the surface layer of the iron oxyhydroxide fine particles is at the time when the neutralization reaction between the raw material iron salt aqueous solution and the alkaline agent is completed, or when the oxidation of air etc. At the time of completion of the oxidation reaction by gas blowing, or on the paste obtained after washing and filtration, or on the dried product of the paste, or on the calcined product of the dried product, whichever of the following: It can be applied even if

There are no particular restrictions on the specific method of adhesion, but known methods such as adhesion treatment to the surface layer of solid particles in an aqueous solution system using stirring and mixing, a mortar, a rice cooker, a ball mill, etc. It can be deposited by a solid-solid mixing method using a kneader or the like. Particularly when a water-insoluble compound is used for surface coating, it is preferable to carry out the above-mentioned method sufficiently.

By this method, it is possible to deposit at least an atomic weight ratio of P and Fe of 0.01/100,
When the ratio is 0.05/100 or more, the effects of the present invention are significantly exhibited. By depositing it on the surface layer rather than simply containing it, an advantage in terms of manufacturing technology is expressed in its suitability for reduction reactions.

The ferrous salt used in the neutralization reaction between the raw material iron salt aqueous solution and the alkaline agent is a sulfate, a chloride, or various mineral acid salts, and they can be used alone or in combination of two or more. Among them, sulfates are often used. Further ferric salts include sulfates, nitrates, carbonates, chlorides and various mineral acid salts. When a sulfate is used as the ferrous salt, the ferric salt used in combination is preferably a sulfate and/or a nitrate, but is not necessarily limited thereto.

On the other hand, alkalis include alkali hydroxides such as KOH and NaOH, alkali carbonates such as K ₂ CO ₃ and Na ₂ CO ₃ , aqueous solutions of NH ₃ , and even urea, which can be thermally decomposed by heating in an aqueous solution state. refers to a substance that has substantially the same effect as _NH3 . It is essentially possible to implement the present invention by selecting any of these.

The iron oxyhydroxide particles used for surface coating in the method of the present invention are preferably acicular iron oxyhydroxide particles, and these can be produced according to known methods. That is, a ferrous salt or a mixture of a ferrous salt and a ferric salt is made into an aqueous solution, then an alkaline aqueous solution is added to perform a neutralization reaction to form an insoluble substance, and then an oxidation reaction is performed with air. If this continues, fine acicular iron oxyhydroxide is formed.

In this wet neutralization and oxidation reaction, the type, amount, and aqueous solution concentration of the iron salt, as well as the type and amount of the alkaline substance,
There are many operating factors such as the amount and concentration of the aqueous solution, as well as the temperature and maintenance time in the neutralization reaction stage, the temperature and air supply amount, rate, and time for proceeding with the oxidation reaction. Subtly affects particle morphology.

However, almost no effect on particle morphology is observed when a phosphate compound is applied as a subcomponent in the manner of particle surface treatment.

The acicular iron oxyhydroxide particles formed by this wet neutralization and oxidation reaction and optionally subjected to adhesion treatment on the surface layer of the particles are washed with water and filtered, and then heated to a temperature of usually 100 to 150°C. The powder is dried in an air bath and, if necessary, pulverized or granulated to obtain dry iron oxyhydroxide particles.

In some cases, it may be further calcined at 250 to 300°C to obtain calcined iron oxyhydroxide particles.

The metal phosphate compound is deposited by the method described above, but in order to produce ferromagnetic metal iron particles using the thus obtained dried or calcined iron oxyhydroxide particle powder as a raw material. This can be carried out according to a known method.

That is, for example, it is equipped with a preheater for the raw material gas for reaction,
In addition, ferromagnetic metallic iron particles can be produced by filling dried or calcined iron oxyhydroxide fine particles into a steel pipe reactor whose temperature can be regulated from the outside and carrying out a catalytic reduction reaction with a reducing gas at 200 to 500°C. can be manufactured. The reactor for the reduction reaction may be of either fixed bed or moving bed type, and does not need to be a normal pressure reaction, but may be under pressure.

In the present invention, there is no need in principle to impose large restrictions on the supply amount and supply rate of raw material gas for reaction, but if expressed in gas hourly space velocity (GHSV),
100Nl/gr-Fe/hr, preferably 2-50Nl/gr
-Fe/hr range is appropriate. If the amount is less than this range, the reaction progresses slowly and is not practical.
Moreover, if the amount is larger than this, the pressure loss within the reactor increases, so it is not necessarily suitable for reaction operation.

Furthermore, if the reaction temperature range deviates from the above range, at low temperatures the reaction progresses slowly and takes a long time to complete, making it unrealistic, while at high temperatures the reaction rate is too fast, resulting in unnecessary particle breakage and
This tends to lead to destruction and even sintering.

According to the method of the present invention, ferromagnetic metal iron particles obtained by gas-solid catalytic reduction reaction using acicular iron oxyhydroxide particles coated with a metal phosphate compound as a subcomponent as a raw material have a high morphology. According to high-magnification electron microscopy, the morphology of the acicular iron oxyhydroxide fine particles used as the raw material was almost completely maintained, and the particles were not damaged.
Phenomena such as destruction and interparticle crosslinking, that is, sintering, are hardly observed.

Furthermore, the magnetic properties of the ferromagnetic metal iron particles produced by the method of the present invention, for example, in terms of coercive force (Hc), vary depending on the particle size and acicularity ratio, but Hc = 1000 to 1500 Oe, which is extremely high. has a high value,
It satisfies the properties required for ferromagnetic metallic iron particles for magnetic recording and has high practical value.

Hereinafter, the present invention will be explained in detail with reference to Examples and Comparative Examples.

〔Example〕

Example 1 A Production and evaluation of iron oxyhydroxide with potassium phosphate coated on the particle surface layer.

FeSO ₄・7H ₂ O1000gr water kept at 45℃
20 to make an aqueous solution, and this and separately prepared NaOH500gr were dissolved in 1000ml of water.45
℃ aqueous solution was continued to be stirred and mixed for 50 minutes to complete the neutralization reaction.

At this point, add a 45°C aqueous solution of 1.50 gr of potassium phosphate KPO ₄ dissolved in 200 ml of water.
After stirring and mixing for 10 minutes, the entire system was heated to 60℃ and air was blown at a feed rate of 100Nl/min to start the oxidation reaction, which continued for 6 hours to produce yellow oxyhydroxide. Iron was obtained as insoluble precipitated particles.

The system was cooled to room temperature, and then washed with water and filtered under suction to obtain a paste of the K--P-modified iron oxyhydroxide particles. Dry overnight at 110°C, K-P
- A modified dry iron oxyhydroxide particle solid was obtained.

This material was adjusted to 6 to 12 mesh granules using a wooden hammer to prepare a KP-modified dry iron oxyhydroxide particle fluid.

When this granule was subjected to electron microscopy at a magnification of 50,000 times using a conventional method, the smallest unit was a well-shaped needle-like fine particle, and the size was mainly 0.5 to 0.6 μm on the long axis and 0.02 to 0.02 μm on the short axis. It was 0.03 μm.

Furthermore, when the granules were subjected to elemental analysis by atomic absorption spectroscopy, the weight ratios of Fe atoms to K and P were K/Fe=0.17/100 and P/Fe=0.14/100.

B Production and evaluation of KP-modified α-Fe particles.

100g of the above K-P modified acicular iron oxyhydroxide fine particle granules were heated using a preheater for the reaction gas.
A fluidized bath made of SiC particles, etc. is used to fill a steel pipe reactor with an inner diameter of 1.5 inches, which allows for uniform heating control in the long axis direction, and _H2 gas is GHSV = 35Nl-
Distributed at a supply rate of H2/gr-Fe/hr,
The reduction reaction was carried out at 375°C for 8 hours.

After the reaction was completed, the temperature was lowered to room temperature, the reduced particle granules were collected under an N2 gas atmosphere, and the X-ray diffraction image was measured.
Fe crystals were shown. When the particle morphology of the α-Fe particle granules was observed using an electron microscope and the magnetic properties were investigated, the particle morphology closely inherited the raw material particle morphology, with almost no breakage, destruction, or even sintering observed. , Furthermore, Hc=1210Oe, σs=175.0emu/
gr., and R=0.53.

Example 2 A Production of iron oxyhydroxide with chromium phosphate coated on the particle surface layer.

_{FeSO 4 .7H 2 O} and
Neutralization reaction with NaOH followed by air oxidation reaction yielded yellow iron oxyhydroxide as an insoluble precipitated material. Next, _CrPO4・
Add 6H ₂ O at P/Fe=0.50/100 weight ratio,
Stirring was continued for 30 minutes, after which the entire system was returned to room temperature, washed with water, filtered, and dried overnight at 110°C to obtain Cr-P-
A salt-coated dry iron oxyhydroxide fine particle solid was obtained, and then granules were obtained in the same manner as in Example 1.

According to observation using an electron microscope, the granules have needle-shaped fine particles as the smallest unit, and the major axis is 0.5 to 0.6 μm and the short axis is 0.02 to 0.03 μm.
It was m. Further, as a result of quantitative analysis by atomic absorption spectrometry, it was found that it contained P atoms at a weight ratio of P/Fe=0.47/100.

B Production of α-Fe fine particles.

Using the dried iron oxyhydroxide fine particle granules coated with chromium phosphate as a raw material, a reduction reaction was carried out under exactly the same conditions as in Example 1 to obtain α-Fe fine particle granules.

According to electron microscopic observation, the α-Fe fine particle granules have needle-shaped fine particles as the smallest particle unit, and the size thereof is 0.5 to 0.6μ in the main long axis diameter.
m, the minor axis diameter was 0.02 to 0.04 μm, and almost no particle breakage, destruction, or sintering was observed. In addition, the magnetic properties of the granules are: Hc=1270Oe, σs=
It was 175.0emu/gr, R=0.53.

Examples 3-9 A Production of iron oxyhydroxide with aluminum phosphate and cobalt phosphate deposited on the particle surface.

A dry solid iron oxyhydroxide fine particle was obtained in exactly the same manner as in Example 1 except that K ₃ PO ₄ was not used. Then the solids and AlPO ₄ and Co ₃
(PO ₄ ) ₂ Add an appropriate amount of water, mix with a sieve, dry at 110°C for 3 hours, and then dry for 6 to 30 minutes.
The mesh size was adjusted to 12 to obtain Al--Co--P-coated dry iron oxyhydroxide fine particle granules.

The amounts of AlPO ₄ and Co ₃ (PO ₄ ) ₂ mentioned above are the atomic weight ratio of Al, Co and P to iron,
Al/Fe=0.5/100, Co/Fe=2.0/100 and P/Fe=1.26/100.

As a result of electron microscopy observation, it was found that the granules had fine acicular diameter particles as the smallest particle unit. The needle-shaped fine particles are mainly long-axis shaped.
The size was 0.5 to 0.6 μm, and the short axis was 0.02 to 0.03 μm.

B Production and evaluation of Al-Co-P-modified α-Fe fine particles.

Next, the granules were subjected to a reduction reaction under the same conditions as in Example 1 to obtain Al-Co-P-modified α-Fe fine particle granules.

According to electron microscopic observation, the granules have fine needle-shaped particles as basic units, and the size of the granules is 0.5 to 0.6 μm in major axis diameter and 0.02 to 0.03 μm in minor axis diameter.
The shape of the raw material was well preserved in M, and there was almost no particle damage, destruction, or sintering.

When we evaluated the magnetic properties, Hc=1250Oe,
σs=185.2 and R=0.53.

Comparative Example 1 Example 1 except that metal phosphate is not deposited
The main major axis diameter is 0.5 to 0.6 μm using exactly the same method as
Dry iron oxyhydroxide fine particle granules having acicular fine particles with a minor axis diameter of 0.02 to 0.03 μm as the minimum unit were produced, and subjected to a reduction reaction under the same conditions as in Example 1.
α-Fe fine particle granules were obtained.

According to electron microscopic observation of the granules, most of them were
It has changed into spherical fine particles of about 0.4 to 0.5 μm,
Furthermore, it was observed that sintering had occurred. Furthermore, when the magnetic properties were evaluated, Hc=704Oe, σs=
141.0, R=0.37. Both particle morphology and magnetic properties were unsatisfactory.

Comparative Example 2 An appropriate amount _of the fine acicular dry iron oxyhydroxide fine particle granules described in Comparative Example 1, which do not substantially contain metal elements other than Fe, and Zn(PO ₄ ) 2.8H ₂ O While adding water as appropriate, the mixture is mixed with a sieve, and then dried and adjusted to produce a dry modified oxyhydroxide with Zn-phosphate mixed on the surface layer of the particles at a weight ratio of P/Fe=9.5/100. Fine particle granules were produced. The granules were subjected to a reduction reaction under the same conditions as in Example 1 to obtain Zn-P-modified α-Fe fine particle granules.

When the granules were observed using an electron microscope,
The particle morphology inherited the morphology of the smallest particle unit of the acicular iron oxyhydroxide particle granules used as the raw material, but small particles of about 0.1 μm, estimated to be Zn ₃ (PO ₄ ) ₂ particles, It was mixed. Evaluation of magnetic properties is
Hc=710Oe, σs=105.0emu/gr, R=0.49, which were not satisfactory.

Comparative Example 3 A dry powder of P-modified iron oxyhydroxide particles was produced in exactly the same manner as in Example 1 except that phosphoric acid was used instead of potassium phosphate. The shape of the microparticles was very similar to that described in Example 1. As a result of elemental analysis, the weight ratio of P/Fe was 0.10/100. Next, in the same manner as in Example 1, P-modified α-Fe fine particle granules were produced. When the morphology of the α-Fe fine particle granules was observed, it was found that although the morphology of the smallest particle unit was acicular, many particles were observed to be sintered with each other. In addition, the evaluation of magnetic properties is as follows: Hc=
1185Oe, σs=173.0emu/gr, R=0.49,
It was inferior to Example 1.

〔effect〕

As is clear from the above Examples and Comparative Examples, it is clear that the effects of the present invention are particularly remarkable as a raw material production method for producing α-Fe fine particles, even when compared with simple phosphates.

Claims (1)

[Claims] 1 Acicular iron oxyhydroxide particles contain metal components,
A metal phosphate compound of K, Cr or a phosphate compound of Co and a phosphate compound of Al are deposited in a ratio of P to Fe in the range of 0.05/100 to 5/100,
A method for producing ferromagnetic α-Fe fine particles for magnetic recording, characterized by heating and reduction.