JPS6362803A - Production of ferromagnetic metallic power - Google Patents

Abstract

PURPOSE:To provide a material for magnetic recording having superior magnetic characteristics and oxidation stability by coating the surface of iron or an iron-base compd. with an amorphous Al compd. or an amorphous Al-base compd. and carrying out reduction under heating. CONSTITUTION:An iron-base compd. such as needlelike iron oxyhydroxide is synthesized by hydrolyzing a ferrous sulfate soln. and sodium hydroxide. The iron oxyhydroxide is diluted with water and stirred. The surface is coated with an amorphous Al compd. such as sodium aluminate or aluminum sulfate, and reduction is carried out under heating in a flow of hydrogen or a hydrogen- base gas to form metallic powder. Thus, ferromagnetic metallic powder can be formed and a material for magnetic recording having superior oxidation stability can be provided.

Description

[Detailed description of the invention] Child! The present invention relates to a method for producing fine ferromagnetic metal powder particles as a magnetic material in a magnetic recording medium suitable for high-density recording.

A magnetic powder useful as a magnetic tape and a magnetic recording medium is γ
- Iron oxide was the main ingredient, but in recent years there has been a demand for high-density recording media for VTRs and high-end audio, and powders mainly composed of dioxyiron hydroxide or iron oxide are brought into contact with the vapor phase using a reducing gas. Magnetic powders with high coercive force mainly made of metallic iron, cobalt, or an alloy of nickel and iron obtained by reduction reaction have come to be used, because the coercive force of metallic magnetic fine particles has strong shape anisotropy. Although it depends on the particle size, acicularity, etc., appropriate coercive force and residual magnetic flux density are required for tape recording.

Magnetic recording media, whether used for audio or video, have higher output and lower noise in a wide recording frequency band.In other words, the shape of magnetic powder tends to be finer, and it is also compatible with paint resins. It is desired to further improve the dispersibility, orientation and filling properties of coating films, and research is being carried out to improve binder resins and various additives, as well as paint dispersion and media processing technology (for example, Akashi Sanbe). "Advances in magnetic tape" 1 Journal of the Japanese Society of Applied Magnetics, ? (3), 185 (1983),
).

Conventionally, several important techniques have been required to obtain iron or iron-based ferromagnetic metal powders by heating and reducing starting materials in a reducing atmosphere using iron or iron-based metal compounds. Ta.

First, in order to prevent sintering caused by thermal reduction in a reducing atmosphere and maintain the shape of the raw material, phosphorus, silicon, aluminum, chromium, boron compounds, etc. are added as sintering prevention components.
It has been proposed to co-precipitate or adhere to a starting material, iron or a metal hydroxide or oxide mainly composed of iron, followed by thermal reduction.

In addition, since iron or iron-based metals obtained by thermal reduction easily oxidize and burn in the atmosphere, it is possible to safely handle them in the atmosphere, and the oxidation of ferromagnetic metals progresses. It is known that in order to prevent the deterioration of magnetic properties over time due to such thermal reduction, the surface of iron or iron-based metals obtained by such thermal reduction may be intentionally oxidized or stabilized by coating with inorganic compounds. It is being

Furthermore, it is known to treat ferromagnetic metal powder with various organic primary compounds or organometallic compounds for the purpose of improving the affinity between ferromagnetic metal powder and paint binder resin.

As mentioned above, producing ferromagnetic metal powder that fully satisfies various properties as a magnetic material for magnetic recording requires an extremely complicated process and is difficult to achieve. It was extremely rare for the addition of a processing technology in the hope of achieving a certain effect to work on its own without affecting other properties. The manufacturing process was in great need.

The inventors of the present invention fully grasped the conventionally known technology and continued basic research on the crystal morphology of the oxide layer and oxide film of ferromagnetic metal powder, and as a result, they discovered excellent magnetic properties. The present invention has been achieved which has excellent corrosion resistance, high affinity with paint binder resins, and a simple and inexpensive manufacturing process.

That is, the gist of the present invention is to convert iron or iron-based compounds, such as oxyhydroxides or oxides, into crystallographically amorphous aluminum compounds or crystallographically amorphous aluminum-based compounds. After the surface is coated with a compound, this is heated and reduced in hydrogen or a reducing atmosphere mainly composed of hydrogen, whereby a metal powder with excellent magnetic properties can be obtained.

Conventionally, the use of aluminum compounds in the production process of ferromagnetic metal powder is already a well-known technology, and aluminum compounds are doped in the production of iron oxyhydroxide, which is one of the starting materials. matters (for example, special public relations in 1972)
No.-30477, No. 59-19165, JP-A No. 1983-
No. 114833) etc. are known.

These methods yield raw materials with excellent acicularity and particle size distribution, and are said to be effective in preventing interparticle sintering and particle porosity in the subsequent calcining and reduction process. There is.

However, in this case, increasing the amount of aluminum compound doped is not preferable because the acicularity of the iron oxyhydroxide deteriorates and magnetite is also likely to be generated. Also, since aluminum is uniformly dissolved in iron oxyhydroxide,
In the calcination and reduction process, iron spinel (FeA1204
) is generated, making it difficult to reduce, and furthermore, saturation magnetization decreases, which is not preferable.

Furthermore, methods for surface-coating aluminum compounds on iron or iron-based metal compounds include, for example, JP-A-56-114833, JP-B-Sho 59-19168,
There are No. 59-19163, No. 57-29523, etc.

Among these, JP-A-56-114833 was proposed by the present inventors, and is a method in which phosphorus and aluminum are deposited simultaneously, which may result in the formation of an amorphous aluminum compound. However, since the accompanying phosphorus component forms oxidation points on the surface layer of the final product, iron fine particles,
There is a tendency for the affinity with paint resins to decrease. On the other hand, Japanese Patent Publications No. 59-19168, No. 59-19163, No. 57-29523, etc. all involve the use of a silicon compound in combination with an amorphous silicon compound or an amorphous silicon and aluminum compound. It is effective to some extent when generating. However, increasing the amount of silicon compound increases hydrophilicity and reduces affinity with the binder resin, which is undesirable. Also, increasing the amount of aluminum compound to be deposited causes crystalline alumina hydrate to form during the deposition process. So-called gibbsite, vialite, boehmite gel, etc. are generated, reducing the adhesion efficiency. Examples of methods for using aluminum compounds alone include Japanese Patent Publication No. 56-28967, but in this case, the essential crystal form of the aluminum compound is not specified or controlled in any way, and as a result, alumina hydrate is produced. In many cases, the effect is not noticeable, and this method basically involves dissolving the aluminum compound in water or an organic solvent, and then immersing the iron or iron-based metal compound in the solution. However, there are problems in that the aluminum compound is eluted by filtration, and segregation of the aluminum compound inevitably occurs during drying, making it impossible to achieve uniform adhesion.

Furthermore, methods for improving the stability of the reduced ferromagnetic metal powder in the atmosphere and its affinity with binder resins are disclosed, for example, in JP-A-58-16170'9 and JP-A-58-16170'9.
No. 161725, and if applied to the present invention, the effect will be even more remarkable, but it has the disadvantage that the manufacturing process becomes longer.

Furthermore, the affinity between iron oxyhydroxide or iron oxide, which is a starting material, and aluminum compounds, especially alumina hydrate and aluminum oxide, is extremely high, such as hematite (
Up to 10% of aluminum oxide is dissolved in α-iron oxide). In addition, a solid solution is formed in the magnetite produced during the thermal reduction process of iron or iron-based compounds as iron spinel of iron-aluminum composite oxide (
Phase Diagra+s for Ceram
ists, Figs 26-27+2095-2098
+ The Aa+erican Ceramic
5ociety, Inc.) *Iron spinel is difficult to reduce to metallic iron under normal reducing conditions. Therefore, when coating a surface with alumina hydrate, it is necessary to control the solid solution of aluminum oxide into the surface layer of iron oxide or magnetite while controlling the crystal form and particle size of the alumina hydrate that is the deposit. things are important.

The present inventors have intensively studied methods for controlling the solid solution of aluminum oxide on the surface of iron oxide or magnetite, and have achieved the present invention as a result of pursuing a method for controlling the crystal form and particle size of alumina hydrate. did.

That is, as a method in an aqueous system, an aluminum-based hydrogel containing at least one of phosphorus, silicon, or nickel as a subcomponent in an amount of 1% or more by weight relative to aluminum is mixed with iron or iron in an aqueous system. It is adsorbed onto the surface layer of fine particles of metal compounds mainly composed of iron, and then heated to a temperature of 90 to 13
By heating at 0'C, homogeneous adhesion with a dense amorphous gel progresses, and aluminum oxide becomes a solid solution in the surface layer of iron oxide or magnetite in the process of manufacturing ferromagnetic metal powder. can be suppressed. In this case, if the heat treatment conditions are less than the above, a dense and uniform film of gel will not be formed, and if the heat treatment conditions are exceeded, gel crystallization will substantially proceed, and aluminum will be formed in the subsequent calcination and reduction steps. Assolubility is promoted and the object of the present invention cannot be achieved.

In addition, as another non-aqueous method, fine particles of metal compounds mainly composed of iron or iron compounds are suspended in an organic solvent.
By adding an organoaluminum compound and adsorbing the organoaluminum compound onto the surface layer of the fine particles, and then adding a poor solvent such as acetone or alcohol to turn the adsorbed aluminum compound into a gel, a dense non-aluminum compound is formed. Uniform adhesion by the crystalline gel progresses, and it is also possible to prevent aluminum oxide from becoming a solid solution in the surface layer of iron oxide or magnetite in the process of producing ferromagnetic metal powder. The latter method is more preferable than the water-based method because it can form a deposited film of only aluminum.

The aluminum compound used for adhesion in the present invention is as follows:
In aqueous systems, inorganic compounds such as nitrates, sulfates, chlorides, basic acetates, or alkali aluminates can be used, and in non-aqueous systems, organic metal compounds such as alkoxide compounds and chelate compounds can be used.

In the case of the former surface adhesion of the inorganic compound, it is preferable to carry out the process under conditions that suppress the formation of hydrates produced by hydrolysis, such as crystalline hydrates such as so-called gibbsite, vialite, or boehmite gel. Furthermore, the formation of crystalline hydrates can be more preferably prevented by using together with phosphates such as diammonium hydrogen phosphate and sodium metaphosphate, silicates such as water glass, or inorganic compounds such as nickel and magnesium. Can be done.

When using the latter organoaluminum compound, if the organoaluminum compound is easily hydrolyzed by moisture, it can be treated in a dry atmosphere, that is, without water, to form a crystallographically amorphous deposited film. I can do that.

If necessary, the iron or iron-based compound deposited on the surface is calcined at 300 DEG C. to 800 DEG C. to form α-iron oxide deposited on the surface. Calcining at a high temperature exceeding 800° C. is not preferable because aluminum oxide becomes a significant solid solution in α-iron oxide, and interparticle sintering also becomes severe.

Next, thermal reduction is carried out at 300° C. to 600° C. in an atmosphere of hydrogen or a reducing gas mainly composed of hydrogen to produce iron or a ferromagnetic metal powder mainly composed of iron. 300℃
At a temperature lower than 600° C., reduction is slow and takes a long time, and at a temperature higher than 600° C., sintering between metal particles becomes severe, which is not preferable.

Reduced iron or ferromagnetic metal powder mainly composed of iron will oxidize and burn in the atmosphere if left as is, so the metal powder is immersed in an organic solvent such as toluene according to a standard method, and oxidizing gas such as air is gradually removed from the metal. The metal surface is oxidized and stabilized by bringing it into contact with powder or by gradually passing an oxidizing gas such as air in an atmosphere of an inert gas such as nitrogen.

In the present invention, by making the deposited film of the aluminum compound amorphous, a remarkable effect can be achieved with a small amount of deposition. =0.00L to 0.1 is preferable.

Note that if the amount of aluminum compound deposited is further increased, the shape of the ferromagnetic metal powder will become even better, but since the coating becomes thicker, the reduction will be slower and the saturation magnetization will decrease by the weight of the aluminum oxide, so this is not practical ^1 /Fe・0.1 is the limit. Although the effect can be exerted to some extent even if the amount of the aluminum compound deposited is small, the lower limit of the deposit amount suitable for a magnetic recording material is AI/Fe.0.001.

TatsuriThe ferromagnetic metal powder obtained by the method of the present invention has an amorphous deposited film quality, which results in high deposition efficiency and uniformity, resulting in excellent shape retention and magnetic properties. It is characterized by its excellent oxidation stability.

1. Hereinafter, the method of the present invention and its effects will be explained in detail with reference to Examples and Comparative Examples.

Example 1 After hydrolyzing a ferrous sulfate solution with a sodium hydroxide solution in a conventional manner, acicular iron oxyhydroxide was synthesized by passing air through the solution. Specific surface area (SA) determined by nitrogen gas adsorption method
) was 72.5 m2/g, and the ratio of the long axis to short axis (L/D) was 12 when observed using a transmission electron microscope. The iron oxyhydroxide is diluted with water and stirred, and the pH is
Sodium hexametaphosphate, 3 while maintaining at 10,0
P/Fe-0,4/100. Si/FeJ,l
/100. AI/Fe-4,0/100 and Ni/Fe
= 3.0/100 was adhered to the surface, the pH was lowered to 8.0 with nitric acid, and the 1&cough slurry was boiled at 98°C for 5 hours, filtered and washed with water.

Next, it was dried in a box-type hot air dryer at 120°C for 18 hours.
It was ground into raw material powder using a grinder (Nara type free grinder). In order to examine the crystal morphology of the deposited film, X-ray diffraction measurements were performed on a gel-like material treated under the same conditions with only a depositing reagent containing no iron oxyhydroxide. As a result, the quality of the deposited film was found to be amorphous. The surface-adhered iron oxyhydroxide was charged into a fixed-bed reduction furnace, and nitrogen gas was introduced at a gas hourly velocity of 20.
8m2-Nz/kgr-Fe, circulated at hr, temperature 50
After calcination at 0°C for 4 hours, gas phase catalytic reduction reaction using hydrogen gas (temperature: 450°C, 6 hours, gas space velocity*20 N
m'-H2/kgr-Fe,)lr,) to form reduced iron powder.Then, the fine particles were thoroughly immersed in toluene, and the fine particle slurry was placed on an enamel vat to a thickness of about 1 cm. The plant was moved to a new facility and treated with toluene dispersion in the atmosphere. When the smell of the solvent disappeared, the magnetic powder was collected and made into air-dried metal iron powder. When the shape of the air-dried metallic iron powder is observed with a transmission electron microscope, it appears that it closely follows the shape of the primary raw material, iron oxyhydroxide, and there is almost no damage, destruction, or interparticle sintering. There wasn't. The magnetic properties of the air-dried metallic iron powder were measured using a sample vibrating magnetometer (VSM-III manufactured by Toei Kogyo Co., Ltd.).
), and the specific surface area was measured by nitrogen gas adsorption method, He・15000e, σ5-135 ee
au/g, R-0,52,5A-53,2m"/g
It was found that it has excellent magnetic properties. We also conducted a corrosion resistance test on the metal powder. 5.0g of air-dried iron powder at temperature 5
The saturation magnetization (σS) was 115 emu/g after being held for 60 hours in a constant temperature bath adjusted to 0°C and relative humidity of 80χ. The obtained metal powder was found to have excellent oxidation stability. Furthermore, in order to investigate the affinity with the paint binder resin, vinyl chloride - vinyl acetate - manufactured by Tanezu Kagaku Co., Ltd.
The adsorption amount of vinyl alcohol copolymer resin S-LEC A was measured. Cough wind dry iron yJ 2.5g to Srefuku A 1.0g
The adsorption amount after 24 hours immersion at room temperature in a toluene/MEK mixed solution (1:1) containing 1 volume of
It was found that it is an iron powder with high affinity.

Comparative Example 1 The same adhesion treatment as in Example 1 was performed, but the boiling treatment was not performed. When the crystal morphology of the deposited film was examined in the same manner as in Example 1, it was found that vialite (JCPDS Card No. 20-11), which is a crystalline alumina hydrate, was produced.Example The properties of the metal powder that was calcined and reduced in the same manner as in 1 and then subjected to the same slow oxidation treatment are Hc
=12800e, σs□t22 emu/g, 1i
−0,47,5A=50.5 m”7g, and when the shape of the air-dried metallic iron powder was observed with a transmission electron microscope, it was found that the shape of the iron oxyhydroxide used as the next raw material was partially damaged and destroyed; Interparticle sintering was observed. After the corrosion resistance test of the air-dried metal iron powder, σ5-103 e+wu/g, and the amount of resin adsorption was also 0.8 m
g/m'', indicating that both oxidation stability and resin affinity were inferior to Example 1.

Comparative Example 2 A1/Fe sodium aluminate was prepared by the method of Example 1.
-7.0/100 was added to synthesize iron oxyhydroxide. Chemical analysis of acid iron oxyhydroxide revealed that AI/Fe
I found out that it was doped by -5,6/100. The SA by nitrogen gas adsorption method was 65.3 m''/g, and the ratio of long axis to short axis (L/D) by transmission electron microscopy was 8. <Reduced for 10 hours in the same manner as in Example 1 to obtain an air-dried metal powder.
l1c-8800e, σ5=128 emu/g 5
R = 0.38.5A-49,211"7g, and showed insufficient properties despite being reduced for a long time. When the air-dried metallic iron powder was observed with a transmission electron microscope, it was found that the inside of the particles was Significant crystallite growth and interparticle sintering occurred.Until the oxidation stability and resin adsorption amount of the metal powder were measured, it was found that it was unsuitable as a magnetic recording material.

Example 2 The iron oxyhydroxide of Example 1 was used, diluted with water and stirred, aluminum sulfate was added in an amount of AI/Fe 3.0/100, and urea was added in an equivalent amount 3 times that of aluminum sulfate. Boiling treatment was performed for 15 hours, followed by filtration and washing with water. Example 1
The crystallinity of the deposited film was examined in the same manner as above, and it was found to be amorphous. Reduction was carried out in the same manner as in Example 1 to obtain an air-dried metal powder. The air-dried metal powder is Hc-14700e, σ5-1
28 emu/g, R=0.49.5A=50.6
11z/g, showing excellent properties. When dry metal iron powder is observed with a transmission electron microscope, it appears that it closely follows the shape of iron oxyhydroxide, the primary raw material, and shows damage, destruction, and damage.
Furthermore, almost no interparticle sintering was observed. It was found that the oxidation stability (σS 113elIu 7g) and resin adsorption amount (1.2mg/m') of the metal powder were also excellent.

Comparative Example 3 Iron oxyhydroxide was diluted with toluene and stirred, and aluminum trisethyl acetoacetate was diluted with AI/Fe・4.0
1/100 was coated, filtered, dried under reduced pressure, and pulverized. The crystallinity of the deposited film was examined in the same manner as in Example 1, and it was found to be amorphous. However, chemical analysis of the blue powder revealed that it had an AI/Fe ratio of 1.4/100, indicating that the aluminum compound had been eluted by filtration.

After reducing at 375°C for 10 hours in the same manner as in Example 4,
The same stabilization treatment as in Example 4 was carried out to obtain a metal powder that was non-flammable even in the atmosphere. The air-dried metal powder is He-123
0, σ5-102 emu/g, R-0,46, S
A.45.2 m" 1 g, which showed insufficient characteristics. When the air-dried metallic iron powder was observed with a transmission electron microscope, it appeared that the particles had a shape that closely inherited the shape of the primary raw material, iron oxyhydroxide. However, it was found that uniform adhesion was not possible because many aggregates with severe interparticle sintering were observed.Until the oxidation stability and resin adsorption amount of the metal powder were measured. It was found that the material was unsuitable as a magnetic recording material.

Example 3 The same iron oxyhydroxide as in Example 1 was dried, diluted with toluene and stirred in an atmosphere of dry air, and aluminum isopropoxide was added in an amount of AI/Fe-4,07100. Furthermore, methanol was added to gel the aluminum compound, which was then deposited, followed by filtration, drying, and pulverization. Chemical analysis of the blue powder revealed that no aluminum compounds were eluted during filtration. The crystallinity of the deposited film was examined in the same manner as in Example 1, and it was found to be amorphous. The raw material powder was subjected to reduction and stabilization treatment under the same conditions as in Example 4 to obtain metal powder. The metal powder is Hc・1520
, σ5-131 e+mu/g, R-0,50,5
A-54.3m" 1g and showed excellent properties. When the metallic iron powder was observed with a transmission electron microscope, it was found that it closely followed the shape of iron oxyhydroxide, the primary raw material, and showed no damage or damage.
Almost no fracture or interparticle sintering was observed. Oxidation stability of the metal powder (σg=116 emu/g)
- It was found that the resin adsorption amount (1.4 mg/m") was also excellent.

Just 24 again! As is clear from the above description, in the present invention, iron or an iron-based compound is coated on the surface with a crystallographically amorphous aluminum compound and an aluminum-based compound. Magnetic recording with excellent shape retention, magnetic properties, and oxidation stability can be achieved by producing iron or ferromagnetic metal powder mainly composed of iron by thermal reduction in hydrogen or a reducing gas atmosphere mainly composed of hydrogen. We can provide materials for

Claims (3)

[Claims] (1) When producing iron or a ferromagnetic metal powder mainly composed of iron by heating and reducing iron or a metal compound mainly composed of iron compounds in a reducing atmosphere, 1. A method for producing a ferromagnetic metal powder, which comprises applying a coating treatment with an amorphous compound or a crystallographically amorphous compound mainly composed of aluminum, and then carrying out the reduction. (2) A metal compound mainly composed of iron or a metal compound mainly composed of iron, in which a hydrogel body mainly composed of aluminum containing 1% or more of phosphorus, silicon, or nickel by weight of aluminum is used in an aqueous system. It is adsorbed to the surface layer of the fine particles, and then heated to 90 to 1 at normal pressure to 10 atm or less.
The method according to claim 1, wherein a dense amorphous gel body is deposited by heat treatment at 30°C. (3) Fine particles of a metal compound mainly composed of iron or an iron compound are suspended in an organic solvent, an organic aluminum compound is added to the surface of the particles for adsorption treatment, and then a poor solvent is added to make the aluminum compound adsorbed. The method according to claim 1, which promotes gelation of.