JPS62139803A - Production of ferromagnetic metallic powder - Google Patents

Abstract

PURPOSE:To produce ferromagnetic metallic powder as a magnetic material for magnetic recording by adding a basic aq. soln. to an aq. soln. of a soluble ferrous falt or ferric salt or said salts added with a bivalent metallic salt to prepare ultrafine particles of hydrated metallic oxide and using the same as a raw material. CONSTITUTION:The aq. soln. of the soluble ferrous salt such as ferrous chloride or soluble ferric salt such as ferric chloride having 0.1-5mol/l concn. is prepd. and the soluble aq. soln. of the halide, perchlorate, etc., of the bivalent metal such as Co, Ni, or Cd is added to said aq. soln. or further the aq. soln. of a basic compd. such as NaOH or KOH having 0.5-5mol/l concn. is added thereto, then the ultrafine particles of the metallic hydroxide corresponding to the above- mentioned metals are formed. A surface active agent such as sodium dodecyl sulfate is added to the aq. soln. to once solidify the ultrafine particles. The particles are separated from the water through filtration and are thoroughly rinsed and dried; further the particles are heated to 250-600 deg.C in a reducing gaseous atmosphere of H2, etc., by which the particles are reduce. The ferromagnetic metallic powder as the magnetic material for magnetic recording is thus produced.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a method for producing ferromagnetic metal powder used as a magnetic material for magnetic recording.

(I) Conventional technology Magnetic recording is a method in which a magnetic medium such as a magnetic tape, magnetic drum, or magnetic disk is magnetized using hysteresis by the gap magnetic flux of a magnetic head, and is recorded as changes in residual magnetism on the magnetic material. Because of its multi-characteristics, it is widely used not only in audio recording, but also in electronic meters, rock storage devices, and other fields.

Conventionally, materials used for this magnetic recording include acicular r-Fezes, cobalt-doped r-Fe203,
Furthermore, iron oxide-based magnetic materials such as acicular Fe5O4 and cobalt-doped FezO- may be mentioned.

However, in recent years, there has been a growing demand for improved quality and characteristics of magnetic recording media, such as smaller size, lighter weight, higher density, higher output, and more stable playback output, and these iron oxide magnetic materials are needed to meet these demands. Therefore, research on iron or ferromagnetic metal powders containing iron as a main component is being actively conducted.

In response to such demands, various proposals have been made regarding methods for producing ferromagnetic metal powder. Specifically, for example, ■Co, Mn%N to iron oxyhydroxide or iron oxyhydroxide
A material doped with metals such as i is suspended in water, the suspension and Zn and/or Cr hydroxide are coprecipitated, and then the treated product is dried and reduced (Japanese Patent Publication No. 1983). -396
Publication No. 82).

(2) Iron or iron-cobalt alloy is precipitated by electrolyzing iron salt or a mixed salt of iron salt and cobalt salt by mercury electrolysis, and then mercury is removed.

■It decomposes metal carbonyls such as iron carbonyl and nickel carbonyl to obtain metal powders such as iron and nickel.

(e) Problems to be Solved by the Invention However, the above method (2) does not provide sufficient magnetic properties.

That is, although the coercive force (He) and saturation magnetic flux density (δS) of the obtained metal powder are shown in Japanese Patent Publication No. 56-39682, judging from the values expected for metal powder, they are not necessarily sufficient. It's hard to say that it's a thing.

In addition, in the above method (2), it is necessary to remove mercury by some method, and this work is quite troublesome and takes a long time in practical use.

Furthermore, in the method (2) above, the metal carbonyl is highly toxic and requires considerable care in handling, and is also expensive.

(d) Means to Solve the Problems In order to solve the above-mentioned problems, the present inventors have repeatedly studied ferromagnetic metal powder for many years.

As a result, in order to obtain metal powder with excellent magnetic properties, it is important that the shape of the metal powder is acicular and free of pores, that the particle size range is narrow, and that it does not contain distorted particles such as fragments or lump particles. Moreover, the ↑ of these particles occurs during dehydration and reduction of iron oxyoxide, etc., and the generation of distortion and pores in these particles is caused by coating metal oxides such as iron oxyoxide with a surfactant. However, they discovered that this can be prevented by dehydrating and reducing it, leading to the completion of the present invention.

That is, the present invention involves adding a basic aqueous solution to an aqueous solution containing a soluble ferrous salt and/or a soluble ferric salt, or a soluble ferrous salt and/or a soluble ferric salt, and a divalent soluble metal salt. Then, transparent particles of hydrated metal oxides corresponding to these metals are prepared, a surfactant is added thereto to cause the transparent particles to aggregate, and then this aggregate is washed and dried, and this dried product is It is characterized by converting the p element in the presence of a reducing gas.

The present invention will be explained in detail below.

In the present invention, first, a basic aqueous solution is added to an aqueous solution containing a soluble ferrous salt and/or a soluble ferric salt, or a soluble ferrous salt and/or a soluble ferric salt and a divalent soluble metal salt. In addition, step A of preparing transparent particles of hydrated metal oxides corresponding to these metals is carried out.

The soluble ferrous salt used in the present invention is not particularly limited as long as it is soluble in water or hot water. Ferrous [Fe(C104)2 ・6 H20], ferrous bromide, ferrous iodide, ferrous sulfate, ferrous nitrate, ferrous thiocyanate, ferrous acetate, ferrous ammonium sulfate Examples include iron, ferrous potassium sulfate, and the like.

In addition, the soluble ferric salt binder used in the present invention is not particularly limited as long as it is a ferric salt that is soluble in water or hot water, and specifically, for example, ferric heptadide, Ferric chloride, ferric perchlorate, ferric bromide, ferric sulfate, ferric nitrate, ferric thiocyanate, ferric oxalate, ferric ammonium sulfate, ferric potassium sulfate etc.

Furthermore, in the present invention, the divalent soluble metal salt is Go
Soluble inorganic salts and organic salts such as %Ni, Mn%Cd, Cu, Zn, Ba, etc., such as halides of these metals,
Refers to salts that are soluble in water or hot water among perchlorates, sulfates, nitrates, oxalates, acetates, etc., and these 18
It may contain one or more types.

In this case, the amount of the divalent soluble metal salt added varies depending on the type 81 metal salt used, but it must be kept within a range that does not impair the various magnetic properties of the resulting ferromagnetic metal powder. Generally, it is desirable that M be in a proportion of 1 to 50 atomic % based on the total of Fe and M (divalent metal).

Examples of the above basic aqueous solutions include aqueous solutions of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; aqueous solutions of carbonates such as sodium carbonate and potassium carbonate;
Examples include aqueous solutions of hydrogen carbonates such as 17um hydrogen carbonate, potassium hydrogen carbonate, and ammonium hydrogen carbonate, aqueous ammonia, and the like.

The concentration of the metal salt aqueous solution such as the above-mentioned soluble ferrous salt is preferably in the range of 0.1 to 5 mo12/1, and if it exceeds 5 ff1 ol/(l), turbidity or particle size distribution may occur. On the other hand, if it is less than 0.1 + no 1/1, the concentration becomes too thin, resulting in a lack of mass productivity and being extremely uneconomical.

In addition, the concentration of the basic aqueous solution is 0.5-5 +
It is preferable to set the concentration to no. 1/l. If it exceeds 5 mol/l, the concentration will be too high and it will be difficult to adjust the pit described below. On the other hand, if it is less than 0.5 mol/l, the concentration will become too thin and the liquid volume will decrease. This is not desirable because there are too many.

When reacting this metal salt aqueous solution with a basic aqueous solution to prepare ultrafine particles of a hydrated metal oxide corresponding to the metal, the reaction is preferably carried out at a pH of 3.5 or higher;
If H is less than 3.5, it is difficult to obtain acicular ultrafine particles of hydrated metal oxide.

The particle size and shape of the ultrafine particles of hydrated metal oxide obtained in this step A become the size and shape of the metal oxide particles as they are, and therefore, when preparing the ultrafine particles in this step A, the reaction temperature and aging conditions are important.

The reaction temperature is preferably in the range from room temperature to 150°C.

Further, although the aging time varies depending on the temperature, it is preferably in the range of 5 hours to 50 hours from the economic point of view.

When ferrous sulfate is used as the soluble ferrous salt and γ-Fe2O3 is prepared from this aqueous solution via Q Fe0OH, it is preferable to blow air during ripening, and In order to prevent the generation of α-FeoOH, it is desirable to generate α-FeoOH from an alkaline solution.

In the present invention, step B is then carried out in which a surfactant is added to the solution obtained in step A above to once aggregate the 'Hi fine particles of hydrated metal oxide.

That is, the feature of the present invention is that a surfactant is directly added to the solution obtained in the above step A to once aggregate the transparent particles of hydrated metal oxide.

By coating the surface of the ultrafine particles of hydrated metal oxide with a surfactant, pores are not generated within the particles during the dehydration process of the ultrafine particles, and moreover, sintering occurs during heating and drying of the ultrafine particles. does not occur.

Examples of the surfactant used in the present invention include sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium caproate, sodium caprylate,
Sodium laurate, sodium oleate, sodium alkylnaphthalene sulfonate, or phosphate ester salt type anionic surfactants, such as higher alcohol phosphate monoester monoester salt, higher alcohol phosphate diester sodium salt, etc. Anionic surfactant, oleic acid, sulfuric acid, rillic acid, lauric acid,
Fatty acids such as palmitic acid, myristic acid, stearic acid, salts of low polymerization degree polycarboxylic acids, such as low polymerization degree sodium polyacrylate, low polymerization degree butyl polyacrylate, low polymerization degree polysodium methacrylate, and the following: Examples include surfactants such as sulfonated polystyrene represented by the general formula (%), among which oleic acid, linoleic acid,
It is preferable to use fatty acids such as oleic acid, lauric acid, palmitic acid, myristic acid, and stearic acid because they can be easily removed when reducing ultrafine oxide particles.

In this process, the amount of surfactant added varies depending on the type and amount of hydrated metal oxide and the type of surfactant used, so it is determined appropriately, but in short, ultrafine particles of hydrated metal oxide aggregate. It is sufficient to add up to

In the present invention, Step C is performed in which the two suspicious fruits obtained in Step B are filtered and washed.

Filtering and washing the aggregates has the following advantages.

(a) First, productivity is greatly improved, mass production can be realized, and ultrafine particles of hydrated metal oxide can be obtained economically.

In other words, the ultrafine particles of the hydrated metal oxide are washed by repeating filtration and washing, so the cleaning effect is very good, the pH can be easily neutralized, and the hydrated metal oxide has a high purity. Ultrafine particles can be obtained.

The aggregate obtained in step B above is spongy and has a very good flow of water during filtration, so that the aggregate can be washed and filtered extremely well.

(b) Since the excess surfactant that is oriented and adsorbed can be easily removed, the content of ultrafine metal oxide particles can be increased.

The filtration method is not particularly limited, and conventionally known methods such as suction filtration, natural filtration,
Various methods can be used, such as pressure filtration.

In the present invention, the step of obtaining ultrafine metal oxide particles is carried out by subjecting the ultrafine metal oxide particles obtained in step C above to heat treatment under normal pressure or vacuum to dehydrate them.

This drying method is not particularly limited,
The drying may be carried out by heating and drying in the air, or by heating and drying in an inert bath. The temperature is such that the surfactant adsorbed on the surface does not decompose.

Therefore, the drying temperature varies depending on the drying method, the hydrated metal oxide, and the type of surfactant used, but is usually 350° C. or lower.

During this heating and drying, the surfactant prevents the formation of pores within the ultrafine particles.

In the present invention, finally, a step E is carried out in which the dried product obtained in the above step is reduced in the presence of a reducing gas to obtain a ferromagnetic metal powder.

Examples of the reducing gas used in the present invention include hydrogen, ammonia, and carbon oxide, and these may be used alone or in combination of two or more. The temperature of the reduction reaction is preferably 250 to 600"C, particularly 350 to 5"C.
A range of 00°C is desirable.

If the temperature is less than 250°C, there is a risk that the ultrafine metal oxide particles may not be reduced to the metal, and conversely, if the temperature is lower than 600°C, the ultrafine metal oxide particles may be reduced and the resulting ultrafine metal particles may be sintered. Yes, I don't like it in any way.

In this case, according to the experimental results of the present inventors, the metal powder that is reduced and generated is sintered even at a temperature of about 400°C when a surfactant is not used, but when a surfactant is used, the metal powder is sintered at a temperature of 600°C. No sintering was observed unless the temperature exceeded .

In addition, if the obtained metal particles are active and may be oxidized in the air, the ultrafine metal particles may be immersed in air. Sv/v
%, nitrogen 99.5 v/v% is passed through a bath, or the ultrafine metal particles are dispersed in an organic solvent such as toluene,
A dense oxide film may be formed on the surface of the ultrafine metal particles by, for example, blowing air into the particles.

Furthermore, it has been found that when metal oxides are reduced with ammonia or a reducing gas containing ammonia, nitrides are formed on the surfaces of metal particles, improving oxidation resistance.

By going through each of the above steps, it is possible to obtain a ferromagnetic metal powder that has excellent magnetic properties such as coercive force (Hc) and saturation magnetic flux density (δS), has a uniform particle size distribution, and has excellent dispersibility and filling properties. .

(e) Effect In the present invention, it is not clear why pores are generated during drying of M fine particles of hydrated metal oxide or sintering of particles is prevented during reduction of dried metal oxide. However, it is assumed that the surfactant regulates the evaporation of water and thereby prevents the generation of pores, while the presence of the surfactant between the particles prevents the particles from sintering together. .

Further, this surfactant is removed by evaporation, decomposition, or elution when reducing the gold R oxide ultrafine particles or during surface oxidation treatment of the ferromagnetic metal ultrafine particles.

(f) Examples Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto. 2mo
l/l aqueous sodium hydroxide solution 1.051! was added to make 31 M fine particles of hydrated iron oxide, which were heated at a temperature of 40°C.
After aging for 16 hours, 0.2 mol/1 lauric acid aqueous solution was added to coagulate the ultrafine particles of hydrated iron oxide.
let Filter this and remove the aggregates from o, oi ~ 0°0
After repeating washing and filtration with 2 mol/(l) of ammonia water to adjust pi to 6.5 to 7.0, washing and filtration are further performed 5 times with hot water 241 at a temperature of 60 to 70°C.

Next, this aggregate was heated and dried at a temperature of 270°C for 2 hours, and then the dried product was heated in a hydrogen stream at a temperature of 450°C for 10 hours.
Ferromagnetic iron powder was obtained by time reduction. The magnetic properties of the obtained ferromagnetic iron powder are shown in Table 1.

Example 2 1 + no 1/1 ferrous sulfate aqueous solution 2N and 2 mo
Ultrafine particles of hydrated ferrous oxide were prepared in 1.5 p of a +7 um aqueous solution, and the particles were added to the
Acicular α-FeOOH was formed by blowing air at oC for 15 hours.
f: Got it. Next, add 0, 2 mol/(
1 of an aqueous solution of sodium dodecylbenzenesulfonate is added to aggregate the acicular α-FeOOH.

Thereafter, ferromagnetic iron powder was obtained by filtration, washing, drying, and reduction in the same manner as in Example 1.

The obtained ferromagnetic iron powder was dispersed in toluene, and air was blown into it to partially oxidize the surface of the ferromagnetic iron powder to form a dense oxide film.

The magnetic properties of this ferromagnetic iron powder are shown in Table 1.

Example 3 0,5 mo1/1 ferric chloride aqueous solution 250b+
Add 800+a1 of a sodium hydroxide aqueous solution of Nl:0°5IIIO1/1 to prepare ultrafine particles of hydrated iron oxide,
This was hydrothermally treated in an autoclave at a temperature of 150°C for 5 hours, then lowered to 35°C, and then 1 mol
/ 1 lauric acid was added to once aggregate the above ultrafine particles, and hereinafter, 7 ammonia SOv/v% was added as a reducing agent.
Ferromagnetic iron powder was obtained by filtration, washing, drying, and reduction in the same manner as in Example 1, except that a mixed gas containing 50 v/v% of hydrogen was used.

When ammonia is used as a reducing agent in this way, an oxide is formed on the surface, thereby improving oxidation resistance.

The magnetic properties of the obtained ferromagnetic iron powder are shown in Table 1.

Example 4 1 tool/1 ferric chloride aqueous solution 1.51 and 1 t
A hydrated iron oxide-hydrated cobalt oxide composite ultrafine particle was prepared by adding 2.51 of a 3 mol/1 sodium hydroxide aqueous solution to a mixed solution consisting of a nol/l cobalt chloride aqueous solution 11, and heated at a temperature of 40°C. After aging for 15 hours in
, 5 tools/e of a lauric acid aqueous solution was added to once aggregate the composite ultrafine particles, and then in the same manner as in Example 1, ferromagnetic FeCo powder was obtained.

The magnetic properties of the obtained ferromagnetic Fe-Co powder are
Shown in the table.

Example 5 A mixed solution of 0,9 won/l of ferric sulfate aqueous solution filR and 0.1 tnol/l2 of nickel sulfate aqueous solution 11 was added with 2 tools/fl of hydroxide.
．． 5e was added to prepare hydrated iron oxide-nickel hydroxide composite ultrafine particles, and then ferromagnetic Fc
-Ni powder was obtained.

The magnetic properties of the obtained ferromagnetic Fe Ni powder are shown in Table 1.

Comparative Example 1 A sample in which no surfactant was used in Example 1 was used.

Comparative Example 2 In Example 2, a sample was prepared in which no surfactant was used.

(hereinafter referred to as Utaguchi) Table 1 20 copies of each example and each comparative example (hereinafter referred to as each sample) (
'' mm (the same applies hereafter) into a bangu solution consisting of 5 parts of polyurethane resin and 15 fflS of toluene,
After mixing and dispersing in a ball mill for 8 hours,
12 parts of urethane resin and 50 parts of toluene were added and mixed for 2 hours. At this time, when each sample was uniformly dispersed, it was marked as ○, and when there was even a small amount of aggregates, it was marked as ×.

Note 2 - side Each sample was measured by the BET method.

Although the method for producing ferromagnetic metal powder according to the present invention is as described above, ferromagnetic metal powders other than those in the above examples can also be produced by the method according to the present invention.

(g) Effect of the invention The method for producing ferromagnetic metal powder of the present invention has the above configuration,
It has the effect of easily producing ferromagnetic metal and metal powder with excellent magnetic properties such as coercive force and saturation magnetic flux density, good dispersibility, and narrow particle size range.

Claims (1)

[Claims] (1) Adding a basic aqueous solution to an aqueous solution containing a soluble ferrous salt and/or a soluble ferric salt, or a soluble ferrous salt and/or a soluble ferric salt and a divalent soluble metal salt; Ultrafine particles of hydrated metal oxide corresponding to the metal are prepared, a surfactant is added to the ultrafine particles to cause the ultrafine particles to aggregate, the aggregate is then washed and dried, and the dried material is exposed to a reducing gas. A method for producing ferromagnetic metal powder, characterized by reducing the powder in the presence of.