JPS5919166B2 - Manufacturing method of metal magnetic powder - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a method for producing magnetic powder mainly composed of metallic iron, which allows the axial ratio and size of the particles to be adjusted.
Moreover, it is an object of the present invention to provide the above-mentioned manufacturing method, which suppresses sintering and deformation of the particles during the heat treatment step, and obtains a magnetic powder that is dense and has excellent magnetic properties.

Generally, magnetic powder mainly composed of metallic iron is Fe3o4
It has the advantage of superior magnetic properties such as coercive force (Hc) compared to iron oxide magnetic powders such as γ-Fe2O3 and γ-Fe2O3, and can be used as recording elements for various magnetic recording media such as magnetic tapes. However, it is usually produced by thermal reduction using α-iron oxyhydroxide, which is made up of acicular particles that are collected from the wet reaction process, and α-Fe2O3, which is obtained by heating and dehydrating it, as a raw material. Therefore, properties such as the particle diameter and i5 shape of the particles largely depend on the properties of the raw material itself, and these properties greatly influence the magnetic properties and suitability for magnetic recording media.

On the other hand, during the heat treatment process, that is, during the above-mentioned thermal reduction and thermal dehydration when passing through α-Fe2O3, sintering between particles, partial melting of individual particles, and porosity of the particles due to dehydration and deoxidation occur. This is likely to occur due to nonuniform particle size and loss of acicular shape and density of particles.
The magnetic properties of the obtained magnetic powder mainly composed of metallic iron tend to deteriorate significantly.

Therefore, in order to obtain excellent magnetic powder, the above-mentioned α
- Making the iron oxyhydroxide itself have good properties, and improving the above 10 defects in the heat treatment process to improve the sharp acicular shape and uniformity of the raw material α-iron oxyhydroxide. There is a need to inherit this to the magnetic powder particles, but at present there is no known method that is fully satisfactory.

The inventors conducted extensive research in light of the above circumstances! In the process of accumulating 5, a reaction that produces α-iron oxyhydroxide,
In other words, in a method of oxidizing ferrous hydroxide by introducing an oxygen-containing gas into a suspension of ferrous hydroxide obtained by applying an alkali to a ferrous salt, the suspension is maintained in an alkaline region. When the reaction is carried out, the magnetic powder mainly composed of metallic iron produced by thermal reduction using the generated α-iron oxyhydroxide or α-Fe2O3 obtained by heating and dehydrating it as a raw material becomes extremely dense particles. have already been refined.

In the course of further research, this invention revealed that in the reaction for producing α-iron oxyhydroxide described above in an alkaline region, a metal selected from magnesium hydroxide and calcium hydroxide was added to a suspension of ferrous hydroxide. a silicon compound is deposited on the particle surface of the object to be treated when at least one of If thermal dehydration and/or thermal reduction is performed, α-iron oxyhydroxide produced by adjusting the amount of at least one selected from magnesium hydroxide and calcium hydroxide, and finally the metallic iron obtained. It is possible to adjust the axial ratio and size of the main magnetic powder particles, suppress the sintering and deformation of the particles during the heat treatment process, and maintain the already mentioned denseness of the particles due to the reaction in the alkaline region. This was achieved by discovering.

As specific examples of at least one selected from the above-mentioned magnesium hydroxide and calcium hydroxide, magnesium hydroxide and calcium hydroxide are preferable, and the more these are present, the more they will precipitate when oxygen-containing gas is introduced. α
-The axial ratio (major axis/minor axis) of iron oxyhydroxide particles tends to be large, and the b1 particle size also tends to become somewhat small. Therefore, by increasing or decreasing the amount, the final product is mainly metallic iron. V1 which allows adjustment of magnetic powder particles and α which further precipitates
- The presence of at least one member selected from magnesium and calcium in or on the surface of the iron oxyhydroxide particles suppresses sintering and deformation of the particles during the subsequent heat treatment step.

The means for incorporating at least one selected from magnesium hydroxide and calcium hydroxide into the suspension of ferrous hydroxide may include a method of adding at least one selected from magnesium hydroxide and calcium oxide itself. but,
Usually, a method is adopted in which at least one water-soluble salt selected from various types of magnesium calcium is added and a hydroxide precipitate is precipitated by adjusting the pH. As a preferred specific example of the latter method, in a reaction in which a ferrous salt such as ferrous sulfate is reacted with an alkali to precipitate a colloidal precipitate of ferrous hydroxide, water-soluble alkaline earth metals are present in the system. A method of adding salt to produce at least one kind of coprecipitate selected from ferrous hydroxide, magnesium hydroxide and calcium hydroxide is mentioned. According to such a method, an oxygen-containing gas is introduced and α- When iron oxyhydroxide is precipitated,
Since at least one selected from magnesium and calcium is mainly incorporated into the precipitated particles, the addition efficiency for the above-mentioned effects is particularly good in the heat treatment process, even compared to other methods. The amount of at least one selected from magnesium hydroxide and calcium hydroxide is such that the alkaline earth metal atom is M
When e is the atomic ratio of Me/Fe to ferrous hydroxide, it is preferable that the amount is 0.001 to 0.1. If it is too little, no substantial effect can be expected, and if it is too much, the magnetic properties will deteriorate. There are negative side effects.

In this invention, an oxygen-containing gas such as air is introduced into a suspension of ferrous hydroxide, and the reaction for producing α-iron oxyhydroxide is carried out in an alkaline region. There are various means.

For example, an excess amount of alkali is used in a common process in which ferrous hydroxide is produced by reacting an aqueous solution of a ferrous salt, such as ferrous sulfate, with an aqueous alkaline solution, such as sodium hydroxide. In particular, the alkali can be easily carried out, and an alkali can be added afterwards to the suspension of ferrous hydroxide obtained by various methods. In either case, it is sufficient that the pH before introducing the oxygen-containing gas is in a highly alkaline region of 11 or higher, and the magnetic powder particles mainly composed of metallic iron that are finally obtained by the reaction in such an alkaline region are dense. It becomes rich in sexuality. The generated α-iron oxyhydroxide is washed with water and dried, and then dehydrated directly or by heating to form α-iron oxyhydroxide.
-Fe, O3 and then heated in a reducing atmosphere to obtain a powder mainly composed of metallic iron. A silicon compound is deposited on the surface.

The silicon compounds include various sodium silicates,
Inorganic silicates, such as potassium silicate, and organosilicon compounds, such as various silicone oils, can be used, and these act synergistically with the alkaline earth metals to prevent particle sintering and deformation during the heat treatment process. It has an extremely effective suppressing function.

Adhesion treatment with silicon compounds is carried out by simply immersing the powder to be treated in a solution containing these compounds, such as an aqueous alkali solution for alkali silicates and various organic solvents for silicone oil. However, when using alkali silicate, it is recommended to blow carbon dioxide gas or add acid under the above immersion conditions and deposit it on the particle surface in the form of silicate sol. be done.

In addition, when thermal reduction is performed after thermal dehydration, the above-mentioned adhesion treatment may be performed as a pretreatment for either the thermal dehydration or thermal reduction process, but it may be performed at the same time as a pretreatment for both processes. can not use. The total amount of silicon compound deposited is preferably such that the Si/Fe atomic ratio is within the range of 0.001 to 0.06; if it is less, no substantial effect can be expected, and if it is more than that, the magnetic There are problems with the characteristics. Optimum conditions for thermal reduction vary depending on the above-mentioned type and particle size of the material to be reduced, but usually 300~
It is carried out at a temperature of 500°C. The obtained powder mainly composed of metallic iron contains at least one selected from magnesium calcium and silicon on the particle surface or inside the particle, and has a sharp acicular shape of α-iron oxyhydroxide. Uniformity is inherited, and coercive force (Hc) and squareness ratio (
It has excellent magnetic properties such as σr/σs).

This invention will be specifically illustrated in Examples below.

Example 12007/t(7I) Fe(0H)2 was added by adding 1.5t of a 200t/TONaOH aqueous solution with stirring into 1.5t of an aqueous solution in which FesO4.7r0 and 0.897/t MgSO4.7H20 were dissolved. and Mg(0H)
A suspension containing a coprecipitate of 2 was obtained.

At this time, the pH of the suspension was 12 or higher. Next, the liquid temperature was raised to 40° C., and air was blown into the liquid at a rate of 2 t/min for 8 hours to precipitate needle-like particles of α-FeOOH.
After washing the obtained α-FeOOH with water and drying, its 107
Collect 4f! /t concentration of Na4siO4 aqueous solution 0.
CO2 gas is dispersed in 5t/min at a rate of 2t/min.
The particles were blown into the solution for neutralization to obtain α-FeOOH in which silicic acid sol was deposited on the particle surface. Wash this α-FeOOH with water,
After drying, 1 ton of the powder was collected and reduced in an electric furnace at a temperature of 400° C. at a H2 gas flow rate of 1 ton/min for 2 hours to obtain metallic iron powder containing magnesium and silicon. This powder had an average major axis of 0.3 μm and a uniaxial ratio of 10. Example
2 In the method of Example 1, 1.5 t of ferrous sulfate monomagnesium sulfate mixed aqueous solution having a dissolved amount of MgSO4.7H20 of 3.55 v/t was used, and all other conditions were the same as in Example 1. , a metallic iron powder containing magnesium and silicon was obtained.

This powder had an average major axis of 0.4 μm and a uniaxial ratio of 12. Example 3 Instead of the ferrous sulfate monomagnesium sulfate mixed aqueous solution in the method of Example 1, 2007/t FeSO4.7
H20 and 1.70v/t Ca(NO3)2・4H20
Metallic iron powder containing calcium and silicon was obtained using 1.5 t of an aqueous solution in which .

This powder had an average major axis of 0.35 μm and a uniaxial ratio of 10. Example 4 NaOH aqueous solution with a concentration of 2007/t1.
2007/TOFeSO4・7H while stirring during 5t
20 and 1.7v/t(7)Ca(NO3)2・4H20
1.5 t of an aqueous solution in which Fe(0H)2 and Ca(0H)2 were dissolved was added to obtain a suspension containing a coprecipitate of Fe(0H)2 and Ca(0H)2.

At this time, the pH of the suspension was 12 or higher. Next, while maintaining the liquid temperature at 20°C, air was blown in at a rate of 1 t/min for 1 hour to generate α-FeOOH seed crystals, and then the liquid temperature was further raised to 50°C and air was blown at a rate of 2 t/min. Air was blown into the solution for 10 hours to precipitate acicular particles of α-FeOOH. After washing and drying the obtained α-FeOOH, 10 t of it was collected and oxidized in a Matsufuru furnace at a temperature of τ 600′C for 10 hours by passing air at a rate of 1.5 t/min. Let this α-Fe2O3 be 47/
Dispersed in 0.5 t of Ma4siO4 aqueous solution of t concentration,
A 0.1N-Hct aqueous solution was added to neutralize the solution until the pH reached 6.0, and silicic acid sol was deposited on the surface of the particles.
-Fe2O3 particles were obtained. Wash this α-Ft2O3 with water,
After drying, 1 ton of the powder was collected and reduced in an electric furnace at a temperature of 450° C. at a H2 gas flow rate of 1 ton/min for 2 hours to obtain metallic iron powder containing calcium and silicon. This powder had an average major axis of 0.4 μm and a uniaxial ratio of 10. Comparative Example 1 In place of the ferrous sulfate monomagnesium sulfate mixed aqueous solution in the method of Example 1, 200 p/t of FeSO4.7H was added.
Metallic iron powder containing silicon was obtained using an aqueous solution in which only 20 was dissolved and all other conditions were the same as in Example 1.

This powder had an average major axis of 0.45 μm and a uniaxial ratio of 12. Comparative Example 2 All conditions were the same as in Example 2, except that the treatment with Na4siO4 was not performed in the method of Example 2,
A metallic iron powder containing magnesium was obtained.

This powder had an average major axis of 0.35 μm and a uniaxial ratio of 10. Saturation magnetization (σs) and coercive force (Hc) of the metallic iron powders obtained in the above examples and comparative examples, respectively.
The results of measuring the squareness ratio (σr/σs) are shown in the table below.

As is clear from the results of Examples and Comparative Examples, according to the method of the present invention, sintering between particles and deformation of particles during heat treatment steps such as thermal reduction are effectively suppressed, resulting in excellent magnetic properties. A magnetic powder mainly composed of metallic iron is obtained,
Moreover, the axial ratio and particle size can be adjusted by increasing or decreasing the amount of at least one selected from magnesium hydroxide and calcium hydroxide.

Claims (1)

[Claims] 1. Introducing an oxygen-containing gas into an alkaline suspension of ferrous hydroxide adjusted to pH 11 or higher to produce α-iron oxyhydroxide, or iron oxide obtained by heating and dehydrating this α-iron oxyhydroxide. At least one member selected from magnesium and calcium is added to the suspension to produce a magnetic powder mainly composed of metallic iron by thermal reduction in a gas phase.
containing a seed hydroxide, and including a step of depositing a silicon compound on the surface of the α-oxyiron hydroxide or iron oxide particles as a pretreatment for at least one of the steps of the thermal dehydration and thermal reduction. Characteristic method for producing metal magnetic powder.