JPS5919165B2 - Manufacturing method of metal magnetic powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing magnetic powder mainly composed of metallic iron, which allows for easy particle size adjustment, suppresses sintering and deformation of particles during the heat treatment process, and produces dense particles. An object of the present invention is to provide the above manufacturing method for obtaining magnetic powder having 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 a recording element for various types of magnetic recording media including magnetic tapes. Although it has been in the spotlight, it is usually manufactured by heating and reducing α-iron oxyhydroxide, which is made up of acicular particles that are left behind in the wet reaction process, and α-Fe2O3, which is obtained by heating and dehydrating it, as a raw material. Properties such as particle diameter and particle shape greatly depend on the properties of the raw materials themselves, and these properties greatly influence 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. As a result, the magnetic properties of the obtained magnetic powder mainly composed of metallic iron tend to deteriorate significantly due to non-uniform particle size and loss of oblique shape and compactness of the particles. Therefore, in order to obtain an excellent magnetic powder, the α-iron oxyhydroxide itself must have good properties;
In addition, it is necessary to improve the above-mentioned drawbacks in the heat treatment process and inherit the sharp acicular shape and uniformity of the raw material α-iron oxyhydroxide to the magnetic powder particles mainly composed of metallic iron. There is no known satisfactory method.

In the course of intensive research in light of the above-mentioned circumstances, the inventors discovered ferrous hydroxide obtained by a reaction that produces α-iron oxyhydroxide, that is, a method in which alkali is applied to ferrous salt. In the method of oxidizing by introducing an oxygen-containing gas into a suspension of iron, if the suspension is maintained in an alkaline region and the reaction is carried out, the α-iron oxyhydroxide produced or this can be heated and dehydrated. It has already been found that magnetic powder mainly composed of metallic iron produced by heating and reducing α-Fe2O3 as a raw material forms extremely dense particles. In the course of further research, this invention discovered that at least one compound selected from a zinc compound and an aluminum compound was added to a suspension of ferrous hydroxide in a reaction for producing α-iron oxyhydroxide described above in an alkaline region. A silicon compound is added to the particle surface of the object to be treated by heating and reducing the α-oxyiron oxide produced by dissolving one kind of α-oxyiron oxide or the iron oxide obtained by heating and dehydrating it to obtain a magnetic powder mainly composed of metallic iron. By applying heat dehydration and/or heat reduction after depositing α-iron oxyhydroxide, which is produced depending on the amount of zinc compounds and aluminum compounds to be dissolved, the final product is mainly composed of metallic iron. This was achieved by discovering that the particle size of the magnetic powder can be adjusted, that sintering and deformation of the particles during the heat treatment process are suppressed, and that the already mentioned density of the particles is not lost due to the reaction in the alkaline region. .

The drawings show that zinc compound (ZuSq) and aluminum compound [A4 (SO
4) α- produced when varying the amount of addition of 3]
The average major axis of iron oxyhydroxide is shown.

In the figure, curve A is for a zinc compound, and curve B is for an aluminum compound, and in both cases, the larger the amount added, the smaller the particles of α-iron oxyhydroxide produced. Therefore, by increasing or decreasing the amount of these additives, it is possible to easily adjust the particle size of the magnetic powder mainly composed of metallic iron that is finally obtained through heating. Zinc compounds to be used include zinc sulfate, zinc chloride, zinc nitrate, etc., and aluminum compounds include aluminum sulfate, aluminum chloride, aluminum nitrate, etc., and these may be added to the suspension of ferrous hydroxide. It may be added to the stock solution of the reaction to produce ferrous hydroxide or to the system during the reaction.

When the atoms of zinc and aluminum are represented by Me, the appropriate amount is such that the atomic ratio of Me/Fe is 0.001 to 0.1. If it is less than 1, no substantial effect will be observed, and if it is too much, The particles produced have become too fine and there are problems in terms of magnetic properties. Zinc and aluminum are dissolved in alkaline solutions without forming hydroxide precipitates, but α. During the production process of iron oxyhydroxide, iron oxyhydroxide is trapped in the particles in an ionized state, or it is firmly attached to the surface of the particles and remains without being removed even by washing with water.

Therefore, in the method of the present invention, the zinc compound and the aluminum compound exhibit the above-mentioned particle size adjustment effect as well as the function of suppressing sintering and deformation of particles in a heat treatment process such as thermal reduction. 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 α-iron oxyhydroxide produced is
After washing with water and drying, α-Fe can be directly or heated and dehydrated.
After converting to 2O3, it is heated in a reducing atmosphere to form a powder mainly composed of metallic iron.In the present invention, a silicon compound is added to the particle surface of the object to be treated to be subjected to the above-mentioned thermal dehydration and/or thermal reduction. to cover.

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 aforementioned zinc and aluminum to greatly reduce sintering and deformation of particles during the heat treatment process. It has the ability to effectively suppress For adhesion treatment with silicon compounds, the powder to be treated is simply immersed in a solution containing these compounds, such as an aqueous alkaline solution for alkali silicate, and various organic solvents for silicone oil, and the powder is adhered to the particle surface. However, when using alkali silicate, it is recommended to neutralize it by blowing carbon dioxide gas or adding acid under the above immersion conditions and deposit it on the particle surface in the form of silicate sol. .

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. Thermal reduction requires the above-mentioned types and particle sizes of the material to be reduced. Optimum conditions vary depending on the situation, but usually 300°C in a hydrogen stream.
It is carried out at a temperature of ~500°C. The obtained powder mainly composed of metallic iron contains zinc or/and aluminum and silicon on the particle surface or inside the particle, and α
- Inheriting the sharp acicular shape and uniformity of iron oxyhydroxide, it has excellent magnetic properties such as coercive force (Hc) and squareness ratio (σr/σs).

The present invention will be specifically illustrated below with reference to Examples.

Example 1.5t of NaOH aqueous solution with a concentration of 1200y/t
Inside, 200v/t (7) FesO4・7H with stirring
20 and 1.17t/t(7) At2(SO4)3 ・1
1.5 t of an aqueous solution containing 7H20 was added and mixed, and Fe
A suspension of (0H)2 was obtained.

At this time, the pH was 12 or higher. Next, increase the liquid temperature to 40℃
Air was blown into the liquid at a rate of 2 t/min for 8 hours to precipitate acicular particles of α-FeOOH. After washing and drying the obtained α-FeOOH, 10V of it was collected and dispersed in 0.5t of Na4.SiO4 solution with a concentration of 47/t, and CO2 gas was added to the liquid at a rate of 1.5t/min. 30
α-F with silicic acid sol deposited on the particle surface after blowing for minutes
eOOH was obtained. After washing this α-FeOOH with water and drying,
The sample No. 17 was collected and reduced in an electric furnace at a temperature of 450° C. at a hydrogen gas flow rate of 1 t/min for 2 hours to obtain metallic iron powder containing aluminum and silicon. Example 2 200v/t concentration of NaOH was added to 1.4t of an aqueous solution containing 200y/TOFeSO4・7H20 while stirring.
1.5 t of aqueous solution was added to obtain a suspension of Fe(0H)2.

Then, in this suspension, 23.4f/t<7)At2(
Add and mix 0.1 t of an aqueous solution containing SO4)3 ・17H20 to obtain a suspension with a pH of 2 or more, then heat the liquid temperature to 30°C, blow air at a rate of 2 t/min for 30 minutes, and α Seed crystals of -F'EOOH were generated, and the liquid temperature was further raised to 50 DEG C., and air was blown at a rate of 2 t/min for 10 hours to precipitate needle-like particles of α-FeOOH.

After washing the obtained α-FeOOH with water and drying, 10 tons of it
was collected and heated in a Matsufuru furnace at a temperature of 600°C with 1 part of air.
．． α-
It was set as Fe2O3. This α-Fe2O3 was dispersed in 0.5t of Na4siO4 aqueous solution with a concentration of 2v/t, and 0.1
Neutralize by adding N-HCt aqueous solution until pH 7,
α-Fe2O3 particles with silicic acid sol deposited on the particle surface were obtained. After washing and drying this α-Fe2O3, 1 ton of
The sample was collected and reduced in an electric furnace at a temperature of 450° C. at a hydrogen gas flow rate of [t/min] for 2 hours to obtain a metal powder containing aluminum and silicon. Example 3 In place of the ferrous sulfate monoaluminum sulfate mixed aqueous solution in Example 1, 200 f/t of FeSO4.7H20 was added.
Metallic iron powder containing zinc and silicon was obtained using 1.5 t of an aqueous solution in which 2,07 t/t<7) ZnSO4.7H20 was dissolved, and all other conditions were the same as in Example 1.

Comparative Example 1 In place of the ferrous sulfate monoaluminum sulfate mixed aqueous solution in Example 1, 200 v/t of FeSO4.7H20 was added.
Metallic iron powder containing silicon was obtained using 1.5 t of an aqueous solution in which only silicon was dissolved, and all other conditions were the same as in Example 1.

Comparative Example 2 All conditions were the same as in Example 1 except that the treatment with Na4siO4 was not performed in the method of Example 1.
Metal magnetic powder containing aluminum was obtained.

Comparative Example 3 All conditions were the same as in Example 1, except that the treatment with Na4siO4 was not performed in the method of Example 3.
Metal magnetic powder containing zinc was obtained.

The saturation magnetization (σs), coercive force (Hc), and squareness ratio (σr/σs) of the metallic iron powders obtained in the above Examples and Comparative Examples were measured, and the results are shown in the table below.
As shown in the above table, according to the method of the present invention, sintering between particles and deformation of particles during heat treatment processes such as thermal reduction are suppressed, and magnetic properties mainly made of metallic iron have excellent magnetic properties. A powder is obtained, and the particle size can be easily adjusted by increasing or decreasing the amount of zinc compound and aluminum compound added, as shown in the drawing.

[Brief explanation of drawings]

The drawing is a diagram showing the relationship between the amounts of zinc compounds and aluminum compounds added and the average length of the produced α-iron oxyhydroxide in the method of the present invention. A...zinc compound, B...aluminum compound.

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. In producing a magnetic powder mainly composed of metallic iron by thermal reduction in a gas phase, at least one selected from a zinc compound and an aluminum compound is dissolved in the suspension, and the above-mentioned thermal dehydration and heating are performed. A method for producing metal magnetic powder, comprising a step of depositing a silicon compound on the surface of the α-iron oxyhydroxide or iron oxide particles as a pretreatment for at least one step of reduction.