JPS6354762B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing metal magnetic powder mainly composed of iron. Metal magnetic powders mainly composed of iron are usually produced by heating and reducing metal compound powders consisting of acicular particles containing mainly iron oxyhydroxide or iron oxide with hydrogen gas, etc. As the reduction furnace used, a fluidized bed reduction furnace is generally used, which has good contact efficiency with the powder particle gas and can perform uniform reduction. However, although fluidized bed reduction furnaces can perform efficient reduction, they have drawbacks in operability; for example, when reducing iron oxide powder in a fluidized bed reduction furnace, the powder particles start flowing in a hydrogen stream. There is a relationship between the fluidization start speed (hydrogen gas flow rate) and the particle size as shown in the graph in Figure 1, and powder particles cannot maintain a fluid state in the hydrogen gas stream and are carried out of the system. Since the terminal velocity (flow velocity of hydrogen gas) and the particle size have a relationship as shown in the graph of Figure 2, iron oxide powder with a particle size of 10 to 600μ distributed as shown in the graph of Figure 3 is If you try to return it,
As shown in Figure 1, at a speed of 55cm/sec at which particles with a particle size of 600μ begin to flow, all particles with a diameter of 40μ or less are carried out of the system, as is clear from Figure 2, and furthermore, this iron oxide Since the secondary agglomerated particles are gradually refined by the flow, there is a problem in that it becomes impossible to maintain the fluid state eventually and the particles are carried out of the system by the hydrogen gas. For this reason, in conventional fluidized bed reduction furnaces, it is necessary to install a filter above the fluidized bed to collect the scattered particles, or to change the furnace diameter of the reduction furnace and reduce the gas flow rate to suppress the scattering of particles. However, when a filter is installed, the filter becomes clogged, and fine particles accumulate on the front of the filter, making reduction impossible. It has the disadvantage that it cannot completely change the particle size and prevent particles from scattering. The scattering of such particles cannot be avoided even in moving beds and fixed beds other than fluidized beds when handling fine iron powder, etc., and if the scattered particles are released into the atmosphere together with hydrogen gas, they will become active. There is also a risk of explosion due to spontaneous ignition of iron particles. As a result of various studies conducted by the inventors to overcome this problem, they have already developed metal compound powder consisting of acicular particles mainly containing iron oxyhydroxide or iron oxide into lumps using various means. It has been found that by granulating and then heating and reducing with hydrogen gas etc., scattering of particles can be prevented and the amount of hydrogen etc. supplied can be increased, allowing efficient reduction. However, in this method, the powder to be reduced is granulated into lumps before thermal reduction, which may result in uneven reduction reactions.
A new problem arises in that sintering occurs between granulated particles, which may result in insufficient reduction or loss of uniformity and acicularity of the reductant powder particles. It is difficult to obtain metal magnetic powder with excellent properties. This invention was made as a result of further intensive studies to avoid this problem. An aluminum compound and a silicon compound are added to the surface of the particles of a metal compound powder mainly containing iron oxyhydroxide or iron oxide. All of the above-mentioned problems are solved by sequentially applying two layers with heat treatment at a temperature of 500 ° C, followed by granulation molding into a lump, and then heating and reducing in a reducing atmosphere. Furthermore, the magnetic properties of the obtained metal magnetic powder are further improved. According to this invention, an aluminum compound is first deposited on the particle surface of the reductant powder, and then
After heat treatment at a temperature of 200 to 500°C, a silicon compound is further deposited, so the heat treatment passesivates the aluminum compound and forms a strong and dense film. The coating forms two layers, and this function strongly prevents sintering between granulated particles, sintering between powder particles, and deformation of powder particles during heat reduction after granulation molding. is suppressed. Therefore, thermal reduction can be carried out sufficiently without sintering between the granulated particles, hydrogen gas etc. can be evenly distributed, and the non-uniformity of the reduction reaction can be eliminated, and rather uniform reduction can be achieved. At the same time, the uniformity and acicularity of the reductant powder particles can be maintained well, so that a metal magnetic powder with even better magnetic properties can be obtained. Suitable aluminum compounds used in this invention include water-soluble salts such as aluminum sulfate, aluminum nitrate, and aluminum chloride, and water-soluble aluminates such as sodium aluminate. In order to adhere to the particle surface of the reductant powder, these aluminum compounds are usually dissolved in an alkaline aqueous solution, the reductant powder is dispersed in this solution, and then carbon dioxide gas is blown in or acid is added. The aluminum oxide is deposited on the particle surface as crystalline or amorphous hydrated aluminum oxide. The amount of adhesion is 0.01 to 2.0 in atomic weight ratio of Al/Fe to the material to be reduced.
It is preferable to apply the particles within a range of % by weight; if the amount is too small, the desired effect may not be obtained, and if the amount is too large, the particles may become porous or lose their shape. Heat treatment after adhesion of aluminum compound is 200
If the temperature is lower than 0.degree. C., the aluminum compound will not be sufficiently passivated and will be redissolved in the alkaline solution. On the other hand, if the temperature is higher than 500℃, some of the iron oxide will begin to sinter, and the dense film of the aluminum compound will begin to collapse.
It is preferable to carry out the heating in a gas phase at a heating temperature of 200 to 500°C, and the aluminum compound deposited on the particle surface of the reductant powder by this heating becomes a hydrous oxide,
Alternatively, it becomes an oxide and becomes a form that does not dissolve in an alkaline aqueous solution, and forms a strong and dense film, which is more effective in preventing sintering between granulated particles and between powder particles and deformation of powder particles during heat reduction. is suppressed. In this case, this heat treatment may also serve as a heat dehydration treatment from iron oxyhydroxide to iron oxide. According to this method, when iron oxyhydroxide is converted to iron oxide and the subsequent processing is performed, one heat treatment is required. This simplifies the process by eliminating the re-grinding process after heating, and the aluminum compound that is applied suppresses sintering and deformation of particles during heating and dehydration. . As the silicon compound to be further deposited on the particle surface of the reductant powder to which the aluminum compound has been deposited, water-soluble silicates such as sodium orthosilicate, sodium metasilicate, potassium metasilicate, and water glass of various compositions can be used. These silicon compounds can also be deposited by dispersing a powder of the reducible material coated with an aluminum compound in an aqueous solution in which these silicon compounds are dissolved. As in the case of depositing the aluminum compound described above, the powder of the reducible material coated with the aluminum compound is dispersed in an alkaline aqueous solution of these silicon compounds, and the powder is neutralized by blowing carbon dioxide gas or adding acid. , a method of depositing it on the particle surface as a silicic acid hydrate is recommended. The amount of deposition is based on the reduced material.
It is preferable to deposit the Si/Fe in an atomic weight ratio of 0.1 to 10% by weight. If it is too small, the effect of preventing sintering and deformation will not be sufficient, and if it is too large, the saturation magnetic moment (σ _s ) decreases. As a metal compound powder mainly containing iron oxyhydroxide or iron oxide as a reductant, α-
FeOOH, β-FeOOH, γ-FeOOH, α-
In addition to Fe ₂ O ₃ , γ-Fe ₂ O ₃ , Fe ₃ O ₄ and their intermediate equivalents, Ni, Co, Cr,
Suitable examples include those containing metal components such as Mn, Mg, Ca, Zn, Sn, and Bi, and those with good acicular properties are preferably used. As a means of granulating and molding the powder of the reductant coated with aluminum compounds and silicon compounds into lumps, the powder is dispersed in water, and then compressed and heated to a water content of 60 to 80% by weight using a filter press. A compression molding method in which the powder is molded into a lump, or an extrusion molding method in which water is added to the powder to make the water content 35 to 45% by weight, the mixture is kneaded using a kneader, and the mixture is molded into a lump using an extruder, or the above-mentioned There is a tableting method in which powder is compressed in a dry state using a tablet machine with a compression force of 200 to 1000 kg/cm ² to form it into a block.
Any means may be used. The particle size of the granulated particles formed into lumps by this method is 0.5
It is preferable to keep it within the range of ~30mm,
If the particle size is smaller than 0.5 mm, there is a risk of uneven flow of hydrogen gas, etc. during thermal reduction, or particles may be scattered outside the system when the flow rate of hydrogen gas, etc. is increased, so it is difficult to supply hydrogen gas, etc. effectively. Therefore, efficient reduction cannot be performed. In addition, if the particle size is made larger than 30 mm, it takes time for hydrogen gas, etc. to spread inside the particles, and at the same time, the diffusion of water vapor in the granulated particles, which controls the rate of the reduction reaction, becomes slow, so the reduction time becomes longer and the production of metal magnetic powder becomes longer. Efficiency decreases.
It should be noted that the rate of the reduction reaction is determined by the diffusion of water vapor within the granulated particles.
The same is true for cases within the range of If the particle size is within the range of 0.5 to 30 mm, it will not be a major hindrance, and the reduction reaction will tend to proceed gradually compared to when reducing the product to be reduced in powder form, but the reduction will not be completed. The time required for this is almost the same as when reducing the powder to be reduced. Therefore, the particle size of the granulated particles is 0.5 to 30 mm.
Within this range, efficient reduction can be performed without increasing the reduction time. Moreover, the shape is not particularly limited as long as the particle size of the granulated particles is within the range of 0.5 to 30 mm. In this way, the aluminum compound and silicon compound are successively deposited in two layers with heat treatment at 200 to 500°C, and then the material to be reduced is granulated into a lump using a fixed bed reduction furnace. , by heating at a temperature of 300 to 600° C. in a reducing gas atmosphere such as hydrogen gas to produce metal magnetic powder mainly composed of iron. Next, embodiments of the invention will be described. Example Sodium hydroxide aqueous solution with a concentration of 5 mol/100
While stirring at room temperature, the concentration of 0.719 mol/
100% of an aqueous solution of ferrous sulfate (FeSO ₄ .7H ₂ O) was added and reacted to obtain a greenish milky white precipitate of ferrous hydroxide. The pH of this suspension was 12 or higher. The precipitate suspension was then incubated at 110°C while keeping it at 60°C.
Blow in air at a rate of /min and stir for 8 hours.
- A suspension of iron oxyhydroxide was obtained. Obtained α-
The particle size of iron oxyhydroxide was 0.6μ, and the axial ratio was 15. The pH of the suspension after the reaction was 13.6. Next, 1.4 of an aqueous solution of aluminum sulfate (Al ₂ (SO ₄ ) ₃ ) with a concentration of 0.1 mol/mole was added to this strongly alkaline α-iron oxyhydroxide suspension and stirred. After thorough stirring, carbon dioxide gas was added. was blown to neutralize the pH to below 10, and hydrated aluminum oxide (Al ₂ C ₃ .nH ₂ O) was deposited on the surface of α-iron oxyhydroxide particles.
Thereafter, it was washed with water, dried, and then heated in an electric furnace at 300°C for 3 hours to dehydrate it and transform it into α-iron oxide. Then α- coated with hydrous aluminum oxide
Iron oxide was again dispersed in an aqueous solution 150 adjusted to pH 13 or above with sodium hydroxide, and sodium orthosilicate (Na ₄ SiO ₄ ) with a concentration of 1 mol/8 was added.
Add carbon dioxide gas while stirring well, and adjust the pH.
Silicic acid hydrate (SiO ₂ .nH ₂ O) was deposited on the surface of α-iron oxide particles that had been neutralized to 10% or less and coated with hydrous aluminum oxide. Next, after washing the α-iron oxide double coated with hydrated aluminum oxide and hydrated silicic acid with water, it was heated at a pressure of 5 kg/cm ² using a filter press.
Dehydrated and molded to a size of 0.5cm x 1.0cm x 1.0cm, 130
Dry at °C to make vertical axis diameter 0.3 cm x horizontal vertical axis diameter 0.7
5Kg of granular block molded product of cm×horizontal axis 0.7cm
I got it. The obtained block molded product (3 kg) was molded into a mold with an inner diameter of 20 cm and a depth of 50 cm.
Fill a vertical fixed bed reduction furnace to a height of 25 cm, and
Aerate 17Nm ³ of hydrogen gas (flow rate 15cm/sec)
The mixture was heated and reduced at 500°C for 4 hours to obtain metallic iron powder containing aluminum and silicon. The obtained powder is acicular particles with a particle diameter of 0.35μ and an axial ratio of 10, and the specific surface area determined by the _N2 gas adsorption method is
It was 42.5m ² /g. Comparative Example 1 In the same manner as in Example, ferrous sulfate was reacted in an aqueous sodium hydroxide solution and further oxidized to obtain α-iron oxyhydroxide having a particle size of 0.6 μm and an axial ratio of 15. Next, this was filtered, washed with water, dried at 130°C, and crushed with a milk pestle to obtain α-iron oxyhydroxide powder having the distribution shown in Table 1 below.

[Table] 3Kg of this α-iron oxyhydroxide powder with an inner diameter of 20cm,
A vertical fixed-bed reduction furnace with a depth of 50 cm was filled with a bed height of 30 cm, and hydrogen gas was aerated at a rate of 30 min to 500°C.
The mixture was heated and reduced for 24 hours to obtain metallic iron powder. The obtained powder was acicular particles having an average particle size of 0.30μ and an axial ratio of 10. The filter installed at the top of the reduction furnace was filled with approximately 200 g of fine black particles, and the magnetic properties of these particles were measured and found to have a coercive force (Hc) of 720 oersteds and a saturation magnetic moment (σ _s ) is 110emu/g,
The squareness ratio (σ _r /σ _s ) was 0.43, and it was a mixture of iron oxide powder and iron powder. This shows that the reduction reaction does not proceed sufficiently in this method. Comparative Example 2 Metallic iron powder was obtained in the same manner as in the example except that the coating treatment of hydrated aluminum oxide and silicic acid hydrate was omitted. The obtained powder has a particle size of
They were acicular particles with an average particle size of 0.3μ and an axial ratio of 3, and a specific surface area of 11 m ² /g by the N ₂ gas adsorption method. Coercive force (Hc) and saturation magnetism were measured using a vibrating magnetometer (VSM) manufactured by Toei Kogyo Co., Ltd. with an applied magnetic field of 10,000 oersteds for the metal magnetic powders mainly composed of iron obtained in the examples and comparative examples. The moment (σ _s ) and squareness ratio (σ _r /σ _s ) were measured. Table 2 below shows the results.

[Table] As is clear from the above table, the results obtained in Examples were compared to those obtained in Comparative Examples 1 and 2.
Both coercive force and squareness ratio are high, and the particle properties are also good. Therefore, according to the manufacturing method of the present invention, sintering between granulated particles and powder particles and deformation of powder particles can be avoided. It can be seen that as a result of effectively suppressing thermal reduction and performing thermal reduction sufficiently and uniformly, a metal magnetic powder mainly composed of iron with even better magnetic properties can be obtained.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the particle size of iron oxide powder and the fluidization start speed (hydrogen gas flow rate) at which the powder particles start flowing in a hydrogen stream when the iron oxide powder is reduced in a fluidized bed reduction furnace. Figure 2 is a relationship diagram between the particle size of the iron oxide powder and the terminal velocity (flow velocity of hydrogen gas) at which the powder particles are no longer able to maintain a fluid state in the hydrogen gas stream and are carried out of the system. , FIG. 3 is a relationship diagram between the cumulative weight distribution and the particle size of the iron oxide powder, showing an example of the distribution of iron oxide powder having a particle size of 10 to 600 μm.

Claims (1)

[Claims] 1. An aluminum compound is deposited on the particle surface of a metal compound powder mainly containing iron oxyhydroxide or iron oxide, and heat treatment is performed at a temperature of 200 to 500°C, and a silicon compound is further coated on the particle surface of the obtained powder. 1. A method for producing a metal magnetic powder, which comprises depositing the powder, granulating it into a lump, and then heating and reducing it in a reducing atmosphere to obtain a metal magnetic powder mainly made of iron.