JPH0152441B2 - - 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. The reduction furnace used is a cylindrical ring furnace, and when the metal compound powder is supplied inside the cylindrical reduction furnace and reduced in a fluidized state while passing hydrogen gas,
Reduction in such a fluidized state is generally performed because the contact efficiency between the powder particles and the gas is good and uniform reduction can be performed. However, although the method of reducing in a fluidized state using a cylindrical reduction furnace allows efficient reduction, it has a drawback in operability. For example, when reducing iron oxide powder in a fluidized state in a cylindrical reduction furnace, , the fluidization start speed (hydrogen gas flow rate) at which powder particles start flowing in a hydrogen gas flow and the particle diameter have a relationship as shown in the graph in Figure 1, and the powder particles start flowing in a hydrogen gas flow. The relationship between the terminal velocity (flow velocity of hydrogen gas) and the particle diameter, which cannot maintain the state and is carried out of the system, is as shown in the graph of Figure 2, so as shown in the graph of Figure 3. When attempting to ring form iron oxide powder with a distributed particle size of 10 to 600μ,
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, when reducing in a fluidized state in a conventional cylindrical reduction furnace, it is necessary to install a filter on the top of the cylindrical reduction furnace to collect the scattered particles, or change the diameter of the reduction furnace to reduce the gas flow rate. However, if a filter is installed, the filter will become clogged, and fine particles will accumulate on the front of the filter, making it impossible to carry out reduction. Simply changing the diameter cannot effectively change the gas flow rate;
It has the disadvantage that it cannot fully prevent particles from scattering. The scattering of such particles cannot be avoided in a cylindrical reduction furnace as it handles fine iron powder, etc., and if the scattered particles are released into the atmosphere together with hydrogen gas, the active iron particles may spontaneously ignite. There is also a risk of explosion. 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. If it is granulated and then fed into a cylindrical reduction furnace and heated and reduced while passing hydrogen gas etc.,
It has been found that the scattering of particles is prevented, and the amount of hydrogen gas etc. supplied can be increased, making it possible to carry out 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. In order to avoid this problem, this invention has continued to conduct intensive studies, and has found that by depositing a silicon compound on the particle surface of the reductant powder before granulating the reductant powder into a lump, It is possible to effectively suppress sintering between granulated particles and sintering between powder particles and deformation during the process, and as a result, thermal reduction can be performed sufficiently and hydrogen gas etc. can be evenly distributed. This method not only eliminates the heterogeneity of the reduction reaction, but also allows the reduction reaction to be performed uniformly, while at the same time maintaining good uniformity and acicularity of the reductant powder particles, resulting in even better magnetic properties. It was discovered that metal magnetic powder can be obtained. In addition, if the reductant powder with a silicon compound adhered to the particle surface is further heat-treated at a temperature of 200 to 1000°C and then thermally reduced before or after granulation, this heat treatment will cause the reductant powder particles to The dehydration pores formed inside are sealed and the entire particle is burned, reducing the surface area.
It has been found that since the deformation of the powder particles is more effectively suppressed and the saturation magnetic moment decreases less, a metal magnetic powder with even more excellent magnetic properties can be obtained. Preferred silicon compounds used in this invention include water-soluble silicates such as sodium orthosilicate, sodium metasilicate, potassium metasilicate, and water glass of various compositions. In order to deposit the reductant on the particle surface, the reductant powder may be dispersed in an aqueous solution of these silicon compounds and adsorbed onto the particle surface, but preferably, the reductant powder is adsorbed on the particle surface in an alkaline aqueous solution of these silicon compounds. A recommended method is to disperse the powder of the reductant and neutralize it by blowing carbon dioxide gas or adding acid to deposit it on the particle surface as a silicic acid hydrate. The amount of deposition is 0.1 to 0.1 to the atomic weight ratio of Si/Fe to the material to be reduced.
The content is preferably in the range of 10% by weight; if it is too small, the desired effect may not be achieved, and if it is too large, the saturation magnetic moment of the resulting metal magnetic powder may decrease. 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, these include Ni, Co, Al,
Suitable examples include those containing metal components such as Cr, Mn, Mg, Ca, Zn, Sn, Bi, etc., and those with good acicular properties are preferably used. As a means of granulating the powder of the reductant coated with a silicon compound into a lump, the powder is dispersed in water, and then the water content is reduced to 60 to 80 using a filter press.
A compression molding method in which the powder is compressed and dehydrated to % by weight and molded into a lump, or water is added to the powder to make the moisture content 35 to 45.
An extrusion molding method in which the mixture is made into weight%, then kneaded using a kneading machine, and then molded into a lump using an extruder;
Alternatively, the powder may be used in a dry state using a tablet machine.
There is a tableting method in which the material is compressed with a compression force of 200 to 1000 Kg/cm ² to form a block, and granulation may be performed using any of these methods. It is preferable that the particle size of the granulated particles of the powder to be reduced to be granulated into lumps by such means is within the range of 0.5 to 30 mm, and if the particle size is smaller than 0.5 mm, the heating ring At times, uneven flow of hydrogen gas may occur, and when the flow rate of hydrogen gas, etc. is increased, there is a risk that particles may be scattered outside the system, making it impossible to supply hydrogen gas, etc. effectively, and therefore making it difficult to carry out efficient ring production. do not have.
On the other hand, 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 inside the granulated particles, which determines the rate of the ring reaction, is slowed down, so the ring formation time becomes longer and the metal The production efficiency of magnetic powder decreases. Note that the ring element reaction is rate-determined by the diffusion of water vapor between the granulated particles, even when the particle size of the granulated particles is within the range of 0.5 to 30 mm. There are dehydration pores for the water contained in the hydrate and crystallization water of the hydrate, and there are also gaps between particles, so the particle size is 0.5 to 30.
If it is within the range of The time required is almost the same as when reducing the product in powder form. Therefore, if the particle size of the granulated particles is within the range of 0.5 to 30 mm, efficient cyclization can be carried out without increasing the cyclization 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 reductant powder that is granulated into a lump after the silicon compound is deposited on the particle surface may be heat-treated at a temperature of 200 to 1000°C before or after granulation. When such heat treatment is performed, the dehydration pores that occur in the particles of the reductant powder during subsequent heating annealing are sealed, and the entire particles are burned, reducing the surface area and causing the powder particles to lose their shape. Since this is effectively suppressed, the uniformity and acicularity of the reductant powder particles are maintained well, and the decrease in the saturation magnetic moment is also reduced, so that the magnetic properties of the obtained metal magnetic powder are further improved. In addition, when such heat treatment is performed, the silicon compound becomes passivated and a strong and dense film is formed.
Sintering between granulated particles and between powder particles is also more effectively suppressed. This kind of heat treatment
If the temperature is lower than 200℃, sufficient effect will not be obtained, and if the temperature is higher than 1000℃, sintering will occur in the iron oxide particles themselves and the acicularity will be lost. The coercive force and squareness ratio of the metal magnetic powder obtained by this process decrease. Therefore, this heat treatment is preferably carried out at a temperature within the range of 200 to 1000°C.
Note that this heat treatment may also serve as a heat dehydration treatment for converting iron oxyhydroxide to iron oxide. A material to be reduced that has been coated with a silicon compound in this way and then granulated into a lump, or a material that has been heat-treated at a temperature of 200 to 1000°C before and after granulation, is heated in a cylindrical ring furnace. metal magnetic powder mainly composed of iron is produced by heating at a temperature of 300 to 600°C in an atmosphere of a ring-forming gas such as hydrogen gas. Next, embodiments of the invention will be described. Example 1 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 milky white precipitate with a rim color of ferrous hydroxide. The pH of this suspension was 12 or higher. Then, while keeping this precipitate suspension at 60℃
Air was blown at a rate of 110/min and the mixture was stirred for 8 hours to obtain a suspension of α-iron oxyhydroxide. The particle size of the α-iron oxyhydroxide obtained was 0.6μ, and the axial ratio was 15.
It was hot. The pH of the suspension after the reaction was 13.6. Next, an aqueous solution of sodium orthosilicate (Na ₄ SiO ₄ ) with a concentration of 2 mol/5.37 was added to this strongly alkaline α-iron oxyhydroxide suspension and stirred. After thorough stirring, carbon dioxide gas was blown into the solution to bring the pH to 10. After neutralization, silicic acid hydrate (SiO ₂ .nH ₂ O) was deposited on the surface of α-iron oxyhydroxide particles. Next, the α-iron oxyhydroxide coated with the silicic acid hydrate was washed with water, and then dehydrated and molded to a size of 0.5 cm x 1.0 cm x 1.0 cm at a pressure of 5 kg/cm ² using a filter press. , dried at 130℃, vertical axis diameter 0.3cm
A granular block-like molded product having a diameter of 0.7 cm in the vertical axis in the horizontal direction and a diameter of 0.7 cm in the horizontal axis in the horizontal direction was obtained. Next, the obtained block molded product was placed in an electric furnace, and heated and dehydrated in air at 300°C for 4 hours, so that the particle surface was coated with a silicon compound.
Got Kg. This α-iron oxide (3 kg) was charged into a vertical cylindrical reduction furnace with an inner diameter of 20 cm and a depth of 50 cm at a height of 25 cm, producing a rate of 17 Nm ³ per hour.
Hydrogen gas was passed through the mixture (flow rate: 15 cm/sec) and heating was carried out at 500° C. for 4 hours to obtain metal iron powder containing silicon. The obtained powder has a particle size of 0.35μ and an axial ratio of 10.
The acicular particles had an average particle size of 35 m 2 /g, and the specific surface area measured by the N ₂ gas adsorption method was 35 m ² /g. Example 2 Aqueous sodium hydroxide solution with a concentration of 5 mol/100
While stirring at room temperature, 100% of a mixed aqueous solution of ferrous sulfate (FeSO ₄ ) and nickel sulfate (NiSO ₄ ) (concentration of FeSO ₄ 0.719 mol/, concentration of NiSO ₄ 0.03 mol/) was added and reacted. A milky white co-precipitate with a fringe color of ferrous hydroxide and nickel hydroxide was obtained. Next, while maintaining this coprecipitate suspension at 60°C, air was blown at a rate of 110/min and stirred for 10 hours to form α-
A suspension of iron oxyhydroxide was obtained. The obtained nickel solid solution α-iron oxyhydroxide had a particle size of 0.6μ and an axial ratio of 15. Also, the pH of the suspension after the reaction is
It was 13.6. Next, 5.37% of an aqueous solution of sodium orthosilicate (Na ₄ SiO ₄ ) with a concentration of 2 mol/mole was added to this nickel solid solution α-iron oxyhydroxide suspension and stirred. After thorough stirring, carbon dioxide gas was removed. By blowing, the pH was neutralized to below 10, and silicic acid hydrate (SiO ₂ .nH ₂ O) was deposited on the particle surface of the nickel solid solution α-iron oxyhydroxide. Thereafter, granulation molding and heating dehydration were carried out in the same manner as in Example 1, and further heating and reduction were carried out to obtain metallic iron powder containing nickel and silicon. The obtained powder was acicular particles having an average particle size of 0.30 μm in particle diameter and an axial ratio of 15, and had a specific surface area of 39 m ² /g as determined by the N ₂ gas adsorption method. Comparative Example 1 Ferrous sulfate and nickel sulfate were reacted in an aqueous sodium hydroxide solution in the same manner as in Example 2,
Further oxidation produced nickel solid solution α-iron oxyhydroxide with a particle size of 0.6μ and an axial ratio of 15. Next, this was filtered, washed with water, dried at 130°C, and crushed with a milk wasp to form a nickel solid solution α- having the distribution shown in Table 1 below.
Iron oxyhydroxide powder was obtained.

[Table] This nickel solid solution α-iron oxyhydroxide powder 3Kg
into a vertical cylindrical reduction furnace with an inner diameter of 20 cm and a depth of 50 cm.
The tube was filled with 30 cm of hydrogen gas and heated at 500° C. for 24 hours while hydrogen gas was passed through the tube at a rate of 30 cm to obtain metallic iron powder containing nickel. The obtained powder has a particle size
They were acicular particles with 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 about 200g of fine black particles, and when we measured and investigated the magnetic properties of these particles, we found that the coercive force (Hc) was 780 oersted, and the saturation magnetic moment (σ _s ) is 108emu/g, and the squareness ratio (σ _r /
σ _s ) was 0.42, and it was a mixture of iron oxide powder and iron powder containing nickel. 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 Example 1 except that the silicate hydrate deposition treatment in Example 1 was omitted. The obtained powder was acicular particles having an average particle size of 0.30 μm in particle diameter and an axial ratio of 3, and had a specific surface area of 8 m ² /g by the N ₂ gas adsorption method. Comparative Example 3 Metallic iron powder containing nickel was obtained in the same manner as in Example 2 except that the treatment for adhering silicic acid hydrate was omitted. The obtained powder has a particle size of
Acicular particles with an average particle size of 0.25 μ and an axial ratio of 4, and a specific surface area of 10 m ² /g by N ₂ gas adsorption method.
It was hot. Using a vibrating magnetometer (VSM) manufactured by Toei Kogyo Co., Ltd., the coercive force (Hc) and saturation were measured using a vibrating magnetometer (VSM) manufactured by Toei Kogyo Co., Ltd. with an applied magnetic field of 10,000 oersteds. The air 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 products obtained in Examples 1 and 2 required less reduction time than those obtained in Comparative Example 1, and the coercive force, saturation magnetic moment, and The squareness ratio is high and the particle properties are also improved. Furthermore, compared to Comparative Examples 2 and 3, the coercive force and squareness ratio are large, and the acicularity is excellent. Therefore, according to the manufacturing method of the present invention, sintering between granulated particles and powder particles and deformation of powder particles can be effectively suppressed, and thermal reduction can be performed sufficiently and uniformly, resulting in further improvement. It can be seen that a metal magnetic powder mainly composed of iron with excellent magnetic properties can be obtained.

[Brief explanation of drawings]

Figure 1 shows 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 gas stream when the iron oxide powder is reduced in a fluidized state in a cylindrical reduction furnace. ), and Figure 2 shows the relationship 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 flow and are carried out of the system. Relationship diagram, 3rd
The figure 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)

[Scope of Claims] 1. A method for producing metal magnetic powder, in which a metal compound powder containing iron oxyhydroxide or iron oxide as a main ingredient is supplied into a cylindrical reduction furnace and heated and reduced while a reducing gas is passed through the furnace. In this step, a silicon compound is deposited on the particle surface of a metal compound powder mainly containing iron oxyhydroxide or iron oxide, and then this is granulated into a lump to form granulated particles with a particle size of 0.5 to 30 mm. . A method for producing metal magnetic powder, which comprises supplying it to the inside of a cylindrical reduction furnace, and heating and annealing it while aerating reducing gas to produce a metal magnetic powder mainly composed of iron. 2 A silicon compound is deposited on the particle surface of a metal compound powder mainly containing iron oxyhydroxide or iron oxide, and then this is granulated into a lump to reduce the particle size.
The method for producing metal magnetic powder according to claim 1, wherein the metal magnetic powder is heat-treated at a temperature of 200 to 1000°C before being made into granulated particles of 0.5 to 30 mm. 3 After granulating and molding into granulated particles with a particle size of 0.5 to 30 mm, the particles are further heat-treated at a temperature of 200 to 1000°C, and then supplied to the inside of a cylindrical ring furnace. 2. The method for producing metal magnetic powder according to claim 1, wherein heating is carried out while a magnetic gas is passed through.