JPS6354763B2 - - 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 between powder particles and 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 natural fire 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 if the particles are granulated and then heated and reduced using hydrogen gas or the like, scattering of particles can be prevented and the amount of hydrogen gas or the like supplied can be increased, allowing efficient reduction. However, in this method, the powder to be reduced is granulated into lumps before thermal reduction, which creates new problems such as uneven reduction reaction and sintering between granulated particles. Since the reduction may be insufficient or the uniformity and acicularity of the reduced powder particles may be impaired, it is still difficult to obtain metal magnetic powders with sufficiently excellent magnetic properties. This invention was made as a result of further intensive studies to avoid this problem.A zinc compound and a silicon compound are simultaneously coated on the particle surface of a metal compound powder that mainly contains iron oxyhydroxide or iron oxide. This method solves all of the above-mentioned problems and further improves the magnetic properties of the resulting metal magnetic powder by granulating it into blocks and then reducing it by heating in a reducing atmosphere. According to this invention, since the zinc compound and the silicon compound are coated on the particle surface of the reductant powder, the upper particles whose sintering is suppressed by the zinc compound are retained in their original structure. In addition to suppressing the deformation of the particles, the silicon compound exhibits an excellent sintering prevention effect, and the sintering between the granulated particles during heat reduction after granulation molding is effectively suppressed. Sintering between particles and deformation of powder particles are also effectively suppressed. Therefore, thermal reduction can be carried out sufficiently and hydrogen gas etc. can be evenly distributed, which not only eliminates the non-uniformity of the reduction reaction but also makes it possible to perform a uniform reduction.
At the same time, since the uniformity and acicularity of the reductant powder particles can be maintained well, a metal magnetic powder with even better magnetic properties can be obtained. Preferred examples of the zinc compound used in this invention include water-soluble salts such as zinc sulfate, zinc nitrate, and zinc chloride, and examples of silicon compounds include sodium orthosilicate, sodium metasilicate, potassium metasilicate, and various other compounds. Preferred examples include water-soluble silicates such as water glass having a composition of: In order to simultaneously coat the zinc compound and silicon compound on the particle surface of the reductant powder, usually the zinc compound and the silicon compound are simultaneously dissolved in an alkaline aqueous solution, and the reductant powder is added to this solution. After dispersion, this is done by blowing carbon dioxide gas or adding acid to neutralize it, and it adheres to the particle surface as crystalline or amorphous zinc oxide hydrate and silicic acid hydrate. be done. The amount of zinc compound deposited in this way is
The atomic weight ratio of Zn/Fe to the reductant is 0.1
The amount is preferably within the range of ~10% by weight; if it is too small, the desired effect may not be obtained, and if it is too large, the particles may become porous or lose their shape. In addition, the amount of the silicon compound deposited at the same time is preferably within the range of 0.1 to 10% by weight based on the Si/Fe atomic weight ratio based on the material to be reduced. If the amount is too large, the saturation magnetic moment (σ _s ) will 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, Ni, Co, Al,
Suitable examples include those containing metal components such as Cr, Mn, Mg, Ca, Sn, Bi, etc., and those with good acicularity are preferably used. The method for granulating the powder of the reductant coated with zinc compounds and silicon compounds into lumps is to disperse the powder in water, compress and dehydrate it with a filter press to a moisture content of 60 to 80% by weight, and form the powder into lumps. A compression molding method in which water is added to the powder to make the moisture content 35 to 45% by weight, and the mixture is kneaded using a kneader and then molded into a lump using an extruder. There is a tableting method in which the dry state is compressed using a tableting machine with a compression force of 200 to 1000 kg/cm ² to form a block, and any method may be used. It is preferable that the particle size of the granulated particles formed into lumps by such means is within the range of 0.5 to 30 mm;
If it is smaller than 0.5 mm, there is a risk that hydrogen gas, etc. will be scattered outside the system when the flow rate of hydrogen gas, etc. is increased during thermal reduction, so hydrogen gas, etc. cannot be supplied effectively.
Efficient reduction is not possible. 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. Note that the rate of the reduction reaction is determined by the diffusion of water vapor within the granulated particles, which means that the particle size of the granulated particles is 0.5
The same is true when the particle size is within the range of ~30 mm, but there are dehydration pores for water contained during granulation and crystallized water of hydrates in the granulated particles, and there are also gaps between particles. Therefore, if the particle size is within the range of 0.5 to 30 mm, it will not be a major problem, and although the reduction reaction may progress gradually compared to when reducing the product to be reduced in powder form, the reduction will not be completed. The time required to achieve this is almost the same as when reducing the powder to be reduced. Therefore, the particle size of the granulated particles is 0.5~
Within the range of 30 mm, 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 zinc compound and silicon compound are simultaneously deposited, and then the material to be reduced is granulated into a lump, and then heated at 300 to 600°C in a reducing gas atmosphere such as hydrogen gas using a fixed bed reduction furnace. It is reduced by heating at a high temperature, producing a metal magnetic powder with excellent magnetic properties that is 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, 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 greenish, opalescent co-precipitate of ferrous hydroxide and nickel hydroxide was obtained. Next, air was blown into this coprecipitate suspension at a rate of 110/min while keeping it at 60°C, and the mixture was stirred for 10 hours to form a solid solution of 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. Furthermore, the pH after the reaction was completed was 13.6. Next, zinc sulfate (ZnSO ₄ ) with a concentration of 1 mol/mole was added to this nickel solid solution α-iron oxyhydroxide suspension.
Add 580 ml of aqueous solution and 5.37 ml of sodium orthosilicate (Na ₄ SiO ₄ ) aqueous solution with a concentration of 2 mol/ml, stir.
After thorough stirring, carbon dioxide gas is blown into this suspension to neutralize it to below 10, and zinc oxide hydrate (ZnO.
nH ₂ O) and silicic acid hydrate (SiO ₂ .nH ₂ O) were deposited. Next, the nickel solid solution α-iron oxyhydroxide double coated with zinc oxide hydrate and silicic acid hydrate was washed with water, and then washed with water using a filter press.
Dehydrated and molded to a size of 0.5cm x 1.0cm x 1.0cm under a pressure of Kg/ ^cm2 , dried at 130℃, vertical axis diameter 0.3cm x hydrogen direction vertical axis diameter 0.7cm x hydrogen direction horizontal axis diameter 0.7cm 6 kg of granular block molded product was obtained. Next, 3 kg of the obtained block molded material was packed into a vertical fixed bed reduction furnace with an inner diameter of 20 cm and a depth of 50 cm at a height of 25 cm, and hydrogen gas was aerated at a rate of 17 Nm ³ per hour (flow rate of 15 cm/hour).
sec) and heat-reduced at 500°C for 4 hours to obtain metallic iron powder containing nickel, zinc, and silicon. The obtained powder was acicular particles having a particle size of 0.30 μm and an axial ratio of 15, and had a specific surface area of 46 m ² /g 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, and further oxidized to form a nickel solid solution α-oxywater with a particle size of 0.6μ and an axial ratio of 15. Obtained iron oxide. 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
A vertical fixed-bed reduction furnace with an inner diameter of 20 cm and a depth of 50 cm was filled with a bed height of 30 cm, hydrogen gas was aerated at a rate of 30/min, and the mixture was heated and reduced at 500°C for 24 hours to produce metallic iron containing nickel. A powder was obtained. The obtained powder has a particle size
They were acicular particles with an average particle size of 0.30μ and an axial ratio of 15. The filter installed at the top of the reduction furnace was filled with about 200 g of fine black particles, and the magnetic properties of these particles were measured and found to have a coercive force (Hc) of 820 oersted and a saturation magnetic moment (σ _s ) is 110emu/g, squareness ratio (σ _r /σ _s )
was 0.42, indicating that it was a mixture of iron oxide powder and iron powder containing nickel. This shows that the reduction reaction did not proceed sufficiently with this method. Comparative Example 2 Metallic iron powder containing nickel was obtained in the same manner as in the example except that the coating treatment of zinc oxide hydrate and silicate hydrate was omitted. The obtained powder was acicular particles having an average particle size of 0.25 μm in particle diameter and an axial ratio of 4, and had a specific surface area of 13 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 particles obtained in Examples had higher coercive force and squareness ratio than those obtained in Comparative Examples 1 and 2, and also had better particle properties. 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. It can be seen that 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 A zinc compound and a silicon compound are simultaneously deposited on the particle surface of a metal compound powder containing iron oxyhydroxide or iron oxide as a main component, and then this is granulated into a lump, and then heated and reduced in a reducing atmosphere to reduce iron. A method for producing metal magnetic powder, characterized in that the metal magnetic powder is mainly composed of: