JPS58159311A - Manufacture of metallic magnetic powder - Google Patents

Abstract

PURPOSE:To obtain powder, the principal ingredient thereof is iron having excellent oxidation stability, by forming oxide films containing iron onto the surface of the particles of powder formed when a metallic salt aqueous solution, which is dissolved into water while using iron salt as the principal ingredient, is reduced by an alkali metal borohydride and metallic powder, the principal ingredient thereof is iron, is formed, an alkaline aqueous solution is added to the water dispersant of powder formed, and an oxidizing gas is blown in while agitating the liquid. CONSTITUTION:Varieties of water-soluble salt, such as a sulfate of nickel, etc., a halide or the like is used as metallic salt used, sodium boron hydride or the like is used as the alkali metal borohydrides, and the concentration of the alkali metal borohydrides in the case when these alkali metal borohydrides are added to the metallic salt aqueous solution and reduced is kept within a range of 0.1- 10mol/l. An aqueous solution of sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, magnesium hydroxide, ammonia water, ammonium hydroxide or the like is used as the alklaine aqueous solution added to the dispersant of metallic powder, and air or oxygen gas or the like is used as the oxidizing gas blown in.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a metal magnetic powder containing iron as a main component, and an object thereof is to provide a method for producing the metal magnetic powder described above which has excellent stability in oxidation of Fi.

Metal magnetic powders mainly composed of iron have superior magnetic properties compared to conventional oxide-based magnetic powders, and methods for producing such metal magnetic powders include, for example, adding 0/% alkali metal particles to a metal salt aqueous solution. A method has been proposed in which hydrides are added and reduced while applying a magnetic field.

However, the metal magnetic powder mainly composed of iron obtained by this method is easily susceptible to KII formation, and the saturation magnetization decreases over time, resulting in a lack of storage stability.

The inventors conducted various studies to improve these drawbacks, and as a result, they produced a metal powder mainly composed of iron by reducing an aqueous solution of a metal salt mainly composed of iron salt dissolved in water with an alkali metal gyromoidide. After that, an alkaline aqueous solution is added to the aqueous dispersion of the resulting powder, and a oxidizing gas is blown into the resulting powder while stirring. As a result, an iron-containing oxide film is formed on the particle surface of the resulting powder, which improves the stability of the powder. It was discovered that a metal magnetic powder mainly composed of iron with excellent properties could be obtained, and this invention was completed.

The metal salts used in this invention include sulfates, herogenides, nitrates of iron, cobalt, nickel, etc.
Various water-soluble salts such as carbonate, silica, etc. are preferably used, and the iron salt is the main salt, and if necessary, it is used by dissolving it in water together with other metal salts.

In addition, as the alkali metal borohydride, sodium borohydride, potassium borohydride, lithium borohydride, etc. are preferably used. Concentration of hydride 0.1 mol/
If the amount is less than 1 mol/l, sufficient reduction cannot be achieved, and if it is more than 10 mol/1, the reduction reaction becomes too rapid, resulting in loss of acicularity of the resulting metal powder and deterioration of magnetic properties.
It is preferably within the range of l-10 mol/l.

When reducing a metal salt aqueous solution with such an alkali metal borohydride, the reaction temperature F is higher than 150°C, since the iron salt will be oxidized, so it is preferable to keep the temperature below 50°C. It is preferable to carry out the reduction reaction in a magnetic field, since metal magnetic powder with a high coercive force can be obtained by doing so.

When an aqueous alkaline solution is added to raw metal powder containing iron as described above and oxidizing gas is blown in while stirring, an oxide film containing iron such as magnetite is formed on the surface of the metal powder particles. A metal magnetic powder with excellent oxidation stability is obtained. It is preferable to use this method to form an oxide film on the surface of the metal powder particles, since using the reaction solution that has produced the metal powder as it is will shorten the process and eliminate the need for separate equipment, but this method is not always necessary. There is no need to do this, and the produced metal powder may be once dried and then redispersed in water.

Suitable aqueous alkaline solutions to be added to the dispersion of metal powder thus produced include aqueous solutions of sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, magnesium hydroxide, aqueous ammonia, ammonium hydroxide, etc. The alkali concentration is preferably PH8 or higher, and the higher the alkali concentration, the more secretive the oxide film will be. Further, as the oxidizing gas that is blown into the metal powder dispersion after adding these alkaline aqueous solutions, air, oxygen gas, etc. are preferably used.

It is preferable to carry out the reaction temperature at room temperature or above, and the higher the temperature, the less the oxide will be formed. The temperature is preferably within the range of 20 to 100°C since the temperature is measured in an aqueous solvent.

Note that when adding an alkaline aqueous solution to the metal powder dispersion produced in this way and blowing oxidizing gas into the dispersion, (
Metal powder particle surface IIc generated by dissolving iron salt
# It is preferable to add an iron salt because a compound film is easily formed. If the reaction solution that produced the metal powder is used as it is, the excess iron salt may be dissolved at the beginning.

Next, embodiments of the invention will be described.

Example 1 Ferrous sulfate (FeSO,) aqueous solution with a concentration of 1 mol/l 90
- and an aqueous solution of nickel chloride (NiC12) with a concentration of 1 mol/l 10- were placed in a container and mixed, and a magnetic field of 1000 Gauss was applied. Next, while stirring the mixed aqueous solution, a sodium borohydride aqueous solution with a concentration of 1 mol/l (100-) was added dropwise little by little to effect reduction, and after the dropwise addition was completed, the reaction was continued for 2 minutes to obtain an Fe-Ni alloy powder. was generated. Next, an aqueous sodium hydroxide solution with a concentration of 1 mol/l was added to the dispersion of the formed Fe-Ni alloy powder, and air was blown at a rate of 0.11/min while stirring to 25°C. The reaction was carried out at C for 200 minutes. After the reaction was completed, it was filtered and dried to obtain a Fe-Ni alloy powder covered with a film made of magnetite.The obtained Fe-Ni alloy powder had a minor axis particle size of 0.03j% saturation magnetization σS is 12
The coercive force was #11" and 170 oersted at 3 emu/9.

Example 2 In Example 1, when an aqueous solution of F hydroxide was added to the dispersion of the produced Fe-Ni alloy powder, 1 mol/l concentration of ferrous sulfate (FeSO) was added at the same time.

・7HO) Aqueous solution of 2.80% was added in the same manner as in Example 1, short axis grain size 0.03μ, saturated magnetization gs 120 emu/9, covered with a film made of magnetite.
Fe--Ni alloy powder having a coercive force of 1160 oersted was obtained.

Example 3 A short film covered with a film made of magnetite was prepared in the same manner as in Example 1 except that the amount of the ferrous sulfate aqueous solution with a concentration of 1 mol/l was changed from 90 to 1991 m17!4. Axial grain diameter 0.03μ, saturation magnetization amount σs 118
emu/9, coercive force 1160 oersted Fe
-Ni alloy powder was obtained.

Comparative Example Fe-Ni alloy powder was produced in the same manner as in Example 1 except that the treatment for forming a film made of magnetite was omitted, filtered and dried to obtain a short axis particle size of 0.03μ and a saturation magnetization amount. Fe-Ni alloy powder with σs of 147 emu/g and coercive force of 1170 oersted was obtained.

The 4Fe-Ni alloy powder obtained in each example and comparative example was left in the air for 24 hours at 60°C and 90% RH, and the saturation magnetization after being left was measured. We investigated the rate of decline from

The table below shows the results.

As is clear from Table F, 1 Fe-N obtained by this invention
All the i alloy powders (Examples 1 to 3) were conventional Fe-N
Compared to the i-alloy powder (comparative example), the rate of decrease in the saturation magnetization σS is smaller, which indicates that the production method of the present invention provides a metal magnetic powder mainly composed of round iron with excellent oxidation stability. I understand.

Claims (1)

[Claims] 1. A metal salt aqueous solution containing iron salt as the main component and dissolved in water is reduced with an alkali metal bop hydride to produce a metal powder mainly consisting of iron, and then an aqueous alkali solution is added to the aqueous dispersion of the produced powder. Then, while stirring, blowing gas into the iron-containing metal powder on the surface of the particles of the metal powder, which mainly consists of iron.
A method for producing metal magnetic powder characterized by forming a J-humidity film