JP2022134575A - soft magnetic metal powder - Google Patents

Abstract

Kind Code: A1 A soft magnetic metal powder composed of fine particles that can be used to produce a powder compact with a high compacting density. Provided is a soft magnetic metal powder that can form a thin layer with excellent surface smoothness because it is an aggregate of fine particles with a narrow particle size distribution. SOLUTION: The average particle size is 0.05 μm or more and 1.5 μm or less, the variation coefficient represented by the following (formula) is 0.25 or less, and the boron content is 5.0% by weight. A soft magnetic metal powder that is less than (but does not include 0). (Formula) Standard deviation of particle size/Average particle size [Selection] Fig. 2

Description

The present invention relates to soft magnetic metal powder. Specifically, since the soft magnetic metal powder is composed of fine particles, it is possible to produce a powder compact with a high compacting density, and since the content of boron that reduces saturation magnetization is small, a powder magnetic core with excellent magnetic properties can be produced. The present invention also relates to a soft magnetic metal powder that can form a thin layer with excellent surface smoothness because it is an aggregate of fine particles with a narrow particle size distribution.

Inductors and transformers built into electrical devices are required to have improved magnetic properties and thinner layers as various electrical devices become more sophisticated and smaller and thinner.

In order to improve the magnetic properties of inductors and the like, dust cores are required to have a high compacting density.

If the soft magnetic metal powder is an aggregate composed of fine particles, an improvement in compacting density of the powder magnetic core can be expected.

As a method for producing fine-particle soft magnetic metal powder, there is a liquid-phase reduction method in which a reducing liquid containing a boron (B)-based reducing agent is added dropwise to an aqueous metal salt solution as described in Patent Document 1.

However, since B lowers the saturation magnetization, there is a problem that a dust core made of a soft magnetic metal powder containing a large amount of B has a lower saturation magnetization.

The compacting density of the powder magnetic core can also be improved by using a soft magnetic metal powder with a wide particle size distribution and filling the gaps between large particles with medium and small particles.

A soft magnetic metal powder with a wide particle size distribution can be produced by a general method such as a water atomization method, a gas atomization method, or a spray pyrolysis method.

However, a soft magnetic metal powder with a wide particle size distribution has a problem that it is difficult to obtain good smoothness on the surface when it is made into a thin layer.

Therefore, a soft magnetic metal powder composed of fine particles that has a high compacting density, a low B content and can produce a dust core with excellent magnetic properties, and a thin layer with a narrow particle size distribution and excellent surface smoothness. Development of a soft magnetic metal powder capable of forming is desired.

JP 2010-261065

Patent Document 1 discloses a liquid-phase reduction method in which a reducing liquid containing a B-based reducing agent is added dropwise to an aqueous iron salt solution containing an iron salt, a complexing agent, a dispersant, a pH adjuster, and a P-based reducing agent. A method for producing soft magnetic metal powder with a small particle size is described.

However, since the soft magnetic metal powder described in Patent Document 1 contains a large amount of B, there is a problem that the saturation magnetization is lowered.

The present inventors have made it a technical task to solve the above-mentioned problems, and as a result of repeated trial and error trial production and experiments, the average particle diameter is 0 even if a large amount of B-based reducing agent is not added. 0.05 μm or more and 1.5 μm or less fine particles, and a coefficient of variation represented by standard deviation of particle diameter/average particle diameter is 0.25 or less, and a narrow particle size distribution is produced. It succeeded in doing so and solved the above technical problem.

Since the soft magnetic metal powder according to the present invention can produce a powder compact with a high compacting density, it is possible to produce a powder magnetic core with improved magnetic properties due to densification, and the content of B that lowers the saturation magnetization is low, it is a soft magnetic metal powder that can produce a powder magnetic core with even better magnetic properties, and can also form a thin layer with excellent surface smoothness.

The above technical problems can be solved by the present invention as follows.

The present invention has an average particle diameter of 0.05 μm or more and 1.5 μm or less, a coefficient of variation represented by the following (formula) of 0.25 or less, and a boron (B) content of 5.0 μm or less. It is a soft magnetic metal powder containing less than 0% by weight (but not including 0).
(Formula) Standard deviation of particle size/average particle size (σ/D)

Further, the present invention is the soft magnetic metal powder having an iron (Fe) content of 90% by weight or more.

Further, the present invention is the soft magnetic metal powder coated with one or more metal oxides.

The present invention also provides the soft magnetic metal powder, wherein the metal element of the metal oxide is aluminum (Al), silicon (Si), zirconium (Zr), titanium (Ti), yttrium (Y) or phosphorus (P). is.

Further, the present invention provides the soft magnetic metal powder produced by a liquid phase reduction method in which a reducing liquid containing a B-based reducing agent is dropped into an aqueous metal salt solution containing a metal salt, a complexing agent, a pH adjuster, and a P-based reducing agent. is a manufacturing method.

The present invention is a soft magnetic metal powder having an average particle size of 0.05 μm to 1.5 μm and is an aggregate of fine particles, so that a high compacting density can be achieved, so that a powder magnetic core with high magnetic properties can be produced. can be done.

In addition, since the soft magnetic metal powder has a narrow particle size distribution with a coefficient of variation represented by "standard deviation of particle size/average particle size" of 0.25 or less, a thin layer with excellent surface smoothness can be formed.

Moreover, since the content of B, which lowers the saturation magnetization, is less than 5.0% by weight, it is possible to manufacture a powder magnetic core with even better magnetic properties.

Also, if the content of iron (Fe) is 90% by weight or more, a powder magnetic core with high saturation magnetization can be produced.

Also, if the soft magnetic metal powder is coated with a metal oxide, electrical insulation between the particles can be ensured, and energy loss can be suppressed.

It is a SEM photograph (10000 times) of the soft magnetic metal powder (σ/D=0.180) in the present invention. It is a SEM photograph (10000 times) of the soft magnetic metal powder (σ/D=0.167) in the present invention. It is a SEM photograph (10000 times) of the soft magnetic metal powder (σ/D=0.113) in the present invention.

Since the soft magnetic metal powder in the present invention is an aggregate of fine particles and has a narrow particle size distribution, it is possible to produce a powder compact with a high compacting density and to form a thin layer with excellent surface smoothness.

The average particle size of the soft magnetic metal powder is preferably 0.05 μm to 1.5 μm, more preferably 0.07 μm to 1.0 μm.

If the average particle size is less than 0.05 μm, the ratio of the oxide film on the particle surface increases, resulting in a decrease in saturation magnetization. ) is increased and the surface smoothness of the thin layer may be lowered.

The oxygen (O) content in the soft magnetic metal powder is preferably less than 8.0% by weight, more preferably 5.0% by weight or less, in order to suppress a decrease in saturation magnetization due to an oxide film.

The variation coefficient represented by "standard deviation of particle size/average particle size" of soft magnetic metal powder particles is preferably 0.25 or less, more preferably 0.22 or less.

This is because if the coefficient of variation exceeds 0.25, the value of Rmax in the case of thinning the layer increases, and there is a risk that the surface smoothness of the thin layer will decrease.

According to the present invention, even a thin layer of 10-30 μm can have Rmax of less than 3.5 μm.

The particle size of the soft magnetic metal powder can be measured using image analysis software after photographing with a scanning microscope (SEM) at a magnification of 2,000 to 10,000 times.

The content of B contained in the soft magnetic metal powder of the present invention is less than 5.0% by weight, but not 0% by weight.

Since B lowers the saturation magnetization, it is preferable that the amount is as small as possible. However, if the B-based reducing agent is not used, non-spherical fine particles may increase and the molding density may decrease.

The soft magnetic metal powder in the present invention may be coated with metal oxide. This is because an improvement in insulation effect can be expected.

Al, Si, Zr, Ti, Y, and P can be exemplified as metal elements contained in the metal oxide.

The content of the metal element in the metal oxide is preferably 0.1% by weight to 3.0% by weight. This is because if the content exceeds 3.0% by weight, the saturation magnetization may decrease.

In order to produce a powder magnetic core having sufficient magnetic properties, the soft magnetic metal powder preferably has a saturation magnetization of 150 Wb·m/kg or more and a coercive force of 10 kA/m or less.

The present invention can be produced by a liquid phase reduction method in which an aqueous metal salt solution is reduced with a B-based reducing agent.

Metal salts are not limited, but iron salts are preferred.

Examples of iron salts include iron (II) sulfate, iron (II) chloride, iron (II) acetate, iron (II) oxalate, iron (III) chloride, and iron (III) sulfate.

A complexing agent or reducing agent may be added to the aqueous metal salt solution.

Although the complexing agent is not particularly limited, glycine, alanine, ammonium sulfate, ammonium chloride, and III sodium citrate can be exemplified.

Although the reducing agent is not particularly limited, it is preferable to use a P-based reducing agent.

Examples of P-based reducing agents include sodium hypophosphite and calcium hypophosphite.

It is preferable to adjust the pH of the aqueous metal salt solution to 6.5 to 11.0.

Although the pH adjuster is not particularly limited, examples thereof include sodium hydroxide, aqueous ammonia, and sodium hydrogen carbonate.

A dispersant, a catalyst, and an antifoaming agent may be added to the aqueous metal salt solution as appropriate.

A B-based reducing agent is used as the reducing agent for reducing the aqueous metal salt solution.

Examples of B-based reducing agents include sodium borohydride, potassium borohydride, and dimethylaminoborane.

B-free hydrazine may be used in conjunction with the B-based reducing agent.

The reduction temperature is preferably 10°C to 95°C.

Examples of the present invention are shown, but the present invention is not limited to these.

(Example 1)
Iron (II) sulfate heptahydrate 0.2 mol/L, glycine 0.08 mol/L, sodium hypophosphite 0.1 mol/L. A metal salt aqueous solution with a pH of 7.0 to 8.5 was prepared using sodium hydroxide while stirring at a rotation speed of 100 to 300 rpm.

The prepared metal salt aqueous solution was heated to 45° C. while stirring at a rotational speed of 100 rpm to 300 rpm while the inside of the beaker was made inert with nitrogen gas.

Sodium borohydride was mixed with 300 ml of distilled water so as to have a concentration of 0.25 mol/L, and dissolved by stirring at room temperature at 100 to 300 rpm to prepare a B-system reducing solution.

The prepared B-based reducing agent was gradually added dropwise to an aqueous metal salt solution at 45° C. in a nitrogen atmosphere while stirring at a rotational speed of 100 to 300 rpm.
The end point of the reduction reaction was defined as the point where foaming from the aqueous metal salt solution ceased.

After completion of the reduction reaction, the powder was washed with distilled water, replaced with alcohol, and dried in an inert atmosphere of nitrogen gas to obtain the soft magnetic metal powder of Example 1.

(Examples 2-5 and Comparative Examples 1-3)
Production was carried out under the same conditions as in Example 1 except that the raw materials for Examples 2 to 5 and Comparative Examples 1 to 3 were as shown in Table 1.

(Example 6)
The soft magnetic metal powder obtained in Example 1 was weighed to a concentration of 0.30 mol/L, tetraethoxysilane (TEOS) 0.04 mol/L, and ammonia water 0.20 mol/L. The mixture was added together with 150 ml of alcohol and stirred at room temperature for 1 hour at a rotation speed of 100 to 300 rpm to hydrolyze the TEOS, thereby coating the surfaces of the fine particles of the soft magnetic metal powder with silica.

After washing with isopropyl alcohol, it was dried in an inert atmosphere of nitrogen gas to obtain a silica-coated soft magnetic metal powder.

(Comparative Example 4)
Iron (II) chloride hydrate 1.0 mol/L, ammonium chloride 1.5 mol/L, trisodium citrate hydrate 0.8 mol/L, sodium hypophosphite hydrate 1.5 mol/L, dispersion Polyvinylpyrrolidone as an agent is weighed so that the concentration is 0.004 mol/L, put into a glass container with 200 ml of distilled water, and stirred at room temperature at a rotation speed of 160 rpm to 300 rpm for 60 to 120 minutes to obtain an aqueous metal salt solution. was made.

While stirring the prepared metal salt aqueous solution at room temperature at a rotational speed of 160 rpm to 300 rpm, an aqueous sodium hydroxide solution was added dropwise to adjust the pH to 10.

The same B-based reducing solution as in Example 1 was gradually added dropwise to the aqueous metal salt solution being stirred at a rotation speed of 160 to 300 rpm, and it was confirmed that no bubbles were generated from the surface of the aqueous metal salt solution. The precipitated powder was separated from the liquid, washed with water and alcohol, and then dried in an inert atmosphere of nitrogen gas to obtain an amorphous soft magnetic alloy powder.

(Comparative Example 5)
Fe particles were synthesized by the polyol method.
100 ml of ethylene glycol was placed in a glass container equipped with a reflux device, nitrogen gas was blown in at a flow rate of 300 ml/min, and the liquid was stirred at a rotational speed of 100 rpm with a Teflon (registered trademark) stirring blade.

Ferrous chloride tetrahydrate FeCl ₂ .4H ₂ O was added to the stirred liquid so as to have a concentration of 0.1 mol/L.

Then, NaOH was added so that the ratio [OH ^- ]/[Fe] of [OH ^- ] concentration to [Fe] was 40.

Furthermore, 2.0×10 ⁻⁸ mol/L of hexachloridoplatinic (IV) acid was added as a platinum precursor for nucleation.

After charging, cooling water was flowed into the reflux vessel, nitrogen gas was blown in, and heating was continued while mechanical stirring was continued, and the temperature was maintained at 170°C for 20 minutes while refluxing to carry out a reduction reaction.

The precipitated particles were allowed to cool until the solution reached room temperature, then transferred into ethanol, repeatedly washed by centrifugal separation, and dried in a nitrogen atmosphere to obtain Fe particle powder.

(Comparative Example 6)
Carbonyl iron powder (product name: manufactured by HQ BASF) was used.

(Particle shape)
It was visually observed with a scanning electron microscope (SEM) (S-4800 type FE-SEM/manufactured by Hitachi High-Tech Co., Ltd.) photograph (10,000 magnification).

The ratio (a/b) of the longest diameter a to the shortest diameter b of the particles was calculated to evaluate the shape as shown below.

Spherical: a/b≦1.7 and 1.0≦a/b≦1.2 ratio is 90% or more Spherical/granular: a/b≦1.7 and 1.0≦a/b≦1.2 ratio of 50% or more and less than 90% Granular: ratio of a/b ≤ 1.7 and 1.0 ≤ a/b ≤ 1.2 is less than 50% Acicular: a/b>1.7

(Average particle size, standard deviation and coefficient of variation)
Photographed with a scanning electron microscope at a magnification of 2000 to 10000 times, and the longest diameter of all particles in the photographed field of view was measured using image analysis software Azo-kun (manufactured by Asahi Kasei Engineering Co., Ltd.) and averaged. The particle size was calculated and the standard deviation was also calculated. Also, the coefficient of variation was calculated from those values.

(Crystal structure)
Measurement was performed using an X-ray diffractometer (D8 ADVANCE, manufactured by Bruker Japan Co., Ltd.), and the crystal phase in the sample was identified by Riedveld analysis.

(composition analysis)
<Fe, P, Si>
Using a fluorescent X-ray diffractometer (ZSX PrimusII/manufactured by Rigaku Corporation), measurement was carried out according to JIS K0119 "General Rules for Fluorescent X-ray Analysis".

<B>
Measurement was performed using an inductively coupled plasma (ICP) emission spectrometer (iCAP6500/manufactured by Thermo Fisher Scientific Co., Ltd.).

<O>
Measurement was performed using an oxygen/nitrogen/hydrogen analyzer (EMGA-930/manufactured by HORIBA, Ltd.).

(Magnetic properties)
Saturation magnetization (σs) and coercive force (Hc) were measured at an applied magnetic field of 797.7 kA/m using a vibrating sample magnetometer (VSM) (TM-VSM2130MRHL type/manufactured by Tamagawa Seisakusho Co., Ltd.).

(Thin layer characteristics)
To 5.0 g of the soft magnetic metal powder of Example 1, 0.5 ml of castor oil and 4.5 g of nitrocellulose clear lacquer (clear for P (standard sample) 151-009/manufactured by Kansai Paint Co., Ltd.) were added, and a rotation/revolution mixer was added. (Awatori Mixer ARE-310/manufactured by Thinky Co., Ltd.) was used to stir at 1500 rpm for 3 minutes to prepare a paste.

The prepared paste was applied to a PET film using a 3 milliliter applicator and dried at room temperature to prepare a thin layer of about 20 μm.

The maximum height (Rmax) of the thin layer was measured using a non-contact surface roughness meter (NewView600/manufactured by Canon Marketing Japan Inc.).

Tables 1 and 2 prove that the soft magnetic metal powder of the present invention has high saturation magnetization and coercive force and can form a thin layer with excellent surface smoothness.

Since the soft magnetic metal powder in the present invention consists of fine particles, it is possible to produce a powder compact with a high compacting density, and since the B content is low, it is possible to produce a powder magnetic core with excellent magnetic properties. can.
In addition, since it is an aggregate of fine particles with a narrow particle size distribution, a thin layer with excellent surface smoothness can be produced.
Therefore, the present invention is an invention with high industrial applicability.

Claims (5)

The average particle diameter is 0.05 μm or more and 1.5 μm or less, the coefficient of variation represented by the following (formula) is 0.25 or less, and the boron content is less than 5.0% by weight (however, 0 is not included).
(Formula) Standard deviation of particle size/Average particle size 2. The soft magnetic metal powder according to claim 1, having an iron content of 90% by weight or more. 3. The soft magnetic metal powder according to claim 1, which is coated with one or more metal oxides. 4. The soft magnetic metal powder according to claim 3, wherein the metal element of said metal oxide is aluminum, silicon, zirconium, titanium, yttrium or phosphorus. 3. The soft magnetic metal according to claim 1 or 2, which is produced by a liquid-phase reduction method in which a reducing liquid containing a boron-based reducing agent is added dropwise to an aqueous metal salt solution containing a metal salt, a complexing agent, a pH adjuster, and a phosphorus-based reducing agent. How to make powder.

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