JPS60135506A - Production of ferromagnetic metallic powder - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention Among the magnetic powders that are the main raw materials of the magnetic recording medium of the present invention,
Recently, improvements in recording density, sensitivity, and output are expected.
It relates to the production of ferromagnetic metal powder.

The magnetic material (powder) does not have high magnetic properties such as saturation magnetization (σB) and coercive force (C), but also has good dispersibility in paint, and also has a smooth surface condition in the paint film. It is necessary to fill a large amount of magnetic powder densely and uniformly. In other words, the metal powder must have a large axial ratio, be fine, and have a narrow particle size distribution. In general, chemical stability and excellent corrosion resistance are important for practical use, as there is no drop in output or sensitivity even after repeated use.

The present invention solves these problems.

That is, hydroxide obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution is oxidized to produce acicular goethite, which is used for sealing in the dehydration/reduction process and for acicular flood control in the reduction reaction. In the entire process of manufacturing iron powder in the range of o, 1 to α5, by depositing StO as a heat-resistant component on the surface of goethite to prevent sintering between particles, and then by dehydration tube reduction treatment. As a result of various investigation tests, the present invention was arrived at.

That is, in the present invention, a hydroxide suspension obtained by neutralizing a ferrous salt aqueous solution with an alkaline bath liquid is brought into contact with an oxidizing gas and oxidized to produce acicular goethite particles, which are then dehydrated and oxidized. In a method for producing a ferromagnetic metal powder by performing a reduction treatment, (1) dissolving a nickel salt in an amount containing 1 to 10% by weight of nickel based on iron in an aqueous ferrous salt solution; is neutralized with an alkaline aqueous solution to produce hydroxides of iron and nickel, and this is brought into contact with an oxidizing gas to produce nickel-containing goethite. 2nd step of separating goethite, pickling it and adjusting the pH to 7Hf to make a neutral or acidic suspension +81 Add nickel in an amount of 1 to 40% by weight based on iron to the resulting neutral or acidic suspension. A fifth step (4) in which a nickel salt water bath solution containing nickel salt is added together with an alkaline water bath solution, the surface of the nickel-containing goethite particles is coated with nickel hydroxide, and the particles are filtered and washed to form a water suspension. 2 to 1 for iron in aqueous suspension.
The nickel compound and the nickel-containing goethite coated with the silicon compound obtained through the fourth step of adding a silicon compound in an amount containing 0% by weight of silicon and further coating the particle surface of the nickel-containing goethite with a silicon compound are The present invention provides a method for producing ferromagnetic metal powder, which is characterized by dehydration treatment at 500°C and hydrogen reduction at 500 to 550°C.

Next, each step of the present invention will be specifically explained.

First, a water-soluble nickel salt solution is added to an aqueous solution of ferrous salt in an amount of Ni/F6-1 to 10% (weight ratio), preferably 2 to 7% (weight ratio), and after thorough stirring, a predetermined amount of alkali is added. An aqueous solution is added to produce a suspension containing Ni (OH) and F" (OH)*. Strong stirring is continued, and at the same time nitrogen gas is introduced for about 1 hour, and 70% of the hydroxide is added. The liquid is broken down and dispersed finely, and the dissolved oxygen in the system is expelled to prepare for the next homogeneous oxidation reaction.The oxidation reaction is carried out continuously by controlling the liquid viscosity so that the liquid viscosity becomes 150~so a C-P.
Nickel-containing d,-FeOOH particles are produced in this way by blowing air to control the reaction rate.

However, when Nt/F@ is 2.5% or more, α-Ff100H
If these 11 are only attached to the surface of particles and are dehydrated and reduced, they tend to become iron powder with segregated components. In other words, this nickel-containing α-F・00Ht-PH is repeated until the pH is 7 or less, preferably 7 to 5.
), then repulped again and further repulped by 1 to 40% based on iron.
A nickel salt aqueous solution of (weight ratio) is attached together with an alkaline aqueous solution and coating S is performed.

At this time, if carboxylic acid etc. are added at the same time, α-Fe
The dispersibility of 00H has been significantly improved, and the Ni (OH) generated by adding an aqueous alkaline solution is uniformly attached to the individual surfaces of α-FI100H particles, and the floating N1 (OH),
This is one of the preferred methods, as the particles are no longer visible in electron micrographs.

This nickel-adhered α-Fe00H was re-r
The concentration of α-peOOH slurry in silica deposition is 401/
-e or less, preferably 201/11 or less, α-
Fe 00I (no particle agglomerates, uniform dispersion, improved silica adhesion efficiency, nickel-containing α-F60
The α-F@OOH particles are uniformly deposited on the surface of the 0H particles, and the deformation of the α-F@OOH particles during subsequent dehydration and reduction prevents sintering between the particles, resulting in iron powder with excellent magnetic properties. Not only that, but also the specific surface area is large and the dispersion-orientation properties are excellent. The amount of adhesion is S1/l'e (weight ratio)
From the above, it was found that setting tL< to 4% or more achieves the above-mentioned purpose of silica deposition. As a raw material for silica, silica sol is easy to operate considering the Na content and the increase in pH of the reaction system, and the silica deposition efficiency is high, so that almost all of the silica remains deposited. In particular, colloidal silica with fine particles is effective, but ordinary colloidal silica can also be used. In addition, silicates such as water glass are more effective than silica gel in terms of reducing the viscosity of the slurry liquid and improving dispersibility, but there are problems with Na5PH in the product and silica coating. There are operational difficulties in improving the sorption rate. In this respect, the use of colloidal silica is advantageous, but it should be noted that by taking measures such as reducing the slurry concentration, conditions must be added to match the low viscosity and uniform adhesion of silica when using water glass. There is a need.

Synthesis of the above α-i'eooH and necessary components.

Nickel-containing α-FeO uniformly deposited on its surface
OH is alloyed in the dehydration tube reduction process to obtain an appropriate coercive force (H
l). As a result of various studies, the dehydration conditions, especially the retention time 1
It has been found that by holding the sample for at least 5 hours, preferably for at least 5 hours, only the coercive force gradually decreases without any change in the specific surface area (BET) or saturation magnetization (σ8).

The hydrogen reduction conditions at this time were as follows: -45 to -55°C for hydrogen gas at the end of the reaction, and at 400°C for about 5 to 6 hours ((1F'h0s: about tokg, H1: 200M, N )
It was retained.

The effect of hydrogen reduction on the characteristic values of iron powder is due to the coercive force (
The I value is determined by the overall balance of He) - saturation magnetization (σS) - specific surface area (BET), and each value is subject to change depending on the conditions of the previous processing steps. In particular, when the dehydration temperature is fixed in the range of 700 to 750''C, the above values vary as follows.

HC: Decrease as retention time increases.

σS: There is almost no change.

BET; Further, as an effect of the hydrogen reduction temperature, as the temperature increases, σS increases, and BET conversely decreases.

Chin (it varies slightly depending on the dehydration temperature) has a peak in a certain reduction temperature range and then decreases. That is 72
In 5°C dehydration, a faint peak is seen at 430°C, but the value is almost flat between about 400 and 460°C. 460℃
In the above reduction, deformation of particles and sintering between particles occur, but it is possible to control the balance of He-σB-BET within the above-mentioned temperature range.

The acicular magnetic iron powder produced by the above process is extremely active due to its ultra-fine size, and in 11 cases it is self-combustible, and its magnetic properties change drastically over time, making it unsuitable for general use. Since the iron powder is not durable, the iron powder after reduction is immersed in an organic solvent.
A well-known method is to gradually evaporate the organic solvent in the air and cause an oxidation reaction on the surface of the iron powder little by little by overlifting to form a dense oxide film. Generally, iron powder is immersed in a sufficient amount of an organic solvent, and then oxidized by blowing in an oxidizing gas. others,
There is also a gas phase oxidation method in which the partial pressure of oxygen in an inert gas such as N, Ar, or the like is increased from a low concentration in a reactor after the reduction reaction is completed to form an oxide film. In the present invention, there is no particular restriction on the stabilization treatment method using the oxide film, and any method may be used.

The present invention will be explained in more detail below with reference to Examples.

Example 1 4.80 kg of electrolytic iron was dissolved in hydrochloric acid aqueous solution (55XHCn2a1
kg't - 240 kg of water (mixed with 1C) and Fel
10 Aqueous solution of FeC-13 with concentration 2011/-C3 240
Create a swamp and fill it with N'C of N1m + concentration 2o1/-e.
14.44 of an aqueous solution of -e was added, and 24 (l) of an aqueous NaOH solution (concentration 172.5.F/J) was added to make the amount (mol) about 6 times the theoretical value (alkali equivalent). During this time, nitrogen gas ( (teeth) was introduced with strong stirring at a flow rate of 1oN and #z4M.

After 50 minutes, fine Fe(0H)t(and N1(OH)
t) A suspension in which particles were uniformly dispersed and mixed was obtained.

Next, while introducing nitrogen gas, the temperature of Suspension 1 was raised from room temperature to 40°C for 30 minutes, and then the nitrogen gas was exchanged with air.
Horse-shaped soft tube (nozzle: 2*%
Goethite (α-FeOOH) was synthesized by homogeneously introducing 50 pieces of powder and carrying out an oxidation reaction and a hydrolysis reaction.

The reaction required 2 hours and 50 minutes.

In this reaction, the amount of nickel added was 6%wt in Ni/Fe.
and the viscosity at the end of the reaction is low (approximately 2600.P).
The synthesized a-Fe00H has a small particle size (long axis: approximately 0
．． 55jIm, axial ratio: about 20), and the particle size is relatively uniform.

This suspension was filtered and washed with water, and the remaining NnOH and Na
After removing Cff1, 2,sskg from this cake
(water 71%) was collected and ribbed with 46% water, and under strong stirring, sulfuric acid aqueous solution was added dropwise to adjust the pH to 5, and α-Fg1
α-F, in which free N1 (OH) not contained in 00H is dissolved in salt, and excess N1 is removed by repeated f-filtration and water washing.
A cake of e00H was obtained, which was further reparibbed with 21.8 g of water.

Next, this is added to an aqueous solution of nickel chloride (Ni(ffl).

・Add 0.55 g of 2o1i'/J in 6H20, and add NaOH solution (concentration: 175 &/A) under strong stirring.
) 0.151 dropwise to neutralize fine Ni (OH)!
It was deposited on the surface of α-FeOOH. α-FeOOH containing approximately 6% nickel in weight ratio to iron was synthesized using the f-hydrogenation method with a pH of 9 or less. Furthermore, add 46% of water to this cake, repulp it under strong stirring,
α-Fe00H't-Uniformly dispersed colloidal silica (Nichikagaku Snowtex-30SiO, medium 50-51
% wt) was added for about 460 d.

(St/Fe1-4%wt in silica addition amount) Homo-no-Kisa 8. manufactured by Tokushu Kikai Kogyo Co., Ltd. After uniformly suspending silica at approximately 500 ORPM in a T-type, SiQ and α-
A cake of Fe00H was obtained. Dry at about 100°C, crusher (Atomizer manufactured by Tokyo Atomizer Manufacturing Co., Ltd.)
After being crushed in a Matsufuru furnace set at 725° C. in the atmosphere for 5 hours, it was made into α-Fe*0 s.

Next, it was reduced by hydrogen gas at 400°C to about 0. '4
8 kg of magnetic iron powder was produced. A hydrogen reduction furnace is a fluidized bed type furnace that uses hydrogen gas for fluidization.

The produced iron powder had a needle shape with a long axis of 0.15 μm and an axial ratio of 15, and was very active, so it was stabilized by immersing it in toluene and gradually drying it in air. The powder has extremely excellent magnetic properties and specific surface area as shown in Table 1. In addition, Fig. 1 shows 4 electron microscopes of the iron powder obtained (
Magnification: 27.000 times).

Example 2 A part of α-FeOOH obtained by oxidation and hydrolysis in Example 1 was repeatedly filtered and washed with water to obtain α-FeOOH with pH<10.
Approximately 2.6 kg (moisture 76%) of α-peQOH was made into a slurry and washed with acid, f-force and water in the same manner as in Example 1.
Got the cake. Next, 21 J of water was added to this and revived under strong stirring, followed by an aqueous solution of nickel chloride (N1C1
*・After adding 201i/J)t-164J at 6L0 and stirring thoroughly, add caustic soda solution C1ysl/43)0.44
Neutralized in the swamp and converted to α-Fe0 as fine N1(OH)*
It was deposited on the surface of 0H. α-FeOOH containing 10% nickel in weight ratio to iron was synthesized by adjusting the pH to 9 or less by f-filtering and washing with water.

Furthermore, this C1-Fe0OHIt was repulped and about 16g
After adding water to a slurry concentration of /43, sodium silicate (JISS No.) was added, and a dilute aqueous nitric acid solution was added dropwise to finally adjust the pH to 7, making the weight ratio to iron (81/F6) about 6. sio and t- were deposited on the surface of the above-mentioned N1-containing a-Fe00H so as to form 'X'.

It was drained and dried, and dehydrated using the same equipment as in Example 1 (725°C
10 hours) to obtain iron powder gold.

Table 1 shows the magnetic property values.

Example 3 The amount of air blown in goethite synthesis was changed to 1013Al
51/M, and the Nt content after synthesis t-
Iron powder was produced in the same manner as in Example 2, except that nickel chloride was added and neutralized so that Ni/F. was approximately 15X. Table 1 shows the magnetic properties.

α-Fe00H was synthesized using the same method, omitting the N1 coprecipitation and subsequent Ni deposition, and produced iron powder by dehydration and reduction. Iron powder has irregular grain shapes and branching, poor filling properties, and poor dispersibility. Table 1 shows the magnetic properties of the obtained iron powder, and FIG. 2 shows an electron micrograph (magnification: 27.000 times).

Table 1

[Brief explanation of the drawing]

FIG. 1 shows an electron micrograph of magnetic iron powder obtained in an example of the present invention, and FIG. 2 shows an electron micrograph of magnetic iron powder obtained in a comparative example. The magnification is 27.000 times in both cases. Patent applicant: Toyo Ichida Kogyo Co., Ltd. 41-

Claims (1)

[Claims] t A hydroxide suspension obtained by neutralizing a ferrous salt aqueous solution with an alkaline aqueous solution is brought into contact with an oxidizing gas and oxidized to produce acicular goethite particles, and dehydrated. , a method for producing ferromagnetic metal powder by performing a reduction treatment, (1) dissolving a nickel salt in an amount containing 1 to 10% by weight of nickel based on iron in an aqueous ferrous salt solution, and dissolving the ferrous salt in an aqueous solution; The first step (2) of neutralizing the aqueous solution with an alkaline aqueous solution to generate iron and nickel hydroxides, and contacting this with an oxidizing gas to generate nickel-containing goethite (2) from a suspension of nickel-containing goethite The second step is to separate the nickel-containing goethite and pickle it to adjust the concentration to 7 or less to make a neutral or acidic suspension.13) Add 1 to the iron to the resulting neutral or acidic suspension. A third step (4) in which an aqueous solution of a nickel salt containing ~40% by weight of nickel is added together with an aqueous alkaline solution to coat the surface of the nickel-containing goethite particles with nickel hydroxide, which is filtered and washed with water to form an aqueous suspension. The resulting aqueous suspension is then added with 2 to 1
The nickel compound and silicon compound gold-coated nickel-containing goethite obtained through the fourth step of adding a silicon compound in an amount containing 0% by weight of silicon and further coating the particle surface of the nickel-containing goethite with a silicon compound has a nickel content of 600 to 900%. A method for producing a ferromagnetic metal powder, which comprises dehydrating the powder at a temperature of 300 to 550°C and reducing it with hydrogen.