JPH04183806A - Manufacture of metallic magnetic powder - Google Patents

Abstract

PURPOSE:To manufacture magnetic metal powder having oxide film on a surface and excellent magnetic characteristic by supplying transition metal carbonyl compound and high temp. dilution gas into a reaction tube impressing magnetic field and reaction the metal fine powder obtd. with gas phase decomposition reaction and oxygen or steam at the specific temp. CONSTITUTION:Into a lower nozzle part 6 in the reaction tube 7, the high temp. dilution gas of H2, CO, inert gas, etc., from an introducing pipe 1 and low temp. mixed gas mixing the transition metal carbonyl compound 2 and the dilution gas 3 in a mixing chamber 4, are introduced and also the magnetic field is impressed with a magnet 8. The transition metal carbonyl compound is decomposed in a gas phase in the reaction tube 7 to obtain the metal super fine particles controlling acicular shape with the influence of the magnetic field. This is supplied to an oxide film forming reaction tube 10 through a tubular passage 9 and at the same time, the mixed gas 12 of oxidizing gas of O2 or steam, etc., and inert gas of N, etc., and these are mixedly reacted at >=600 deg.C to manufacture the metallic magnetic powder having the oxide film on the surface, high resistance to the coercive force and magnetic variation with the lapse of time, high ignition point and excellent weather resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Background of the Invention] (Field of Industrial Application) The present invention relates to a method for producing metal magnetic powder. More specifically, the present invention relates to a simple and economical method for producing metal magnetic powder that has strong resistance to magnetic deterioration, a high ignition point, and excellent weather resistance.

(Prior Art) In recent years, ferromagnetic metal powder containing iron as a main component has been attracting attention and being used as a magnetic material for magnetic recording media.

This ferromagnetic metal powder has superior coercive force and saturation magnetization compared to conventional iron oxide magnetic materials, making it possible to achieve high-density recording, but on the other hand, it has poor oxidation resistance. It has the following disadvantages.

Ferromagnetic metal powder used in magnetic recording media has a large specific surface area and is extremely chemically active, and if taken out into the atmosphere, heat generation and ignition will occur due to rapid oxidation reactions.

For this reason, as a method to stabilize ferromagnetic metal powder,
A method of forming an oxide film on the surface of a metal powder has been proposed. Specifically, a method of immersing the metal powder in an organic solvent and passing an oxygen-containing inert gas to form an oxide film in the solution has been proposed (Japanese Patent Application Laid-Open No. 1983-52). -85054, etc.), and a method of forming an oxide film by contacting oxygen-containing inert gas in the gas phase (Japanese Patent Application Laid-open No. 4
No. 8-79153, etc.).

In addition, the present inventors have previously proposed a method for producing ferromagnetic powder by diluting a transition metal carbonyl compound in an inert gas and performing gas phase thermal decomposition.
No. 570,405 and others attempted to stabilize the ferromagnetic powder by the above-mentioned slow oxidation method.

However, in these slow oxidation methods, the oxidation reaction is carried out in a strongly magnetically agglomerated state, resulting in the inconvenience that the oxidation reaction occurs unevenly due to insufficient diffusion of oxygen into the surface layer of the metal particles. The problem remains that the formation reaction is insufficient and deterioration occurs over time under practical usage conditions.

[Summary of the invention]

(Summary) In view of the above circumstances, the inventors of the present invention have made the present invention as a result of intensive studies on a method for producing metal magnetic powder with improved oxidation resistance.

That is, the method for producing metal magnetic powder according to the present invention uses hydrogen,
A transition metal carbonyl compound diluted with a diluent gas consisting of carbon monoxide, an inert gas, or a mixture thereof is subjected to vapor phase pyrolysis to produce a magnetic powder of the metal, and then a reaction section where the magnetic powder is produced is produced. and forming an oxide film on the surface of the generated magnetic powder by bringing the generated magnetic powder into contact with oxygen and water vapor, which may be diluted with an inert gas, at a temperature of 60° C. or higher between the collection unit and the collecting section. It is characterized by:

(Effects) According to the present invention, it is possible to form an extremely stable and uniform oxide film on the metal magnetic powder, and the stable metal magnetic powder has a small change in magnetic properties (saturation magnetization) over time and a high ignition point. can be easily obtained without complicated operations.

In the method of the present invention, the formation reaction of an oxide film on the metal magnetic powder is performed immediately after the metal powder is generated, while the metal powder is dispersed in a diluent gas, and moisture is interposed between the particles to prevent agglomeration. Therefore, compared to the case where the oxide film is formed while the metal magnetic particles are aggregated together after collection, oxygen is sufficiently diffused into the surface layer of the metal particles, and a uniform oxide film is formed. As a result, an extremely stable metal magnetic powder can be obtained.

In addition, according to the method of the present invention, since the formation of an oxide film on the metal magnetic powder is carried out during the metal powder transfer process, there is no need for a special reactor for slow oxidation, and there is no need for a special reactor for gradual oxidation. Since the dilution gas can be reused, the amount of dilution gas can also be reduced, which is economically advantageous.

[Detailed description of the invention]

Production of Metal Magnetic Powder> The metal magnetic powder on which an oxygen film is to be formed according to the present invention is disclosed in, for example, Japanese Patent Laid-Open No. 63-27 filed by the present inventors.
No. 0405, No. 64-83605, Patent Application No. 1983-22
No. 1952, No. 63-284760, Patent Application No. 1-65
No. 724 and others.

Specifically, for example, a gas mixture in which a transition metal carbonyl compound is diluted with hydrogen, carbon monoxide, or an inert gas to a concentration of 3% by volume or less is placed in a reaction system in which a magnetic field of 100 Gauss or more is applied. It can be produced by performing a gas phase thermal decomposition reaction by retaining at 300° C. or higher for 5 seconds or less.

The metal magnetic powder obtained by this method is acicular ultrafine particles, for example, with a major axis diameter of 0.5 microns or less and a minor axis diameter of 0.
．． It is a metal magnetic powder with a specific surface area of 0.05 microns or less and a specific surface area of 30rd/g or more.

FIG. 1 shows an example of an apparatus for implementing the present invention.

In Fig. 1, a high-temperature diluent gas is introduced through the introduction tube 1, and a mixed gas of metal carbonyl and dilution gas at a low temperature is introduced through the introduction tube 5, and the two are brought into contact at the nozzle outlet 6 where a magnetic field is applied. By heating, the temperature is 300°C or higher, preferably 400 to 800°C, which is necessary for the decomposition of metal carbonyl.
Heat in the range of 100 to 100% can be instantaneously supplied from high-temperature diluent gas.

At this time, in order to prevent blockage due to the decomposition reaction of low-temperature metal carbonyl in the introduction pipe 5, low-temperature diluent gas is introduced from the introduction pipe 11 for protection.

The mixed gas introduced through the introduction pipe 5 is produced by mixing a metal carbonyl compound (introduced through the introduction pipe 2) and a diluent gas (introduced through the introduction pipe 3) in the mixing chamber 4 to produce a metal carbonyl compound mixed gas having a predetermined concentration. obtained as. The concentration of the transition metal carbonyl compound in the gas mixture introduced through the introduction pipe 5 is 0.1 to 30% by volume, preferably 0.5 to 30% by volume.
The range is 25% by volume. If this concentration is too high, the particle size of the metal particles obtained will grow large, making it impossible to obtain the magnetic ultrafine powder having a high coercive force, which is the object of the present invention.On the other hand, if the concentration is too low, productivity will be poor.

The mixed gas introduced through the introduction pipe 5 has a temperature range of 200°C or less, preferably 180 to 30°C,
The amount introduced is 1 to 30% by volume, preferably 3 to 20% by volume, based on the total supply amount of introduction tube 1, introduction tube 5, and introduction tube 11.
% by volume.

If the amount introduced is too small, the productivity will be poor, while if it is too large, sufficient reaction heat will not be obtained, so the reaction rate will be reduced, and the produced metal particles will grow large, making it impossible to obtain ultrafine particles. Moreover, if the temperature of this mixed gas is too high, desired ultrafine particles cannot be obtained.

In addition, the high temperature diluent gas introduced from the introduction pipe 1 is
0°C or higher, preferably 450°C or higher (upper limit is 1000°C)
degree), and the amount introduced is 96 to 55% by volume with respect to the total supply amount of introduction tube 1, introduction tube 5, and introduction tube 11,
Preferably it is 92 to 70% by volume. If the temperature of this gas is too low or the amount introduced is too small, sufficient reaction heat will not be obtained and the reaction rate will drop significantly, and the amount of nuclei generated during metal particle formation will also decrease, causing the particle size to grow larger. The ultrafine particles targeted by the present invention cannot be obtained.

Also, the low temperature diluent gas introduced from the introduction pipe 11 is
00℃ or less, preferably 100℃ or less, and the amount introduced is 3 to 15% by volume of the total supply amount, preferably 5 to 10%.
It is volume %. If the amount of gas introduced is small, it will not be possible to prevent blockage due to decomposition reaction within the raw material metal carbonyl compound introduction tube 5 or adhesion at the tip of the introduction tube 5.
Unable to continue stable operation for long periods of time. On the other hand, if the amount is too large, the reaction temperature cannot be maintained sufficiently and the desired ultrafine particles cannot be obtained.

The gases catalytically mixed at the nozzle outlet 6 remain in the reaction tube 7 for 5 seconds or less, preferably 2 seconds or less, to perform a gas phase decomposition reaction.

Any device 8 such as a permanent magnet, an electromagnet, or a solenoid coil can be used to apply the magnetic field to the reaction system. The applied magnetic field is 300 Gauss or more, preferably 400 to 15
00 Gauss range.

By applying a magnetic field, the acicularity of the produced ultrafine metal particles can be controlled and the coercive force can be increased.

Formation of Oxide Film> Formation of an oxide film on the metal magnetic powder according to the present invention involves introducing the metal magnetic powder generated by the thermal decomposition into the oxide film forming reaction tube 10 through the pipe 9, and introducing it through the oxidizer entry pipe 12. by instantaneous contact with oxygen and water vapor or oxygen and water vapor diluted with an inert gas. Nitrogen, helium, argon, etc. are commonly used as the inert gas, but nitrogen, which is inexpensive, is preferably used. Furthermore, since the water vapor is instantaneously vaporized due to the high temperature inside the reaction tube, the water vapor can also be supplied by introducing it into the reaction tube in the form of liquid water.

The metal magnetic powder introduced into the reaction tube 10 is sufficiently diluted in the gas, and furthermore, due to the presence of moisture, it is difficult to aggregate, and it does not form like the magnetic powder collected in the collector. Particles are not strongly aggregated. Therefore, oxygen is sufficiently diffused into the surface layer of the metal particles, so that a stable oxide film can be formed under relatively high temperature and short reaction conditions.

The reaction temperature in the reaction tube 10 is 60°C or higher, preferably 80°C.
℃ or more and 300°C or less, and the residence time is 1 second or more, preferably 10 seconds or more and 100 seconds or less.

In addition, the amount of oxygen and water vapor introduced, or the amount of oxygen and water vapor diluted with an inert gas, is the concentration of oxygen diluted in the reactor 10 by the dilution gas from the pipe 9 and the inert gas from the oxidizing agent introduction pipe 12. The water vapor concentration is 0.01 to 5% by volume, preferably 0.05 to 2% by volume, and the water vapor concentration is 1 to 4% by volume.
0% by volume, preferably 5-20% by volume.

If the reaction temperature is below 60°C, the oxidation rate is slow and it is not suitable for forming the desired oxide film, and if it exceeds 300°C, the oxidation reaction is rapidly accelerated, making it difficult to control and causing unevenness of the oxide film. This is not desirable in terms of quality.

Further, if the residence time is 100 seconds or more, the reactor volume becomes too large and it is not economical, and if the residence time is 1 second or less, it is insufficient for forming an oxide film.

The metal powder on which the oxide film has been formed is sent to the collection chamber 13 and collected. After collection, gradual oxidation may be further performed according to a conventional method to complete the formation of an oxide film.

Example 1 In a reaction apparatus as shown in FIG.
A magnetic field of 600 Gauss was applied to the reaction tube 7 with a length of 1 m, and Fe (CO) s was produced under the reaction conditions (a) to (e) below.
A gas phase pyrolysis reaction is carried out to produce ultrafine iron particles, and then in a reaction tube 10 with an inner diameter of 102 mm and a length of 2 m.
The oxide film was formed under the conditions of ~(h). The obtained metal powder is collected in the collection section 13 and kept at 60°C for 4 hours.
After maintaining the oxygen concentration at , it was taken out into the atmosphere.

(a) Amount of nitrogen introduced from pipe 1 Nitrogen: 500°C, 855 volume of the total amount of gas flowing into reaction tube 7 (b) Amount of mixed gas introduced from pipe 5 Nitrogen: 60°C, flowing into reaction tube 7 8.5% by volume of the total amount of gas F e (CO) 5: 60°C, 1.5% by volume of the total amount of gas flowing into the reaction tube 7 (c) Amount of diluent gas introduced from the pipe 11 Nitrogen: 60°C,
5% by volume of the total amount of gas flowing into the reaction tube 7 (d) Residence time 0. 1 second (e) Reaction tube (7) average temperature 495°C (f) Amount of nitrogen, oxygen and water vapor introduced from pipe 12 (relative to 100 parts by volume of total gas flowing into reaction tube 7) Nitrogen: 120°C, 4 parts by volume Oxygen: 120°C, 1 part by volume Water vapor: 120°C, 5 parts by volume (T) Residence time 3.2 seconds (H) Reaction tube (1o) Average temperature 180"C The obtained magnetic iron powder was permeated. Observation of electron micrographs reveals that it has a needle-like shape with a short axis diameter of 0.02 microns and a long sleeve diameter of 0.20 microns, and its magnetic properties are saturation magnetization (6s): 135
en+u/g, magnetic coercivity 1550 (Oe), squareness ratio: 0.5'l.

In addition, the oxidation stability of this powder is 60°C and 90°C in air.
Decrease rate of 68 after standing for 3 days under the condition of %RH (Δ6s
) and 0. It was 5%.

In addition, when the ignition point was measured using a differential thermal analyzer, it was found to be 130
It was ℃.

Comparative Example 1 The same operation as in Example 1 was performed except that the sample was collected without going through the oxide film forming step under the conditions (f) to (h) in Example 1.

The magnetic properties of the obtained magnetic iron powder are saturation magnetization (6s) +
135 cmu/g, magnetic coercivity 1550 (Oe), and squareness ratio: 0.51.

Further, the oxidation resistance stability of this powder was evaluated by the rate of decrease over 6 seconds (△6゛s) and was 5.2%.

In addition, when the ignition point was measured using a differential thermal analyzer, it was found to be 105
It was °C.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of an apparatus for carrying out the method of the present invention. DESCRIPTION OF SYMBOLS 1... High temperature dilution gas introduction pipe, 2... Transition metal carbonyl compound introduction pipe, 3... Dilution gas introduction pipe, 4...
-Mixing tank, 5...Mixed gas introduction pipe, 6...Nozzle outlet, 7...Reaction tube, 8...Magnetic field application device, 9...
Pipe line, 10... Reaction tube, 11... Low temperature dilution gas introduction tube, 12... Oxidizing agent introduction tube, 13... Collection chamber. Applicant's agent Mr. Sato

Claims (1)

[Claims] vapor phase pyrolysis of a transition metal carbonyl compound diluted with a diluent gas consisting of hydrogen, carbon monoxide, an inert gas, or a mixture thereof to produce a magnetic powder of the metal; Forming an oxide film on the surface of the generated magnetic powder by bringing the generated magnetic powder into contact with oxygen and water vapor, which may be diluted with an inert gas, at a temperature of 60° C. or higher between the reaction section and the collection section. A method for producing metal magnetic powder, characterized by: