JPH1111951A - Spindle goethite particle powder and its production, spindle hematite particle powder and its production and spindle metallic magnetic particle powder consisting essentially of iron and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a spindle goethite particle powder and a spindle metallic magnetic particle powder obtained by using the spindle goethite particle powder as a starting material. SOLUTION: In the spindle goethite particle powder consisting of the goethite particles being a spindle particle having 0.05-1.0 μm average major axis diameter and in which the particles are composed of a seed crystal part and a surface layer part, and the seed crystal part is incorporated with 0.5-25 atom % Co per total iron and the surface layer part is incorporated with 0.5-15 atom % Al per total iron and 0.5-10 atom % rare earth elements. When the spindle goethite particle powder is formed by aging in a non-oxidizing atmosphere an aq. suspension containing a ferrous salt- containing precipitate obtained by allowing a mixed alkali soln. of an alkali carbonate and an alkali hydroxide to react with a ferrous salt soln., forming spindle goethite seed crystal particles by passing an oxygen-containing gas, adding again the mixed alkali soln. and the ferrous salt soln., mixing the mixture, then subjecting the mixture to growth reaction, 0.5-25 atom % Co compd., 0.5-15 atom % Al compd. and 0.5-10 atom % rare earth elements compd. per total iron are added.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a uniform particle size, no dendritic particles, and an appropriate particle shape and a large axial ratio (major axis diameter / minor axis diameter-the same applies hereinafter). Spindle-shaped goethite particle powder, spindle-shaped hematite particle powder, and having high coercive force and excellent coercive force distribution obtained by using the spindle-shaped goethite particle powder or the spindle-shaped hematite particle powder as a starting material. The present invention relates to spindle-shaped metal magnetic particles containing iron as a main component.

[0002]

2. Description of the Related Art In recent years, long-time recording, miniaturization and lightening of magnetic recording / reproducing devices for video and audio have been intensified. In particular, VTRs (video tape recorders) have been remarkably popular recently. 2. Description of the Related Art VTRs aiming at long-term recording and reduction in size and weight have been actively developed. On the other hand, demands for higher performance and higher density recording of magnetic tapes, which are magnetic recording media, are increasing.

[0003] That is, the magnetic recording medium is required to have high image quality, high output characteristics, and especially improvement in frequency characteristics.
Improvement of residual magnetic flux density Br, high coercive force and dispersibility,
It is necessary to improve the filling property and the smoothness of the tape surface, and the S / N ratio is increasingly required to be improved. These various properties of the magnetic recording medium have a close relationship with the magnetic particle powder used in the magnetic recording medium, but in recent years, the high coercive force and the large Attention has been paid to metal magnetic particle powders composed mainly of iron having saturation magnetization, and digital audio tapes (DA
T), 8 mm video tapes, Hi-8 tapes, and video floppy and other magnetic recording media. However, it is strongly desired to further improve the properties of these metal magnetic particle powders containing iron as a main component.

Now, the relationship between the characteristics of the magnetic recording medium and the characteristics of the magnetic particle powder used will be described in detail as follows. In order to obtain high image quality as a video magnetic recording medium, it is clear from the recording of Nikkei Electronics (1976), May 3, Issue No. 82-105, (1)
It is required to improve video S / N ratio, (2) chroma S / N ratio, and (3) video frequency characteristics.

[0005] In order to improve the video S / N ratio and the chroma S / N ratio, it is necessary to improve the dispersibility of the magnetic particle powder in a vehicle, the orientation and the filling property in a coating film, and It is important to improve the surface smoothness of the magnetic recording medium, and as such magnetic particle powder, the particle size is uniform, dendritic particles are not mixed, and the appropriate particle shape and axis It is required to be a ratio.

Next, in order to improve video frequency characteristics, it is necessary that the coercive force Hc of the magnetic recording medium be high and the residual magnetic flux density Br be high. In order to increase the coercive force Hc of the magnetic recording medium, it is required that the coercive force Hc of the magnetic particle powder be as high as possible. Since the coercive force of the magnetic particle powder generally occurs due to its shape anisotropy, the coercive force tends to increase as the axial ratio of the particles increases.

In order to increase the output of a magnetic recording medium,
FIG. 1 of JP-A-63-26821 shows the relationship between the SFD measured for the above magnetic disk and the recording / reproducing output. 1, the relationship between the recording and reproduction output becomes a straight line, which indicates that the recording and reproduction output can be increased by using a ferromagnetic powder having a small SFD. In order to increase the recording / reproducing output, it is desirable that the SFD is small.
The following S. F. D. is necessary. "
S. of magnetic recording medium F. D. (Switching F
In this case, it is required that the coercive force distribution is small, and for this purpose, it is required that the particle size of the magnetic particles is as uniform as possible and that dendritic particles are not mixed.

As described above, the particles have a uniform particle size, do not contain dendritic particles, have an appropriate particle shape and axial ratio, and have high coercive force and excellent coercive force distribution. At present, metal magnetic particle powder containing iron as a main component is most demanded at present.

Generally, metal magnetic particle powder containing iron as a main component is prepared by adding goethite particles as a starting material, hematite particles obtained by heating and dehydrating the goethite particles, or dispersing a foreign metal other than iron into each of the above particles. The particles are obtained by heat-treating particles and the like in a non-reducing atmosphere, if necessary, and then reducing them by heating in a reducing gas atmosphere. Therefore, the metal magnetic particle powder containing iron as a main component similarly inherits the shape of the goethite particle powder that is the starting material thereof,
It is known that the higher the axial ratio of the goethite particles, the higher the axial ratio of the metal magnetic particles.When obtaining the metal magnetic particle powder containing iron as a main component having the above-mentioned characteristics, the particle size is uniform. And dendritic particles are not mixed,
In addition, it is necessary to use goethite particle powder having an appropriate particle shape and an axial ratio, and it is necessary to retain and inherit the particle shape and uniform particle size in a subsequent heat treatment step. .

Conventionally, various methods have been known as methods for producing goethite particle powder, which is a starting material for metal magnetic particle powder containing iron as a main component. In particular, when a metal magnetic particle powder is used as Co, which has an effect of improving magnetic properties, and when a metal magnetic particle powder is used, a metal compound such as Al which has an excellent shape retention property has an effect of preventing sintering. The following is known as a method of adding in advance in the production process. For example, a suspension containing a ferrous hydroxide colloid obtained by adding an equivalent amount or less of an alkali hydroxide aqueous solution to a ferrous salt aqueous solution in the presence of a cobalt compound is subjected to an oxidation reaction by passing an oxygen-containing gas at 50 ° C. A method of producing acicular goethite particles by conducting a growth reaction (Japanese Unexamined Patent Publication (Kokai) No. 7-1310).
An oxygen-containing gas is passed through a suspension containing FeCO ₃ obtained by reacting an aqueous ferrous salt solution to which an acidic salt compound of Al is added with an aqueous alkali carbonate solution to which a basic salt compound of Al is added to oxidize the suspension. A method of producing spindle-shaped goethite particles by performing a reaction (Japanese Patent Laid-Open No. 6-22861).
No. 4), a mixed aqueous solution of a ferric salt and a Co compound is neutralized with an aqueous alkali hydroxide solution, and the goethite seed crystal particles obtained by hydrolysis are dispersed in an aqueous ferric salt solution in which an Al compound is present. A method in which a growth reaction is carried out by a hydrolysis reaction by neutralizing an aqueous alkali hydroxide solution (JP-A-58-17)
No. 6902), a suspension containing a ferrous-containing precipitate obtained by reacting an aqueous solution of an alkali carbonate and an aqueous solution of ferrous salt is aged in a non-oxidizing atmosphere. In producing goethite particles having a spindle shape by performing an oxidation reaction by passing an oxygen-containing gas through the
In any one of the aqueous solution of ferrous salt, the suspension containing the ferrous-containing precipitate, and the suspension containing the aged ferrous-containing precipitate before the oxidation reaction, , C
o compound in the aqueous solution of ferrous salt.
During the oxidation reaction developing liquid in the range of 50-90% with respect to e ^2+, under the same conditions and the oxidation reaction, Al, Si,
The aqueous solution of one or more compounds selected from rare earth elements such as Ca, Mg, Ba, Sr and Nd is added to Fe ²⁺ in the aqueous ferrous salt solution in terms of each element. (JP-A-7-126704) and the like are known.

The above publications also describe metal magnetic particle powders containing iron as a main component and obtained using each goethite particle powder described in each publication as a starting material.

Further, the ratio of the X-ray crystal grain size of the hematite particles is specified as the X-ray crystal grain ratio in the direction perpendicular to the (104) plane.
The ratio D ₁₀₄ / D ₁₁₀ of the line crystal grain size D ₁₀₄ and (110) X-ray in a direction perpendicular to the plane crystal grain size D ₁₁₀ is in the range of 1-2,
There is fine acicular α-ferric oxide particles having a specific surface area of 40 to 50 m ² / g (JP-A-7-206446).

[0013]

The particle size is uniform, dendritic particles are not mixed, the particles have an appropriate particle shape and a high axial ratio, and a high coercive force and excellent coercive force distribution are obtained. Spindle-shaped metal magnetic particles having iron as a main component having the following are currently the most demanded, but the metal obtained when each goethite particle powder described in each of the above publications is used as a starting material It is difficult to say that the magnetic particle powder sufficiently satisfies these characteristics.

That is, in the case of the production method described in the above-mentioned Japanese Patent Application Laid-Open No. 7-11310, acicular goethite particles having an axial ratio of 10 or more in which Co atoms are present in goethite particles are produced, but dendritic. Particles are mixed, and in terms of particle size, it is hard to say that the particles have a uniform particle size.

In the case of the production method described in the above-mentioned Japanese Patent Application Laid-Open No. 6-228614, goethite particles which do not contain dendritic particles and have a uniform particle size are devised by a method of adding Al. However, it is not enough in terms of the axial ratio.

In the production method described in Japanese Patent Application Laid-Open No. Hei 7-126704, Al is added in the middle of the oxidation reaction. At the intermediate stage of the oxidation reaction, Co ions remain in the solution.
When l is added and residual ferrous ions are oxidized to grow goethite particles, remarkable growth in the short axis direction is observed,
The present inventor has found that the axial ratio decreases as described later. Therefore, it is difficult to produce spindle-shaped goethite particles having a large axial ratio, particularly 13 or more.

The production method described in the above-mentioned JP-A-58-176902 uses trivalent iron as a starting material, the reaction mechanism is not oxidation but hydrolysis, and the secondary reaction is one-step.
Hydrothermal treatment is performed at a high temperature exceeding 00 ° C., which is different from the reaction in the present invention.

[0018] The metal magnetic particle powder containing iron as a main component and obtained from the goethite particle powder obtained by the production method described in each of the aforementioned publications as a starting material is also uniform in particle size and contains dendritic particles. However, it is hard to say that it has a large axial ratio.

The needle-like α-ferric oxide particles described in the above-mentioned Japanese Patent Application Laid-Open No. 7-206446 have a X-ray crystal particle size ratio D.
₁₀₄ / _D110 is in the range of 1-2, and X in the present invention
It is not in the specific range of the linear crystal grain size ratio D ₁₀₄ / D ₁₁₀ , but rather has a completely different crystallinity because D ₁₁₀ is smaller than D ₁₀₄ . Moreover, the acicular α-ferric oxide particles are obtained by a hydrothermal reaction. On the other hand, as a comparative example, it is described that hematite particles obtained by heating and dehydrating goethite particle powder have an X-ray crystal particle size ratio D ₁₀₄ / D ₁₁₀ of 0.7. It is not in the specific range of the ratio of the crystal grain size.

Therefore, the present invention provides a spindle-shaped goethite particle powder having a uniform particle size, free of dendritic particles, and having an appropriate particle shape and an axial ratio. It is a technical object to obtain a spindle-shaped metal magnetic particle powder containing iron as a main component and having a high coercive force and an excellent coercive force distribution using goethite particle powder as a starting material.

[0021]

The above technical objects can be achieved by the present invention as described below.

That is, according to the present invention, the average major axis diameter is 0.05 to
1.0 μm spindle-shaped particles, comprising a goethite seed crystal part and a goethite surface layer part, wherein the seed crystal part has C
0.5 to 25 atomic% based on the total Fe, and
The surface layer contains 0.5 to 15 atomic% of Al with respect to the total Fe and contains a rare earth element in an amount of 0.1 to 0.1 with respect to the total Fe.
Spindle-shaped goethite particle powder comprising goethite particles containing 5 to 10 atomic%.

In the present invention, the average major axis diameter is 0.05 to
1. Spindle-shaped particles of 1.0 μm, comprising a hematite seed crystal part and a hematite surface layer part, wherein the seed crystal part has C
0.5 to 25 atomic% based on the total Fe, and
The surface layer portion contains 0.5 to 15 atomic% of Al with respect to the total Fe, and the surface layer portion or the particle surface other than the seed crystal portion contains a rare earth element in an amount of 0.5 to 15 atomic% with respect to the total Fe. %, And the ratio of the X-ray crystal particle diameter D ₁₀₄ / D
₁₁₀ is a spindle-shaped hematite particle powder, characterized by comprising hematite particles in the range of 0.20 to 0.65.

The present invention also relates to a non-oxidizing aqueous suspension containing a ferrous-containing precipitate obtained by reacting a mixed aqueous alkali solution of an aqueous alkali carbonate solution and an aqueous alkali hydroxide solution with an aqueous ferrous salt solution. After aging under a neutral atmosphere, an oxygen-containing gas was passed through the aqueous suspension to generate spindle-shaped goethite seed crystal particles. A mixed alkali aqueous solution and a ferrous salt aqueous solution of and alkali hydroxide are newly added and mixed, and an oxygen-containing gas is ventilated to grow a goethite layer on the surface of the spindle-shaped goethite seed crystal particles. In producing spindle-shaped goethite particles, at the time of the generation reaction of the seed crystal particles, an aqueous ferrous salt solution, an aqueous suspension containing a ferrous-containing precipitate, and a ferrous content during aging before the start of the oxidation reaction. Aqueous suspension containing precipitate Water suspension in forming reaction, the total Fe
And a Co compound in an amount of 0.5 to 25 atomic% in terms of Co, and at the time of the growth reaction of the goethite layer,
The aqueous solution containing each alkali aqueous solution to be added, the aqueous ferrous salt solution, the spindle-shaped goethite seed crystal particles before the start of the oxidation reaction and the ferrous-containing precipitate, or the aqueous suspension during the growth reaction, Wherein 0.5 to 15 atomic% of an Al compound and a rare earth element in terms of Al are added, and 0.5 to 10 atomic% of a rare earth element compound with respect to the total Fe, respectively. This is a method for producing particle powder.

Further, the present invention provides a method for preventing sintering of the above-mentioned spindle-shaped goethite particles with a sintering inhibitor.
A method for producing the spindle-shaped hematite particle powder, wherein a heat treatment is performed at a temperature in the range of -850 ° C.

Further, the present invention is the method for producing spindle-shaped hematite particles, wherein the sintering inhibitor is any one of an Al compound, a compound of a rare earth element or a compound of an Al compound and a rare earth element. .

[0027] Further, the present invention provides a method in which the spindle-shaped goethite particles are subjected to a sintering-preventive treatment with a sintering-preventive agent.
Producing a spindle-shaped metal magnetic particle powder containing iron as a main component, which is subjected to a heat treatment at a temperature in the range of 850 ° C. to 850 ° C. and further reduced by heating in a reducing gas atmosphere at a temperature of 400 to 600 ° C. Is the law.

The present invention also provides a spindle-shaped metal magnetic particle powder comprising iron as a main component, wherein the spindle-shaped hematite particle powder is reduced by heating in a reducing gas atmosphere at a temperature in the range of 400 to 600 ° C. It is a manufacturing method of.

The present invention also relates to spindle-shaped particles having an average major axis diameter of 0.05 to 0.5 μm obtained by the method for producing spindle-shaped metal magnetic particles containing iron as a main component.
Is contained in an amount of 0.5 to 25 atomic% based on the total Fe, and A
1 to 0.5 to 15 atomic% of the total Fe and 0.5 to 15 atomic% of the rare earth element to the total Fe. Is a spindle-shaped metal magnetic particle powder containing iron as a main component.

The structure of the present invention will be described in more detail as follows. First, the spindle-shaped goethite particles according to the present invention will be described.

The particles constituting the spindle-shaped goethite particles according to the present invention have an average major axis diameter of 0.05 to 1.0 μm, preferably 0.05 to 0.5 μm. The shape is a spindle shape and the axial ratio (major axis diameter / minor axis diameter) is 10 to 15, preferably 13 to 15.

The spindle-shaped goethite particles according to the present invention have a BET specific surface area of 50 to 180 m ² / g, preferably 60 to 150 m ² / g.

The particles constituting the spindle-shaped goethite particles according to the present invention are formed of a seed crystal portion and a surface layer portion. The seed portion refers to a goethite seed particle portion formed by oxidizing all of the ferrous salt added first. Specifically, it is a portion of a weight ratio determined by a ratio with the ferrous salt added in the growth reaction, and is preferably 50 to 80% by weight, more preferably 55 to 75% by weight from the inner center of the seed crystal particles. Parts by weight. The Co contained in the goethite seed particles in the seed portion is 0.5 to 25 atomic%, preferably 1.0 to 20 atomic%, based on the total Fe.
It is. When the content is less than 0.5 atomic%, the effect of improving the magnetic properties cannot be obtained. If it exceeds 25 atomic%, a high axial ratio cannot be obtained. The surface layer portion refers to a goethite layer that has grown on the surface of the goethite seed particles by oxidizing all of the ferrous salt added in the growth reaction. Specifically, it is 20 to 50% by weight, preferably 25 to 45% by weight from the outermost surface of the particles. Al contained in the goethite layer in the surface layer is 0.5 to 1 with respect to all Fe.
It is 5 atomic%, preferably 1.0 to 10 atomic%. 0.
If it is less than 5 atomic%, no sintering preventing effect can be obtained. 1
If it exceeds 5 atomic%, it is difficult to obtain a high axial ratio.
The rare earth element contained in the goethite layer of the surface layer portion,
0.5 to 10 atomic%, preferably 1.0 atomic%, based on all Fe
To 8.0 at%, more preferably 1.0 to 6.0 at%
It is.

Next, a method for producing the spindle-shaped goethite particles according to the present invention will be described.

The particles constituting the spindle-shaped goethite particles according to the present invention are obtained by first producing spindle-shaped goethite seed crystal particles and then performing a growth reaction for growing a goethite layer on the surface of the seed crystal particles. .

The spindle-shaped goethite seed crystal particles are an aqueous suspension containing a ferrous-containing precipitate obtained by reacting a mixed alkali aqueous solution of an aqueous alkali carbonate solution and an aqueous alkali hydroxide solution with an aqueous ferrous salt solution. After aging under a non-oxidizing atmosphere, an oxygen-containing gas is passed through the aqueous suspension to produce spindle-shaped goethite seed crystal particles. The aqueous suspension containing the ferrous-containing precipitate during aging before the start of the oxidation reaction, or the aqueous suspension during the formation reaction, contained 0.5 to 25 atoms in terms of Co with respect to all Fe. % Of a Co compound.

In the formation reaction of the spindle-shaped goethite seed crystal particles, an aqueous ferrous salt solution may be an aqueous ferrous sulfate solution, an aqueous ferrous chloride solution, or the like. The concentration of ferrous iron after mixing the aqueous ferrous salt solution and the mixed alkaline aqueous solution is 0.1 to 1.0 mol / l, preferably 0.1 to 1.0 mol / l.
2 to 0.8 mol / l. When it is less than 0.1 mol / l, the yield is low and it is not industrial. 1.0mol
If it exceeds / l, the particle size distribution is undesirably large.

In the formation reaction of the spindle-shaped goethite seed crystal particles, the aqueous alkali solution includes an aqueous sodium carbonate solution, an aqueous potassium carbonate solution as an aqueous alkali carbonate solution,
Sodium hydroxide, potassium hydroxide and the like can be used as an aqueous solution of an alkali hydroxide mixed with an alkali carbonate such as an aqueous solution of ammonium carbonate.

The mixed alkaline aqueous solution used in the production reaction of the spindle-shaped goethite seed particles is obtained by mixing an alkaline carbonate aqueous solution and an alkaline hydroxide aqueous solution. In this case, the ratio of the aqueous alkali hydroxide solution is 5 to 35 mol% as a mixing ratio (% display by a specified conversion).
(Specific conversion%), preferably 10 to 30% (specific conversion%), and more preferably 15 to 25% (specific conversion%). If it is less than 5%, a sufficient axial ratio cannot be obtained, and if it exceeds 35%, particulate magnetite may be mixed.

The amount of the mixed alkaline aqueous solution to be used is from 1.3 to 1.3 as an equivalent ratio to the total Fe in the aqueous ferrous salt solution.
3.5, preferably 1.5 to 2.5. If the ratio is less than 1.3, magnetite may be mixed.
If it exceeds 5, it is not industrially preferable.

The pH value in the formation reaction of the spindle-shaped goethite seed particles is 8.0 to 11.0, preferably 8.
It is in the range of 5 to 10.0. When the pH is less than 8.0, a large amount of acid radicals are contained in the goethite particle powder and cannot be easily removed by washing. In this case, sintering of the particles is caused. If it exceeds 11.0, the desired high coercive force cannot be obtained when the metal magnetic particles are used.

The oxidizing means in the production reaction of the spindle-shaped goethite seed crystal particles is performed by passing an oxygen-containing gas (for example, air) through the liquid.

The temperature in the formation reaction of the spindle-shaped goethite seed crystal particles is usually set at 80 ° C. at which goethite particles are formed.
It may be performed at a temperature of not more than ℃. If the temperature exceeds 80 ° C,
Magnetite may be mixed in the spindle-shaped goethite particles. Preferably it is in the range of 45 to 55 ° C.

In the formation reaction of the spindle-shaped goethite seed crystal particles, cobalt sulfate, cobalt chloride, cobalt nitrate or the like can be used as the Co compound. Co
The compound may be added to the aqueous solution of the ferrous salt, the suspension containing the ferrous-containing precipitate, and the suspension containing the ferrous-containing precipitate that has been aged before the oxidation reaction, or during the formation reaction. It can be added in any liquid of the water suspension. In particular, it is preferable to add it just before starting the oxidation reaction. The amount of the Co compound to be added is 0.5 to 25 atomic%, preferably 1.0 to 20.0 atomic%, based on the total Fe in the spindle-shaped goethite particles as the final product. 0.
If it is less than 5 atomic%, there is no effect of improving the magnetic properties of the metal magnetic particle powder, and if it exceeds 25 atomic%, the axial ratio decreases due to miniaturization.

In the aqueous suspension containing the spindle-shaped goethite seed crystal particles, a mixed alkali aqueous solution of an aqueous alkali carbonate solution and an aqueous alkali hydroxide solution and a ferrous salt aqueous solution are newly added and mixed, and an oxygen-containing gas is added. When growing a goethite layer on the surface of the spindle-shaped goethite seed crystal particles, the alkali aqueous solution, the ferrous salt aqueous solution to be added, and the spindle-shaped goethite seed crystal particles before the start of the oxidation reaction and the first In an aqueous suspension containing an iron-containing precipitate or an aqueous suspension during a growth reaction, 0.5 to 15 atomic% of an Al compound and a rare earth element in terms of Al relative to the total Fe are added in an amount of 0.1 to 0.1% based on the total Fe. 5-
By adding 10 atomic% of a compound of a rare earth element, a desired spindle-shaped goethite particle powder can be obtained.

Examples of the ferrous salt aqueous solution used in the growth reaction of the goethite layer include an aqueous ferrous sulfate solution and an aqueous ferrous chloride solution. The addition amount of the ferrous salt is 20 to 50 mol based on the total amount of the addition amount of the ferrous salt in the formation reaction of the goethite seed crystal particles.
%, Preferably 25 to 45 mol%. 20mol
%, The growth reaction of the spindle-shaped goethite particles does not sufficiently occur, and a desired spindle-shaped goethite particle powder cannot be obtained. When it exceeds 50 mol%, dendritic particles are generated by generating new seed crystals of goethite particles, and the particle size of the generated goethite particles becomes uneven.

The aqueous alkali solution used in the growth reaction of the goethite layer can be selected from those usable in the reaction for producing the spindle-shaped goethite seed crystal particles, and the amount of addition is also selected from the same range. be able to. Further, the growth reaction of the goethite layer is preferably performed under the same conditions as possible for the production reaction of the spindle-shaped goethite seed crystal particles, and the ratio of the alkali hydroxide aqueous solution in the mixed alkaline aqueous solution and the ferrous salt aqueous solution It is further preferable that the alkali equivalent ratio with respect to all Fe is the same.

PH in the growth reaction of the goethite layer
The value is between 8.0 and 11.0, preferably between 8.5 and 10.0.
Range. If the pH is less than 8.0, a large amount of acid radicals will be contained in the goethite particle powder and cannot be easily removed by washing. It will cause the result. If it exceeds 11.0, the desired high coercive force cannot be obtained when the metal magnetic particles are used.

The pH value of the reaction solution at the time of the formation reaction of the spindle-shaped goethite seed crystal particles and the pH value of the reaction solution at the time of the growth reaction of the goethite layer are the pH values of the respective reaction solutions.
The difference between the values is within a range of ± 0.5. The difference in pH value is ± 0.
If it exceeds 5, the coercive force of the metal magnetic particle powder is still insufficient. Preferably it is ± 0.3, more preferably ± 0.1.

The oxidizing means in the growth reaction of the goethite layer is performed by passing an oxygen-containing gas (for example, air) through the liquid.

The temperature for the growth reaction of the goethite layer may be generally at a temperature of 80 ° C. or less at which goethite particles are formed. When the temperature exceeds 80 ° C., magnetite may be mixed in the spindle-shaped goethite particles. Preferably it is in the range of 45 to 55 ° C.

In the growth reaction of the goethite layer, A
Examples of the compound include acid salts such as aluminum sulfate, aluminum chloride, and aluminum nitrate, and aluminates such as sodium aluminate, potassium aluminate, and ammonium aluminate. The addition time of the Al compound is determined by the ferrous salt aqueous solution added in the growth reaction,
Each alkali aqueous solution, an aqueous suspension containing spindle-shaped goethite seed crystal particles before passing oxygen-containing gas and a ferrous-containing precipitate, or an aqueous suspension during a growth reaction may be used. In particular, it is preferable before starting the growth reaction of the goethite layer. Further, the effects of the present invention are not changed even if the Al compound is dividedly added or added continuously or intermittently, but rather can be improved. In this case, the addition of the Al compound is performed in a state where no Co compound remains in the aqueous suspension. When the addition of the Al compound is performed in the presence of the Co compound, the axial ratio of the generated goethite particles is undesirably reduced.

The amount of the Al compound to be added is 0.5 to 0.5 with respect to the total Fe in the spindle-shaped goethite particles as the final product.
It is 15 atomic%, preferably 1.0 to 10 atomic%.
If it is less than 0.5 atomic%, there is no sintering prevention effect, and 1
If it exceeds 5 atomic%, the axial ratio decreases.

In the growth reaction of the goethite layer, as the compound of the rare earth element to be added, one or more compounds such as yttrium, lanthanum, cerium, prasedium, neodymium, and samarium are preferable. Chloride, sulfate, nitrate and the like can be used. The method of use may be either a dry method or a wet method, preferably a wet coating treatment. The addition of the rare earth element compound may be performed simultaneously or separately with the addition of the Al compound. The addition period is a ferrous salt aqueous solution to be added in the growth reaction, an aqueous alkali solution, an aqueous suspension containing spindle-shaped goethite seed crystal particles and a ferrous-containing precipitate before aeration with an oxygen-containing gas, or during the growth reaction. May be present in any of the aqueous suspensions. In particular, it is preferable before starting the growth reaction of the goethite layer. Further, the compound of the rare earth element may be dividedly added, or continuously and intermittently.

The amount of the rare earth element is 0.5 to 10 atomic%, preferably 1.0 to 8.0, based on the total amount of Fe.
Atomic%, more preferably 1.0 to 6.0 atomic%.
If the content is less than 0.5 at%, the effect of preventing sintering during subsequent heating and reduction during heating and heating is not sufficient, and the SFD (coercive force distribution) deteriorates when metal magnetic particles are used.
If it exceeds 10 atomic%, it is not preferable because it is not contained in the goethite surface layer portion but precipitates alone and causes dropout when formed into a sheet.

In the formation reaction of the spindle-shaped goethite seed crystal particles, it is preferable to perform so-called ripening, which is performed by maintaining and stirring the suspension containing the ferrous precipitate in a non-oxidizing atmosphere. In this case, the aging is preferably carried out in a temperature range of usually from 40 to 80 ° C. for the suspension under a non-oxidizing atmosphere. When the temperature is lower than 40 ° C., the axial ratio is small and it is difficult to obtain a sufficient aging effect. When the temperature is higher than 80 ° C., magnetite may be mixed. The aging time is 30 to 300 minutes. If the time is less than 30 minutes, the axial ratio cannot be sufficiently increased. 30
Although it may be longer than 0 minutes, there is no point in making the time longer than necessary. Ripening may also be performed during the growth reaction of the goethite layer.

To make the non-acidic atmosphere, an inert gas (such as nitrogen gas) or a reducing gas (such as hydrogen gas) may be passed through the reaction vessel of the suspension.

In the present invention, in order to improve various characteristics of the spindle-shaped metal magnetic particles containing iron as a main component, Mg usually added during the formation reaction of the spindle-shaped goethite particles is used.
The compound may be added during the seed crystal particle formation reaction or during the seed crystal particle growth reaction.

Next, the spindle-shaped hematite particles according to the present invention will be described.

The particles constituting the spindle-shaped hematite particles according to the present invention have an average major axis diameter of 0.05 to 1.0 μm,
Preferably it is 0.05 to 0.5 μm. The shape is a spindle shape and the axial ratio (major axis diameter / minor axis diameter) is 10 to 15, preferably 11 to 15.

The spindle-shaped hematite particles according to the present invention have a BET specific surface area of 30 to 140 m ² / g, preferably 35 to 100 m ² / g.

The particles constituting the spindle-shaped hematite particles according to the present invention are formed of a seed crystal part and a surface part. The seed portion is a portion in which the seed portion of the goethite particles is changed as it is, preferably 50 to 80% by weight, more preferably 5 to 80% by weight from the inner center of the seed particles.
5 to 75% by weight. The Co contained in the hematite seed particles in the seed portion is 0.5 to 25 atomic%, preferably 1.0 to 20 atomic%, based on the total Fe. If it is less than 0.5 atomic%, the effect of improving magnetic properties cannot be obtained.
If it exceeds 25 atomic%, a high axial ratio cannot be obtained.
The surface layer portion is a portion in which the surface layer portion of the goethite particles is changed as it is, and is preferably a portion of 20 to 50% by weight, more preferably 25 to 45% by weight from the outermost surface of the particles. Al contained in the hematite layer in the surface layer is 0.5 to 15 atomic%, preferably 1.0 to 10 atomic%, based on the total Fe. If it is less than 0.5 atomic%, no sintering preventing effect can be obtained. If it exceeds 15 atomic%, it is difficult to obtain a high axial ratio.

The content of the rare earth element in the particles constituting the spindle-shaped hematite particle powder according to the present invention is 0.5 to 15 atomic%, preferably 0.5 to 15 atomic%, based on the total Fe in the surface layer other than the seed crystal part or on the particle surface. 1.0 to 12 atomic%. If it is less than 0.5 atomic%, no sintering preventing effect can be obtained. Fifteen
If it exceeds atomic%, the saturation magnetization decreases. In the rare earth element content, the surface layer portion preferably has a content of 0.5 to 10 atomic%, more preferably 1.0 to 8 atomic%, and still more preferably 1.0 to 6 atomic% based on the total Fe.
It is. On the particle surface, the compound of the rare earth element is 0 to 14.5 atomic%, preferably 0 to 11 atomic%, based on the total Fe as a rare earth element.

The particles constituting the spindle-shaped hematite particles according to the present invention have a ratio D of X-ray crystal particle diameters D ₁₁₀ and D ₁₀₄ .
₁₀₄ / D ₁₁₀ is in the range of 0.20 to 0.65,
The following inequality for the content x (atomic%) with respect to the total Fe as the rare earth element preferably contained, 0.5 ≦ x ≦
In the case of 10, 0.500-0.03x ≦ D ₁₀₄ / D ₁₁₀ ≦ 0.665
In the case of −0.03 × 10 <x ≦ 15, it is within a range satisfying 0.20 ≦ D ₁₀₄ / D ₁₁₀ ≦ 0.365. This range is as shown in FIG. X-ray crystal grain size ratio D ₁₀₄
Regardless of whether / D ₁₁₀ is less than 0.20 or more than 0.65, the SFD (coercive force distribution) when the metal magnetic particle powder obtained by reducing this spindle-shaped hematite particle powder is formed into a sheet Worsens.

Next, a method for producing the spindle-shaped hematite particles according to the present invention will be described.

In the present invention, the surface of the obtained spindle-shaped goethite particles is coated with a sintering inhibitor to prevent sintering prior to the heating and dehydration treatment.

As the sintering inhibitor, it is preferable to use a compound of a rare earth element, an Al compound or a compound of an Al compound and a rare earth element, and a compound of another metal element can be used in combination.

As the compound of the rare earth element, one or more compounds such as scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, and samarium are preferable, and the rare earth element chloride, sulfate, nitrate, etc. Etc. can be used. The treatment method may be either a dry method or a wet method, preferably a wet coating treatment. When a compound of a rare earth element is used, the amount of the rare earth element is preferably 0.5 to 15.0 atoms based on the total Fe as the total of the rare earth element content contained in the goethite surface layer portion as the rare earth element. %, More preferably 1.0 to 12.0 atomic%. If the number is less than 0.5 atom, the effect of preventing sintering is not sufficient, and the SFD (coercive force distribution) deteriorates when the metal magnetic particles are used. 15.0
If it exceeds atomic%, the saturation magnetization value will be low.

Examples of the Al compound include acidic salts such as aluminum sulfate, aluminum chloride, and aluminum nitrate;
Aluminates such as sodium aluminate, potassium aluminate and ammonium aluminate can be used. The amount of the Al compound used is defined as the total amount of Fe and the total amount of Al contained in the surface layer of the spindle-shaped goethite particles.
Is preferably 0.5 to 15 atomic%, more preferably 1.0 to 10 atomic% in terms of Al. 0.5 atomic%
If it is less than 15%, there is no sintering prevention effect, and if it exceeds 15 atomic%, the magnetic properties of the metal magnetic particles become poor.

In order to improve the effect of preventing sintering, other elements such as Si, B, Ca, Mg, Ba,
One or more compounds of the element selected from Sr and the like may be used. These compounds not only have the effect of preventing sintering but also have the function of controlling the reduction rate, and thus may be used in combination as necessary. The total amount used in this case is preferably 1 as the total amount of the Al compound and the rare earth element compound used as the sintering inhibitor with respect to all Fe of the spindle-shaped goethite particles.
１５15 atomic%. If the amount is small, the effect of preventing sintering is not sufficient, and if the amount is too large, the saturation magnetization decreases when the metal magnetic particles are used. Therefore, the optimum amount may be appropriately selected depending on the type of combination.

By coating in advance with the sintering inhibitor or the like, sintering between the particles and the particles is prevented, and the spindle-shaped hematite particles which inherit and maintain the particle shape and the axial ratio of the spindle-shaped goethite particles more. A powder can be obtained, which makes it easier to obtain spindle-shaped metal magnetic particle powders that retain the above-mentioned shape and the like and are individually independent and mainly composed of iron.

The fusiform goethite particles coated with the sintering inhibitor are subjected to a 400-
Heat treatment is performed within the range of 850 ° C. to obtain spindle-shaped hematite particles. In this case, the temperature of the heat treatment is determined by the ratio D ₁₀₄ of the X-ray crystal grain size of the hematite particles.
/ D ₁₁₀ can be appropriately selected so as to be within a specific range.

Further, the hematite after the heat treatment may be washed to remove impurity salts such as Na ₂ SO ₄ .
In this case, it is preferable to remove unnecessary impurities by performing washing under conditions where the coated sintering inhibitor does not elute. Specifically, the pH can be increased to remove the cationic impurities, and the pH can be reduced to remove the anionic impurities, whereby the washing can be performed more efficiently.

Next, a method for producing the spindle-shaped metal magnetic particles containing iron as a main component according to the present invention will be described.

In the present invention, when the spindle-shaped goethite particles according to the present invention are previously subjected to a sintering prevention treatment with a sintering inhibitor and directly reduced by heating, the heating treatment is performed prior to the heating reduction. In this case, the spindle-shaped metal magnetic particle powder containing iron as a main component can be obtained by performing heat reduction after that, or by directly heating and reducing the spindle-shaped hematite particle powder according to the present invention.

Pre-coating with the sintering inhibitor or the like prevents sintering between the particles and between the particles, making it easier to maintain and inherit the particle shape and axis ratio of the spindle-shaped goethite particles. In addition, a spindle-shaped metal magnetic particle powder containing iron as a main component is easily obtained.

As well-known, as the sintering inhibitor, A
One or more compounds selected from the group consisting of l, Si, B, Ca, Mg, Ba, Sr and compounds of rare earth elements can be used. Preferably, it is a compound of a rare earth element and / or an Al compound. These compounds not only have the effect of preventing sintering but also have the function of controlling the reduction rate, and thus may be used in combination as necessary.

As the rare earth element compound, one or more compounds such as scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, and samarium, for example, chlorides, sulfates, and nitrates are preferable. The treatment method may be either a dry method or a wet method, but a wet coating treatment is preferable. When a compound of a rare earth element is used, the amount of the rare earth element is preferably 0.5 to 15 atm based on the total Fe as the total amount of the rare earth element and the rare earth element contained in the particles to be treated. %, More preferably 1.0 to 12.0 atomic%. If the number is less than 0.5 atom, the effect of preventing sintering is not sufficient, and the SFD (coercive force distribution) deteriorates when the metal magnetic particles are used. If it exceeds 15 atomic%, the saturation magnetization value will be low.

Examples of the Al compound include acidic salts such as aluminum sulfate, aluminum chloride, and aluminum nitrate.
Aluminates such as sodium aluminate, potassium aluminate and ammonium aluminate can be used. The amount of the Al compound used is defined as the total amount of Fe and the total amount of Al contained in the surface layer of the spindle-shaped goethite particles.
Is preferably 0.5 to 15 atomic%, more preferably 1.0 to 10 atomic% in terms of Al. 0.5 atomic%
If it is less than 15%, there is no sintering prevention effect, and if it exceeds 15 atomic%, the magnetic properties of the metal magnetic particles become poor.

The total amount of the sintering inhibitor used is preferably 1.0 to 15 atom as the total amount of the rare earth element compound and / or the Al compound with respect to the total Fe of the spindle-shaped goethite particles. %. If the amount is too small, the effect of preventing sintering is not sufficient, and if it is too large, the saturation magnetization decreases. Therefore, the optimum amount may be appropriately selected depending on the type of combination.

In order to improve the sintering prevention effect, other elements such as Si, B, Ca, Mg, Ba,
One or more compounds of the element selected from Sr and the like may be used. These compounds not only have the effect of preventing sintering but also have the function of controlling the reduction rate, and thus may be used in combination as necessary. The total amount used in this case is preferably 1 as the total amount of the Al compound and the rare earth element compound used as the sintering inhibitor with respect to all Fe of the spindle-shaped goethite particles.
１５15 atomic%. If the amount is small, the effect of preventing sintering is not sufficient, and if the amount is too large, the saturation magnetization decreases when the metal magnetic particles are used. Therefore, the optimum amount may be appropriately selected depending on the type of combination.

As described above, by coating in advance with a sintering inhibitor or the like, sintering between the particles and the particles is prevented, and the particle shape and axis ratio of the spindle-shaped goethite particles are further retained and inherited. Spindle-shaped metal magnetic particles containing iron as a main component, which are individually independent, are easily obtained.

The spindle-shaped goethite particle powder coated with the above compound can be directly reduced to obtain the desired spindle-shaped metal magnetic particle powder containing iron as a main component. In order to control the characteristics and control the shape, it is preferable to perform a heat treatment in a non-reducing gas atmosphere in advance by a conventional method before the reduction.

The non-reducing gas atmosphere may be one or more gas flows selected from air, oxygen gas, nitrogen gas and the like. Heat treatment temperature is 300 ~ 850 ℃
The heat treatment temperature is more preferably appropriately selected according to the type of the compound used for the coating treatment of the spindle-shaped goethite particles. When the temperature exceeds 850 ° C., deformation of the particles and sintering between the particles and the particles are caused.

In the heat reduction in the present invention, when the spindle-shaped goethite particle powder treated with the sintering inhibitor is directly subjected to heat reduction, the spindle-shaped goethite particle powder treated with the sintering inhibitor is heated beforehand. The heat reduction can be performed either continuously or when the spindle-shaped hematite particles according to the present invention are subjected to heat reduction.

The temperature range of the heat reduction in the present invention is 3
00-600 degreeC is preferable. When the temperature is lower than 300 ° C., the progress of the reduction reaction is slow and a long time is required. Also, 6
If the temperature exceeds 00 ° C., the reduction reaction proceeds rapidly, causing deformation of the particles and sintering between the particles.

The spindle-shaped metal magnetic particles containing iron as a main component after heat reduction according to the present invention can be obtained by a known method, for example, a method of immersing the particles in an organic solvent such as toluene, and a method of using a spindle containing iron as a main component after reduction. After the atmosphere of the metallic magnetic particles is once replaced with an inert gas, the oxygen content in the inert gas is gradually increased while the air is finally converted to air to be gradually oxidized to be taken out into the air. Can be.

Next, the spindle-shaped metal magnetic particles containing iron as a main component according to the present invention will be described.

The particles constituting the spindle-shaped metal magnetic particles containing iron as a main component according to the present invention have an average major axis diameter of 0.05.
０．５0.50 μm, preferably 0.06 to 0.3 μm. The shape is spindle shape and the axial ratio (major axis diameter / minor axis diameter)
Is 9 or more, preferably 9.5 or more.

The spindle-shaped metal magnetic particles mainly composed of iron according to the present invention have a BET specific surface area of 30 to 80 m ² /
g, preferably 35 to 60 m ² / g.

The particles constituting the spindle-shaped metal magnetic particles containing iron as a main component according to the present invention contain 0.5 to 25 atomic%, preferably 1.0 to 20 atomic% of Co with respect to the total Fe. I do. Al is contained in an amount of 0.5 to 15 atomic%, preferably 1.0 to 10 atomic%, based on the total amount of Fe. Further, the rare earth element is contained in an amount of 0.5 to 15 atomic%, preferably 1.0 to 12 atomic% based on the total Fe.

The spindle-shaped metal magnetic particles mainly composed of iron according to the present invention have a coercive force Hc of 1200 to 2200O.
e, preferably 1500 to 2000 Oe. Also,
Saturation magnetization σs is 100 emu / g or more, preferably 11
0 emu / g or more.

The spindle-shaped metal magnetic particles containing iron as a main component according to the present invention have a coercive force distribution SFD in sheet properties.
Is 0.50 or less, preferably 0.45 or less.

[0094]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention is as follows.

The average major axis diameter and the axial ratio of the particles constituting the particle powder were all represented by the average values of the numerical values measured from electron micrographs.

The specific surface area of the particle powder is “Monosorb MS”.
-11 "(manufactured by Cantachrome Co., Ltd.) and the value measured by the BET method.

X-ray crystal grain size (D in the case of hematite particles)
₁₀₄ or D ₁₁₀ , D of metal magnetic particles mainly composed of iron
₁₁₀ ) indicates the size of the crystal grains measured by the X-ray diffraction method, the (104) crystal plane in the case of hematite particles or (1).
10) Crystal plane, (11) of metal magnetic particles mainly composed of iron
0) It represents the thickness of a crystal grain in a direction perpendicular to each of the crystal planes, and is a value calculated from the diffraction peak curve of each crystal plane using the following Scherrer's formula. .

[0098] D ₁₀₄ or D ₁₁₀ = Kλ / βcosθ However, beta = half width (radians) K = Scherrer constant true diffraction peaks obtained by correcting the machine width due to device (= 0.9) λ = X-ray Wavelength (Fe Kα ray 0.1935 nm) θ = diffraction angle (corresponding to diffraction peaks on (104) plane and (110) plane)

The magnetic properties of the metal magnetic particles containing iron as a main component were measured using an “oscillating sample magnetometer VSM-3S-15” (manufactured by Toei Kogyo Co., Ltd.) under an external magnetic field of 10 kOe.

The amount of Co, the amount of Al, and the content of other metal elements in the spindle-shaped goethite particle powder and the spindle-shaped metal magnetic particle powder containing iron as a main component are determined by “Inductively Coupled Plasma Atomic Emission Spectrometer SPS4000” (Seiko Electronics Co., Ltd.). Industrial Co., Ltd.
Was used for the measurement.

A sheet-shaped sample piece contains the following components in an amount of 100 cc.
The magnetic paint prepared by putting the mixture in the following ratio in a polybin at the following ratio and mixing and dispersing for 8 hours with a paint shaker (manufactured by Red Devil Co., Ltd.) was applied to a polyethylene terephthalate film having a thickness of 25 μm using an applicator.
And then dried in a magnetic field of 5 kGauss. 3 mmφ steel ball 800 parts by weight Spindle-shaped metal magnetic particle powder mainly composed of iron 100 parts by weight Polyurethane resin having sodium sulfonate group 20 parts by weight Cyclohexanone 83.3 parts by weight Methyl ethyl ketone 83.3 parts by weight Toluene 83.3 parts by weight The magnetic properties of the obtained sheet-shaped sample piece were measured.

In a reactor under a non-oxidizing atmosphere by passing N ₂ gas, 3.7 l of a 6.5N Na ₂ CO ₃ aqueous solution was introduced.
32.0 L of a 0.374 N NaOH aqueous solution (NaOH corresponds to 33.3 mol% based on the mixed alkali.)
To form a mixed solution, and then Fe ²⁺ 1.5 mol /
13.3 l of an aqueous solution of ferrous sulfate containing 1 l (an alkali aqueous solution corresponds to 1.5 equivalents of ferrous sulfate), and the temperature is raised to 50 ° C. and maintained for 130 minutes. 311 g of cobalt sulfate (corresponding to 3.67 atomic% in terms of Co with respect to all Fe in the seed crystal particle formation reaction and growth reaction) was dissolved in 1 L of pure water and added thereto, followed by stirring and mixing. Further, after so-called ripening is performed for 180 minutes at a pH of 9.5 and in a non-oxidizing atmosphere, so-called ripening is performed. Generated.

A portion of the slurry containing the produced spindle-shaped goethite seed particles was extracted, filtered, washed with water and dried to obtain needle-like goethite seed particles having an average major axis diameter of 0.30 μm and an axis Ratio 13.3, BET specific surface area 80.2
The particles consisted of particles of m ² / g, without dendritic particles at all, and had a uniform particle size. Further, when the filtrate obtained by subjecting the extracted slurry to solid-liquid separation and the spindle-shaped goethite seed crystal particle powder were analyzed, no Co ion was detected in the filtrate. On the other hand, in the spindle-shaped goethite seed crystal powder, C is used as Co for all Fe in the seed crystal particles.
5.5 atomic% in terms of o (equivalent to 3.7 atomic% in terms of Co with respect to all Fe of the goethite particles after the growth reaction of the seed crystal particles), and the added Co ions 1
00% was adsorbed.

Next, 1.85 l of a 6.5N aqueous solution of Na ₂ CO ₃ was added to a suspension containing spindle-shaped goethite seed crystal particles in which a N ₂ gas was passed and the reactor was in a non-oxidizing atmosphere.
And 2.0 L of 3.0 N NaOH aqueous solution (NaOH corresponds to 33.3 mol% based on the mixed alkali) and 6.7 L of an aqueous ferrous sulfate solution containing 1.5 mol / L of Fe ²⁺ . (The aqueous alkali solution corresponds to 1.5 equivalents with respect to ferrous sulfate.), And the temperature is raised to 47 ° C. and maintained for 20 minutes, and the pH is increased to 9.5 (the pH during the formation reaction of goethite seed crystal particles). In the suspension (Al ₂ O ₃ content: 19% by weight).
403 g (corresponding to 5.0 atomic% in terms of Al with respect to all Fe) and 225 m of a 2.0 mol / l Nd nitrate solution
1 (corresponding to 1.5 atomic% in terms of Nd with respect to all Fe), followed by stirring and mixing.
, 150 l of air per minute was passed for 2.0 hours to carry out a growth reaction of the spindle-shaped goethite seed crystal particles.

After completion of the growth reaction, the acicular goethite particle powder obtained by filtration, washing, drying and pulverizing by a conventional method has a spindle shape, an average major axis diameter of 0.31 μm, and an axial ratio of 1
3.6, particles having a BET specific surface area of 102.0 m ² / g, dendritic particles were not mixed at all, and the particle size was uniform. Further, Co contained 3.6 atomic% in terms of Co with respect to all Fe, and 5.0 atomic% in terms of Al with respect to all Fe.

A press cake corresponding to 2500 g (25.1 mol as Fe) of a spindle-shaped goethite particle powder separated and washed with water was suspended in 40 l of water. At this time, the pH of the suspension was 7.9. Then, 2mol / l
125.5 ml of an aqueous solution of neodymium nitrate (1.0 atomic% as Nd based on the total Fe in the goethite particle powder)
Corresponds to. ) Was added and stirred for 10 minutes.

Then, while adjusting the pH to 9.5 by adding an aqueous sodium hydroxide solution, pure water was added, and the total amount was adjusted to 10%.
After stirring for 10 minutes as l, the mixture was separated by filtration with a filter press, washed with water, and dried to obtain goethite particle powder coated with an Nd compound. Co in the obtained goethite particle powder
Is 3.6 atomic% with respect to the total Fe, the Al content is 5.1 atomic% with respect to the total Fe, and the Nd content is
Was 2.5 atomic%.

800 g of the spindle-shaped goethite particles coated with the Nd compound was heated at 770 ° C. in air to obtain spindle-shaped hematite particles coated with the Nd compound. The obtained hematite particle powder had an average major axis diameter of 0.28 μm, an axial ratio of 12.8, and a BET specific surface area of 36.1.
m ² / g, X-ray crystal particle diameter D ₁₀₄ is 14.5 nm, D
₁₁₀ has a particle size of 26.8 nm and the ratio D ₁₀₄ / D ₁₁₀ is 0.54, and the content of Co in the particles is 3.6 atomic% with respect to the total Fe, and the content of Al is Is all F
The content of Nd was 5.1 at.% with respect to e, and the content of Nd was 2.5 at.

100 g of the spindle-shaped hematite particle powder coated with the Nd compound was put into a fixed bed reducing device having an inner diameter of 72 mm, and 35 l of H ₂ gas per minute were passed therethrough.
It was reduced by heating at 00 ° C.

The metal magnetic particle powder containing iron as a main component and containing Co, Al and Nd obtained by reduction is initially ventilated only with nitrogen so as not to cause rapid oxidation when taken out into the air. After that, a stable oxide film was formed on the surface while using a mixed gas of air and nitrogen and increasing the ratio of air with time. The obtained metal magnetic particle powder containing iron as a main component containing Co, Al and Nd has an average major axis diameter of 0.18 μm, an axial ratio of 10.8, a BET specific surface area of 40.2 m ² / g, and X-rays. D ₁₁₀ of grain size 1
It consisted of particles of 6.0 nm, had a spindle shape, a uniform particle size, and had few dendritic particles. Also, Co in the particles
Is 3.7 atomic% with respect to the total Fe, the Al content is 5.0 atomic% with respect to the total Fe, and the Nd content is
Was 2.5 atomic%. The magnetic properties of the metal magnetic particles are such that the coercive force Hc is as high as 1710 Oe, the saturation magnetization s is 154.3 emu / g, the squareness ratio (σr / σs) is 0.504, and the sheet property is , Sheet Hc is 1640 Oe, sheet squareness ratio (Br /
Bm) was 0.860 and SFD was 0.446.

[0111]

Conventionally, in order to improve the shape and the like of goethite particles as a starting material of metal magnetic particles containing iron as a main component, various metal salts have been added. Among them, it is known that Co forms a solid solution with iron when it is made into metal magnetic particle powder, has a function of increasing magnetization, and increasing its coercive force Hc. It is known that Al contributes to prevention of sintering when used as metal magnetic particles and is excellent in shape retention.

However, when Co is dissolved in the goethite particle formation reaction, fine particles are obtained and the axial ratio is appropriately large due to the small particle size in the minor axis direction. It is known that particles are obtained. On the other hand, it is difficult to obtain a material suitable for use because it is extremely finely divided. Also, it is known that Al has a crystal growth control effect and the axial ratio varies greatly depending on the timing and amount of addition. For example, if an Al compound is added during the production of goethite particles, the axial ratio is reduced. Is expected. The present inventor has found that when a reaction for forming goethite particles is performed in the presence of an Al compound in the presence of Co as a divalent ion, the axial ratio is most reduced.

The present inventor has conducted intensive studies, and as a result, separated the formation reaction of goethite particles into a seed crystal generation reaction and a growth reaction, and converted Co, which has an effect of appropriately improving the axial ratio, to the seed crystal particles. In the growth reaction performed by adding Co during the formation reaction to form a solid solution of Co in the goethite seed crystal particles, and further adding an aqueous ferrous salt solution and an aqueous mixed alkali solution, in a state where Co is not present in the solution, By adding Al having an effect of preventing sintering and allowing Al to exist only during the growth reaction,
It was found that particles having an axis ratio required for a seed crystal particle formation reaction were produced, and spindle-shaped goethite particles having a large seed crystal particle axis ratio and an appropriate particle shape could be obtained also in a growth reaction.

By using, as a starting material, powder composed of spindle-shaped goethite particles in which Co is dissolved in the seed crystal goethite particles and Al is dissolved in the surface goethite layer. Mainly iron, which has a uniform particle size, no dendritic particles are mixed, has an appropriate particle shape and a large axial ratio, and has a high coercive force and an excellent coercive force distribution. Spindle-shaped metal magnetic particle powder as a component can be obtained.

Further, as a result of various studies, the present inventors have found that the presence of a rare earth element compound together with an Al compound during the growth reaction of the spindle-shaped goethite seed crystal particles allows
Alternatively, further, by using a rare earth element compound as a sintering inhibitor to be processed into the goethite particle powder, by allowing the rare earth element to be present in the goethite surface layer portion other than the goethite seed crystal portion or the particle surface, the heating dehydration temperature can be reduced. The ratio D ₁₀₄ / D ₁₀₄ of the X-ray crystal grain diameter of the spindle-shaped hematite particles obtained by appropriate selection can be in a specific range, and iron obtained by heating and reducing this is the main component. It has been found that SFD (coercive force distribution), which is a sheet property of metal magnetic particle powder, can be improved, and the present invention has been completed.

[0116]

Next, examples and comparative examples will be described.

Examples 1 to 6 and Comparative Examples 1 and 2 <Production of Spindle-Shaped Goethite Particles> Examples 1 to 6 and Comparative Examples 1 and 2 Table 1 shows various properties of the goethite seed crystal particles that were extracted during the process. Further, spindle-like goethite particles were obtained in the same manner as in the embodiment of the present invention except that the conditions for the growth reaction of the goethite seed crystal particles were variously changed as shown in Table 3. Table 4 shows properties of the obtained spindle-shaped goethite particles.

Comparative Example 1 The procedure of Example 6 was repeated except that neodymium nitrate added during the reaction for forming goethite particles was added together with the cobalt compound during the reaction for forming goethite seed crystal particles. A production reaction was performed. In the obtained goethite seed crystal powder, foreign particles other than goethite particles were generated and mixed, and the shape of the goethite seed crystal particles could not be said to be spindle-shaped.

Comparative Example 2 The same procedure as in Example 1 was carried out except that neodymium nitrate added during the formation reaction of the goethite particles was added together with the aluminum compound during the growth reaction of the goethite seed crystal particles. A production reaction was performed. The obtained goethite particles had a mixture of spindle-shaped goethite particles as seed crystal particles and foreign particles, both of which were formed.

[0120]

[Table 1]

[0121]

[Table 2]

[0122]

[Table 3]

[0123]

[Table 4]

<Production of Spindle-Shaped Hematite Particle Powder> Examples 1 to 6 The type of spindle-shaped goethite particle powder as a precursor, the type and amount of coating used for sintering prevention treatment, heating dehydration temperature, and subsequent heating Other than changing the processing temperature variously,
Spindle-shaped hematite particle powder was obtained in the same manner as in the embodiment. Table 5 shows the conditions and various characteristics of the obtained spindle-shaped hematite particles.

In the rare earth elements contained in the spindle-shaped hematite particles obtained in the above embodiment, examples and comparative examples, the ratio of the content x (atomic%) to the total Fe with respect to the total Fe and the X-ray crystal grain size D ₁₀₄ / the relationship between D ₁₁₀ in ○ the embodiments and examples of the embodiment, shown in FIG. 1 Comparative example ●. Here, the straight line A is expressed as D ₁₀₄ / D ₁₁₀ = 0.5 ≦ x ≦ 10.
0.500−0.03 × x, and the straight line A ′ is 10 <
D ₁₀₄ / D ₁₁₀ = 0.20 when x ≦ 15. The straight line B is expressed as D ₁₀₄ / D ₁₁₀ = 0.5 ≦ x ≦ 10.
0.665−0.03 × x, and the straight line B ′ is 10 <
D ₁₀₄ / D ₁₁₀ = 0.365 when x ≦ 15.
X-ray values of the ratio D ₁₀₄ / D ₁₁₀ of the crystal grain size of the particles constituting the spindle-shaped hematite particles according to the present invention, 0.20
0.65, and preferably within the range of line A in FIG.
Straight line B, straight line A ', straight line B', x = 0.5 and x = 10
Within the range surrounded by.

[0126]

[Table 5]

<Production of Metal Magnetic Particle Powder Containing Iron as Main Component> Examples 1-3, 5-6 Types of particles to be treated, type and amount of coating used for sintering prevention treatment, heating temperature, heating Metal magnetic particle powder containing iron as a main component was obtained in the same manner as in the embodiment of the present invention except that the reduction temperature in the reduction step was variously changed. Table 6 shows the reducing conditions at this time and various properties of the obtained metal magnetic particle powder containing iron as a main component.

Example 4 In the heat reduction, 200 g of the hematite particle powder was washed with 2 l of pure water, molded using a molded plate having an inner diameter of 4 mm, and dried to be used for the heat reduction. Metal magnetic particle powder containing iron as a main component was obtained in the same manner as in the embodiment of the present invention. Table 6 shows the reducing conditions at this time and various properties of the obtained metal magnetic particle powder containing iron as a main component.

[0129]

[Table 6]

[0130]

The spindle-shaped goethite particle powder and spindle-shaped hematite particle powder according to the present invention have a uniform particle size, do not contain dendritic particles, and have an appropriate particle shape and axis ratio. Since the spindle-shaped goethite particle powder or the spindle-shaped hematite particle powder obtained from the starting particles, the spindle-shaped metal magnetic particle powder containing iron as a main component obtained as a starting material has a particle size as described in the above Examples. Since it is uniform and contains no dendritic particles, and is composed of particles having an appropriate particle shape and axial ratio, it has a high coercive force and an excellent coercive force distribution, Recording density, high sensitivity,
It is suitable as a high-output magnetic particle powder.

[Brief description of the drawings]

FIG. 1 shows the total Fe as a rare earth element contained in spindle-shaped hematite particles according to the embodiment, examples and comparative examples of the present invention.
Ratio between the content (atomic%) and the X-ray crystal grain size with respect to D ₁₀₄ /
Shows the relationship between the D _110.

Claims (8)

[Claims] 1. Spindle-shaped particles having an average major axis diameter of 0.05 to 1.0 μm, comprising a goethite seed crystal portion and a goethite surface layer portion, wherein the seed crystal portion contains Co with respect to all Fe. 0.5 to 25 atomic%, and the surface layer contains 0.5 to 15 atomic% of Al with respect to all Fe and a rare earth element of 0.5 to 10 atomic% with respect to all Fe.
Spindle-shaped goethite particle powder, comprising goethite particles. 2. Spindle-shaped particles having an average major axis diameter of 0.05 to 1.0 μm, comprising a hematite seed crystal part and a hematite surface layer part, wherein the seed crystal part contains Co with respect to all Fe. 0.5 to 25 atomic%, and the surface layer portion contains Al
0.5 to 15 atomic% with respect to the total Fe, and 0.5 to 15 atomic% of the rare earth element with respect to the total Fe in the surface layer portion or the particle surface other than the seed crystal portion, Moreover, the ratio D ₁₀₄ / D ₁₁₀ of the X-ray crystal grain size from 0.20 to 0.
65. Spindle-shaped hematite particle powder comprising hematite particles in the range of 65. 3. An aqueous suspension containing a ferrous-containing precipitate obtained by reacting a mixed alkali aqueous solution of an aqueous alkali carbonate solution and an aqueous alkali hydroxide solution with an aqueous ferrous salt solution under a non-oxidizing atmosphere. After aging, an oxygen-containing gas is passed through the aqueous suspension to generate spindle-shaped goethite seed crystal particles. Then, the aqueous suspension containing the seed crystal particles contains alkali carbonate and alkali hydroxide. The aqueous alkali solution and the ferrous salt aqueous solution are newly added and mixed with each other, and an oxygen-containing gas is ventilated to grow a goethite layer on the surface of the spindle-shaped goethite seed crystal particles. In producing the seed crystal particles, a ferrous salt aqueous solution, an aqueous suspension containing a ferrous-containing precipitate, and a ferrous-containing precipitate during ripening before the start of the oxidation reaction are included. During aqueous suspension or formation reaction To the aqueous suspension, a Co compound of 0.5 to 25 atomic% in terms of Co with respect to the total Fe is added, and at the time of the growth reaction of the goethite layer, each alkali aqueous solution and ferrous salt aqueous solution to be added are added. A water suspension containing spindle-shaped goethite seed crystal particles and a ferrous-containing precipitate before the start of the oxidation reaction or a water suspension during the growth reaction was mixed with Al for all Fe.
2. The spindle-shape according to claim 1, wherein the Al compound and the rare earth element are added in an amount of 0.5 to 15 at.% In terms of the total Fe, and the compound of the rare earth element is added in an amount of 0.5 to 10 at. Method for producing goethite particle powder. 4. The spindle-shaped hematite according to claim 2, wherein the spindle-shaped goethite particle powder according to claim 1 is treated with a sintering inhibitor, and then heat-treated at a temperature of 400 to 850 ° C. Manufacturing method of particle powder. 5. The method for producing spindle-shaped hematite particle powder according to claim 4, wherein the sintering inhibitor is any of an Al compound, a compound of a rare earth element, or a compound of an Al compound and a rare earth element. 6. After treating the spindle-shaped goethite particles according to claim 1 with a sintering inhibitor, heat treatment is performed at a temperature in the range of 400 to 850 ° C., and further, 400 to 850 ° C. in a reducing gas atmosphere. A process for producing spindle-shaped metal magnetic particles containing iron as a main component, wherein the powder is heated and reduced within a range of 600 ° C. 7. A spindle-shaped metal magnetic particle powder containing iron as a main component, wherein the spindle-shaped hematite particle powder according to claim 2 is heat-reduced in a reducing gas atmosphere at a temperature of 400 to 600 ° C. Manufacturing method. 8. An average major axis diameter obtained by the production method according to claim 6 or the production method according to claim 7, which is 0.05 to 0.5.
μm spindle-shaped particles, wherein Co is added to the total Fe in an amount of 0.
5 to 25 atomic%, and Al is 0.5 to
A spindle comprising iron as a main component, comprising metal magnetic particles containing 15 atomic% and containing a rare earth element in an amount of 0.5 to 15 atomic% with respect to the total Fe; Metal magnetic particles powder.