JPS62128931A - Production of magnetic iron oxide grain powder having spindle type - Google Patents

Abstract

PURPOSE:To produce spindle-type magnetite grain or maghemite grain by adding citric acid (citrate) in a midway process in case of producing magnetite or the like by forming an FeCO3-contg. liquid in the reaction of a ferrous salt aq. soln. and alkali carbonate and oxidizing it with O2 and thereafter reducing it. CONSTITUTION:An FeCO3-contg. aq. soln. is formed by allowing an alkali carbonate aq. soln. such as Na2CO3 and (NH4)2CO3 in the proportion of >=1.8 equivalent expressed in terms of CO3 for Fe contained in a ferrous salt aq. soln. such as FeCl2 and FeSO4 to react with this aq. soln. and it is oxidized by blowing air or oxygen, etc., therein. In this case, 0.1-1.5mol% citric acid (citrate) for contained Fe is previously added to the above-mentioned aq. solns. of ferrous salt and alkali carbonate or FeCO3 and the mixture is oxidized. After forming spindle type hematite grain by oxidation of an FeCO3-contg. soln., it is reduced by reducing gas to obtain magnetite grain or furthermore oxidized to form spindle type maghemite grain and thereby magnetic iron oxide grain powder for magnetic recording is produced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing magnetic iron oxide particles for magnetic recording, which have substantially no pores on the particle surface or inside the particles. Magnetic iron oxide consisting of magnetite particles or maghemite particles that have a high density, are uniform in particle size, do not contain dendritic particles, and have a spindle shape with a small axis ratio (major axis: short axis). The purpose is to provide particulate powder.

[Prior art]

2. Description of the Related Art In recent years, as magnetic recording and reproducing equipment has become longer recording time and has become smaller and lighter, there has been an increasing need for higher performance recording media such as magnetic tapes and magnetic disks.

That is, high recording density, high sensitivity characteristics, high output characteristics, low noise characteristics, etc. are required.

In order to satisfy the above requirements for magnetic recording media, magnetic particles must have excellent dispersibility, high coercive force, and a small axial ratio (long axis: short axis). It is.

This fact can be seen, for example, in the book published by Sogo Gijutsu Center Co., Ltd.
"Development of magnetic materials and high dispersion technology of magnetic particles" (1982)
``The conditions for high-density recording in coated tapes are to be able to maintain high output characteristics with low noise for short wavelength signals, but in order to do so, the coercive force lie
It is necessary that both the residual magnetization Br and the residual magnetization Br be large, and that the thickness of the coating film be thinner.

” and Japanese Patent Application Laid-Open No. 57483626 “Also, in recent years, the idea of perpendicular magnetization recording has been introduced, and there is also a proposal to effectively use the residual magnetization component in the direction perpendicular to the surface of the magnetic recording medium. According to the above definition, the recording density increases, and the particle size is made short with a longitudinal/axial ratio of more than 1 and less than 3. Due to this, the tendency of particles to lie in-plane and align, such as in-plane orientation due to thinning of the coating film in the thickness direction during application and drying, and orientation in the casting direction due to flow during application. It is characterized by suppressing the vertical residual magnetization, and actively increasing the vertical residual magnetization if necessary.''

In addition, the residual magnetization Br of a magnetic recording medium depends on the dispersibility of the magnetic particles in the vehicle, the orientation and filling properties in the coating film, and in order to improve these characteristics, it is necessary to The magnetic particles to be dispersed in the powder have substantially high density with no pores on the particle surface or inside the particles, have uniform particle sizes, are free from dendritic particles, and have a high density of particles. In terms of shape, spindle-shaped particles are required.

As is well known, the magnitude of the coercive force of magnetic particles depends on shape anisotropy, crystal anisotropy, strain anisotropy, exchange anisotropy, or their interaction. the current,
The acicular magnetophyte particles or the acicular maghemite particles used as magnetic particles for magnetic recording use the anisotropy derived from their shape, that is, the axial ratio (long axis: short axis). A relatively high coercive force is obtained by increasing the size of the shaft.

In this way, known acicular magnetite particles or acicular maghemite particles utilize their shape anisotropy to obtain a relatively high coercive force, but it is possible to add Co to these particles. It is generally known that the coercive force can be further improved by utilizing the crystal anisotropy.

These known acicular magnetite particle powders or maghemite particle powders generally contain ferrous hydroxide particles obtained by reacting an aqueous ferrous salt solution with an alkali.
Air oxidation of an aqueous solution of n or more colloids is usually called a "wet reaction."

) The acicular goethite particles obtained are heated and dehydrated in air at around 300°C to form hematite particles, and further reduced at 300 to 400°C in a reducing gas such as hydrogen to form acicular maghatite particles. , or then this in air at 200
It is obtained by oxidation at ~300'C to form acicular maghemite particles.

[Problem that the invention seeks to solve]

There are no pores on the particle surface or inside the particle, and the particle size is substantially high, the particle size is uniform, there are no resinous particles, and the axial ratio (major axis: short axis) There is currently a demand for magnetic iron oxide particles with a small spindle shape, and in order to obtain magnetic particles with such characteristics, it is necessary that the starting material particles themselves In addition, there are no pores inside the particles and the particles are substantially dense, the particle size is uniform, there are no dendritic particles mixed, and the axial ratio (long axis: short axis) is small. It is necessary that the particles exhibit a spindle shape, but the particle powder obtained by the above-mentioned known method for producing acicular goethite particles as a starting material has an axial ratio (long axis: short axis) of 10. :1
These particles have the above-mentioned acicular shape, contain dendritic particles, and in terms of particle size, it is difficult to say that the particles have a uniform particle size.

On the other hand, as a method for producing goethite particles,
There is a method described in Japanese Patent No. 80999. That is, JP-A-5
The method described in Japanese Patent No. 0-80999 is a method of oxidizing an aqueous solution containing FeCO3 obtained by reacting a ferrous salt solution with an alkali carbonate by passing an oxygen-containing gas through it.

When this method is used, goethite particles with uniform particle size, no dendritic particles mixed therein, and a spindle shape are obtained.

However, the above-mentioned known method or the above-mentioned JP-A-50-80
When magnetic iron oxide particles are obtained by a conventional method using the acicular goethite particles obtained by the method described in Japanese Patent No. 999 as a starting material, the hematite particles obtained by heating and dehydrating the goethite particles become particles by dehydration. Magnetite particles or maghemite particles obtained by producing a large number of pores on the surface and inside the particles, and then reducing the hematite particles or further oxidizing them if necessary, also have a large number of pores distributed on the particle surface and inside the particles. It is observed that what is happening.

As described above, magnetic iron oxide particles having a large number of pores on the particle surface and inside the particles have a low coercive force 11c and have poor dispersion in a vehicle.

This fact can be seen, for example, in Japanese Patent Application Laid-Open No. 55-47227: For this purpose, the manufactured γ
-Fe, 0. is its low salt content iron oxyhydroxide (α, β
, γ-FeOOH), it is necessary to maintain the acicular form and eliminate the dehydration pores (vacancies). These dehydration pores (vacancies) are generated during dehydration of low-salt iron oxyhydroxide, and these are the product γ-Pet (h
If it remains in the particles, it reduces the coercive force. ” and Electrochemistry and Industrial Physical Chemistry Vol. 38 No. 7 (1
970), page 544, ``...Although various dispersion techniques in vehicles have been considered, the dispersion in the manufactured r-Fez03 tape is still poor.
・r-Pe, 03 has holes (holes) as shown in Figure 17, and a magnetic pole appears on the edge of the hole and a Lorentz magnetic field is generated, so the needles that were initially well dispersed during ball milling are attracted. This is clear from the description "..." which lowers the magnetostatic energy and forms a chestnut burr-shaped agglomerate.

As mentioned above, magnetic iron oxide particles suitable for high-density recording are required to have a small axial ratio (long axis: short axis); Magnetic iron oxide particles with a small particle size cannot utilize the anisotropy derived from the shape, so only coercive force lie of less than 2000e can be obtained. It is particularly strongly desired to improve the coercive force as much as possible by eliminating this.

Attempts have been made to eliminate pores generated on the surface and inside of magnetic iron oxide particles. For example, in Japanese Patent Publication No. 38-26156, there is a method for reducing the composition to magnetite at a low temperature and then changing its composition. In order to prevent
A method of annealing at temperatures below 0° C. is described.

In addition, the Powder and Powder Metallurgy Association 1960 Spring Conference Lecture Abstracts 2-6 states that as the dehydration temperature of acicular goethite increases, the pores on the surface of the acicular hematite particles and inside the particles increase. Although it will be less, this dehydration temperature is 700
It has been reported that when the temperature rises above °C, the pores disappear, but sintering progresses and the acicular crystal grains collapse.

In both of the above methods, it is necessary to heat the particles at high temperatures in order to eliminate pores generated on the surface and inside the particles.As a result, sintering occurs between the particles and between the particles, which is reduced and oxidized. The coercive force of the magnetic iron oxide particles thus obtained is extremely low, and the dispersibility into a vehicle when producing a magnetic paint is also poor.

On the other hand, instead of the method of eliminating the pores once generated on the particle surface and inside of the magnetic iron oxide particles, a method of obtaining magnetic iron oxide particles using particles without pores on the particle surface and inside the particles as a starting material has also been attempted. ing.

This method produces maquito particles directly into needle-like crystals from an aqueous solution, and then reduces and oxidizes the maquito particles as a starting material to form needle-like crystals.

This is a method for obtaining iron oxide particles.

That is, as mentioned above, the pores on the particle surface and inside the particles are generated by dehydration when acicular goethite particles are heated and dehydrated to convert them into acicular crystals into maquito particles.
If maquito particles are produced directly into needle-like crystals from an aqueous solution, the dehydration step can be omitted, and therefore maquito particles can be obtained into needle-like crystals with no pores on the particle surface or inside the particles. The acicular magnetic iron oxide particles obtained by reducing and oxidizing the hematite particles as a starting material also have no pores on the particle surface or inside the particle.

As a method for producing maquito particles directly into needle crystals from an aqueous solution, there is, for example, the method described in Japanese Patent Publication No. 55-22416. Uchi, the method described in Japanese Patent Publication No. 55-22416 is a method in which an aqueous slurry in which three components coexist: ferric hydroxide, citric acid or/and its salt, and an alkali compound is heated, and the amount of the alkali compound is reduced. The pi of the three-component coexisting aqueous slurry at 25°C is 10~
13, and the heat treatment temperature is 100~
Acicular hematite particles are obtained by heating the temperature to 250°C.

However, this method requires a high temperature of 100° C. or higher and requires a special device called an autoclave, which is not industrially or economically viable.

As a method for producing hematite particles from an aqueous solution at a temperature of 100° C. or lower, there is a method described in JP-A-51-8193. That is, the method described in JP-A-51-8193 involves adding alkali hydrogen carbonate alone to a ferrous salt solution, or adding alkali hydrogen carbonate and alkali carbonate,
The oxidation reaction is carried out at a pH of 7 to 11 and a temperature of 65°C to 100°C.

In the case of this method, the shape of the hematite particles produced is spherical, and other types of particles other than hematite particles are produced and mixed.

As is clear from the above, there are no pores on the particle surface or inside the particle, and the particle has a substantially high density,
In addition, there is a strong desire to establish a method for producing magnetic iron oxide particle powder that has uniform particles, does not contain dendritic particles, and has a spindle shape with a small axis ratio (long axis: short axis). .

[Means for solving problems]

The present inventor has discovered that the particles have no pores on the surface or inside the particles, have a high density in terms of real π, have uniform particle sizes, are free from dendritic particles, and have an axial ratio (length). Axis: short axis)
As a result of various studies in order to obtain magnetic iron oxide particle powder exhibiting a small spindle shape, we found that a ferrous salt aqueous solution and a ratio of 1.8 equivalents or more to Fe in the ferrous salt aqueous solution in terms of CO2 were obtained. FeCO obtained by reacting with an aqueous alkali carbonate solution
When oxidizing the aqueous solution containing FeCO3 by passing an oxygen-containing gas through the aqueous solution containing FeCO3, any one of the ferrous salt aqueous solution, the alkali carbonate aqueous solution, and the aqueous solution containing FeCO3 before being oxidized by passing an oxygen-containing gas through the aqueous solution. When citric acid or its salt is added in an amount of 0.1-1.5 mol% based on re, the particle size of the starting material is uniform, dendritic particles are not mixed, and the axial ratio (length The present invention was completed based on the novel finding that spindle-shaped hematite particles with small axis (minor axis) can be directly produced from an aqueous solution at 100° C. or lower.

That is, the present invention provides an aqueous solution containing FeCO3 obtained by reacting a ferrous salt aqueous solution with an alkali carbonate aqueous solution having a ratio of 1.8 equivalents or more in terms of CO1 to Fe in the ferrous salt aqueous solution. When oxygen-containing gas is aerated and oxidized,
The FeC before being oxidized by passing the ferrous salt aqueous solution, the alkali carbonate aqueous solution, and the oxygen-containing gas in advance.
0.1 for Fe in any of the aqueous solutions containing 0*
~1.5 mol% of citric acid or its salt is added and then oxidized by passing oxygen-containing gas to produce spindle-shaped hematite particles from an aqueous solution, and the spindle-shaped hematite particles are produced. consisting of spindle-shaped magnetic iron oxide particles obtained by heating and reducing in a reducing gas to produce spindle-shaped magnetite particles, or further oxidizing to produce spindle-shaped maghemite particles. A method for producing magnetic iron oxide particles, and a method for producing magnetic iron oxide particles obtained by reacting an aqueous ferrous salt solution with an aqueous alkali carbonate solution having a ratio of 1.8 equivalents or more in terms of COi to Fe in the aqueous ferrous salt solution. Fe
When the aqueous solution containing CO5 is oxidized by passing an oxygen-containing gas through it, any one of the ferrous salt aqueous solution, the alkali carbonate aqueous solution, and the aqueous solution containing FeCO3 before being oxidized by passing the oxygen-containing gas through the aqueous solution. Inside, Fe
0.1 to 1.5 mol% of citric acid or its salt and 0.5 to 10.0 atomic% of water-soluble cobalt salt in terms of Co are added to Fe, and then oxygen-containing gas is bubbled through. Co-containing spindle-shaped hematite particles are generated from an aqueous solution by oxidation, and the Co-containing spindle-shaped hematite particles are heated and reduced in a reducing gas to form spindle-shaped Co-containing hematite particles. A method for producing magnetic iron oxide particle powder consisting of spindle-shaped magnetic iron oxide particles by further oxidizing to obtain spindle-shaped maghemite particles containing Co. It is.

C action] First of all, the most important point in the present invention is that the particles have substantially high density with no pores on the surface or inside the particles, have a uniform particle size, and have dendritic particles mixed therein. Not yet,
Moreover, in producing spindle-shaped magnetic iron oxide particles with a small axis ratio (major axis: minor axis), the starting material is essentially high-density, with no pores on the particle surface or inside the particles. A hematite particle powder is used, which has a uniform particle size, does not contain dendritic particles, and has a spindle shape with a small axis ratio (long axis: short axis). Point 2.

In the present invention, one spindle-shaped hematite particle is
By directly generating hematite particles from an aqueous solution at temperatures below 00°C, we obtain hematite particles with no pores on the particle surface or inside the particles, and no special equipment such as an "autoclave" is required for production. .

Further, in the present invention, only spindle-shaped hematite particles can be produced from an aqueous solution at 100° C. or lower.

In the present invention, it is not yet clear why only spindle-shaped hematite particles with a small axial ratio can be produced, but the present inventor has developed a ferrous salt aqueous solution and a ferrous salt aqueous solution. 1.0% in terms of CO3 for Fe inside.
When citric acid or its salt is added under conditions of 8 equivalents or less, granular magnetite particles are mixed in the spindle-shaped hematite particles, so it is due to the synergistic effect of alkali carbonate and citric acid or its salt. I think of it as something.

In the present invention, magnetic iron oxide particles having a higher coercive force are produced by adding a water-soluble cobalt salt in the reaction for producing spindle-shaped hematite particles, thereby producing spindle-shaped hematite particles containing Co. and reducing the Co-containing spindle-shaped hematite particles or, if necessary, further oxidizing them to obtain Co-containing spindle-shaped magnetic iron oxide particles,
The obtained spindle-shaped magnetic iron oxide particles containing Co are not only equilateral in shape but also magnetically equilateral, and are suitable as magnetic iron oxide particles for magnetic recording.

Next, various conditions for implementing the present invention will be described.

Examples of the ferrous salt aqueous solution used in the present invention include a ferrous sulfate aqueous solution and a ferrous chloride aqueous solution.

As the alkali carbonate used in the present invention, sodium carbonate, potassium carbonate, ammonium carbonate, etc. can be used alone or in combination.

The ferrous salt aqueous solution and the alkali carbonate may be added either first or simultaneously.

The reaction temperature in the present invention is 70 to 100°C.

If the temperature is 70° C. or lower, goethite particles will be mixed in the hematite particles. Although the object of the present invention can be achieved when the temperature is 100° C. or higher, it requires special equipment such as an autoclave, which is not economical.

The amount of alkali carbonate used in the present invention is 1.8 equivalents or more based on CO + N'l relative to Fe. If the amount is 1.8 equivalents or less, granular magnetite particles will be mixed in the spindle-shaped hematite particles.

In the present invention, citric acid or a salt thereof can be used. Here, the salt includes sodium citrate, potassium citrate, lithium citrate, ammonium citrate, and the like.

The amount of citric acid or its salt added in the present invention is 0.1 to 1.5 mol% based on Fe. When the content is 0.1 mol% or less, spindle-shaped goethite particles and granular hematite particles coexist. If the content is 1.5 mol% or more, fine amorphous particles will be produced. Considering the particle morphology of the produced hematite particles, 0.1 to 1.0 mol% is preferable.

The citric acid or its salt in the present invention affects the type and form of the generated particles through a synergistic effect with the alkali carbonate, and therefore, before the reaction for producing spindle-shaped hematite particles starts. It can be added to either a ferrous salt aqueous solution, an aqueous alkali carbonate solution, or an aqueous solution containing FeC0+ before being oxidized by aerating an oxygen-containing gas.

As the water-soluble cobalt salt in the present invention, cobalt sulfate, cobalt chloride, etc. can be used.

The amount of water-soluble cobalt salt added is 0.5 to 1000 atomic % based on Co in terms of Pe.

If the amount is 0.5 at % or less, the effect of improving the coercive force of the resulting spindle-shaped magnetite particles or maghemite particles cannot be sufficiently achieved.

If the content is 10.0 at % or more, the temperature stability of the resulting spindle-shaped magnetite particles or maghemite particles will deteriorate.

The water-soluble cobalt salt in the present invention needs to be contained in the spindle-shaped hematite particles to be produced, and therefore, it is added before the production reaction of the spindle-shaped hematite particles is started. It can be added to either a ferrous salt aqueous solution, an aqueous alkali carbonate solution, or an aqueous solution containing FeC0 before being oxidized by bubbling oxygen-containing gas.

Furthermore, in the present invention, it is possible to add metals other than Pe, such as Hg, AI, Cr, Zn, and Ni, which are conventionally added during the production of starting material particles to improve various properties of magnetic iron oxide particles. can.

The heating reduction treatment and oxidation treatment in a reducing gas in the present invention can be performed by conventional methods.

In addition, the hematite particles, which are the starting material, are treated in advance with a substance that has a sintering prevention effect, such as Si, AI, or P compounds, which is usually carried out prior to heat treatment, to form spindle-shaped particles with better dispersibility. It is possible to obtain magnetic iron oxide particles exhibiting the following properties.

(Example〕 Next, the present invention will be explained with reference to Examples and Comparative Examples.

In addition, the axial ratio (long axis: short axis) and long axis of the particles in the following Examples and Comparative Examples are both shown as average values of numerical values measured from electron micrographs.

The magnetic properties of magnetic iron oxide particles can be measured using a vibrating sample magnetometer V.
Using the SM P-1 type (manufactured by Toei Kogyo), the measurement magnetic field 5
Measured in KOe.

Generation of spindle-shaped hematite particles Example 1
~14, Comparative Examples 1 to 3; Example I 1.5 mo1 of ferrous sulfate obtained by adding 3.3 g of sodium citrate to contain 0.5 mol% based on Fe
/II aqueous solution 1.5 ff, 1.54 mol/1 NazCO1 aqueous solution 3. In addition to O2 (COs/Fe =
This corresponds to 2.0 equivalent.

), PeC0z was generated at a temperature of 80°C.

Particles were generated by blowing 2M air per minute into the aqueous solution containing FeCO3 at a temperature of 80° C. for 4.5 hours.

The end point of the oxidation reaction was determined by extracting a portion of the reaction solution, adjusting it to acidity with hydrochloric acid, and then using a red blood salt solution to determine the presence or absence of a blue coloring reaction of Fe''.

The generated particles were separated in a furnace, washed with water, dried, and pulverized using a conventional method.

This particle powder is shown in the electron micrograph (X20.
000), the average value of the major axis is 0.25 μm
Consists of spindle-shaped particles with a uniaxial ratio (major axis: short axis) of 3.5:l, there are no pores on the particle surface or inside the particles, the particle size is uniform, and dendritic particles are not mixed. It was something.

Moreover, the X-ray diffraction diagram of this particle is shown in FIG. As is clear from FIG. 2, peak A is a peak indicating hematite, and it can be seen that it consists only of hematite.

Examples 2 to 14 Varying the type of ferrous salt, the type, concentration, and equivalence ratio of alkali carbonate, the type, amount, and timing of addition of citric acid or its salt, and the type, amount, and timing, and temperature of metal ion. Particles exhibiting a spindle shape were produced in the same manner as in Example 1 except that the particles were changed.

As a result of X-ray diffraction, it was confirmed that all the particles obtained in Examples 2 to 14 were only hematite particles.

Table 1 shows the main manufacturing conditions and characteristics of the produced hematite particles.

Electron micrograph of spindle-shaped hematite particles containing Co obtained in Example 11 (X 20.000
) is shown in FIG. 3, and the X-ray diffraction diagram is shown in FIG.

Comparative Example 1 1, I2mol/jl NazCO3 aqueous solution 3.0I
Particles were produced in the same manner as in Example 1, except that 1 (corresponding to COs/Fe 2 =1.4 equivalent) was used.

The generated particles were separated in a furnace, washed with water, dried, and pulverized using a conventional method.

This particle powder is shown in the electron ra micrograph (X 2
0.000), granular particles were mixed in the spindle-shaped particles. Moreover, the results of X-ray diffraction showed peaks of hematite and magnetite.

Comparative Example 2 Sodium citrate 13.2 g (2.0 g for Fe
Corresponds to mole%. ) Particles were produced in the same manner as in Example 1, except that .

The generated particles were separated in a furnace, washed with water, dried, and pulverized using a conventional method.

This particle powder is shown in the electron R micrograph (x20,
000), they were fine amorphous particles.

Comparative Example 3 Particles were produced in the same manner as in Example 1 except that the temperature was 65°C.

The generated particles were separated in a furnace, washed with water, dried, and pulverized using a conventional method.

As is clear from the X-ray diffraction diagram shown in FIG. 7, this particle powder was a mixture of hematite particles and goethite particles.

In Figure 7, peak A indicates hematite, peak B
is a peak indicating goethite.

(Production of spindle-shaped magnetite particle powder) Examples 15 to 29; Example 15 80 g of the spindle-shaped hematite particle powder obtained in Example 1 was put into a retort reduction container No. 11, and the drive rotation Hz gas was vented at a rate of 0.2ff per minute,
A spindle-shaped magnetite particle powder was obtained by reduction at a reduction temperature of 330°C.

As a result of electron W microscopic observation, the obtained spindle-shaped magnetite particles were found to have substantially no pores on the particle surface or inside the particles, to have substantially high density, and to have a uniform particle size. No dendritic particles mixed, average long axis 0.23
μm, and the axial ratio (long axis: short axis) was 3:1.

Further, as a result of magnetic measurement, the coercive force 11c was 2720e, and the saturation magnetization σS was 81.3 emu7g.

Examples 16 to 29 Spindle-shaped magnetite particles were obtained in the same manner as in Example 15, except that the type of starting material and the reduction temperature were varied. Table 2 shows the main conditions and characteristics of the powder particles at this time.
Shown below.

As a result of electron microscopic observation, all of the spindle-shaped magnetite particles obtained in Examples 16 to 29 had substantially high density with no pores on the particle surface or inside the particles, and The particle size was uniform, and dendritic particles were not mixed.

Production of maghemite particle powder exhibiting a spindle shape) Examples 30 to 43; Example 30 75 g of the magnetite particle bundle exhibiting a spindle shape obtained in Example 15 was oxidized in air at 300° C. for 60 minutes to obtain a spindle shape. A maghemite particle powder exhibiting the following was obtained.

As a result of electron microscopy, the obtained spindle-shaped maghemite particles were found to have substantially high density with no pores on the particle surface or inside the particles, and to have uniform particle size and dendritic particles. are not mixed, and the average value is 0223 μm on the long axis.
, the axial ratio (long axis: short axis) was 3:1.

Further, as a result of magnetoelectric measurement, the coercive force tic was 2320e, and the saturation magnetization σS was 73.5 emu/g.

Examples 31 to 43 Spindle-shaped maghemite particles were obtained in the same manner as in Example 30, except that the type of spindle-shaped magnetite particles was varied. Table 3 shows the main manufacturing conditions and characteristics of the particles at this time.

As a result of electron microscopic observation, all of the spindle-shaped maghemite particles obtained in Examples 31 to 43 had substantially high density with no pores on the particle surface or inside the particle, and In addition, the particle size was uniform and dendritic particles were not mixed.

Table 2 Table 3 [Effects] According to the method for producing spindle-shaped magnetic iron oxide particles according to the present invention, as shown in the previous example, pores are present on the particle surface and inside the particle. magnetite particles or maghemite particles that are spindle-shaped, have substantially high density, are uniform in particle size, do not contain dendritic particles, and have a small axis ratio (long axis: short axis). Since it is possible to obtain magnetic iron oxide particles consisting of powder, it is suitable as a magnetic material particle powder for high recording density, high sensitivity, high output, and low noise, which are currently most required.

In addition, when the above-mentioned magnetite particle powder or maghemite particle powder is used in the production of magnetic paint, it has good dispersibility in vehicles, extremely excellent orientation and filling properties in the coating film, and is preferred for magnetic recording. medium can be obtained.

[Brief explanation of drawings]

1 and 2 are an electron micrograph (X20.0OO) and an X-ray diffraction diagram showing the particle structure of the spindle-shaped hematite particles obtained in Example 1, respectively. 3 and 4 are an electron micrograph (x 20 , 000) and an X-ray diffraction diagram showing the particle structure of spindle-shaped hematite particles containing 20 obtained in Example 11, respectively. Figures 5 and 6 are both electron micrographs (×'0.0
00), which shows the particle structure of the powder particles obtained in Comparative Example 1 and Comparative Example 2, respectively. FIG. 7 is an X-ray cycle diagram of the particle powder obtained in Comparative Example 3.

Claims (2)

[Claims] (1) Oxygen-containing gas is added to the FeCO_2-containing aqueous solution obtained by reacting a ferrous salt aqueous solution with an alkali carbonate aqueous solution having a ratio of 1.8 equivalents or more in terms of Co_3 to Fe in the ferrous salt aqueous solution. When aerating and oxidizing, the FeCO_3 before being oxidized by aerating the ferrous salt aqueous solution, the alkali carbonate aqueous solution, and the oxygen-containing gas in advance.
0.1 to Fe in any aqueous solution containing
Add 1.5 mol% of citric acid or its salt, and then oxidize by passing oxygen-containing gas to produce spindle-shaped hematite particles from the aqueous solution. From spindle-shaped magnetic iron oxide particles that are thermally reduced in a reducing gas to produce spindle-shaped magnetite particles, or further oxidized to produce spindle-shaped maghemite particles. A method for producing magnetic iron oxide particles. (2) Oxygen-containing gas is added to the FeCO_3-containing aqueous solution obtained by reacting a ferrous salt aqueous solution with an alkali carbonate aqueous solution having a ratio of 1.8 equivalents or more in terms of CO_3 to Fe in the ferrous salt aqueous solution. When aerating and oxidizing, the FeCO_3 before being oxidized by aerating the ferrous salt aqueous solution, the alkali carbonate aqueous solution, and the oxygen-containing gas in advance.
0.1 to Fe in any aqueous solution containing
Co for 1.5 mol% citric acid or its salt and Fe
Adding a water-soluble cobalt salt of 0.5 to 10.0 atomic % in terms of conversion, and then oxidizing by passing oxygen-containing gas to generate spindle-shaped hematite particles containing Co from the aqueous solution, The Co-containing spindle-shaped hematite particles are thermally reduced in a reducing gas to produce Co-containing spindle-shaped magnetite particles, or are further oxidized to form Co-containing spindle-shaped hematite particles. A method for producing magnetic iron oxide particle powder consisting of magnetic iron oxide particles exhibiting a spindle shape, characterized in that the magnetic iron oxide particles are made into maghemite particles having a spindle shape.