JPS6183631A - Production of strip type of fine particles of magnetic iron oxide - Google Patents

Abstract

PURPOSE:Specific particles in the form of spindle is added, as a seed crystal, to a specific suspension, then a gas containing oxygen gas is passed through and the resultant goethite particles in the form of strips are reduced with heat to give the title particles completely free from resins and uniform in particles size. CONSTITUTION:An aqueous suspension of Fe(OH)2 over 11 pH resulting from reaction of an aqueous ferrous salt such as ferrous sulfate with aqueous alkaline solution such as alkali carbonate is combined with 0.1-20atom%, based on the Fe salt calculated as Si atom, of a water-soluble silicate and 10-60wt%, based on the stri-form goethite particles as seeds, of spindle-type goethite particles of less than 4:1 axis ratio. Then, an oxygen-containing gas is passed through to allow the seed crystals to grown to give goethite particles in the form of strips. The resultant particles or product after dehydration is reduced with heat at 300-500 deg.C in a reductive gas atmosphere, as needed, further oxidized to give the title particles of magnetite or maghemite in the form of strips.

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 contain no dendritic particles and have a uniform particle size. The purpose is to obtain short-sided magnetic iron oxide particles.

[Prior Art (+i)] In recent years, as magnetic recording and reproducing equipment has become smaller and lighter, there has been an increasing need for higher performance in magnetic recording media such as magnetic tapes and magnetic disks. There is a demand for improvements in basic characteristics such as high power characteristics, high intensity characteristics, and frequency characteristics.

Output characteristics of magnetic recording media such as magnetic tapes and magnetic disks,
The arbitrariness characteristics depend on the residual magnetic flux density Br, and the residual (n flux density Br) depends on the dispersibility of the magnetic iron oxide particles in the vehicle, the orientation and filling properties in the coating film.

In order to improve the dispersibility in the vehicle, the orientation and filling properties in the coating film, the magnetic iron oxide particles to be dispersed in the vehicle must be free of dendritic particles and have a particle size of is required to be uniform.

Currently, acicular magnetite particles or acicular maghemite particles are used as magnetic recording materials. These are generally ferrous brine i8? pH 1 containing ferrous hydroxide particles obtained by reacting & with an alkali
Air oxidation of one or more aqueous colloids is usually called a "warm reaction." ) The acicular goethite particles prepared in (1) are heated in a reducing gas such as hydrogen to form acicular magnetite particles, or the acicular goethite particles are then heated in air for 200 min.
It is obtained by oxidizing at ~300°C to form acicular maghemite particles.

As mentioned above, a powder with no dendritic particles and a uniform particle size (d-characterized iron particles ↑5) is currently most in demand, and powders with such characteristics (+15
In order to obtain the obtained magnetic iron oxide particles, the starting material, goethite particles or hematite particles obtained by heating and dehydrating them, must be free of dendritic particles and have a uniform particle size. It is necessary.

Conventionally, acicular goethite J was produced in the alkaline region with pH 1 or higher.
The most typical known method for producing Yi-mi 71]
A solution containing ferrous hydroxide particles obtained by adding 1 volume of alkaline water equal to or more than 787 ml of ferrous salt was adjusted to pH 11.
Acicular goethite particles are obtained by carrying out the oxidation reaction at a temperature of 80° C. or lower.

[Problem that the invention seeks to solve]

Magnetic iron oxide particles, which are not mixed with dendritic particles and have a uniform particle size, are most in demand at present, but they cannot be obtained by the above-mentioned known method of producing goethite particles as a starting material. The powder particles contain dendritic particles due to the goethite production mechanism described in detail below, and in terms of particle size, they cannot be said to have a uniform particle size.

The reason for the formation of goethite particles in which dendritic particles are mixed and the particle size is asymmetric will be discussed below.

Goethite particles are produced through two steps: generation of goethite particles and growth of the goethite nuclei.

Goethite nuclei are generated by the reaction between ferrous hydroxide particles obtained by reacting an aqueous salt solution with 1 volume of alkaline water and dissolved oxygen, according to the above-mentioned known method L. For example, the contact reaction between ferrous hydroxide particles and dissolved oxygen may be partial and non-uniform, or the generation of goethite nuclei and the growth of goethite nuclei may occur simultaneously, and the goethite production reaction may occur at the same time. New nuclei are generated in mffT until the process is completed/), and the resulting goethite particles are thought to contain dendritic particles and have asymmetric particle sizes.

In this way, acicular magnetite particles or acicular maghemite particles obtained by reducing and oxidizing goethite particles in which dendritic particles are mixed and the particle size is asymmetric also contain dendritic particles, and, The particle size becomes asymmetric.

When a magnetic recording medium is manufactured using such magnetic particle powder, the dispersibility in the vehicle, the orientation and filling properties in the coating film are poor, and the residual magnetic flux density is therefore reduced. .

Conventionally, various methods have been attempted to obtain goethite particles with less dendritic particles.

For example, Japanese Patent Publication No. 51-86795 and Japanese Patent Publication No. 55
There is a method described in Japanese Patent No.-23215. Japanese Patent Application Publication No. 1973-
The method described in Japanese Patent Publication No. 86795 is to obtain acicular goethite particles by oxidizing ferrous hydroxide particles at a low rate, and the method described in Japanese Patent Publication No. 55-23215 is to obtain acicular goethite particles by oxidizing ferrous hydroxide particles at a low rate. Acicular goethite particles are obtained by air oxidizing the particles in a strong alkali/8 solution at a temperature of 20°C or higher and 40°C or lower.

However, each method attempts to suppress the generation of dendritic particles as much as possible, and cannot completely eliminate the generation of dendritic particles.

In fact, Japanese Patent Application Laid-Open No. 51-86795 states, ``The present invention produces α-Fe0.
It is characterized by creating 011 (Goetite),...
``...'', and Japanese Patent Publication No. 55-23215 states, ``The present invention relates to a method for producing acicular goethite crystals with less branching (dendritic particles). ” is stated.

As is clear from the above, when goethite is produced by a known method, due to its production mechanism, dendritic particles are essentially mixed and the particle size is asymmetric.
There is a strong demand for establishing a method for producing goethite particles that are completely free of dendritic particles and have uniform particle sizes.

[Means for solving problems]

The present inventor has found that dendritic particles are not mixed at all, and
As a result of various studies on methods for obtaining magnetic iron oxide particles with uniform particle size, we found that in a suspension containing ferrous hydroxide with a pH of 11 or more obtained by reacting an aqueous ferrous salt solution with an aqueous alkaline solution. When generating goethite particles by passing an oxygen-containing gas through and oxidizing the ferrous hydroxide, if spindle-shaped goethite particles are present as seed crystals in the suspension containing ferrous hydroxide, It is possible to obtain goethite particles having a rectangular shape with no dendritic particles mixed therein and having a uniform particle size, and by heating and dehydrating the short mt-shaped goethite particles or the goethite particles.j) Magnetite particles and maghemite particles obtained by reducing or further oxidizing short-sided hematite particles also have a rectangular shape with no dendritic particles mixed therein and uniform particle size. We have obtained a completely new finding that the iron oxide particles are free iron oxide particles.

That is, in the present invention, goethite particles are oxidized by passing an oxygen-containing gas into a suspension containing ferrous hydroxide having a pH of 1 or more, which is obtained by reacting an aqueous ferrous salt solution with an aqueous alkaline solution. In order to produce the ferrous hydroxide, spindle-shaped goethite particles are present as seed crystals in the suspension containing ferrous hydroxide, and then oxygen-containing gas is aerated to grow the nuclide crystal particles. , generate goethite particles exhibiting a rectangular shape, and heating and reducing the rectangular goethite particles or the rectangular hematite particles obtained by heating and dehydrating the rectangular goethite particles in a reducing gas to obtain a rectangular shape. This is a method for producing rectangular magnetic iron oxide particles, which comprises obtaining maghemite particles exhibiting the following properties, or, if necessary, further oxidizing to obtain maghemite particles exhibiting a rectangular shape.

[For production]

First, the goethite particles according to the present invention are strip-shaped particles that do not contain any dendritic particles and have a uniform particle size. It has the characteristic that all particles are not generated.

In the case of the present invention, the present inventor has investigated why it is possible to generate strip-shaped goethite particles with no dendritic particles mixed therein and whose particle size is uniform. When spindle-shaped goethite particles are present as crystal grains, the spindle-shaped goethite particles themselves do not contain any dendritic particles and are uniform in particle size. It is thought that this is because the goethite particles serve as the nucleus and the growth of Ebitakinoyaru occurs.

Furthermore, in the case of the present invention, the seed crystal particles become goethite nuclei and only the goethite growth reaction occurs, without the generation of goethite and the growth of nuclei occurring simultaneously as seen in known methods. We believe that this is the case.

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

As the ferrous salt aqueous solution in the present invention, a ferrous sulfate aqueous solution, a ferrous chloride aqueous solution, etc. can be used.

As the alkaline aqueous solution in the present invention, sodium hydroxide, potassium hydroxide, etc. can be used.

The goethite particles exhibiting a vi cone shape in the present invention can be obtained by the following method.

That is, goethite particles exhibiting a spindle shape are FeCO,
It can be obtained by oxidizing an aqueous solution containing oxygen by passing an oxygen-containing gas through it. In this case, the axial ratio (major axis/minor axis) of the spindle-shaped goethite particles obtained is 6:1 to 7.
・About 1.

As described above, the present invention uses spindle-shaped goethite particles as seed crystal particles to cause epitaxial growth. ) The shapes of the rectangular goethite particles produced are similar to each other.

In other words, as the axial ratio (long axis, short axis) of spindle-shaped goethite particles increases, the axial ratio (long axis, short axis) of the generated strip-shaped goethite particles also tends to increase. Goethite particles exhibiting a spindle shape with an axial ratio that matches the axial ratio of the target goethite particles may be selected.

By appropriately selecting spindle-shaped goethite particles, the axial ratio (long axis), which is usually used as a starting material when manufacturing magnetic particle powder for magnetic recording, can be obtained.

It is possible to obtain rectangular goethite particles with a short axis) of 2.1 to io:t, and the axial ratio (long axis/short axis) of lO.1 can be obtained as necessary.
It is also possible to obtain the above rectangular goethite particles.

In recent years, for the purpose of high-density recording, a method has been proposed in which a recording medium is provided with a 6FF capacity in five isotropic directions.

In this way, in a 4ft recording medium, magnetic iron oxide particles have an easy magnetization direction isotropic to the medium.
It is necessary to randomly orient the particles three-dimensionally in the coating film, and such magnetic iron oxide particles have an axial ratio (
I1211J+: Short axis) should be as small as possible.
It is effective. When the axial ratio is large, they tend to line up in the longitudinal direction in the n-air recording medium, and it is difficult to orient them randomly.

The present inventor has been involved in the production and development of goethite particles for many years, and in the process, he developed a technology to obtain goethite particle powder exhibiting a spindle shape with a small axis ratio (major axis/minor axis). has already been established (patent application 1982-2)
No. 00621).

That is, goethite particles exhibiting a spindle shape with a small axis ratio (major axis: minor axis) are obtained by adding ferrous brine I8 liquid, alkali carbonate, and oxygen-containing gas in the method for producing spindle-shaped goethite particles described above. FeC0 before aeration and oxidation reaction
Water containing □? Add water-soluble silicate to any of the 8 liquids.
It can be obtained by adding 0.1 to 20 atomic % in terms of S+ to e.

In this case, as the amount of Si added increases, the axis ratio (long axis, short axis) of the spindle-shaped goethite particles produced tends to decrease, and when Si is added at 0.1 atomic % or more, can make the axial ratio of the produced goethite particles 4.1 or less, and when 0.3 atomic % or more is added, the axial ratio of the produced goethite particles can be made 2=1 or less.

If the present invention is carried out using the thus obtained spindle-shaped goethite particles with a small axial ratio as seed crystal particles,
It is possible to obtain rectangular goethite particles with a small axial ratio and without any dendritic particles mixed therein.

The amount of spindle-shaped goethite particles, which are seed crystal particles in the present invention, is 10 to 10% of the generated goethite particles.
It is 60% by weight.

If it is less than 10% by weight, new goethite core particles are generated at the same time as the seed crystal particles grow epitaxially, making it impossible to obtain the strip-shaped goethite particles that are the object of the present invention.

If it is 60% by weight or more, the seed crystal grains will not grow sufficiently, and the short-sided goethite grains that are the object of the present invention (1) cannot be produced.

The goethite particles exhibiting a spindle shape in the present invention need to be present before the growth reaction of seed crystal particles occurs. The ferrous hydroxide can be present in any of the H/R A solutions containing ferrous hydroxide prior to the oxidation reaction.

The heating reduction temperature in the present invention is 300 to 5
It can be carried out at 00°C.

If the temperature is below 300°C, the reduction reaction will proceed slowly (and it will take a long time).If the temperature is above 500°C, the reduction reaction will proceed rapidly, causing deformation of the particle morphology and damage to the particles and their mutual interaction. This will cause sintering between the parts.

〔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 amount of Si, Co, Zn, and Ni in the particles were measured using a Fluorescent X-ray analyzer 3063 h type (manufactured by Rigaku 1 Kai Kogyo) in accordance with JIS 0119 "General Rules for Fluorescent X-ray Analysis". It was measured by performing optical X-ray analysis.

Production of goethite particles j′J) powder exhibiting a rectangular shape> Examples 1 to 15. Comparative Example 1; Example I Ferrous sulfate water containing 0.60 mol/l of ferrous sulfate solution 251 was prepared, and 5,
2-N NaOH aqueous solution 1 (125x plus pH 13,
3. Ferrous hydroxide particles were generated at a temperature of 45°C.

The major axis is 0.2μ in the water l8 solution containing the above ferrous hydroxide particles.
666 g of spindle-shaped goethite particles with an axis ratio (major axis: short axis) of 7; After that, the air was heated at 150 f/min at 55°C for 2.
Aeration was performed for 1 hour to perform a goethite growth reaction.

The end point of the oxidation reaction was determined by taking out a portion of the reaction solution and adjusting the 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 produced particles were washed with water, separated from P, dried, and crushed by a conventional method. As a result of electron microscopic observation, the obtained strip-shaped goethite particles had a long axis of 0.25 μm and an axial ratio (long axis: short axis).
8.5: I, dendritic particles were not mixed at all, and the particle size was uniform.

Examples 2 to 15 Other than changing the type of spindle-shaped goethite particles, the presence (2), the timing of addition, the temperature during the growth reaction of goethite, the type and concentration of the ferrous salt aqueous solution, and the type and concentration of the alkaline aqueous solution. A goethite growth reaction was carried out in the same manner as in Example 1.

Table 1 shows the main manufacturing conditions and characteristics at this time.

As a result of electron microscopic VL observation, the obtained rectangular goethite particles were found to have uniform particle size without any dendritic particles mixed therein.

An electron gQ micrograph (x 50,000) of the goethite particles obtained in Example 2 is shown in Figure 1, and a particle size distribution diagram is shown in Figure 2.
Shown below.

An electron micrograph (X 50,000) of the goethite particles t'A powder obtained in Example 10 is shown in FIG. 3, and a particle size distribution diagram is shown in FIG.

Comparative Example 1 A goethite production reaction was carried out in the same manner as in Example 1, except that no spindle-shaped goethite particles were present.

As is clear from the electron micrograph (x20.ooo) shown in FIG. 5, the obtained acicular goethite particles have a long axis of 0.
．． 7 μm, axial ratio (long axis: short axis) 10:i, f+
There were grain-like particles, and the particle size was asymmetric. FIG. 6 shows a particle size distribution diagram of this particle powder.

Production of hematite particle powder exhibiting a rectangular shape) Example 1
6; 800 g of the goethite l'i powder obtained in Example 1 which had a rectangular shape was heated and dehydrated at 300'C in air to obtain a hematite particle powder which had a rectangular shape. As a result of electron microscopic observation, this particle powder has a long axis of 0.25 μm and an axial ratio (long axis; short axis) 8. s: 1, no dendritic particles were mixed, and the particle size was uniform.

Production of magnetite particle powder exhibiting a rectangular shape> Examples 17 to 32. Comparative Example 2; Example 17 Goethite particles having a rectangular shape obtained in Example 1↑5
) end 500g 1.0! 11. Pour into the retort reducing solution and drive while rotating. 21 gas per minute! The mixture was aerated at a rate of 350° C. and reduced at a reduction temperature of 350'C to obtain magnetite particle powder having a rectangular shape. As a result of electron microscopic observation, the obtained magnetite particle powder exhibiting the shape of a strip had a long axis of 0.22 μm and an axial ratio (long axis: short IF, 1I) of 8.3:
1, no dendritic particles were mixed in, and the particle size was uniform.

In addition, as a result of magnetic measurement, the fusing force 11c was 3820e-
Saturation 6) 1 σS was 89.2 emu/g.

Examples 18-32. Comparative Example 2 Magnetite particles having a rectangular shape were obtained in the same manner as in Example 17, except that the type of starting material and the reduction temperature were varied.

Table 2 shows the main manufacturing conditions and various properties of the powder particles.

As a result of electron microscopy, all of the strip-shaped magnetite particle powders obtained in Examples 18 to 32 were found to have no coexistence of trees (branches 1' and sores) and were uniform in particle size. there were.

An electron micrograph (x50,000) of the rectangular magnetite particles produced in Example 25 i) is shown in FIG. 7-2, and the particle size distribution is shown in FIG. Further, the particle size distribution of the short L-shaped magnetite particles obtained in Example 27 is shown in FIG.

The magnetite particles obtained in Comparative Example 2 are shown in the electron micrograph F! shown in FIG. As is clear from (x20.000), the major axis is 0.5 μm, ! , 41 ratio (major axis/minor axis) is 6.5.1, and there are 7[l] of dendritic particles,
The particle size was asymmetric. The particle size distribution of the FFi powder is shown in FIG. In addition, (as a result of magnetic measurement, the coercive force Hc is 3950e saturation [I1ization σS is 8 lemu
/H.

Production of mag/mite particle powder exhibiting a rectangular shape> Examples 33 to 48. Comparative Example 3; Example 33 300 mm of rectangular maghemite particles obtained in Example 17 were oxidized in air at 300'C for 90 minutes to obtain short ml-shaped maghemite particles. Ta.

(As a result of electron microscopy, the maghemite particle Jul powder exhibiting a rectangular shape has a length of φJ + 0.22 μm, an axial ratio (long axis: short axis) of 8.3: l, and no M branched particles. They were not mixed and the particle size was uniform.

In addition, as a result of magnetic measurement, the coercive force 11c is 3570e,
hM Wausuka σS is 78. It was Oemu/g.

Examples 34-48. Comparative Example 3 Maghemite particles having a rectangular shape were obtained in the same manner as in Example 33, except that the type of starting material was varied.

Table 3 shows the main manufacturing conditions and characteristics of the particles at this time.

As a result of electron microscopy, all of the rectangular maghemite particles obtained in Examples 34 to 48 were found to have no dendritic particles mixed therein, and the particle size was uniform.

An electron micrograph (X 50,000) of the rectangular maghemite particles obtained in Example 41 is shown in FIG. 12, and the particle size distribution is shown in FIG. Also, in Example 43, i'4
Fig. 14 shows the grain distribution of the short ++n-shaped maghemite particles.

As is clear from the electron micrograph (x20,000) shown in FIG. 15, the maghemite particles obtained in Comparative Example 3 had a long axis of 0.5 μm and an axial ratio (long axis: short axis) of 6.5:l. Yes, dendritic particles are mixed, the particle size is 3420e,
What is the saturation magnetization σS? It was 9.7 emu/g.

Examples 49 to 64 Comparative Example 4.5; Example 49 Using the strip-shaped magnetite particle powder obtained in Example 17, an appropriate amount of a dispersant and a vinyl chloride-vinyl acetate copolymer was added. , a thermoplastic polyurethane resin, and a mixed solvent consisting of toluene, methyl ethyl ketone, and methyl isobutyl ketone were blended to a certain composition, and then mixed and dispersed in a ball mill for 8 hours to obtain a magnetic paint.

The above-mentioned mixed solvent was added to the obtained magnetic paint to adjust the viscosity of the O material to an appropriate value, and the mixture was coated on a polyester resin film and dried in a conventional manner to produce a magnetic tape.

The coercive force 11c of this magnetic tape is 3800c, the residual magnetic flux richness Br is 1850 Gauss, and the rectangular Or/Bm is 0.
, 92, and the degree of orientation was 3.0.

Examples 50 to 64 Comparative Example 4.5 Examples 50 to 53. 55 to 60 and 62 to 64 and Comparative Example 4.5 were the same as Example 49 except that the type of magnetic iron oxide particles was variously changed. Magnetic tape was manufactured using

JR1 Example 54 and Example 6) are! d A magnetic tape was produced in the same manner as in Example 49, except that the type of magnetic iron oxide particles was changed and the orientation treatment was not performed.

Table 4 shows the characteristics of this magnetic tape.

〔effect〕

According to the method for producing magnetic iron oxide particles according to the present invention, as shown in the above-mentioned example, magnetite particles are not mixed with any dendritic particles and have a uniform particle size and are strip-shaped. Since powder and maghemite particles can be obtained, it is suitable as a magnetic material for magnetic recording, which is currently most in demand.

In particular, the magnetic iron oxide particles obtained by thermal reduction or further oxidation using the rectangular Gekeite particles with a small axial ratio (long axis: short axis) according to the present invention as a starting material also have a small axial ratio (long axis: short axis). Since it has a small axis (minor axis), when dispersed in a magnetic recording medium, it is easy to orient it three-dimensionally at random, making it suitable as a magnetic material for high-density recording. In addition, when this magnetite particle powder or maghemite particle powder is used in the production of magnetic paint,
It has good dispersibility in a vehicle, excellent orientation and filling properties in a coating film, and a desirable magnetic recording medium can be obtained.

The above-mentioned effects of the present invention can be obtained by adding Go, Mg, AI, Cr, Zn-, which are conventionally added during the production of goethite particles as a starting material, in order to improve various properties of magnetic iron oxide particles.
It also works effectively when adding metals other than Fe, such as N+, Ti, Mn, Sn, and Pb.

[Brief explanation of drawings]

1, 3, and 5 are all electron micrographs showing the particle structure of goethite particles, and FIG. 3 is an electron micrograph (x50,000) of the rectangular goethite particles obtained in Example 10, and FIG. 5 is an electron micrograph (x50,000) of the acicular goethite particles obtained in Comparative Example 1. Electron micrograph (x20,0
00). 2, 4, and 6 are particle size distribution diagrams of goethite particles. FIG. 2 shows the goethite particles obtained in Example 2 and has a strip shape. FIG. 4 shows the goethite particles obtained in Example 10. The obtained goethite particle powder exhibiting a rectangular shape, FIG. 6, is the acicular goethite particle powder obtained in Comparative Example 1. 12I7 and FIG. 1O are both electron micrographs showing the particle structure of the magnetite particles, and FIG. 7 is an electron micrograph of the strip-shaped magnetite particles obtained in Example 25 (X50,000> , FIG. 10 is an electron micrograph (X20.000) of the acicular MAGTITE particles obtained in Comparative Example 2. FIGS. 8, 9, and 1O all show the particle size distribution of the magnetite particles. FIG. 8 shows the strip-shaped magnetite particles obtained in Example 25. FIG. 9 shows Example 27.
Magnetite particle powder exhibiting a rectangular shape obtained in Figure 1
1 is the acicular magnetite particle powder obtained in Comparative Example 2. 12 and 15 are electron micrographs showing the particle structure of maghemite particles, and FIG. 12 is an electron micrograph (x50 ,000), FIG. 15 is an electron micrograph (x 20,000) of the acicular maghemite particle powder obtained in Comparative Example 3. 13, 14, and 16 are particle size distribution charts of maghemite particles, and FIG. 13 shows Example 41 (
Maghemite particle powder exhibiting a rectangular shape, Fig. 14
16 shows the short-sided maghemite particles obtained in Example 43, and FIG. 16 shows the acicular maghemite particles obtained in Comparative Example 3.

Claims (6)

[Claims] (1) Goethite particles are generated by passing an oxygen-containing gas through a suspension containing ferrous hydroxide with a pH of 11 or higher, which is obtained by reacting an aqueous ferrous salt solution with an aqueous alkaline solution to oxidize it. In this process, spindle-shaped goethite particles are present as seed crystals in the suspension containing ferrous hydroxide, and then an oxygen-containing gas is aerated to grow the seed crystal particles. Goethite particles exhibiting a shape were produced, and the goethite particles exhibiting a rectangular shape or hematite particles exhibiting a rectangular shape obtained by heating and dehydrating the same were heated and reduced in a reducing gas to exhibit a rectangular shape. A method for producing strip-shaped magnetic iron oxide particle powder, characterized by obtaining magnetite particles. (2) The method for producing strip-shaped magnetic iron oxide particles according to claim 1, wherein the spindle-shaped goethite particles are present in an amount of 10 to 60% by weight based on the produced strip-shaped goethite particles. (3) The seed crystal grain has an axial ratio (long axis: short axis) of 4:1 or less, and contains 0.1 to 20.0 at% of Si to Fe.
A method for producing strip-shaped magnetic iron oxide particle powder according to claim 1 or 2, which is spindle-shaped goethite particles containing. (4) Goethite particles are produced by passing a gas containing ferrous hydroxide into a suspension containing ferrous hydroxide with a pH of 11 or higher and oxidizing it, which is obtained by reacting an aqueous ferrous salt solution and an aqueous alkaline solution. In order to do this, spindle-shaped goethite particles are present as seed crystals in the suspension containing ferrous hydroxide, and then oxygen-containing gas is aerated to grow the seed crystal particles. Goethite particles having a rectangular shape are generated, and the goethite particles having a rectangular shape or hematite particles having a rectangular shape obtained by heating and dehydrating the goethite particles are reduced by heating in a reducing gas, and then further oxidized. A method for producing rectangular magnetic iron oxide particles, the method comprising obtaining rectangular maghemite particles. (5) The method for producing strip-shaped magnetic iron oxide particles according to claim 4, wherein the spindle-shaped goethite particles are present in an amount of 10 to 60% by weight based on the produced strip-shaped goethite particles. (6) The seed crystal grain has an axial ratio (long axis: short axis) of 4:1 or less, and contains 0.1 to 20.0 at% of Si to Fe.
The method for producing strip-shaped magnetic iron oxide particle powder according to claim 4 or 5, which is spindle-shaped goethite particles containing.