WO2016199937A1

WO2016199937A1 - Epsilon iron oxide and method for producing same, magnetic paint, and magnetic recording medium

Info

Publication number: WO2016199937A1
Application number: PCT/JP2016/067554
Authority: WO
Inventors: 慎一大越; 俊介岡; 飛鳥生井; 憲司正田
Original assignee: 国立大学法人東京大学; Ｄｏｗａエレクトロニクス株式会社
Priority date: 2015-06-12
Filing date: 2016-06-13
Publication date: 2016-12-15

Abstract

Provided are: epsilon iron oxide which has an average particle size of 10 to 18 nm, in which a part of an iron element is substituted with a substitution element, and which has a coercive force of 14 kOe or less, the coefficient of variation of the particle size being 40% or less; and a method for producing the same. This method for producing the epsilon iron oxide includes: a step of applying metal which is the substitution element to iron oxide-hydroxide to obtain iron oxide-hydroxide to which the metal is applied; a step of coating the iron oxide-hydroxide to which the metal is applied with silicon oxide to obtain iron oxide-hydroxide coated with the silicon oxide; and a step of heat-treating the iron oxide-hydroxide coated with the silicon oxide under an oxidizing atmosphere. The method is characterized by producing an epsilon iron oxide in which a part of the iron element is substituted with the substitution element.

Description

Epsilon iron oxide and method for producing the same, magnetic paint and magnetic recording medium

The present invention relates to an epsilon iron oxide applied to a high-density magnetic recording medium, a radio wave absorber, and the like, a manufacturing method thereof, a magnetic paint and a magnetic recording medium using the epsilon iron oxide.

In order to achieve high recording density in magnetic recording media, it is necessary to reduce the recording unit. It is also necessary for the magnetic recording medium to be maintained in a ferromagnetic state under a normal environment where it is exposed during storage and use, for example, at room temperature. In particular, the stability of magnetization with respect to heat is considered to be proportional to the magnetic anisotropy constant and the particle volume. Here, it is considered that the magnetic anisotropy constant can be increased by increasing the coercive force of the magnetic recording medium. Therefore, in order to obtain particles having a small particle volume and high thermal stability, it is considered effective to use a substance having a high coercive force as a magnetic material.

Based on the above considerations, the present inventors have found epsilon iron oxide as a material that develops a huge coercive force of 20 kOe under room temperature conditions even though it is nano-order particles, and published it as Non-Patent Document 1. Further, it has been found that the coercive force can be controlled by substituting a part of the iron element of the epsilon iron oxide with a metal element different from iron, and disclosed in Patent Documents 1 to 4.

Japanese Patent Application No. 2006-096907 Japanese Patent Application No. 2006-224954 Japanese Patent Application No. 2006-234958 Japanese Patent Application No. 2009-517830

The epsilon iron oxide announced by the present inventors in Non-Patent Document 1 is a substance having a huge coercive force of 20 kOe level. However, in order to use such magnetic particles having a huge coercive force for magnetic recording, a magnetic head having a higher saturation magnetic flux density is used to generate a high magnetic field and write information. Necessary. However, since it is known as a head material at present and there is no material that satisfies such requirements, it is considered difficult to apply such magnetic particles for magnetic recording media.

Here, as disclosed in Patent Documents 1 to 3, the present inventors can reduce the coercive force to a desired value by using epsilon iron oxide in which a part of Fe site is replaced with a different trivalent metal. It was thought that. And as disclosed in Patent Document 4, it became possible to impart thermal stability while ensuring arbitrary adjustability of the coercivity of epsilon iron oxide.

However, in order to achieve high recording density using epsilon iron oxide, the inventors have made the particle size of the epsilon iron oxide smaller to reduce the recording unit (for example, an applied magnetic field of 70 kOe). It was thought that it is important to set the coercive force to 14 kOe or less and to make the particle size of the epsilon iron oxide more uniform.
Therefore, the technical problem to be solved by the present invention is epsilon iron oxide having an average particle diameter of 10 to 18 nm, a part of the iron element being substituted with a substitution element, and a coercive force of 14 kOe or less. It is to provide an epsilon iron oxide having a particle size variation coefficient of 40% or less, a method for producing the same, a magnetic paint using the epsilon iron oxide, and a magnetic recording medium.

Under the circumstances described above, the present inventors conducted research. Then, a metal compound as a substitution element is deposited on iron oxide hydroxide to obtain iron oxide hydroxide to which the metal compound is deposited, and iron oxide hydroxide to which the metal compound is deposited is converted into silicon oxide. And iron oxide hydroxide coated with silicon oxide, and heat treating the iron oxide hydroxide coated with silicon oxide in an oxidizing atmosphere. It is possible to obtain epsilon iron oxide in which a part of the element is replaced with epsilon iron oxide having an average particle diameter of 10 to 18 nm and a coefficient of variation of the particle diameter is 40% or less. As a result, the present invention was completed.

That is, the first invention for solving the above-described problem is
Applying a metal compound as a substitution element to iron oxide hydroxide to obtain iron oxide hydroxide to which the metal compound is applied;
Coating iron oxide hydroxide coated with the metal compound with silicon oxide to obtain iron oxide hydroxide coated with the silicon oxide;
Heat-treating the iron oxide hydroxide coated with the silicon oxide in an oxidizing atmosphere,
A method for producing epsilon iron oxide, characterized in that epsilon iron oxide in which a part of iron element is substituted with the substitution element is produced.
The second invention is
A method for producing epsilon iron oxide according to the first invention, comprising:
The heat treated powder obtained in the heat treatment step is further treated with an alkaline aqueous solution to produce epsilon iron oxide, which is a method for producing epsilon iron oxide.
The third invention is
The step of obtaining the iron oxide hydroxide to which the metal compound is deposited,
Dissolving a metal salt of the substitution element in the iron oxide hydroxide suspension;
Adding an alkaline aqueous solution to a suspension of iron oxide hydroxide in which the metal salt is dissolved to obtain iron oxide hydroxide to which the metal compound is deposited. It is a manufacturing method of the epsilon iron oxide as described in 2 invention.
The fourth invention is:
The method for producing epsilon iron oxide according to any one of the first to third inventions, wherein the iron oxide hydroxide coated with the metal compound is coated with silicon oxide and then dried to form the silicon oxide. A method for producing epsilon iron oxide characterized by obtaining iron oxide hydroxide coated with a product.
The fifth invention is:
Epsilon iron oxide in which part of the iron element is substituted with a substitution element,
Epsilon iron oxide having an average particle diameter of 10 to 18 nm and a coefficient of variation of the particle diameter of 40% or less.
The sixth invention is:
The value of the particle volume (1) is not less 500 nm ³ or more, epsilon iron oxide according to the fifth invention, wherein the value of the grain volume (2) is 10000 nm ³ or less.
However, the particle volume (1) is a value obtained by calculating the standard deviation of the particle size distribution of the epsilon iron oxide described in the fifth invention and subtracting the value of the standard deviation from the value of the average particle diameter of the epsilon iron oxide. Is the lower limit of the particle diameter of the epsilon iron oxide, and the volume is obtained by approximating the epsilon iron oxide particles to a spherical shape. The particle volume (2) is obtained by calculating the standard deviation of the particle size distribution of the epsilon iron oxide described in the fifth invention, and adding the value of the standard deviation to the value of the average particle diameter of the epsilon iron oxide. It is a value obtained by considering the epsilon iron oxide particle diameter as an upper limit of the particle size of the epsilon iron oxide particle by approximating the epsilon iron oxide particle into a spherical shape.
The seventh invention
The value obtained by subtracting the value of the particle volume (1) from the value of the particle volume (2) is 5000 nm ³ or less, and is the epsilon iron oxide according to the sixth invention.
The eighth invention
A magnetic paint characterized by using the epsilon iron oxide according to any one of the fourth to seventh inventions.
The ninth invention
A magnetic recording medium using the epsilon iron oxide according to any one of the fourth to seventh inventions.

The epsilon iron oxide according to the present invention can have a coercive force of 14 kOe or less, an average particle diameter of 10 to 18 nm, and a coefficient of variation of the particle diameter of 40% or less. Suitable as iron oxide.

It is the first half part (before heat processing) of the manufacturing flow of the epsilon iron oxide which concerns on an Example. It is the heat processing conditions in manufacture of the epsilon iron oxide which concerns on an Example. It is the latter half part (after heat processing) of the manufacturing flow of the epsilon iron oxide which concerns on an Example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments for carrying out the present invention will be described below. Epsilon iron oxide, substitution element, transmission electron microscope (TEM) observation, particle volume distribution, epsilon iron oxide manufacturing method, magnetic paint manufacturing method, magnetic recording medium manufacturing method This will be explained in the order.

(Epsilon iron oxide)
The epsilon iron oxide according to the present invention is an epsilon iron oxide powder in which part of the iron element is substituted with a substitution element, has an average particle diameter of 10 to 18 nm, and a coefficient of variation of the particle diameter is 40% or less. Is an epsilon iron oxide powder (may be referred to as “epsilon iron oxide” in the present invention). The epsilon iron oxide according to the present invention having the above-described configuration can be maintained (for example, at an applied magnetic field of 70 kOe) by using, for example, a predetermined amount of Ga, Al, Co, Ti or the like alone or as a mixture as the substitution element. The magnetic force can be controlled to 14 kOe or less. As a result, the epsilon iron oxide according to the present invention is optimal as an iron oxide for high density recording.
Further, when the epsilon iron oxide according to the present invention is used for different applications such as a magnetic shielding film, it is possible to set the required coercive force by controlling the type and amount of the substitution element. .

(Substitution element)
As the substitution element, it is preferable to use a divalent metal, a tetravalent metal, or a trivalent metal in order to keep the crystal structure of epsilon iron oxide stable. Further, the divalent metal is selected from one or more metal elements selected from Co, Ni, Mn, and Zn, the tetravalent metal is selected from Ti, and the trivalent metal is selected from In, Ga, and Al. One or more metal elements can be cited as preferred examples.

By replacing the epsilon iron oxide according to the present invention with a metal element so as to satisfy the above-described configuration, the coercive force of the magnetic material can be controlled relatively easily by the amount of element added. As a result, if the magnetic material is applied to magnetic recording, the magnetic material can be controlled to a level that can be used even by a known and public magnetic recording head.

(Transmission electron microscope (TEM) observation)
A transmission electron microscope (JEOL Ltd., JEM2000EX) was used to take a 1 million times photograph of the epsilon iron oxide sample powder according to the present invention. From the photograph, the longest diameter and the shortest diameter of each particle of epsilon iron oxide were taken. The particle diameter was determined by measuring the diameter and calculating the average value. The average value of the particle diameters obtained for at least 100 particles of independent epsilon iron oxide particles was taken as the average particle diameter of the sample powder. And the data of the said particle diameter were statistically processed, and the standard deviation and the variation coefficient were computed.

Here, when the standard deviation of the calculated particle diameter is 40% or less, it is preferable because the dispersion of the particle diameter is small and the dispersion of the coercive force distribution is small. Furthermore, the average particle diameter is preferably so fine that each particle has a single magnetic domain structure, and the average particle diameter observed with a transmission electron microscope is preferably 18 nm or less. However, if the average particle size becomes too small, there is a concern that the magnetic properties per unit weight of the magnetic particle powder deteriorate. Therefore, the average particle diameter is preferably 10 nm or more, more preferably 15 nm or more.

(Particle volume distribution)
From the viewpoint of controlling the coercive force of the above-described epsilon iron oxide to an appropriate value, the substitution element is preferably at least one selected from In, Ga, Al, Co, and Ti.
However, according to the study by the present inventors, epsilon iron oxide using these different metals as a substitution element tends to easily generate a particle group having a non-uniform particle size distribution as compared with epsilon iron oxide without substitution.

Here, the standard deviation of the particle size distribution of the epsilon iron oxide according to the present invention is obtained, and the value obtained by subtracting the value of the standard deviation from the value of the average particle diameter of the epsilon iron oxide is a lower limit of the particle diameter of the epsilon iron oxide. Thus, the epsilon iron oxide particles were approximated to a sphere, and the volume of the particles was obtained and defined as the particle volume (1). Similarly, the value obtained by adding the value of the standard deviation to the value of the average particle diameter of the epsilon iron oxide is considered as the upper limit of the particle diameter of the epsilon iron oxide, and the volume of the particles Was determined as the particle volume (2).
Average particle volume = (4/3) × π × ((average particle size (nm) / 2) ³
Particle volume (1) = (4/3) × π × ((average particle diameter (nm) −standard deviation of particle diameter (nm)) / 2) ³
Particle volume (2) = (4/3) × π × ((average particle diameter (nm) + standard deviation of particle diameter (nm)) / 2) ³

At this time, when the value of the grain volume (1) is 500 nm ³ or more, if the particle group value of the grain volume (2) satisfies 10000 nm ³ or less, the uniformity of the particle size distribution mentioned above is secured, a magnetic recording medium It was conceived that it is suitable as a magnetic particle for use in magnetic shielding films and the like.
This means that if the value of the particle volume (1) is 500 nm ³ or more, it will not be affected by thermal fluctuation, and the possibility of becoming a superparamagnetic material will be reduced. On the other hand, if the value of the particle volume (2) is 10000 nm ³ or less, it is possible to avoid the situation that the particle volume is too large and causes noise when the magnetic medium is used, and the coercive force becomes excessively high. it is conceivable that.

Further, according to the study by the present inventors, in epsilon iron oxide using a different metal as a substitution element, the particle volume [(2) − (1) obtained by subtracting the value of the particle volume (1) from the value of the particle volume (2). It has been found that the value of)] is more preferably 5000 nm ³ or less. That the value is 5000 nm ³ or less indicates that the particle volume distribution is uniform, and it can be considered that variation in the coercive force distribution is suppressed.

As described above, the heteroelement-substituted epsilon oxide according to the present invention is suitable for use as a magnetic powder for the next generation magnetic recording medium because the particle volume distribution is uniform although the particle volume is small. Is. Moreover, since it can be adjusted to a desired coercive force value by adjusting the addition amount of different elements as required, it can also be used as a magnetic shielding film and a magnetic shielding material in a wide range of applications.

(Method for producing epsilon iron oxide)
An example of the method for producing epsilon iron oxide according to the present invention will be described.
Iron oxide (III) hydroxide nanoparticles (β-FeO (OH)) having an average particle size of 15 nm or less and pure water are mixed, and the iron (Fe) equivalent concentration is 0.01 mol / L or more, 1 mol / L Prepare a dispersion of L or less.
A predetermined amount of a water-soluble metal salt solution of a substitution element is added to the dispersion and stirred at 0 to 100 ° C., preferably 20 to 60 ° C.
3 to 30 mol of ammonia per 1 mol of the iron (III) oxide hydroxide is added dropwise to the dispersion, and the mixture is stirred at 0 to 100 ° C., preferably 20 to 60 ° C. for 30 minutes or more. . By this stirring, iron oxide hydroxide to which a metal element as a substitution element is deposited is generated.
Here, 0.5 to 15 moles of tetraethoxysilane (TEOS) per 1 mole of the iron oxide hydroxide (III) was dropped into the dispersion to which the ammonia was added, and the mixture was stirred for 15 hours to 30 hours. Then, it is allowed to cool to room temperature. When the cooling is completed, it is preferable to add a predetermined amount of a precipitating agent (for example, ammonium sulfate).
The cooled dispersion is centrifuged (for example, 3500 rpm, 50 minutes), the supernatant is removed, and the precipitate is washed with pure water. Pure water is added to the precipitate and stirred to obtain a dispersion, which is centrifuged again to remove the supernatant. After the centrifugation and pure water washing are repeated three times or more, the precipitate is collected and dried at about 60 ° C. to obtain a dry powder.
The dried powder is heat-treated at 900 ° C. or higher and lower than 1200 ° C., preferably 950 ° C. or higher and 1150 ° C. or lower for 0.5 to 10 hours, preferably 2 to 5 hours in an oxidizing atmosphere to obtain heat-treated powder. . The use of air as the oxidizing atmosphere is preferable from the viewpoints of cost and workability.
The obtained heat-treated powder is pulverized and then added to a sodium hydroxide (NaOH) aqueous solution having a liquid temperature of 60 ° C. or higher and 70 ° C. or lower and a concentration of about 5 M, and stirred for 15 hours or longer and 30 hours or shorter Silicon oxide is removed from the heat-treated powder to produce epsilon iron oxide powder partially substituted with iron element.
Next, the epsilon iron oxide partially substituted with the produced iron element is recovered by filtration or centrifugation, and the iron element is partially substituted and has an average particle diameter of 10 to 18 nm. An epsilon iron oxide according to the present invention having a particle size variation coefficient of 40% or less could be obtained.

Although an example of a method for producing epsilon iron oxide has been described above, the iron oxide hydroxide fine particles described above are not necessarily β-FeO (OH) fine particles having an average particle diameter of 15 nm or less. For example, if a slurry containing iron (III) oxide hydroxide particles and excellent in dispersibility of the particles is used, the epsilon iron oxide according to the present invention can be obtained.

(Method of manufacturing magnetic paint)
In order to use the magnetic powder according to the present invention as a magnetic paint, for example, the following method can be employed.
That is, 0.500 g of sample powder (the above-mentioned precipitated powder) is weighed, put in a pot (inner diameter 45 mm, depth 13 mm), and left for 10 minutes with the lid open. Next, vehicle [vinyl chloride resin MR-110 (22 mass%), cyclohexanone (38.7 mass%), acetylacetone (0.3 mass%), n-butyl stearate (0.3 mass%), methyl ethyl ketone (MEK; 38.7% by mass) is collected and added to the pot.
Immediately thereafter, 30 g of steel balls (2 mm diameter) and 10 nylon balls (8 mm diameter) are added to the pot, and the lid is closed and allowed to stand for 10 minutes. Thereafter, the pot is set on a centrifugal ball mill, and the number of revolutions is slowly increased, and the dispersion process is performed for 60 minutes at 600 rpm. After the centrifugal ball mill is stopped, the pot is taken out and 1.800 mL of a preliminarily mixed solution in which MEK and toluene are mixed at a ratio of 1: 1 is added. A magnetic coating material can be prepared by setting this pot again in a centrifugal ball mill and dispersing it at 600 rpm for 5 minutes.

(Method of manufacturing magnetic recording medium)
As a method for producing a magnetic recording medium using the magnetic powder according to the present invention, for example, the following method can be employed.
After the dispersion process is completed in the above (Magnetic paint manufacturing method), the pot lid is opened, the nylon balls are removed, the prepared paint is put together with the steel balls into an applicator (gap 55 μm), and applied to the support film. Do. After the coating, the magnetic recording medium using the magnetic powder according to the present invention can be obtained by quickly placing the film at the center of the coil of the aligner having a magnetic flux density of 0.55T, orienting the magnetic field, and then drying. . Here, the method of forming a single magnetic layer is exemplified, but if a known method is employed, a multilayer magnetic recording medium can be formed.

Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to the following examples.

(Example 1)
<Manufacture of epsilon iron oxide>
A method for producing epsilon iron oxide according to Example 1 will be described with reference to FIGS. 1 and 3 which are flowcharts of the production method and FIG. 2 showing heat treatment conditions.
As shown in FIG. 1, in a 1 L Erlenmeyer flask, 420 g of pure water and 6.2 g of a sol of iron oxide (III) oxide nanoparticles (β-FeO (OH)) having an average particle diameter of about 6 nm, Ga (NO ₃ ) Put 700.72 mg of ₃ · nH ₂ O powder, 72.86 mg of Co (NO ₃ ) ₂ · 6H ₂ O powder, 0.05 ml of TiCl ₄ solution with a Ti equivalent concentration of 16 wt%, and heat to 50 ° C. And stirred until a uniform dispersion was obtained.
To this, 19.2 mL of a 25% aqueous ammonia solution was added dropwise and stirred at 50 ° C. for 30 minutes. Furthermore, 24 mL of tetraethoxysilane (TEOS) was added dropwise to this dispersion, and the mixture was stirred at 50 ° C. for 20 hours, and then allowed to cool to room temperature. The dispersion was allowed to cool to room temperature. After allowing to cool, 20 g of ammonium sulfate was added to precipitate a precipitate.
The deposited precipitate was centrifuged (3500 rpm, 50 minutes), the supernatant was removed, and the precipitate was collected. The collected precipitate was washed with pure water and centrifuged again.
After carrying out the centrifugal separation treatment and pure water washing three times, the precipitate was transferred to a petri dish and dried in a 60 ° C. drier to obtain a dry powder.

The pulverized powder was loaded into a furnace and heat treated under the heat treatment conditions shown in FIG. 2 in an air atmosphere to obtain heat treated powder.

As shown in FIG. 3, the obtained heat-treated powder was charged into a 250 mL Erlenmeyer flask and stirred with 140 ml of 5 mol / L sodium hydroxide (NaOH) aqueous solution at a liquid temperature of 70 ° C. for 24 hours. Silicon oxide was removed.
Next, the heat-treated powder from which the silicon oxide was removed was centrifuged (5000 rpm, 10 minutes), the supernatant was removed, and the precipitate was collected. The collected precipitate was washed with about 35 ml of pure water, centrifuged again (10000 rpm, 5 minutes), the supernatant was removed, and the precipitate was collected. The collected precipitate was washed with about 35 ml of pure water, centrifuged (14000 rpm, 60 minutes), and the process of removing the supernatant was repeated twice to obtain epsilon iron oxide according to Example 1.

<Analysis and measurement results of epsilon iron oxide>
Table 1 shows the results of elemental analysis of the obtained epsilon iron oxide according to Example 1 using a high frequency induction plasma emission spectrometer ICP (Agilent 7700x) manufactured by Agilent Technologies.
Moreover, when the epsilon iron oxide which concerns on Example 1 was observed with the transmission electron microscope (TEM) and the average particle diameter was calculated | required, it was 16.4 nm.

The average particle diameter, standard deviation, coefficient of variation, average particle volume, particle volume (1), particle volume (2), particle volume [(2)-(1)] of the obtained epsilon iron oxide according to Example 1 Values are shown in Table 1.
Furthermore, the magnetic properties (coercivity, saturation magnetization, residual magnetization) of the epsilon iron oxide according to Example 1 were measured. Specifically, using a SQUID (superconducting quantum interferometer) of MPMS7 manufactured by Quantum Design, measurement was performed at a maximum applied magnetic field of 70 kOe and a temperature of 300K.
Table 1 shows values of the obtained coercive force, saturation magnetization, and residual magnetization.

(Example 2)
In a 1 L Erlenmeyer flask, 420 g of pure water and 7.2 g of a sol of iron oxide (III) nanoparticle (β-FeO (OH)) having an average particle size of about 6 nm, Ga (NO ₃ ) ₃ .nH ₂ O powder Was carried out in the same manner as in Example 1, except that 200.74 mg of Co, (NO ₃ ) ₂ .6H ₂ O powder, 72.93 mg, and 0.05 ml of TiCl ₄ solution having a Ti equivalent concentration of 16 wt% were added. The epsilon iron oxide according to Example 2 was obtained.
As a result of elemental analysis using ICP in the obtained epsilon iron oxide according to Example 2, the average particle size, standard deviation, value of coefficient of variation, average particle volume, particle volume (1), particle volume (2), Table 1 shows the values of the particle volume [(2)-(1)], coercive force, saturation magnetization, and residual magnetization.

(Example 3)
In 1L Erlenmeyer flask, sol _{_{7.6g, Co (NO 3) 2}} · 6H 2 O powder of pure water 420mL and average particle size of about 6nm oxide iron (III) hydroxide nanoparticles (β-FeO (OH)) Was obtained in the same manner as in Example 1 except that 0.05 ml of a TiCl ₄ solution having a Ti equivalent concentration of 16 wt% was added to obtain epsilon iron oxide according to Example 3.
As a result of elemental analysis using ICP in the obtained epsilon iron oxide according to Example 3, the average particle size, standard deviation, coefficient of variation, average particle volume, average particle volume, particle volume (1), particle volume Table 1 shows the values of (2), particle volume [(2)-(1)], coercive force, saturation magnetization, and residual magnetization.

Example 4
In a 1 L Erlenmeyer flask, 420 mL of pure water and sol of iron oxide (III) oxide nanoparticles (β-FeO (OH)) having an average particle diameter of about 6 nm, 7.6 g, Ga (NO ₃ ) ₃ .nH ₂ O powder The epsilon iron oxide according to Example 4 was obtained in the same manner as in Example 1 except that 201.21 mg was added.
As a result of elemental analysis using ICP in the obtained epsilon iron oxide according to Example 4, the average particle size, standard deviation, coefficient of variation, average particle volume, average particle volume, particle volume (1), particle volume Table 1 shows the values of (2), particle volume [(2)-(1)], coercive force, saturation magnetization, and residual magnetization.

(Example 5)
In a 1 L Erlenmeyer flask, 420 mL of pure water and sol of iron oxide (III) oxide nanoparticles (β-FeO (OH)) having an average particle size of about 6 nm, 6.6 g, Ga (NO ₃ ) ₃ .nH ₂ O powder The epsilon iron oxide according to Example 5 was obtained in the same manner as in Example 1 except that 701.05 mg was added.
As a result of elemental analysis using ICP in the obtained epsilon iron oxide according to Example 5, average particle size, standard deviation, coefficient of variation, average particle volume, average particle volume, particle volume (1), particle volume (2) Particle volume [(2)-(1)], coercive force, saturation magnetization, and residual magnetization values are shown in Table 1.

(Example 6)
In 1L Erlenmeyer flask, sol 6.6g of pure water 420mL and average particle size of about 6nm oxide iron (III) hydroxide nanoparticles (β-FeO (OH)) , the _{_{Al (NO 3) 3 · 9H}} 2 O compound Epsilon iron oxide according to Example 6 was obtained in the same manner as in Example 1 except that 656.53 mg was added.
As a result of elemental analysis using ICP in the obtained epsilon iron oxide according to Example 6, the average particle size, standard deviation, coefficient of variation, average particle volume, average particle volume, particle volume (1), particle volume Table 1 shows the values of (2), particle volume [(2)-(1)], coercive force, saturation magnetization, and residual magnetization.

(Comparative Example 1)
[Procedure 1]
Two types of solutions are prepared: a raw material solution and a neutralizer solution.
(Preparation of raw material solution)
Put 24.3 mL of pure water into a Teflon (registered trademark) flask. There, iron nitrate (III) 9 hydrate, gallium nitrate (III) n hydrate, cobalt nitrate (II) hexahydrate, and titanium sulfate (IV) n hydrate are produced. The composition of the epsilon iron oxide according to Comparative Example 1 was added so that the composition was Fe _1.60 Ga _0.27 Co _0.05 Ti _0.06 O _3, and dissolved while stirring well at room temperature to obtain a raw material solution. .
(Preparation of neutralizer solution)
Add 2.0 mL of 25% ammonia water to 22.3 mL of pure water and stir to obtain a neutralizer solution.
[Procedure 2]
While thoroughly stirring the raw material solution at 1500 rpm, the neutralizing agent solution is dropped into the raw material solution, both solutions are stirred and mixed, and the neutralization reaction proceeds. After the whole amount of the neutralizing agent solution has been dropped, the mixture is kept stirred for 30 minutes.
[Procedure 3]
While stirring the mixed solution obtained in Procedure 2, 0.495 mL of tetraethoxysilane is added dropwise to the mixed solution, and stirring is continued for about 1 day.
[Procedure 4]
The mixed solution obtained in the procedure 3 is filtered, and the precipitate is collected and washed with pure water.
[Procedure 5]
After drying the precipitate obtained in the procedure 4, heat treatment is performed at 1100 ° C. for 4 hours in an air atmosphere furnace to obtain heat treated powder.
[Procedure 6]
The heat-treated powder obtained in the procedure 5 is put into a 2 mol / L NaOH aqueous solution and stirred for 24 hours to remove the silica present on the surface of the heat-treated powder particles. Following the silica removal treatment, filtration, washing with water and drying were performed to obtain epsilon iron oxide according to Comparative Example 1.
As a result of elemental analysis using ICP in the obtained epsilon iron oxide according to Comparative Example 1, the average particle size, standard deviation, coefficient of variation, average particle volume, average particle volume, particle volume (1), particle volume The values of (2) and particle volume [(2)-(1)] are shown in Table 1.
Since the coefficient of variation exceeded 40%, the measurement of magnetic characteristics was omitted.

(Comparative Example 2)
In the procedure 1, 24.3 mL of pure water is put into a Teflon (registered trademark) flask. There, iron nitrate (III) 9 hydrate, gallium nitrate (III) n hydrate, cobalt nitrate (II) hexahydrate, and titanium sulfate (IV) n hydrate are produced. A comparison was made by operating in the same manner as in Comparative Example 1 except that the composition of the epsilon iron oxide according to Comparative Example 2 was added so that the composition was Fe _1.79 Ga _0.10 Co _0.05 Ti _0.06 O _3. The epsilon iron oxide according to Example 2 was obtained.
As a result of elemental analysis using ICP in the obtained epsilon iron oxide according to Comparative Example 2, the average particle size, standard deviation, coefficient of variation, average particle volume, average particle volume, average particle volume, particle volume (1 ), Particle volume (2), and particle volume [(2)-(1)] are shown in Table 1.
Since the coefficient of variation exceeded 40%, the measurement of magnetic characteristics was omitted.

(Comparative Example 3)
[Procedure 1]
Two types of solutions, a solution A and a neutralizer solution B described below, are prepared.
(Preparation of solution A)
24.3 mL of pure water was put into a Teflon (registered trademark) flask, and iron (III) nitrate nonahydrate, cobalt nitrate (II) hexahydrate, and titanium sulfate (IV) n hydrated there. The product is added so that the composition of the epsilon iron oxide according to Comparative Example 3 to be manufactured becomes Fe _1.79 Co _0.10 Ti _0.11 O ₃ . When the addition is complete, they are stirred to dissolve to obtain solution A.
(Preparation of neutralizer solution B)
A solution B is obtained by adding 2.0 mL of 25% aqueous ammonia to 22.3 mL of pure water and stirring.
[Procedure 2]
To the solution A, the neutralizer solution B is added dropwise. After completion of the dropwise addition, the resulting mixture is continuously stirred for 30 minutes.
[Procedure 3]
While stirring the mixed solution obtained in the procedure 2, 0.49 mL of tetraethoxysilane is added to the mixed solution. And stirring is continued for about one day after the said addition.
[Procedure 4]
The mixed solution obtained in the procedure 3 is filtered, and the precipitate is collected and washed with pure water.
[Procedure 5]
After drying the precipitate obtained in the procedure 4, heat treatment is performed at 1100 ° C. for 4 hours in an air atmosphere furnace to obtain heat treated powder.
[Procedure 6]
The heat-treated powder obtained in the procedure 5 is put into a 2 mol / L NaOH aqueous solution and stirred for 24 hours to remove the silica present on the surface of the heat-treated powder particles. Subsequent to the silica removal treatment, filtration, washing with water and drying were performed to obtain epsilon iron oxide according to Comparative Example 3.
As a result of elemental analysis using ICP in the obtained epsilon iron oxide according to Comparative Example 3, the average particle size, standard deviation, and coefficient of variation were calculated as average particle volume, average particle volume, average particle volume, particle volume ( Table 1 shows the values of 1), particle volume (2), and particle volume [(2)-(1)].
Since the coefficient of variation exceeded 40%, the measurement of magnetic characteristics was omitted.

(Comparative Example 4)
Example 1 except that 420 mL of pure water and only 8.0 g of a sol of iron oxide (III) oxide nanoparticles (β-FeO (OH)) having an average particle diameter of about 6 nm were placed in a 1 L Erlenmeyer flask. The same operation was performed to obtain epsilon iron oxide according to Comparative Example 4.
As a result of elemental analysis using ICP in the obtained epsilon iron oxide according to Comparative Example 4, the average particle size, standard deviation, coefficient of variation, average particle volume, average particle volume, average particle volume, particle volume (1 ), Particle volume (2), particle volume [(2)-(1)], coercive force, saturation magnetization, and residual magnetization are shown in Table 1.

Claims

Applying a metal compound as a substitution element to iron oxide hydroxide to obtain iron oxide hydroxide to which the metal compound is applied;
Coating iron oxide hydroxide coated with the metal compound with silicon oxide to obtain iron oxide hydroxide coated with the silicon oxide;
Heat-treating the iron oxide hydroxide coated with the silicon oxide in an oxidizing atmosphere,
A method for producing epsilon iron oxide, comprising producing epsilon iron oxide in which a part of an iron element is substituted with the substitution element.
A method for producing epsilon iron oxide according to claim 1,
A method for producing epsilon iron oxide, wherein the heat treated powder obtained in the heat treatment step is further treated with an alkaline aqueous solution to produce epsilon iron oxide.
The step of obtaining the iron oxide hydroxide to which the metal compound is deposited,
Dissolving a metal salt of the substitution element in the iron oxide hydroxide suspension;
A step of adding an aqueous alkaline solution to a suspension of iron oxide hydroxide in which the metal salt is dissolved to obtain iron oxide hydroxide to which the metal compound is deposited is provided. 2. The method for producing epsilon iron oxide according to 2.
4. The method of producing epsilon iron oxide according to claim 1, wherein the iron oxide hydroxide to which the metal compound is deposited is coated with silicon oxide and then dried to form the silicon oxide. A process for producing epsilon iron oxide, characterized in that a coated iron oxide hydroxide is obtained.
Epsilon iron oxide in which part of the iron element is substituted with a substitution element,
Epsilon iron oxide having an average particle diameter of 10 to 18 nm and a coefficient of variation of the particle diameter of 40% or less.
The value of the particle volume (1) is not less 500 nm 3 or more, epsilon iron oxide according to claim 5, the value of the grain volume (2), characterized in that at 10000 nm 3 or less.
However, the particle volume (1) is obtained by calculating the standard deviation of the particle size distribution of the epsilon iron oxide according to claim 5 and subtracting the value of the standard deviation from the value of the average particle diameter of the epsilon iron oxide. This is a value obtained by considering the epsilon iron oxide particles as a lower limit of the particle diameter and approximating the epsilon iron oxide particles to a spherical shape. The particle volume (2) is a value obtained by calculating a standard deviation of the particle size distribution of the epsilon iron oxide according to claim 5 and adding the value of the standard deviation to the value of the average particle diameter of the epsilon iron oxide. This is a value obtained by considering the epsilon iron oxide particles as a sphere and considering the upper limit of the particle diameter of the iron oxide.
The value obtained by subtracting the value of the grain volume from the value of the grain volume (2) (1), epsilon iron oxide according to claim 6, characterized in that at 5000 nm 3 or less.
A magnetic paint using the epsilon iron oxide according to any one of claims 4 to 7.
A magnetic recording medium using the epsilon iron oxide according to any one of claims 4 to 7.