JP2016098131A - Precursor of iron-based oxide magnetic particle powder and method for producing iron-based oxide magnetic particle powder using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a precursor suitable for obtaining an iron-based oxide magnetic particle powder having a narrow coercive force distribution and being suitable for increasing the recording density of a magnetic recording medium, and to provide a method for producing an iron-based oxide magnetic particle powder using the precursor.SOLUTION: A precursor of an ε-type iron-based oxide magnetic particle powder containing a substituted metal element is produced by reacting one or more selected from a divalent iron ion and a trivalent iron ion, a substituted metal ion, and a neutralizer in an aqueous solution in the presence of a hydroxycarboxylic acid to neutralize the pH to 7.0-10.0. An ε-type iron-based oxide magnetic particle powder containing a substituted metal element is obtained by, preferably after washing the precursor with water, coating the precursor with a silicon oxide and heating the coated precursor.SELECTED DRAWING: Figure 1

Description

  The present invention uses an iron-based oxide magnetic particle powder suitable for a high-density magnetic recording medium, a radio wave absorber, and the like, in particular, a particle powder precursor having an average crystal particle size of nanometer order and a precursor thereof. The present invention relates to a method for producing iron-based oxide magnetic particle powder.

ε-Fe ₂ O ₃ is an extremely rare phase among iron oxides, but at room temperature, particles with a nanometer order size are about 20 kOe (1.59 × 10 ⁶ A / m) and have a huge coercive force (Hc). In the past, studies have been made on a production method for synthesizing ε-Fe ₂ O ₃ in a single phase (Patent Document 1). Further, when ε-Fe ₂ O ₃ is used for a magnetic recording medium, there is no corresponding material for a magnetic head having a high saturation magnetic flux density at the present time. Therefore, the Fe site of ε-Fe ₂ O ₃ The coercive force is also adjusted by substituting a part of the metal with a trivalent metal such as Al, Ga, In, etc., and the relationship between the coercive force and the radio wave absorption characteristics has been investigated (Patent Document 2). ).
On the other hand, in the field of magnetic recording, a magnetic recording medium having a high reproduction signal level and particulate noise ratio (C / N ratio: Carrier to Noise Ratio) has been developed. There is a demand for miniaturization of magnetic particles constituting the magnetic recording layer. However, in general, miniaturization of the magnetic particles that environmental stability, easy cause the thermal stability of the deterioration, the magnetic properties decrease of the magnetic particles under use or storage environment is concerned, the ε-Fe ₂ O ₃ a part of the Fe site, by substituting other metals having excellent heat resistance, the general formula _{ε-a x B y Fe 2} -xy O 3 or _{ε-a x B y C z} Fe 2-xyz O 3 (Where A is a divalent metal element such as Co, Ni, Mn and Zn, B is a tetravalent metal element such as Ti, and C is a trivalent metal element such as In, Ga and Al). In addition, various ε-Fe ₂ O ₃ partial substitutes have been developed that reduce the particle size, make the coercive force variable, and are excellent in environmental stability and thermal stability (Patent Document 3). .
Since ε-Fe ₂ O ₃ is not a thermodynamic stable phase, its production requires a special method. In the above-mentioned Patent Documents 1 to 3, ε-Fe ₂ O is prepared by using, as a precursor, fine crystals of iron oxyhydroxide generated by a liquid phase method, and applying heat treatment after the precursor is coated with silica by a sol-gel method. The production method ₃ is disclosed, and as the liquid phase method, a reverse micelle method using an organic solvent as a reaction medium and a method using only an aqueous solution as a reaction medium are disclosed.

JP 2008-174405 A International Publication WO2008 / 029861 Pamphlet International Publication WO2008 / 149785 Pamphlet

The ε-type iron-based oxide partially substituted with ε-Fe ₂ O ₃ or Fe manufactured by the conventional manufacturing method disclosed in Patent Documents 1 to 3 described above has excellent magnetic properties. However, depending on the manufacturing conditions, variation in coercive force distribution may be observed. As a result of diligent research by the present inventors, magnetic particle powder containing ε-type iron-based oxide partially substituted with ε-Fe ₂ O ₃ or Fe produced by a conventional method has a wide particle size distribution and is coarse. It was found to contain some particles. If the magnetic particle powder contains coarse particles, when used in a magnetic recording medium, SFD (Switching Field Distribution) increases and the C / N ratio deteriorates.
Further investigation by the present inventors revealed that the appearance frequency of coarse particles in the magnetic particle powder is a precursor when producing an ε-type iron-based oxide partially substituted with ε-Fe ₂ O ₃ or Fe. It turned out that it changed depending on the property of the oxyhydroxide which passed as a body.
That is, the technical problem to be solved in the present invention is that a precursor suitable for producing an iron-based oxide magnetic particle powder in which a part of the Fe site of ε-Fe ₂ O ₃ is substituted with another metal element. In addition to providing a production method, it is an object to provide a production method of iron-based oxide magnetic particle powder using the precursor and having a narrow coercive force distribution and suitable for increasing the recording density of a magnetic recording medium.

In the case of the reverse micelle method using an organic solvent in the reaction system, production of ε-type iron-based oxide fine particles powder in which the Fe sites of ε-Fe ₂ O ₃ or ε-Fe ₂ O ₃ are partially substituted with other metal elements In the method, the size of the precursor iron oxyhydroxide (partially substituted) depends on the size of the aqueous phase dispersed in the organic solvent, but the precursor in a system using only water as the reaction solvent. About the size of, there was no knowledge from the past. However, in the case of a reaction system using only water as a solvent, the present inventors agglomerated primary particles of hydroxide in which iron oxyhydroxide or iron oxyhydroxide Fe sites are partially substituted with other metal elements. Ε-type iron in which the average secondary particle diameter of the precursor, which is a secondary particle, is partially substituted with the other ε-Fe ₂ O ₃ or ε-Fe ₂ O ₃ Fe sites in the final ε-Fe ₂ O ₃ The present invention has been completed by finding out that it affects the magnetic properties of the system oxide fine particle powder.

In order to solve the above problems, in the present invention,
A method for producing a precursor of an iron-based oxide magnetic particle powder in which a part of an Fe site of ε-Fe ₂ O ₃ is substituted with another metal element, which is a divalent solution in an aqueous solution in the presence of hydroxycarboxylic acid. An iron-based oxide comprising a neutralization treatment step in which one or more selected from iron ions and trivalent iron ions, a substituted metal ion, and a neutralizing agent are reacted to adjust the pH to 7.0 to 10.0 A method for producing a precursor of magnetic particle powder is provided.
The hydroxycarboxylic acid used in this neutralization treatment step is preferably citric acid, and the neutralizing agent is preferably an aqueous solution containing ammonium ions or an aqueous solution containing carbonate ions added to an aqueous solution containing ammonium ions.
As a specific embodiment of the neutralization treatment step, in an aqueous solution in the presence of hydroxycarboxylic acid, an acidic aqueous solution containing a trivalent iron ion and a substituted metal ion as a source of iron is reacted with a neutralizing agent, Obtaining iron oxyhydroxide in which a part of the Fe site that is the precursor is replaced with another metal element,
After reacting the neutralizing agent with an acidic aqueous solution containing both divalent iron ions and trivalent iron ions as a source of iron, or only divalent iron ions and further containing substituted metal ions, The one obtained by oxidizing the divalent iron incorporated in the oxide to obtain iron oxyhydroxide in which a part of the Fe site as a precursor is substituted with another metal element,
After reacting an acidic aqueous solution containing divalent iron ions with a neutralizing agent as a source of iron, an acidic aqueous solution containing substituted metal ions while oxidizing the divalent iron incorporated in the hydroxide. By adding, what obtains iron oxyhydroxide in which a part of the Fe site as a precursor is substituted with another metal element,
Is mentioned. In these production methods, the hydroxycarboxylic acid may be added to either an aqueous solution containing an iron supply source or a neutralizing agent.

In the present invention,
As a method for producing an iron-based oxide magnetic particle powder containing, as magnetic particles, an iron-based oxide in which a part of the Fe site of ε-Fe ₂ O ₃ is substituted with another metal element, the iron-based oxide magnetic particles described above are used. A step of coating silicon oxide on the precursor obtained by the powder precursor manufacturing method;
There is provided a method for producing an iron-based oxide magnetic particle powder comprising heating a precursor coated with silicon oxide to form iron oxide containing a substituted metal element coated with silicon oxide.
In this method for producing iron-based oxide magnetic particle powder, it is preferable to wash the precursor with water before the step of coating the precursor of iron-based oxide magnetic particle powder with silicon oxide. Further, silicon oxide may be removed from the iron-based oxide magnetic particle powder coated with silicon oxide depending on the application.
The iron oxide magnetic particles powder made according to the present _{invention, ε-A x B y C} z Fe 2-xyz O 3 as the magnetic particles (although, A is chosen Co, Ni, Mn, from Zn 1 More than one kind of divalent metal element, B is one or more kinds of tetravalent metal elements selected from Ti and Sn, C is one or more kinds of trivalent metal elements selected from In, Ga and Al, It may include 0 <x, y, z <1).

  As described above, by using the production method of the present invention, it is possible to obtain an iron-based oxide magnetic particle powder having a narrow coercive force distribution and suitable for increasing the recording density of a magnetic recording medium, and a precursor used for the production thereof. Can be obtained.

2 is a TEM photograph of a precursor obtained in Example 1. 2 is a TEM photograph of a precursor obtained in Comparative Example 1. 4 is a TEM photograph of a precursor obtained in Example 3. 4 is a TEM photograph of a precursor obtained in Example 6. 7 is a TEM photograph of iron-based oxide magnetic particle powder obtained in Example 7. 10 is a TEM photograph of a precursor obtained in Example 8.

[Iron-based oxide magnetic particles]
The production method of the present invention is for producing an iron-based oxide magnetic particle powder containing, as magnetic particles, an iron-based oxide in which a part of the Fe site of ε-Fe ₂ O ₃ is substituted with another metal element. In addition to the magnetic particles, a case where heterogeneous phases inevitable in the production are mixed is included.
Whether or not a partially substituted product obtained by substituting a part of the Fe site of ε-Fe ₂ O ₃ with another metal element has an ε structure, X-ray diffraction (XRD), high-energy electron diffraction (HEED), etc. It is possible to confirm using
Examples of partially substituted products that can be produced by the production method of the present invention include the following.
Formula _{ε-C z Fe 2-z} O 3 ( where C is In, Ga, 1 or more trivalent metallic element selected from Al) represented by one.
1 the general formula _{ε-A x B y Fe 2} -xy O 3 ( where A Co, Ni, Mn, 1 or more bivalent metal elements selected from Zn, the B selected from Ti, Sn Represented by a tetravalent or higher-valent metal element).
Formula _{ε-A x B y C z} Fe 2-xyz O 3 ( where A is Co, Ni, Mn, 1 or more divalent metal element selected from Zn, B is selected Ti, Sn, One or more tetravalent metal elements, and C is one or more trivalent metal elements selected from In, Ga, and Al).
Here, the type substituted only with the C element has the advantage that the coercive force of the magnetic particles can be arbitrarily controlled and has the advantage that it is easy to obtain the same space group as ε-Fe ₂ O _3. Inferior. The type substituted with two elements A and B is excellent in thermal stability and can maintain high coercivity of magnetic particles at room temperature, but a single phase in the same space group as ε-Fe ₂ O ₃ is somewhat difficult to obtain. . In this case, the two elements A and B are simultaneously replaced due to the charge balance.
The three-element substitution types of A, B, and C have the best balance of the above-described characteristics, and are excellent in heat resistance, ease of obtaining a single phase, and controllability of coercive force. Hereinafter, in the present specification, this three-element substitution product will be mainly described.

The preferred ranges of the substitution amounts x, y and z of the three-element substitution product are as follows.
x and y can take arbitrary ranges of 0 <x and y <1, but if the values of x and y are greatly different, different phases are likely to be mixed into the magnetic particles in order to balance the charge. Therefore, x≈y is preferable, and x = y is more preferable. Considering the magnetic recording application, it is necessary to change the coercive force of the magnetic particles of the three-element substituted substance to that of the unsubstituted ε-Fe ₂ O ₃ to some extent, so that 0.01 ≦ x and y ≦ 0.2. It is preferable to do.
Similarly to x and y, z may be in the range of 0 <z <1, but from the viewpoint of coercive force control and ease of obtaining a single phase, 0 <z ≦ 0.5 may be set. preferable.
The three-element substituted magnetic particles obtained by the production method of the present invention can maintain a high coercive force at room temperature by appropriately adjusting the values of x and y, and further, x, y and z It is possible to control the coercive force to a desired value by adjusting.

[Average particle diameter of magnetic particles]
The average particle size of the magnetic particles obtained by the production method of the present invention is not particularly defined in the present invention, but it is preferable that each particle is fine enough to have a single domain structure. The average particle diameter measured with a transmission electron microscope is preferably 30 nm or less, and more preferably 20 nm or less. However, if the average particle size becomes too small, the magnetic properties per unit weight of the magnetic particle powder deteriorate, so that it is preferably 10 nm or more.

[precursor]
In the production method of the present invention, iron ions (divalent or trivalent alone or a mixture of divalent and trivalent), which will be described later, and a metal element metal that finally replaces the Fe site of the iron oxide as a starting material A precipitate obtained by reacting ions with a neutralizing agent in the presence of hydroxycarboxylic acid, and a precipitate obtained by reacting with a neutralizing agent in the presence of hydroxycarboxylic acid and then oxidizing. Is a precursor of iron-based oxide magnetic particle powder. This precipitate is a mixture of iron oxyhydroxide and a hydroxide of a substituted metal element, or iron oxyhydroxide in which a part of the Fe site is substituted with another metal element. Things are called “precursors”.
The aforementioned precursor is secondary particles in which primary particles of iron and substituted metal hydroxide or oxyhydroxide are aggregated. In general, the secondary particles aggregated by the neutralization treatment are those in which the primary particles are gradually aggregated, and the degree of aggregation varies greatly depending on the charged state of the primary particles in the aqueous solution. In particular, when the surface charge of the primary particles is close to zero, the aggregation density tends to increase. In the case of the production method of the present invention, since the hydroxycarboxylic acid coexists during the neutralization treatment, the dissociated hydroxycarboxylic acid ions are adsorbed on the surface of the primary particles, and the hydroxide ions in the primary particles By substituting, the surface charge density of the primary particles is increased, so that secondary particles having a low aggregation density are estimated to be formed. That is, the precursor obtained by the production method of the present invention is considered to have a so-called pledget-like structure with many gaps.
The precursor obtained by the production method of the present invention is obtained by adding and stirring the silane compound to the slurry containing the precursor without subsequent drying to obtain the iron-based oxide magnetic particle powder. Is coated with a hydrolyzed silanol derivative. At that time, the silanol derivative enters the gaps and coats the precursor while subdividing it, so that the particle size distribution of the iron-based oxide magnetic particle powder finally obtained becomes narrow and the coercive force distribution also narrows. it is conceivable that.
The average secondary particle diameter of the precursor is preferably 2.5 μm or less. When the average secondary particle diameter is 2.5 μm or less, the silanol derivative can easily enter the precursor.
The crystal structure of the precursor preferably includes a ferrihydrite structure. The more the ferrihydrite structure precursor is contained, the easier it is to obtain an ε-type iron-based oxide. The reason why it is easy to obtain ε-type iron-based oxides via ferrihydrite structure oxyhydroxide is currently unknown, but ferrihydrite is a hexagonal close-packed array of O ²⁻ and OH ^−. When a layer having a cubic close-packed arrangement is irregularly laminated and a part of Fe octahedron is missing, it has a defect-rich structure, and when this is covered with silicon oxide and heat-treated under restraint conditions, ε It is estimated that it is easy to change to a type of iron-based oxide. Furthermore, in order to substitute a part of the Fe site of ε-Fe ₂ O ₃ with another metal element, even when an element other than Fe is added, it is easy to coprecipitate with Fe, and a different phase other than ferrihydrite is present. It is difficult to produce and is presumed to be preferable from the viewpoint of composition uniformity and particle uniformity.
Ferrihydrite has two structures called 6Line (6L) and 2Line (2L), and the 2L structure ferrihydrite changes to an ε-type iron-based oxide rather than the 6L structure. easy.

[Starting material]
In the production method of the present invention, iron ions (divalent or trivalent alone or a mixture of divalent and trivalent) as a starting material of iron-based oxide magnetic particle powder, and a metal that eventually replaces the Fe site An acidic aqueous solution containing elemental metal ions (hereinafter referred to as a raw material solution) is used. The raw material solution may contain iron ions and metal ions of substitution elements in the same solution, or may be used as separate solutions.
When divalent iron ions are used as a starting material, it is necessary to finally oxidize to trivalent iron. As the oxidation method, either a method using an oxidizing agent such as hydrogen peroxide or an oxygen oxidation such as air oxidation may be used. When divalent iron ions are used as a starting material, the particle growth time can be made relatively long, so it is possible to control the particle shape, particle size, particle size distribution, etc. by adjusting the oxidation conditions, When other elements are added, there is a merit that each particle can be evenly substituted. Furthermore, it is possible to obtain single-phase particles that do not include a different phase, which are preferable precursor particles.
As a supply source of these iron ions or metal ions of substitution elements, it is preferable to use water-soluble inorganic acid salts such as nitrates, sulfates, and chlorides from the viewpoint of availability and cost. When these metal salts are dissolved in water, metal ions are dissociated and the aqueous solution becomes acidic. When this acidic aqueous solution containing metal ions is reacted with a hydroxide ion contained in a neutralizing agent described later, a mixture of iron oxyhydroxide and a hydroxide of a substitution element, or a part of Fe site is changed to another part. An iron oxyhydroxide substituted with a metal element is obtained.
The total metal ion concentration in the raw material solution is not particularly defined in the present invention, but is preferably 0.01 to 0.5 mol / L. If it is less than 0.01 mol / L, the amount of the iron-based oxide magnetic particle powder obtained by one reaction is small, which is economically undesirable. If the total metal ion concentration exceeds 0.5 mol / L, it is not preferable because the reaction solution is likely to gel due to rapid hydroxide precipitation.

[Neutralizer]
In the production method of the present invention, an alkaline aqueous solution is used as the neutralizing agent for the acidic raw material solution. The alkaline aqueous solution may be either an alkali metal or alkaline earth hydroxide aqueous solution or an aqueous solution containing an ammonium salt such as aqueous ammonia. It is preferable to use ammonia water in which impurities are less likely to remain.
Advantages of using ammonia water include the following in addition to the above. That is, since the aqueous ammonia is weakly alkaline, when it is reacted with the raw material solution in the neutralization treatment step, the rate of precipitation formation reaction is reduced, and rapid growth of secondary aggregated particles is suppressed. From the viewpoint of suppressing the growth of secondary agglomerated particles, and from the viewpoint of suppressing heterogeneous phase formation by buffer action (small pH change during the reaction), an aqueous solution in which ammonia water is partially neutralized by adding carbonate ions may be used as a neutralizing agent. More preferred. The addition of carbonate ions can be performed by blowing carbonate ions into ammonia water or by adding ammonium hydrogen carbonate.

[Neutralization process]
In the production method of the present invention, it is preferable that the raw material solution and the neutralizing agent are reacted in the presence of hydroxycarboxylic acid so that the pH of the reaction solution is 7.0 to 10.0. If the pH exceeds 10.0, it is not preferable because a heterogeneous phase such as magnetite is likely to be generated, and if it is less than 7.0, it is not preferable because other elements are not substituted or the yield decreases.
The neutralization treatment may be performed by adding a neutralizing agent to the raw material solution or adding the raw material solution to the neutralizing agent.
In addition, the value of pH described in this specification refers to a value measured using a glass electrode based on JIS Z8802. In this case, the measured value indicated by the pH meter calibrated using an appropriate pH standard solution corresponding to the pH range to be measured and compensated by the temperature compensation electrode is a value directly read under the reaction temperature condition.

[Hydroxycarboxylic acid]
In the production method of the present invention, hydroxycarboxylic acid is allowed to coexist in the neutralization treatment step. The reason for allowing the hydroxycarboxylic acid to coexist is to suppress excessive aggregation during the production of the precursor, as described in the section of [Precursor].
There are many types of hydroxycarboxylic acids such as glycolic acid, lactic acid, various hydroxybutyric acids, glyceric acid, malic acid, tartaric acid, citric acid, and mevalonic acid. Group hydroxycarboxylic acids are preferred, and citric acid is more preferred due to its price and availability.
The amount of hydroxycarboxylic acid added is preferably 0.01 to 0.5 in terms of a molar ratio with respect to the total amount of metal ions contained in the reaction solution. When the molar ratio is less than 0.01, the effect of addition of hydroxycarboxylic acid cannot be obtained, and when the molar ratio exceeds 0.5, the metal ions are complexed and the yield is lowered.
Hydroxycarboxylic acid may be added to either the raw material solution or the neutralizing agent.

[Coating process with silicon oxide]
In the method for producing an iron-based oxide magnetic particle powder of the present invention, in order to obtain an iron-based oxide magnetic particle powder using the precursor generated in the above steps, a silicon oxide is added to the precursor prior to heat treatment. Cover. This is because the precursor is unlikely to change into an ε-type iron-based oxide even if heat treatment is performed as it is. As a silicon oxide coating method, a sol-gel method is preferably applied. Here, the silicon oxide includes not only a stoichiometric composition but also a non-stoichiometric composition such as a silanol derivative described later.
In the case of the sol-gel method, an aqueous solution of iron oxyhydroxide crystals containing a substitution element dispersed by washing with water, a silicon compound having a hydrolytic group, such as tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), A silane compound such as a silane coupling agent is added to cause a hydrolysis reaction under stirring, and the surface of the iron oxyhydroxide crystal is coated with the produced silanol derivative. Further, an acid catalyst or an alkali catalyst may be added. It is preferable to add it in consideration of the treatment time. As a typical example, the acid catalyst is hydrochloric acid, and the alkali catalyst is ammonia. In the case of using an acid catalyst, it is necessary to limit the addition so that the iron oxyhydroxide particles containing the substitution element do not dissolve. In addition, it is also possible to use inorganic silicon compound sodium silicate (water glass).
In addition, the specific method about the coating | cover of a silicon oxide can be made to be the same as that of the sol-gel method in a well-known process. For example, the reaction temperature of the silicon oxide coating by the sol-gel method is 20 to 60 ° C., and the reaction time is about 1 to 20 hours. After being coated with silicon oxide, solid-liquid separation and drying are performed to obtain a sample before the heating process. Here, at the time of solid-liquid separation, solid-liquid separation may be performed after adding a flocculant such as ammonium sulfate.

[Heating process]
In the method for producing iron-based oxide magnetic particle powder of the present invention, an ε-type iron-based oxide is obtained by heat-treating the silicon oxide-coated precursor. Before the heat treatment, washing and drying steps may be provided. The heat treatment is performed in an oxidizing atmosphere, but the oxidizing atmosphere may be an air atmosphere. Heating can be performed in the range of approximately 700 to 1300 ° C., but when the heating temperature is high, α-Fe ₂ O ₃ (which is an impurity from ε-Fe ₂ O ₃ ), which is a thermodynamically stable phase, is easily generated. Therefore, the heat treatment is preferably performed at 900 to 1200 ° C, more preferably at 950 to 1150 ° C. The heat treatment time can be adjusted in the range of about 0.5 to 10 hours, but good results are easily obtained in the range of 2 to 5 hours. The presence of a silicon-containing substance covering the particles is considered to have an advantageous effect in causing a phase change to an ε-type iron-based oxide rather than a phase change to an α-type iron-based oxide. In addition, the silicon oxide coating has an action of preventing sintering during heat treatment of iron oxyhydroxide crystals containing a substitution element.
Through the above steps, an ε-Fe ₂ O ₃ crystal in which part of the Fe site is replaced with another metal ion is obtained in a state where silicon oxide is coated. The powder obtained after the heat treatment may contain α-type iron-based oxide, γ-type iron-based oxide, and Fe ₃ O ₄ crystal as impurities in addition to the ε-type iron-based oxide crystal. These are called iron-based oxide magnetic particle powders.
The iron-based oxide magnetic particle powder obtained by the production method of the present invention can be used in a state where it is coated with silicon oxide. It is also possible to use it in the removed state.

[Washing process]
In the method for producing iron-based oxide magnetic particle powder of the present invention, it is preferable to wash the slurry containing the precursor with water prior to the coating step with the silicon oxide. When the precursor is washed, the degree of aggregation of the secondary particles is reduced and a structure with more gaps is formed, so that the silanol derivative easily enters the gaps.
As the water washing method, a known method such as a water washing method using an ultrafiltration membrane or an ion exchange membrane or a water washing method using centrifugal separation can be used. In the case of washing with an ultrafiltration membrane, use a membrane having a molecular weight cut off so that particles do not escape to the filtrate side, and finish washing up to 50 mS / m or less, more preferably 10 mS / m or less in the electric conductivity of the filtrate. It is preferable to do. When there are many residual ions, there exists a problem that a heterogeneous phase is easy to produce.

[Silicon oxide coating removal process]
When the iron-based oxide magnetic particle powder does not require a silicon oxide coating or when classification is performed to improve the magnetic recording characteristics of the iron-based oxide magnetic particle powder, ε-Fe ₂ O ₃ The silicon oxide covering the crystal is removed. In coating-type magnetic recording medium applications, it is necessary to perform magnetic field orientation treatment on magnetic particles coated on a tape, and silicon oxide, which is a nonmagnetic component, increases in a state where silicon oxide is coated. For this reason, the amount of magnetization per unit area of the tape drops (the signal from the tape becomes weak), so that it is preferable to remove the silicon oxide that has been covered by a process described later. As a specific method, since silicon oxide is soluble in an alkaline aqueous solution, the powder after heat treatment is immersed in an aqueous solution in which a strong alkali such as NaOH or KOH is dissolved and dissolved and removed by stirring. it can. In order to increase the dissolution rate, the aqueous alkali solution may be heated. Typically, when an alkali such as NaOH is added in an amount of 3 times mol or more with respect to silicon oxide, and the powder is stirred in an aqueous solution temperature of 60 to 70 ° C., the silicon oxide can be dissolved well. . The degree of silicon oxide coating removal is appropriately adjusted according to the purpose.
After removal, in order to ensure good dispersibility in the next step, it is necessary to wash unnecessary ions with water until the electrical conductivity of the filtrate reaches ≦ 50 mS / m.

[Fiber probe observation]
The precursor obtained in the neutralization treatment step or the precursor after washing it with water was observed using a fiber probe in a slurry state without drying, and the average secondary particle size of the precursor was measured. . For the observation, a FPAR-1000K high-sensitivity specification manufactured by Otsuka Electronics Co., Ltd., and a diluted probe was used as the fiber probe. The measurement conditions were as follows: measurement time (seconds) 180 seconds, number of repetitions once, solvent setting water. The analysis mode was the Cumulant method.

[Transmission electron microscope (TEM) observation]
JEOL Ltd. (JEM-1011) was used for the TEM observation of the precursor of the iron-based oxide magnetic particle powder and the iron-based oxide magnetic particle powder obtained by the production method of the present invention.
Observation of the precursor of the iron-based oxide magnetic particle powder was performed using a TEM photograph taken at × 10,000 magnification and then enlarged three times during development. (Slurry, wet state used)
The iron-based oxide magnetic particle powder was photographed at a magnification of × 10,000 and × 100,000, and then evaluated for each characteristic using a TEM photograph enlarged three times during development (after removing the silicon oxide coating) Used).
For the measurement of the average particle diameter, digitization was used, and the distance between two points that were the most distant from one particle was measured. About 300 pieces or more were measured.

[Measurement of X-ray diffraction (XRD) pattern]
The obtained sample was subjected to powder X-ray diffraction (XRD: RINT2000 manufactured by Rigaku Corporation, radiation source CoKα ray, voltage 40 kV, current 30 mA, 2θ = 10 to 80 °). By this measurement, the crystallite size (X-ray average particle diameter) was calculated from Scherrer's formula using precursor phase confirmation, ε phase generation confirmation, heterophase confirmation, and a peak of 37 ° to 40 °.

[Composition analysis]
Composition analysis was performed with an ICP-720ES manufactured by Agilent. The measurement wavelength (nm) was Fe: 259.940 nm, Ga: 294.363 nm, Co: 230.786 nm, Ti: 336.122 nm, Si: 288.158 nm.

[Evaluation of magnetic properties]
An iron-based oxide magnetic particle powder sample is packed in a φ6 mm plastic container, and a coercive force Hc is applied with an external magnetic field of 795.8 kA / m (10 kOe) using a VSM device (VSM-P7) manufactured by Toei Industry Co., Ltd. (KA / m, Oe), saturation magnetization σs (Am ² / kg), squareness ratio SQ, coercive force distribution SFD (SFD value in powder bulk state) were measured.

[Measurement of specific surface area]
About the iron-type oxide magnetic particle powder sample, the specific surface area BET by the BET single point method was calculated | required using Yuasa Ionics Co., Ltd. 4-sorb U2.

[Example 1]
In a 5 L reactor, 3274.8 g of pure water, 549.4 g of Fe (NO ₃ ) ₃ .9H ₂ O (powder, purity 99.2 mass%), 148.0 g of a gallium (III) nitrate solution with a Ga concentration of 10.30 mass% , Co (NO ₃ ) ₂ .6H ₂ O (powder, purity 97 mass%) 12.4 g, Ti (SO ₄ ) ₂ .nH ₂ O (powder, n = 2 to 7, Ti concentration 15.2 mass%) 13. 0g and 17.3g of citric acid (powder, purity 99.5 mass%), dissolved in and mixed at 30 ° C in the atmosphere using a rotary stirrer (stirring blade) (hereinafter the same) Was used as a raw material solution (procedure 1). The molar ratio of the metal elements contained in this raw material solution is Fe: Ga: Co: Ti = 1.635: 0.265: 0.05: 0.05, and citric acid is based on the total amount of metal ions. 5 mol% is contained.
While stirring at 30 ° C. in the atmosphere, 22.6.5 mass% ammonia water (466.5 g) was added to the raw material solution over about 17.5 minutes, and then the stirring was continued for 30 minutes for neutralization. The reaction was allowed to proceed to obtain a precursor (Procedure 2).
The slurry in which the precursor obtained in the procedure up to the procedure 2 was dispersed was divided into two parts for use in other tests, and 470.5 g of tetraethoxysilane was added to one side over 35 minutes, and then 30 ° C. in the atmosphere. And stirring was continued for about 1 day, and the precursor was coated with a silanol derivative. Thereafter, a solution in which 88.9 g of ammonium sulfate was dissolved in 300 g of pure water was added, and the resulting solution was washed and solid-liquid separated, and the precursor coated with the silanol derivative was recovered as a cake (procedure 3).
After drying the precipitate obtained in step 3 (precursor coated with silanol derivative), the dried powder was subjected to heat treatment at 1065 ° C. for 4 hours in a furnace in an air atmosphere and coated with silicon oxide. An iron oxide magnetic particle powder was obtained. The silanol derivative changes to silicon oxide when heat-treated in an air atmosphere (Procedure 4).
The heat-treated powder obtained in the procedure 4 was stirred in a 20 mass% NaOH aqueous solution at 70 ° C. for 24 hours to remove the silicon oxide on the particle surface. Then, after centrifugal washing, solid-liquid separation, and drying, it was subjected to chemical analysis of composition, XRD measurement, TEM observation, measurement of magnetic properties, and the like (procedure 5).
As a result of chemical analysis, the molar ratio of the metal elements of the obtained iron oxide magnetic particle powder was almost the same as that at the time of preparation.
In FIG. 1, the TEM photograph of the precursor obtained by operation to the procedure 2 is shown. Here, the scale of the TEM image is shown in the photograph. The TEM image of the precursor obtained in this example is generally brighter than that of the precursor obtained in Comparative Example 1 described later, and the precursor obtained in this example transmits an electron beam. It can be seen that the amount of the substance is small, that is, the aggregate density of the secondary aggregate particles is small. The average secondary particle diameter of the precursor obtained by fiber probe observation is 2.35 μm, which is smaller than the 2.90 μm of the precursor obtained in Comparative Example 1. In Table 1, the average secondary particle diameter of the precursor obtained in the present Example is shown together with the average secondary particle diameter of the precursor obtained in Examples 2 to 8 and Comparative Example 1 described later.
Table 1 shows the average particle size and magnetic properties of the iron oxide-based magnetic particle powder obtained by the operations up to Procedure 5 in this example. Table 1 also shows the average particle diameter and magnetic properties of the iron oxide magnetic particles obtained in Examples 2 to 8 and Comparative Example 1 described later. The iron-based oxide magnetic particle powder obtained in this example had an Hc of 288.7 kA / m (3628 Oe) and an SFD of 1.356, which was better than the Hc of 254.6 kA / m (3199 Oe) and SFD of 1.609 in Comparative Example 1. Showed good magnetic properties.
As a result of measurement by XRD, all the precursors obtained in Examples 1 to 8 and Comparative Example 1 have a ferrihydrite structure, and all iron oxide magnetic particle powders are the same as ε-Fe ₂ O _3. It was shown to have a crystal structure of

[Comparative Example 1]
In a 5 L reactor, 3282 g of pure water, 550.5 g of Fe (NO ₃ ) ₃ .9H ₂ O (powder, purity 99 mass%), 137.9 g of a gallium (III) nitrate solution having a Ga concentration of 11.05 mass%, Co (NO _{3) 2} · 6H ₂ O (powder, purity 98mass%) 12.3g, and placed _{Ti (SO 4) 2 · nH} 2 O ( powder, n = 2 to 7, the Ti concentration 15.2mass%) 13.3g Then, the mixture was stirred at 30 ° C. in the atmosphere and dissolved and mixed to obtain a raw material solution (procedure 1). The molar ratio of the metal elements contained in this raw material solution is the same as in Example 1, and citric acid is not contained.
While stirring at 30 ° C. in the atmosphere, 22.5.4 mass% ammonia water (445.4 g) was added to the raw material solution over about 17.5 minutes, and then the stirring was continued for 30 minutes for neutralization. The reaction was allowed to proceed to obtain a precursor (Procedure 2).
After adding 961.8 g of tetraethoxysilane over 35 minutes to the slurry in which the precursor obtained in the procedure up to procedure 2 was dispersed, stirring was continued at 30 ° C. in the atmosphere for about 1 day, and the precursor was converted with a silanol derivative. Covered. Thereafter, the obtained slurry was washed and solid-liquid separated, and the precursor coated with the silanol derivative was recovered as a cake (procedure 3).
The operations after step 3 are the same as those in the first embodiment.
FIG. 2 shows a TEM photograph of the precursor obtained in Comparative Example 1, and Table 1 shows the average secondary particle diameter of the precursor, the average particle diameter of the iron oxide-based magnetic particle powder, and the magnetic characteristics. As described above, in Comparative Example 1, a dense precursor was obtained as compared with Example 1, and the magnetic properties of the iron oxide-based magnetic particle powder were inferior to those obtained in Example 1. It was.

[Example 2]
In a 5 L reactor, 3281.1 g of pure water, 549.4 g of Fe (NO ₃ ) ₃ .9H ₂ O (powder, purity 99.2 mass%), 142.5 g of a gallium (III) nitrate solution having a Ga concentration of 10.70 mass% , Co (NO ₃ ) ₂ .6H ₂ O (powder, purity 97 mass%) 12.4 g, Ti (SO ₄ ) ₂ .nH ₂ O (powder, n = 2 to 7, Ti concentration 15.2 mass%) 13. 0 g and 34.7 g of citric acid (powder, purity 99.5 mass%) were added, stirred at 30 ° C. in the atmosphere, and dissolved and mixed to obtain a raw material solution (procedure 1). The molar ratio of the metal elements contained in this raw material solution is the same as in Example 1, and citric acid is contained at 10 mol% with respect to the total amount of metal ions.
While stirring at 30 ° C. in the atmosphere, 464.4 g of 22.19 mass% ammonia water was added to the raw material solution over about 17.5 minutes, followed by neutralization by continuing stirring for 30 minutes. The reaction was allowed to proceed to obtain a precursor (Procedure 2). At this point, the volume of the mixed solution is 4180 mL.
After 500 mL was sampled from the slurry in which the precursor obtained in the procedure up to step 2 was dispersed for use in other tests, ¼ of the remaining mixture was put in a 5 L reaction vessel, and the liquid volume was reduced to 4000 mL. While adding pure water so that the mixture is stirred at 30 ° C. in the atmosphere, 110.1 g of 22.09 mass% ammonia water is added, and 222.3 g of tetraethoxysilane is added over 35 minutes. Stirring was continued for about 1 day at 0 ° C., and the precursor was coated with a silanol derivative. Thereafter, a solution in which 188.2 g of ammonium sulfate was dissolved in 300 g of pure water was added, and the resulting solution was washed and solid-liquid separated, and the precursor coated with the silanol derivative was recovered as a cake (procedure 3).
The operations after step 3 are the same as those in the first embodiment.
Table 1 shows the average secondary particle diameter of the precursor obtained in Example 2, the average particle diameter of the iron oxide magnetic particle powder, and the magnetic properties. The average secondary particle size of the precursor obtained in Example 2 is smaller than that of Comparative Example 1, and the magnetic properties (coercivity, SFD) of the iron oxide-based magnetic particle powder are also larger than those of Comparative Example 1. Was also excellent.

[Example 3]
206.4 g of an iron (II) sulfate solution having an Fe concentration of 5.42 mass%, 20.5 g of a gallium (III) nitrate solution having an Ga concentration of 11.05 mass%, and cobalt (II) sulfate having a Co concentration of 5.10 mass% To a mixed solution of 7.1 g of solution, 2.0 g of Ti (SO ₄ ) ₂ .nH ₂ O (powder, n = 2 to 7, Ti concentration 15.2 mass%) was added and dissolved to obtain a raw material solution. (Procedure 1). The molar ratio of the metal elements contained in this raw material solution is the same as in Example 1.
In advance, 3058.3 g of pure water, 214.3 g of 22.35 mass% aqueous ammonia, and 2.6 g of citric acid (powder, purity 99.5 mass%) were mixed in a 5 L reactor, and the mixture was mixed with nitrogen (N ₂ ) While stirring in an atmosphere at 40 ° C., 32.9 L of carbon dioxide (CO ₂ ) was blown in over 30 minutes into the neutralizer solution prepared and stirred at 40 ° C. in a nitrogen (N ₂ ) atmosphere. After adding the raw material solution over 60 seconds, stirring was continued for 50 minutes to carry out a neutralization reaction. Subsequently, after raising the temperature of the mixture to 60 ° C. over 45 minutes, an oxidizing agent prepared by mixing 9.7 g of 35 mass% hydrogen peroxide water with 63.3 g of pure water was added over 130 minutes, and iron ( II) was oxidized to iron (III) (Procedure 2). At this point, the volume of the mixed solution is 3572 mL. In addition, 5 mol% of citric acid is contained in the mixed solution of the raw material solution and the neutralizing agent with respect to the total amount of metal ions.
After sampling 1000 mL from the slurry in which the precursor obtained in the procedure up to procedure 2 was dispersed, 100.6 g of tetraethoxysilane was added to the remaining slurry over 35 minutes, and then stirred at 30 ° C. in the atmosphere for about 1 day. Continuing, the precursor was coated with a silanol derivative. Thereafter, the obtained slurry was washed and solid-liquid separated, and the precursor coated with the silanol derivative was recovered as a cake (procedure 3).
The operations after step 3 are the same as those in the first embodiment.
FIG. 3 shows a TEM photograph of the precursor obtained in Example 3, and Table 1 shows the average secondary particle diameter of the precursor, the average particle diameter of the iron oxide-based magnetic particle powder, and the magnetic characteristics. In Example 3, a precursor thinner than that of Comparative Example 1 was obtained, and the average secondary particle size was smaller than that of Comparative Example 1, and the magnetic properties (coercivity, SFD) of the iron oxide-based magnetic particle powder were obtained. ) Was also superior to that of Comparative Example 1.

[Example 4]
95.6 g of iron (III) sulfate solution with an Fe concentration of 11.7 mass%, 21.2 g of gallium (III) nitrate solution with a Ga concentration of 10.70 mass%, and cobalt (II) sulfate with a Co concentration of 5.10 mass% To a mixed solution of 7.1 g of solution, 2.0 g of Ti (SO ₄ ) ₂ .nH ₂ O (powder, n = 2 to 7, Ti concentration 15.2 mass%) was added and dissolved to obtain a raw material solution. (Procedure 1). The molar ratio of the metal elements contained in this raw material solution is the same as in Example 1.
In a 5 L reactor, 3153.2 g of pure water, 216.8 g of 22.09 mass% aqueous ammonia, and 2.6 g of citric acid (powder, purity 99.5 mass%) were mixed and the mixture was mixed with nitrogen (N ₂ ) While stirring in an atmosphere at 40 ° C., 32.9 L of carbon dioxide (CO ₂ ) was blown in over 30 minutes into the neutralizer solution prepared and stirred at 40 ° C. in a nitrogen (N ₂ ) atmosphere. After adding the raw material solution over 60 seconds, stirring was continued for 50 minutes to carry out a neutralization reaction. Subsequently, the temperature of the mixture was raised to 60 ° C. over 45 minutes, and stirring was continued at that temperature for 130 minutes (procedure 2). At this point, the volume of the mixed solution is 3350 mL. In addition, 5 mol% of citric acid is contained in the mixed solution of the raw material solution and the neutralizing agent with respect to the total amount of metal ions.
After sampling 1000 mL from the slurry in which the precursor obtained in the procedure up to Step 2 was dispersed, 92.0 g of tetraethoxysilane was added to the remaining slurry over 35 minutes, and then stirred at 30 ° C. in the atmosphere for about 1 day. Continuing, the precursor was coated with a silanol derivative. Thereafter, the obtained slurry was washed and solid-liquid separated, and the precursor coated with the silanol derivative was recovered as a cake (procedure 3).
The operations after step 3 are the same as those in the first embodiment.
Table 1 shows the average secondary particle diameter of the precursor obtained in Example 4, the average particle diameter of the iron oxide magnetic particle powder, and the magnetic properties. The average secondary particle size of the precursor obtained in Example 4 is smaller than that of Comparative Example 1, and the magnetic properties (coercivity, SFD) of the iron oxide-based magnetic particle powder are also larger than those of Comparative Example 1. Was also excellent.

[Example 5]
47.8 g of iron (III) sulfate solution with an Fe concentration of 11.7 mass%, 103.4 g of iron (II) sulfate solution with an Fe concentration of 5.41 mass%, and gallium (III) nitrate solution with an Ga concentration of 10.70 mass% To a mixed solution of 21.2 g and a cobalt (II) sulfate solution (7.1 g) with a Co concentration of 5.10 mass%, Ti (SO ₄ ) ₂ .nH ₂ O (powder, n = 2 to 7, Ti concentration 15. 2 mass%) 2.0 g was added and dissolved to obtain a raw material solution (procedure 1). The molar ratio of the metal elements contained in this raw material solution is the same as in Example 1.
In advance, 3104.0 g of pure water, 216.8 g of 22.09 mass% aqueous ammonia, and 2.6 g of citric acid (powder, purity 99.5 mass%) were mixed in a 5 L reactor, and the mixture was mixed with nitrogen (N ₂ ) While stirring in an atmosphere at 40 ° C., 32.9 L of carbon dioxide (CO ₂ ) was blown in over 30 minutes into the neutralizer solution prepared and stirred at 40 ° C. in a nitrogen (N ₂ ) atmosphere. After adding the raw material solution over 60 seconds, stirring was continued for 50 minutes to carry out a neutralization reaction. Subsequently, after raising the temperature of the mixture to 60 ° C. over 45 minutes, an oxidizing agent prepared by mixing 2.9 g of 35 mass% hydrogen peroxide water with 31.6 g of pure water was added over 130 minutes, and iron ( II) was oxidized to iron (III) (Procedure 2). At this point, the volume of the mixed solution is 3370 mL. In addition, 5 mol% of citric acid is contained in the mixed solution of the raw material solution and the neutralizing agent with respect to the total amount of metal ions.
After sampling 1000 mL from the slurry in which the precursor obtained in the procedure up to Step 2 was dispersed, 93.7 g of tetraethoxysilane was added to the remaining slurry over 35 minutes, and then stirred at 30 ° C. in the atmosphere for about 1 day. Continuing, the precursor was coated with a silanol derivative. Thereafter, the obtained slurry was washed and solid-liquid separated, and the precursor coated with the silanol derivative was recovered as a cake (procedure 3).
The operations after step 3 are the same as those in the first embodiment.
Table 1 shows the average secondary particle size of the precursor obtained in Example 5, the average particle size of the iron oxide magnetic particle powder, and the magnetic properties. The average secondary particle diameter of the precursor obtained in Example 5 is smaller than that of Comparative Example 1, and the magnetic properties (coercivity, SFD) of the iron oxide-based magnetic particle powder are also larger than those of Comparative Example 1. Was also excellent.

[Example 6]
206.8 g of an iron (II) sulfate solution having an Fe concentration of 5.41 mass% is prepared as a raw material solution 1 and separately from that, 10.6 g of pure water is added to gallium nitrate (III) having a Ga concentration of 10.70 mass%. 21.2 g of solution, 7.1 g of cobalt (II) sulfate solution having a Co concentration of 5.10 mass%, and Ti (SO ₄ ) ₂ .nH ₂ O (powder, n = 2 to 7, Ti concentration of 15.2 mass%) 1 A solution in which 0.9 g was added and dissolved was prepared as raw material solution 2 (procedure 1). The molar ratio of the metal elements contained in the raw material solution 1 and the raw material solution 2 as a whole is the same as in Example 1.
In advance, 3076.1 g of pure water, 216.8 g of 22.09 mass% aqueous ammonia, and 5.2 g of citric acid (powder, purity 99.5 mass%) were mixed in a 5 L reactor, and the mixture was mixed with nitrogen (N ₂ ) While stirring at 60 ° C. in the atmosphere, 32.9 L of carbon dioxide (CO ₂ ) was blown in over 30 minutes, and the mixture was stirred at 60 ° C. in a nitrogen (N ₂ ) atmosphere. Was added over 60 seconds, and stirring was continued for 95 minutes to carry out a neutralization reaction. Subsequently, air as an oxidizing agent was blown into the mixed solution to which the raw material solution 1 was added for 65 minutes at a flow rate of 93.2 mL / min to oxidize iron (II) to iron (III), and the above raw material solution 2 was added to 65 The mixture was continuously added over a period of time, and after completion of the addition, the mixed solution was kept for 40 minutes (procedure 2). When the addition of the raw material solution 2 is finished, citric acid is contained in an amount of 10 mol% with respect to the total amount of metal ions.
After sampling 1000 mL from the slurry in which the precursor obtained in the procedure up to Step 2 was dispersed, 94.9 g of tetraethoxysilane was added to the remaining slurry over 35 minutes, and then stirred at 30 ° C. in the atmosphere for about 1 day. Continuing, the precursor was coated with a silanol derivative. Thereafter, a solution in which 136.1 g of ammonium sulfate was dissolved in 300 g of pure water was added, and the resulting slurry was washed and solid-liquid separated, and the precursor coated with the silanol derivative was recovered as a cake (procedure 3).
The operations after step 3 are the same as those in the first embodiment.
A TEM photograph of the precursor obtained in Example 6 is shown in FIG. 4, and the average secondary particle diameter of the precursor, the average particle diameter of the iron oxide-based magnetic particle powder, and the magnetic properties are shown in Table 1. In Example 6, a precursor thinner than that of Comparative Example 1 was obtained, and the average secondary particle diameter was smaller than that of Comparative Example 1, and the magnetic properties (coercive force, SFD) of the iron oxide-based magnetic particle powder were obtained. ) Was also superior to that of Comparative Example 1.

[Example 7]
In a 5 L reactor, 3281.1 g of pure water, 549.4 g of Fe (NO ₃ ) ₃ .9H ₂ O (powder, purity 99.2 mass%), 142.5 g of a gallium (III) nitrate solution having a Ga concentration of 10.70 mass% , Co (NO ₃ ) ₂ .6H ₂ O (powder, purity 97 mass%) 12.4 g, Ti (SO ₄ ) ₂ .nH ₂ O (powder, n = 2 to 7, Ti concentration 15.2 mass%) 13. 0 g and 34.7 g of citric acid (powder, purity 99.5 mass%) were added, stirred at 30 ° C. in the atmosphere, and dissolved and mixed to obtain a raw material solution (procedure 1). The molar ratio of the metal elements contained in this raw material solution is the same as in Example 1, and citric acid is contained at 10 mol% with respect to the total amount of metal ions.
While stirring at 30 ° C. in the atmosphere, 464.4 g of 22.19 mass% ammonia water was added to the raw material solution over about 17.5 minutes, followed by neutralization by continuing stirring for 30 minutes. The reaction was allowed to proceed to obtain a precursor (Procedure 2-1).
After sampling 500 mL from the slurry containing the precursor obtained in the procedure 2-1, the remaining half of the mixed solution was filtered with an ultrafiltration membrane and a membrane with a UF fraction molecular weight of 50,000. Washing was performed to a conductivity of 16 mS / m (procedure 2-2).
Half of the slurry obtained by washing the slurry in which the precursor obtained in the procedure up to Step 2-2 is dispersed is collected and placed in a 5 L reaction tank, and pure water is added so that the liquid volume becomes 4000 mL. While stirring at ℃, 22.01 mass% of ammonia water (110.1 g) was added, and then tetraethoxysilane (222.3 g) was added over 35 minutes, and then the stirring was continued in the atmosphere at 30 ℃ for about 1 day. The body was coated with a silanol derivative. Thereafter, a solution in which 188.2 g of ammonium sulfate was dissolved in 300 g of pure water was added, and the resulting solution was washed and solid-liquid separated, and the precursor coated with the silanol derivative was recovered as a cake (procedure 3).
The operations after step 3 are the same as those in the first embodiment.
Table 1 shows the average secondary particle diameter of the precursor obtained in Example 7, the average particle diameter of the iron oxide magnetic particle powder, and the magnetic properties. A TEM photograph of the iron oxide magnetic particle powder is shown in FIG. The average secondary particle diameter of the precursor obtained in Example 7 is smaller than that of Comparative Example 1, and the magnetic properties (coercivity, SFD) of the iron oxide-based magnetic particle powder are also larger than those of Comparative Example 1. Was also excellent.

[Example 8]
205.6 g of an iron (II) sulfate solution having an Fe concentration of 5.44 mass% is prepared as a raw material solution 1, and separately from that, 125.5 g of pure water is added to gallium (III) nitrate having a Ga concentration of 10.30 mass%. 22.0 g of solution, 7.5 g of cobalt (II) sulfate solution having a Co concentration of 4.83 mass%, and Ti (SO ₄ ) ₂ .nH ₂ O (powder, n = 2 to 7, Ti concentration of 15.2 mass%) 1 A solution in which 0.9 g was added and dissolved was prepared as raw material solution 2 (procedure 1). The molar ratio of the metal elements contained in the raw material solution 1 and the raw material solution 2 as a whole is the same as in Example 1.
In a 5 L reactor, 3077.1 g of pure water, 216.8 g of 22.09 mass% aqueous ammonia, and 5.2 g of citric acid (powder, purity 99.5 mass%) were mixed and the mixture was mixed with nitrogen (N ₂ ) While stirring at 60 ° C. in the atmosphere, 32.9 L of carbon dioxide (CO ₂ ) was blown in over 30 minutes, and the mixture was stirred at 60 ° C. in a nitrogen (N ₂ ) atmosphere. Was added over 60 seconds, and stirring was continued for 95 minutes to carry out a neutralization reaction. Subsequently, air as an oxidizing agent was blown into the mixed solution to which the raw material solution 1 was added for 65 minutes at a flow rate of 93.2 mL / min to oxidize iron (II) to iron (III), and the raw material solution 2 was added for 65 minutes. The mixture solution was continuously added over 40 minutes after the addition was completed (procedure 2-1). When the addition of the raw material solution 2 is finished, citric acid is contained in an amount of 10 mol% with respect to the total amount of metal ions.
After sampling 1000 mL from the slurry containing the precursor obtained in the procedure 2-1, the remaining mixed solution was filtered with an ultrafiltration membrane and a membrane having a UF fraction molecular weight of 50,000, and the conductivity of the washing slurry was 28.7 mS / (Procedure 2-2).
Half of the washed slurry obtained in the procedure up to step 2-2 was collected and placed in a 5 L reactor, and 69.0 g of 22.09 mass% ammonia water was added while stirring at 30 ° C. in the atmosphere. Subsequently, 50.8 g of tetraethoxysilane was added over 35 minutes, and then stirring was continued in the atmosphere at 30 ° C. for about 1 day to coat the precursor with a silanol derivative. Thereafter, a solution in which 184.8 g of ammonium sulfate was dissolved in 300 g of pure water was added, and the resulting solution was washed and solid-liquid separated, and the precursor coated with the silanol derivative was recovered as a cake (procedure 3).
The operations after step 3 are the same as those in the first embodiment.
FIG. 6 shows a TEM photograph of the precursor obtained in Example 8, and Table 1 shows the average secondary particle diameter of the precursor, the average particle diameter of the iron oxide-based magnetic particle powder, and the magnetic properties. In Example 8, a precursor thinner than that of Comparative Example 1 was obtained, and the average secondary particle size was smaller than that of Comparative Example 1, and the magnetic properties (coercive force, SFD) of the iron oxide-based magnetic particle powder were obtained. ) Was also superior to that of Comparative Example 1.

Claims (10)

A method for producing a precursor of an iron-based oxide magnetic particle powder in which a part of an Fe site of ε-Fe ₂ O ₃ is substituted with another metal element, which is a divalent solution in an aqueous solution in the presence of hydroxycarboxylic acid. An iron-based oxide comprising a neutralization treatment step in which one or more selected from iron ions and trivalent iron ions, a substituted metal ion, and a neutralizing agent are reacted to adjust the pH to 7.0 to 10.0 A method for producing a precursor of magnetic particle powder.   The method for producing a precursor of iron-based oxide magnetic particle powder according to claim 1, wherein the hydroxycarboxylic acid is citric acid.   The method for producing a precursor of iron-based oxide magnetic particle powder according to claim 1, wherein the neutralizing agent is an aqueous solution containing ammonium ions or an aqueous solution obtained by adding carbonate ions to an aqueous solution containing ammonium ions.   4. The method according to claim 1, wherein the neutralization treatment step is a reaction between an acidic aqueous solution containing trivalent iron ions and substituted metal ions and a neutralizing agent in an aqueous solution in the presence of hydroxycarboxylic acid. A method for producing a precursor of the iron-based oxide magnetic particle powder according to claim 1.   In the neutralization treatment step, an acidic aqueous solution containing a divalent iron ion and a trivalent iron ion or a divalent iron ion and a substituted metal ion and a neutralizing agent in an aqueous solution in the presence of a hydroxycarboxylic acid. The method for producing a precursor of an iron-based oxide magnetic particle powder according to any one of claims 1 to 3, wherein divalent iron is oxidized after the reaction.   In the neutralization treatment step, after reacting an acidic aqueous solution containing divalent iron ions with a neutralizing agent in an aqueous solution in the presence of hydroxycarboxylic acid, the substituted metal ion is oxidized while oxidizing the divalent iron. The manufacturing method of the precursor of the iron-type oxide magnetic particle powder of any one of Claim 1 to 3 which adds the acidic aqueous solution to contain. A method for producing an iron-based oxide magnetic particle powder containing, as magnetic particles, an iron-based oxide in which a part of the Fe site of ε-Fe ₂ O ₃ is substituted with another metal element,
A step of coating silicon oxide on a precursor obtained by the method for producing a precursor of iron-based oxide magnetic particle powder according to any one of claims 1 to 6,
A method for producing iron-based oxide magnetic particle powder, comprising heating the precursor coated with silicon oxide to form iron oxide containing a substituted metal element coated with silicon oxide. A method for producing an iron-based oxide magnetic particle powder containing, as magnetic particles, an iron-based oxide in which a part of the Fe site of ε-Fe ₂ O ₃ is substituted with another metal element,
Washing the precursor obtained by the method for producing a precursor of iron-based oxide magnetic particle powder according to any one of claims 1 to 6;
Coating the water-washed precursor with silicon oxide;
A method for producing iron-based oxide magnetic particle powder, comprising heating the precursor coated with silicon oxide to form iron oxide containing a substituted metal element coated with silicon oxide.   The manufacturing method of the iron-type oxide magnetic particle powder of any one of Claim 7 or 8 including the process of removing the silicon oxide which has coat | covered the iron oxide containing the said substitution metal element. Iron oxide _{ε-A x B y C z} Fe 2-xyz O 3 ( provided that, A is Co, Ni, Mn, 1 or more divalent metal element selected from Zn, B is Ti, Sn One or more tetravalent metal elements selected from C, C is one or more trivalent metal elements selected from In, Ga, and Al, and 0 <x, y, z <1) Item 10. The method for producing an iron-based oxide magnetic particle powder according to any one of Items 7 to 9.