TWI761154B - Iron-based oxide magnetic powder, and green compact and radio wave absorber using the same - Google Patents

Abstract

An objective of this invention is to provide an iron-based oxide magnetic powder having excellent thermal stability and small variation in radio wave absorption even in a high temperature environment, which is composed of ε-iron oxide particles with a part of Fe sites being replaced by other metal elements, a radio wave absorber using the iron-based oxide magnetic powder, a green compact using the iron-based oxide magnetic powder, and a method for manufacturing the same.

According to the present invention, an iron-based oxide magnetic powder having excellent thermal stability and small variation in radio wave absorption even in a high temperature environment, which is composed of ε-iron oxide particles with a part of Fe sites being replaced by other metal elements, is obtained by coexisting of phosphorus-containing ions when a precipitate of iron hydroxide containing substituting metal elements, which is produced by neutralizing an acidic aqueous solution containing trivalent iron ions and metal ions for replacing a part of Fe sites, is coated with silicon oxide by using a silane compound

Description

Iron-based oxide magnetic powder, and powder compact and radio wave absorber obtained by using the magnetic powder

The present invention relates to iron-based oxide magnetic powders suitable for high-density magnetic recording media, radio wave absorbers, and the like, and particularly to magnetic powders excellent in thermal stability.

ε-Fe ₂ O ₃ is an extremely rare phase in iron oxide, however, at room temperature, due to the nano ^- sized particles exhibit a huge coercivity ( Hc), therefore, the production method of synthesizing ε-Fe ₂ O ₃ in a single phase has been gradually studied in the past (Patent Document 1, Non-Patent Documents 1 and 2). In addition, when ε-Fe ₂ O ₃ is used in a magnetic recording medium, at present, there is no material for a magnetic head having a high level of saturation magnetic flux density corresponding to it, so Al, Ga, In, etc. are also used. A trivalent metal is used to replace a part of the Fe site of ε-Fe ₂ O ₃ to adjust the coercive force, and the relationship between the coercive force and the radio wave absorption characteristics is also being investigated (Patent Document 2, Non-Patent Documents 3 to 6).

On the other hand, in the field of magnetic recording, the development of a magnetic recording medium with a high ratio of reproduction signal level to particle noise (C/N ratio: Carrier to Noise Ratio) is underway, and in order to achieve high recording density The miniaturization of the magnetic particles constituting the magnetic recording layer is required. However, in general, the miniaturization of magnetic particles tends to lead to deterioration of the environmental stability and thermal stability, and there is a concern that the magnetic properties of the magnetic particles in the use or storage environment will decrease. In Patent Document 3, it is disclosed that a compound with the general formula ε-A _x By Fe _{2-xy O 3} or ε-A _{x By C z Fe 2-xyz} O ₃ (here, A, B, and C are excluded) The different metals of Fe, represented by 0<x, y, z<1), are magnetic iron oxide particles with ε-Fe ₂ O ₃ as the main phase, which have high Hc and high Curie point, and can control these Magnetic materials with magnetic properties and without the use of scarce or expensive raw materials. In addition, in this specification, the iron-based oxide magnetic powder having the same crystal structure as ε-Fe ₂ O ₃ and a part of its Fe site substituted by other metal elements is described as ε-type iron-based oxide magnetic powder in the following. pink.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2008-174405

[Patent Document 2] Japanese International Publication No. 2008/029861

[Patent Document 3] Japanese International Publication No. 2008/149785

[Non-patent literature]

[Non-Patent Document 1] J. Jin, S. Ohkoshi, K. Hashimoto, Adv. Mater., 16, 48-51 (2004).

[Non-Patent Document 2] S. Ohkoshi, A. Namai, K.Imoto, M. Yoshikiyo, W. Tarora, K. Nakagawa, M. Komine, Y. Miyamoto, T. Nasu, S. Oka and H. Tokoro, Scientific Reports, 5, 14414 (2015).

[Non-Patent Document 3] S. Ohkoshi, S. Kuroki, S. Sakurai, K. Matsumoto, K. Sato and S. Sasaki, Angew. Chem. Int. Ed., 46, 8392-8395 (2007).

[Non-Patent Document 4] A. Namai, S. Sakurai, M. Nakajima, T. Suemoto, K. Matsumoto, M. Goto, S. Sasaki and S. Ohkoshi, J. Am. Chem. Soc., 131, 1170 -1173 (2009).

[Non-Patent Document 5] A. Namai, M. Yoshikiyo, K. Yamada, S. Sakurai, T. Goto, T. Yoshida, T. Miyazaki, M. Nakajima, T. Suemoto, H. Tokoro and S. Ohkoshi, Nature Communications, 3, 1035/1-6 (2012).

[Non-Patent Document 6] A. Namai, K. Ogata, M. Yoshikiyo and S. Ohkoshi, Broadband-millimeter-wave absorber based on ε -(Ti ^IV Co ^II ) _x Fe ^III _2-2x O ₃ for advanced driver assistance systems, Bull. Chem. Soc. Jpn., 93, 20-25 (2020).

The ε-type iron-based oxide magnetic powder described in Patent Document 3 has a high Curie point, but the coercive force changes in a high-temperature environment such as 60°C or higher, and when used as a magnetic material in a high-temperature environment , which sometimes causes problems. That is, when the ε-type iron-based oxide magnetic powder is used as a radio wave absorbing material, if the coercive force changes in a high temperature environment, there is a problem that the radio wave absorption amount also changes.

The production method of the ε-type iron-based oxide magnetic powder disclosed in Patent Document 3 is to coat the precursor of the iron-based oxide magnetic powder with a silane derivative by using a sol-gel method, and then sintering to obtain the ε-type iron-based magnetic powder. The method of oxide magnetic powder, the precursor of the iron-based oxide magnetic powder is obtained by using reverse micelle or water-based reaction solution by replacing Fe with two or three different metal ions. part. However, the thermal stability of the ε-type iron-based oxide magnetic powder obtained by this conventional method is not necessarily satisfactory as described above, and thus a thermal stability from normal temperature to about 90°C is required. ε-type iron-based oxide magnetic powder with little change in radio wave absorption under high temperature environment, radio wave absorber using the iron-based oxide magnetic powder, and powder compact using the iron-based oxide magnetic powder, and a method for producing the same .

The inventors of the present invention have conducted various investigations, and as a result, have found that when a hydrolysis product of a silane compound is coated with hydrogen containing a substituted metal at an Fe site, which is a precursor of an ε-type iron-based oxide magnetic powder, by a sol-gel method ε-type iron oxides with good thermal stability and small changes in radio wave absorption even in high temperature environments can be obtained by coexisting phosphorus-containing ions in the reaction solution in the case of a precipitate of iron hydroxide as an oxide. magnetic powder, thus completing the present invention described below.

In order to solve the above-mentioned problems, in the present invention,

To provide an iron-based oxide magnetic powder, which is composed of ε iron oxide particles in which a part of the Fe site is substituted by other metal elements, and the absolute value of ΔF ₉₀ ℃ defined by the following formula (1) is 3.0 Below GHz,

△F ₉₀ ℃=F ₉₀ ℃-F ₃₀ ℃...(1)

Here, F ₉₀ ° C. and F ₃₀ ° C. are, respectively, for a cylindrical powder body with a diameter of 13 mm obtained by press-molding 1.2 g of the iron-based oxide magnetic powder at 28 MPa, using the terahertz method. time domain spectroscopy) and in the transmission attenuation spectrum measured in the frequency range 50 to 100 GHz, the frequency showing the maximum transmission attenuation at the measurement temperature of 90 °C is F ₉₀ °C, and the maximum penetration attenuation at the measurement temperature of 30 °C is F 90 °C. The frequency of transmission attenuation is F ₃₀ ℃.

The metal element that replaces a part of the Fe site is preferably one or more selected from Ti, Co, Ga, and Al, and more preferably Ti, Co, and Ga.

Further, in the present invention, a powder compact composed of the iron-based oxide magnetic powder described above is provided.

Moreover, in this invention, the radio wave absorber which disperse|distributed the said iron-type oxide magnetic powder in resin or rubber is provided.

Furthermore, in the present invention, there is provided a method for producing a powder compact in which the iron-based oxide magnetic powder is compression-molded to obtain a powder compact.

By using the production method of the present invention, an ε-type iron-based oxide magnetic powder having good thermal stability and little change in the amount of radio wave absorption can be obtained even in a high-temperature environment.

1 is a megahertz time-domain spectroscopic spectrum of the iron-based oxide magnetic powder obtained in Comparative Example 1.

FIG. 2 is a megahertz time-domain spectroscopic spectrum of the iron-based oxide magnetic powder obtained in Example 1. FIG.

[Iron oxide magnetic powder]

The production method of the present invention is a method for producing an ε-type iron-based oxide magnetic powder excellent in thermal stability, and the obtained ε-type iron-based oxide is exemplified as follows.

It is represented by the general formula ε-C _z Fe _2-z O ₃ (here, C is Ga or Al).

It is represented by the general formula ε-A _x By Fe _{2-xy O 3} (here, A is Co and B is Ti).

It is represented by the general formula ε-A _{x By C z Fe 2-xyz} O ₃ (here, A is Co, B is Ti, and C is Ga or Al).

It is preferable to contain Ti or Co, which has the effect of improving the heat resistance of the iron-based oxide magnetic powder, as an element substituted for the Fe site. From the viewpoint of maintaining high thermal stability and the coercive force of the magnetic particles at room temperature, it is particularly preferable to simultaneously substitute with two elements of Ti and Co. In addition to thermal stability and coercivity control, the three-element substitution type also has the advantage of being easy to obtain the same space group as ε-Fe ₂ O ₃ , so the element to replace the Fe site is preferably selected from Ti, Co, Ga and at least one of Al, more preferably Ti, Co, and Ga.

The preferable ranges of the substitution amounts x, y and z of the tri-element substituted body are as follows.

x and y can take any range of 0<x<1 and 0<y<1, but in order to obtain ε iron oxide with excellent thermal stability, the composition must be controlled, so it is preferable to set it as 0.01≦x≦0.5, 0.01≦ y≦0.5. From the viewpoint of coercive force control and availability of a single phase, it is more preferable to set it in the range of 0.01≦x≦0.2 and 0.01≦y≦0.2. z is also the same as x and y, and it suffices to be in the range of 0<z<1, but from the viewpoint of control of thermal stability and easy availability of a single phase, it is preferably in the range of 0<z≦0.5 .

The average particle diameter is preferably 70 nm or less, particularly preferably 50 nm or less. When it exceeds 70 nm, the absorption amount becomes small when used as a radio wave absorber. In addition, the lower limit of the average particle diameter is not particularly limited, and the iron-based oxide magnetic powder having an average particle diameter of about 20 nm or more can be obtained by the production method of the present invention.

From the viewpoint of securing the absorption amount when used as a radio wave absorber, the BET specific surface area of the iron-based oxide magnetic powder of the present invention is preferably 35 m ² /g or less. The lower limit of the BET specific surface area is not particularly limited, but by the production method of the present invention, an iron-based oxide magnetic powder having a BET specific surface area of about 13 m ² /g or more can be obtained.

In the iron-based oxide magnetic powder of the present invention, in addition to ε-type iron-based oxide crystals, α-type iron-based oxides, γ-type iron-based oxides, and Fe ₃ O ₄ crystals may also be present as impurities. , including these are called iron-based oxide magnetic powders.

[Pressed powder and radio wave absorber]

The iron-based oxide magnetic powder obtained by the present invention functions as a radio wave absorber having excellent radio wave absorption ability by forming the filled structure of the powder particles. The filled structure here means that each particle forms a three-dimensional structure in a state in which the particles are in contact or close to each other. The filling structure must be maintained for the practical use of the electric wave absorber. Examples of this method include a method of compression molding iron-based oxide magnetic powder to form a powder compact, or a method of fixing the iron-based oxide magnetic powder by using a nonmagnetic polymer compound as a binder to form a filling method of structure.

In the method of using a binder, a kneaded product is obtained by mixing the iron-based oxide magnetic powder with a non-magnetic polymer base material. The blending amount of the radio wave absorbing material powder in the kneaded product is preferably 60% by mass or more. The more the amount of the radio wave absorbing material powder is, the better the radio wave absorption properties are. However, if it is too large, it will be difficult to mix with the polymer base material, so be careful. For example, the blending amount of the radio wave absorbing material powder can be set to 80 to 95 mass % or 85 to 95 mass %.

Depending on the environment of use, the polymer base material can be used with various base materials that satisfy heat resistance, flame retardancy, durability, mechanical strength, and electrical properties. For example, a suitable one can be selected from resins (nylon etc.), gels (polysilicon gel etc.), thermoplastic elastomers, rubbers and the like. In addition, two or more types of polymer compounds may be blended to form a base material.

[Thermal stability]

Regarding the thermal stability of the iron-based oxide magnetic powder obtained by the present invention, a cylindrical powder body with a diameter of 13 mm obtained by press-molding 1.2 g of the iron-based oxide magnetic powder at 28 MPa was used in the megahertz time domain. In the transmission attenuation spectrum measured by spectroscopic method and in the frequency range of 50 to 100 GHz, the frequency that shows the maximum transmission attenuation at the measurement temperature of 90 °C is set to F ₉₀ °C, and the maximum transmission attenuation is shown at the measurement temperature of 30 °C. When the frequency of the attenuation amount is set to F ₃₀ °C, it is evaluated by the absolute value of ΔF ₉₀ °C defined by the following formula (1). In this case, the reason why the absolute value is used for evaluation is that the ΔF ₉₀ ℃ may take a positive value and a negative value depending on the production conditions of the iron-based oxide magnetic powder obtained by the present invention. Therefore.

△F ₉₀ ℃=F ₉₀ ℃-F ₃₀ ℃...(1)

The absolute value of ΔF ₉₀ °C is preferably 3.0 GHz or less, particularly preferably 2.7 GHz or less. When the absolute value of △F ₉₀ ℃ exceeds 3.0GHz, when the iron-based oxide magnetic powder is exposed to a high temperature environment during use, the wavelength at which the maximum radio wave absorption energy is displayed as a radio wave absorber changes. times are not good.

[Production method]

The iron-based oxide magnetic powder of the present invention can be produced by the following method for producing an iron-based oxide magnetic powder, wherein the iron-based oxide magnetic powder has an absolute value of ΔF ₉₀ °C defined by the aforementioned formula (1) is 3.0 GHz or less, and the method for producing the iron-based oxide magnetic powder includes a neutralization step of neutralizing a trivalent iron ion, an ion of a metal substituted for a part of the Fe site, and a phosphorus-containing ion with an aqueous alkaline solution. An acidic aqueous solution of ions is obtained to obtain a slurry containing a precipitate of iron hydroxide of a substituted metal element, wherein the amount of phosphorus contained in the phosphorus-containing ions is equal to the amount of Si in the silane compound added in the coating step described later. The ear ratio (P/Si) is not less than 0.0001 and not more than 0.01; in the coating step, a silane compound is added to the slurry containing the precipitate of the iron hydroxide containing the substituted metal element, and in the presence of phosphorus-containing ions, the silane compound is added to the slurry. The hydrolysis product of the compound is coated on the precipitate of the iron hydroxide containing the substituted metal element; the recovery process is to recover the silane compound-coated hydrolysis product containing the iron hydroxide containing the substituted metal element by solid-liquid separation. The precipitation of the product; the heating step is to heat the precipitation of the iron hydroxide containing the substituted metal element of the hydrolysis product covered with the silane compound recovered above, and obtain the iron containing the substituted metal element covered with the silicon oxide. Oxide powder; dissolving process, which is obtained by immersing the silicon oxide-coated iron oxide powder containing a substituted metal element obtained by the aforementioned heating process in an alkaline aqueous solution to dissolve the silicon oxide coating to obtain a substituted metal element containing iron oxide powder. Iron oxide powder of metallic element.

In these production methods, the other metal element that substitutes a part of the Fe site is preferably one or more selected from Ti, Co, Ga, and Al, and more preferably Ti, Co, and Ga. Moreover, it is preferable that the said phosphorus-containing ion is 1 or more types chosen from phosphate ion, a phosphite ion, and a hypophosphite ion.

[Precursor]

In the above-mentioned production method, an iron hydroxide in which a part of the Fe site obtained by the wet method is substituted with a substituted element, or a mixture of an iron hydroxide and a substituted element hydroxide, is used, as the precursor of iron oxide magnetic powder. The concept of hydroxide here is a general term for hydroxide, oxyhydroxide, hydrated oxide, and the like. In Patent Documents 2 and 3, a method of using an organic solvent like the inverse microcellular method or a method of using only water as a reaction solvent is disclosed as a method of generating the precursor. In the production method of the present invention, any generally known method can be used for the production of the precursor, but from the viewpoint of economy, it is preferable not to use an expensive organic solvent, but to synthesize the precursor only in an aqueous system. .

[Starting material and neutralization process]

In the above-mentioned production method, an acidic aqueous solution (hereinafter referred to as a raw material solution) containing trivalent iron ions or a metal ion containing a trivalent iron ion and a metal element finally replacing the Fe site is used as the iron-based oxide magnetic material. Powder precursor starting material. From the viewpoint of availability and price, the supply source of these iron ions or metal ions of the substituted element is preferably a supply source such as nitrate, sulfate, or chloride. Water-soluble inorganic acid salt. When these metal salts are dissolved in water, the metal ions dissociate and the aqueous solution becomes acidic. When an alkali is added to an acidic aqueous solution containing this metal ion for neutralization, ferric oxyhydroxide, a mixture of ferric oxyhydroxide and a hydroxide of a substituted element, or a part of the Fe site is substituted with another metal element. of ferric hydroxide. In the production method of the present invention, these ferric oxyhydroxide, or a mixture of ferric oxyhydroxide and a hydroxide of a substituted element, or ferric oxyhydroxide in which a part of the Fe site is substituted with another metal element, are used. As a precursor of iron-based oxide magnetic powder.

As will be described later, the method for producing an iron-based oxide magnetic powder of the present invention is characterized in that phosphorus-containing ions coexist when the precursor produced in the neutralization step is coated with silicon oxide, but it may also be preceded by the neutralization treatment. , adding phosphorus-containing ions to the raw material solution in advance.

In the present invention, the concentration of all metal ions in the raw material solution is not particularly specified, but is preferably 0.01 mol/kg or more and 0.5 mol/kg or less. If it is less than 0.01 mol/kg, the amount of the iron-based oxide magnetic powder obtained by one reaction is small, which is not economical. When the total metal ion concentration exceeds 0.5 mol/kg, the reaction solution is easily gelled due to the rapid precipitation of hydroxide, which is not preferable.

In the above-mentioned production method, since alkali is added to the raw material solution to precipitate the hydroxides of trivalent iron and the substituted element, it is preferable to stir by a generally known mechanical means in the neutralization treatment. reaction solution. In this neutralization step, various methods such as coexisting with hydroxycarboxylic acid in the treatment liquid and neutralization treatment in two stages are proposed, and any method can be used in the production method of the present invention. However, the pH of the final treatment liquid in the neutralization process is set to be 7.0 or more and 10.0 or less. When the pH after neutralization is less than 7.0, the generation of the hydroxide of the substituted element tends to be insufficient. In addition, when the pH after neutralization exceeds 10.0, the neutralization effect is saturated, and both are not good.

In addition, the value of pH described in this specification was measured using a glass electrode according to JIS Z8802. pH standard solution refers to the use of an appropriate buffer solution for the pH region to be measured and calibrated by the value measured by the pH meter. In addition, the pH described in this specification means the value which directly reads the measured value displayed by the pH meter compensated by the temperature compensation electrode under reaction temperature conditions.

The alkali used for neutralization can be any of ammonium salts such as alkali metal or alkaline earth hydroxides, ammonia water, ammonium bicarbonate, etc., but it is preferably used in the final heat treatment to form ε-type iron oxides that are not easy to remain. Impurities of ammonia or ammonium bicarbonate. These bases may be added as a solid in the aqueous solution of the starting material, but from the viewpoint of ensuring the uniformity of the reaction, they are preferably added as an aqueous solution.

In the method for producing the iron-based oxide magnetic powder of the present invention, the reaction temperature at the time of neutralization treatment is not particularly limited, but it is preferably 60°C or lower. When the reaction temperature exceeds 60° C., the finally obtained magnetic powder is likely to contain heterophases such as α-type, which is not preferable.

[Coating process by silicon oxide]

Even if the precursor generated in the neutralization step is subjected to heat treatment in this state, it is not easy to be transformed into an ε-type iron-based oxide. Therefore, in the method for producing an iron-based oxide magnetic powder of the present invention, this The precursor is coated with silicon oxide. The sol-gel method is suitable for the coating method of silicon oxide. The so-called sol-gel method as used herein refers to a hydrolysis reaction using a silane derivative having the property of reacting with water to be hydrolyzed. After the hydrolysis product of the silane derivative is coated on the surface of the precursor, it is heated to gel. process of transformation. In addition, the term "silicon oxide" here means not only a stoichiometric chemical composition, but also a non stoichiometric chemical composition such as a silanol derivative to be described later. Sodium silicate (water glass) can also be used in place of silane derivatives. In addition, in the slurry containing the precursor obtained in the neutralization step, the ions of the inorganic acid salt contained in the raw material solution or the alkali added in the neutralization step can be washed before the coating step. slurry, but this step may be performed without washing the slurry.

The molar ratio (Si/(Fe+M)) of the amount of Si of the silane compound added in this step and the sum of the amount of iron ions and the amount of the substituted metal ions contained in the raw material solution (Fe+M) is compared with Preferably, it is 0.50 or more. At When (Si/(Fe+M)) is less than 0.50, the amount of the silanol derivative coexisting with the precipitate of the ferric oxyhydroxide containing the substituted element is small, and the silanol derivative or its condensation reaction product is uniform. The effect of coating the precipitation of the ferric oxyhydroxide containing the substituted element is low, so it is not good. (Si/(Fe+M)) is preferably 0.75 or more, more preferably 1.0 or more. Further, (Si/(Fe+M)) is preferably 10 or less. When (Si/(Fe+M) exceeds 10, the processing amount of the heating step and the silicon oxide removal step to be described later increases, which increases the manufacturing cost, which is not preferable. (Si/(Fe+M)) is particularly preferable. It is 5.0 or less, and it is more preferable that it is 3.0 or less. In addition, here, M represents the sum total of the amount of the metal ion which replaces a part of Fe site|parts.

In the case of the sol-gel method, silicon compounds with hydrolyzable groups, such as tetraethoxysilane (TEOS: Tetraethoxysilane), tetramethoxysilane (TMOS: Tetramethoxysilane) or various silane coupling agents, are added to the silane compound. The slurry in which the aforementioned precursor is dispersed causes a hydrolysis reaction under stirring, and the crystal surface of the precursor is coated with the generated silanol derivative. When hydrolysis is caused, a generally known hydrolysis catalyst such as an acid catalyst and an alkali catalyst can be added, and the catalyst is preferably added in consideration of the treatment time. A representative example of the acid catalyst is hydrochloric acid, and the alkali catalyst is ammonia. When an acid catalyst is used, it must be added in such an amount that the ferric oxyhydroxide particles containing the substituted element do not dissolve. In addition, the specific method of coating the silicon oxide can be the same as the sol-gel method in the generally known process. For example, the reaction temperature of the silicon oxide coating by the sol-gel method is 20° C. or more and 60° C. or less, and the reaction time is about 1 hour or more and 20 hours or less.

[phosphorus ions]

The aforementioned manufacturing method is characterized in that, in the aforementioned coating step, when the precursor is coated with the silicon oxide by a sol-gel method, phosphorus-containing ions are allowed to coexist in an aqueous solution.

As a supply source of phosphorus ions, phosphoric acid, ammonium phosphate, sodium phosphate, and soluble phosphoric acid (PO ₄ ^3- ) salts such as mono-hydrogen salts and di-hydrogen salts thereof can be used. Here, phosphoric acid is a 3-proton acid, and it will undergo 3-stage dissociation in an aqueous solution. Therefore, in the aqueous solution, the existence forms of phosphoric acid ion, phosphoric acid 1 hydrogen ion, and phosphoric acid 2 hydrogen ion can be adopted, but the existence form is not determined by the use of The type of the chemical that is the source of the phosphate ion is determined by the pH of the aqueous solution, so the ions containing the above-mentioned phosphate groups are collectively referred to as phosphate ions. In addition, in the case of the present invention, diphosphoric acid (pyrophosphoric acid) which is a condensed phosphoric acid can also be used as a supply source of phosphoric acid ions. In addition, in the present invention, a phosphite ion (PO ₃ ^3- ) or a hypophosphite ion (PO ₂ ^2- ) having a different oxidation number of P may be used in place of the phosphate ion (PO ₄ ^3- ). These oxide ions containing phosphorus (P) are collectively referred to as phosphorus-containing ions.

The following three types of implementations for coexisting phosphorus-containing ions can be considered. In the first embodiment, phosphorus-containing ions are added to the raw material solution in the neutralization process, and after the precursor is formed in the presence of phosphorus-containing ions, a silicon compound having a hydrolyzable group is added to the solution containing the obtained precursor and the containing compound. The form of the slurry of phosphorus ions. The second embodiment is that when the silicon compound having a hydrolyzable group is added to the slurry in which the precursor is dispersed, phosphorus-containing ions are simultaneously added. The third embodiment is that after adding the silicon compound having a hydrolyzable group to the slurry in which the precursor is dispersed, phosphorus-containing ions are added before the reaction of coating the precursor with the silicon oxide is completed. In the manufacturing method of the iron-based oxide magnetic powder of the present invention, in any embodiment, the iron-based oxide magnetic powder with good thermal stability and little change in the amount of radio wave absorption can be obtained even in a high temperature environment.

The reason why the iron-based oxide magnetic powder with good thermal stability can be finally obtained by heating the precursor after coating the precursor with the hydrolyzed product of the silane compound in the coexistence of phosphorus-containing ions has not yet been made. Obviously, it can only be considered that the physical properties of the silicon oxide coating are changed due to the reaction between the silicon oxide and the phosphorus-containing ions. In addition, it is also considered that by adsorbing phosphorus-containing ions on the surface of the precursor, the isoelectric point of the precursor is changed, and the aggregation state of the precursor in the slurry is changed. In addition, it can also be considered that the change in the physical properties of the silicon oxide coating promotes the sintering of the iron-based oxide magnetic powder precursor particles and the diffusion of the substitution elements inside the particles. As a result, the amount of substitution at the substitution site of the element that is effective in improving thermal stability is increased compared to the system in which phosphoric acid is not added.

The molar ratio (P/Si) of the amount of phosphorus-containing ions coexisting in the slurry in the coating step and the Si amount of the silane compound added in the coating step is preferably 0.0001 or more and 0.01 or less. When P/Si is less than 0.0001, the firing acceleration effect cannot be obtained by adding phosphoric acid. P/Si is preferably 0.0005 or more, more preferably 0.001 or more. In addition, when P/Si exceeds 0.01, the ratio of the α-type iron-based oxide powder contained in the final product increases, and as a result, the absorption amount when used as a radio wave absorbing material becomes small, and the obtained iron-based oxide magnetic powder The thermal stability deteriorates, and the coercive force in a high temperature environment changes greatly, so it is not good. P/Si is preferably 0.008 or less, more preferably 0.006 or less.

[Recycling process]

The silicon oxide-coated precursor obtained by the coating step of the iron-based oxide magnetic powder of the present invention is recovered by generally known solid-liquid separation such as filtration, centrifugation, and decantation. Here, water washing may be performed after the coating treatment and before the solid-liquid separation. In addition, during solid-liquid separation, a coagulant can be added to perform solid-liquid separation. In addition, the solid-liquid separation can be carried out several times through water washing.

[heating process]

In the method for producing an iron-based oxide magnetic powder of the present invention, the precursor covered with the silicon oxide is heat-treated to obtain an ε-type iron-based oxide. Washing and drying steps can be set before the heat treatment. This drying treatment is for the purpose of removing water adhering to the sediment, and can be performed at a temperature of about 110° C. or higher than the boiling point of water. The heat treatment is performed in an oxidizing environment, and the oxidizing environment may be an atmospheric environment. The heat treatment temperature varies depending on the coating amount of silicon oxide, and cannot be generalized, but heating can be performed in the range of approximately 700° C. or higher and 1300° C. or lower. When the heating temperature is too low, compounds with different phases or insufficient phase change are likely to be mixed. In addition, the particle diameter of the obtained product may also become small, which is not preferable. If the lower limit of the above heating temperature is set to 700°C or more, the ε-type iron oxide which is the object of the present invention can be selectively and stably obtained, and the generation of compounds with different phases or insufficient phase change can be suppressed, so that a complete magnetic field can be obtained. Magnetic powder with characteristic and suitable for high-density magnetic recording. When the heating temperature is high, α-Fe ₂ O ₃ (an impurity in terms of ε-Fe ₂ O ₃ ), which is a thermodynamically stable phase, is easily formed, so it is preferably 900°C or higher and 1200°C or lower, especially 950°C. The heat treatment is performed at a temperature of ℃ or higher and 1150°C or lower. The heat treatment time can be adjusted in the range of about 0.5 hours or more and 10 hours or less, and good results are easily obtained in the range of 2 hours or more and 5 hours or less.

[Dissolution process]

The silicon oxide coating layer obtained in the above heating process is not useful as an electromagnetic wave absorbing material, and if it remains, the electromagnetic wave absorption energy will be deteriorated, so the iron oxide coated with silicon oxide is immersed in the Alkaline solution to dissolve and remove silicon oxide coating. In the iron-based oxide magnetic powder of the present invention, when an insulating coating layer needs to be used, the sol-gel method is used again after this process to coat the silicon oxide under the condition that no phosphorus-containing ions are present.

The specific method is as follows: Since silicon oxide is soluble in an alkaline aqueous solution, the ε-type iron oxide coated with silicon oxide after heat treatment can be immersed in an aqueous solution in which a strong alkali such as NaOH or KOH is dissolved. , and stir to dissolve and remove. In the case of increasing the dissolution rate, the alkaline aqueous solution may be heated. Typically, an alkali such as NaOH is added in an amount of 3 times moles or more relative to the silicon oxide, and the silicon oxide can be well dissolved when the slurry containing the powder is stirred in a state where the temperature of the aqueous solution is 60°C or higher and 70°C or lower.

The ε-type iron-based oxide magnetic powder obtained by dissolving and removing the silicon oxide coating is recovered by a generally known solid-liquid separation method, and may be subjected to water washing treatment and drying treatment as necessary.

[Composition analysis by high-frequency inductively coupled plasma emission spectrometry (ICP-AES)]

The composition of the obtained ε-type iron-based oxide magnetic powder was analyzed by a dissolution method. In the composition analysis, ICP-720ES manufactured by Agilent Technology was used, and the measurement wavelengths (nm) were Fe; 259.940 nm, Ga; 294.363 nm, Co; 230.786 nm, Ti; 336.122 nm.

[Measurement of hysteresis curve (overall B-H curve)]

Vibration sample type magnetometer VSM (VSM-5 manufactured by Toei Industrial Co., Ltd.) is used, the maximum applied magnetic field is 1193kA/m (15kOe), the M measurement range is 0.005A·m ² (5emu), and the step bit is 80Bit , the time constant is 0.03 seconds, and the waiting time is 0.1 seconds to measure the hysteresis curve. The coercive force Hc and the saturation magnetization σ s were evaluated from the BH curve.

[Evaluation of particle size by TEM: Transmitting Electron Microscope]

The particle size of ε iron oxide was determined by observation with a transmission electron microscope (TEM). The TEM observation system used JEM-1011 manufactured by JEOL Corporation. For a certain particle, the length of the long side of the rectangle whose area becomes the smallest circumscribed rectangle is set as the particle diameter (major axis) of the particle. Specifically, in a TEM photograph taken at a magnification of 100,000 times, 300 particles were randomly selected to observe the entire outer edge portion, and their particle diameters were measured, and the average value was defined as the average particle size of the ε iron oxide. path.

[BET specific surface area]

The BET specific surface area was determined by the BET single-point method using MACSORB MODEL-1210 manufactured by Mounttech Co., Ltd.

[Measurement of radio wave absorption characteristics]

1.2 g of the iron-based oxide magnetic powder was press-molded at 28 MPa (20 kN) to obtain a cylindrical powder body having a diameter of 13 mm. The obtained powder compact was subjected to transmission attenuation measurement by megahertz time-domain spectroscopy. Specifically, a megahertz spectroscopic system TAS7400SL manufactured by Advantest was used, and the powder compact was placed Measurements were performed in the case of the sample holder and in the case of the blank. Using the temperature control module TAS1030 manufactured by Advantest, the samples were heated to 30°C, 60°C, and 90°C, and the penetration attenuation at each temperature was measured. The measurement conditions are as follows.

10mm ‧Sample holder diameter:

10mm

‧Measurement Mode: Transmission

‧Frequency Resolution: 1.9GHz

‧Vertical Axis: Absorbance

‧Horizontal Axis: Frequency[THz]

‧Cumulated Number (Sample): 2048

‧Cumulated Number (Background): 2048

The signal waveform of the observed sample and the reference waveform of the blank are expanded to 2112ps and Fourier transform is performed to obtain the ratio (Ssig/Sref) of the obtained Fourier spectrum (set as Sref and Ssig respectively), and calculate the ratio (Ssig/Sref) placed in the The penetration attenuation of the powder compact of the sample holder.

[Example]

[Comparative Example 1]

In a 5L reaction tank, 527.22 g of iron (III) sulfate solution with Fe concentration of 11.58 mass%, 71.61 g of gallium (III) nitrate solution with Ga concentration of 11.55 mass%, and 9.57 g of cobalt (II) nitrate hexahydrate with a purity of 97% were prepared. , 10.11 g of titanium (IV) sulfate with a Ti concentration of 15.1 mass% was added to 3688.56 g of pure water, and dissolved in the atmospheric environment by mechanical stirring with a stirring blade (step 1). The pH of this solution is about 1. The molar ratio of the metal ions put into the solution was Fe:Ga:Co:Ti=1.714:0.186:0.050:0.050. In addition, Roman numerals in parentheses after the reagent name indicate the valence of the metal element.

In the atmospheric environment, under the condition of 30 ℃, while stirring the input solution mechanically by a stirring blade, add 388.91 g of 22.30 mass% ammonia solution for 10 minutes, and continue stirring for 30 minutes after the dripping is completed to carry out the generated precipitation. maturation of things. At this point the pH of the slurry containing the precipitate was about 9 (step 2). While stirring the slurry obtained in step 2, 794.40 g of tetraethoxysilane (TEOS) with a purity of 95.0 mass% was added dropwise to the atmosphere at 30° C. for 10 min. Then, stirring was continued for 20 h to coat the precipitate with the hydrolysis product of the silane compound generated by the hydrolysis (step 3). In addition, under these conditions, the molar ratio Si/(Fe+M of the amount of Si element contained in the tetraethoxysilane dropped into the slurry and the amount of iron, gallium, cobalt, and titanium ions contained in the aforementioned solution ) is 2.84.

The slurry obtained in Step 3 was filtered, and after removing as much as possible the moisture of the precipitate covered with the hydrolyzed product (silanol derivative) of the obtained silane compound, it was dispersed in pure water again and re-dispersed. Pulp wash. The washed slurry was filtered again, and the obtained filter cake was dried at 110° C. in the air (step 4).

The dried product obtained in step 4 was heat-treated at 1090° C. for 4 hours in the atmosphere using a box-type firing furnace to obtain iron-based oxide magnetic powder coated with silicon oxide (step 5). In addition, the above-mentioned silanol derivative is subjected to heat treatment in an atmospheric environment to be dehydrated and converted into oxides.

Table 1 shows the production conditions such as the input conditions of the raw material solution in this comparative example. In Table 1, the production conditions of other Examples and Comparative Examples are also shown together.

In a 20 mass% NaOH aqueous solution, the heat-treated powder obtained in step 5 was stirred at about 60° C. for 24 hours to perform the removal treatment of the silicon oxide coating on the particle surface (step 6 ). Next, it was washed with a centrifugal separator until the electrical conductivity of the slurry became 15 mS/m or less, filtered through a membrane filter, and then dried for chemical analysis of the composition of the obtained iron-based oxide magnetic powder and magnetic properties. And the measurement of penetration attenuation and so on. The results of these measurements are shown in Table 2. In addition, for reference, also in Table 2, when F ₃₀ ℃, the frequency that shows the maximum penetration attenuation at the measurement temperature of 60 ℃ is F ₆₀ ℃, and ΔF ₆₀ ℃ (=F ₆₀ ℃-F ₆₀ °C). In addition, Table 2 also shows the physical property values of the iron-based oxide magnetic powder obtained in the other Examples and Comparative Examples. In addition, the measurement spectrum by the megahertz time-domain spectrometry of the iron-based oxide magnetic powder obtained in this comparative example is shown in FIG. 1 .

From Table 2, it can be seen that the chemical composition of the obtained iron-based oxide magnetic powder is almost the same as the composition of the raw material solution at the time of injection.

From the fact that the absolute value of ΔF ₉₀ °C of the iron-based oxide magnetic powder obtained in this comparative example was 9.5 GHz, it was found that the thermal stability was poor when the ambient temperature was raised to 90°C.

[Comparative Example 2]

Except that the amount of each raw material used was changed to 529.56 g of iron(III) sulfate solution with Fe concentration of 11.65 mass%, 71.61 g of gallium(III) nitrate solution with Ga concentration of 11.55 mass%, and cobalt(II) nitrate with 97% purity hexahydrate Iron-based oxide magnetic powder was produced under the same conditions as in Comparative Example 1, except for 7.65 g of material and 8.06 g of titanium (IV) sulfate with a Ti concentration of 15.1 mass%. The molar ratio of the metal ions put into the solution was Fe:Ga:Co:Ti=1.734:0.186:0.040:0.040. In addition, Roman numerals in parentheses after the reagent name indicate the valence of the metal element.

From the fact that the absolute value of ΔF ₉₀ °C of the iron-based oxide magnetic powder obtained in this comparative example was 8.1 GHz, it was found that the thermal stability was poor when the ambient temperature was raised to 90°C.

[Comparative Example 3]

32,800.16 g of pure water, 2,436.16 g of iron (III) nitrate nonahydrate with a purity of 99.7%, 618.74 g of a gallium (III) nitrate solution with a gallium concentration of 9.33%, and titanium (IV) sulfate n-hydrate with a titanium element content of 15.1 mass % were prepared. 57.06 g and 54.01 g of cobalt (II) nitrate hexahydrate with a purity of 97% were put into a 45 L reaction tank, and were mixed while mechanically stirring with a stirring blade under the conditions of an atmospheric environment and 30° C. to obtain a mixed solution. what you get The molar ratios of the added element ions in the mixed solution were Fe:Ga:Ti:Co=1.67:0.23:0.05:0.05, respectively.

Under the conditions of atmospheric environment and 30°C, while stirring the aforementioned mixed solution mechanically by a stirring blade, 2508.61 g of ammonia solution with a concentration of 22.5% was continuously added for 10 minutes, and then continued to stir for 30 minutes to obtain a precursor slurry. .

While mechanically stirring the aforementioned precursor slurry, 4484.14 g of tetraethoxysilane (TEOS) as a silicon compound was continuously added for 10 minutes, and the stirring was continued for about 1 day. Next, the obtained slurry after stirring was separated into solid and liquid, and the separated solid content was washed, and then the filter cake was recovered.

The collected cake was dried, and then pulverized to obtain dry powder. The obtained dry powder was subjected to a heat treatment at 1088° C. for 4 hours in a furnace in an atmospheric environment to obtain an iron-based oxide magnetic powder coated with silicon oxide.

The obtained iron-based oxide magnetic powder coated with silicon oxide was put into a 17.59% NaOH aqueous solution as an alkaline aqueous solution, and stirred at about 60° C. for 24 hours, and the silicon oxide magnetic powder on the surface was subjected to siliconization. Oxide removal treatment. After the removal treatment, the obtained slurry was subjected to centrifugation treatment at 3000 rpm for 10 minutes using a centrifuge to perform solid-liquid separation.

After removing the supernatant from the obtained solid-liquid separation, pure water was added to redisperse the slurry. Then, the redispersed slurry was subjected to centrifugation treatment at 5000 rpm for 5 minutes to perform solid-liquid separation to obtain a solid-liquid separated product. After removing the supernatant from the obtained solid-liquid separation, pure water was added to redisperse the slurry. Then, the redispersed slurry was subjected to centrifugation treatment at 8000 rpm for 15 minutes to perform solid-liquid separation to obtain iron-based oxide magnetic powder. It is used for chemical analysis of the composition of the obtained iron-based oxide magnetic powder, measurement of magnetic properties and penetration attenuation, and the like. These measurement results are shown in Table 2.

From the fact that the absolute value of ΔF ₉₀ °C of the iron-based oxide magnetic powder obtained in this comparative example was 7.6 GHz, it was found that the thermal stability was poor when the ambient temperature was raised to 90°C.

[Comparative Example 4]

In a 1L reaction tank, 110.07 g of iron(III) sulfate solution with Fe concentration of 11.65 mass%, 9.49 g of gallium(III) nitrate solution with Ga concentration of 9.37 mass%, and 1.91 g of cobalt(II) nitrate hexahydrate with 97% purity were prepared 2.02 g of titanium (IV) sulfate with a Ti concentration of 15.1 mass% was added to 666.01 g of pure water, and dissolved in the atmosphere while mechanically stirring with a stirring blade (step 1). The pH of this solution is about 1. The molar ratio of the metal ions put into the solution was Fe:Ga:Co:Ti=1.800:0.100:0.050:0.050. In addition, Roman numerals in parentheses after the reagent name indicate the valence of the metal element.

In the atmosphere, while mechanically stirring the mixed aqueous solution with a stirring blade at 30°C, a 21.39 mass % ammonia solution was added until the pH became 3.0, and then tetraethoxysilane (TEOS) was added as a hydrolyzable group. of silicon compounds. Here, TEOS is an amount in which the molar ratio Si/(Fe+M) of the amount of Si element contained in TEOS and the amount of iron, gallium, cobalt, and titanium ions contained in the aforementioned mixed aqueous solution becomes 2.84, and lasted for a period of time. 5min added. After the addition of TEOS was completed, 28.27 g of a 21.39 mass % ammonia solution was added and stirring was continued for 20 hours, so that the precipitate of ferric oxyhydroxide containing the substitution element was covered with the hydrolysis product of the silicon compound. During this 20 h of stirring, the pH of the slurry containing the precipitate was about 9 (step 2).

The slurry obtained in step 2 was filtered, and after removing as much as possible the moisture of the precipitate covered with the hydrolyzed product (silanol derivative) of the obtained silane compound, it was dispersed in pure water again and re-treated. Pulp wash. The washed slurry was filtered again, and the obtained filter cake was dried at 110° C. in the air (step 3).

The dried product obtained in step 3 was heat-treated at 1090° C. for 4 hours in the atmosphere using a box-type firing furnace to obtain iron-based oxide magnetic powder coated with silicon oxide (step 4 ).

From the fact that the absolute value of ΔF ₉₀ °C of the iron-based oxide magnetic powder obtained in this comparative example was 8.1 GHz, it was found that the thermal stability was poor when the ambient temperature was raised to 90°C.

[Example 1]

861.7 g of a mixed aqueous solution of iron (III) nitrate, gallium (III) nitrate, cobalt (II) nitrate, titanium (IV) sulfate and phosphoric acid H ₃ PO ₄ was prepared as a raw material solution containing phosphorus ions (step 1). In this mixed aqueous solution, the molar ratio of metal ions was Fe:Ga:Co:Ti=1.755:0.165:0.040:0.040, and the total molar concentration of Fe ions, Ga ions, Co ions and Ti ions was 0.35 mol/kg , the molar ratio P/(Fe+M) of the amount of P element contained in phosphoric acid and the amount of Fe ions, Ga ions, Co ions and Ti ions contained in the raw material solution was 0.017. The pH of this mixed aqueous solution was about 1.

In an atmospheric environment, while stirring this mixed aqueous solution mechanically with a stirring blade at 30°C, a 22.3 mass % ammonia solution was added until the pH became 3.0, and then tetraethoxysilane (TEOS) was added as a hydrolyzable group. of silicon compounds. Here, TEOS is an amount in which the molar ratio Si/(Fe+M) of the amount of Si element contained in TEOS and the amount of iron, gallium, cobalt, and titanium ions contained in the aforementioned mixed aqueous solution becomes 2.84, and lasted for a period of time. 5min added. Under these conditions, the molar ratio P/Si of the amount of P element contained in H ₃ PO ₄ and the amount of Si element contained in the dropped tetraethoxysilane was 0.006. After the addition of TEOS was completed, 26.8 g of a 22.3 mass % aqueous ammonia solution was added, and stirring was continued for 20 hours, so that the precipitate of ferric oxyhydroxide containing the substitution element was covered with the hydrolysis product of the silicon compound. During this 20 h of stirring, the pH of the slurry containing the precipitate was about 9 (step 2).

The slurry obtained in Step 2 was filtered, and after removing as much moisture as possible of the precipitate covered with the hydrolyzed product of the silicon compound obtained, it was dispersed again in pure water and reslurried and washed. The washed slurry was filtered again, and the obtained filter cake was dried at 110° C. in the air (step 3).

The dried product obtained in step 3 was heat-treated at 1090° C. for 4 hours in the atmosphere using a box-type firing furnace to obtain iron-based oxide magnetic powder coated with silicon oxide (step 4 ).

Table 1 shows the production conditions such as the input conditions of the raw material solution in this example. In Table 1, the production conditions of other Examples and Comparative Examples are also shown together.

The iron-based oxide magnetic powder coated with the silicon oxide obtained in step 4 was stirred in a 20 mass % NaOH aqueous solution at about 60° C. for 24 hours to remove the silicon oxide coating on the particle surface ( step 5). Next, the operations of centrifugal separation, removal of supernatant, and addition of pure water were repeated using a centrifugal separator, and the slurry was washed until the conductivity of the slurry became 500 mS/m or less, filtered through a membrane filter, and then dried. It is used for chemical analysis of the composition of the obtained iron-based oxide magnetic powder, measurement of average particle size, BET specific surface area, magnetic properties, and penetration attenuation. The results of these measurements are shown in Table 2. Table 2 also shows the physical property values of the iron-based oxide magnetic powder obtained in other examples and comparative examples.

From Table 2, it can be seen that the chemical composition of the obtained iron-based oxide magnetic powder is almost the same as the composition of the raw material solution at the time of injection.

The average particle size of the iron-based oxide magnetic powder obtained in this example is 46.6 nm, which is larger than that of Comparative Examples 1 to 4, and the BET specific surface area is 17.2 m ² /g, which is smaller than that of Comparative Example. In addition, using the iron-based oxide magnetic powder obtained in this example and the powder compact obtained by following the above steps, the frequency at which the maximum penetration attenuation is displayed at the measurement temperature of 30°C is 30°C when F ₃₀ °C , 60 ℃ and 90 ℃ penetration attenuation A ₃₀ ℃, A ₆₀ ℃ and A ₉₀ ℃ are 16.2, 14.6 and 16.0dB, respectively. A ₃₀ ℃, A ₆₀ ℃ and A ₉₀ ℃ of Comparative Example 1 are 10.4, 8.9 and 4.4 dB, respectively. It can be seen that the iron-based oxide magnetic powder obtained in this example has a different temperature at F ₃₀ ℃. The penetration attenuation is larger than that of Comparative Example 1, and the change in the amount of radio wave absorption from low temperature to high temperature is smaller than that of Comparative Example 1.

In addition, the absolute value of ΔF ₉₀ ℃ of the iron-based oxide magnetic powder obtained in this example is 0 GHz, which is lower than the ΔF ₉₀ ℃ of the above-mentioned Comparative Examples 1 to 4. It can be seen that during the silicon oxide coating When the phosphorus-containing ions were allowed to coexist, the thermal stability when the ambient temperature was raised to 90° C. was further improved compared with Comparative Examples 1 to 4.

[Example 2]

In the mixed aqueous solution, iron-based oxide magnetic powder was produced under the same conditions as in Example 1, except that the molar ratio of metal ions was changed to Fe:Ga:Co:Ti=1.789:0.121:0.045:0.045 . In addition, the molar ratio P/(Fe+M) of the amount of P element contained in H ₃ PO ₄ and the amounts of iron, gallium, cobalt, and titanium ions contained in the solution solution under these conditions was 0.017. In addition, in this condition, the molar ratio P/Si of the amount of P element contained in H ₃ PO ₄ and the amount of Si element contained in the dropped tetraethoxysilane was 0.006. The absolute value of ΔF ₉₀ °C of the iron-based oxide magnetic powder obtained in this example was 2.4 GHz, and the thermal stability was good when the ambient temperature was raised to 90°C.

[Example 3]

In the mixed aqueous solution, iron-based oxide magnetic powder was produced under the same conditions as in Example 1, except that the molar ratio of metal ions was changed to Fe:Ga:Co:Ti=1.791:0.121:0.044:0.044 . In addition, the molar ratio P/(Fe+M) of the amount of P element contained in H ₃ PO ₄ and the amounts of iron, gallium, cobalt, and titanium ions contained in the solution solution under these conditions was 0.017. In addition, in this condition, the molar ratio P/Si of the amount of P element contained in H ₃ PO ₄ and the amount of Si element contained in the dropped tetraethoxysilane was 0.006. The absolute value of ΔF ₉₀ °C of the iron-based oxide magnetic powder obtained in this example was 0.5 GHz, and the thermal stability was good when the ambient temperature was raised to 90°C.

[Example 4]

In the mixed aqueous solution, iron-based oxide magnetic powder was produced under the same conditions as in Example 1, except that the molar ratio of metal ions was changed to Fe:Ga:Co:Ti=1.796:0.110:0.047:0.047 . In addition, the molar ratio P/(Fe+M) of the amount of P element contained in H ₃ PO ₄ and the amounts of iron, gallium, cobalt, and titanium ions contained in the solution solution under these conditions was 0.017. In addition, in this condition, the molar ratio P/Si of the amount of P element contained in H ₃ PO ₄ and the amount of Si element contained in the dropped tetraethoxysilane was 0.006. The absolute value of ΔF ₉₀ °C of the iron-based oxide magnetic powder obtained in this example was 0.9 GHz, and the thermal stability was good when the ambient temperature was raised to 90°C.

[Example 5]

In the mixed aqueous solution, iron-based oxide magnetic powder was produced under the same conditions as in Example 1, except that the molar ratio of metal ions was changed to Fe:Ga:Co:Ti=1.800:0.110:0.045:0.045 . In addition, the molar ratio P/(Fe+M) of the amount of P element contained in H ₃ PO ₄ and the amounts of iron, gallium, cobalt, and titanium ions contained in the solution solution under these conditions was 0.017. In addition, in this condition, the molar ratio P/Si of the amount of P element contained in H ₃ PO ₄ and the amount of Si element contained in the dropped tetraethoxysilane was 0.006. The absolute value of ΔF ₉₀ °C of the iron-based oxide magnetic powder obtained in this example was 0.5 GHz, and the thermal stability was good when the ambient temperature was raised to 90°C.

[Example 6]

In the mixed aqueous solution, iron-based oxide magnetic powder was produced under the same conditions as in Example 1, except that the molar ratio of metal ions was changed to Fe:Ga:Co:Ti=1.802:0.110:0.044:0.044 . In addition, the molar ratio P/(Fe+M) of the amount of P element contained in H ₃ PO ₄ and the amounts of iron, gallium, cobalt, and titanium ions contained in the solution solution under these conditions was 0.017. In addition, in this condition, the molar ratio P/Si of the amount of P element contained in H ₃ PO ₄ and the amount of Si element contained in the dropped tetraethoxysilane was 0.006. The absolute value of ΔF ₉₀ °C of the iron-based oxide magnetic powder obtained in this example was 0.5 GHz, and the thermal stability was good when the ambient temperature was raised to 90°C.

[Example 7]

In the mixed aqueous solution, the iron-based oxide magnetic powder was produced under the same conditions as in Example 1, except that the molar ratio of the metal ions was changed to Fe:Ga:Co:Ti=1.806:0.110:0.042:0.042 . In addition, the molar ratio P/(Fe+M) of the amount of P element contained in H ₃ PO ₄ and the amounts of iron, gallium, cobalt, and titanium ions contained in the solution solution under these conditions was 0.017. In addition, in this condition, the molar ratio P/Si of the amount of P element contained in H ₃ PO ₄ and the amount of Si element contained in the dropped tetraethoxysilane was 0.006. The absolute value of ΔF ₉₀ °C of the iron-based oxide magnetic powder obtained in this example was 2.4 GHz, and the thermal stability was good when the ambient temperature was raised to 90°C.

[Example 8]

In the mixed aqueous solution, iron-based oxide magnetic powder was produced under the same conditions as in Example 1, except that the molar ratio of metal ions was changed to Fe:Ga:Co:Ti=1.794:0.116:0.045:0.045 . In addition, the molar ratio P/(Fe+M) of the amount of P element contained in H ₃ PO ₄ and the amounts of iron, gallium, cobalt, and titanium ions contained in the solution solution under these conditions was 0.017. In addition, in this condition, the molar ratio P/Si of the amount of P element contained in H ₃ PO ₄ and the amount of Si element contained in the dropped tetraethoxysilane was 0.006. The absolute value of ΔF ₉₀ °C of the iron-based oxide magnetic powder obtained in this example was 1.5 GHz, and the thermal stability was good when the ambient temperature was raised to 90°C.

[Example 9]

In the mixed aqueous solution, iron-based oxide magnetic powder was produced under the same conditions as in Example 1, except that the molar ratio of metal ions was changed to Fe:Ga:Co:Ti=1.817:0.095:0.044:0.044 . In addition, the molar ratio P/(Fe+M) of the amount of P element contained in H ₃ PO ₄ and the amounts of iron, gallium, cobalt, and titanium ions contained in the solution solution under these conditions was 0.017. In addition, in this condition, the molar ratio P/Si of the amount of P element contained in H ₃ PO ₄ and the amount of Si element contained in the dropped tetraethoxysilane was 0.006. The absolute value of ΔF ₉₀ °C of the iron-based oxide magnetic powder obtained in this example was 0.9 GHz, and the thermal stability was good when the ambient temperature was raised to 90°C.

[Example 10]

In the mixed aqueous solution, the iron-based oxide magnetic powder was produced under the same conditions as in Example 1, except that the molar ratio of the metal ions was changed to Fe:Ga:Co:Ti=1.830:0.080:0.045:0.045 . In addition, the molar ratio P/(Fe+M) of the amount of P element contained in H ₃ PO ₄ and the amounts of iron, gallium, cobalt, and titanium ions contained in the solution solution under these conditions was 0.017. In addition, in this condition, the molar ratio P/Si of the amount of P element contained in H ₃ PO ₄ and the amount of Si element contained in the dropped tetraethoxysilane was 0.006. The absolute value of ΔF ₉₀ °C of the iron-based oxide magnetic powder obtained in this example was 0.5 GHz, and the thermal stability was good when the ambient temperature was raised to 90°C.

[Example 11]

In the mixed aqueous solution, the iron-based oxide magnetic powder was produced under the same conditions as in Example 1, except that the molar ratio of the metal ions was changed to Fe:Ga:Co:Ti=1.714:0.186:0.050:0.050 . In addition, the molar ratio P/(Fe+M) of the amount of P element contained in H ₃ PO ₄ and the amounts of iron, gallium, cobalt, and titanium ions contained in the solution solution under these conditions was 0.017. In addition, in this condition, the molar ratio P/Si of the amount of P element contained in H ₃ PO ₄ and the amount of Si element contained in the dropped tetraethoxysilane was 0.006. The absolute value of ΔF ₉₀ °C of the iron-based oxide magnetic powder obtained in this example was 2.4 GHz, and the effect of coexistence of phosphorus-containing ions was confirmed by comparing with Comparative Example 1.

[Table 1]

[Table 2]

Claims (6)

An iron-based oxide magnetic powder, which is composed of ε iron oxide particles in which a part of Fe site is substituted by other metal elements, and the absolute value of ΔF ₉₀ ℃ defined by the following formula (1) is 3.0GHz the following, △F ₉₀ ℃=F ₉₀ ℃-F ₃₀ ℃...(1) Here, F ₉₀ ° C. and F ₃₀ ° C. are, respectively, for a cylindrical powder body with a diameter of 13 mm obtained by press-molding 1.2 g of the iron-based oxide magnetic powder at 28 MPa. In the transmission attenuation spectrum measured in the range of 50 to 100 GHz, the frequency that shows the maximum transmission attenuation at the measurement temperature of 90 °C is F ₉₀ °C, and the frequency of the maximum transmission attenuation at the measurement temperature of 30 °C is F ₃₀ °C. The iron-based oxide magnetic powder according to claim 1, wherein the metal element substituting a part of the Fe site is at least one selected from the group consisting of Ti, Co, Ga, and Al. The iron-based oxide magnetic powder according to claim 1, wherein the metal elements substituting a part of the Fe site are Ti, Co, and Ga. A powder compact comprising the iron-based oxide magnetic powder according to claim 1 or 2. A radio wave absorber obtained by dispersing the iron-based oxide magnetic powder according to claim 1 or 2 in resin or rubber. A method for producing a powder compact, which comprises compression-molding the iron-based oxide magnetic powder according to claim 1 or 2 to obtain a powder compact.

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