TWI732499B - SUBSTITUTION TYPE ε IRON OXIDE MAGNETIC PARTICLE POWDER, METHOD FOR MANUFACTURING SUBSTITUTION TYPE ε IRON OXIDE MAGNETIC PARTICLE POWDER, POWDER COMPACT, METHOD FOR MANUFACTURING POWDER COMPACT, AND RADIO WAVE ABSORBER - Google Patents

Abstract

An objective of the present invention is to provide a substitution type ε iron oxide magnetic particle powder and a method for producing substitution type ε iron oxide magnetic particle powder. The substitution type ε iron oxide magnetic particle powder is a reduced content of non-magnetic α-type iron oxides in which some of the Fe sites of ε-Fe2O3 have been replaced by other metal elements.

The solution to the above objective is a manufacturing method that after an acidic aqueous solution containing trivalent iron ions and metal ions for partially replacing Fe sites being neutralized to a pH of 2.0 or more and 7.0 or less, a silicon compound having a hydrolyzable group is added to the generated dispersion of iron oxyhydroxide containing replacement metal elements or mixture of iron oxyhydroxide and hydroxide containing replacement metal elements. Next, the dispersion is neutralized to pH 8.0 or higher for maintenance and maturation, such that the chemical reaction product of the silicon compound is coated on iron oxyhydroxide containing the replacement metal elements or the mixture of the iron oxyhydroxide and the hydroxide containing replacement metal elements and heated, thereby obtaining a substitution type ε iron oxide magnetic particle powder of a reduced content of the α-type iron oxide.

Description

Replacement type ε iron oxide magnetic particle powder, production method of replacement type ε iron oxide magnetic particle powder, powder compact, powder compact manufacturing method, and radio wave absorber

The present invention relates to replacement type ε iron oxide magnetic particle powder suitable for high-density magnetic recording media, radio wave absorbers, etc., and in particular, the content of non-magnetic α type iron oxides that are out of phase with the replacement type ε iron oxide is reduced The displacement type epsilon iron oxide magnetic particle powder and its manufacturing method. Furthermore, the present specification, a part of it had been replaced by other metal elements Fe oxides site ε-F _e2 O ₃ is referred to as [epsilon] iron-based oxide, and the crystalline α-Fe ₂ O ₃ is Substitution-type α iron oxide particles with the same crystal system are called α-type iron-based oxides.

ε-Fe ₂ O ₃ is an extremely rare phase in iron oxide, but in order to make nano-sized particles show a huge coercive force (Hc) of about ^{20 kOe (1.59×10 6 A/m) at room temperature,} In the past, a manufacturing method of synthesizing _{ε-Fe 2} O ₃ in a single phase has been continuously explored (Patent Document 1). However, when ε-Fe ₂ O _{3 is} used in a magnetic recording medium, since there is no tape head material with a high level of saturation magnetic flux density corresponding to this at present, it is necessary to use ε-Fe ₂ O in the application. ₃ part of the Fe site to trivalent metal Al, Ga, in other substitutions, to adjust the coercive force, and as the wavelength of the radio wave absorbent absorbing material, must also change the amount of the Fe site replaced to comply with the required Patent Document 2 discloses an ε-type iron-based oxide magnetic particle having a peak of radio wave absorption in the frequency region of 25 to 160 GHz, and Patent Document 3 discloses an epsilon that has radio wave absorption and release characteristics even in a frequency region exceeding 120 GHz. Type iron-based oxide magnetic particles.

On the other hand, since the magnetic particles of ε-type iron-based oxides are extremely fine, in order to improve environmental stability and thermal stability, it has also been explored to use part of the Fe sites of _{ε-Fe 2} O _{3 to have excellent heat resistance.} Other metal substitutions, such as 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 (here, A is Co, Ni, Mn, Zn, etc. Divalent metal elements, B is a tetravalent metal element such as Ti, and C is a trivalent metal element such as In, Ga, Al, etc.) The parts _{of various ε-Fe 2} O _{3 that are excellent in environmental stability and thermal stability.} Substitute (Patent Document 4).

Since ε-Fe ₂ O ₃ and ε-type iron-based oxides are not thermodynamically stable phases, special methods are required for their production. The above-mentioned Patent Documents 1 to 4 respectively disclose the use of fine crystals of iron oxyhydroxide produced by a liquid phase method or iron oxyhydroxide containing replacement elements as a precursor, and the precursor is used by the sol-gel method _{A method for producing ε-Fe 2} O ₃ or ε-type iron oxides that are coated with silicon oxide and then heat-treated, and for the liquid phase method, the reverse microcellular method that uses an organic solvent as the reaction medium is disclosed, and only an aqueous solution is used as the reaction. Medium method.

In addition, for example, Patent Documents 2 and 3 disclose that the aforementioned ε-Fe ₂ O ₃ and ε-type iron-based oxide systems have radio wave absorption peaks in a high frequency region exceeding 100 GHz, and are also expected to be used as radio wave absorbers.

Patent Document 5 discloses a technique for reducing the amount of α-type iron-based oxide as an impurity contained in the substitution type ε-iron oxide magnetic particle powder.

Patent Document 6 discloses a method for producing an ε-type iron-based oxide, which is to coat silicon oxide by a sol-gel method in a wide pH range.

[Prior Technical Literature]

[Patent Literature]

[Patent Document 1] JP 2008-174405 A

[Patent Document 2] JP 2008-277726 A

[Patent Document 3] JP 2009-224414 A

[Patent Document 4] International Publication No. 2008/149785

[Patent Document 5] JP 2016-130208 A

[Patent Document 6] Japanese Patent Application Publication No. 2018-092691

Since the α-type iron-based oxide is non-magnetic, the substitution type ε-iron oxide magnetic particle powder does not contribute to the electromagnetic wave absorption characteristics when used as a radio wave absorbing material, and it does not contribute to the improvement of the recording density when used as a magnetic recording medium. Therefore, it is necessary to reduce its content.

However, the manufacturing methods disclosed in Patent Documents 2 and 3 use the inverse microcellular method, and the magnetic particle powder obtained by these manufacturing methods contains a considerable amount of non-magnetic α-type iron in addition to the ε-type iron-based oxide. It is the impurity of oxide.

In addition, the replacement type ε iron oxide particle powder disclosed in Patent Document 3 has the maximum point of radio wave absorption in the frequency region exceeding 120 GHz. However, in order to set the frequency region to 150 GHz or more, the replacement amount is reduced to x<0.10. There is a problem that the saturation magnetization σ s becomes lower. If the saturation magnetization σ s is low, when used as a radio wave absorbing material, there will be a problem of reduced radio wave absorption.

The ε-type iron-based oxide manufactured by the manufacturing method disclosed in Patent Document 4 has a reduced content of the α-type iron-based oxide, which is an impurity, compared to the ε-type iron-based oxide manufactured by the conventional method. However, when the substitution amount is small, even if the manufacturing method disclosed in Patent Document 4 is used, it is difficult to obtain the _{same space group as ε-Fe 2} O ₃ , and the content of α-type iron-based oxides may be insufficiently reduced. The situation.

That is, the technical problem to be solved by the present invention is to provide a replacement type ε iron oxide magnetic particle powder and a production method of the replacement type ε iron oxide magnetic particle powder. The replacement type ε iron oxide magnetic particle powder is in the frequency range of 150 GHz or more. The ε-type iron-based acid compound with a small amount of substitution with radio wave absorption energy, and the content of the non-magnetic α-type iron-based acid compound is reduced and the saturation magnetization σ s is higher.

In order to obtain the replacement type ε iron oxide magnetic particle powder, the inventors focused on those who must heat the precursor of the magnetic particle powder in the state where the silicon oxide was coated. The hydrolyzable silicon compound is added to the aqueous solution containing the precursor at a time when the pH is above 2.0 and below 7.0, thereby reducing the content of α-type iron-based oxides.

Based on the above knowledge, the inventors of the present invention have completed the present invention as described below.

In order to solve the above-mentioned problems, the present invention provides a substituted type ε iron oxide magnetic particle powder in which _{a part of Fe sites of ε-Fe 2} O ₃ has been replaced with another metal element, wherein the aforementioned substituted type ε iron oxide magnetic When the molar number of Fe contained in the particle powder is set to Fe, and the molar number of the total metal elements replaced by Fe sites is set to Me, it is defined by Me/(Fe+Me) by other metals The replacement amount of Fe by the element is 0.025 or more and 0.070 or less, and the content of the α-type iron-based oxide measured by the X-ray diffraction method is 20% or less.

The aforementioned substitution type ε iron oxide magnetic particle powder preferably has a saturation magnetization σs of 15.5 Am ² /kg or more.

In addition, the aforementioned other metal element to replace part of the Fe site is preferably one or two selected from Ga and Al.

In addition, the present invention provides a compressed powder body comprising the aforementioned substituted type ε iron oxide magnetic particle powder.

In addition, the present invention provides a radio wave absorber obtained by dispersing the aforementioned substitution type ε iron oxide magnetic particle powder in resin or rubber.

In addition, the present invention provides a method for manufacturing substitution type ε iron oxide magnetic particle powder, the substitution type ε iron oxide magnetic particle powder is one _{in which a part of Fe sites of ε-Fe 2} O ₃ has been replaced with another metal element, and The manufacturing method includes the following steps: a neutralization step, using an acidic aqueous solution containing trivalent iron ions and metal ions to partially replace Fe sites as a raw material solution, and adding an alkali to the raw material solution to neutralize to pH 8.0 or higher 10.0 or less, a dispersion liquid is obtained, which contains a mixture of iron oxyhydroxide or iron oxyhydroxide containing a replacement metal element and a hydroxide of the replacement metal element; the silicon compound addition step is based on the aforementioned oxyhydroxide containing the replacement metal element In the dispersion liquid of the mixture of iron or the iron oxyhydroxide and the hydroxide of the replacement metal element, a silicon compound having a hydrolyzable group is added; and the aging step is to include the iron oxyhydroxide containing the replacement metal element or the hydroxyl group The mixture of iron oxide and the hydroxide of the replacement metal element and the dispersion of the aforementioned silicon compound are maintained at a pH of 8.0 or more and 10.0 or less, so that the chemical reaction product of the aforementioned silicon compound is coated on the iron oxyhydroxide containing the replacement metal element or the hydroxyl group A mixture of iron oxide and a hydroxide of a replacement metal element; wherein, in the aforementioned neutralization step, the addition of the aforementioned silicon compound with hydrolyzable groups is carried out when the pH of the dispersion is 2.0 or more and 7.0 or less, and it will be added to the pH When the molar number of the aforementioned silicon compound in the dispersion of 2.0 to 7.0 is set to S, the molar number of Fe ions contained in the raw material solution is set to F, and the total molar number of replacement metal element ions is set to M , S/(F+M) is 0.50 or more and 10.0 or less.

In the aforementioned manufacturing method, the aforementioned other metal element to be partially replaced with Fe sites is preferably one or two selected from Ga and Al.

In addition, the present invention provides a method for producing a compact, which is obtained by compressing and molding the aforementioned displacement type epsilon iron oxide magnetic particle powder.

As described above, by using the manufacturing method of the present invention, it is possible to obtain substituted type ε iron oxide magnetic particle powder with a reduced content of α-type iron-based oxide and a high saturation magnetization σs, and a compact using the magnetic particle powder, Radio wave absorber.

Fig. 1 is a schematic diagram showing an example of the embodiment of the present invention.

〔Magnetic iron oxide particles〕

The manufacturing method of the present invention is a method for manufacturing substitution type ε iron oxide magnetic particle powder in which a part of Fe sites of _{ε-Fe 2} O _{3 is replaced with other metal elements.} Different phases of impurities to avoid. The different phase is mainly α-type iron-based oxide, and the iron oxide magnetic particle powder obtained by the present invention substantially includes ε-type iron-based oxide magnetic particles and α-type iron-based oxide. The purpose of the present invention is to reduce the content of α-type iron-based oxides belonging to different phases and to suppress the decrease of saturation magnetization σs.

Whether a part of the Fe site of ε-Fe ₂ O ₃ is replaced by another metal element has an ε structure or not can be confirmed by X-ray diffraction (XRD), high-speed electron diffraction (HEED), etc. In the present invention, the identification of ε-type and α-type iron-based oxides is performed by XRD.

The partial replacement bodies that can be manufactured by the manufacturing method of the present invention can be listed as follows.

It is represented by the general formula ε-C _z Fe _2-z O ₃ (here, C is one or more trivalent metal elements selected from In, Ga, and Al).

For example, the general formula ε-A _x B _y Fe _2-xy O ₃ (here, A is one or more divalent metal elements selected from Co, Ni, Mn, and Zn, and B is one or more divalent metal elements selected from Ti and Sn Tetravalent metal element).

For example, the general formula ε-A _x C _z Fe _2-xz O ₃ (here, A is one or more divalent metal elements selected from Co, Ni, Mn, and Zn, and C is one selected from In, Ga, Al The above trivalent metal element).

Such as the general formula ε-B _y C _z Fe _2-yz O ₃ (here, B is one or more tetravalent metal elements selected from Ti and Sn, and C is one or more trivalent metal elements selected from In, Ga, Al Metal elements) are shown.

Such as the general formula ε-A _x B _y C _z Fe _2-xyz O ₃ (here, A is selected from one or more divalent metal elements selected from Co, Ni, Mn, and Zn, and B is selected from Ti, Sn One or more types of tetravalent metal elements, and C is one or more types of trivalent metal elements selected from In, Ga, and Al).

Here, the type replaced by only the C element has the advantages of being able to arbitrarily control the coercive force of the magnetic particles and easily obtaining the same space group as _{ε-Fe 2} O _3. The production method of the present invention described later can also be applied when the replacement amount of the metal element replaced by the Fe site is any value, but it is effective to apply it with a replacement amount that easily generates an α-type iron-based oxide. In order to set the frequency domain of the peak of the radio wave absorption to 150 GHz or more, it is preferable to set C to one or two selected from Ga and Al, and set the replacement amount defined by Me/(Fe+Me) to Above 0.025 and below 0.070. With this manufacturing method, it is possible to obtain the substitution type ε iron oxide magnetic particle powder that cannot be obtained by the conventional method, that is, the content of the α-type iron-based oxide measured by XRD is 20% or less and has a high saturation magnetization σs The replacement type ε iron oxide magnetic particle powder.

〔Powder and radio wave absorber〕

The replacement type ε iron oxide magnetic particle powder obtained in the present invention has a powder particle filling structure formed, and functions as a radio wave absorber with excellent radio wave absorbing ability. The “filled structure” referred to here means a state in which the particles are in contact with or close to each other to form a three-dimensional structure. In order for the radio wave absorber to be actually used, the filling structure must be maintained. The method can include, for example, a method of compressing and molding the displacement type ε iron oxide magnetic particle powder to form a compact; or, using a non-magnetic polymer compound as a binder to solidify it with the displacement type ε iron oxide magnetic particle powder. To form a method of filling the structure.

In the method of using a binder, the displacement type ε iron oxide magnetic particle powder is mixed with a non-magnetic polymer base material to obtain a kneaded product. The blending quantity of the radio wave absorbing material powder in the mixture is better The system is set to 60% by mass or more. The more the amount of the radio wave absorbing material powder blended, the more beneficial it is to improve the radio wave absorption characteristics, but if too much, it will become 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% by mass or 85 to 95% by mass.

The polymer base material can be used to meet various requirements of heat resistance, flame retardancy, durability, mechanical strength, and electrical characteristics according to the use environment. For example, it is only necessary to select an appropriate one from resin (nylon, etc.), gel (silicone gel, etc.), thermoplastic elastomer, rubber, and the like. In addition, two or more polymer compounds may be blended to form a substrate.

〔Saturation magnetization〕

In the present invention, the saturation magnetization σs of the iron oxide magnetic particle powder obtained by the manufacturing method of the present invention is preferably 15.5 Am ² /kg or more. When σs is less than 15.5 Am ² /kg, the amount of radio wave absorption will decrease when used as a radio wave absorbing material, which is not good. The upper limit of σs is not specifically defined, but it is usually ^{about 19.0 Am 2} /kg or less.

〔The average particle size〕

In the present invention, the average particle size of the iron oxide magnetic particle powder obtained by the manufacturing method of the present invention is not particularly defined, but it is preferable that each particle is as fine as a single magnetic domain structure. Generally, those with an average particle diameter of 10 nm or more and 40 nm or less as measured by a penetrating electron microscope can be obtained.

〔Starting substances and precursors〕

In the manufacturing method of the present invention, an acidic aqueous solution containing trivalent iron ions as the starting material of the iron-based oxide magnetic particle powder and metal ions of the metal element that finally replaces the Fe site is used (hereinafter referred to as the raw material solution ). If divalent Fe ions are used instead of trivalent Fe ions as the starting material, a mixture of hydrated oxides or magnetite containing divalent iron in addition to trivalent iron hydrates or magnetite will be generated as a precipitate. Shape of the resulting iron-based oxide particles Uneven distribution occurs, and therefore, it is impossible to obtain the substituted type ε iron oxide magnetic particle powder with the content of the α-type iron-based oxide of the present invention reduced. Here, the so-called acidity refers to the situation where the pH of the solution does not reach 7.0. Regarding the supply source of the iron ions or the metal ions of the replacement element, from the viewpoint of the ease of acquisition and the price. Preferably, water-soluble inorganic acid salts such as nitrate, sulfate, and chloride are used. When these metal salts are dissolved in water, the metal ions will dissociate, making the aqueous solution acidic. When an alkali is added to neutralize the acidic aqueous solution containing the metal ion, a mixture of iron oxyhydroxide and a hydroxide of the replacement element, or iron oxyhydroxide in which a part of the Fe site has been replaced by other metal elements (in this In the specification, these are collectively referred to as the precipitation of iron oxyhydroxide containing replacement elements. In the production method of the present invention, iron oxyhydroxide containing these substitution elements is used as a precursor of substitution type ε iron oxide magnetic particle powder.

Although the total metal ion concentration in the raw material solution is not specifically defined in the present invention, it is preferably 0.01 mol/L or more and 0.5 mol/L or less. If it is less than 0.01 mol/L, the amount of substituted ε iron oxide magnetic particle powder obtained in one reaction is small, which is economically poor. When the total metal ion concentration exceeds 0.5 mol/L, the rapid precipitation of hydroxide will cause the reaction solution to easily gel, which is not preferable.

〔Neutralization Step〕

In the production method of the present invention, an alkali is added to the raw material solution and neutralized until the pH becomes 8.0 or more and 10.0 or less to obtain a dispersion liquid containing a precipitate of iron oxyhydroxide containing a substitution element. In addition, the hydroxide of trivalent iron ion mainly contains oxyhydroxide. Here, the pH of the dispersion liquid is set to 8.0 or higher in order to complete the precipitation and formation of the hydroxide of the replacement metal element such as Ga or Al, and to promote the condensation reaction of the silanol derivative which is a hydrolysis product. In the manufacturing method of the present invention, the upper limit of the pH reached in the neutralization step is not specifically defined, but the neutralization Since the effect is saturated and the effect of promoting the condensation reaction of the silanol derivative described later is reduced, it is preferably set to 10.0.

The alkali used in the neutralization can be any of alkali metal or alkaline earth metal hydroxides, ammonia water, ammonium bicarbonate and other ammonium salts, but it is not easy to leave impurities when the final heat treatment is used to make ε-type iron-based oxides The ammonia or ammonium bicarbonate is preferred. These bases may be added in a solid state to the aqueous solution of the starting material, but from the viewpoint of ensuring the uniformity of the reaction, they are preferably added in the state of an aqueous solution.

As mentioned above, when an alkali is added to the raw material solution to perform the neutralization treatment, the precipitate of the iron oxyhydroxide containing the replacement element will precipitate. Therefore, the dispersion liquid containing the precipitate is used for the neutralization treatment by a well-known mechanical means. Stir it.

The addition of the alkali to the raw material solution can be carried out continuously from the start of the addition until the end. In addition, before the pH of the dispersion reaches 8.0, the addition of alkali can be interrupted and a predetermined pH holding time can be set. At this time, the pH holding time can be set several times to intermittently add the alkali. In addition, the number of times the pH holding time is set, that is, the number of times the addition of the alkali is interrupted, is preferably set to 3 times or less in order to avoid the complexity of the manufacturing process.

In the production method of the present invention, the reaction temperature during the neutralization treatment is set to 5°C or more and 60°C or less. When the reaction temperature is less than 5°C, the cost will increase due to cooling, which is not preferable. When the temperature exceeds 60°C, α-type oxides that belong to different phases are likely to be formed eventually, which is not preferable. More preferably, it is 10°C or more and 40°C or less. In the production method described in Patent Document 4, the neutralization treatment must be carried out at 5°C or higher and 25°C or lower, and a refrigerator is required for the reaction. However, in the production method of the present invention, it can also be carried out at a reaction temperature higher than normal temperature. Neutralization treatment.

In addition, the value of pH described in this specification is based on JIS Z8802 and measured using a glass electrode. The pH standard solution refers to the value measured by a calibrated pH meter using an appropriate buffer solution corresponding to the pH region to be measured. In addition, the pH described in this specification is the value obtained by directly reading the measured value shown by the pH meter compensated by the temperature compensation electrode under the reaction temperature condition.

〔Steps for adding silicon compound〕

In the manufacturing method of the present invention, the precursor of the substitution type ε-iron oxide magnetic particle powder produced in the foregoing steps, that is, the iron oxyhydroxide containing the substitution element, even if it is heat-treated in its original state, the ε-type iron-based oxide It is also not easy to produce phase change. Therefore, before the heat treatment, the iron oxyhydroxide containing the replacement element must be coated with the chemical reaction product obtained by the hydrolysis reaction and the condensation reaction of the silicon compound. Here, the chemical reaction product of a silicon compound is not only a silicon oxide with a stoichiometric composition, but also a non-quantitative composition such as a silanol derivative or a polysiloxane structure described later, and is transformed into silicon by subjecting it to heat treatment. Oxide, the latter, etc. are used collectively.

In the production methods described in Patent Documents 1 to 6, the sol-gel method is used to coat the chemical reaction product of the silicon compound. The neutralization treatment of the raw material solution is completed, and the pH of the reaction solution will be hydrolyzed after reaching the alkaline side. The base silicon compound is added to the reaction solution. On the other hand, in the production method of the present invention, although the sol-gel method is also used for the coating method of silicon oxide, it is characterized in that the pH of the reaction solution is on the acid side before the neutralization of the raw material solution is completed. When the pH is above 2.0 and below 7.0, the addition of silicon compounds with hydrolyzed groups is started.

In the sol-gel method, a silicon compound with hydrolyzable groups, such as tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), etc., is added to the dispersion containing the iron oxyhydroxide containing the replacement element. Oxysilanes, or add various silane coupling agents and other silane compounds, and stir Then, it causes a hydrolysis reaction to condense the generated silanol derivative to form a polysiloxane bond, thereby covering the surface of the iron oxyhydroxide containing the replacement element.

The inventors of the present invention found that starting the addition of the aforementioned silicon compound with hydrolyzable groups at a pH of 2.0 or more and 7.0 or less, the α-type iron-based oxide contained in the finally obtained substituted type ε iron oxide magnetic particle powder can be reduced The reason for the decrease in the content rate is believed to be as follows.

The rate of the hydrolysis reaction of the aforementioned silicon compound having a hydrolyzed group and the condensation reaction of the silanol derivative which is a hydrolysis product varies depending on the pH of the reaction system. The rate of the hydrolysis reaction is generally greater in the low pH region on the acidic side, and decreases with the increase of pH, and increases again in the high pH region on the alkaline side. In contrast, the speed of the condensation reaction is small in the low pH region on the acidic side, and increases as the pH rises, and increases in the pH region on the neutral to alkaline side.

In a dispersion containing a precipitate of iron oxyhydroxide containing a substitution element, when a silicon compound with a hydrolyzed group is added to the low pH region on the acidic side, the aforementioned silicon compound is rapidly hydrolyzed to produce a silanol derivative with less organic components On the other hand, the resulting silanol derivative does not undergo condensation reaction. Here, the silanol derivative has an OH group which is a hydrophilic group and will be uniformly distributed in the aqueous solution. Therefore, it is considered that the precipitate of the iron oxyhydroxide containing the replacement element and the silanol derivative are uniformly dispersed and coexist in the dispersion liquid. status.

Then, when the pH of the dispersion is further increased, since the condensation reaction of the silanol derivative is dominant, the precipitate of the iron oxyhydroxide containing the substitution element is uniformly covered by the silanol derivative or its condensation reaction product. Therefore, it is considered that the content of the α-type iron-based oxide contained in the substituted ε-iron oxide magnetic particle powder finally subjected to heat treatment will be reduced, and as a result, the decrease in the saturation magnetization σ s is also suppressed.

In addition, the aforementioned Patent Document 6 discloses that silicon oxide is coated by the sol-gel method in a wide range of pH regions, but in this case, the addition of the silicon compound is performed at a constant pH after the neutralization treatment is completed. The invention also considers the technical idea of both the hydrolysis reaction speed and the condensation reaction speed of the silicon compound.

The pH at which the silicon compound having a hydrolyzed group is initially added is preferably 2.0 or more. When the pH is less than 2.0, the main component of the displacement type ε iron oxide magnetic particle powder, that is, the formation of the hydroxide of the trivalent iron ion contained in the raw material solution may be insufficient. The pH of the initial addition is more preferably 3.0 or more. In addition, the pH at which the silicon compound having a hydrolyzable group is initially added is preferably 7.0 or less. When the pH exceeds 7.0, the hydrolysis reaction becomes slow and the formation of the silanol derivative is insufficient. Therefore, it is impossible to obtain a state in which the precipitation of the iron oxyhydroxide containing the substitution element and the silanol derivative are uniformly dispersed and coexist in the dispersion liquid, so that the content The precipitation of the iron oxyhydroxide of the substitution element is difficult to be uniformly coated by the silanol derivative or its condensation reaction product. The pH of the initial addition is preferably 6.0 or less, more preferably 4.0 or less.

The addition of the silicon compound having a hydrolyzable group is started when the pH of the raw material solution reaches a desired value in the neutralization step. The addition of the silicon compound can be continuously performed after the start of the addition until the end. Here, the term “continuously” includes adding the entire amount of the silicon compound added to the dispersion to the dispersion at once. In addition, the addition of the silicon compound may be divided into multiple times and performed intermittently.

In addition, the addition of the silicon compound is started when the pH of the dispersion is 2.0 or more and 7.0 or less. However, considering the hydrolysis effect of the silicon compound, it is preferable to end the addition when the pH is 7.0 or less. The addition of the silicon compound may be performed while keeping the pH of the dispersion constant, or may be performed simultaneously with the addition of the alkali. In addition, before and after the addition of the silicon compound, The dispersion is homogenized, and the time to maintain the dispersion at a constant pH can be set. Here, the term "starting the addition of the silicon compound when the pH of the dispersion liquid is 7.0 and ending when the pH is 7.0" means that the addition of the silicon compound is performed while maintaining the pH of the dispersion liquid at 7.0.

Fig. 1 schematically shows an example of the time transition of an embodiment in which the addition of the alkali is interrupted in the middle of the neutralization step and the silicon compound is added while keeping the pH of the dispersion constant. The arrow in the figure is the time axis. At this time, the addition of the alkali was once interrupted, and the entire amount of the silicon compound was continuously added during the pH holding time during which the addition of the alkali was interrupted. In addition, the implementation aspects of the present invention are not limited to the implementation aspects listed in FIG. 1.

In the production method of the present invention, the amount of the silicon compound added to the dispersion with a pH of 2.0 or more and 7.0 or less, if the total moles of the added silicon compound is set to S, the Fe ions contained in the raw material solution When the molar number of is F and the total molar number of the replacement metal element ion is M, S/(F+M) is preferably 0.50 or more and 10.0 or less.

When S/(F+M) is less than 0.50, the coating amount of the chemical reaction product of the silicon compound on the surface of the precipitation of the iron oxyhydroxide containing the substitution element will decrease, and as a result, the α-type iron-based oxide will be easily formed. The shortcomings are therefore not good. In addition, when S/(F+M) exceeds 10.0, the processing volume of the heating step and the silicon oxide removal step described later will increase, increasing the manufacturing cost, which is not good.

〔Steps of maturation〕

Even if the pH is set to 8.0 or higher, the condensation reaction of the silanol derivative will proceed slowly, so the chemical reaction product containing the iron oxyhydroxide containing the substitution element and the silicon compound obtained after the aforementioned neutralization step and the silicon compound addition step is used The dispersion is maintained at a pH of 8.0 or more and 10.0 or less for maturation, allowing the silanol derivative to undergo condensation reaction. As a result, the condensation reaction product of the silanol derivative is formed on the surface of the precipitate of the iron oxyhydroxide containing the replacement element to form a uniform coating Cladding. It is believed that the coating layer covers almost the entire surface of the precipitate surface of the iron oxyhydroxide containing the replacement element, but within the range that can achieve the effect of the present invention, the surface of the precipitate of the iron oxyhydroxide containing the replacement element is allowed to exist The uncovered part. The aforementioned aging time is preferably 1 hour or more and 24 hours or less. When the retention time is less than 1 hour, the precipitation of the iron oxyhydroxide containing the replacement element is not completed by the condensation of the silanol derivative, and α-type iron-based oxides are easily formed. When it exceeds 24 hours, the maturation effect is saturated, so Bad.

In the manufacturing method of the displacement type ε iron oxide magnetic particle powder of the present invention, the steps subsequent to the above-mentioned aging step can be the same steps as the conventional manufacturing methods described in Patent Documents 1 to 5, for example. Specifically, the following steps can be cited.

〔Heating Step〕

In the production method of the present invention, the iron oxyhydroxide containing the substitution element coated with the condensation reaction product of the silanol derivative is recovered using a known solid-liquid separation method, and then subjected to heat treatment to obtain ε-type iron Department of oxides. Before the heat treatment, washing and drying steps can be set. The heating treatment may be performed in an oxidizing environment, and the oxidizing environment may be an atmospheric environment. Heating can be carried out in the range of about 700°C to 1300°C, but when the heating temperature is higher, α-Fe ₂ O ₃ (in terms of ε-Fe ₂ O ₃ is an impurity), which is a thermodynamically stable phase, is likely to be generated, so heating The treatment is preferably performed at 900°C or higher and 1200°C or lower, more preferably 950°C or higher and 1150°C or lower.

The heat treatment time can be adjusted in the range of 5h or more and 10h or less, but it is easy to obtain good results in the range of 2h or more and 5h or less. In addition, it is believed that the presence of the silicon-containing substance that coats the particles has a beneficial effect on causing a phase change toward an ε-type iron-based oxide, rather than causing a phase change toward an α-type iron-based oxide. In addition, the silicon oxide coating has the effect of preventing the iron oxyhydroxide crystals containing the substitution element from being sintered during heat treatment.

When the ε-type iron-based oxide magnetic particle powder does not need to be coated with silicon oxide, it is only necessary to remove the silicon oxide coating after the heat treatment.

〔Analysis of composition by high frequency inductively coupled plasma emission spectroscopy (ICP)〕

The composition analysis of the obtained ε-type iron-based oxide magnetic powder was carried out by the dissolution method. In the composition analysis, ICP-720ES manufactured by Agilent Technologies was used, and the measurement wavelength (nm) was performed with Fe; 259.940 nm, Ga; 294.363 nm, Co; 230.786 nm, Ti; 336.122 nm, Al; 396.152 nm, Si; 288.158 nm.

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

A high-temperature superconducting type VSM (VSM-5HSC-6T manufactured by Toei Kogyo Co., Ltd.) was used to apply a magnetic field of 4786kA/m (60kOe) and a M measuring range of 0.002A. m ² (2emu), stepping bit 300bit, time constant 0.03sec, waiting time 0.2sec to measure magnetic characteristics. Based on the BH curve, the coercive force Hc and the saturation magnetization σs are evaluated.

[Evaluation of crystallinity by X-ray diffraction (XRD)]

The obtained sample was supplied to powder X-ray diffraction (XRD: sample horizontal type multi-purpose X-ray diffraction device Ultima IV manufactured by Rigaku Corporation, line source CuKα line, voltage 40kV, current 40mA, 2θ=10° or more and 70° or less). The obtained diffraction pattern was used with integrated powder X-ray analysis software (PDXL2: manufactured by Rigaku Corporation), and ICSD (Inorganic Crystal Structure Database) No.173025: Iron(III) Oxide-Epsilon, No.82134: Hematite were used as Basically, it is evaluated by Rietveld analysis to confirm the crystal structure and the existence rate of the α phase.

〔BET specific surface area〕

The BET specific surface area was determined by the BET one-point method using Macsorb model-1210 manufactured by Mountech Co., Ltd.

[Measurement of radio wave absorption characteristics]

1.2 g of the replacement type ε iron oxide powder was press-molded at 28 MPa (20 kN) to obtain a compact having a diameter of 13 mm and a thickness of 3 mm. For the obtained compressed powder, the penetration attenuation was measured by Terahertz Time Domain Spactroscopy (Terahertz Time Domain Spactroscopy). Specifically, the megahertz spectrum system TAS7400SL manufactured by Advantest was used, and the measurement was performed in the case of placing the compact in the sample rack and the case of a blank sample. The measurement conditions are as follows.

10mm ‧Diameter of sample holder:

10mm

‧Measurement mode: transmission

‧Frequency resolution: 1.9GHz

‧Vertical axis: Absorbance

‧Horizontal axis: Frequency [THz]

‧Cumulative number (sample): 2048

‧Cumulative number (background): 2048

Extend the observed signal waveform of the sample and the reference waveform of the blank group to 2112ps for Fourier transformation, calculate the ratio (Ssig/Sref) of the obtained Fourier spectrum (set as Sref, Ssig, respectively), and place it in the sample rack. The penetration attenuation of the pressed powder body.

(Example)

[Example 1]

In a 1L reaction tank, 116.79g of iron(III) nitrate solution with Fe concentration of 11.65 mass% and 4.39g of aluminum(III) nitrate nonahydrate with 98% purity were mechanically stirred in the atmosphere by stirring blades. While stirring, it was dissolved in 746.07 g of pure water as a raw material solution (sequence 1). The pH of the raw material solution is about 1. The molar ratio of the metal ions in the raw material solution is Fe:Al=1.910:0.090.

In an atmospheric environment, the raw material solution was mechanically stirred by a stirring blade under the condition of 30°C. At the same time, it took 60 minutes to add 51.71g of 22.30mass% ammonia solution (first neutralization), and continue to stir after the completion of the dripping. The homogenization of the formed precipitate is carried out for 10 minutes. At this time, the pH of the slurry containing the precipitate is about 3 (sequence 2). The slurry obtained in step 2 was stirred, and 80.56 g of tetraethoxysilane (TEOS) with a purity of 95.0 mass% was dropped into the atmosphere at 30°C for 5 minutes. After the addition of TEOS, 27.15 g of 22.30 mass% ammonia solution was added within 14 minutes (second neutralization). The pH after the second neutralization step was 8.9. Then, stirring was continued for 20 hours to coat the precipitate with the hydrolysis product of the silane compound generated by the hydrolysis (sequence 3). In addition, under this condition, the molar ratio Si/(Fe+M) of the amount of Si element contained in the TEOS dropped into the slurry and the amount of iron and aluminum ions contained in the aforementioned solution is 1.44 .

The slurry obtained in step 3 is filtered, and the resulting precipitates of iron oxyhydroxide containing replacement elements covered by the hydrolyzed product of the silane compound are removed as much as possible, and then dispersed in pure water for re-slurrying Wash. The washed slurry was filtered again, and the resulting filter cake was dried at 110°C in the air (sequence 4).

The dried product obtained in Step 4 was heated in a box-type sintering furnace at 1090°C for 4 hours in the atmosphere to obtain substituted type ε iron oxide magnetic particle powder coated with silicon oxide (Step 5). In addition, the hydrolyzed product of the aforementioned silane compound undergoes heat treatment in an atmospheric environment, and is dehydrated to change into an oxide.

Table 1 shows the production conditions such as the addition conditions of the raw material solution in this example.

The heat-treated powder after heat treatment is applied to the precipitates of iron oxyhydroxide containing replacement elements that are covered by the hydrolysis product of the silane compound obtained in step 5, and the particles are stirred in a 17.58mass% NaOH aqueous solution at about 60°C for 24 hours. The silicon oxide coating on the surface is removed (sequence 6). Next, use a centrifuge to clean the slurry until the conductivity of the slurry becomes 500mS/m or less, filter it with a membrane filter, and dry it. The resulting iron-based oxide magnetic powder is subjected to chemical analysis, XRD measurement, and composition analysis. Measurement of magnetic properties, etc. The results of these measurements are shown in the table. The table also shows the physical property values of the substituted ε iron oxide magnetic particle powder obtained in the comparative example.

XRD measurement was performed on the replacement type ε iron oxide powder of this example, and the existence rate of the α phase was determined, and the result was 14.2%. In addition, the saturation magnetization σs is 16.5 Am ² /kg.

This value is compared with the ratio of the existence rate and saturation of the α phase of the replacement type ε iron oxide magnetic particle powder obtained in the comparative example using iron (III) nitrate as the iron raw material and adding TEOS after the addition of the ammonia solution after the pH reaches 8.9. The magnetization σs is more excellent. In addition, chemical analysis of composition and evaluation of magnetic properties are performed. The measurement results are shown in Table 2 together.

With respect to the obtained replacement type ε iron oxide magnetic particle powder, the radio wave absorption characteristics were measured by the aforementioned method. As a result, the maximum absorption frequency of the compressed powder in the frequency range of 50 GHz to 100 GHz was 160.7 GHz, and the penetration attenuation per unit thickness was 13.9 dB/mm.

[Comparative Example 1]

The following is the conventional procedure for silicon oxide coating by the sol-gel method. In a 1L reaction tank, 98.72g of 99% purity iron (III) nonahydrate and 4.39g purity of 98% aluminum nitrate (III) nonahydrate are mechanically stirred by a stirring blade in the atmosphere, and simultaneously dissolved in 746.07 g of pure water was used as a raw material solution (procedure 1). The pH of the raw material solution is about 1. The molar ratio of the metal ions in the raw material solution is Fe:Al=1.910:0.090.

In an atmospheric environment, the raw material solution was mechanically stirred by a stirring blade at 30°C, and at the same time, 78.86g of 22.30 mass% ammonia solution was added for 10 minutes, and after the addition, it was continuously stirred for 30 minutes to generate a precipitate. The homogenization. At this time, the pH of the slurry containing the precipitate was about 8.9 (sequence 2). The slurry obtained in step 2 was stirred, and 80.56 g of tetraethoxysilane (TEOS) with a purity of 95.0 mass% was dropped into the atmosphere at 30°C for 10 minutes. After the addition of TEOS, stirring was continued for 20 hours to coat the precipitate with the hydrolysis product of the silane compound generated by the hydrolysis (sequence 3). In addition, under this condition, the molar ratio Si/(Fe+M) of the amount of Si element contained in the TEOS dropped into the slurry and the amount of iron and aluminum ions contained in the aforementioned solution is 1.44 .

Then, in the same procedure as in Example 1, a displacement type ε iron oxide magnetic particle powder was obtained. The replacement type ε iron oxide magnetic particle powder of Comparative Example 1 was subjected to XRD measurement, and the existence rate of the α phase was determined. The result was 46.6%, which was a higher value than the example with the same additive composition. The saturation magnetization σs It is the lower value of ^{11.1Am 2 /kg.} Table 2 shows the evaluation results of the chemical analysis of the composition, the magnetic properties, and the radio wave absorption properties. (The following examples and comparative examples are also the same)

[Example 2]

Except that the 98% purity aluminum (III) nitrate nonahydrate used was changed to 3.42 g, the same conditions as in Example 1 were used to produce the replacement type epsilon iron oxide magnetic particle powder. In addition, the molar ratio of the metal ions in the additive solution is Fe:Al=1.930:0.070. The existence rate of the α phase in the substituted ε iron oxide magnetic particle powder obtained in this example was calculated, and the result was 16.0%, and the saturation magnetization σs was 15.6 Am ² /kg.

[Example 3]

Except that the 98% purity aluminum (III) nitrate nonahydrate used was changed to 6.93 g of Ga (III) nitrate solution with a Ga concentration of 11.55 mass%, the rest was made under the same conditions as in Example 1 to produce a displacement type ε iron oxide magnet. Particle powder. In addition, the molar ratio of the metal ions in the additive solution is Fe:Ga=1.910:0.090. The existence rate of the α phase in the substituted ε iron oxide magnetic particle powder obtained in this example was calculated, and the result was 11.9%, and the saturation magnetization σs was 18.0 Am ² /kg.

[Comparative Example 2]

Except that the 98% purity aluminum (III) nitrate nonahydrate used was changed to 6.93 g of a Ga(III) nitrate solution with a Ga concentration of 11.55 mass%, the rest was made under the same conditions as in Comparative Example 1 to produce a displacement type ε iron oxide magnet. Particle powder. In addition, the molar ratio of the metal ions in the additive solution is Fe:Ga=1.910:0.090. The existence rate of the α phase in the substitution type ε iron oxide magnetic particle powder obtained by this example is calculated, and the result is 26.4%, which is a higher value than the example with the same additive composition, and the saturation magnetization σs is 15.0 Am ² /kg.

From the above results, it can be seen that when the silicon compound is not added in the low pH region where the hydrolysis reaction of the silicon compound is dominant, the condensation reaction of the silanol derivative is formed even in the high pH region where the condensation reaction of the silanol derivative is dominant. When the material is matured, it is impossible to obtain the substitution type ε iron oxide magnetic particle powder with a low content of α phase and a high saturation magnetization σs.

[Table 1]

[Table 2]

Claims (8)

A replacement type ε iron oxide magnetic particle powder, _{in which a part of the Fe site of ε-Fe 2} O ₃ has been replaced by other metal elements, wherein the content of Fe contained in the aforementioned replacement type ε iron oxide magnetic particle powder is When the number of ears is set to Fe, and the number of moles of the total metal elements replaced by Fe sites is set to Me, the replacement amount of Fe by other metal elements defined by Me/(Fe+Me) is 0.025 or more and 0.070 or less, and the α-type iron-based oxide content measured by X-ray diffraction method is 20% or less. The replacement type ε iron oxide magnetic particle powder described in claim 1 has a saturation magnetization σ s of 15.5 Am ² /kg or more. The replacement type ε iron oxide magnetic particle powder according to claim 1 or 2, wherein the other metal element to be replaced with a part of Fe sites is one or two selected from Ga and Al. A pressed powder body comprising the replacement type epsilon iron oxide magnetic particle powder according to any one of claims 1 to 3. A radio wave absorber obtained by dispersing the substitution type ε iron oxide magnetic particle powder described in any one of claims 1 to 3 in resin or rubber. A method for manufacturing substitution type ε iron oxide magnetic particle powder. The substitution type ε iron oxide magnetic particle powder is one _{in which a part of Fe sites of ε-Fe 2} O ₃ has been replaced with other metal elements, and the manufacturing method includes the following steps : The neutralization step uses an acidic aqueous solution containing trivalent iron ions and metal ions to partially replace the aforementioned Fe sites as a raw material solution, and an alkali is added to the raw material solution to neutralize it to pH 8.0 or more and 10.0 or less, to obtain a dispersion liquid, the dispersion liquid containing iron oxyhydroxide containing a replacement metal element or a mixture of iron oxyhydroxide and a hydroxide of the replacement metal element; The silicon compound addition step is to add a silicon compound having a hydrolyzed group to the dispersion liquid containing the iron oxyhydroxide containing the replacement metal element or the mixture of the iron oxyhydroxide and the hydroxide of the replacement metal element; and The maturation step is to maintain a dispersion liquid containing the iron oxyhydroxide containing the replacement metal element or the mixture of the iron oxyhydroxide and the hydroxide of the replacement metal element and the silicon compound at a pH of 8.0 or more and 10.0 or less to make the silicon compound The chemical reaction product is coated on the iron oxyhydroxide containing the replacement metal element or the mixture of the iron oxyhydroxide and the hydroxide of the replacement metal element; wherein, In the aforementioned neutralization step, the addition of the aforementioned silicon compound having a hydrolyzable group is carried out when the pH of the dispersion is 2.0 or more and 7.0 or less. The number of moles of the aforementioned silicon compound added to the dispersion of pH 2.0 or more and 7.0 or less is set to S, the number of moles of Fe ions contained in the raw material solution is set to F, and the total number of moles of replacement metal element ions When it is set to M, S/(F+M) is 0.50 or more and 10.0 or less. The method for producing substitutional epsilon iron oxide magnetic particle powder according to claim 6, wherein the other metal element to be partially substituted for Fe sites is one or two selected from Ga and Al. A method for manufacturing a compact is obtained by compressing and molding the displacement type ε iron oxide magnetic particle powder according to any one of claims 1 to 3.

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