CN113508442A - Substituted epsilon-iron oxide magnetic particle powder, method for producing substituted epsilon-iron oxide magnetic particle powder, green compact, method for producing green compact, and radio wave absorber - Google Patents
Substituted epsilon-iron oxide magnetic particle powder, method for producing substituted epsilon-iron oxide magnetic particle powder, green compact, method for producing green compact, and radio wave absorber Download PDFInfo
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- CN113508442A CN113508442A CN202080018538.9A CN202080018538A CN113508442A CN 113508442 A CN113508442 A CN 113508442A CN 202080018538 A CN202080018538 A CN 202080018538A CN 113508442 A CN113508442 A CN 113508442A
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- 239000006249 magnetic particle Substances 0.000 title claims abstract description 48
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 128
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- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims abstract description 85
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- Compounds Of Iron (AREA)
- Hard Magnetic Materials (AREA)
- Soft Magnetic Materials (AREA)
- Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
Abstract
[ problem ] to]Providing a non-magnetic alpha-iron-based oxide with a reduced content, replacing epsilon-Fe with other metal elements2O3A powder of substituted-type epsilon ferromagnetic oxide particles having some Fe sites and a method for producing the powder of substituted-type epsilon ferromagnetic oxide particles. [ solution means ] to]After an acidic aqueous solution containing iron ions having a valence of 3 and ions of a metal to be substituted for a part of the Fe sites is neutralized to ph2.0 or more and 7.0 or less, a silicon compound having a hydrolyzable group is added to a dispersion containing the generated iron oxyhydroxide containing a substitution metal element or a mixture of the iron oxyhydroxide and a hydroxide of the substitution metal element, and then the dispersion is neutralized to ph8.0 or more, and then the dispersion is held and aged, and a chemical reaction product of the silicon compound is coated on the iron oxyhydroxide containing the substitution metal element or the mixture of the iron oxyhydroxide and the hydroxide of the substitution metal element and heated, thereby obtaining a substitution type epsilon iron oxide magnetic particle powder having a reduced content of alpha type iron-based oxide.
Description
Technical Field
The present invention relates to a substituted epsilon ferromagnetic oxide particle powder suitable for high-density magnetic recording media, radio wave absorbers, and the like, particularly to a substituted epsilon ferromagnetic oxide particle powder having a reduced content of a nonmagnetic alpha-iron oxide having a different phase from that of the substituted epsilon iron oxide, and a method for producing the same. In this specification,. epsilon. -Fe will be replaced with other metal elements, respectively2O3An oxide having a part of Fe sites is called an epsilon-type iron oxide, and a crystal system is formed with alpha-Fe2O3Crystal system ofThe same substituted alpha iron oxide particles are referred to as alpha iron-based oxides.
Background
ε-Fe2O3Is a very rare phase even in iron oxide, and nano-sized particles exhibit 20kOe (1.59X 10) at room temperature6A/m) and so on, and thus, the synthesis of ε -Fe in a single phase has been discussed in the past2O3The method of (1). However, in the presence of ε -Fe2O3In the case of magnetic recording media, there is no material for magnetic heads which has a saturation magnetic flux density at a high level corresponding to the magnetic recording media, and therefore, In practical use, it is necessary to replace ε -Fe with a 3-valent metal such as Al, Ga, In, etc2O3When the magnetic material is used as a radio wave absorbing material, the amount of substitution of Fe sites needs to be changed according to the required absorption wavelength (patent document 2).
On the other hand, since magnetic particles of an epsilon-type iron oxide are very fine, for the purpose of improving environmental stability and thermal stability, substitution of epsilon-Fe with another metal having excellent heat resistance has also been studied2O3A part of the Fe sites of (A), is proposed by the general formula ε -AxByFe2-x-yO3Or ε -AxByCzFe2-x-y-zO3(wherein A is a 2-valent metal element such as Co, Ni, Mn, Zn, etc., B is a 4-valent metal element such as Ti, etc., and C is a 3-valent metal element such as In, Ga, Al, etc.) and various ε -Fe having excellent environmental stability and heat resistance2O3A partial substitution body of (1) (patent document 3).
ε-Fe2O3And epsilon iron-based oxides are not thermodynamically stable phases, and thus, a special method is required for the production thereof. Patent documents 1 to 3 disclose epsilon-Fe in which fine crystals of iron oxyhydroxide or iron oxyhydroxide containing a substitution element produced by a liquid phase method are used as precursors, silicon oxide is coated on the precursors by a sol-gel method, and heat treatment is performed2O3Or epsilon-type iron-based oxides, and the use of organic solvents as liquid phase processesThe reverse micelle method using an agent as a reaction medium and the method using only an aqueous solution as a reaction medium.
In addition, the above-mentioned ε -Fe2O3And epsilon-type iron oxides have a peak of radio wave absorption in a high frequency region exceeding 100Ghz as shown in, for example, patent documents 4 to 5, and are expected to be used as a radio wave absorber.
However, the magnetic particle powder obtained by the production methods disclosed in patent documents 1 to 3 has only epsilon-Fe2O3And a non-magnetic alpha-iron oxide as impurities in a substantial amount in addition to the epsilon-iron oxide.
Patent document 6 discloses a technique for reducing the amount of an α -type iron oxide as an impurity contained in a replacement-type ∈ iron oxide magnetic particle powder.
Patent document 7 discloses a method for producing an epsilon-type iron oxide in which a silicon oxide is coated by a sol-gel method over a wide pH range.
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open No. 2008-174405
Patent document 2: international publication No. 2008/029861
Patent document 3: international publication No. 2008/149785
Patent document 4: japanese patent laid-open No. 2008-277726
Patent document 5: japanese laid-open patent publication No. 2009-224414
Patent document 6: japanese patent laid-open publication No. 2016-
Patent document 7: japanese laid-open patent publication No. 2018-092691
Disclosure of Invention
Problems to be solved by the invention
The epsilon-type iron oxide having a part of the Fe sites replaced, which is produced by the production method disclosed in patent document 4, has a reduced content of alpha-type iron oxide as an impurity compared to epsilon-type iron oxide produced by a conventional method. However, the epsilon-type iron-based oxide is a metastable phase and is substituted by Fe of other metal elementWhen the amount is small, it is difficult to obtain the same amount of ε -Fe even when the production method disclosed in patent document 4 is used2O3In the same space group, the content of the α -type iron oxide may not be sufficiently reduced.
Since the α -type iron oxide is nonmagnetic, it does not contribute to the radio wave absorption property when the substitution-type ∈ iron oxide ferromagnetic particle powder is used as a radio wave absorbing material, and does not contribute to the improvement of the recording density when used in a magnetic recording medium, and therefore, it is necessary to reduce the content thereof.
That is, the technical problem to be solved by the present invention is to provide a substituted-type ∈ iron oxide magnetic particle powder having a reduced content of nonmagnetic α -type iron oxide, and a method for producing the substituted-type ∈ iron oxide magnetic particle powder.
Means for solving the problems
The present inventors have made intensive studies focusing on the need to heat a precursor of the magnetic particle powder in a state coated with a silicon oxide in order to obtain a substituted-type e-iron oxide magnetic particle powder, and have found that the content of an α -type iron oxide can be reduced by adding a silicon compound having a hydrolyzable group for coating to an aqueous solution containing the precursor at a ph of 2.0 or more and 7.0 or less.
Based on the above findings, the present inventors have completed the present invention described below.
In order to solve the above problems, the present invention provides a substituted-type epsilon-iron oxide magnetic particle powder mainly comprising epsilon-Fe substituted with another metal element2O3Wherein when the number of moles of Fe contained in the substituted epsilon-iron oxide particle powder is Fe and the number of moles of all metal elements substituting for Fe sites is Me, the amount of substitution of Fe by other metal elements defined by Me/(Fe + Me) is 0.08 to 0.17 inclusive, and the content of alpha-iron oxide measured by X-ray diffraction method is 3% or less.
The other metal element that substitutes for a part of the Fe sites is preferably Co, Ti, or one or more selected from Ga and Al. For example, an epsilon-type iron-based oxide containing Co and Ti and containing one or more selected from Ga and Al as another metal element substituting for a part of the Fe sites is suitable.
The present invention also provides a green compact containing the above-mentioned substituted epsilon-ferromagnetic oxide particle powder.
The present invention also provides a radio wave absorber in which the above-described powder of the substitution type epsilon ferromagnetic oxide particles is dispersed in a resin or rubber.
The present invention also provides a method for producing a substituted-type epsilon-iron oxide magnetic particle powder mainly comprising substituting epsilon-Fe with another metal element2O3The method for producing a substituted epsilon-iron oxide magnetic particle powder of epsilon-iron oxide having a part of Fe sites, comprising: a neutralization step of adding an alkali to the raw material solution and neutralizing the raw material solution to a ph of 8.0 or more and 10.0 or less using an acidic aqueous solution containing ions of iron ions having a valence of 3 and ions of a metal to be substituted for a part of the Fe sites to obtain a dispersion containing a mixture of iron oxyhydroxide containing a substituted metal element or iron oxyhydroxide and a hydroxide of a substituted metal element; a silicon compound addition step of adding a silicon compound having a hydrolyzable group to the dispersion containing the iron oxyhydroxide containing the substituted metal element or the mixture of the iron oxyhydroxide and the hydroxide of the substituted metal element; and a curing step of maintaining a dispersion liquid containing the silicon compound and a mixture of iron oxyhydroxide containing the substituted metal element or a mixture of iron oxyhydroxide and a hydroxide of the substituted metal element at a ph of 8.0 to 10.0 inclusive, and coating the mixture of iron oxyhydroxide containing the substituted metal element or a mixture of iron oxyhydroxide and a hydroxide of the substituted metal element with a chemical reaction product of the silicon compound; wherein the addition of the silicon compound having a hydrolyzable group is started at a point in time when the pH of the dispersion is in the range of 2.0 to 7.0 in the neutralization step, the number of moles of the silicon compound added to the dispersion having a pH of 2.0 to 7.0 is S1, the number of moles of Fe ions contained in the raw material solution is F, and the substitution metal is addedWhen the total mole number of the element ions is M, S1/(F + M) is 0.01 to 10.0, and when the total mole number of the silicon compound added is S2, S2/(F + M) is 0.50 to 10.0.
In the above production method, the alkali addition in the neutralization step and the silicon compound addition in the silicon compound addition step may be performed continuously, the alkali addition may be performed continuously or the silicon compound addition may be performed intermittently, the alkali addition and the silicon compound addition may be performed intermittently, or the alkali addition may be performed intermittently or the silicon compound addition may be performed continuously.
In the above production method, the other metal element that substitutes for a part of the Fe sites is preferably Co, Ti, or one or more selected from Ga and Al. For example, the other metal element that substitutes for a part of the Fe sites preferably contains Co and Ti and contains one or more selected from Ga and Al.
The present invention also provides a process for producing a green compact, which comprises compression-molding the above-mentioned powder of substituted-type epsilon-ferromagnetic oxide particles to obtain a green compact.
Effects of the invention
As described above, by using the production method of the present invention, it is possible to obtain a substituted-type ∈ iron oxide magnetic particle powder with a reduced α -type iron oxide content, and a green compact and a radio wave absorber using the same.
Drawings
Fig. 1 is a schematic diagram showing an example of an embodiment of the present invention.
Fig. 2 is a schematic diagram showing an example of the embodiment of the present invention.
Fig. 3 is a schematic diagram showing an example of the embodiment of the present invention.
Fig. 4 is a schematic diagram showing an example of the embodiment of the present invention.
Fig. 5 is a schematic diagram showing an example of the embodiment of the present invention.
Fig. 6 is a schematic diagram showing an example of the embodiment of the present invention.
Detailed Description
[ iron oxide magnetic particle powder ]
The production method of the present invention is used for producing a catalyst mainly comprising substituting epsilon-Fe with another metal element2O3A magnetic particle powder of a substituted epsilon-iron oxide of epsilon-iron based oxide wherein a heterogeneous phase which is an inevitable impurity for the production thereof is mixed. The heterogeneous phase is mainly an α -type iron oxide, and the ferromagnetic oxide particle powder obtained by the present invention is substantially composed of magnetic particles of an ∈ -type iron oxide and an α -type iron oxide. The invention aims to reduce the content of alpha-type iron oxides as heterogeneous phase.
Relating to the replacement of epsilon-Fe by other metal elements2O3Whether or not a partial substitution body of (1) a partial Fe site has an epsilon structure can be confirmed by X-ray diffraction (XRD), high-speed electron diffraction (HEED), or the like. In the present invention, the identification of the epsilon-type and alpha-type iron oxides is carried out by XRD.
The following examples are given for some of the substituted bodies that can be produced by the production method of the present invention.
From the general formula ε -CzFe2-zO3(wherein C is at least one 3-valent metal element selected from In, Ga and Al).
From the general formula ε -AxByFe2-x-yO3(wherein A is at least one 2-valent metal element selected from Co, Ni, Mn and Zn, and B is at least one 4-valent metal element selected from Ti and Sn).
From the general formula ε -AxCzFe2-x-zO3(wherein A is at least one 2-valent metal element selected from Co, Ni, Mn and Zn, and C is at least one 3-valent metal element selected from In, Ga and Al).
From the general formula ε -ByCzFe2-y-zO3(wherein B is at least one metal element having a valence of 4 selected from Ti and Sn, and C is at least one metal element having a valence of 3 selected from In, Ga and Al).
From the general formula ε -AxByCzFe2-x-y-zO3(wherein A is at least one 2-valent metal element selected from Co, Ni, Mn and Zn, B is at least one 4-valent metal element selected from Ti and Sn, and C is at least one 3-valent metal element selected from In, Ga and Al).
Here, the type in which only C element is substituted can arbitrarily control the coercive force of the magnetic particles, and has a structure in which e-Fe is easily obtained2O3The same space group is advantageous, but the thermal stability is sometimes poor. In particular, when Ga and Al are used as C, the resulting substituted-type ∈ ferromagnetic oxide particle powder is slightly inferior in thermal stability, and therefore, it is preferable to further simultaneously substitute a and/or B elements. A. The three-element substitution type of B and C is best in balance with the above properties, and is excellent in heat resistance, single-phase availability, and coercivity controllability, and when Ga and Al are used as C, it is preferable to simultaneously substitute Co and Ti.
The production method of the present invention is applicable to any of the above-described replacement-type ferromagnetic oxide particles.
The production method of the present invention described later is applicable even if the substitution amount of the metal element for substituting the above-mentioned Fe site is an arbitrary value, but it is effective to apply the substitution amount at which the α -type iron oxide is easily generated. Specifically, when the molar number of Fe contained in the above-mentioned substituted epsilon-iron oxide magnetic particle powder is Fe and the molar number of all metal elements substituting for Fe sites is Me, if the substitution amount of Fe by other metal elements defined by Me/(Fe + Me) is 0.08 or more and 0.17 or less, it is possible to obtain a substituted epsilon-iron oxide magnetic particle powder having a content of alpha-iron-based oxide measured by XRD of 3% or less, which has not been obtained by the conventional method.
[ powder compact and radio wave absorber ]
The substituted-type epsilon-iron oxide magnetic particle powder obtained by the present invention functions as a radio wave absorber having excellent radio wave absorption energy by forming a filling structure of the powder particles. The filling structure as used herein means that the particles form a three-dimensional structure in a state where the particles are in contact with or close to each other. In order to be used for practical use of the radio wave absorber, it is necessary to maintain a filling structure. Examples of the method include a method of compacting a powder of the substitution type e ferromagnetic oxide particles to form a green compact, and a method of forming a filled structure by adhering the powder of the substitution type e ferromagnetic oxide particles using a non-magnetic polymer compound as a binder.
In the case of the method using a binder, the substituted-type epsilon-ferromagnetic oxide particle powder is mixed with a nonmagnetic polymer base material to obtain a kneaded product. The amount of the radio wave absorbing material powder in the kneaded product is preferably 60 mass% or more. The larger the amount of the radio wave absorbing material powder blended, the more advantageous the radio wave absorbing property is in terms of improvement, but if too much, kneading with the polymer base material becomes difficult, and therefore, attention is required. For example, the amount of the radio wave absorbing material powder may be 80 to 95 mass% or 85 to 95 mass%.
As the polymer base material, various base materials satisfying heat resistance, flame retardancy, durability, mechanical strength, and electrical characteristics can be used depending on the use environment. For example, a suitable material may be selected from a resin (nylon or the like), a gel (silicone or the like), a thermoplastic elastomer, rubber, and the like. Further, 2 or more kinds of polymer compounds may be blended to prepare a base material.
[ average particle diameter ]
In the present invention, the average particle diameter of the ferromagnetic oxide particle powder obtained by the production method of the present invention is not particularly limited, and is preferably as fine as each particle has a single magnetic domain structure. In general, magnetic particle powder having an average particle diameter of 10nm or more and 40nm or less as measured by a transmission electron microscope is obtained.
[ starting materials and precursors ]
In the production method of the present invention, an acidic water-soluble material (hereinafter referred to as a raw material solution) containing a 3-valent iron ion and a metal ion of a metal element that eventually replaces an Fe site is used as a starting material of the iron-based oxide magnetic particle powder. When 2-valent Fe ions are used instead of 3-valent Fe ions as the starting material, a mixture containing 2-valent iron hydroxides, magnetite, and the like is generated as the precipitate, and the shape of the finally obtained iron-based oxide particles varies, so that the powder of the substituted-type ∈ iron oxide magnetic particles having a reduced content of α -type iron-based oxides as in the present invention cannot be obtained. Here, acidic means that the pH of the liquid is less than 7.0. As a source of the metal ions of the iron ions or the substitution elements, a water-soluble inorganic acid salt such as nitrate, sulfate, or chloride is preferably used from the viewpoint of availability and price. When these metal salts are dissolved in water, metal ions are dissociated, and the aqueous solution is acidic. When the alkali is added to the acidic aqueous solution containing the metal ions for neutralization, a mixture of iron oxyhydroxide and a hydroxide of a substitution element, or a precipitate of iron oxyhydroxide in which a part of the Fe sites are substituted with another metal element (hereinafter, these are collectively referred to as iron oxyhydroxide containing a substitution element in the present specification) is obtained. In the production method of the present invention, iron oxyhydroxide containing these substitution elements is used as a precursor of the substitution-type epsilon-iron oxide magnetic particle powder.
The total concentration of metal ions in the raw material solution is not particularly limited in the present invention, and is preferably 0.01mol/L to 0.5 mol/L. When the amount is less than 0.01mol/L, the amount of the substituted ε iron oxide magnetic particle powder obtained by 1-time reaction is small, which is not preferable from the viewpoint of economical efficiency. When the total metal ion concentration exceeds 0.5mol/L, rapid precipitation of hydroxide occurs, and the reaction solution is liable to gel, which is not preferable.
[ neutralization step ]
In the production method of the present invention, a base is added to the raw material solution and neutralized to a pH of 8.0 or more and 10.0 or less to obtain a dispersion liquid containing a precipitate of iron oxyhydroxide containing a substitution element. The hydroxide of the iron ion having a valence of 3 mainly contains an oxyhydroxide. The reason why the pH of the dispersion is set to 8.0 or more is to complete precipitation of a hydroxide of a substitution metal element (e.g., Co) and to promote condensation reaction of a silanol derivative which is a hydrolysis product. In the production method of the present invention, the upper limit of the pH reached in the neutralization step is not particularly limited, but is preferably 10.0, because the effect of neutralization is saturated, and the effect of promoting the condensation reaction of the silanol derivative described later is reduced.
The alkali used for neutralization may be any of alkali metal or alkaline earth metal hydroxides, ammonia water, ammonium hydrogen carbonate and other ammonium salts, and it is preferable to use ammonia water or ammonium hydrogen carbonate in which impurities are less likely to remain when the epsilon-type iron oxide is finally obtained by heat treatment. These bases may be added as solids to the aqueous solution of the starting material, and are preferably added in the form of an aqueous solution from the viewpoint of ensuring the uniformity of the reaction.
As described above, since the precipitate containing iron oxyhydroxide as a substitution element is precipitated when the alkali is added to the raw material solution to perform the neutralization treatment, the dispersion liquid containing the precipitate is stirred by a known mechanical means in the neutralization treatment.
The addition of the base to the raw material solution may be continuously performed from the start of the addition to the end thereof. Further, the addition of the base may be stopped before the pH of the dispersion reaches 8.0, and a predetermined pH holding time may be set. In this case, the base may be added intermittently with a plurality of pH holding times. The number of times the pH holding time is set, that is, the number of times the addition of the base is interrupted, is preferably 3 or less, in order to avoid complication of the production process.
In the production method of the present invention, the reaction temperature at the time of neutralization treatment is 5 ℃ to 60 ℃. When the reaction temperature is less than 5 ℃, the cost due to cooling is increased, and therefore, it is not preferable. When the temperature exceeds 60 ℃, the final α -type oxide as a hetero-phase is liable to be generated, which is not preferable. More preferably, it is 10 ℃ or higher and 40 ℃ or lower. In the case of the production method described in patent document 4, the neutralization treatment needs to be performed at 5 ℃ or higher and 25 ℃ or lower, and a refrigerator is used for the reaction.
The pH value described in the present specification was measured using a glass electrode according to JIS Z8802. The pH value is measured by using a pH meter calibrated by using an appropriate buffer solution corresponding to the measured pH range as a pH standard solution. The pH described in the present specification is a value obtained by directly reading a measurement value displayed by a pH meter compensated by a temperature compensation electrode under reaction temperature conditions.
[ procedure for adding silicon Compound ]
In the production method of the present invention, since iron oxyhydroxide containing a substitution element, which is a precursor of the substitution-type ∈ iron oxide magnetic particle powder produced in the above-described step, is less likely to be transformed into an ∈ -type iron-based oxide even if heat treatment is performed in the as-is state, it is necessary to coat the iron oxyhydroxide containing a substitution element with a coating using a chemical reaction product obtained by a hydrolysis reaction and a condensation reaction of a silicon compound before the heat treatment. The chemical reaction product of the silicon compound is not only silicon oxide having a stoichiometric composition, but also a non-stoichiometric composition such as a silanol derivative or a polysiloxane structure, which will be described later, or a silicon oxide obtained by heat treatment.
In the production methods described in patent documents 1 to 4, a sol-gel method is used as a coating method of a chemical reaction product of a silicon compound, a neutralization treatment of a raw material solution is completed, and a silicon compound having a hydrolyzable group is added to a reaction solution after the pH of the reaction solution becomes an alkali side. On the other hand, in the production method of the present invention, the same sol-gel method is used as a method for coating a silicon oxide, but the addition of the silicon compound having a hydrolyzable group is started at a point in time in the range of pH2.0 or more and 7.0 or less where the pH of the reaction solution is on the acidic side before the neutralization of the raw material solution is completed. The timing of the completion of the addition of the silicon compound will be described later.
In the case of the sol-gel method, a silane compound such as alkoxysilane, e.g., silicon compound having a hydrolyzable group (e.g., Tetraethoxysilane (TEOS), Tetramethoxysilane (TMOS)), or various silane coupling agents is added to a dispersion containing iron oxyhydroxide containing a substitution element, and a hydrolysis reaction is caused under stirring, and the resulting silanol derivative is condensed to form a polysiloxane bond, thereby coating the surface of the iron oxyhydroxide containing a substitution element.
The present inventors have found that when the addition of the silicon compound having a hydrolyzable group is started at a ph of 2.0 or more and 7.0 or less, the content of the α -type iron oxide contained in the finally obtained substituted-type ∈ -iron oxide magnetic particle powder can be reduced, and the reason for this is considered as follows.
The speed of the hydrolysis reaction of the silicon compound having a hydrolyzable group and the condensation reaction of the silanol derivative as a hydrolysis product varies depending on the pH of the reaction system. The hydrolysis reaction rate is generally high in a low pH region on the acidic side, decreases with an increase in pH, and increases again in a high pH region on the alkaline side. The rate of the condensation reaction is low in the low pH region on the acidic side, increases with an increase in pH, and increases in the pH region from the neutral to basic side.
When a silicon compound having a hydrolyzable group is added to a dispersion containing a precipitate of iron oxyhydroxide containing a substitution element in a low pH region on the acidic side, hydrolysis of the silicon compound proceeds rapidly, a silanol derivative having a small organic component is produced, and a condensation reaction of the produced silanol derivative does not proceed. Here, since the silanol derivative has an OH group as a hydrophilic group and is uniformly distributed in the aqueous solution, it is considered that a precipitate of iron oxyhydroxide containing a substitution element and a state in which the silanol derivative is uniformly dispersed in the dispersion liquid and coexists are formed.
Thereafter, when the pH of the dispersion is further increased, the condensation reaction of the silanol derivative becomes dominant, and therefore, the precipitate of iron oxyhydroxide containing the substitution element is uniformly coated with the silanol derivative or the condensation reaction product thereof. Therefore, it is considered that the content of the α -type iron oxide contained in the substituted-type ∈ iron oxide magnetic particle powder finally obtained by the heat treatment decreases.
Patent document 5 discloses that silicon oxide is coated by a sol-gel method in a wide pH range, but in this case, the addition of the silicon compound is performed at a constant pH after the completion of the neutralization treatment, and does not disclose a technical idea in which both the hydrolysis reaction rate and the condensation reaction rate of the silicon compound are considered as in the present invention.
The pH at the time of starting the addition of the silicon compound having a hydrolyzable group is preferably 2.0 or more. When the pH is less than 2.0, precipitation of a hydroxide of iron ions having a valence of 3 contained in the raw material solution, which is a main component of the replacement-type ∈ ferromagnetic oxide particle powder, may be insufficient. The pH at the time of starting the addition is more preferably 3.0 or more. The pH at the time of starting the addition of the silicon compound having a hydrolyzable group is preferably 7.0 or less. When the pH exceeds 7.0, the hydrolysis reaction becomes slow and the generation of the silanol derivative becomes insufficient, so that the precipitate of the iron oxyhydroxide containing the substitution element and the silanol derivative are not obtained in a state of being uniformly distributed and coexisting in the dispersion, and the precipitate of the iron oxyhydroxide containing the substitution element is hardly uniformly coated with the silanol derivative or the condensation reaction product thereof. The pH at the time of starting the addition is preferably 6.0 or less, and more preferably 4.0 or less.
The addition of the silicon compound having a hydrolyzable group is started at the time when the pH of the stock solution in the neutralization step becomes a desired value. The addition of the silicon compound may be continuously performed from the start of the addition to the end thereof. The term continuous here means that the entire amount of the silicon compound added to the dispersion is added to the dispersion at once. The addition of the silicon compound may be performed intermittently in several times.
In the production method of the present invention, the amount of the silicon compound added to the dispersion liquid needs to satisfy the following 2 conditions at the same time.
The first condition is the amount of the silicon compound added to the dispersion having a ph of 2.0 or more and 7.0 or less. When the number of moles of the silicon compound added to the dispersion having a ph of 2.0 or more and 7.0 or less is S1, the number of moles of Fe ions contained in the raw material solution is F, and the total number of moles of the replacement metal element ions is M, S1/(F + M) is 0.01 or more and 10.0 or less. When S1/(F + M) is less than 0.01, the amount of silanol derivative coexisting with the precipitate of iron oxyhydroxide containing a substitution element is small, and the effect of uniformly coating the precipitate of iron oxyhydroxide containing a substitution element with a silanol derivative or a condensation reaction product thereof is reduced, which is not preferable. When the amount of the silicon compound to be added is increased, the amount of treatment in the heating step and the silicon oxide removal step, which will be described later, is increased, and the production cost is increased, so S1/(F + M) is preferably 10.0 or less.
The second condition is the amount of the silicon compound added in the entire production process. When the total number of moles of the silicon compound to be added is S2, the number of moles of Fe ions contained in the raw material solution is F, and the total number of moles of the replacement metal element ions is M, S2/(F + M) is 0.50 to 10.0 inclusive. When S2 is less than 0.50, the amount of the chemical reaction product of the silicon compound coated on the surface of the precipitate of iron oxyhydroxide containing the substitution element is decreased, and as a result, the α -type iron oxide is liable to be generated disadvantageously, which is not preferable. When S2/(F + M) exceeds 10.0, the amount of treatment in the heating step and the silicon oxide removal step, which will be described later, increases, which is not preferable because the manufacturing cost increases.
When the total amount of the silicon compound is added in the range of ph2.0 or more and 7.0 or less, S1 is S2.
[ embodiments of the invention ]
As described above, in the production method of the present invention, the addition of the base in the neutralization step and the addition of the silicon compound in the silicon compound addition step can be performed continuously or intermittently. Therefore, in the production method of the present invention, various embodiments can be adopted by a combination of the method of adding the base and the method of adding the silicon compound. Some embodiments of the present invention are exemplified below, but the manufacturing method of the present invention is not limited to the embodiments described below.
Fig. 1 schematically illustrates the passage of time in an embodiment in which both the addition of the base and the addition of the silicon compound are continuously performed. In this case, after the addition of the alkali is started, the addition of the silicon compound is started at a point in time when the pH of the raw material solution reaches a predetermined pH in a range of 2.0 to 7.0. In the case of this embodiment, the neutralization step and the silicon compound addition step are not temporally continuous steps but are parallel steps. As shown in this figure, the addition of the silicon compound may be continued after the addition of the base is completed, may be completed when the addition of the base is completed, or may be completed when the pH is 7.0 or less. When the silicon compound is added after the completion of the addition of the base, the addition of the silicon compound is preferably completed within 120min after the completion of the addition of the base, in view of the time of the entire production process. After the addition of the silicon compound is completed, a curing step described later is provided.
Although not particularly shown, in the embodiment of fig. 1, the silicon compound may be added in a plurality of portions and intermittently.
Fig. 2 schematically illustrates the elapse of time in an example of the embodiment in which the addition of the alkali is interrupted in the middle of the neutralization step. In this case, the addition of the base is interrupted once, and the entire amount of the silicon compound is continuously added during the pH holding time in which the addition of the base is interrupted, and S1 is S2.
Fig. 3 schematically illustrates the elapse of time in another example of the embodiment in which the alkali addition is once interrupted. In this case, the addition of the silicon compound is started when the pH of the raw material solution reaches a predetermined pH in the range of 2.0 to 7.0, but the addition is continued after the neutralization step.
Fig. 4 and 5 schematically illustrate the time course of an example of an embodiment in which the alkali addition is once interrupted and the silicon compound is added intermittently. The addition of the silicon compound is divided into two in fig. 4 and three in fig. 5.
Fig. 6 schematically illustrates the passage of time in an example of an embodiment in which the addition of the silicon compound is intermittently performed three times while the addition of the alkali is interrupted twice.
As described above, the production method of the present invention is not limited to the embodiments illustrated in fig. 1 to 6, and the form of adding the base in the neutralization step and the form of adding the silicon compound in the silicon compound addition step may be arbitrarily combined.
[ aging Process ]
Since the condensation reaction of the silanol derivative proceeds slowly even when the pH is set to 8.0 or more, the dispersion containing the chemical reaction product of iron oxyhydroxide containing a substitution element and a silicon compound obtained through the neutralization step and the silicon compound addition step is kept at pH8.0 or more and aged to perform the condensation reaction of the silanol derivative. As a result, a uniform coating layer of the condensation reaction product of the silanol derivative is formed on the surface of the precipitate of iron oxyhydroxide containing the substitution element. The coating layer is considered to cover almost the entire surface of the precipitate surface of the iron oxyhydroxide containing the substitution element, but the uncoated portion of the precipitate surface of the iron oxyhydroxide containing the substitution element is allowed to exist within a range that can achieve the effect of the present invention. The aging time is preferably 1 to 24 hours. When the holding time is less than 1 hour, the coating by condensation of the silanol derivative of the precipitate of iron oxyhydroxide containing a substitution element is not completed, and the α -type iron oxide is easily formed, and when it exceeds 24 hours, the effect of aging is saturated, which is not preferable. The aging time is a time after the addition of the silicon compound when the addition of the silicon compound is continued after the neutralization step, and a time after the addition of the alkali when the addition of the silicon compound is completed before the neutralization step.
In the method for producing a substituted-type epsilon-ferromagnetic oxide particle powder of the present invention, the same steps as those of the conventional production method described in, for example, patent documents 1 to 4 can be used for the steps after the aging step. Specifically, the following steps may be mentioned.
[ heating Process ]
In the production method of the present invention, iron oxyhydroxide containing a substitution element, which is coated with a condensation reaction product of the silanol derivative, is recovered by a known solid-liquid separation method, and then subjected to a heat treatment to obtain an epsilon-type iron oxide. Before the heat treatment, a washing and drying process may be provided. The heat treatment is performed in an oxidizing atmosphere, and the oxidizing atmosphere may be an atmospheric atmosphere. The heating may be performed in a range of about 700 ℃ or more and 1300 ℃ or less, and when the heating temperature is high, α -Fe which is a thermodynamically stable phase is easily generated2O3(with respect to. epsilon. -Fe2O3Is an impurity), and is therefore preferably 900 ℃ or higher and 1200 ℃ or lower, moreThe heat treatment is preferably performed at 950 ℃ or higher and 1150 ℃ or lower.
The heat treatment time can be adjusted in the range of about 0.5H to 10H, and favorable results can be easily obtained in the range of 2H to 5H. It is considered that the presence of the silicon-containing substance covering the particles does not cause a phase transition to the α -type iron-based oxide but favorably acts to cause a phase transition to the e-type iron-based oxide. The silicon oxide coating also has an effect of preventing sintering of iron oxyhydroxide crystals containing a substitution element during heat treatment.
When the epsilon-type iron oxide magnetic particle powder does not require a coating due to silicon oxide, the silicon oxide coating can be removed after the heat treatment.
[ composition analysis by high-frequency inductively coupled plasma emission Spectroscopy (ICP) ]
The composition of the obtained substituted-type epsilon-ferromagnetic oxide particle powder was analyzed by a dissolution method. For the composition analysis, ICP-720ES (product of アジレントテクノロジー) was used, and the wavelength (nm) was measured and the ratio of Fe: 259.940nm, Ga: 294.363nm, Co: 230.786nm, Ti: 336.122nm, Si: 288.158 nm.
[ measurement of hysteresis Curve (volume B-H Curve) ]
A vibration sample type magnetometer VSM (VSM-P7, manufactured by Toyobo Co., Ltd.) was used to measure the magnetic field 1193kA/M (15kOe) and the M in the range of 0.005A · M2(5emu), step bit 140bit, time constant 0.03 second, and waiting time 0.1 second measured the magnetic properties. The coercive force Hc and the saturation magnetization σ s were evaluated from the B-H curve.
[ evaluation of crystallinity by X-ray diffraction (XRD) ]
The obtained sample was subjected to powder X-ray diffraction (XRD: sample horizontal multi-purpose X-ray diffractometer Ultima IV manufactured by リガク K.K., radiation source CuKa radiation, voltage 40kV, current 40mA, 2 theta 10 DEG or more and 70 DEG or less). The diffraction pattern thus obtained was analyzed by integrated powder X-ray analysis software (PDXL 2: リガク, manufactured by co., ltd.) using an ICSD (inorganic crystal structure database) No. 173025: iron (III) oxide-Epsilon, No. 82134: evaluation was performed by Rietveld analysis based on hematite, and the crystal structure and the content of the α phase were confirmed.
[ BET specific surface area ]
The BET specific surface area was determined by the BET single-point method using a Macsorb model-1210, manufactured by マウンテック K.K.
TEM observation of the substituted-type epsilon-ferromagnetic oxide particle powder obtained by the production method of the present invention was performed under the following conditions. For TEM observation, JEM-1011, manufactured by JEOL Ltd was used. For the particle observation, TEM photographs taken at a magnification of 10,000 times and a magnification of 100,000 times were used. (use the product after removing the silicon oxide coating).
Determination of average particle diameter and evaluation of particle size distribution (coefficient of variation (%)))
The TEM average particle size and the particle size distribution were evaluated (coefficient of variation (%) was digitized, Mac-View ver.4.0 was used as image processing software, and when this image processing software was used, the particle size of a certain particle was calculated as the length of the long side of the rectangle having the smallest area in the rectangle circumscribing the particle, and 200 or more were measured with respect to the number.
The selection criteria for the particles measured among the particles reflected on the transmission electron micrograph are as follows.
[1] Particles with a portion of the particles seen outside the field of view of the photograph were not measured.
[2] And (3) determining particles which are clear in outline and exist in isolation.
[3] Particles that are independent and can be measured as individual particles, even in the case of particle shapes that deviate from the average.
[4] Particles in which the boundaries between particles are clear and the shape of the entire particle can be determined even when the particles overlap each other are measured as individual particles.
[5] The particles that are overlapped and have unclear boundaries and the overall shape of the particles cannot be determined are not measured as particles whose shape cannot be determined.
The number average value of the particle diameters of the particles selected in the above-mentioned criteria was calculated as the average particle diameter of the substituted-type epsilon-iron oxide magnetic particle powder observed by TEM.
[ measurement of radio wave absorption characteristics ]
1.2g of the replacement type ε iron oxide powder was press-molded at 28MPa (20kN) to obtain a compact having a diameter of 13mm and a thickness of 3 mm. The obtained powder compact was subjected to transmission attenuation measurement by terahertz time-domain spectroscopy. Specifically, measurement was performed while the green compact was placed on a sample holder and measurement was performed while the green compact was placed on a sample holder using a terahertz spectroscopic system TAS7400SL manufactured by アドバンテスト co. The measurement conditions were as follows.
Sample holder diameter:
measurement mode: transmission through
Frequency resolution 1.9GHz
Longitudinal axis: absorbance of the solution
Horizontal axis: frequency [ THz ]
Cumulative number (sample): 2048
Cumulative number (blank): 2048
The observed signal waveform of the sample and the reference waveform of the blank sample were expanded to 2112ps and fourier transformed to obtain the ratio (Ssig/Sref) of the obtained fourier spectra (Sref and Ssig, respectively), and the transmission attenuation of the compact placed in the sample holder was calculated.
Examples
[ example 1]
In a 5L reaction tank, 283.26g of 99% pure iron nitrate 9 hydrate (III), 56.36g of a Ga (III) nitrate solution having a Ga concentration of 11.55 mass%, 6.25g of 97% pure cobalt (II) nitrate 6 hydrate, and 6.61g of titanium (IV) sulfate having a Ti concentration of 15.1 mass% were dissolved in 3813.21g of pure water while being mechanically stirred by a stirring blade in an atmospheric atmosphere to prepare a raw material solution (step 1). The pH of the feed solution was about 1. The molar ratio of metal ions in the raw material solution is Fe: ga: co: ti 1.677:0.223:0.050: 0.050. Note that the roman numerals in parentheses after the reagent name indicate the valence of the metal element.
In an atmosphere, 294.85g of a 22.30 mass% aqueous ammonia solution was added to the raw material solution at 20 ℃ for 90min while mechanically stirring the solution with a stirring blade (step 2).
After 60min, in a stage where the pH of the reaction solution in the aqueous ammonia solution was 4.0, 519.22g of Tetraethoxysilane (TEOS) having a purity of 95.0 mass% as a silicon compound having a hydrolyzable group was added in parallel, and dropwise addition was continued over 30 min. After the entire amount of the aqueous ammonia solution was added, stirring was continued for 20 hours in this state, and the precipitate of iron oxyhydroxide containing the substitution element was coated with the chemical reaction product of the silicon compound (step 3). The pH of the reaction solution at the time of completion of the addition of the aqueous ammonia solution and the pH of the reaction solution after the stirring for 20 hours were both 8.8. Under these conditions, the molar ratio S1/(F + M) of the amount of Si element contained in tetraethoxysilane added to the dispersion at ph2.0 or more and 7.0 or less to the amount of iron, gallium, cobalt, and titanium ions contained in the raw material solution was 0.34, and the molar ratio S2/(F + M) of the total amount of Si element contained in tetraethoxysilane added dropwise to the dispersion to the amount of iron, gallium, cobalt, and titanium ions contained in the raw material solution was 2.84.
The slurry obtained in step 3 was filtered to remove as much as possible the water content of the precipitate of iron oxyhydroxide containing the substitution element coated with the chemical reaction product of the silicon compound, and then the precipitate was dispersed again in pure water to be washed by bubbling. The washed slurry was filtered again, and the obtained cake was dried at 110 ℃ in the air (step 4).
The dried product obtained in step 4 was heat-treated at 1090 ℃ for 4 hours in an air atmosphere using a box-type firing furnace, to obtain an iron-based oxide magnetic powder coated with a silicon oxide (step 5). The chemical reaction product of the silicon compound is dehydrated and changed into an oxide when heat treatment is performed in an atmospheric atmosphere.
The production conditions such as the charging conditions of the raw material solution in the present example are shown in table 1. Table 1 also shows the production conditions of other examples and comparative examples.
The heat-treated powder obtained by heat-treating the precipitate of iron oxyhydroxide containing a substitution element coated with the chemical reaction product of the silicon compound obtained in step 5 was stirred in a 17.58 mass% NaOH aqueous solution at about 60 ℃ for 24 hours to remove the silicon oxide coating on the particle surface (step 6). Next, the slurry was washed with a centrifugal separator until the conductivity became 500mS/m or less, filtered with a membrane filter, and dried, and subjected to chemical analysis of the composition of the obtained iron-based oxide magnetic powder, XRD measurement, measurement of magnetic properties, and the like. The measurement results are shown in table 2. Table 2 also shows the physical property values of the substituted-type epsilon-ferromagnetic oxide particle powders obtained in other examples and comparative examples.
The content of the α phase was determined by XRD measurement of the substituted-type ∈ ferromagnetic oxide particle powder according to example 1, and found to be 1.3%. This value is superior to the value of the substituted epsilon iron oxide powder obtained in comparative example 1, in which TEOS was added at pH8.9 after the ammonia solution was added, followed by an intermediate aging step, and then at pH 8.9. Further, chemical analysis of the composition and evaluation of magnetic properties were performed. The measurement results are shown in Table 2.
[ example 2]
A substituted-type ∈ ferromagnetic oxide particle powder was obtained in the same manner as in example 1, except that the temperature at the time of addition of the aqueous ammonia solution was 30 ℃, the time of addition of the aqueous ammonia solution was 30min, the pH at which addition of TEOS started was 6.0, the addition rate of TEOS was 5.88 g/mm during addition of the aqueous ammonia solution, and the amount of added TEOS was 22.47g/min after the end of addition of the aqueous ammonia solution in example 2. The pH at the end of the addition of the aqueous ammonia solution was 8.9, and the pH of the reaction solution at the end of the addition of TEOS and the pH of the reaction solution after the 20-hour stirring were both 8.8. The content of the α phase was determined by XRD measurement of the substituted-type ∈ ferromagnetic oxide particle powder according to example 2, and found to be 3.0%. This value is superior to the value of the substituted-type epsilon iron oxide magnetic particle powder obtained in comparative example 3 in which TEOS was added at pH8.9 after the ammonia solution was added and then the aging step was set for 30min, and thereafter, TEOS was added at pH 8.9. Further, chemical analysis of the composition and evaluation of magnetic properties were performed. The measurement results are shown in Table 2.
Comparative example 1
A powder of substituted-type ∈ ferromagnetic oxide particles was obtained in the same manner as in example 1, except that in comparative example 1, TEOS was added at the time when the pH became 8.9 by adding an aqueous ammonia solution, and then a ripening step was provided. The pH at the end of the ammonia addition was 8.9, and the pH of the reaction solution at the end of the TEOS addition and the pH of the reaction solution after the 20-hour stirring were both 8.8. When XRD measurement was performed on the powder of the substituted-type epsilon-iron oxide magnetic particles according to comparative example 1, the content of the alpha phase was found to be 3.6%, which is a value higher than those of examples 1 to 6. Further, chemical analysis of the composition and evaluation of magnetic properties were performed. The measurement results are shown in Table 2.
Comparative example 2
As comparative example 2, a substituted-type ∈ ferromagnetic oxide particle powder was obtained by the same procedure as in example 1, except that the temperature at the time of addition of the aqueous ammonia solution was 25 ℃, the time of addition of the aqueous ammonia solution was 60min, the pH of the dispersion after addition of the aqueous ammonia solution was 8.9, the intermediate aging step was 30min, and then TEOS was added in a state of pH 8.9. The pH of the reaction solution at the time when the TEOS addition was completed and the pH of the reaction solution after the 20-hour stirring were both 8.8. When XRD measurement was performed on the powder of the substituted-type epsilon-iron oxide magnetic particles according to comparative example 2, the content of the alpha phase was found to be 7.4%, which is a value higher than those of examples 1 to 6. Further, chemical analysis of the composition and evaluation of magnetic properties were performed. The measurement results are shown in Table 2.
Comparative example 3
A powder of substituted-type ∈ ferromagnetic oxide particles was obtained in the same manner as in example 2, except that in comparative example 3, an ammonia aqueous solution was added, the pH was adjusted to 8.9, and then an aging step was provided, and TEOS was added in a state of pH 8.9. The pH of the reaction solution at the time when the TEOS addition was completed and the pH of the reaction solution after the 20-hour stirring were both 8.8. When XRD measurement was performed on the powder of the substituted-type epsilon-iron oxide magnetic particles according to comparative example 3, the content of the alpha phase was found to be 5.4%, which is a value higher than those of examples 1 to 6. Further, chemical analysis of the composition and evaluation of magnetic properties were performed. The measurement results are shown in Table 2.
From the above results, when the neutralization treatment was continuously performed, the effect of setting the addition start timing of TEOS to ph2.0 or more and 7.0 or less was remarkable. As shown in the results of example 2, in the case of the production method of the present invention, even when the neutralization treatment was performed at a temperature 30 ℃ higher than the normal temperature, the substituted-type ∈ ferromagnetic oxide particle powder having a low α -phase content was obtained.
[ example 3]
As example 3, a powder of substituted-type ∈ ferromagnetic oxide particles was obtained by the same procedure as in example 1 except that the addition of the aqueous ammonia solution was stopped until ph4.0 was reached (first neutralization step), the addition of TEOS was started without providing an intermediate aging step, and the remaining aqueous ammonia solution was added after the addition of TEOS was completed (second neutralization step). The pH of the reaction solution at the end of the second neutralization step and the pH of the reaction solution after the 20-hour stirring were both 8.8. The content of the α phase was determined by XRD measurement of the substituted-type ∈ ferromagnetic oxide particle powder according to example 3, and found to be 0%. This value is superior to those of the substituted-type epsilon-iron oxide magnetic particle powders obtained in comparative examples 4 and 5 in which the addition of the aqueous ammonia solution was stopped after the aqueous ammonia solution was added until the ph became 4.0 or 6.0 (first neutralization step), the intermediate aging step was provided for 30min, and the addition of TEOS was started thereafter, but the second neutralization step was not provided after the addition of TEOS was completed. Further, chemical analysis of the composition and evaluation of magnetic properties were performed. The measurement results are shown in Table 2.
[ example 4]
In a 1L reaction vessel, 104.81g of an iron (III) sulfate solution having an Fe concentration of 11.65 mass%, 14.32g of a Ga (III) nitrate solution having a Ga concentration of 11.55 mass%, 1.91g of a 97% pure cobalt (II) nitrate 6 hydrate, and 2.02g of a 15.1 mass% Ti sulfate were dissolved in 737.71g of pure water under mechanical stirring with a stirring blade in an atmospheric atmosphere (step 1). The pH of the dissolution solution was about 1. The molar ratio of metal ions in the charging solution is Fe: ga: co: ti is 1.714:0.186:0.050: 0.050.
In an atmosphere, 15.00g of 22.30 mass% aqueous ammonia solution was added to the charged solution at 30 ℃ for 1.9min while mechanically stirring the solution with a stirring blade (first neutralization step), and after completion of the addition, stirring was continued for 30min to age the formed precipitate (intermediate aging step). At this time, the pH of the slurry containing the precipitate was 2.0 (step 2).
158.88g of Tetraethoxysilane (TEOS) having a purity of 95.0 mass% was added dropwise to the slurry obtained in step 2 while stirring at 30 ℃ for 10 minutes in the atmosphere. After the addition of TEOS was completed, 62.77g of a 22.30 mass% ammonia solution was added for 8.1min (second neutralization step). The pH after the second neutralization step was 8.8. Thereafter, the stirring was continued for 20 hours in this state, and the precipitate was coated with a chemical reaction product of the silicon compound (step 3). The pH of the reaction mixture was 8.8 during the stirring for 20 hours. Under these conditions, the molar ratio S1/(F + M) of the amount of Si element contained in tetraethoxysilane added to the dispersion at ph2.0 or more and 7.0 or less to the amount of iron, gallium, cobalt, and titanium ions contained in the raw material solution was 2.84, and the molar ratio S2/(F + M) of the total amount of Si element contained in tetraethoxysilane added dropwise to the dispersion to the amount of iron, gallium, cobalt, and titanium ions contained in the raw material solution was also 2.84.
Thereafter, a powder of substituted-type e ferromagnetic oxide particles was obtained in the same manner as in example 1. The content of the α phase was determined by XRD measurement of the substituted epsilon iron oxide powder according to example 4 and was 0%. This value is superior to those of the substituted form epsilon-oxidized magnetic particle powders obtained by comparative examples 4 and 5 described later. Further, chemical analysis of the composition and evaluation of magnetic properties were performed. The measurement results are shown in Table 2.
[ example 5]
A substituted-type epsilon ferromagnetic oxide particle powder was obtained by the same procedure as in example 4, except that in example 5, the amount and the addition time of the aqueous ammonia solution used in the first neutralization step were 51.00g and 6.5min, the pH after the first neutralization step was 3.0, and the amount and the condition time of the aqueous ammonia solution used in the second neutralization step were 27.24g and 3.5 min. The pH of the reaction solution at the end of the second neutralization step and the pH of the reaction solution during the 20-hour stirring were both 8.8. The content of the α phase was determined by XRD measurement of the substituted-form ∈ ferromagnetic oxide particle powder according to example 5, and found to be 0%. This value is superior to those of the replacement-type epsilon-iron oxide magnetic particles obtained in comparative examples 4 and 5 described later. Further, chemical analysis of the composition and evaluation of magnetic properties were performed. The measurement results are shown in Table 2.
[ example 6]
A substituted-type epsilon ferromagnetic oxide particle powder was obtained by the same procedure as in example 4, except that in example 6, the amount and the adding time of the aqueous ammonia solution used in the first neutralization step were 53.00g and 6.8min, the pH after the first neutralization step was 4.0, and the amount and the condition time of the aqueous ammonia solution used in the second neutralization step were 24.78g and 3.2 min. The pH of the reaction solution after the second neutralization step and the pH of the reaction solution during the 20-hour stirring were 8.8. The content of the α phase was determined by XRD measurement of the substituted epsilon iron oxide powder according to example 6 and was 0%. This value is superior to those of the substituted-type epsilon-ferromagnetic oxide particle powders obtained in comparative examples 4 and 5 described later. Further, chemical analysis of the composition and evaluation of magnetic properties were performed. The measurement results are shown in table 1.
[ example 7]
In a 1L reaction tank, 102.73g of an iron (III) sulfate solution having an Fe concentration of 11.65 mass%, 10.74g of aluminum (III) nitrate 9 hydrate having a purity of 98%, 1.91g of cobalt (II) nitrate 6 hydrate having a purity of 97%, and 2.02g of titanium (IV) sulfate having a Ti concentration of 15.1 mass% were dissolved in 746.26g of pure water while being mechanically stirred by a stirring blade in an atmospheric atmosphere (step 1). The pH of the dissolution solution was about 1. The molar ratio of metal ions in the charging solution is Fe: al: co: ti is 1.680:0.220:0.050: 0.050.
This charge solution was added to 51.59g of 22.30 mass% aqueous ammonia solution at 60min under mechanical stirring with a stirring blade at 30 ℃ in an atmospheric atmosphere (first neutralization step), and after completion of the addition, stirring was continued for 10min to age the formed precipitate (intermediate aging step). At this time, the pH of the slurry containing the precipitate was 3.0 (step 2).
158.88g of Tetraethoxysilane (TEOS) having a purity of 95.0 mass% was added dropwise to the slurry obtained in step 2 while stirring at 30 ℃ for 5 minutes in the atmosphere. After the TEOS addition was completed, 27.09g of a 22.30 mass% ammonia solution was added for 14min (second neutralization step). The pH after the second neutralization step was 8.8. Thereafter, the stirring was continued for 20 hours in this state, and the precipitate was coated with a chemical reaction product of the silicon compound (step 3). The pH of the reaction mixture was 8.8 during the stirring for 20 hours. Under these conditions, the molar ratio S1/(F + M) of the amount of Si element contained in tetraethoxysilane added to the dispersion at ph2.0 or more and 7.0 or less to the amount of iron, aluminum, cobalt, and titanium ions contained in the raw material solution was 2.84, and the molar ratio S2/(F + M) of the total amount of Si element contained in tetraethoxysilane added dropwise to the dispersion to the amount of iron, aluminum, cobalt, and titanium ions contained in the raw material solution was 2.84.
Thereafter, a powder of substituted-type e ferromagnetic oxide particles was obtained in the same manner as in example 1. The content of the α phase was determined by XRD measurement of the substituted epsilon iron oxide powder according to example 7 and was 0%. This value is superior to those of the substituted-type epsilon-ferromagnetic oxide particle powders obtained in comparative examples 4 and 5 described later. Further, chemical analysis of the composition and evaluation of magnetic properties were performed. The measurement results are shown in Table 2.
The radio wave absorption characteristics of the obtained replacement-type epsilon-ferromagnetic oxide particle powder were measured by the above-described method. As a result, the maximum absorption frequency of the green compact in the frequency range from 50GHz to 100GHz was 80.1GHz, and the transmission attenuation per unit thickness was 4.1 dB/mm.
Comparative example 4
A substituted epsilon iron oxide powder was obtained in the same manner as in example 6, except that the second neutralization step was not performed as in comparative example 4. The pH of the reaction solution at the time when the TEOS addition was completed and the pH of the reaction solution during the above-mentioned 20-hour stirring were 4.0. When XRD measurement was performed on the powder of the substituted-type epsilon-iron oxide magnetic particles according to comparative example 4, the content of the alpha phase was found to be 87.5% which was higher than those in examples 1 to 7. Further, chemical analysis of the composition and evaluation of magnetic properties were performed. The measurement results are shown in Table 2.
Comparative example 5
A powder of substituted-type e ferromagnetic oxide particles was obtained in the same manner as in comparative example 4, except that the amount and time of addition of the aqueous ammonia solution used in the first neutralization step were set to 57.00g and 7.3min, and the pH at the end of the first neutralization step was set to 6.0 as comparative example 5. The pH of the reaction solution at the time when the TEOS addition was completed and the pH of the reaction solution during the 20-hour stirring were 6.0. When XRD measurement was performed on the powder of the substituted-type epsilon-iron oxide magnetic particles according to comparative example 5, the content of the alpha phase was found to be 36.9%, which is higher than those of examples 1 to 7. Further, chemical analysis of the composition and evaluation of magnetic properties were performed. The measurement results are shown in Table 2.
From the above results, it was determined that when the second neutralization step was not provided, the substituted-type e ferromagnetic oxide particle powder having a low α -phase content could not be obtained. In addition, almost the same results were obtained using either nitrate or sulfate as the starting iron material.
[ example 8]
A powder of substituted-type ∈ ferromagnetic oxide particles was obtained in the same manner as in example 5, except that the stirring time in the intermediate aging step was set to 10min and Tetraethoxysilane (TEOS) was added over 5 min. The pH of the reaction solution at the time of completion of the TEOS addition was 3.0, and the pH of the reaction solution during the above-mentioned 20-hour stirring was 8.6.
The content of the α phase in the obtained powder of the substituted-type ∈ ferromagnetic oxide particles was 0%, and the radio wave absorption characteristics were measured by the method described above. As a result, the maximum absorption frequency of the green compact in the frequency range from 50GHz to 100GHz was 67.2GHz, and the transmission attenuation per unit thickness was 4.6 dB/mm.
Comparative example 6
In a 5L reaction tank, 527.22g of an iron (III) sulfate solution having an Fe concentration of 11.58 mass%, 71.61g of a Ga (III) nitrate solution having a Ga concentration of 11.55 mass%, 9.57g of a 97% pure cobalt (II) nitrate 6 hydrate, and 10.11g of a 15.1 mass% titanium (IV) sulfate were dissolved in 3688.56g of pure water while mechanically stirring them with a stirring blade in an atmospheric atmosphere (step 1). The pH of the dissolution solution was about 1. The molar ratio of metal ions in the charging solution is Fe: ga: co: ti is 1.714:0.186:0.050: 0.050.
In an atmospheric atmosphere, 388.91g of 22.30 mass% aqueous ammonia solution was added to the charged solution at 30 ℃ for 10min while mechanically stirring with a stirring blade (first neutralization step), and after completion of the addition, stirring was continued for 30min to mature the formed precipitate (intermediate maturation step). At this time, the pH of the slurry containing the precipitate was 8.6 (step 2).
794.40g of Tetraethoxysilane (TEOS) having a purity of 95.0 mass% was added dropwise to the slurry obtained in step 2 while stirring at 30 ℃ for 10 minutes in the atmosphere. Thereafter, the stirring was continued for 20 hours in this state, and the precipitate was coated with a chemical reaction product of the silicon compound (step 3). The pH of the reaction mixture was 8.6 during the stirring for 20 hours. Under these conditions, the molar ratio S1/(F + M) of the amount of Si element contained in tetraethoxysilane added to the dispersion at ph2.0 or more and 7.0 or less to the amount of iron, gallium, cobalt, and titanium ions contained in the raw material solution was 0, and the molar ratio S2/(F + M) of the total amount of Si element contained in tetraethoxysilane added dropwise to the dispersion to the amount of iron, gallium, cobalt, and titanium ions contained in the raw material solution was 2.84.
Thereafter, a powder of substituted-type e ferromagnetic oxide particles was obtained in the same manner as in example 1. The content of the α phase was determined by XRD measurement of the substituted epsilon iron oxide powder of comparative example 6, and was 4.9% which was higher than that of example 8. Further, chemical analysis of the composition, and evaluation of magnetic properties and radio wave absorption properties were performed. The measurement results are shown in Table 2.
[ example 9]
A substituted-type epsilon iron oxide powder was obtained in the same manner as in example 7, except that 101.50g of iron (III) nitrate solution and 11.7g of aluminum (III) nitrate 9 hydrate were used. The pH of the reaction solution at the time of completion of the TEOS addition was 3.0, and the pH of the reaction solution during the above-mentioned 20-hour stirring was 8.6. The molar ratio of metal ions in the charging solution is Fe: al: co: ti 1.660:0.240:0.050: 0.050. Chemical analysis of the composition, and evaluation of magnetic properties and radio wave absorption properties were performed. The measurement results are shown in Table 2.
Comparative example 7
In a 1L reaction tank, 101.51g of an iron (III) sulfate solution having an Fe concentration of 11.65 mass%, 11.72g of 98% al (III) nitrate 9 hydrate, 1.91g of 97% cobalt (II) nitrate 6 hydrate, and 2.12g of titanium (IV) sulfate having a Ti concentration of 15.1 mass% were dissolved in 746.36g of pure water while being mechanically stirred by a stirring blade in an atmospheric atmosphere (step 1). The pH of the dissolution solution was about 1. The molar ratio of metal ions in the charging solution is Fe: al: co: ti 1.660:0.240:0.050: 0.050.
In an atmospheric atmosphere, 78.68g of 22.30 mass% aqueous ammonia solution was added to the charged solution at 30 ℃ for 10min while mechanically stirring with a stirring blade (first neutralization step), and after completion of the addition, stirring was continued for 30min to age the formed precipitate (intermediate aging step). At this time, the pH of the slurry containing the precipitate was 8.6 (step 2).
158.88g of Tetraethoxysilane (TEOS) having a purity of 95.0 mass% was added dropwise to the slurry obtained in step 2 while stirring at 30 ℃ for 10 minutes in the atmosphere. Thereafter, the stirring was continued for 20 hours in this state, and the precipitate was coated with a chemical reaction product of the silicon compound (step 3). The pH of the reaction mixture was 8.6 during the stirring for 20 hours. Under these conditions, the molar ratio S1/(F + M) of the amount of Si element contained in tetraethoxysilane added to the dispersion at ph2.0 or more and 7.0 or less to the amount of iron, aluminum, cobalt, and titanium ions contained in the raw material solution was 0, and the molar ratio S2/(F + M) of the total amount of Si element contained in tetraethoxysilane added dropwise to the dispersion to the amount of iron, aluminum, cobalt, and titanium ions contained in the raw material solution was 2.84.
Thereafter, a powder of substituted-type e ferromagnetic oxide particles was obtained in the same manner as in example 1. The content of the α phase was determined by XRD measurement of the substituted epsilon iron oxide powder of comparative example 7, and was 8.7% which was higher than that of additional example 2. Further, chemical analysis of the composition, and evaluation of magnetic properties and radio wave absorption properties were performed. The measurement results are shown in Table 2.
Comparative example 8
This comparative example is an experimental example of a conventional production method corresponding to the composition ratio of example 7.
A substituted-type epsilon ferromagnetic oxide particle powder was obtained by following the same procedure as in comparative example 2, except that 102.73g of an iron (III) sulfate solution having an Fe concentration of 11.65 mass% and 10.74g of an al (III) nitrate 9 hydrate having a purity of 98%.
The pH of the reaction solution at the time when the TEOS addition was completed and the pH of the reaction solution during the 20-hour stirring were both 8.6. When XRD measurement was performed on the substituted-type epsilon-iron oxide magnetic particle powder according to this comparative example, the content of the alpha phase was found to be 8.1%, which is a value higher than that in example 7. Further, chemical analysis of the composition and evaluation of magnetic properties were performed. The measurement results are shown in Table 2.
[ Table 1]
[ Table 2]
Claims (11)
1. A substituted-type epsilon-iron oxide magnetic particle powder mainly comprising substitution of epsilon-Fe with other metal elements2O3A powder of substituted-type epsilon-iron oxide particles of epsilon-iron oxide having a part of Fe sites, wherein the substituted-type epsilon-iron oxide particles areWhen the number of moles of Fe contained in the sub-powder is Fe and the number of moles of all metal elements substituting for Fe sites is Me, the substitution amount of Fe by other metal elements defined by Me/(Fe + Me) is 0.08 to 0.17, and the content of the α -type iron-based oxide measured by the X-ray diffraction method is 3% or less.
2. The powder of substituted-type epsilon-ferromagnetic oxide particles according to claim 1, wherein the other metal element substituting a part of the Fe sites is Co, Ti or one or more selected from Ga and Al.
3. A green compact comprising the powder of substituted-type epsilon ferromagnetic oxide particles according to claim 1 or 2.
4. A radio wave absorber comprising the powder of the replacement-type ε iron oxide magnetic particles according to claim 1 or 2 dispersed in a resin or a rubber.
5. A process for producing a powder of substituted-type epsilon-iron oxide magnetic particles which comprises substituting epsilon-Fe with another metal element2O3The method for producing a substituted epsilon-iron oxide magnetic particle powder of epsilon-iron oxide having a part of Fe sites, comprising:
a neutralization step of adding an alkali to the raw material solution and neutralizing the raw material solution to a ph of 8.0 or more and 10.0 or less using an acidic aqueous solution containing ions of iron ions having a valence of 3 and ions of a metal to be substituted for a part of the Fe sites to obtain a dispersion containing a mixture of iron oxyhydroxide containing a substituted metal element or iron oxyhydroxide and a hydroxide of a substituted metal element;
a silicon compound addition step of adding a silicon compound having a hydrolyzable group to the dispersion containing the iron oxyhydroxide containing the substituted metal element or the mixture of the iron oxyhydroxide and the hydroxide of the substituted metal element; and
a curing step of maintaining a dispersion liquid containing the silicon compound and a mixture of iron oxyhydroxide containing the substituted metal element or a mixture of iron oxyhydroxide and a hydroxide of the substituted metal element at a ph of 8.0 or more and 10.0 or less, and coating the chemical reaction product of the silicon compound on the mixture of iron oxyhydroxide containing the substituted metal element or the mixture of iron oxyhydroxide and the hydroxide of the substituted metal element;
wherein the addition of the silicon compound having a hydrolyzable group is started at a point in time when the pH of the dispersion liquid becomes 2.0 or more and 7.0 or less in the neutralization step,
S1/(F + M) is 0.01 to 10.0 inclusive, and S1 is the number of moles of the silicon compound added to the dispersion at a pH of 2.0 to 7.0 inclusive, F is the number of moles of Fe ions contained in the raw material solution, and M is the total number of moles of the ions of the replacement metal element
S2/(F + M) is 0.50 to 10.0, where S2 represents the total number of moles of the silicon compounds added.
6. The method for producing a substituted-type epsilon ferromagnetic oxide particle powder as defined in claim 5, wherein the addition of the alkali in the neutralization step and the addition of the silicon compound in the silicon compound addition step are both continuously performed.
7. The method for producing a substituted-type epsilon ferromagnetic oxide particle powder as defined in claim 5, wherein the alkali addition in the neutralization step is continuously performed, and the silicon compound addition in the silicon compound addition step is intermittently performed.
8. The method for producing a substituted-type epsilon ferromagnetic oxide particle powder as defined in claim 5, wherein the addition of the alkali in the neutralization step and the addition of the silicon compound in the silicon compound addition step are both carried out intermittently.
9. The method for producing a substituted-type epsilon ferromagnetic oxide particle powder as defined in claim 5, wherein the alkali addition in the neutralization step is intermittently performed, and the silicon compound addition in the silicon compound addition step is continuously performed.
10. The method for producing a substituted-type epsilon-ferromagnetic oxide particle powder according to claim 3, wherein the other metal element substituting a part of the Fe sites is Co, Ti or one or more selected from Ga and Al.
11. A method for producing a powder compact, wherein the powder of substituted-type ε -iron oxide magnetic particles according to any one of claims 1 to 3 is compression-molded to obtain a powder compact.
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| JP2009224414A (en) * | 2008-02-20 | 2009-10-01 | Univ Of Tokyo | Radio wave absorption material, radio wave absorber using the same, and electromagnetic wave absorption rate measurement method |
| CN101687665A (en) * | 2007-05-31 | 2010-03-31 | 国立大学法人东京大学 | Magnetic iron oxide particle, magnetic material, and radio wave absorber |
| WO2016111224A1 (en) * | 2015-01-09 | 2016-07-14 | Ｄｏｗａエレクトロニクス株式会社 | Iron-based oxide magnetic particle powder, method for producing same, coating, and magnetic recording medium |
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| CN101512686A (en) * | 2006-09-01 | 2009-08-19 | 国立大学法人东京大学 | Magnetic crystal for radio wave absorbing material and radio wave absorbent |
| CN101687665A (en) * | 2007-05-31 | 2010-03-31 | 国立大学法人东京大学 | Magnetic iron oxide particle, magnetic material, and radio wave absorber |
| JP2009224414A (en) * | 2008-02-20 | 2009-10-01 | Univ Of Tokyo | Radio wave absorption material, radio wave absorber using the same, and electromagnetic wave absorption rate measurement method |
| WO2016111224A1 (en) * | 2015-01-09 | 2016-07-14 | Ｄｏｗａエレクトロニクス株式会社 | Iron-based oxide magnetic particle powder, method for producing same, coating, and magnetic recording medium |
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