JP2009249739A - Metal magnetic particulate, method for producing the same and powder magnetic core - Google Patents
Metal magnetic particulate, method for producing the same and powder magnetic core Download PDFInfo
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Abstract
Description
本発明は、磁気テープ又は磁気記録ディスク等の磁気記録媒体、電波吸収体、インダクタ又はプリント基板等の電子デバイス(ヨーク等の軟磁性体)、圧粉磁芯、光触媒、核酸抽出用磁気ビーズ、医療用マイクロスフィア等に用いる金属磁性微粒子、及びその製造方法に関する。 The present invention is a magnetic recording medium such as a magnetic tape or a magnetic recording disk, a radio wave absorber, an electronic device such as an inductor or a printed board (soft magnetic body such as a yoke), a dust core, a photocatalyst, a magnetic bead for nucleic acid extraction, The present invention relates to metal magnetic fine particles used for medical microspheres and the like, and a method for producing the same.
電子機器の小型軽量化及び高性能化に伴い、電子機器を構成する電子デバイスに用いられる材料においても高性能化及びナノサイズ化が要求されている。例えば磁気テープに塗布する磁性微粒子は、磁気記録密度の向上を目的として、ナノサイズ化と飽和磁化の向上が同時に要求されている。 As electronic devices become smaller and lighter and have higher performance, materials used for electronic devices constituting electronic devices are also required to have higher performance and nano-size. For example, magnetic fine particles applied to a magnetic tape are required to be nanosized and to improve saturation magnetization simultaneously for the purpose of improving magnetic recording density.
またアレルギーなどの疾病を診断するために抗原等のタンパク質を回収する方法として、磁気分離法が広く用いられるようになってきており、高飽和磁化を有し耐食性に優れたナノサイズの磁気ビーズの要求が高まってきている。特許文献１においては酸化鉄よりも高飽和磁化である金属鉄微粒子を用いた磁気ビーズが提案されている。また電子機器の駆動周波数の高周波化に伴い、高周波下においても高効率の磁性素子を実現できるような高性能な磁性材料が求められている。このため特許文献２では飽和磁束密度の高い鉄系の金属粉末が提案されている。 In addition, magnetic separation methods have been widely used as a method for recovering proteins such as antigens for diagnosing diseases such as allergies. Nano-sized magnetic beads having high saturation magnetization and excellent corrosion resistance have been widely used. There is an increasing demand. Patent Document 1 proposes a magnetic bead using metallic iron fine particles having higher saturation magnetization than iron oxide. Further, as the driving frequency of electronic equipment is increased, a high-performance magnetic material capable of realizing a highly efficient magnetic element even under a high frequency is required. For this reason, Patent Document 2 proposes an iron-based metal powder having a high saturation magnetic flux density.
金属の磁性微粒子はフェライト等の酸化物微粒子に比べて飽和磁化が大きいため、工業的利用への期待が大きい。例えば、金属Feの飽和磁化は２１８Ａｍ２／ｋｇと酸化鉄に比べて非常に大きいので、磁場応答性に優れ、信号強度が大きくとれるという利点がある。しかし金属Ｆｅ等の金属微粒子は容易に酸化し、例えば１０μｍ以下の微粒子状にすると、比表面積の増大により大気中で激しく酸化燃焼するので、大気中にて乾燥状態で取り扱うのが難しい。そのため、フェライトやマグネタイト等の化学的に安定な酸化物微粒子が広く利用されている。 Since metal magnetic fine particles have a larger saturation magnetization than oxide fine particles such as ferrite, they are highly expected for industrial use. For example, the saturation magnetization of metallic Fe is 218 Am 2 / kg, which is very large compared to iron oxide, and therefore has an advantage of excellent magnetic field response and high signal intensity. However, metal fine particles such as metal Fe readily oxidize. For example, if they are formed into fine particles of 10 μm or less, they violently oxidize and burn in the atmosphere due to an increase in specific surface area, so it is difficult to handle them in the air in a dry state. Therefore, chemically stable oxide fine particles such as ferrite and magnetite are widely used.
金属磁性微粒子の酸化を防ぐため、特許文献３においてはＦｅの酸化物をほう素または炭素で固相還元することにより、ほう素、窒素、炭素の少なくとも一つを主要元素として含む化合物で金属Ｆｅ微粒子を被覆している。しかしこの方法では金属磁性微粒子の被覆が十分ではなく、例えば水溶液中で用いる場合には被覆が不完全な部分から腐食してしまい、磁気ビーズ等の高耐食性が要求される用途には適さない。 In order to prevent oxidation of metal magnetic fine particles, Patent Document 3 discloses a compound containing at least one of boron, nitrogen, and carbon as a main element by solid-phase reduction of an oxide of Fe with boron or carbon. It is coated with fine particles. However, in this method, the coating of the metal magnetic fine particles is not sufficient. For example, when used in an aqueous solution, the coating is corroded from an incomplete portion, and is not suitable for applications requiring high corrosion resistance such as magnetic beads.
また炭素で被覆された金属Ｆｅ微粒子においては核粒子に炭素が固溶することによってオーステナイト相と呼ばれる常磁性のγ−（Ｆｅ，Ｃ）相が安定化する、あるいは炭化鉄が形成されることによって飽和磁化が低下してしまうという問題があった。特に金属微粒子の粒径が１０μｍ以下、更には１μｍ以下の微粒子となる場合にはγ−（Ｆｅ，Ｃ）相の安定化が顕著となり、高飽和磁化の微粒子を得ることが困難であった。以上より高飽和磁化でなおかつ高耐食性の金属微粒子を安価に製造し得る工業生産性に優れた方法が望まれている。 Moreover, in the metal Fe fine particles coated with carbon, the paramagnetic γ- (Fe, C) phase called austenite phase is stabilized by the solid solution of carbon in the core particles, or iron carbide is formed. There is a problem that the saturation magnetization is lowered. In particular, when the particle size of the metal fine particles is 10 μm or less, and further 1 μm or less, the γ- (Fe, C) phase is remarkably stabilized, and it is difficult to obtain fine particles with high saturation magnetization. As described above, a method excellent in industrial productivity that can produce metal particles having high saturation magnetization and high corrosion resistance at low cost is desired.
従って、本発明の目的は、高飽和磁化を有し、なおかつ耐食性に優れた金属磁性微粒子、及びその製造方法を提供することである。 Accordingly, an object of the present invention is to provide a metal magnetic fine particle having high saturation magnetization and excellent corrosion resistance, and a method for producing the same.
上記目的に鑑み鋭意研究の結果、本発明に至った。
本発明の金属磁性微粒子の製造方法は、Ｆｅの酸化物粉末と元素Ｘ（ＸはＡｌ、Ｃｏ、Ｎｉ及びＳｉから選ばれる少なくとも１種である。）を含む化合物粉末と、炭素を含む化合物粉末とを混合し、
得られた粉末を、非酸化性雰囲気中、８００〜１６００℃の範囲内で熱処理する（第１の熱処理）ことによって、核粒子（核粒子はＦｅ及びＸを含有する）及び炭素被膜を有する金属磁性微粒子を形成し、
前記第１の熱処理の後、前記金属磁性微粒子を４００〜７５０℃の範囲内で熱処理する（第２の熱処理）ことを特徴とする。
As a result of intensive studies in view of the above object, the present invention has been achieved.
The method for producing metal magnetic fine particles of the present invention includes a compound powder containing Fe oxide powder and element X (X is at least one selected from Al, Co, Ni and Si), and a compound powder containing carbon. And mix
The obtained powder is heat-treated in a non-oxidizing atmosphere within a range of 800 to 1600 ° C. (first heat treatment), whereby a core particle (the core particle contains Fe and X) and a metal having a carbon film Forming magnetic particles,
After the first heat treatment, the metal magnetic fine particles are heat-treated within a range of 400 to 750 ° C. (second heat treatment).
第１の熱処理ではＦｅの酸化物を還元する。第２の熱処理では第１の熱処理時に生成したγ−（Ｆｅ，Ｃ）相あるいは炭化鉄をα−Ｆｅ相と炭素に分解する反応を促進させる。この分解反応は元素Ｘの添加によって促進されるものであり、元素Ｘを無添加とした場合は分解が不十分である。このため本発明の金属磁性微粒子を製造するためには２段熱処理（前記第１及び第２の熱処理）を実施することが好ましい。 In the first heat treatment, the Fe oxide is reduced. In the second heat treatment, the reaction of decomposing the γ- (Fe, C) phase or iron carbide generated during the first heat treatment into the α-Fe phase and carbon is promoted. This decomposition reaction is promoted by the addition of the element X, and the decomposition is insufficient when the element X is not added. For this reason, in order to produce the metal magnetic fine particles of the present invention, it is preferable to carry out a two-stage heat treatment (the first heat treatment and the second heat treatment).
前記本発明の製造方法の第２の熱処理を経ることにより、核粒子はα−Ｆｅ相と前記α−Ｆｅ相とは異なる強磁性相とを有し、前記強磁性相はメスバウアー分光分析によって得られる内部磁場の値が２５〜３２Ｔの範囲内となる相であり、前記核粒子には前記強磁性相が２０〜５５ｖｏｌ％含まれている金属磁性粒子を得る。前記元素Ｘを無添加とした場合は内部磁場の低い炭化鉄（Ｆｅ３Ｃの内部磁場は約２０Ｔである。）が１０ｖｏｌ％以上析出し、全体的な飽和磁化を低下させてしまう。前記元素Ｘを添加することにより内部磁場の値が２５〜３２Ｔの範囲内となる強磁性相が２０〜５５ｖｏｌ％含まれるため、高飽和磁化を維持することができる。 Through the second heat treatment of the production method of the present invention, the core particles have an α-Fe phase and a ferromagnetic phase different from the α-Fe phase, and the ferromagnetic phase is obtained by Mossbauer spectroscopy. The obtained magnetic phase is a phase in which the value of the internal magnetic field is in the range of 25 to 32 T, and the core particles obtain metal magnetic particles containing 20 to 55 vol% of the ferromagnetic phase. When the element X is not added, 10 vol% or more of iron carbide having a low internal magnetic field (the internal magnetic field of Fe 3 C is about 20 T) is precipitated, thereby reducing the overall saturation magnetization. By adding the element X, 20 to 55 vol% of a ferromagnetic phase having an internal magnetic field value in the range of 25 to 32 T is included, so that high saturation magnetization can be maintained.
前記金属磁性微粒子において、前記核粒子はＡｌ、Ｃｏ、Ｎｉ及びＳｉから選ばれる少なくとも１種の元素を１〜１０ｍａｓｓ％含むことが好ましい。これら元素は核粒子であるＦｅ中の炭素を黒鉛として析出させる作用があるため、常磁性のγ−Ｆｅ相や低飽和磁化の炭化鉄の分解を促進するだけでなく、炭素を被覆層へと析出させて被覆率を向上させ、耐食性を向上させる。 In the metal magnetic fine particle, the core particle preferably contains 1 to 10 mass% of at least one element selected from Al, Co, Ni, and Si. These elements have the effect of precipitating carbon in Fe, the core particle, as graphite, so they not only promote the decomposition of the paramagnetic γ-Fe phase and low saturation magnetization iron carbide, but also convert the carbon into a coating layer. Precipitates to improve coverage and improve corrosion resistance.
本発明により、高い飽和磁化と高耐食性を両立した金属磁性微粒子を得ることができる。 According to the present invention, metal magnetic fine particles having both high saturation magnetization and high corrosion resistance can be obtained.
[1]金属磁性微粒子の製造方法
本発明の金属磁性微粒子は、Ｆｅの酸化物を炭素（Ｃ）で熱還元する固相還元反応において熱処理時にＣがＦｅ中に固溶する、あるいはＦｅと反応してＦｅ−Ｃ相を形成することを避けるために、２段熱処理を実施すると共にＣ析出を促進する元素Ｘを原料に添加することを特徴としている。
[1] Method for Producing Metal Magnetic Fine Particle The metal magnetic fine particle of the present invention is a solid-phase reduction reaction in which Fe oxide is thermally reduced with carbon (C). In order to avoid the formation of the Fe—C phase, element X that promotes C precipitation is added to the raw material while performing a two-step heat treatment.
(1)Ｆｅの酸化物粉末
Ｆｅの酸化物粉末の粒径は、金属磁性微粒子の目標粒径に合わせて選択し得るが、０．００１〜５μｍの範囲内であるのが好ましい。粒径が０．００１μｍ未満では、２次凝集が著しく起こるため、以下の製造工程での取り扱いが困難である。また５μｍ超では、金属酸化物粉末の比表面積が小さすぎるため、還元反応の進行が遅い。より好ましい金属酸化物粉末の実用的な粒径は０．００５〜１μｍである。Ｆｅの酸化物としてはＦｅ２Ｏ３、Ｆｅ３Ｏ４、ＦｅＯ等が挙げられ、Ｆｅ２Ｏ３が安価である点で好ましい。
(1) Fe Oxide Powder The particle size of the Fe oxide powder can be selected according to the target particle size of the metal magnetic fine particles, but is preferably in the range of 0.001 to 5 μm. When the particle size is less than 0.001 μm, secondary aggregation occurs remarkably, so that it is difficult to handle in the following manufacturing process. If it exceeds 5 μm, the specific surface area of the metal oxide powder is too small, so that the reduction reaction proceeds slowly. The practical particle size of the metal oxide powder is more preferably 0.005 to 1 μm. Examples of the Fe oxide include Fe 2 O 3 , Fe 3 O 4 , FeO, and the like, and Fe 2 O 3 is preferable in that it is inexpensive.
(2)元素Ｘ（ＸはＡｌ、Ｃｏ、Ｎｉ及びＳｉから選ばれる少なくとも1種である。）を含む化合物粉末
元素ＸはＡｌ、Ｃｏ、Ｎｉ及びＳｉから選ばれる少なくとも1種であることが好ましく、特にＳｉはＣ析出促進作用が大きいので好適である。前記元素Ｘの化合物粉末とは元素Ｘ単体、炭化物、窒化物、酸化物のいずれかが好ましい。ただし前記元素Ｘの酸化物の中で酸化鉄よりも熱力学的に安定であるものは熱還元されたＦｅと反応することが困難となり相応しくない。Ｘ化合物として具体的にはＡｌ、ＡｌＣ、ＡｌＮ、Ｃｏ、Ｃｏ３Ｏ４、Ｎｉ、ＮｉＯ、Ｎｉ３Ｎ、Ｓｉ、ＳｉＣ、Ｓｉ３Ｎ４、及びこれら合金などが挙げられる。Ａｌ２Ｏ３、ＳｉＯ２は熱力学的に安定であるので不適である。固相反応性を考慮すると、前記元素Ｘの化合物粉末の粒径は０．００１〜５μｍの範囲内であるのが好ましい。粒径が０．００１μｍ未満では比表面積が大きすぎて容易に酸化し、取り扱いが困難である。また５μｍ超では比表面積が小さすぎるため、Ｆｅとの反応性が低く添加効果が期待できない。より好ましくは０．００１〜１μｍが好ましい。
(2) Compound powder containing element X (X is at least one selected from Al, Co, Ni and Si) Element X is preferably at least one selected from Al, Co, Ni and Si In particular, Si is suitable because it has a large C precipitation promoting effect. The element X compound powder is preferably element X alone, carbide, nitride, or oxide. However, among the oxides of the element X, those which are thermodynamically more stable than iron oxide are not suitable because it is difficult to react with the thermally reduced Fe. Specific examples of the X compound include Al, AlC, AlN, Co, Co 3 O 4 , Ni, NiO, Ni 3 N, Si, SiC, Si 3 N 4 , and alloys thereof. Al 2 O 3 and SiO 2 are not suitable because they are thermodynamically stable. In consideration of solid phase reactivity, the particle size of the element X compound powder is preferably in the range of 0.001 to 5 μm. If the particle size is less than 0.001 μm, the specific surface area is too large and it is easily oxidized and difficult to handle. If it exceeds 5 μm, the specific surface area is too small, so the reactivity with Fe is low and the effect of addition cannot be expected. More preferably, 0.001-1 micrometer is preferable.
(3)炭素を含む化合物粉末
炭素供給源となる原料の粉末としては、炭素粉（グラファイト、カーボンブラック、或いは天然黒鉛等）が適しているが、炭素を含む化合物であってもよい。すなわち石炭や活性炭、コークスや脂肪酸、ポリビニルアルコールなどの高分子、Ｂ−Ｃ化合物、金属を含む各種炭化物であってもよい。ただし、被膜の炭素純度を高くするためには、炭素粉を用いるとよい。
(3) Compound powder containing carbon As a raw material powder to be a carbon supply source, carbon powder (graphite, carbon black, natural graphite or the like) is suitable, but a compound containing carbon may also be used. That is, it may be various carbides including coal, activated carbon, coke, fatty acid, polymer such as polyvinyl alcohol, BC compound, and metal. However, carbon powder may be used to increase the carbon purity of the coating.
(4)原料粉末の混合
Ｆｅの酸化物粉末と元素Ｘ（ＸはＡｌ、Ｃｏ、Ｎｉ及びＳｉから選ばれる少なくとも1種である。）を含む化合物粉末、及び炭素を含む化合物粉末を混合するためには、ボールミル、ビーズミル、Ｖ型ミキサー、乳鉢、ライカイ機、各種ミキサーを用いるのが好ましい。より均一に混合するためには水やアルコールなどの有機溶媒中で湿式混合することが好ましい。
(4) Mixing of raw material powders In order to mix an oxide powder of Fe and a compound powder containing element X (X is at least one selected from Al, Co, Ni and Si) and a compound powder containing carbon For this, it is preferable to use a ball mill, a bead mill, a V-type mixer, a mortar, a reiki machine, or various mixers. In order to mix more uniformly, it is preferable to perform wet mixing in an organic solvent such as water or alcohol.
Ｆｅの酸化物粉末に対する炭素化合物粉末の配合比率は、少なくとも還元反応に必要な化学量論比であることが好ましい。前記化学量論比よりも少ない場合には熱処理の際に焼結粒成長してしまい微粒子を得ることが出来ない。また元素Ｘ（ＸはＡｌ、Ｃｏ、Ｎｉ及びＳｉから選ばれる少なくとも１種である。）を含む化合物粉末の配合比は、元素Ｘの濃度がＦｅ対比で１〜１０ｍａｓｓ％となる比率であることが好ましい。元素ＸのＦｅ対比濃度が１ｍａｓｓ％未満の場合はＣ析出促進効果が十分に得られず好ましくない。また元素ＸのＦｅ対比濃度が１０ｍａｓｓ％を超える場合は高飽和磁化を発現する強磁性相の含有率が低下し、飽和磁化の低下を招くので好ましくない。また上記原料粉末を均一に混合するため、必要に応じて分散剤を添加することが好ましい。Ｆｅ対比濃度とは、各原料粉末に含まれるＦｅとＸの合計質量を１００ｍａｓｓ％としたときのＸの割合を表し、一般式ではＸ／（Ｆｅ＋Ｘ）×１００(ｍａｓｓ％)で表される。 The mixing ratio of the carbon compound powder to the Fe oxide powder is preferably at least a stoichiometric ratio necessary for the reduction reaction. When it is less than the stoichiometric ratio, sintered grains grow during the heat treatment and fine particles cannot be obtained. The compounding ratio of the compound powder containing the element X (X is at least one selected from Al, Co, Ni, and Si) is such that the concentration of the element X is 1 to 10 mass% in comparison with Fe. Is preferred. When the Fe contrast concentration of the element X is less than 1 mass%, the C precipitation promoting effect cannot be sufficiently obtained, which is not preferable. On the other hand, when the Fe contrast concentration of the element X exceeds 10 mass%, the content of the ferromagnetic phase exhibiting high saturation magnetization is lowered, and the saturation magnetization is lowered. Moreover, in order to mix the said raw material powder uniformly, it is preferable to add a dispersing agent as needed. The Fe contrast concentration represents the ratio of X when the total mass of Fe and X contained in each raw material powder is 100 mass%, and is represented by X / (Fe + X) × 100 (mass%) in the general formula.
(5)熱処理
前記原料の混合粉末は以下に述べる２段熱処理を施すことが好ましい。まず第１の熱処理は８００〜１６００℃の範囲で熱処理し、Ｆｅの酸化物を炭素によって金属Ｆｅへと還元する。８００℃未満であると還元反応の進行が不十分であり、好ましくない。１６００℃を超える高温では粉末中の粒子同士が焼結粒成長するため好ましくない。また熱処理に用いる炉にも耐熱性が要求され製造コストが嵩んでしまう。前記第１熱処理においては還元反応が進行すると共に元素Ｘ（ＸはＡｌ、Ｃｏ、Ｎｉ及びＳｉから選ばれる少なくとも1種である。）とＦｅとが合金化し、ＦｅへのＣ固溶限を低下させる効果もある。更に第２の熱処理として４００〜７５０℃の範囲で熱処理することが好ましい。この温度範囲はＦｅ−Ｃ２元状態図においてα−Ｆｅ相が安定な温度領域である。この第2熱処理を施すことによって高温相であるγ−Ｆｅ相の残留を抑制することができる。γ−Ｆｅ相は常磁性相であるため、高飽和磁化を維持するためには残留を抑制することが好ましい。第２熱処理の温度は４００℃未満であるとγ−Ｆｅ相からα−Ｆｅ相への相転移が不十分であり好ましくない。また７５０℃超であるとγ−Ｆｅ相の安定領域に到達するので好ましくない。γ−Ｆｅ相の残留を十分抑制するには温度範囲は６００〜７５０℃がより好ましい。
なお、上述の熱処理において還元反応を十分に進行させるためには非酸化性雰囲気であることが好ましく、Ａｒ、Ｈｅなどの不活性ガスや水素、窒素、炭酸ガスなどが選択される。特に安全かつ安価な点では窒素雰囲気がより好ましい。
(5) Heat treatment The mixed powder of the raw materials is preferably subjected to the two-stage heat treatment described below. First, the first heat treatment is performed in the range of 800 to 1600 ° C., and the Fe oxide is reduced to metal Fe by carbon. If the temperature is less than 800 ° C., the progress of the reduction reaction is insufficient, which is not preferable. A high temperature exceeding 1600 ° C. is not preferable because particles in the powder grow into sintered grains. Further, the furnace used for the heat treatment is also required to have heat resistance, which increases the manufacturing cost. In the first heat treatment, the reduction reaction proceeds and the element X (X is at least one selected from Al, Co, Ni and Si) and Fe are alloyed to lower the C solid solubility limit in Fe. There is also an effect. Furthermore, it is preferable to heat-process in the range of 400-750 degreeC as 2nd heat processing. This temperature range is a temperature region in which the α-Fe phase is stable in the Fe-C binary phase diagram. By applying this second heat treatment, the residual γ-Fe phase, which is a high temperature phase, can be suppressed. Since the γ-Fe phase is a paramagnetic phase, it is preferable to suppress the residual in order to maintain high saturation magnetization. If the temperature of the second heat treatment is less than 400 ° C., the phase transition from the γ-Fe phase to the α-Fe phase is insufficient, which is not preferable. Further, if it exceeds 750 ° C., it reaches the stable region of the γ-Fe phase, which is not preferable. In order to sufficiently suppress the residual γ-Fe phase, the temperature range is more preferably 600 to 750 ° C.
In order to allow the reduction reaction to proceed sufficiently in the heat treatment described above, a non-oxidizing atmosphere is preferable, and an inert gas such as Ar or He, hydrogen, nitrogen, carbon dioxide gas, or the like is selected. In particular, a nitrogen atmosphere is more preferable in terms of safety and low cost.
(6)精製・磁気分離
本発明の金属磁性微粒子は前記熱処理によって製造されるが、非磁性成分として原料として用いた炭素を含む化合物粉末の余剰分などが含まれる。したがってより高飽和磁化を有する金属磁性微粒子を得るためには、磁気分離操作によって金属磁性微粒子のみに精製することが好ましい。この精製処理には予め熱処理直後の粉末をイソプロピルアルコール、エタノールなどのアルコール中またはアセトン中に十分分散させた後、永久磁石などで磁性粒子を固定化し、その他の非磁性成分を流出除去することが好ましい。アルコール中での分散には分散機能を発現する界面活性剤を用いたり、あるいは機械的に分散力を付与することが好ましい。
(6) Purification / Magnetic Separation The metal magnetic fine particles of the present invention are produced by the heat treatment, and include a surplus of a compound powder containing carbon used as a raw material as a nonmagnetic component. Therefore, in order to obtain metal magnetic fine particles having higher saturation magnetization, it is preferable to purify only metal magnetic fine particles by magnetic separation operation. In this refining treatment, the powder immediately after the heat treatment is sufficiently dispersed in alcohol such as isopropyl alcohol or ethanol or acetone, and then the magnetic particles are fixed with a permanent magnet, and other nonmagnetic components are discharged and removed. preferable. For dispersion in alcohol, it is preferable to use a surfactant that exhibits a dispersion function, or mechanically impart a dispersion force.
[2]金属磁性微粒子の構造及び特性
(1)金属磁性微粒子の構造
本発明の金属磁性微粒子は炭素で被覆されており、核粒子は金属鉄である。前記核粒子においてα−Ｆｅ相の他にメスバウアー分析によって得られる内部磁場の値が２５〜３１Ｔの範囲となる強磁性相が２０〜５５ｖｏｌ％含まれていることが好ましい。内部磁場の値が２５Ｔ未満であると磁性が弱まり飽和磁化が小さくなってしまう。また内部磁場が３１Ｔ超であるとα−Ｆｅ相以外に酸化鉄Ｆｅ３Ｏ４が含まれてしまう。前記内部磁場が２５〜３１Ｔの範囲となる強磁性相は体積比で２０〜５５ｖｏｌ％含まれていることが好ましい。前記強磁性相の含有率が２０ｖｏｌ％未満であると元素Ｘ（ＸはＡｌ、Ｃｏ、Ｎｉ及びＳｉから選ばれる少なくとも１種である。）の添加効果が十分に得られずＦｅ中に炭素が固溶した状態となり、飽和磁化が低下するだけでなく炭素による被覆が不十分となり耐食性が低下する。また前記強磁性相の含有率が５５ｖｏｌ％を超えると高飽和磁化であるα−Ｆｅ相の含有率が低下してしまい、結果として飽和磁化の低下を招くので好ましくない。
[2] Structure and properties of metal magnetic fine particles
(1) Structure of metal magnetic fine particles The metal magnetic fine particles of the present invention are coated with carbon, and the core particles are metallic iron. In addition to the α-Fe phase, the core particles preferably contain 20 to 55 vol% of a ferromagnetic phase in which the value of the internal magnetic field obtained by Mossbauer analysis is in the range of 25 to 31 T. If the value of the internal magnetic field is less than 25T, the magnetism becomes weak and the saturation magnetization becomes small. If the internal magnetic field exceeds 31T, iron oxide Fe 3 O 4 is contained in addition to the α-Fe phase. The ferromagnetic phase in which the internal magnetic field is in the range of 25 to 31 T is preferably contained in a volume ratio of 20 to 55 vol%. When the content of the ferromagnetic phase is less than 20 vol%, the effect of adding the element X (X is at least one selected from Al, Co, Ni and Si) cannot be sufficiently obtained, and carbon is contained in Fe. Not only does the saturation magnetization decrease, but also the coating with carbon becomes insufficient and the corrosion resistance decreases. On the other hand, if the content of the ferromagnetic phase exceeds 55 vol%, the content of the α-Fe phase, which is highly saturated, is reduced, resulting in a decrease in saturation magnetization, which is not preferable.
前記核粒子を被覆する被覆層は平均膜厚が３０〜４０ｎｍであることが好ましい。平均膜厚が３０ｎｍ未満であると被覆による核粒子の保護が不十分となり耐食性が低下してしまう。一方平均膜厚が４０ｎｍ超であると被覆層の体積が多く磁性成分の体積比率が低下してしまい飽和磁化が低下するので好ましくない。核粒子を十分に保護し、なおかつ磁性成分の体積比率をある程度維持するためには被覆層の平均膜厚が前記範囲であることが好ましい。より好ましくは平均粒径ｄ５０と平均膜厚ｔの比率（=ｔ／ｄ５０）が０．０１６〜０．０２０の範囲となることである。ここで被覆層の平均膜厚は金属磁性微粒子の電子顕微鏡写真を用いて計測できる。１試料につき３０粒以上計測し、その平均値を平均膜厚とする。また平均粒径ｄ５０は体積基準のメディアン径であり、粒径分布（体積基準）から求めた積算分布曲線において５０％の積算値における粒径値である。 The coating layer covering the core particles preferably has an average film thickness of 30 to 40 nm. If the average film thickness is less than 30 nm, the core particles are not sufficiently protected by the coating, and the corrosion resistance is lowered. On the other hand, if the average film thickness is more than 40 nm, the volume of the coating layer is so large that the volume ratio of the magnetic component is lowered and the saturation magnetization is lowered. In order to sufficiently protect the core particles and to maintain the volume ratio of the magnetic component to some extent, it is preferable that the average film thickness of the coating layer is in the above range. More preferably, the ratio of the average particle diameter d50 to the average film thickness t (= t / d50) is in the range of 0.016 to 0.020. Here, the average film thickness of the coating layer can be measured using an electron micrograph of metal magnetic fine particles. 30 or more grains are measured per sample, and the average value is defined as the average film thickness. The average particle diameter d50 is a volume-based median diameter, and is a particle diameter value at an integrated value of 50% in an integrated distribution curve obtained from a particle diameter distribution (volume basis).
また本発明の金属磁性微粒子のｄ５０は０．１〜５μmであることが好ましい。ｄ５０が０．１μｍ未満であると1粒子当りの飽和磁化が小さくなってしまう。また５μm超であると比表面積が小さくなってしまい、例えば医療用磁気ビーズとして用いる場合には目的物質との反応性が低下してしまう。また高周波用部品に用いられる場合には渦電流損が大きくなり好ましくない。０．１〜５μｍの金属磁性微粒子であってもγ−Ｆｅ相の残留が少なく、高飽和磁化を発現する。 Moreover, it is preferable that d50 of the metal magnetic fine particle of this invention is 0.1-5 micrometers. If d50 is less than 0.1 μm, the saturation magnetization per particle will be small. On the other hand, if it exceeds 5 μm, the specific surface area becomes small. For example, when used as medical magnetic beads, the reactivity with the target substance is lowered. Further, when used for high-frequency components, eddy current loss increases, which is not preferable. Even a metal magnetic fine particle of 0.1 to 5 μm exhibits little saturation of γ-Fe phase and exhibits high saturation magnetization.
(2)磁気特性
本発明の金属磁性微粒子の飽和磁化は１００〜１９５Ａｍ２／ｋｇであることが好ましい。飽和磁化が１００Ａｍ２／ｋｇ未満であると酸化鉄の値と同等となってしまう。また１９５Ａｍ２／ｋｇ以上であると被覆層の体積比が少なすぎ、被覆が不十分となるので耐食性が低下してしまう。より好ましくは１５０〜１９５Ａｍ２／ｋｇ、更に好ましくは１８０〜１９５Ａｍ２／ｋｇである。また本発明の金属磁性微粒子の保持力は１．３ｋＡ／ｍであることが好ましい。１．３ｋＡ／ｍ以上であると残留磁化が大きくなり、粒子同士が磁気的凝集してしまうので実用上好ましくないだけでなく、軟磁性材料としての用途に適さなくなってしまう。
(2) Magnetic properties The saturation magnetization of the metal magnetic fine particles of the present invention is preferably 100 to 195 Am 2 / kg. If the saturation magnetization is less than 100 Am 2 / kg, it will be equivalent to the value of iron oxide. On the other hand, if it is 195 Am 2 / kg or more, the volume ratio of the coating layer is too small and the coating becomes insufficient, so that the corrosion resistance is lowered. More preferably, it is 150-195 Am < 2 > / kg, More preferably, it is 180-195 Am < 2 > / kg. Further, the holding force of the metal magnetic fine particles of the present invention is preferably 1.3 kA / m. If it is 1.3 kA / m or more, the remanent magnetization becomes large and the particles are magnetically aggregated, which is not preferable for practical use and is not suitable for use as a soft magnetic material.
(3)耐食性の評価
ＰＢＳバッファー１ｍｌ中に本発明の金属磁性微粒子２５ｍｇを３７℃で１６８ｈ浸漬させた後のＦｅ溶出量が０．８ｍｇ／ｌ未満であることが好ましい。０．８ｍｇ／ｌ以上であると金属Feを主体とする核粒子の被覆が不十分であり水溶液中での腐食が不可避であり磁性材料の安定性が低下するので好ましくない。またカオトロピック塩（グアニジン塩酸塩、グアニジン硝酸塩、グアニジン炭酸塩、グアニジンチオシアネート、尿素）水溶液１ｍｌ中に本発明の金属微粒子２５ｍｇを室温で２４ｈ浸漬させた後のＦｅ溶出量が１７０ｍｇ／ｌ未満であることが好ましい。１７０ｍｇ／ｌ以上であると金属Ｆｅを主体とする核粒子の腐食が著しく、磁性材料としての品質が低下するので好ましくない。本発明の金属磁性微粒子は、Ｆｅ中に固溶していた炭素を十分被覆層へと析出させることにより、核粒子（Ｆｅコア）を十分に被覆することができ、高い耐食性を発現することができる。
(3) Evaluation of corrosion resistance It is preferable that the Fe elution amount after immersing 25 mg of the metal magnetic fine particles of the present invention in 1 ml of PBS buffer at 37 ° C. for 168 h is less than 0.8 mg / l. If it is 0.8 mg / l or more, coating of core particles mainly composed of metallic Fe is insufficient, corrosion in an aqueous solution is unavoidable, and stability of the magnetic material is lowered, which is not preferable. Further, the Fe elution amount after immersion of 25 mg of the metal fine particles of the present invention at room temperature in 1 ml of an aqueous solution of chaotropic salt (guanidine hydrochloride, guanidine nitrate, guanidine carbonate, guanidine thiocyanate, urea) is less than 170 mg / l. Is preferred. If it is 170 mg / l or more, the core particles mainly composed of metal Fe are significantly corroded, and the quality as a magnetic material is deteriorated. The metal magnetic fine particles of the present invention can sufficiently coat the core particles (Fe core) by sufficiently depositing carbon dissolved in Fe into the coating layer and exhibit high corrosion resistance. it can.
本発明により、高飽和磁化を有する耐食性に優れた金属磁性微粒子を安価でかつ簡易に得られる。Ｆｅに固溶しているＣを外部表面へと析出させることで核粒子を内部磁場の高い磁性相のみで構成することができ、なおかつ十分な被覆を実現する。したがって高透磁率の圧粉磁芯や高耐食性が要求される環境下で用いられるバイオ医療用磁気ビーズに好適である。 According to the present invention, metal magnetic fine particles having high saturation magnetization and excellent corrosion resistance can be obtained inexpensively and easily. By precipitating C dissolved in Fe on the outer surface, the core particles can be composed only of a magnetic phase having a high internal magnetic field, and sufficient coating is realized. Therefore, it is suitable for a magnetic core for biomedical use used in an environment where high magnetic permeability powder cores and high corrosion resistance are required.
(4)高周波特性
本発明の金属磁性微粒子と有機樹脂とを混合した後、圧縮成形し、必要に応じて樹脂の熱硬化処理を施すことで、５〜１０ＭＨｚの周波数帯域で優れた磁気特性（透磁率μ＝８〜９）を示す圧粉磁芯を得ることができる。ここで前記樹脂は例えば、フェノール樹脂、アクリル樹脂、シリコーン樹脂或いはエポキシ樹脂等を用いることができる。
(4) High-frequency characteristics After mixing the metal magnetic fine particles of the present invention and an organic resin, compression molding is performed, and if necessary, the resin is heat-cured to provide excellent magnetic characteristics in a frequency band of 5 to 10 MHz ( A dust core exhibiting a permeability μ = 8-9) can be obtained. Here, for example, a phenol resin, an acrylic resin, a silicone resin, or an epoxy resin can be used as the resin.
（実施例１〜４）
平均粒径０．０５μmのα−Ｆｅ２Ｏ３粉末と平均粒径０．０４μｍのＳｉＣ粉末、及び平均粒径０．０２μｍのカーボンブラック粉末（Ｃ．Ｂ．）を表１で示した配合比でそれぞれ秤量し、ボールミルにて２０時間湿式混合した。得られた混合スラリーを乾燥後、この混合粉末をアルミナ製ボートに適量充填して炉の中に配置し、流量が２（ｌ／ｍｉｎ）の窒素ガス気流中で室温から３℃／ｍｉｎの速度で昇温した後、１４００℃で２時間保持して室温まで炉冷し、更に連続的に７００℃まで昇温して１時間保持後に室温まで冷却する２段熱処理を実施した。熱処理直後の試料の飽和磁化を振動試料型磁化測定機（ＶＳＭ）にて最大印加磁場１．６ＭＡ／ｍとして測定した。結果を表１に示す。また熱処理直後の試料粉末についてＸ線回折測定（線源：Cu−Kα線、測定範囲：２０〜１２０°）を行い、相の同定を行った。
(Examples 1-4)
Table 1 shows the mixing ratio of α-Fe 2 O 3 powder having an average particle diameter of 0.05 μm, SiC powder having an average particle diameter of 0.04 μm, and carbon black powder (CB) having an average particle diameter of 0.02 μm. And were wet mixed in a ball mill for 20 hours. After drying the obtained mixed slurry, an appropriate amount of this mixed powder is filled into an alumina boat and placed in a furnace, and the flow rate is from room temperature to 3 ° C./min in a nitrogen gas stream with a flow rate of 2 (l / min). After the temperature was raised, the furnace was cooled to room temperature at 1400 ° C. for 2 hours, further heated to 700 ° C., held for 1 hour, and then cooled to room temperature. The saturation magnetization of the sample immediately after the heat treatment was measured with a vibrating sample magnetometer (VSM) with a maximum applied magnetic field of 1.6 MA / m. The results are shown in Table 1. The sample powder immediately after the heat treatment was subjected to X-ray diffraction measurement (ray source: Cu-Kα ray, measurement range: 20 to 120 °) to identify the phase.
（比較例１）
ＳｉＣ粉末を無添加とした以外は実施例１と同様にして試料を作製し、試料の飽和磁化を測定した。結果を表１に示す。またＸ線回折測定も実施例１と同様に行った。
(Comparative Example 1)
A sample was prepared in the same manner as in Example 1 except that no SiC powder was added, and the saturation magnetization of the sample was measured. The results are shown in Table 1. X-ray diffraction measurement was also performed in the same manner as in Example 1.
（比較例２）
熱処理条件を１４００℃で２時間の１段処理とした以外は比較例１と同様にして試料を作製した。熱処理直後の飽和磁化を表１に示す。
(Comparative Example 2)
A sample was prepared in the same manner as in Comparative Example 1 except that the heat treatment was performed at 1400 ° C. for 1 hour for 2 hours. Table 1 shows the saturation magnetization immediately after the heat treatment.
実施例１〜４では飽和磁化が１４８Ａｍ２／ｋｇ以上であるが、比較例１、２の飽和磁化は１４１、１３０Ａｍ２／ｋｇと比較的低い。これは２段熱処理による効果とＳｉの添加効果によって実施例１〜４の試料粉末中に含まれるγ−Ｆｅ相の体積比率が小さくなった為である。図１にγ−Ｆｅ相の体積比率とＳｉ濃度（＝Ｓｉ／（Ｆｅ＋Ｓｉ））の関係を示す。Ｓｉ濃度が高くなるにしたがってγ−Ｆｅ相の体積比率が低下していく。なお、γ−Ｆｅ相の体積比率（Cγと記載）はγ相の回折ピーク（（１１１）γ、（２００）γ、（２２０）γ）とα相の回折ピーク（（１１０）α、（２００）α、（２１１）α）の各強度と各R値から、以下の［数１］を用いて算出した。Ｒ値は以下の［数２］を用いて算出した。θは各回折ピークの回折角、ｖは格子定数から算出される単位胞の体積を表し実測により求めることができる。それ以外の各パラメータは参考文献（カリティ著「新版 X線回折要論」（松村源太郎・訳） (株)アグネ）に記載されている値を用いた。 In Examples 1 to 4, the saturation magnetization is 148 Am 2 / kg or more, but the saturation magnetizations of Comparative Examples 1 and 2 are relatively low, 141 and 130 Am 2 / kg. This is because the volume ratio of the γ-Fe phase contained in the sample powders of Examples 1 to 4 is reduced by the effect of the two-stage heat treatment and the effect of addition of Si. FIG. 1 shows the relationship between the volume ratio of the γ-Fe phase and the Si concentration (= Si / (Fe + Si)). As the Si concentration increases, the volume ratio of the γ-Fe phase decreases. The volume ratio of the γ-Fe phase (described as C γ ) is the diffraction peak of the γ phase ((111) γ , (200) γ , (220) γ ) and the diffraction peak of the α phase ((110) α , ( 200) α and (211) α ) were calculated from the respective intensities and R values using the following [Equation 1]. The R value was calculated using the following [Equation 2]. θ represents the diffraction angle of each diffraction peak, v represents the volume of the unit cell calculated from the lattice constant, and can be obtained by actual measurement. For each of the other parameters, the values described in the reference (“New edition: X-ray diffraction theory” by Karity (Gentaro Matsumura, translation) Agne, Inc.) were used.
以上より、常磁性であるγ−Ｆｅ相が試料に含まれると飽和磁化が低下するだけでなく、たとえ金属磁性微粒子だけを磁気分離できたとしても分離回収率が低下してしまい好ましくない。実施例１〜４で示したようにＳｉを添加すること、なおかつα−Ｆｅ相が安定な領域で２段熱処理を施すことが、γ−Ｆｅ相の析出抑制に効果的である。表１で“Ｓｉ濃度”は、（Ｓｉ／（Ｆｅ＋Ｓｉ））×１００に相当する。 From the above, when a γ-Fe phase that is paramagnetic is included in the sample, not only the saturation magnetization is lowered, but even if only the metal magnetic fine particles can be magnetically separated, the separation and recovery rate is lowered, which is not preferable. Adding Si as shown in Examples 1 to 4 and performing a two-step heat treatment in a region where the α-Fe phase is stable is effective in suppressing the precipitation of the γ-Fe phase. In Table 1, “Si concentration” corresponds to (Si / (Fe + Si)) × 100.
（実施例５〜８）
実施例１〜４で得た試料粉末から金属磁性微粒子だけを取り出すため、次に述べる精製・磁気分離処理を実施した。まず実施例１〜４の試料粉末２ｇとイソプロピルアルコール１００ｍｌをガラス瓶に投入し、浴槽型の超音波洗浄器にて超音波（２５ｋＨｚ）を５分間照射する。次いで永久磁石で金属磁性微粒子をガラス瓶内壁に固定化し、上澄み液を除去する。この操作を上澄み液が透明となるまで繰り返し、実施例５〜８の磁性粉末を得た。
(Examples 5 to 8)
In order to extract only the metal magnetic fine particles from the sample powders obtained in Examples 1 to 4, the following purification and magnetic separation treatment was performed. First, 2 g of the sample powders of Examples 1 to 4 and 100 ml of isopropyl alcohol are put into a glass bottle, and ultrasonic waves (25 kHz) are irradiated for 5 minutes with a bathtub-type ultrasonic cleaner. Next, the metal magnetic fine particles are fixed to the inner wall of the glass bottle with a permanent magnet, and the supernatant is removed. This operation was repeated until the supernatant became transparent, and magnetic powders of Examples 5 to 8 were obtained.
得られた磁性粉末についてメスバウアー分光分析を実施し、各磁性粉末に含まれる磁性相を解析した。結果を表２に示す。なお、メスバウアー分光分析の際にはＣｏ−５７（Ｒｈ ｍａｔｒｉｘ）を線源として用い、実施例５〜８の試料粉末をそれぞれ粘着テープで固定して測定した。線源の駆動速度はα−Ｆｅ標準試料で校正し、−１０ｍｍ／ｓ〜１０ｍｍ／ｓの範囲で測定した。検出したメスバウアースペクトルはローレンツ関数にてフィッティングさせ、スペクトルのピーク間隔から内部磁場を算出した。またα−Ｆｅ以外に複数の磁性相が検出された場合は各磁性相のスペクトル面積を求めて比をとり各磁性相の体積比率とした。実施例５の磁性粉末は内部磁場３３．０Ｔのα−Ｆｅ相と内部磁場３０．６ＴのＦｅ−Ｓｉ合金相（ｂｃｃ構造におけるＦｅの最隣接原子８個のうち１個だけがＳｉに置き換わった構造、以後はＦｅ−Ｓｉ(Ｉ)と記述する。）とで構成されていた。実施例６〜８の磁性粉末においては実施例５で検出したα−Ｆｅ相、Ｆｅ−Ｓｉ(Ｉ)相に加えて内部磁場約２７ＴのＦｅ−Ｓｉ合金相（ｂｃｃ構造におけるＦｅの最隣接原子８個のうち２個だけがＳｉに置き換わった構造、以後はＦｅ−Ｓｉ(II)と記述する）も含まれることを見出した。各相の体積比を表２に示す。実施例５〜８において、α−Ｆｅ相は４６．４〜７６．３ｖｏｌ％、内部磁場２７〜３１ＴのＦｅ−Ｓｉ合金相は２３．７〜５３．７ｖｏｌ％含まれる。 Mossbauer spectroscopy was performed on the obtained magnetic powder, and the magnetic phase contained in each magnetic powder was analyzed. The results are shown in Table 2. In the Mossbauer spectroscopic analysis, Co-57 (Rh matrix) was used as a radiation source, and the sample powders of Examples 5 to 8 were each fixed with an adhesive tape and measured. The driving speed of the radiation source was calibrated with an α-Fe standard sample and measured in the range of −10 mm / s to 10 mm / s. The detected Mossbauer spectrum was fitted with a Lorentz function, and the internal magnetic field was calculated from the peak interval of the spectrum. When a plurality of magnetic phases other than α-Fe were detected, the spectrum area of each magnetic phase was obtained and the ratio was taken as the volume ratio of each magnetic phase. In the magnetic powder of Example 5, the α-Fe phase with an internal magnetic field of 33.0 T and the Fe—Si alloy phase with an internal magnetic field of 30.6 T (only one of the eight nearest atoms of Fe in the bcc structure was replaced with Si). Structure, hereinafter referred to as Fe-Si (I)). In the magnetic powders of Examples 6 to 8, in addition to the α-Fe phase and Fe—Si (I) phase detected in Example 5, an Fe—Si alloy phase having an internal magnetic field of about 27 T (the nearest atom of Fe in the bcc structure) It has been found that a structure in which only two of the eight are replaced by Si (hereinafter referred to as Fe-Si (II)) is also included. Table 2 shows the volume ratio of each phase. In Examples 5 to 8, the α-Fe phase is contained in 46.4 to 76.3 vol%, and the Fe—Si alloy phase having an internal magnetic field of 27 to 31 T is contained in 23.7 to 53.7 vol%.
また実施例５〜８の磁性粉末について磁気特性（飽和磁化及び保磁力）を実施例１と同様にして測定した。結果を表２に示す。 The magnetic characteristics (saturation magnetization and coercive force) of the magnetic powders of Examples 5 to 8 were measured in the same manner as in Example 1. The results are shown in Table 2.
また各磁性粉末の平均粒径（体積基準のメディアン径）ｄ５０をレーザー回折測定装置（ＨＯＲＩＢＡ、ＬＡ−９２０）を用いて測定した。結果を表３に示す。 Moreover, the average particle diameter (volume-based median diameter) d50 of each magnetic powder was measured using a laser diffraction measuring apparatus (HORIBA, LA-920). The results are shown in Table 3.
さらに実施例５〜８の各磁性粉末を透過型電子顕微鏡（日立製ＦＥ−ＴＥＭ、ＨＦ−２１００）で観察すると炭素（Ｃ）膜で被覆されたＦｅ核粒子を観察できた。代表的な写真を図２に示す。図２は１０枚の写真であり、上段の左側から比較例３及び実施例５〜８に対応し、下段は上段の粒子の被膜近傍（背景／炭素被膜／Ｆｅ核粒子）を拡大した写真である。Ｓｉ濃度が高くなるにつれてＣ被覆膜が厚くなっていることがわかる。各試料において無作為に４０粒ずつ電子顕微鏡写真を撮影し、Ｃ被覆膜の厚みを計測して平均の被覆膜厚ｔを算出した。ｔもＳｉ濃度が高くなるにつれて厚くなっている。また被覆膜厚ｔ、及びｔの平均粒径ｄ５０との比（＝ｔ／ｄ５０）を表３に示す。Ｓｉを添加しても平均粒径が大きく変化しないため、ｔ／ｄ５０は０．０１５〜０．０２２と無添加の場合の１．５倍以上の値となる。 Further, when each of the magnetic powders of Examples 5 to 8 was observed with a transmission electron microscope (Hitachi FE-TEM, HF-2100), Fe core particles coated with a carbon (C) film could be observed. A representative photograph is shown in FIG. FIG. 2 shows 10 photographs, corresponding to Comparative Example 3 and Examples 5 to 8 from the left side of the upper stage, and the lower stage is an enlarged photograph of the vicinity of the upper particle coating (background / carbon coating / Fe core particles). is there. It can be seen that the C coating film becomes thicker as the Si concentration increases. For each sample, 40 electron micrographs were randomly taken, the thickness of the C coating film was measured, and the average coating film thickness t was calculated. t also increases as the Si concentration increases. Table 3 shows the coating thickness t and the ratio of t to the average particle diameter d50 (= t / d50). Since the average particle size does not change greatly even when Si is added, t / d50 is 0.015 to 0.022, which is 1.5 times or more of the value obtained without addition.
次に各試料粉末２５ｍｇをＰＢＳバッファー（GIBCO、Phosphate Buffered Saline、ｐH=7.4、Cat.No.10010-023）１ｍｌ中に３７℃で１６８ｈ浸漬させ、前記ＰＢＳバッファー中に溶出したＦｅイオン濃度をＩＣＰ分析（Inductively Couple Plasma、エスアイアイナノテクノロジー社製：ＳＰＳ３１００Ｈ）により測定した。測定結果を「Ｆｅ溶出量」として表３に示す。またＰＢＳバッファーの代わりにカオトロピック塩水溶液（TOYOBO、MagExtractor-Genome-に付属の溶解・吸着液）を用い、浸漬条件を室温で２４ｈとした場合のＦｅイオン濃度も表３に示す。Ｓｉの添加によりＦｅ溶出量が低下していることが分かる。 Next, 25 mg of each sample powder was immersed in 1 ml of PBS buffer (GIBCO, Phosphate Buffered Saline, pH = 7.4, Cat. No. 10010-023) at 37 ° C. for 168 h, and the Fe ion concentration eluted in the PBS buffer was determined by ICP. It was measured by analysis (Inductively Couple Plasma, manufactured by SII Nano Technology, Inc .: SPS3100H). The measurement results are shown in Table 3 as “Fe elution amount”. Table 3 also shows the Fe ion concentration when the aqueous solution of chaotropic salt (dissolution / adsorption solution attached to TOYOBO, MagExtractor-Genome-) is used instead of the PBS buffer and the immersion conditions are 24 h at room temperature. It can be seen that the Fe elution amount is reduced by the addition of Si.
以上より、Ｓｉの添加によって平均粒径を大きく変えることなくＣ被覆膜厚が厚くなることを見出した。その結果、水溶液中へのＦｅイオン濃度が大きく低下して耐食性が大幅に改善することが分かる。すなわちＳｉ添加によってＦｅ核粒子に対するＣ被覆率が向上した。 From the above, it has been found that the C coating film thickness is increased without greatly changing the average particle diameter by the addition of Si. As a result, it can be seen that the Fe ion concentration in the aqueous solution is greatly reduced and the corrosion resistance is greatly improved. That is, the C coverage to Fe core particles was improved by adding Si.
（比較例３）
比較例１の試料粉末から実施例５〜８と同様にして磁性粉末を精製・磁気分離し、得られた磁性粉末についてメスバウアー分光分析、磁気特性を実施例５〜８と同様にして測定した。結果を表２に示す。また平均粒径ｄ５０、平均の被覆膜厚、及び各水溶液（ＰＢＳバッファー、カオトロピック塩水溶液）へのＦｅ溶出量を実施例５〜８と同様に測定した。結果を表３に示す。
(Comparative Example 3)
The magnetic powder was purified and magnetically separated from the sample powder of Comparative Example 1 in the same manner as in Examples 5 to 8, and the obtained magnetic powder was measured for Mossbauer spectroscopy and magnetic properties in the same manner as in Examples 5 to 8. . The results are shown in Table 2. Moreover, the average particle diameter d50, the average coating film thickness, and the Fe elution amount to each aqueous solution (PBS buffer, chaotropic salt aqueous solution) were measured in the same manner as in Examples 5-8. The results are shown in Table 3.
以上より、比較例３では内部磁場２０．７Ｔの炭化鉄（Ｆｅ３Ｃ）相が１０．６ｖｏｌ％含まれていることが分かった。この炭化鉄相は実施例５〜８で検出したα−ＦｅやＦｅ−Ｓｉ合金相に比べて内部磁場が小さく、飽和磁化を低下させる原因となっている。Ｓｉの添加は磁性粉末の飽和磁化を向上させる効果がある。その理由は磁性の弱い前記炭化鉄相を消失させ、代わりに比較的大きな内部磁場（２７〜３１T）を有するＦｅ−Ｓｉ相を２３．７〜５３．７ｖｏｌ％析出させることに起因している。 From the above, it was found that Comparative Example 3 contained 10.6 vol% of an iron carbide (Fe 3 C) phase having an internal magnetic field of 20.7 T. This iron carbide phase has a smaller internal magnetic field than the α-Fe and Fe—Si alloy phases detected in Examples 5 to 8, and causes a decrease in saturation magnetization. The addition of Si has the effect of improving the saturation magnetization of the magnetic powder. The reason is that the iron carbide phase having weak magnetism disappears, and instead, 23.7 to 53.7 vol% of a Fe—Si phase having a relatively large internal magnetic field (27 to 31 T) is precipitated.
（実施例９〜１１）
ＳｉＣの代わりに平均粒径１μｍのＡｌＮ粉末（添川理化学(株)）を用いた以外は、実施例１〜３と同様にして試料粉末を作製し、実施例５〜７と同様にして精製・磁気分離操作を行って磁性粉末を得た。得られた磁性粉末からの各水溶液中へのＦｅ溶出量を表４にまとめた。
(Examples 9 to 11)
A sample powder was prepared in the same manner as in Examples 1 to 3 except that AlN powder having an average particle diameter of 1 μm (Soekawa Riken Co., Ltd.) was used instead of SiC. A magnetic powder was obtained by performing a magnetic separation operation. Table 4 summarizes the amount of Fe elution from the obtained magnetic powder into each aqueous solution.
（実施例１２〜１４）
ＳｉＣの代わりに平均粒径０．５μｍのＣｏ３Ｏ４粉末（OMG、７２／７３）を用いた以外は、実施例１〜３と同様にして試料粉末を作製し、実施例５〜７と同様にして精製・磁気分離操作を行って磁性粉末を得た。得られた磁性粉末からの各水溶液中へのＦｅ溶出量を表４にまとめた。
(Examples 12 to 14)
Sample powders were prepared in the same manner as in Examples 1 to 3 except that Co 3 O 4 powder (OMG, 72/73) having an average particle size of 0.5 μm was used instead of SiC. Similarly, purification and magnetic separation operations were performed to obtain a magnetic powder. Table 4 summarizes the amount of Fe elution from the obtained magnetic powder into each aqueous solution.
（実施例１５〜１７）
ＳｉＣの代わりに平均粒径０．４μｍのＮｉＯ粉末（添川理化）を用いた以外は、実施例１〜３と同様にして試料粉末を作製し、実施例５〜７と同様にして精製・磁気分離操作を行って磁性粉末を得た。得られた磁性粉末からの各水溶液中へのＦｅ溶出量を表４にまとめた。
(Examples 15 to 17)
A sample powder was prepared in the same manner as in Examples 1 to 3 except that NiO powder (Soekawa Rika) having an average particle size of 0.4 μm was used instead of SiC, and purification and magnetic properties were performed in the same manner as in Examples 5 to 7. Separation operation was performed to obtain a magnetic powder. Table 4 summarizes the amount of Fe elution from the obtained magnetic powder into each aqueous solution.
以上より、黒鉛化促進元素として知られているＡｌ、Ｃｏ、Ｎｉのいずれを添加してもＳｉと同様にＦｅ溶出量の低下に効果があることが分かる。 From the above, it can be seen that the addition of any of Al, Co, and Ni, which are known as graphitization promoting elements, is effective in reducing the amount of Fe elution as with Si.
（実施例１８〜２２）
Ｓｉ濃度（＝Ｓｉ／（Ｆｅ＋Ｓｉ））を表５で示した値となるように配合比を調整し、第１熱処理温度を１２００℃とした以外は実施例１と同様に試料粉末を作製した。更に実施例５と同様に精製・磁気分離操作を施し、実施例１８〜２２の磁性粉末を得た。各磁性粉末の磁気特性を実施例１と同様に測定し、結果を表５に示した。
(Examples 18 to 22)
The sample powder was prepared in the same manner as in Example 1 except that the compounding ratio was adjusted so that the Si concentration (= Si / (Fe + Si)) was the value shown in Table 5 and the first heat treatment temperature was 1200 ° C. Further, purification and magnetic separation operations were performed in the same manner as in Example 5 to obtain magnetic powders of Examples 18-22. The magnetic characteristics of each magnetic powder were measured in the same manner as in Example 1, and the results are shown in Table 5.
この実施例１８〜２２の各磁性粉末を用いて以下の手順で圧粉体を作製した。まず適量のアセトンにエポキシ樹脂粉末（ソマール株式会社、ＥＰＸ−６１３６）を４重量部（磁性粉末対比）溶解し、次いで磁性粉末１００重量部を投入した。この混合物を室温で攪拌混合しながらアセトンのみを蒸発させ、その後目開き５００μｍの篩を通して造粒粉を得た。この造粒粉を成形圧６ｔｏｎ／ｃｍ２（５８８ＭＰａ）にて成形し、外径７ｍｍ、内径４ｍｍ、高さ３ｍｍのリング形状の成形体を得た。この成形体を大気中２００℃にて1時間保持し、エポキシ樹脂を熱硬化させてリング状試料とした。このリング状試料について透磁率μ’の周波数依存性をインピーダンスアナライザー（アジレントテクノロジー社製４２９１Ｂ）にて１ＭＨｚ〜１．８ＧＨｚの範囲で測定し、５ＭＨｚ及び１０ＭＨｚでの透磁率μ’を得た（表５）。 Using the magnetic powders of Examples 18 to 22, green compacts were produced according to the following procedure. First, 4 parts by weight (compared to magnetic powder) of epoxy resin powder (Somal Corporation, EPX-6136) was dissolved in an appropriate amount of acetone, and then 100 parts by weight of magnetic powder was added. While stirring and mixing the mixture at room temperature, only acetone was evaporated, and then granulated powder was obtained through a sieve having an opening of 500 μm. This granulated powder was molded at a molding pressure of 6 ton / cm 2 (588 MPa) to obtain a ring-shaped molded body having an outer diameter of 7 mm, an inner diameter of 4 mm, and a height of 3 mm. This molded body was kept in the atmosphere at 200 ° C. for 1 hour, and the epoxy resin was thermally cured to obtain a ring-shaped sample. The frequency dependence of the magnetic permeability μ ′ of this ring-shaped sample was measured in the range of 1 MHz to 1.8 GHz with an impedance analyzer (Agilent Technology 4291B) to obtain the magnetic permeability μ ′ at 5 MHz and 10 MHz (Table). 5).
表５よりＳｉ無添加（比較例４）に比べてＳｉ添加量が増加するにつれて透磁率μが向上しており、Ｓｉ濃度（＝Ｓｉ／（Ｆｅ＋Ｓｉ））が８ｍａｓｓ％以上で飽和していることが分かる。これはＳｉ添加と共に保磁力が０．８ｋＡ／ｍ未満まで低下していることに起因している。 From Table 5, the magnetic permeability μ is improved as the amount of Si added is increased compared to the case where Si is not added (Comparative Example 4), and the Si concentration (= Si / (Fe + Si)) is saturated at 8 mass% or more. I understand. This is because the coercive force decreases to less than 0.8 kA / m with the addition of Si.
Claims (11)
種である。）を含む化合物粉末と、炭素を含む化合物粉末とを混合し、
得られた粉末を、非酸化性雰囲気中、８００〜１６００℃の範囲内で熱処理する（第１の熱処理）ことによって、核粒子（核粒子はＦｅ及びＸを含有する）及び炭素被膜を有する金属磁性微粒子を形成し、
前記第１の熱処理の後、前記金属磁性微粒子を４００℃〜７５０℃の範囲内で熱処理する（第２の熱処理）ことを特徴とする金属磁性微粒子の製造方法。 Fe oxide powder and element X (where X is at least one selected from Al, Co, Ni and Si)
It is a seed. ) Containing compound powder and carbon containing compound powder,
The obtained powder is heat-treated in a non-oxidizing atmosphere within a range of 800 to 1600 ° C. (first heat treatment), whereby a core particle (the core particle contains Fe and X) and a metal having a carbon film Forming magnetic particles,
After the first heat treatment, the metal magnetic fine particles are heat-treated within a range of 400 ° C. to 750 ° C. (second heat treatment).
前記強磁性相はメスバウアー分光分析によって得られる内部磁場の値が２５〜３２Ｔの範囲内となる相であり、
前記核粒子には、前記強磁性相が２０〜５５ｖｏｌ％含まれることを特徴とする請求項１に記載の金属磁性微粒子の製造方法。 By passing through the second heat treatment, the core particles have an α-Fe phase and a ferromagnetic phase different from the α-Fe phase,
The ferromagnetic phase is a phase in which the value of the internal magnetic field obtained by Mossbauer spectroscopy is in the range of 25 to 32 T.
The method for producing metal magnetic fine particles according to claim 1, wherein the core particles contain 20 to 55 vol% of the ferromagnetic phase.
前記核粒子は、α−Ｆｅ相と、前記α−Ｆｅ相とは異なる強磁性相を有し、
前記強磁性相はメスバウアー分析によって得られる内部磁場の値が２５〜３２Ｔの範囲内であり、
前記核粒子には前記強磁性相が２０〜５５ｖｏｌ％含まれていることを特徴とする金属磁性微粒子。 It is a metal magnetic fine particle in which the core particle is coated with carbon,
The core particles have an α-Fe phase and a ferromagnetic phase different from the α-Fe phase,
The ferromagnetic phase has an internal magnetic field value obtained by Mossbauer analysis in the range of 25 to 32 T,
The metal magnetic fine particles, wherein the core particles contain 20 to 55 vol% of the ferromagnetic phase.
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| JP2004259807A (en) * | 2003-02-25 | 2004-09-16 | Hitachi Metals Ltd | Dust core and magnetic powder therefor |
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