JP2009161414A - Method for manufacturing magnetic material - Google Patents
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本発明は、磁性材料の製造に関し、特に、ナノサイズのマグネタイト（四酸化三鉄）微粒子を主体とする磁性材料の製造に関する。 The present invention relates to the manufacture of a magnetic material, and more particularly to the manufacture of a magnetic material mainly composed of nano-sized magnetite (triiron tetroxide) fine particles.
ＭＲＡＭ(Magnetic Random Access Memory)等の磁気記録媒体、その他のマイクロ磁気デバイスを高性能化するための一手段として、それら電子部品を構成する磁性材料の微細化が挙げられる。強磁性体はその質量が同じ場合、磁性体を構成する粒子サイズを小さくすることによってノイズを低下させ、磁気記録密度をより高くすることが可能となる。このような用途に適する材料として、例えば、強磁性体である四酸化三鉄（Ｆｅ３Ｏ４：マグネタイト）の微粒子を主体とする磁性材料が挙げられる。
かかるマグネタイト微粒子を適当な溶媒中に均一に分散して成る磁性材料は、外部磁場により制御可能であり、磁気機能性流体（磁性流体、磁気レオロジー流体等ともいわれる）として利用され得る。また、かかる磁性流体は、磁気によって分離され得る薬剤送達のための担体としての利用も検討されている。
One means for improving the performance of magnetic recording media such as MRAM (Magnetic Random Access Memory) and other micro magnetic devices is miniaturization of magnetic materials constituting these electronic components. When the mass of the ferromagnetic material is the same, it is possible to reduce the noise and reduce the magnetic recording density by reducing the size of the particles constituting the magnetic material. As a material suitable for such an application, for example, a magnetic material mainly composed of fine particles of triiron tetroxide (Fe 3 O 4 : magnetite), which is a ferromagnetic material, can be cited.
A magnetic material in which such magnetite fine particles are uniformly dispersed in a suitable solvent can be controlled by an external magnetic field and can be used as a magnetic functional fluid (also referred to as a magnetic fluid or a magnetorheological fluid). Such ferrofluids are also being considered for use as carriers for drug delivery that can be separated by magnetism.
従来、磁性材料となり得るマグネタイトその他の酸化鉄微粒子（フェライト微粒子）は、鉄イオンを含む水溶液にアルカリを添加することによるいわゆる共沈法が主流であった（非特許文献１，２）。しかし、かかる従来の共沈法で得られる酸化鉄微粒子は粒径が比較的大きく且つ不揃いであるため、外部磁場により制御を行う磁気機能性流体等に使用する微粒子材料としては好ましくない。
また、最近では、生成される微粒子の高品質化を目指して種々の製造方法が提案されている（特許文献１〜３、非特許文献３）。しかし、これらの方法は、鉄（イオン）供給源の他に多種の試薬類（還元剤、界面活性剤、有機溶媒、等）を使用し、また処理工程も煩雑であるためコスト高や低生産性の要因となり得る。
Conventionally, the so-called coprecipitation method by adding alkali to an aqueous solution containing iron ions has been the mainstream for magnetite and other iron oxide fine particles (ferrite fine particles) that can be magnetic materials (Non-patent Documents 1 and 2). However, the iron oxide fine particles obtained by such a conventional coprecipitation method have a relatively large and irregular particle size, and are not preferable as a fine particle material used for a magnetic functional fluid or the like controlled by an external magnetic field.
Recently, various production methods have been proposed with the aim of improving the quality of the generated fine particles (Patent Documents 1 to 3, Non-Patent Document 3). However, these methods use various reagents (reducing agents, surfactants, organic solvents, etc.) in addition to the iron (ion) source, and the processing steps are complicated, resulting in high costs and low production. It can be a sex factor.
そこで本発明は、上述した課題を解決すべく創出されたものであり、その目的とするところは、使用原料の種類が少なく、且つ、制御の容易な簡素なプロセスによって粒径の揃ったナノレベルの四酸化三鉄（Ｆｅ３Ｏ４：マグネタイト）微粒子を製造することであり、そのための製造方法を提供することである。また、本発明の他の目的は、そのような製造方法により製造した粒径の揃ったナノレベルの四三酸化鉄（Ｆｅ３Ｏ４：マグネタイト）微粒子（即ちナノ粒子）を提供し、さらに該微粒子から構成される磁性材料を提供することである。 Therefore, the present invention has been created to solve the above-described problems, and the object of the present invention is to achieve nano-levels in which the number of raw materials used is small and the particle size is uniform by a simple process that is easy to control. Is to produce fine iron trioxide (Fe 3 O 4 : magnetite) fine particles, and to provide a production method therefor. Another object of the present invention is to provide nano-level iron tetroxide (Fe 3 O 4 : magnetite) fine particles (that is, nanoparticles) having a uniform particle size produced by such a production method. It is to provide a magnetic material composed of fine particles.
上記課題を解決すべく本発明によりマグネタイト（四酸化三鉄、即ちＦｅ３Ｏ４をいう。以下同じ。）微粒子を主体とする磁性材料を製造する方法が提供される。
本発明に係る製造方法は、沸点２００℃以上である脂肪族アミンの液体中に、鉄(III)アセチルアセトナート錯体を添加して原料溶液を調製する工程、上記原料溶液を加熱し、該溶液中に酸化鉄の粒子核を生成する工程、上記生成した粒子核を含む溶液を更に加熱し、上記粒子核を成長させて所望する大きさの酸化鉄微粒子を形成する工程、および、上記酸化鉄微粒子を回収する工程を包含する。
なお、本明細書において「マグネタイト微粒子を主体とする磁性材料」とは、当該磁性材料（磁性組成物）中に含まれる酸化鉄微粒子（群）がマグネタイト（Ｆｅ３Ｏ４）を主体に構成される磁性材料をいう。従って、マグネタイト含有量が酸化鉄全体の５０質量％を上回るものはここでいう「マグネタイト微粒子を主体とする磁性材料」に包含され得るが、マグネタイト以外の酸化鉄（例えばＦｅ２Ｏ３やＦｅＯ）含有量が僅かである（例えば酸化物全体の２０質量％以下、好ましくは１０質量％以下）マグネタイト主体の酸化鉄微粒子を主体とする磁性材料（磁性組成物）が本願における「マグネタイト微粒子から成る磁性材料」の典型例である。
In order to solve the above problems, the present invention provides a method for producing a magnetic material mainly composed of magnetite (triiron tetroxide, that is, Fe 3 O 4 , hereinafter the same) fine particles.
The production method according to the present invention includes a step of preparing a raw material solution by adding an iron (III) acetylacetonate complex to a liquid of an aliphatic amine having a boiling point of 200 ° C. or higher, heating the raw material solution, A step of generating iron oxide particle nuclei therein, a step of further heating the solution containing the generated particle nuclei to grow the particle nuclei to form iron oxide fine particles having a desired size, and the iron oxide Collecting the fine particles.
In this specification, “magnetic material mainly composed of magnetite fine particles” means that the iron oxide fine particles (group) contained in the magnetic material (magnetic composition) are mainly composed of magnetite (Fe 3 O 4 ). Refers to magnetic materials. Accordingly, those having a magnetite content exceeding 50 mass% of the total iron oxide can be included in the “magnetic material mainly composed of magnetite fine particles”, but iron oxides other than magnetite (for example, Fe 2 O 3 and FeO). The magnetic material (magnetic composition) mainly containing magnetite-based iron oxide fine particles with a small content (for example, 20% by mass or less, preferably 10% by mass or less of the whole oxide) This is a typical example of “material”.
かかる構成の製造方法では、上記脂肪族アミンと鉄(III)アセチルアセトナート錯体（Ｆｅ（ａｃａｃ）３）との組み合わせで原料溶液を調製することができる。即ち、原料溶液調製において他の薬剤（化合物）、例えば有機溶媒、錯化剤、界面活性剤を別途使用する必要がない。このため、本発明の製造方法によると、製造工程の簡素化、特に原料溶液の調製プロセスが簡便となり、さらに原料溶液調製に要するコストの低減を実現しつつ目的のマグネタイト微粒子を容易に製造することができる。 In the production method having such a configuration, a raw material solution can be prepared by a combination of the above aliphatic amine and an iron (III) acetylacetonate complex (Fe (acac) 3 ). That is, it is not necessary to separately use other chemicals (compounds) such as an organic solvent, a complexing agent, and a surfactant in preparing the raw material solution. Therefore, according to the production method of the present invention, the production process can be simplified, particularly the raw material solution preparation process can be simplified, and the target magnetite fine particles can be easily produced while realizing the cost reduction required for the raw material solution preparation. Can do.
ここで開示される製造方法の好ましい一態様では、上記脂肪族アミンとして、沸点２００℃以上（より好ましくは沸点３００℃以上）であるモノアルキル１級アミン（例えばオレイルアミン、ラウリルアミン）を使用する。かかる構成によると、当該アミンと鉄(III)アセチルアセトナート錯体との複合体形成（錯形成）が容易であり、効率よく上記粒子核を生成することができる。 In a preferred embodiment of the production method disclosed herein, a monoalkyl primary amine (eg, oleylamine, laurylamine) having a boiling point of 200 ° C. or higher (more preferably, boiling point of 300 ° C. or higher) is used as the aliphatic amine. According to this configuration, complex formation (complex formation) between the amine and the iron (III) acetylacetonate complex is easy, and the particle nuclei can be generated efficiently.
また、ここで開示される製造方法の他の好ましい一態様では、上記粒子核生成工程において、前記原料溶液を１５０℃以上２００℃以下の温度域まで加熱し、該温度域（即ち粒子核生成温度域）で所定時間保持することによって上記粒子核を生成する。かかる構成によると、粒子核の生成を促す一方で、生成した粒子核についての粒成長は抑制することができる。このため、原料溶液中の粒子密度を増大させることができる。
次いで好ましくは、上記酸化鉄微粒子形成工程において、上記生成した粒子核を含む溶液を上記粒子核生成温度域を上回り且つ３００℃未満で設定される粒子成長のための温度域（即ち粒子成長温度域）まで加熱し、該温度域で所定時間保持する。このことによって、上記高密度に生成した粒子核を比較的短時間に成長させ、均等な粒径（即ち粒径分布の狭い）の微粒子を製造することができる。
In another preferable embodiment of the production method disclosed herein, in the particle nucleation step, the raw material solution is heated to a temperature range of 150 ° C. or more and 200 ° C. or less, and the temperature range (that is, the particle nucleation temperature). The particle nuclei are generated by holding for a predetermined time in the region. According to such a configuration, generation of particle nuclei is promoted, while grain growth of the generated particle nuclei can be suppressed. For this reason, the particle density in the raw material solution can be increased.
Next, preferably, in the iron oxide fine particle formation step, a temperature range for particle growth (that is, a particle growth temperature range) that is set to be higher than the particle nucleation temperature range and lower than 300 ° C. in the solution containing the generated particle nuclei. ) And hold in the temperature range for a predetermined time. Thus, the particle nuclei generated at a high density can be grown in a relatively short time, and fine particles having a uniform particle size (that is, a narrow particle size distribution) can be produced.
ここで開示される製造方法として好ましい他の一態様では、上記原料溶液中の上記錯体のモル濃度を０．３〜０．５ｍｏｌ／Ｌに設定する。かかる濃度範囲に設定することによって、特に平均粒径が１０ｎｍ以下、特に平均粒径：５ｎｍ〜１０ｎｍ程度の酸化鉄微粒子を製造することが容易となる。従って、ここで開示される製造方法として特に好ましい態様では、上記酸化鉄微粒子形成工程において形成される酸化鉄微粒子の平均粒子サイズは１０ｎｍ以下である。 In another preferred embodiment as the production method disclosed herein, the molar concentration of the complex in the raw material solution is set to 0.3 to 0.5 mol / L. By setting to such a concentration range, it becomes easy to produce iron oxide fine particles having an average particle diameter of 10 nm or less, particularly an average particle diameter of about 5 nm to 10 nm. Therefore, in a particularly preferable embodiment as the production method disclosed herein, the average particle size of the iron oxide fine particles formed in the iron oxide fine particle forming step is 10 nm or less.
また、本発明は、ここで開示されるいずれかの製造方法により製造されたマグネタイト微粒子を主体とする磁性材料を提供する。かかる磁性材料の好ましい一態様として、マグネタイト微粒子が液状媒体に分散して成る磁性材料（磁性流体、或いはインク又はペースト状磁性組成物）が挙げられる。
また、本発明は、他の側面として、上述した原料溶液を調製する工程と、粒子核生成工程と、酸化鉄微粒子形成工程とを包含するマグネタイト微粒子の製造方法を提供する。本発明により得られるマグネタイト微粒子（マグネタイト微粒子から成る粉体材料）は磁性材料として好適に用いることができる。
The present invention also provides a magnetic material mainly composed of magnetite fine particles produced by any of the production methods disclosed herein. A preferred embodiment of such a magnetic material is a magnetic material (magnetic fluid or ink or paste-like magnetic composition) formed by dispersing magnetite fine particles in a liquid medium.
Moreover, this invention provides the manufacturing method of the magnetite microparticles | fine-particles including the process of preparing the raw material solution mentioned above, a particle nucleus production | generation process, and an iron oxide microparticle formation process as another side surface. Magnetite fine particles (powder material comprising magnetite fine particles) obtained by the present invention can be suitably used as a magnetic material.
以下、本発明の好適な実施形態を説明する。なお、本明細書において特に言及している事項（例えば、錯体やアミン）以外の事柄であって本発明の実施に必要な事柄（例えば、原料溶液の調製方法や加熱方法）は、当該分野における従来技術に基づく当業者の設計事項として把握され得る。本発明は、本明細書に開示されている内容と当該分野における技術常識とに基づいて実施することができる。
ここで開示される磁性材料製造方法は、上述のとおり、酸化鉄微粒子（マグネタイト微粒子が主体である）を製造するための原料溶液が、沸点２００℃以上である脂肪族アミンと、鉄(III)アセチルアセトナート錯体とで構成されればよく、その他の成分は必須ではなく、無くてもよい。
Hereinafter, preferred embodiments of the present invention will be described. In addition, matters other than matters specifically mentioned in the present specification (for example, complexes and amines) and matters necessary for carrying out the present invention (for example, a raw material solution preparation method and a heating method) It can be grasped as a design matter of those skilled in the art based on the prior art. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.
As described above, the method for producing a magnetic material disclosed herein includes an aliphatic amine having a boiling point of 200 ° C. or higher as a raw material solution for producing iron oxide fine particles (mainly magnetite fine particles), iron (III) What is necessary is just to be comprised with an acetylacetonate complex, and other components are not essential and may be omitted.
本発明の実施に好適なアミンとしては、沸点が２００℃以上、好適には３００℃以上であり、且つ、室温域（２５〜３５℃程度、例えば３０℃）または室温よりもやや高い温度条件（好ましくは４０〜６０℃程度、例えば５０℃）で液状であるものが、取り扱いが容易であるため好ましい。この種の脂肪族アミンとしては、Ｃ数が１０〜２０程度（例えばＣ数が１２〜１８）であるアルキル鎖を有するアミンが好ましく、モノアルキル１級アミンが好ましい。例えば、ラウリルアミン、オレイルアミンが好適例として挙げられる。特に沸点が高いオレイルアミンの使用が好ましい。なお、本発明の実施にあたって使用するアミン（液媒）は、１種のアミン化合物から成る純粋品である必要はなく、何種類かのアミン化合物の混合品であってもよい。例えば市販されるアミン製品であって、上記目的に適うもの、例えば室温域或いは６０℃以下の温度で液状であるようなラウリルアミン、オレイルアミン等のモノアルキル１級アミンを主成分とする混合アミン液を好適に使用することができる。
本発明の製造方法では、上記のような脂肪族アミンを錯化剤、界面活性剤、さらには溶媒として機能させることができる。従って、本発明では、これら薬剤や溶媒を別途混合する必要がないため、原料溶液の調製が容易であると共に試薬類の使用を削減して製造コストの低減を実現することができる。
The amine suitable for the practice of the present invention has a boiling point of 200 ° C. or higher, preferably 300 ° C. or higher, and a room temperature range (about 25 to 35 ° C., for example, 30 ° C.) or a temperature condition slightly higher than room temperature ( A liquid that is preferably about 40 to 60 ° C. (for example, 50 ° C.) is preferable because it is easy to handle. As this type of aliphatic amine, an amine having an alkyl chain having a C number of about 10 to 20 (for example, a C number of 12 to 18) is preferable, and a monoalkyl primary amine is preferable. For example, laurylamine and oleylamine are preferable examples. In particular, use of oleylamine having a high boiling point is preferred. The amine (liquid medium) used in the practice of the present invention is not necessarily a pure product composed of one kind of amine compound, and may be a mixture of several kinds of amine compounds. For example, a commercially available amine product that is suitable for the above purpose, for example, a mixed amine solution mainly composed of a monoalkyl primary amine such as laurylamine or oleylamine that is liquid at room temperature or at a temperature of 60 ° C. or lower. Can be preferably used.
In the production method of the present invention, the aliphatic amine as described above can function as a complexing agent, a surfactant, and further a solvent. Therefore, in the present invention, since it is not necessary to separately mix these drugs and solvents, it is easy to prepare a raw material solution, and it is possible to reduce manufacturing costs by reducing the use of reagents.
本発明では、原料溶液を上記のような適切なアミンと共に構成する錯体として、鉄(III)アセチルアセトナート錯体（Ｆｅ（ａｃａｃ）３）を用いる。かかる錯体は、オレイルアミン等の脂肪族アミンと錯形成し、容易に可溶化する。このため、高濃度に鉄イオン（錯体）を含む原料溶液を容易に調製することができる。また、かかる錯体のアミン溶液では、オレイルアミン等の脂肪族アミンが界面活性剤として機能し、生成された粒子核同士の融合が生じ難い。具体的には、アミン中のアミノ基が溶液中で生じた酸化鉄表面に吸着すると当該アミン中のアルキル鎖による立体障害が生じて粒子相互の融合を抑制することができる。このため、原料溶液（アミン溶液）中で粒径の揃った酸化鉄微粒子を高濃度に製造することができる。 In the present invention, an iron (III) acetylacetonate complex (Fe (acac) 3 ) is used as a complex that constitutes the raw material solution together with the appropriate amine as described above. Such complexes complex with aliphatic amines such as oleylamine and are easily solubilized. For this reason, the raw material solution which contains an iron ion (complex) in high concentration can be prepared easily. Moreover, in the amine solution of such a complex, an aliphatic amine such as oleylamine functions as a surfactant, and the generated particle nuclei hardly fuse. Specifically, when the amino group in the amine is adsorbed on the surface of the iron oxide generated in the solution, steric hindrance due to the alkyl chain in the amine is generated, so that fusion between particles can be suppressed. For this reason, iron oxide fine particles having a uniform particle diameter in the raw material solution (amine solution) can be produced at a high concentration.
次に、原料溶液の調製について詳細に説明する。本発明の実施にあたっては、上述した沸点２００℃以上（好適には３００℃以上）の脂肪族アミンからなる液（室温で固体のものは融点以上となるように加熱するとよい）に、典型的には粉末状態である鉄(III)アセチルアセトナート錯体を添加し、混合する（可溶化する）ことのみによって原料溶液を極めて容易に調製することができる。
なお、特に必要はないが、上記２成分（脂肪族アミン＋鉄(III)アセチルアセトナート錯体）のみから成る原料溶液に種々の任意的成分を含ませることができる。例えば、適当量の有機溶媒（例えば沸点２００℃以上の鎖状炭化水素（１−オクタデセン、ヘキサデカン等）あるいは環状炭化水素（ジフェニルエーテル等）類）を添加してもよい。
Next, the preparation of the raw material solution will be described in detail. In practicing the present invention, the above-described liquid composed of an aliphatic amine having a boiling point of 200 ° C. or higher (preferably 300 ° C. or higher) (a solid material at room temperature may be heated so as to have a melting point or higher) is typically used. The raw material solution can be prepared very easily only by adding and mixing (solubilizing) the iron (III) acetylacetonate complex in a powder state.
Although not particularly necessary, various optional components can be contained in the raw material solution consisting only of the two components (aliphatic amine + iron (III) acetylacetonate complex). For example, an appropriate amount of an organic solvent (for example, chain hydrocarbons having a boiling point of 200 ° C. or higher (1-octadecene, hexadecane, etc.) or cyclic hydrocarbons (diphenyl ether, etc.)) may be added.
原料溶液を調製する際、アミン液中の鉄(III)アセチルアセトナート錯体のモル濃度（中心金属イオンたる鉄イオンのモル濃度）を０．５ｍｏｌ／Ｌ以下とすることが好ましい。このことによって粒径（サイズ）の揃った酸化鉄微粒子（ナノ粒子）を製造することができる。特に、０．３〜０．５ｍｏｌ／Ｌとなるように当該錯体のアミンへの添加量を調節することが好ましい。かかるモル濃度範囲に設定することによって平均粒径が１０ｎｍ以下、特に平均粒径が５ｎｍ〜１０ｎｍ程度の粒径（サイズ）の揃った酸化鉄微粒子を容易に効率よく量産することができる。
本明細書において酸化鉄（又はマグネタイト）微粒子（群）に関する「平均粒径」は、当該微粒子が分散してなる組成物を調製後、該組成物をＴＥＭ（透過型電子顕微鏡）観察用のグリッド基板上に希薄に分散・担持してＴＥＭによる観察を行うことによって測定・算出した平均粒径と規定することができる。即ち、酸化鉄微粒子と有機溶媒で電子線に対する透過率が異なるため、ＴＥＭ観察像中で酸化鉄微粒子を識別できる。具体的には、得られた酸化鉄（マグネタイト）微粒子および有機溶媒の面積分布を画像解析により求める。ここで酸化鉄（マグネタイト）微粒子の断面を円形と近似してその面積から当該微粒子の粒径を算出する。次いで算出された粒径分布を所定のサイズ間隔で区切ったヒストグラムで表すとともに、当該得られたヒストグラムの各カラムにおいてその中心値と度数の積を求める。而して各カラムの積の和を度数の総和で除したものを平均粒径とすることができる。その他、動的光散乱法等に基づいて粒径分布および平均粒径を求めることができる。
When preparing the raw material solution, the molar concentration of iron (III) acetylacetonate complex in the amine solution (molar concentration of iron ions as central metal ions) is preferably 0.5 mol / L or less. This makes it possible to produce iron oxide fine particles (nanoparticles) having a uniform particle size (size). In particular, it is preferable to adjust the addition amount of the complex to the amine so as to be 0.3 to 0.5 mol / L. By setting the molar concentration range, iron oxide fine particles having an average particle size of 10 nm or less, particularly an average particle size of about 5 nm to 10 nm and having a uniform particle size can be easily and efficiently mass-produced.
In this specification, “average particle diameter” for iron oxide (or magnetite) fine particles (group) is a grid for observation of a TEM (transmission electron microscope) after preparing a composition in which the fine particles are dispersed. It can be defined as the average particle diameter measured and calculated by carrying out dilute dispersion and support on the substrate and observing with TEM. That is, since the transmittance with respect to the electron beam is different between the iron oxide fine particles and the organic solvent, the iron oxide fine particles can be identified in the TEM observation image. Specifically, the area distribution of the obtained iron oxide (magnetite) fine particles and the organic solvent is obtained by image analysis. Here, the cross section of the iron oxide (magnetite) fine particles is approximated to be circular, and the particle size of the fine particles is calculated from the area. Next, the calculated particle size distribution is represented by a histogram divided by a predetermined size interval, and the product of the center value and the frequency is obtained for each column of the obtained histogram. Thus, the average particle diameter can be obtained by dividing the sum of the products of each column by the sum of the frequencies. In addition, the particle size distribution and the average particle size can be obtained based on a dynamic light scattering method or the like.
原料溶液を調製後、酸化鉄（マグネタイト）の粒子核を生成させるために原料溶液を加熱する。典型的には、核生成が効率よく行われる１５０℃以上２００℃以下（好ましくは１８０〜２００℃）まで加熱する。次いで、当該温度域で所定時間（典型的には１０分〜６０分、例えば２０〜３０分）保持する。これにより、粒子核（種粒子）の形成を促す一方、生成した粒子核の意図しない成長を抑えることができる。即ち、多数の均一的なサイズ（例えば上記ＴＥＭ観察に基づく粒径算出での平均粒径が５ｎｍ以下、例えば２ｎｍ〜４ｎｍ）の粒子核を原料溶液中に生成することができる。
なお、かかる粒子核生成工程及び酸化鉄微粒子形成工程において、大気中で原料溶液を加熱してもよいが、不活性ガス雰囲気（例えばアルゴンガス等の希ガス或いは窒素ガス雰囲気）中で原料溶液を加熱することが好ましい。例えば、原料溶液を撹拌又は振動させつつＡｒ、Ｎ２等の不活性ガスを供給して容器内のガス置換を行うとよい。これにより、マグネタイト微粒子を高効率に形成することができる。また、加熱される際の有機溶媒の引火・発火を確実に防止するという観点からも不活性ガスの使用が好ましい。
After preparing the raw material solution, the raw material solution is heated to generate iron oxide (magnetite) particle nuclei. Typically, heating is performed to 150 ° C. or higher and 200 ° C. or lower (preferably 180 to 200 ° C.) at which nucleation is efficiently performed. Next, the temperature is maintained for a predetermined time (typically 10 to 60 minutes, for example, 20 to 30 minutes). As a result, formation of particle nuclei (seed particles) can be promoted while unintended growth of the generated particle nuclei can be suppressed. That is, particle nuclei having a large number of uniform sizes (for example, an average particle size of 5 nm or less, for example, 2 nm to 4 nm in particle size calculation based on the above TEM observation) can be generated in the raw material solution.
In the particle nucleation step and the iron oxide fine particle formation step, the raw material solution may be heated in the atmosphere, but the raw material solution is heated in an inert gas atmosphere (for example, a rare gas such as argon gas or a nitrogen gas atmosphere). It is preferable to heat. For example, gas replacement in the container may be performed by supplying an inert gas such as Ar or N 2 while stirring or vibrating the raw material solution. Thereby, magnetite fine particles can be formed with high efficiency. In addition, it is preferable to use an inert gas from the viewpoint of reliably preventing the ignition and ignition of the organic solvent when heated.
吸湿した原料物質（粉末状錯体原料）の使用等に起因して原料溶液中に水分が含まれる場合があるため、好ましくは、原料溶液を調製した際の室温域（又は６０℃程度までのやや高い温度域）から１１０〜１５０℃（例えば１３０℃付近）程度の中間温度域まで加熱した後、暫くの時間（特に限定しないが１時間以下が適当であり、例えば１０分〜６０分程度が適当である。）原料溶液を攪拌しつつ当該中間温度域に保持する。このことによって、粒子核生成反応を阻害する要因となり得る原料溶液中の水分や溶存酸素を除去することができる。所定時間経過後、上記中間温度域から上記粒子核生成温度域まで加熱するとよい。 Since moisture may be contained in the raw material solution due to the use of moisture-absorbed raw material (powder complex raw material), preferably, the room temperature range (or slightly up to about 60 ° C. when the raw material solution is prepared) After heating from a high temperature range to an intermediate temperature range of about 110 to 150 ° C. (for example, around 130 ° C.), a short time (although it is not particularly limited, 1 hour or less is appropriate, for example, about 10 to 60 minutes is appropriate. The raw material solution is kept in the intermediate temperature range while being stirred. As a result, it is possible to remove moisture and dissolved oxygen in the raw material solution, which can be a factor that hinders the particle nucleation reaction. After the elapse of a predetermined time, the intermediate temperature region may be heated to the particle nucleation temperature region.
所定時間後、上記粒子核生成温度域からさらに加熱し、粒子成長温度域（３００℃未満）まで昇温する。この場合、緩慢とした昇温ペース（典型的には１〜５℃／１分、例えば１〜２℃／１分）で加熱することが好ましい。次いで、当該温度域で所定時間（特に限定しないが典型的には６０分〜１８０分、例えば９０〜１２０分）保持する。これにより、上記粒子核生成工程において生成した粒子核（種粒子）を成長させ、所望するサイズ（例えば上記ＴＥＭ観察に基づく粒径算出での粒径が１０ｎｍ以下、例えば５ｎｍ〜１０ｎｍ）のマグネタイトを主体とする酸化鉄微粒子を製造することができる。 After a predetermined time, the particle nucleation temperature range is further heated to raise the temperature to a particle growth temperature range (less than 300 ° C.). In this case, it is preferable to heat at a slow rate of temperature rise (typically 1 to 5 ° C / 1 minute, for example 1 to 2 ° C / 1 minute). Subsequently, it hold | maintains for the predetermined time (it does not specifically limit, but typically 60 minutes-180 minutes, for example, 90-120 minutes) in the said temperature range. Thereby, the particle nucleus (seed particle) produced | generated in the said particle nucleus production | generation process is grown, and the magnetite of the desired size (For example, the particle size by the particle size calculation based on the said TEM observation is 10 nm or less, for example, 5 nm-10 nm). Iron oxide fine particles that are the main component can be produced.
酸化鉄微粒子の製造後（反応終了後）、反応液（原料溶液）を室温域まで速やかに冷却（典型的には空冷）する。次いで、好ましくは適当な有機溶媒中に、上記得られた微粒子を回収し、貯蔵する。具体的には、エタノール、プロパノール等の低級アルコールのような極性溶媒を処理溶液に添加して酸化鉄微粒子を沈殿させ、遠心分離により粒子のみを分離・抽出する。こうして得られた微粒子（磁性粉末）をヘキサン、オクタンのようなアルカン（鎖式飽和炭化水素）、或いはトルエンのような芳香族炭化水素、等の無極性有機溶媒中に酸化鉄微粒子（マグネタイトを主体とする磁性ナノ粒子）再分散させるとよい。このような分散液（磁性流体）は、磁気記録媒体その他、種々の磁気デバイス構築用材料（磁性材料）として利用することができる。 After the production of the iron oxide fine particles (after completion of the reaction), the reaction solution (raw material solution) is rapidly cooled (typically air-cooled) to the room temperature region. Next, the fine particles obtained above are preferably collected and stored in a suitable organic solvent. Specifically, a polar solvent such as a lower alcohol such as ethanol or propanol is added to the treatment solution to precipitate iron oxide fine particles, and only the particles are separated and extracted by centrifugation. Fine particles (magnetic powder) obtained in this way are mainly composed of iron oxide particles (magnetite) in nonpolar organic solvents such as alkanes (chain saturated hydrocarbons) such as hexane and octane, or aromatic hydrocarbons such as toluene. It is better to redisperse the magnetic nanoparticles. Such a dispersion (magnetic fluid) can be used as a magnetic recording medium and other various magnetic device construction materials (magnetic materials).
以下、本発明の好適ないくつかの実施例を説明するが、ここに開示した発明の技術的範囲をこれら実施例として記載したものに限定することを意図したものではない。なお、以下に説明する実施例には、次の試薬類を使用した。
（１）鉄(III)アセチルアセトナート錯体（Ｆｅ(acac)3：純度９８％）
（２）オレイルアミン（Ｃ１４〜Ｃ２０のアルキルアミン混合物中の純度７０〜８０ｍｏｌ％の市販品）
Several preferred embodiments of the present invention will be described below, but the technical scope of the present invention disclosed herein is not intended to be limited to those described as these embodiments. In the examples described below, the following reagents were used.
(1) Iron (III) acetylacetonate complex (Fe (acac) 3 : purity 98%)
(2) Oleylamine (commercial product with a purity of 70 to 80 mol% in a C14 to C20 alkylamine mixture)
＜実施例１＞
錯体のモル濃度が０．５ｍｏｌ／Ｌとなるように、２０ｍｍｏｌに相当する量のＦｅ(acac)3と４０ｍＬの上記オレイルアミンとを反応容器（マントルヒーター付き３００ｍＬ容フラスコ）に充填した。その後、スターラー（撹拌子）を用いて原料溶液をよく撹拌しながらフラスコ内に不活性ガスとしてＡｒガスを流してガス置換した。その後、試薬が吸湿している水分を除去するために、撹拌しながら１３０℃まで徐々に温度を上げ、１３０℃で３０分程度の予備加熱を行った。
３０分間の予備加熱終了後、原料溶液を粒子核生成温度域（ここでは１８０〜２００℃）まで還流・加熱した。そして、当該粒子核生成温度域にて２０〜３０分間保持した。これにより、多数の微小な酸化鉄から成る粒子核が溶液内に生成されたことが確認された。
<Example 1>
An amount of Fe (acac) 3 corresponding to 20 mmol and 40 mL of the oleylamine were charged into a reaction vessel (300 mL flask equipped with a mantle heater) so that the molar concentration of the complex was 0.5 mol / L. Thereafter, the gas solution was replaced by flowing Ar gas as an inert gas into the flask while thoroughly stirring the raw material solution using a stirrer. Thereafter, in order to remove moisture absorbed by the reagent, the temperature was gradually raised to 130 ° C. while stirring, and preheating was performed at 130 ° C. for about 30 minutes.
After 30 minutes of preheating, the raw material solution was refluxed and heated to a particle nucleation temperature range (here, 180 to 200 ° C.). And it hold | maintained for 20 to 30 minutes in the said particle nucleation temperature range. Thereby, it was confirmed that the particle nucleus which consists of many fine iron oxides was produced | generated in the solution.
次いで、反応溶液（原料溶液）の温度を粒子成長温度（ここでは２７０℃）まで高めた。昇温速度は１〜２℃／１分とした。そして、当該粒子成長温度域にて１２０分間保持した。これにより、上記粒子核（種粒子）を成長させた。
反応終了後、加熱器であるマントルヒーターをフラスコから取り外し、反応容器を室温まで空冷して粒子成長を終了させた。
室温まで冷却後、反応溶液を遠心分離用小型容器（５０ｍＬ容積の遠沈管）に小分けして入れ、それらにエタノール等の極性溶媒（ここではエタノールと２−プロパノールの容積比１：１の混合液）を加え、酸化鉄微粒子（ナノ粒子）を凝集させた。本実施例では反応溶液１０ｍＬに対して極性溶媒を３０〜４０ｍＬ程度加えた。その後、遠沈管を遠心機にセットし、５０００〜８０００ｒｐｍで３０〜６０分程度遠心分離を行った。
遠心分離後、遠沈管の底あるいは側壁に黒く沈殿した粒子が認められた。遠沈管から透明がかった上澄み液のみを全て捨て、次いで、ヘキサンを遠沈管に加えて粒子を再分散させた後に、再び極性溶媒（エタノールとメタノールの混合液）を上記と同様の要領で加えて微粒子を沈殿させ、再び遠心分離を行った。このような遠心（精製）工程を２〜３回繰り返した。これにより、未反応原料物質、副生成物、余剰のオレイルアミン等を取り除くことができた。最終的に、所定量のヘキサンに酸化鉄微粒子を再分散させた。
Next, the temperature of the reaction solution (raw material solution) was raised to the particle growth temperature (here, 270 ° C.). The temperature rising rate was 1 to 2 ° C./1 minute. And it hold | maintained for 120 minutes in the said particle growth temperature range. Thereby, the particle nucleus (seed particle) was grown.
After completion of the reaction, the mantle heater as a heater was removed from the flask, and the reaction vessel was air-cooled to room temperature to complete particle growth.
After cooling to room temperature, the reaction solution is subdivided into small centrifuge containers (centrifuge tubes with a volume of 50 mL), and a polar solvent such as ethanol (in this case, a mixture of ethanol and 2-propanol in a volume ratio of 1: 1). ) And iron oxide fine particles (nanoparticles) were aggregated. In this example, about 30 to 40 mL of polar solvent was added to 10 mL of the reaction solution. Thereafter, the centrifuge tube was set in a centrifuge and centrifuged at 5000 to 8000 rpm for about 30 to 60 minutes.
After centrifugation, black sedimentation particles were observed on the bottom or side wall of the centrifuge tube. Discard only the clear supernatant from the centrifuge tube, add hexane to the centrifuge tube to redisperse the particles, and then add the polar solvent (mixture of ethanol and methanol) again in the same manner as above. Fine particles were precipitated and centrifuged again. Such centrifugation (purification) process was repeated 2-3 times. As a result, unreacted raw materials, by-products, excess oleylamine and the like could be removed. Finally, the iron oxide fine particles were redispersed in a predetermined amount of hexane.
こうして得られた酸化鉄微粒子をＴＥＭで観察した。即ち、上記ヘキサンに微粒子を分散させた懸濁液をピペットで少量とり、ＴＥＭ用のグリッド上に滴下し乾燥させた。これにより、溶媒のみが蒸発し、酸化鉄微粒子はグリッド上に担持された。このようにして作製した試料を２００ｋＶの加速電圧を有する市販のＴＥＭ（株式会社日立製作所製品「ＨＦ−２０００」）を用いて観察した。そのときの顕微鏡写真を図１の（ａ）に示す。また、上述したＴＥＭ観察に基づく粒径算出法に基づいて得られた粒径分布のヒストグラムを図１の（ｂ）に示す。縦軸は粒径別の粒子数（Ｎ）の分布（頻度）で一目盛りは６０である。横軸は粒径（ｎｍ）である。
図１の（ａ）と（ｂ）から明らかなように、本実施例において得られた酸化鉄微粒子はほぼ均等な粒径であり、その平均粒径（ｄ）は９．５ｎｍ（標準偏差σ＝２１％）であった。また、回収した酸化鉄微粒子の結晶構造を一般的なＸ線回折装置によって解析した。結果（チャート）を図２に示す。その結果、同定されたピーク位置とＦｅ３Ｏ４のピーク位置が一致した。この結果、得られた酸化鉄微粒子はマグネタイト微粒子であることが確認された。
The iron oxide fine particles thus obtained were observed with a TEM. That is, a small amount of a suspension of fine particles dispersed in hexane was pipetted and dropped onto a TEM grid and dried. As a result, only the solvent was evaporated, and the iron oxide fine particles were supported on the grid. The sample thus prepared was observed using a commercially available TEM (Hitachi Ltd. product “HF-2000”) having an acceleration voltage of 200 kV. A micrograph at that time is shown in FIG. Moreover, the histogram of the particle size distribution obtained based on the particle size calculation method based on the above-mentioned TEM observation is shown in FIG. The vertical axis represents the distribution (frequency) of the number of particles (N) by particle size, and one scale is 60. The horizontal axis is the particle size (nm).
As is clear from FIGS. 1A and 1B, the iron oxide fine particles obtained in this example have a substantially uniform particle size, and the average particle size (d) is 9.5 nm (standard deviation σ = 21%). Further, the crystal structure of the recovered iron oxide fine particles was analyzed by a general X-ray diffractometer. The results (chart) are shown in FIG. As a result, the identified peak position coincided with the peak position of Fe 3 O 4 . As a result, it was confirmed that the obtained iron oxide fine particles were magnetite fine particles.
＜実施例２＞
粒子成長温度を２７０℃から２４０℃に変更した以外は、実施例１と同様の材料と手順により処理して酸化鉄微粒子を製造した。得られた微粒子のＴＥＭ写真を図３の（ａ）に示す。また、上述したＴＥＭ観察に基づく粒径算出法に基づいて得られた粒径分布のヒストグラムを図３の（ｂ）に示す。縦軸は粒径別の粒子数（Ｎ）の分布（頻度）で一目盛りは５０である。横軸は粒径（ｎｍ）である。本図から明らかなように、本実施例において得られた酸化鉄微粒子についても、実施例１と同様、ほぼ均等な粒径であり、その平均粒径（ｄ）は７．８ｎｍ（標準偏差σ＝２６％）であった。
<Example 2>
Except that the particle growth temperature was changed from 270 ° C. to 240 ° C., iron oxide fine particles were produced by processing using the same materials and procedures as in Example 1. A TEM photograph of the obtained fine particles is shown in FIG. Moreover, the histogram of the particle size distribution obtained based on the particle size calculation method based on the above-mentioned TEM observation is shown in FIG. The vertical axis is the distribution (frequency) of the number of particles (N) by particle size, and one scale is 50. The horizontal axis is the particle size (nm). As is clear from this figure, the iron oxide fine particles obtained in this example also have a substantially uniform particle size as in Example 1, and the average particle size (d) is 7.8 nm (standard deviation σ = 26%).
＜実施例３＞
粒子成長温度を２１０℃に設定した以外は、実施例１と同様の材料と手順により処理して酸化鉄微粒子を製造した。得られた微粒子のＴＥＭ写真を図４の（ａ）に示す。また、上述したＴＥＭ観察に基づく粒径算出法に基づいて得られた粒径分布のヒストグラムを図４の（ｂ）に示す。縦軸は粒径別の粒子数（Ｎ）の分布（頻度）で一目盛りは３０である。横軸は粒径（ｎｍ）である。本図から明らかなように、本実施例において得られた酸化鉄微粒子についても、実施例１と同様、ほぼ均等な粒径であり、その平均粒径（ｄ）は７．１ｎｍ（標準偏差σ＝２７％）であった。
<Example 3>
Except for setting the particle growth temperature to 210 ° C., iron oxide fine particles were produced by the same material and procedure as in Example 1. A TEM photograph of the obtained fine particles is shown in FIG. Moreover, the histogram of the particle size distribution obtained based on the particle size calculation method based on the above-mentioned TEM observation is shown in FIG. The vertical axis is the distribution (frequency) of the number of particles (N) by particle size, and one scale is 30. The horizontal axis is the particle size (nm). As is apparent from this figure, the iron oxide fine particles obtained in this example also have a substantially uniform particle size as in Example 1, and the average particle size (d) is 7.1 nm (standard deviation σ = 27%).
＜実施例４＞
使用する反応溶液中の錯体モル濃度を０．５ｍｏｌ／Ｌから０．３ｍｏｌ／Ｌに変更した以外は実施例１と同様の材料と手順により処理して酸化鉄微粒子を製造した。得られた微粒子のＴＥＭ写真を図５の（ａ）に示す。また、上述したＴＥＭ観察に基づく粒径算出法に基づいて得られた粒径分布のヒストグラムを図５の（ｂ）に示す。縦軸は粒径別の粒子数（Ｎ）の分布（頻度）で一目盛りは１００である。横軸は粒径（ｎｍ）である。本図から明らかなように、錯体のモル濃度を実施例１〜３よりも低濃度とした本実施例において得られた酸化鉄微粒子についても、実施例１〜３と同様、ほぼ均等な粒径であり、その平均粒径（ｄ）は８．２ｎｍ（標準偏差σ＝１９％）であった。
<Example 4>
Iron oxide fine particles were produced by treating with the same materials and procedures as in Example 1 except that the complex molar concentration in the reaction solution used was changed from 0.5 mol / L to 0.3 mol / L. A TEM photograph of the obtained fine particles is shown in FIG. Moreover, the histogram of the particle size distribution obtained based on the particle size calculation method based on the above-mentioned TEM observation is shown in FIG. The vertical axis is the distribution (frequency) of the number of particles (N) by particle size, and one scale is 100. The horizontal axis is the particle size (nm). As is clear from this figure, the iron oxide fine particles obtained in this example in which the molar concentration of the complex was lower than those in Examples 1 to 3 also had a substantially uniform particle size as in Examples 1 to 3. The average particle size (d) was 8.2 nm (standard deviation σ = 19%).
＜実施例５＞
使用する反応溶液中の錯体モル濃度を０．４ｍｏｌ／Ｌに変更した以外は実施例４と同様の材料と手順により処理して酸化鉄微粒子を製造した。得られた微粒子のＴＥＭ写真を図６の（ａ）に示す。また、上述したＴＥＭ観察に基づく粒径算出法に基づいて得られた粒径分布のヒストグラムを図６の（ｂ）に示す。縦軸は粒径別の粒子数（Ｎ）の分布（頻度）で一目盛りは２００である。横軸は粒径（ｎｍ）である。本図から明らかなように、錯体のモル濃度を実施例４よりも高濃度とした本実施例において得られた酸化鉄微粒子についても、実施例４と同様、ほぼ均等な粒径であり、その平均粒径（ｄ）は８．６ｎｍ（標準偏差σ＝２５％）であった。また、モル濃度の上昇に対応して製造された微粒子数も増加した。
<Example 5>
Iron oxide fine particles were produced by treating with the same materials and procedures as in Example 4 except that the complex molar concentration in the reaction solution used was changed to 0.4 mol / L. A TEM photograph of the obtained fine particles is shown in FIG. Moreover, the histogram of the particle size distribution obtained based on the particle size calculation method based on the above-mentioned TEM observation is shown in FIG. The vertical axis represents the distribution (frequency) of the number of particles (N) by particle size, and one scale is 200. The horizontal axis is the particle size (nm). As is clear from this figure, the iron oxide fine particles obtained in this example in which the molar concentration of the complex was higher than in Example 4 also had a substantially uniform particle size, as in Example 4. The average particle diameter (d) was 8.6 nm (standard deviation σ = 25%). Also, the number of fine particles produced corresponding to the increase in molar concentration increased.
＜実施例６＞
使用する反応溶液中の錯体モル濃度を０．５ｍｏｌ／Ｌ（実施例１〜３と同じ）に変更した以外は実施例４，５と同様の材料と手順により処理して酸化鉄微粒子を製造した。得られた微粒子のＴＥＭ写真を図７の（ａ）に示す。また、上述したＴＥＭ観察に基づく粒径算出法に基づいて得られた粒径分布のヒストグラムを図７の（ｂ）に示す。縦軸は粒径別の粒子数（Ｎ）の分布（頻度）で一目盛りは１５０である。横軸は粒径（ｎｍ）である。本図から明らかなように、錯体のモル濃度を実施例４，５よりも高濃度とした本実施例において得られた酸化鉄微粒子についても、実施例４，５と同様、ほぼ均等な粒径であり、その平均粒径（ｄ）は９．１ｎｍ（標準偏差σ＝２８％）であった。
<Example 6>
Iron oxide fine particles were produced by treating with the same materials and procedures as in Examples 4 and 5 except that the complex molar concentration in the reaction solution used was changed to 0.5 mol / L (same as in Examples 1 to 3). . A TEM photograph of the obtained fine particles is shown in FIG. Moreover, the histogram of the particle size distribution obtained based on the particle size calculation method based on the above-mentioned TEM observation is shown in FIG. The vertical axis is the distribution (frequency) of the number of particles (N) by particle size, and the scale is 150. The horizontal axis is the particle size (nm). As is clear from this figure, the iron oxide fine particles obtained in this example in which the molar concentration of the complex was higher than those in Examples 4 and 5 also had a substantially uniform particle size as in Examples 4 and 5. The average particle size (d) was 9.1 nm (standard deviation σ = 28%).
＜実施例７＞
使用する反応溶液中の錯体モル濃度を１．０ｍｏｌ／Ｌに変更した以外は実施例４〜６と同様の材料と手順により処理して酸化鉄微粒子を製造した。得られた微粒子のＴＥＭ写真を図８の（ａ）に示す。また、上述したＴＥＭ観察に基づく粒径算出法に基づいて得られた粒径分布のヒストグラムを図８の（ｂ）に示す。縦軸は粒径別の粒子数（Ｎ）の分布（頻度）で一目盛りは２５である。横軸は粒径（ｎｍ）である。本図から明らかなように、錯体のモル濃度を実施例６よりも高濃度とした本実施例において得られた酸化鉄微粒子は、モル濃度の上昇に対応して製造された微粒子のサイズが増大傾向にあった。しかし、図８の（ｂ）に示すように、粒径分布がブロードとなり、粒径９．６ｎｍと２２ｎｍに粒径分布のピークが二つ認められた。
<Example 7>
Iron oxide fine particles were produced by treating with the same materials and procedures as in Examples 4 to 6 except that the complex molar concentration in the reaction solution used was changed to 1.0 mol / L. A TEM photograph of the obtained fine particles is shown in FIG. Moreover, the histogram of the particle size distribution obtained based on the particle size calculation method based on the above-mentioned TEM observation is shown in FIG. The vertical axis represents the distribution (frequency) of the number of particles (N) by particle size, and the scale is 25. The horizontal axis is the particle size (nm). As is clear from this figure, the iron oxide fine particles obtained in this example in which the molar concentration of the complex was higher than that in Example 6 increased in size of the fine particles produced corresponding to the increase in the molar concentration. There was a trend. However, as shown in FIG. 8B, the particle size distribution was broad and two particle size distribution peaks were observed at particle sizes of 9.6 nm and 22 nm.
以上、本発明の具体例を詳細に説明したが、これらは例示にすぎず、特許請求の範囲を限定するものではない。特許請求の範囲に記載の技術には、以上に例示した具体例を様々に変形、変更したものが含まれる。 Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
Claims (8)
沸点２００℃以上である脂肪族アミンの液体中に、鉄(III)アセチルアセトナート錯体を添加して原料溶液を調製する工程；
前記原料溶液を加熱し、該溶液中に酸化鉄の粒子核を生成する工程；
前記生成した粒子核を含む溶液を更に加熱し、前記粒子核を成長させて所望する大きさの酸化鉄微粒子を形成する工程；および
前記酸化鉄微粒子を回収する工程；
を包含する、マグネタイト微粒子を主体とする磁性材料の製造方法。 A method for producing a magnetic material mainly composed of magnetite fine particles, comprising the following steps:
Adding an iron (III) acetylacetonate complex to an aliphatic amine liquid having a boiling point of 200 ° C. or higher to prepare a raw material solution;
Heating the raw material solution to produce iron oxide particle nuclei in the solution;
Further heating the solution containing the generated particle nuclei to grow the particle nuclei to form iron oxide fine particles having a desired size; and collecting the iron oxide fine particles;
A method for producing a magnetic material mainly comprising magnetite fine particles.
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| CN104843798A (en) * | 2015-04-14 | 2015-08-19 | 齐齐哈尔医学院 | Device used for preparing ultrasmall superparamagnetic iron oxide (USPIO) nano particles via high-voltage electrostatic helix driven |
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