JP2006342399A - Ultra-fine iron particle and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce ultra-fine iron particles which have large saturation magnetization, superior dispersibility into an organic solvent and superior stability after having been dispersed into the organic solvent, with a simple method. <P>SOLUTION: The method for producing ultra-fine iron particles having a coagulation inhibitor which has an action of inhibiting the coagulation of the ultra-fine iron particles and is coordinated around the iron particles includes thermally decomposing or reducing such an iron compound as to produce zero-valent iron by being thermally decomposed or reduced, in a liquid with the presence of the coagulation inhibitor, wherein the coagulation inhibitor is an aliphatic amine. The coagulation inhibitor includes an oxygen-containing compound in an amount of 0.1 mol or less by a ratio with respect to 1 mol of the aliphatic amine. It becomes possible to obtain ultra-fine iron particles which include little amount of impurities like iron oxide, and accordingly have the large saturation magnetization, by controlling the ratio of the oxygen-containing compound in the coagulation inhibitor to a low level. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to iron ultrafine particles and a method for producing the same. Specifically, the present invention relates to a method for producing iron ultrafine particles having a large saturation magnetization and excellent dispersibility in an organic solvent and stability thereof by a simple method, and an iron ultrafine particle produced by this method.

  In recent years, in communication devices and memory devices, higher frequencies and smaller memory sizes have been achieved, and reduction of power consumption in internal circuits is a major issue. However, there is a limit to increasing the impedance by reducing the dielectric constant, and a high permeability material at a high frequency is required as an alternative material.

  On the other hand, ferromagnetic metal fine particles such as iron, cobalt, and nickel are applied in various fields such as magnetic recording materials, high magnetic permeability materials, and radio wave absorbing materials. In particular, iron is a very useful material because it has the largest bulk saturation magnetization and is inexpensive.

  However, since the surface area of iron increases as it becomes finer, it oxidizes during the manufacturing process or causes defects, making it difficult to make finer particles while maintaining high saturation magnetization.

  Conventionally, as a method for synthesizing magnetic fine particles, a method using oleic acid and oleylamine as stabilizers has been reported. Specifically, a method for synthesizing iron and platinum alloy fine particles has been reported (Non-patent Document 1). reference). In this synthesis method, first, platinum serves as a nucleus, and iron is deposited therearound, so that iron-platinum alloy fine particles can be obtained relatively stably. However, with this technique, when trying to synthesize ferromagnetic fine particles made of iron alone instead of an alloy, the coordination power of iron with carboxylic acid such as oleic acid is very strong. There is a problem that iron oxide is generated.

  In addition, a method for synthesizing iron fine particles by thermally decomposing iron carbonyl in the presence of oleic acid, oleylamine and platinum seeds has been reported (see Non-Patent Document 2). The iron fine particles produced by this method have a large saturation magnetization of 200 emu / g at 10K. However, in this method, there is a possibility that expensive platinum is used or an alloy of iron and platinum is generated as an impurity. There was a problem that there was.

In addition to this, as a method for producing fine iron particles having a large saturation magnetization, Fe [N (SiCH ₃ ) ₂ ] ₂ is used as a raw material compound, and this is thermally decomposed in a hydrogen atmosphere in the presence of hexadecylamine and oleic acid. Has been reported (see Non-Patent Document 3). The iron fine particles synthesized by this production method have a large saturation magnetization of 212 emu / g, but it is difficult to synthesize the raw material compound, and it is necessary to thermally decompose in a hydrogen atmosphere. There wasn't.

  On the other hand, as metal nanoparticles having excellent dispersion stability, metal nanoparticles containing at least one of P, N, and O and having an average particle diameter of 1 to 100 nm are known. A method of heat-treating a starting material containing a metal salt in the presence of an amine compound in an inert gas atmosphere has been proposed (see Patent Document 1). However, in this method, a noble metal, which is a nonmagnetic metal, is particularly preferable as the metal component. For the production of metallic iron nanoparticles, which are magnetic metals, the metal iron nanoparticles and magnetic materials obtained by the above heat treatment are further used. The relationship is not mentioned at all.

In addition, magnetic metal fine particles have been synthesized by a reverse micelle method, which has been conventionally used as a fine particle synthesis method (see Non-Patent Document 4). However, the reverse micelle method has poor productivity because the concentration of particles in the liquid is very low, and in order to use the synthesized particles, it is necessary to take out the iron fine particles in the reverse micelles. It wasn't.
WO2004 / 012884A1 Shouheng Sun et al., “Science, (USA), 287, 2000, p. 1989-1992. Dorothy Farrell et al., “Journal of Physical Chemistry B” (J. Phys. Chem. B), (USA), 107, 2003, p. 11022-11030 Frederic Dumestre et al., “Science” (USA), 303, 2004, p. 821-823 J. Wilcoxon et al., "Journal of Physical Chemistry B" (J. Phys. Chem. B) (USA), 103, 1999, p. 9809-9812

  The present invention has been made in view of the above-described conventional situation, and an object of the present invention is a technique for producing iron ultrafine particles having a large saturation magnetization and excellent dispersibility in an organic solvent and stability thereof by a simple method. Is to provide.

  As a result of intensive studies to solve the above problems, the present inventors have thermally decomposed or reduced an iron compound that is pyrolyzed or reduced to produce zero-valent iron in a liquid containing an aggregation inhibitor. In producing iron ultrafine particles by using an aliphatic amine as an aggregation inhibitor, the content of the oxygen-containing compound contained in the aggregation inhibitor is 0.1 mol or less with respect to 1 mol of the aliphatic amine, The present inventors have found that the above problems can be solved and have completed the present invention.

That is, the gist of the present invention is as follows.
[1] Pyrolysis or reduction of an iron compound that is pyrolyzed or reduced to produce zero-valent iron in a liquid in the presence of an aggregation inhibitor having an action of suppressing aggregation of iron ultrafine particles. In the method for producing iron ultrafine particles having the iron ultrafine particle production step for producing iron ultrafine particles coordinated by the aggregation inhibitor, the aggregation inhibitor contains an aliphatic amine and is contained in the aggregation inhibitor. The method for producing ultrafine iron particles, wherein the ratio of the oxygen-containing compound is 0.1 mol or less per 1 mol of the aliphatic amine.
[2] In [1], an iron ultrafine particle-containing liquid in which iron ultrafine particles are produced in the iron ultrafine particle production step is mixed with an iron compound that is pyrolyzed or reduced to produce zero-valent iron, A method for producing iron ultrafine particles, characterized in that iron is deposited on the iron ultrafine particles.
[3] The method for producing ultrafine iron particles according to [2], wherein the iron compound is an iron compound that is reduced to produce zero-valent iron.
[4] The method for producing ultrafine iron particles according to [1] to [3], wherein the aggregation inhibitor substantially does not contain an oxygen-containing compound.
[5] Iron ultrafine particles produced by the method of [1] to [4].

  According to the method for producing iron ultrafine particles of the present invention, an iron ultrafine particle having a small content of impurities such as iron oxide, a large saturation magnetization, and excellent dispersibility and stability in an organic solvent is obtained. It can be manufactured by a simple method.

  That is, in the method of the present invention, when an iron compound that is pyrolyzed or reduced to produce zero-valent iron is pyrolyzed or reduced to produce ultrafine iron particles, an aliphatic amine that is an aggregation inhibitor is produced. Since the particles are located on the surface of the iron microcrystals to suppress the aggregation of the particles, coarsening due to the aggregation of the particles can be prevented, and iron particles having a very small particle diameter can be easily obtained. Moreover, since the abundance of the aggregation inhibitor containing an oxygen atom that can cause iron oxidation is suppressed to 0.1 mol or less with respect to 1 mol of the aliphatic amine, the generation of impurities such as iron oxide is prevented. Therefore, it is possible to obtain iron ultrafine particles with high saturation magnetization.

  In the conventional method, for example, iron ultrafine particles are produced in the presence of an aggregation inhibitor containing an oxygen atom such as oleic acid, which causes a disadvantage that the oxygen atom in the aggregation inhibitor causes oxidation of iron. It was. In the present invention, an aliphatic amine is used as the aggregation inhibitor, and the proportion of the aggregation inhibitor containing oxygen atoms is 0.1 mol or less with respect to 1 mol of the aliphatic amine, so that the factor of iron oxidation is reduced. In addition, a decrease in saturation magnetization due to the generation of iron oxide is prevented.

  Hereinafter, the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is specified to these contents as long as the gist thereof is not exceeded. Not done.

  The production of ultrafine iron particles according to the present invention is an action that suppresses aggregation of iron compounds that are pyrolyzed or reduced to produce zero-valent iron (hereinafter sometimes referred to as “raw iron compounds”) and ultrafine iron particles. It is carried out by thermally decomposing or reducing the iron compound in a liquid (hereinafter sometimes referred to as “reaction liquid”) containing a coagulation inhibitor having the above and a reducing agent used as necessary. The obtained iron ultrafine particles are purified as necessary and then used for various purposes.

  The “ultrafine particles” as used in the present invention does not simply mean “iron fine crystals” but “iron fine crystals in which a specific amine compound (for example, an aliphatic amine in the present invention) is coordinated on the surface. "Means.

[Aggregation inhibitor]
In the present invention, the aggregation inhibitor is present on the surface of the iron ultrafine particles when the raw iron compound that is pyrolyzed or reduced to produce zero-valent iron is pyrolyzed or reduced to produce iron ultrafine particles. Thus, it is possible to keep the particle size in the nanometer order by suppressing the aggregation of the iron ultrafine particles.

  Examples of such an aggregation inhibitor include amines, phosphine oxides, carboxylic acids, and the like. In the present invention, an aliphatic amine is used as the aggregation inhibitor. The aliphatic amine effectively prevents aggregation of the iron ultrafine particles by being present on the surface of the iron ultrafine particles generated by thermal decomposition or reduction of the raw iron compound. There are various forms of the surface of the iron ultrafine particles of this aliphatic amine, and it cannot be specified in general, and forms some chemical bonds such as coordination bonds and covalent bonds with the iron ultrafine particles. In addition to the case, it may be adsorbed reversibly by any attractive interaction such as van der Waals force, hydrophobic interaction, hydrogen bond, or Coulomb force. In the present invention, these forms of existence are referred to as “coordination”.

  An aliphatic amine does not have an oxygen atom unlike a surface active component generally used as an aggregation inhibitor, and does not cause oxidation of iron. For this reason, it is effective for the production of iron ultrafine particles having a small content of impurities such as iron oxide.

  As the aliphatic amine, any of primary, secondary, and tertiary amines may be used, and among these, primary amines are preferable. In addition, any number of amino groups may be contained in the aliphatic amine, but those having 1 to 2 amino groups are preferably used.

  The carbon chain contained in the aliphatic amine may be linear or branched, but the carbon number is usually 2 to 30, preferably 5 to 25, more preferably 7 to 20, most preferably Preferably, it is 8-18, and specific examples include isobutyl group, hexyl group, octyl group, decyl group, dodecyl group, hexadecyl group, oleyl group and the like, among which octyl group, decyl group, dodecyl group, hexadecyl group, An oleyl group is preferred.

  Examples of the aliphatic amine suitable as the aggregation inhibitor include 1-decylamine, 1-dodecylamine, 1-hexadecylamine, oleylamine and the like. These aliphatic amines may be used alone or in combination of two or more.

  Such an aliphatic amine has a lower limit of usually 0.1 mol or more, preferably 0.5 mol or more, and an upper limit of usually 100 mol or less, preferably 50 mol with respect to 1 mol of an iron atom in the raw material iron compound described later. Used in the following ranges. If the amount of the aliphatic amine used is too small, the effect of suppressing the aggregation of the iron ultrafine particles due to the use of the aliphatic amine cannot be sufficiently obtained, and if too large, the purification process increases, which is not practical in industry.

  In the present invention, the aliphatic amine as described above is used as the aggregation inhibitor, and the proportion of the oxygen-containing compound in the aggregation inhibitor is 0.1 mol or less with respect to 1 mol of the aliphatic amine. It is characterized by. The oxygen-containing compound in the aggregation inhibitor (hereinafter sometimes referred to as “aggregation inhibitor containing oxygen atoms”) is coordinated to the iron ultrafine particles generated by thermal decomposition or reduction of the raw iron compound. Thus, a compound having an action of suppressing the aggregation of iron ultrafine particles and containing an oxygen atom, an oxygen-containing compound mixed as a simple dispersion solvent, a reducing agent or an impurity is referred to as “the oxygen-containing content in the aggregation inhibitor”. Does not fall under “compound”.

  Examples of the oxygen-containing compound as the aggregation inhibitor include the above-described carboxylic acids and phosphine oxides, such as oleic acid, palmitic acid, dodecanoic acid, decanoic acid, hexanoic acid, stearic acid, trioctylphosphine oxide, and tributyl. Examples include phosphine oxide.

  In the present invention, the ratio of the oxygen-containing compound in such an aggregation inhibitor is 0.1 mol or less with respect to 1 mol of the aliphatic amine as the aggregation inhibitor. When the proportion of the aggregation inhibitor containing oxygen atoms exceeds 0.1 mol with respect to 1 mol of the aliphatic amine, the amount of impurities such as iron oxide increases due to the oxidizing action of the aggregation inhibitor containing oxygen atoms. It is impossible to obtain iron ultrafine particles having a large saturation magnetization. The smaller the amount of aggregation inhibitor containing oxygen atoms, the more preferable, and 0.01 mol or less with respect to 1 mol of the aliphatic amine, and most preferable that the aggregation inhibitor containing oxygen atoms is not substantially present in the reaction solution. .

[Raw iron compound]
The raw iron compound used in the production of the iron ultrafine particles of the present invention is a compound that itself thermally decomposes to produce zero-valent metallic iron, and divalent or trivalent iron in the compound is reduced by a reducing agent. As a result, compounds that produce zero-valent metallic iron can be mentioned.

  The raw material iron compound that is pyrolyzed to produce zero-valent metallic iron is not limited as long as it is a compound that generates zero-valent metallic iron by pyrolysis, but iron carbonyl is preferably used, for example, pentacarbonyl iron, Nonacarbonyl diiron, dodecacarbonyl triiron and the like can be mentioned.

  The raw material iron compound that generates zero-valent metallic iron by being reduced is not particularly limited as long as it is a compound that generates zero-valent metallic iron by being reduced. For example, iron chloride, iron bromide, etc. Examples thereof include iron halides; iron carboxylates such as iron acetate and iron oleate; inorganic acid irons such as iron sulfate and iron nitrate; and β-diketone complexes of iron such as acetylacetonato iron. Among them, iron acetate, iron chloride, and a β-diketone complex of iron are particularly preferably used in terms of solubility, compound stability, and operability.

  These raw material iron compounds may be used individually by 1 type, and may use 2 or more types together.

  The content of the raw iron compound in the reaction solution is not particularly limited, but if it is too small, the production efficiency of iron ultrafine particles is poor, and if it is too large, the particles tend to aggregate and maintain a nanometer order particle size. Therefore, it is preferable to set the concentration to 1 mmol / liter or more and 10 mol / liter or less.

[Reducing agent]
When using a compound that generates zero-valent metallic iron by reduction as a raw iron compound, a reducing agent must be present in the reaction solution. The reducing agent is not limited as long as it is a compound that can reduce the raw iron compound to zero-valent metallic iron. Specifically, hydrogen, carbon, hydrazine, borohydride such as sodium borohydride, potassium borohydride, carboxylic acid such as oxalic acid and citric acid, carboxylate such as sodium citrate and sodium ascorbate, Monohydric alcohols such as ethanol, butanol, hexanol, polyhydric alcohols such as 1,2-hexanediol, 1,2-hexadecanediol, ethylene glycol, lithium triethylborohydride (superhydride), lithium aluminum hydride, lithium hydride Examples of the metal hydride such as polyhydric alcohol and metal hydride are preferably used from the viewpoint of reactivity and operability. These reducing agents may be used individually by 1 type, and may use 2 or more types together.

  The lower limit of the amount of the reducing agent used is usually 0.1 mol or more, preferably 0.5 mol or more, and the upper limit is usually 100 mol or less, preferably 50 mol or less, relative to 1 mol of iron atoms in the raw iron compound. It is.

[solvent]
The production of the iron ultrafine particles of the present invention is carried out by heating in a reaction liquid in which a raw material iron compound, an aggregation inhibitor, and a reducing agent used as necessary are mixed. The reaction liquid is further added with an organic solvent. May be diluted. Examples of the organic solvent used in the reaction solution include ethers such as dioctyl ether and diphenyl ether, alkanes such as n-pentane, n-hexane, cyclohexane, n-octane and isooctane, benzene, toluene, xylene, naphthalene and chlorobenzene. , Aromatic hydrocarbons such as dichlorobenzene, nitrogen-containing aromatic compounds such as pyridine, lutidine, collidine, or quinoline, halogenated alkyls such as methylene chloride, chloroform, carbon tetrachloride, 1,2-dichloroethane, N, Examples include amide aprotic solvents such as N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP) and the like.

  These solvents may be used as a mixture of two or more in any kind, combination, and mixing ratio as necessary.

[Reaction temperature, time, atmosphere]
The reaction temperature in the present invention is not particularly limited as long as the raw iron compound is thermally decomposed or reduced. Usually, in the case of a reduction reaction, the lower limit is 0 ° C. or higher, preferably 100 ° C. or higher. In the case of reaction, the lower limit is usually 50 ° C. or higher, preferably 100 ° C. or higher. On the other hand, the upper limit is usually 500 ° C. or lower, preferably 400 ° C. or lower.

  The reaction time is not particularly limited as long as the necessary iron ultrafine particles are produced, but is usually 1 minute or more, preferably 30 minutes or more, and usually 100 hours or less, preferably 50 hours or less.

  The method for producing ultrafine iron particles of the present invention is usually carried out in an inert gas atmosphere such as argon or nitrogen containing 100 ppm or less of oxygen and 100 ppm or less of water so that the produced iron ultrafine particles are not oxidized.

[Adjustment of iron ultrafine particle size]
In the method for producing iron ultrafine particles of the present invention, in order to increase the particle size of the obtained iron ultrafine particles, the iron ultrafine particles are produced after the raw iron compound is pyrolyzed or reduced to produce iron ultrafine particles. The raw material iron compound is further added to the generated liquid, or the liquid in which the iron ultrafine particles are generated is added to and mixed with the raw iron compound, and the raw iron compound in the mixed solution is thermally decomposed or reduced, so that It is possible to deposit iron. In this case, the starting iron compound may be used after being dissolved in a suitable solvent. Further, as the liquid in which the iron ultrafine particles are generated, a liquid containing iron ultrafine particles purified by the method described later may be used.

  By using the iron ultrafine particles generated in this way as nuclei and further precipitating iron thereon, the particle size of the fine particles can be increased.

  The additional raw material iron compound may be the same as or different from the original raw material iron compound. When this raw material iron compound generates zero-valent metallic iron by reduction, the aforementioned reducing agent is also used in combination. Moreover, when mixing a raw material iron compound, you may mix an aliphatic amine further as needed.

[Other substances]
In the production of the ultrafine iron particles of the present invention, substances other than those described above may be present in the reaction solution as long as the object of the present invention is not impaired.

  As described above, the amount of the aggregation inhibitor containing an oxygen atom such as carboxylic acids described above in the reaction solution is usually 0.1 mol or less, preferably 0.01 mol, relative to 1 mol of the aliphatic amine. The iron ultrafine particles of the present invention are most preferably produced in the absence of such an oxygen-containing compound, but after the raw iron compound is thermally decomposed or reduced and the iron ultrafine particles are produced, If present, an aggregation inhibitor containing an oxygen atom such as a carboxylic acid may be present in the reaction solution in an amount exceeding 0.1 mol with respect to 1 mol of the aliphatic amine in order to improve dispersibility.

[Purification of ultrafine iron particles]
The iron ultrafine particles obtained by the method described above may be used as they are after being extracted from the reaction solution. However, in order to increase the composition ratio of metallic iron crystals in the fine particles, the solubility of aliphatic amines is high, but generated. The ultrafine iron particles may be purified by mixing with a solvent having low dispersibility (hereinafter sometimes referred to as “purification solvent”). By mixing the iron ultrafine particles with the purification solvent, the aliphatic amine coordinated to the iron ultrafine particles and other organic components dissolve in the purification solvent, resulting in a suspension in which the fine particles are precipitated. The ultrafine iron particles can be obtained by separating and refining the ultrafine iron particles from the suspension by a separation method such as the above. The purification solvent is appropriately selected according to the aliphatic amine used. For example, when the aliphatic amine is oleylamine, methanol, ethanol, n-propanol, isopropyl alcohol, n-butanol, tert-butanol 1 type (s) or 2 or more types, such as alcohols, etc. can be used.

  In the purification of such iron ultrafine particles, the iron ultrafine particles may be once dispersed in an organic solvent having excellent dispersibility of the iron ultrafine particles, and then mixed with a purification solvent such as the above alcohols. As well-dispersible organic solvents for iron ultrafine particles, ethers such as dioctyl ether and diphenyl ether, alkanes such as n-pentane, n-hexane, cyclohexane, n-octane and isooctane, benzene, toluene, xylene, naphthalene and chlorobenzene , Aromatic hydrocarbons such as dichlorobenzene, nitrogen-containing aromatic compounds such as pyridine, lutidine, collidine, or quinoline, halogenated alkyls such as methylene chloride, chloroform, carbon tetrachloride, 1,2-dichloroethane, N, Examples include amide aprotic solvents such as N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and these may be used alone. More than one species may be used in combination.

  In addition, since the iron ultrafine particles obtained by the present invention are ultrafine particles having a very small particle diameter, when the iron ultrafine particles are dispersed in a solvent having excellent dispersibility of the iron ultrafine particles, the iron ultrafine particles are visually observed. It becomes a state where the fine particles cannot be confirmed, as if it were “dissolved”. When the above-mentioned purification solvent is added to the solution of the iron ultrafine particles in a pseudo-dissolved state, the iron ultrafine particles are in a suspended state, and the development is as if the iron ultrafine particles are precipitated.

[Ultrafine iron particles of the present invention]
(Aliphatic amine content)
The iron ultrafine particles of the present invention obtained by the iron ultrafine particle production method of the present invention are coordinated with an aliphatic amine used as an aggregation inhibitor, and the aliphatic amine is coordinated, so that Generation of coarse particles due to aggregation can be avoided, and good and stable dispersibility in an organic solvent can be obtained.

  The coordination amount of the aliphatic amine of the iron ultrafine particles obtained by the production method of the present invention depends on the particle size or surface area of the fine particles, but in a state where it has been sufficiently purified through the purification step described above, the lower limit is Usually 5% by weight or more, preferably 10% by weight or more, more preferably 15% by weight or more, most preferably 20% by weight or more, and the upper limit is usually 90% by weight or less, preferably 80% by weight or less, more preferably 70% by weight. % Or less, most preferably 60% by weight or less. If the amount of coordination of the aliphatic amine is too small, a sufficient aggregating effect due to the aliphatic amine cannot be obtained, and if it is too large, problems such as precipitation of the aliphatic amine during use may occur. The coordination amount of the aliphatic amine is a weight ratio of the aliphatic amine to the total of iron fine crystals and an iron oxide which is considered to be contained in a small amount.

  This aliphatic amine coordination amount is measured by combining, for example, thermogravimetric analysis or elemental analysis.

(Particle size)
The size of the iron ultrafine particles obtained by the production method of the present invention (this size means a size that does not include an aliphatic amine coordinated with the iron ultrafine particles) is a general-purpose transmission electron. The average particle diameter observed with a microscope (TEM) is usually 1 nm or more, preferably 2 nm or more, usually 500 nm or less, preferably 300 nm or less, more preferably 100 nm or less. If the average particle size of the iron ultrafine particles is too large, the particles are likely to aggregate due to van der Waals force and the like, and the dispersibility in an organic solvent decreases. On the other hand, if the average particle size of the iron ultrafine particles is too small, it is difficult to produce industrially and is not practical. However, the particle diameter observed by TEM is that in which the iron crystal portion in the fine particles is observed. In reality, organic components such as aliphatic amines are coordinated on the surface of this crystal, and the coordination component is The particle size to be included is larger than the above range.

(Construction)
By measuring the electron diffraction pattern and X-ray diffraction pattern of the iron ultrafine particles obtained from the production method of the present invention, it is possible to identify the structure and to confirm the presence of impurities such as iron oxide. is there. For example, in the case of iron, a body-centered cubic structure at room temperature, a cubic close-packed structure at 910 ° C. or higher, and a body-centered cubic structure at 1400 ° C. or higher are stable, which are called α iron, γ iron, and δ iron, respectively.

(Saturation magnetization)
The iron ultrafine particles obtained by the production method of the present invention are usually ferromagnetic, and the saturation magnetization can be measured with a superconducting quantum interference device (SQUID) magnetometer or the like. The saturation magnetization of the iron ultrafine particles is preferably as close as possible to the saturation magnetization (220 emu / g) of bulk iron, but is usually 150 emu / g or more, preferably 165 emu / g or more, more preferably 180 emu / g or more at 5K. .

  In addition, the calculation method of the saturation magnetization of the iron ultrafine particles of the present invention is as follows.

Usually, the saturation magnetization is expressed per gram of iron, but the iron ultrafine particles obtained by the production method of the present invention may contain impurities such as oxidized iron or other oxides. It is very difficult to calculate the ratio. Therefore, in the present invention, once the iron by sintering ultrafine particles and iron oxide (Fe ₂ O _3), to estimate the amount of iron contained in iron ultra fine particles from the weight of iron contained in the iron ultrafine particles The saturation magnetization was calculated assuming that all are zero-valent iron.

(Other ingredients)
In the production method of the present invention, when iron ultrafine particles are produced with a reaction solution containing an aggregation inhibitor containing oxygen atoms such as carboxylic acid, the resulting iron ultrafine particles contain aggregation inhibitors containing oxygen atoms. The agent may be coordinated.

  Moreover, the iron ultrafine particles obtained by the production method of the present invention usually have organic components derived from organic compounds such as diketone derived from the above-mentioned raw material iron compound and solvent components used in the reaction solution in addition to the aliphatic amine. It is coordinated.

  Such an organic component, after undergoing the purification step described above, is any chemical bond such as a coordinate bond or covalent bond with the iron ultrafine particles of the present invention, van der Waals force, hydrophobic interaction, hydrogen bond, Coulomb force, etc. It is reversibly adsorbed by any attractive interaction and coordinated with the iron ultrafine particles.

(shell)
The iron ultrafine particles of the present invention may have a stable shell against oxygen in order to prevent oxidation in the air. For example, the shell can be formed on the iron ultrafine particles by reacting the shell raw material in a liquid containing the iron ultrafine particles. Examples of the compound used as the shell include noble metals such as platinum, gold, silver, and palladium, and oxides such as silicon oxide, aluminum oxide, and zirconium oxide. These may be used alone or in combination of two or more.

  EXAMPLES Specific examples of the present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples unless it exceeds the gist.

  In addition, as a raw material reagent, unless otherwise indicated, a commercially available reagent was used without purification. Moreover, the measuring method of the saturation magnetization and particle size of the obtained iron ultrafine particles is as follows.

[Measurement of saturation magnetization]
As described later, a sample (0.1 g) re-dispersed in hexane after washing the reaction solution with ethanol in an argon atmosphere glove box was placed in a quartz tube and covered with an epoxy resin to obtain a measurement sample. This quartz tube was set in a superconducting quantum interference device (SQUID) magnetic flux system (MPMS-5 manufactured by QUANTOM DESIGN), and the magnetization was measured. The measurement temperature was 5 K, and the measurement magnetic field range was 50 kOe to −50 kOe. On the other hand, the solvent of the liquid containing the same iron ultrafine particles was evaporated, baked at 650 ° C. for 4 hours, and the weight was measured to determine the iron content. The value obtained by dividing the measured saturation magnetization value by the estimated iron weight was defined as the saturation magnetization [emu / g] of the iron ultrafine particles.

[Measurement of particle size]
As described later, after the reaction solution was washed with ethanol, a sample redispersed in hexane was dropped onto the grid and the solvent was evaporated, and then measured with a transmission electron microscope (JEM-2000EX manufactured by JEOL). The sample was exposed to the atmosphere for a few minutes just before the measurement. The average particle size was calculated from a value obtained by measuring the particle size of at least 300 particle images.

Example 1 Production of Ultrafine Iron Particles in the Presence of Oleylamine Dioctyl ether (Aldrich: 25 mL) and oleylamine (Aldrich) were added to a colorless and transparent Pyrex glass three-neck flask (100 mL) equipped with an air-cooled reflux tube and a thermometer. Product: 8 mmol). Dioctyl ether and oleylamine used in advance were evacuated for 1 hour from room temperature to 50 ° C. using a rotary pump.

  Separately, a raw material solution in which iron pentacarbonyl (manufactured by Kanto Chemical Co., Inc .: 2 mmol) was dissolved in a part of the solution in the flask (dioctyl ether + oleylamine; 2 mL) was prepared. The solution in the flask was heated to 200 ° C. with a mantle heater, and this raw material solution was injected at once with a syringe. Immediately after injection, the liquid turned black. After injecting the raw material solution, the mixture was further heated to reflux for 30 minutes (reaction liquid temperature: 289 ° C.), and then the heat source was removed and the mixture was allowed to cool to room temperature.

  After adding dehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd .: 30 mL) to the iron ultrafine particle production solution (10 mL) obtained in this way to produce a black insoluble matter, centrifugation was performed, and further The supernatant was removed by decantation, and the resulting black precipitate (iron ultrafine particles) was dispersed in dehydrated hexane (manufactured by Wako Pure Chemical Industries, Ltd .: 10 mL). The hexane containing the iron ultrafine particles did not precipitate for at least 2 weeks.

  All the above operations were performed in a glove box in an argon atmosphere in which both oxygen and moisture were 10 ppm or less.

  The average particle diameter of the iron ultrafine particles obtained as described above was 5 nm, and the saturation magnetization at 5K was 186 emu / g.

Example 2: Production of ultrafine iron particles in the presence of oleylamine (deposition of iron on ultrafine iron particles)
An iron ultrafine particle production solution (6 mL) obtained by carrying out the reaction in the same manner as in Example 1 was mixed with iron (II) acetate (Aldrich: 1 mmol), oleylamine (Aldrich: 4 mmol) and 1,2- Hexadecanediol (manufactured by Aldrich: 5 mmol) was added to the reaction solution added to dioctyl ether (manufactured by Aldrich: 12 mL). The blended liquid was heated with a mantle heater and refluxed for 1 hour (reaction liquid temperature 289 ° C.).

  After adding dehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd .: 30 mL) to the iron ultrafine particle production liquid (10 mL) thus obtained, a black insoluble matter was produced, followed by centrifugation, and further The supernatant was removed by decantation, and the resulting black precipitate (iron ultrafine particles) was dispersed in dehydrated hexane (manufactured by Wako Pure Chemical Industries, Ltd .: 10 mL). The hexane containing the iron ultrafine particles did not precipitate for at least 2 weeks.

  All the above operations were performed in a glove box in an argon atmosphere in which both oxygen and moisture were 10 ppm or less.

  The iron ultrafine particles obtained as described above had an average particle size of 13 nm and a saturation magnetization at 5K of 182 emu / g.

  In this Example 2, because the liquid in which the iron ultrafine particles were generated in advance and the reaction liquid containing the raw material iron compound, the aliphatic amine, and the reducing agent were mixed, iron was precipitated with the iron ultrafine particles already generated as nuclei. Although iron ultrafine particles having a particle size larger than that in Example 1 were obtained, the saturation magnetization showed almost the same value.

Comparative Example 1: Production of ultrafine iron particles in the presence of oleic acid A colorless and transparent Pyrex glass three-necked flask (100 mL) equipped with an air-cooled reflux tube and a thermometer was added to dioctyl ether (Aldrich: 30 mL) and oleic acid. (Aldrich: 16.1 mmol) was added. Dioctyl ether and oleic acid used in advance were evacuated for 1 hour at room temperature to 50 ° C. using a rotary pump.

  Separately, a raw material solution in which iron pentacarbonyl (manufactured by Kanto Chemical Co., Ltd .: 4.3 mmol) was dissolved in a part of the solution in the flask (dioctyl ether + oleic acid; 2 mL) was prepared. The solution in the flask was heated to 100 ° C. with a mantle heater, and this raw material solution was injected at once with a syringe. Immediately after injection, the liquid turned black. After injecting the raw material solution, the mixture was further heated and refluxed for 70 minutes (reaction liquid temperature: 287 ° C.).

  After adding dehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd .: 30 mL) to the iron ultrafine particle production liquid (10 mL) thus obtained, a black insoluble matter was produced, followed by centrifugation, and further The supernatant was removed by decantation, and the resulting black precipitate (iron ultrafine particles) was dispersed in dehydrated hexane (10 mL).

  All the above operations were performed in a glove box in an argon atmosphere in which both oxygen and moisture were 10 ppm or less.

  The average particle size of the fine particles obtained as described above was 4 nm, which was the same as in Example 1. However, when the magnetization was measured at 5K, it was not saturated at 50 kOe, and the magnetization at that time was Was 6.9 emu / g. Since the magnetization value was extremely small and the magnetization was not saturated, it was judged that the magnetic properties of the obtained iron ultrafine particles were different from those of α iron, which is usually ferromagnetic.

Comparative Example 2: Production of ultrafine iron particles in the presence of oleic acid and oleylamine (1: 1) Dioctyl ether (Aldrich) was added to a colorless and transparent Pyrex glass three-necked flask (100 mL) equipped with an air-cooled reflux tube and a thermometer. Manufactured: 25 mL), oleic acid (manufactured by Aldrich: 2 mmol) and oleylamine (manufactured by Aldrich: 2 mmol) were added. Dioctyl ether, oleic acid, and oleylamine used in advance were evacuated at room temperature to 50 ° C. using a rotary pump for 1 hour.

  Separately, a raw material solution in which iron pentacarbonyl (manufactured by Kanto Chemical Co., Inc .: 2 mmol) was dissolved in a part of the solution in the flask (dioctyl ether + oleic acid + oleylamine; 2 mL) was prepared. The solution in the flask was heated to 200 ° C. with a mantle heater, and this raw material solution was injected at once with a syringe. Immediately after injection, the liquid turned black. After injecting the raw material solution, the mixture was further heated to reflux for 70 minutes (reaction liquid temperature: 289 ° C.), and then the heat source was removed and the mixture was allowed to cool to room temperature.

  After adding dehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd .: 30 mL) to the iron ultrafine particle production liquid (10 mL) thus obtained, a black insoluble matter was produced, followed by centrifugation, and further The supernatant was removed by decantation, and the resulting black precipitate (iron ultrafine particles) was dispersed in dehydrated hexane (10 mL).

  All the above operations were performed in a glove box in an argon atmosphere in which both oxygen and moisture were 10 ppm or less.

  The average particle size of the fine particles obtained as described above was 6 nm, which was the same as that in Example 1, but the saturation magnetization at 5K was 130 emu / g, which is inferior to those in Examples 1 and 2. It was a thing.

Claims (5)

By thermally decomposing or reducing an iron compound that is pyrolyzed or reduced in liquid to produce zero-valent iron in the presence of an aggregation inhibitor having an action of suppressing aggregation of iron ultrafine particles, In the production method of iron ultrafine particles having an iron ultrafine particle production step for producing iron ultrafine particles coordinated with an aggregation inhibitor,
The iron ultrafine particles characterized in that the aggregation inhibitor contains an aliphatic amine, and the ratio of the oxygen-containing compound contained in the aggregation inhibitor is 0.1 mol or less with respect to 1 mol of the aliphatic amine. Production method.   2. The iron ultrafine particle-containing liquid in which the iron ultrafine particles are produced in the iron ultrafine particle production step and an iron compound that is pyrolyzed or reduced to produce zero-valent iron are mixed, and the iron ultrafine particles are mixed. A method for producing iron ultrafine particles, characterized by depositing iron on top.   3. The method for producing ultrafine iron particles according to claim 2, wherein the iron compound is an iron compound that is reduced to produce zero-valent iron.   4. The method for producing ultrafine iron particles according to claim 1, wherein the aggregation inhibitor substantially does not contain an oxygen-containing compound.   Iron ultrafine particles produced by the method according to any one of claims 1 to 4.