Method for producing precursor fine particles, method for producing ε-type ferric oxide fine particles, and precursor fine particles

Abstract

[Problem] To provide: a method for producing precursor fine particles, the method being improved in productivity and quality stability of ε-type ferric oxide fine particles; a method for producing ε-type ferric oxide fine particles; and precursor fine particles. [Solution] This method for producing precursor fine particles can be used for the production of ε-type ferric oxide fine particles, and is characterized by including an irradiation step in which a ferric salt in a solvent 5 is irradiated with a femtosecond pulse laser to produce precursor fine particles P each containing iron hydroxide oxide. In the irradiation step, precursor fine particles P each containing ε-type iron hydroxide oxide may be produced. In the irradiation step, the ferric salt in the solvent 5 that contains an alcohol may be irradiated with the femtosecond pulse laser.

Description

Method for producing precursor particles, method for producing ε-type ferric oxide particles, and precursor particles

[0001] The present invention relates to a method for producing precursor particles for use in producing ε-type ferric oxide (ε-Fe2O3) particles, a method for producing ε-type ferric oxide particles, and precursor particles.

[0002] Currently, research on ε-type ferric oxide particles is being conducted. ε-Type ferric oxide, which is an ε-type iron oxide-based compound, is a rare phase among iron oxides, but it has been confirmed to have a huge coercive force at room temperature in the nano-order particle size. ε-Type ferric oxide is one of the polymorphs having the composition of ferric oxide but different crystal structures, and like the most common α-type ferric oxide and γ-type ferric oxide, it is one phase. According to Non-Patent Documents 1 to 4, the crystal structure and magnetic properties of ε-type ferric oxide have been clarified, and synthesis in a single-phase state has been realized.

[0003] In addition, since ε-type ferric oxide particles have a high coercive force, their applicability in the following industrial fields is expected. ε-Type ferric oxide particles have, for example, millimeter-wave absorption characteristics and can be applied to collision prevention millimeter-wave radars used in autonomous driving technology, absorption of millimeter-wave noise in electronic devices, and absorption means at frequencies exceeding 100 GHz required for next-generation high-speed communication. ε-Type ferric oxide particles have, for example, ferromagnetic properties in the nano-size and can be applied to magnetic tapes for big data preservation.

[0004] Conventional methods for producing ε-type ferric oxide nanoparticles combine the reverse micelle method and the sol-gel method, but have the problem of difficulty in controlling the particle size distribution. To solve this problem, improved methods have been proposed in Patent Documents 1 to 3. According to the manufacturing method disclosed in Patent Document 1, it includes a first heat treatment step of heat-treating oxyiron oxide (α-FeOOH) particles in a weakly reducing atmosphere at a range of 300 to 600°C to produce cubic iron oxide, and a second heat treatment step of heat-treating the cubic iron oxide particles obtained in the first heat treatment step in an oxidizing atmosphere at a range of 700 to 1300°C to produce ε-type ferric oxide crystals (see paragraphs

[0015] to

[0016] ). Furthermore, according to the manufacturing method disclosed in Patent Document 2, it includes a step of coating the surface of a precursor mainly composed of iron hydroxide with a silica-based Si oxide and heat-treating it at 700 to 1300°C (see paragraphs

[0019] to

[0021] ). Furthermore, according to the manufacturing method disclosed in Patent Document 3, the process includes a step of heat-treating the precursor particles within a temperature range of 800°C to 1400°C (see paragraph

[0123] ).

[0005] Japanese Patent Publication No. 2008-100871, Japanese Patent Publication No. 2008-63201, Japanese Patent Publication No. 2019-175532

[0006] Jian Jin, Shinichi Ohkoshi and Kazuhito Hashimoto, ADVANCED MATERIALS 2004, 16, No. 1, January 5, p.48-51Jian Jin, Kazuhito Hashimoto and Shinichi Ohkoshi, JOURNAL OF MATERIALS CHIMISTRY 2005, 15, p.1067-1071Shunsuke Sakurai, Jian Jin, Kazuhito Hashimoto and Shinichi Ohkoshi, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, Vol.74, No.7, July, 2005, p.1946-1949S.PONCE-CASTANEDA, JRMARTINEZ AND S.PALOMARES-SANCHEZ, Journal of Sol-Gel Science and Technology, 27, 2003, 247-254

[0007] In other words, according to the manufacturing methods disclosed in Patent Documents 1 to 3, it is necessary to perform heat treatment at 300°C or higher for precursor production and heat treatment at 700°C or higher for ε-type ferric oxide fine particles. Therefore, there is a problem in that it is difficult to maintain the performance of the manufacturing equipment compared to low-temperature processing processes. In addition, the higher the processing temperature, the greater the risk that the precursor fine particles will melt or crystallize during the heat treatment process, which is a problem in that the quality stability of the ε-type ferric oxide fine particles cannot be improved.

[0008] Therefore, the present invention was devised in view of the above-mentioned problems, and its objective is to provide a method for producing precursor fine particles, a method for producing ε-type ferric oxide fine particles, and precursor fine particles, which improve the manufacturability and quality stability of ε-type ferric oxide fine particles.

[0009] The method for producing precursor nanoparticles in the first invention is a method for producing precursor nanoparticles that can be used for producing ε-type ferric oxide nanoparticles, and is characterized by comprising an irradiation step of irradiating a ferric salt in a solvent with a femtosecond pulse laser to produce precursor nanoparticles containing iron oxyhydroxide.

[0010] The method for producing precursor fine particles in the second invention is characterized in that, in the first invention, the irradiation step generates the precursor fine particles containing ε-type iron oxyhydroxide.

[0011] The method for producing precursor fine particles in the third invention is characterized in that, in the second invention, the irradiation step involves irradiating the ferric salt in the solvent containing alcohol and water with the femtosecond pulse laser.

[0012] The fourth invention is a method for producing ε-type ferric oxide fine particles using any of the precursor fine particles of the first to third inventions, and further comprises a heating step of heating the precursor fine particles generated in the irradiation step at a temperature of 150°C to 200°C.

[0013] The precursor fine particles in the fifth invention are characterized by containing ε-type iron oxyhydroxide.

[0014] According to the first to fourth inventions, the method for producing precursor nanoparticles includes an irradiation step of irradiating a ferric salt in a solvent with a femtosecond pulse laser to produce precursor nanoparticles containing iron oxyhydroxide. Therefore, precursors to ε-type ferric oxide nanoparticles can be easily produced without requiring a heating furnace for high-temperature processing. Furthermore, by using this precursor, ε-type ferric oxide nanoparticles can be produced by low-temperature heat treatment at around 200°C, making it easier to maintain the stable performance of the manufacturing equipment. This improves the manufacturability of ε-type ferric oxide nanoparticles. In addition, the risk of changes in the crystal structure of the nanoparticles due to high-temperature processing adversely affecting magnetism is suppressed. This improves the quality stability of ε-type ferric oxide nanoparticles.

[0015] In particular, according to the second invention, the irradiation step generates precursor fine particles containing ε-type iron oxyhydroxide. That is, precursor fine particles having the same crystal structure as ε-type ferric oxide fine particles are generated. Therefore, ε-type ferric oxide fine particles can be more reliably produced by low-temperature heat treatment at around 200°C. This makes it possible to further improve the quality stability of ε-type ferric oxide fine particles.

[0016] In particular, according to the third invention, the irradiation step involves irradiating a ferric salt in a solvent containing alcohol and water with a femtosecond pulse laser. As a result, ε-type iron oxyhydroxide nuclei can be efficiently generated by the sacrificial oxidation of the alcohol. This improves the manufacturability of ε-type iron oxyhydroxide precursor nanoparticles. Furthermore, precursor nanoparticles with an ε-phase transition temperature of 200°C or lower can be generated. This improves the manufacturability of ε-type ferric oxide nanoparticles.

[0017] In particular, according to the fourth invention, the method for producing ε-type ferric oxide fine particles includes a heating step of heating precursor fine particles at a temperature of 150°C to 200°C. Therefore, ε-type ferric oxide fine particles can be produced by low-temperature heat treatment at around 200°C, and the performance of the manufacturing equipment can be easily maintained stably. This improves the manufacturability of ε-type ferric oxide fine particles. In addition, the risk of changes in the crystal structure of the fine particles due to high-temperature treatment adversely affecting magnetism is suppressed. This improves the quality stability of ε-type ferric oxide fine particles.

[0018] In particular, according to the fifth invention, the precursor fine particles contain ε-type iron oxyhydroxide. That is, the first phase transition temperature to the ε phase is 150°C to 200°C, and the second phase transition temperature to the α phase is 150°C to 300°C. Therefore, ε-type ferric oxide fine particles can be produced by low-temperature heat treatment at around 200°C, making it easier to maintain the stable performance of the manufacturing equipment. This improves the manufacturability of ε-type ferric oxide fine particles. In addition, the risk of changes in the crystal structure of the fine particles due to high-temperature treatment adversely affecting magnetism is suppressed. This improves the quality stability of ε-type ferric oxide fine particles.

[0019] Figure 1 is a schematic diagram showing an example of a manufacturing apparatus for precursor fine particles in this embodiment. Figure 2 is a flowchart showing an example of a method for manufacturing precursor fine particles in this embodiment. Figure 3 is a graph showing the results of X-ray diffraction measurements for the precursor fine particles of Invention Examples 1 to 4 in the Examples. Figure 4 is a graph showing an example of peak data from X-ray diffraction measurements. Figure 5 is a graph showing the measurement results by X-ray diffraction for each heat treatment condition for ferric oxide fine particles obtained by heating the precursor fine particles of Invention Example 1 in the Examples. Figure 6 is a graph showing the measurement results by X-ray diffraction for each heat treatment condition for ferric oxide fine particles obtained by heating the precursor fine particles of Invention Example 2 in the Examples. Figure 7 is a graph showing the measurement results by X-ray diffraction for each heat treatment condition for ferric oxide fine particles obtained by heating the precursor fine particles of Invention Example 3 in the Examples. Figure 8 is a graph showing the measurement results by X-ray diffraction for each heat treatment condition for ferric oxide fine particles obtained by heating the precursor fine particles of Invention Example 4 in the Examples. Figure 9 is an image showing the results of magnetic evaluation for ε-type ferric oxide fine particles of Invention Examples 5 to 8 in the Examples. Figure 10 is an image showing the results of magnetic evaluation for the ε-type ferric oxide fine particles of Examples 9-10 and the precursor fine particles of Example 1 of the present invention in the examples. Figure 11 is a graph showing the measurement results by differential scanning calorimetry (DSC) for the precursor fine particles of Examples 1-4 of the present invention in the examples. Figure 12 is a graph showing an enlarged portion of Figure 11. Figures 13(a) and 13(b) are graphs showing the absorbance spectra of the precursor fine particles of Examples 11-12 of the present invention in the examples.

[0020] Hereinafter, an example of a precursor fine particle P and a method for producing the precursor fine particle S1 as embodiments of the present invention will be described in detail with reference to the drawings. Note that the configurations in each figure are schematically represented for illustrative purposes, and the size of each component, the size comparisons between components, etc., may differ from those shown in the figures.

[0021] (Precursor microparticles P, ε-type ferric oxide microparticles) Referring to Figure 1, an example of precursor microparticles P in this embodiment and ε-type ferric oxide microparticles produced using precursor microparticles P will be described.

[0022] ε-type ferric oxide nanoparticles are a type of ferric oxide nanoparticle. Ferric oxide nanoparticles are produced by heat-treating iron-containing nanoparticles as a precursor. Furthermore, different crystalline phases appear in ferric oxide nanoparticles depending on the heat treatment temperature. According to conventional methods, γ-type ferric oxide nanoparticles containing the γ phase appear at a heat treatment temperature of around 900°C, and α-type ferric oxide nanoparticles containing the α phase appear at a heat treatment temperature of around 1100°C. In between these, ε-type ferric oxide nanoparticles containing the ε phase appear at a heat treatment temperature of around 1000°C. Here, during the process in which ferric oxide nanoparticles change from γ-type to α-type, the particle size of the iron oxide grows significantly to obtain the final nanoparticles, so conventionally, the intermediate product, ε-type ferric oxide nanoparticles, have been treated as impurities.

[0023] On the other hand, the inventors of the present invention investigated a method for producing precursor nanoparticles P with a particle size of about 10 nm using a "laser-induced nucleation method (or laser-induced nuclear reduction method)" with a femtosecond pulsed laser, and then producing ferric oxide nanoparticles from these precursor nanoparticles P using a low-temperature process at a heat treatment temperature of less than 500°C. They discovered that in the ferric oxide nanoparticles produced using the precursor nanoparticles P, an ε-phase with magnetism similar to that of the ε-type ferric oxide nanoparticles produced by the conventional method described above appeared in the region of particle size of about several tens of nm. In other words, the present invention can be described as a method for stably producing ε-type ferric oxide nanoparticles using the above-mentioned ε-type ferric oxide nanoparticles as the product.

[0024] <Precursor Microparticles P> Precursor microparticles P are precursor microparticles that can be used in the production of ε-type ferric oxide microparticles. Specifically, ε-type ferric oxide microparticles, which are orthorhombic iron oxides, can be obtained by heat-treating precursor microparticles P containing iron oxyhydroxide in an atmospheric environment.

[0025] Precursor particles P contain iron oxyhydroxide (FeOOH). Precursor particles P include, for example, ε-type iron oxyhydroxide and ferrihydrite. ε-type iron oxyhydroxide refers to a substance containing an ε-type crystalline structure (orthorhombic) among iron oxyhydroxides. Ferrihydrite refers to a substance with a very fine crystalline structure among iron oxyhydroxides, denoted as Fe2O3・nH2O or Fe5O3(OH)9.

[0026] Precursor fine particles P containing ε-type iron oxyhydroxide have a first phase transition temperature to the ε phase of 150°C to 200°C, and a second phase transition temperature to the α phase of 150°C to 300°C. In this case, ε-type ferric oxide fine particles can be produced by low-temperature heat treatment at around 200°C, making it easier to maintain the stable performance of the manufacturing equipment. This improves the manufacturability of ε-type ferric oxide fine particles. Furthermore, the risk of changes in the crystal structure of the fine particles due to high-temperature treatment adversely affecting magnetism is suppressed. This improves the quality stability of ε-type ferric oxide fine particles.

[0027] The precursor nanoparticles P include, for example, pure iron oxyhydroxide in which the iron sites are not substituted with other metal elements (heterogeneous elements), as well as those in which some of the iron sites are substituted with heterogeneous elements. The precursor nanoparticles P may be doped with heterogeneous elements in amounts less than approximately 50 atomic percent (at%) relative to the iron element. Examples of heterogeneous elements that may be included in the precursor nanoparticles P include magnesium, calcium, barium, strontium, aluminum, gallium, indium, yttrium, etc. The heterogeneous elements may include any elements used to control the shape and particle size of the precursor nanoparticles P.

[0028] The precursor fine particles P include, for example, particles having a particle size of 1 nm to 100 nm. The precursor fine particles P may also include, for example, particles having a median diameter (central diameter: D50) of 1 nm to 20 nm, or particles having an average particle size of 1 nm to 20 nm. The median diameter or average particle size can be measured, for example, using a particle size distribution analyzer. As a particle size distribution analyzer, for example, a particle size distribution analyzer using dynamic light scattering (for example, a Zetasizer Ultra manufactured by Malvern Panalytical) may be used.

[0029] <ε-type ferric oxide nanoparticles> ε-type ferric oxide nanoparticles have an orthorhombic crystal structure. Although the diffraction pattern of ε-type ferric oxide nanoparticles cannot be strictly distinguished from that of spinel-type cubic magnetite (Fe3O4) using general X-ray diffraction methods, for example, their crystal structure and diffraction pattern are different. ε-type ferric oxide nanoparticles include pure ε-Fe2O3 in which the Fe site is not replaced by other metal elements (heterogeneous elements), as well as those in which part of the Fe site is replaced by heterogeneous elements. The heterogeneous elements that may be included in ε-type ferric oxide nanoparticles are the same as those that may be included in the precursor nanoparticles P mentioned above.

[0030] The ε-type ferric oxide nanoparticles include, for example, particles having a particle size similar to that of precursor nanoparticles P.

[0031] (Method for producing precursor fine particles S1) Next, an example of the method for producing precursor fine particles S1 in this embodiment will be described. By the method for producing precursor fine particles S1, precursor fine particles P that can be used for the production of ε-type ferric oxide fine particles can be produced.

[0032] The method for producing precursor nanoparticles S1 involves irradiating a ferric salt with a femtosecond pulse laser in the irradiation step S10 described later, thereby generating precursor nanoparticles P, which are precursors to ε-type ferric oxide nanoparticles. This eliminates the need for a heating furnace that performs high-temperature treatment at around 1000°C. This improves the manufacturability of ε-type ferric oxide nanoparticles.

[0033] First, the precursor microparticle manufacturing apparatus 100 used to carry out the precursor microparticle manufacturing method S1 will be described. The precursor microparticle manufacturing method S1 is realized by the operation of the precursor microparticle manufacturing apparatus 100 shown in Figure 1, for example. In the precursor microparticle manufacturing apparatus 100, each component is executed, for example, via a precursor microparticle manufacturing program that is pre-installed in the apparatus.

[0034] <Precursor Microparticle Manufacturing Apparatus 100> The precursor microparticle manufacturing apparatus 100 is an apparatus for manufacturing precursor microparticles P. The precursor microparticle manufacturing apparatus 100 comprises, for example, a laser device 1, a lens 2, a container 3, and a solution 4. The precursor microparticle manufacturing apparatus 100 may, for example, have multiple containers 3 and solutions 4 connected to one laser device 1.

[0035] The precursor microparticle manufacturing apparatus 100 may be equipped with an integrated circuit that includes, for example, a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). In this case, the CPU may read a program stored in the ROM, use the RAM as a work area to perform calculations to operate each component of the precursor microparticle manufacturing apparatus 100, and control the operation of the precursor microparticle manufacturing apparatus 100 by notifying each component of the precursor microparticle manufacturing apparatus 100 of operation commands based on the calculation results.

[0036] <Laser device 1> Laser device 1 is, for example, 10 -15 The laser device emits a femtosecond pulse laser with a time width of approximately one second. The laser device 1 can produce precursor nanoparticles P in the solution 4 by a nonlinear reduction effect generated when the high-power femtosecond laser is passed through lens 2 and focused into the solution 4.

[0037] The laser device 1 generates precursor nanoparticles P by forming a plasma with a temperature of approximately 1000°C at the focal point of the emitted laser beam. Here, the laser beam output is 0.7 mW or more, and the laser fluence is 1.0 kJ / cm². 2In the above case, it is possible to easily generate sufficient plasma to cause a reduction reaction when generating the precursor fine particles P. As a result, it becomes possible to further improve the generation efficiency of the fine particles.

[0038] As the laser device 1, for example, it exhibits the following characteristics, and a femtosecond pulse laser such as Astrella manufactured by COHERENT can be used. Oscillation wavelength: 800 nm ± 20 nm Pulse width: 100 fs Pulse energy: 7 mJ Repetition frequency: 1000 Hz

[0039] In addition to the above, as the laser device 1, for example, Spitfire Pro manufactured by Spectra Physics is used and can be arbitrarily selected according to the application. The laser emitted from the laser device 1 has an energy of about several mJ. For example, with an energy of about several μJ such as that used in laser processing, it is difficult to efficiently generate fine particles.

[0040] <Lens 2> The lens 2 condenses the laser emitted from the laser device 1. By using the lens 2, the light intensity can be increased for a specific region. In particular, by using the lens 2, the laser can be condensed inside the solution 4 rather than at the interface of the solution 4. As the lens 2, a known lens such as a condenser lens is used. By irradiating the solution 4 with the laser condensed through the lens 2, the generation efficiency of the fine particles can be improved.

[0041] The lens 2 may adjust the position where the laser is condensed inside the solution 4, for example, by adjusting the shape of the lens 2 or the distance from the solution 4. The lens 2 may adjust the position where the laser is condensed inside the solution 4 with the position of the lens 2 fixed, for example, by using a focus-variable lens.

[0042] <Container 3>The container 3 houses the solution 4. As the container 3, a transparent material is used, for example, a quartz cuvette. As the container 3, a material with a lower absorption rate at wavelengths around 800 nm compared to the absorption rate at wavelengths around 400 nm is used. In this case, when irradiating with a laser through the container 3, it is possible to suppress a decrease in the generation efficiency of fine particles.

[0043] <Solution 4>The solution 4 is a liquid containing the raw material of the precursor fine particles P. The precursor fine particles P in the present embodiment are generated by irradiating the solution 4 with the femtosecond pulsed laser emitted from the laser device 1. The solution 4 contains a solvent 5 such as water and a solute that serves as the raw material of the precursor fine particles P.

[0044] <<Solvent 5>>The solvent 5 is a liquid for dissolving the raw material of the precursor fine particles P. As the solvent 5, in addition to water, for example, a mixture of water and alcohol may be used.

[0045] When only water is used as the solvent 5, by irradiating with a femtosecond pulsed laser, reduction species such as hydrated electrons and hydrogen radicals (H·) are generated by the reaction of the water contained in the solvent 5, and the nuclei of the precursor fine particles P can be efficiently generated by the reducing action of the reduction species. On the other hand, oxidation species such as hydroxyl radicals (ОН·) and hydrogen peroxide (H2O2) are generated together with the reduction species. The oxidation species inhibit the reduction reaction of metal ions, complex ions, etc. that directly affect the generation of the precursor fine particles P, and the time for generating the fine particles may be delayed.

[0046] Here, a solvent 5 containing water and alcohol may be used. At this time, the oxidation species that inhibit the reduction reaction of the precursor react with the alcohol. In this case, it is possible to suppress the inhibition of the reduction reaction of metal ions, complex ions, etc. contained in the precursor. In addition, since the alcohol that has reacted with the oxidation species changes to a reducing compound, the reduction reaction of the precursor can be promoted. Thereby, it is possible to improve the generation efficiency of the precursor fine particles P. Also, the irradiation time of the femtosecond pulsed laser light can be optimized, and the structural change of the fine particles can be suppressed. Thereby, it is possible to suppress a decrease in the quality of the precursor fine particles P.

[0047] Furthermore, using only alcohol as solvent 5 is undesirable because it significantly delays the generation time of precursor fine particles P. This is thought to be due to the inability to generate reduced species based on the decomposition reaction of water, which slows down the generation time of the fine particles.

[0048] As the alcohol to be applied to solvent 5, for example, primary alcohols such as methanol (MeOH) or secondary alcohols such as isopropyl alcohol (IPA) can be used. In particular, secondary alcohols are more likely to maintain a stable state of radicals due to hyperconjugation compared to when primary alcohols are used. Also, secondary alcohols react more readily with oxidized species than when tertiary alcohols are used. For these reasons, by using a secondary alcohol as the alcohol, it is possible to further promote the reduction reaction of the precursor. According to the examples described later, using solvent 5 containing methanol makes it easier to produce precursor fine particles P containing ε-type iron oxyhydroxide. Also, using solvent 5 containing isopropyl alcohol makes it easier to produce precursor fine particles P containing ferrihydrite.

[0049] Furthermore, polyhydric alcohols such as glycerin or sorbitol may be used as the alcohol applied to solvent 5. In this case, the number of reaction sites with the oxidizing species can be increased compared to when a monohydric alcohol is used. Therefore, by using a polyhydric alcohol, it is possible to further accelerate the reduction reaction of the precursor.

[0050] <<Solute>> As the solute in solution 4, an iron-containing substance is used. As the solute, for example, an inorganic compound consisting of a ferric salt (ferrous nitrate, ferrous sulfate, etc.) containing trivalent iron ions is used. Alternatively, as the solute in solution 4, for example, a nitrate containing heterogeneous elements that may be contained in the aforementioned precursor fine particles P may be used.

[0051] The concentration of the solute in solution 4 is, for example, 1.0 × 10⁻⁶. -5 mol・dm -3 The above 1.0 x 10 -1 mol・dm-3 The range is as follows, and can be arbitrarily set depending on the application of the generated precursor fine particles P.

[0052] Next, the steps of the method for producing precursor fine particles S1 will be described. The method for producing precursor fine particles S1 includes an irradiation step S10, as shown in Figure 2, for example.

[0053] <Irradiation Step S10> In irradiation step S10, the precursor microparticle manufacturing apparatus 100 focuses a femtosecond pulse laser into the container 3 via the laser device 1 and lens 2, and irradiates the solute in the solvent 5 with the femtosecond pulse laser. As a result, the precursor microparticle manufacturing apparatus 100 can produce precursor microparticles P containing iron oxyhydroxide, which includes at least one of ε-type iron oxyhydroxide and ferrihydrite.

[0054] In irradiation step S10, the precursor microparticle manufacturing apparatus 100 irradiates, for example, a ferric salt in solvent 5 with a femtosecond pulse laser to generate precursor microparticles P containing iron oxyhydroxide. In this case, precursors for ε-type ferric oxide microparticles can be easily produced without requiring a heating furnace for high-temperature processing. Furthermore, by using this precursor, ε-type ferric oxide microparticles can be produced with low-temperature heat treatment at around 200°C, making it easier to maintain the stable performance of the manufacturing apparatus. This improves the manufacturability of ε-type ferric oxide microparticles. In addition, the risk of changes in the crystal structure of the microparticles due to high-temperature processing adversely affecting magnetism is suppressed. This improves the quality stability of ε-type ferric oxide microparticles.

[0055] In irradiation step S10, iron oxyhydroxide is thought to be produced by a reduction reaction described by, for example, one of the following redox reaction equations: Fe 3+ + 3e - → Fe 4Fe + 3O2 + 2H2O → 4FeOOH

[0056] In irradiation step S10, metal ions are reduced by reducing radicals generated in solution 4 by irradiation with a femtosecond pulsed laser, and by secondary radicals generated by reaction with alcohol. The metal atoms then nucleate and grow crystals, forming nanoparticles. They are also oxidized by dissolved oxygen and oxidizing species generated by laser irradiation to form oxide particles, which are then hydrated to form iron oxyhydroxide. If heterogeneous elements are present, they are similarly hydrated to form iron oxyhydroxide containing the heterogeneous elements.

[0057] In this case, a high-temperature, high-pressure region is formed near the laser focal point due to cavitation, so the generated iron oxyhydroxide nanoparticles form the ε phase, and as a result, ε-type iron oxyhydroxide can be formed. However, when solvent 5 containing isopropyl alcohol is used, the reaction proceeds even outside the high-temperature, high-pressure region near the focal point due to the long lifetime of the secondary radicals, so it is thought that ferrihydrite is formed without the formation of almost any ε phase.

[0058] The irradiation step S10 may, for example, generate precursor fine particles P containing ε-type iron oxyhydroxide. That is, precursor fine particles P containing ε-type iron oxyhydroxide having the same crystal structure (ε phase) as ε-type ferric oxide fine particles are generated. In this case, ε-type ferric oxide fine particles can be generated more reliably by low-temperature heat treatment at around 200°C. This makes it possible to further improve the quality stability of ε-type ferric oxide fine particles.

[0059] In the irradiation step S10, for example, a femtosecond pulsed laser may be irradiated onto the ferric salt in the alcohol-containing solvent 5. In this case, the sacrificial oxidation of the alcohol efficiently generates nuclei for the precursor nanoparticles P. This improves the manufacturability of the precursor nanoparticles P of ε-type iron oxyhydroxide. Furthermore, precursor nanoparticles P with an ε-phase transition temperature of 200°C or lower can be produced. This improves the manufacturability of the ε-type ferric oxide nanoparticles.

[0060] The above steps complete the method S1 for producing precursor fine particles in this embodiment.

[0061] (Method for producing ε-type ferric oxide fine particles S2) Next, an example of the method for producing ε-type ferric oxide fine particles S2 in this embodiment will be described.

[0062] The method for producing ε-type ferric oxide fine particles S2 can be achieved, for example, by a known heating method. The method for producing ε-type ferric oxide fine particles S2 may also be achieved, for example, by the operation of the precursor fine particle production apparatus 100 shown in Figure 1, or by an apparatus different from the precursor fine particle production apparatus 100.

[0063] <Heating means> The heating means refers to a means capable of heating the precursor fine particles P to 200°C or below under atmospheric pressure. As the heating means, known heating devices such as a hot plate or an electric furnace may be used. In this case, the heating means may be carried out by a precursor fine particle manufacturing apparatus 100 equipped with a known heating device.

[0064] Next, the steps of the method for producing ε-type ferric oxide fine particles S2 will be described. The method for producing ε-type ferric oxide fine particles S2 includes a heating step S20, as shown in Figure 2, for example.

[0065] <Heating Step S20> In heating step S20, for example, the precursor fine particles P that were previously generated in irradiation step S10 are heated at a temperature of 150°C to 200°C. In this case, ε-type ferric oxide fine particles can be generated by low-temperature heat treatment at around 200°C, making it easier to maintain the stable performance of the precursor fine particle manufacturing apparatus 100 described above. This improves the manufacturability of ε-type ferric oxide fine particles. In addition, the risk of changes in the crystal structure of the fine particles due to high-temperature treatment adversely affecting magnetism is suppressed. This improves the quality stability of ε-type ferric oxide fine particles. Heating step S20 involves heating the precursor fine particles P at a temperature of 150°C to 200°C under normal pressure, for example.

[0066] The heating step S20 may include a drying step in which the colloidal solution in which the precursor fine particles P are suspended is dried using a drying means before heating the precursor fine particles P to 150°C or higher and 200°C or lower. As the drying means, known drying apparatus such as a vacuum dryer or a heating dryer may be used.

[0067] At the completion of the irradiation step S10, the precursor fine particles P are produced as a colloidal solution suspended in solvent 5. By performing a drying step, the solvent 5 is evaporated or dehydrated to obtain powdered precursor fine particles P. Therefore, heat treatment can be performed more efficiently compared to heat treatment of the colloidal solution suspended in solvent 5. This improves the production efficiency of ε-type ferric oxide fine particles. Furthermore, compared to heat treatment of the colloidal solution, the volume of the object to be heated can be reduced, allowing for miniaturization of the heating means and energy savings. This improves the manufacturability of ε-type ferric oxide fine particles.

[0068] The above steps complete the method S2 for producing ε-type ferric oxide fine particles in this embodiment.

[0069] According to this embodiment, the method for producing precursor nanoparticles S1 includes an irradiation step S10 in which a femtosecond pulse laser is irradiated onto a ferric salt in a solvent 5 to produce precursor nanoparticles P containing iron oxyhydroxide. Therefore, precursors to ε-type ferric oxide nanoparticles can be easily produced without requiring a heating furnace for high-temperature processing. Furthermore, by using this precursor, ε-type ferric oxide nanoparticles can be produced by low-temperature heat treatment at around 200°C, making it easier to maintain the stable performance of the manufacturing equipment. This improves the manufacturability of ε-type ferric oxide nanoparticles. In addition, the risk of changes in the crystal structure of the nanoparticles due to high-temperature processing adversely affecting magnetism is suppressed. This improves the quality stability of ε-type ferric oxide nanoparticles.

[0070] Furthermore, according to this embodiment, the irradiation step S10 generates precursor fine particles P containing ε-type iron oxyhydroxide. That is, precursor fine particles P having the same crystal structure as ε-type ferric oxide fine particles are generated. Therefore, ε-type ferric oxide fine particles can be more reliably produced by low-temperature heat treatment at around 200°C. This makes it possible to further improve the quality stability of ε-type ferric oxide fine particles.

[0071] Furthermore, according to this embodiment, the irradiation step S10 involves irradiating a ferric salt in a solvent containing alcohol and water with a femtosecond pulse laser. As a result, nuclei of ε-type iron oxyhydroxide can be efficiently generated by the sacrificial oxidation of alcohol. This improves the manufacturability of precursor fine particles P. Furthermore, precursor fine particles P with an ε-phase transition temperature of 200°C or lower can be generated. This improves the manufacturability of precursor fine particles P of ε-type iron oxyhydroxide. Furthermore, precursor fine particles P with an ε-phase transition temperature of 200°C or lower can be generated. This improves the manufacturability of ε-type ferric oxide fine particles.

[0072] Furthermore, according to this embodiment, the method for producing ε-type ferric oxide fine particles S2 includes a heating step S20 in which precursor fine particles P are heated at a temperature of 150°C to 200°C. Therefore, ε-type ferric oxide fine particles can be produced by low-temperature heat treatment at around 200°C, and the performance of the manufacturing equipment can be easily maintained stably. This improves the manufacturability of ε-type ferric oxide fine particles. In addition, the risk of changes in the crystal structure of the fine particles due to high-temperature treatment adversely affecting magnetism is suppressed. This improves the quality stability of ε-type ferric oxide fine particles.

[0073] Furthermore, according to this embodiment, the precursor fine particles P contain ε-type iron oxyhydroxide. That is, the first phase transition temperature to the ε phase is 150°C to 200°C, and the second phase transition temperature to the α phase is 150°C to 300°C. Therefore, ε-type ferric oxide fine particles can be produced by low-temperature heat treatment at around 200°C, making it easier to maintain the stable performance of the manufacturing equipment. This improves the manufacturability of ε-type ferric oxide fine particles. In addition, the risk of changes in the crystal structure of the fine particles due to high-temperature treatment adversely affecting magnetism is suppressed. This improves the quality stability of ε-type ferric oxide fine particles.

[0074] The following describes experimental results regarding the effects of using the precursor fine particle manufacturing method S1 in the above-described embodiment. In this experiment, the characteristics of precursor fine particles P produced by the precursor fine particle manufacturing method S1 and ferric oxide fine particles produced by the ε-type ferric oxide fine particle manufacturing method S2 were compared under different manufacturing conditions.

[0075] <Experiment 1: Comparative experiment using different solutions 4> In this experiment, it was confirmed that the precursor fine particles P obtained in multiple cases with different compositions of solution 4 contained iron oxyhydroxide.

[0076] Table 1 shows the conditions for each particle used in this experiment.

[0077]

[0078] Example 1 of the present invention is a precursor fine particle P produced using a solution 4 which is a mixture of a solvent 5 obtained by mixing 285 ml of water and 15 ml of methanol, and a solute of 0.003 mol of ferric nitrate.

[0079] Example 2 of the present invention is a precursor fine particle P produced using a solution 4 which is a mixture of solvent 5, which is a mixture of 285 ml of water and 15 ml of methanol, and a total of 0.003 mol of solute in a ratio of ferric nitrate to magnesium nitrate of 99:1 (at% ratio).

[0080] Example 3 of the present invention is a precursor fine particle P produced using a solution 4 which is a mixture of solvent 5, which is a mixture of 285 ml of water and 15 ml of methanol, and a total of 0.003 mol of solute in a ratio of ferric nitrate to barium nitrate of 99:1 (at% ratio).

[0081] Example 4 of the present invention is a precursor fine particle P produced using a solution 4 which is a mixture of a solvent 5 obtained by mixing 285 ml of water and 15 ml of isopropyl alcohol, and a solute of 0.003 mol of ferric nitrate.

[0082] For this experiment, the laser irradiation conditions were as follows: Laser device 1 was set to a femtosecond pulsed laser with a pulse width of 100 fs, pulse energy of 7 mJ, and repetition frequency of 1000 Hz, with an irradiation time of 2 hours. Lens 2 was an f8 mm aspherical lens. A 300 ml quartz beaker was used as container 3.

[0083] For the X-ray diffraction measurement conditions in this experiment, solution 4 was removed from container 3 without using a support and dried on a hot plate at 100°C. The resulting powder was placed on a silicon non-reflective plate and fixed by dropping a few drops of 10% collodion solution onto it and drying. CuKα (40kV / 40mA) was used as the incident X-ray. The divergence / scattering slit was set to 1°, the receiving slit to 0.6 mm, the measurement range to 10° to 80°, the measurement step to 0.04°, and the scan speed to 0.48° / min.

[0084] The results of this experiment are shown in Figure 3. In Figure 3, the vertical axis represents the intensity in an arbitrary unit [a.u.], and the horizontal axis represents the scanning range of 10° to 80° at the diffraction angle 2θ.

[0085] As shown in Figure 3, diffraction peaks were obtained in Examples 1 to 3 of the present invention at positions of approximately 27°, 36°, 55°, and 60°. These correspond to the "ε-FeOOH" pattern among the diffraction patterns of each substance shown in Figure 4. Therefore, it can be said that Examples 1 to 3 of the present invention all contain ε-type iron oxyhydroxide.

[0086] In Example 4 of the present invention, diffraction peaks were obtained at approximately 35°, 40°, 53°, and 63°, as shown in Figure 3. These correspond to the "ferrihydrite" pattern among the diffraction patterns of each material shown in Figure 4. Therefore, Example 4 of the present invention can be said to contain ferrihydrite.

[0087] Based on the above, it has been confirmed that all of the present invention examples 1 to 4 can generate precursor fine particles P containing iron oxyhydroxide.

[0088] <Experiment 2: Comparison of Heat Treatment Temperature Conditions> In this experiment, the crystal structure of ferric oxide nanoparticles obtained under multiple different heat treatment temperatures for precursor nanoparticles P was confirmed by X-ray diffraction. The same conditions as those described above are omitted from this explanation.

[0089] In this experiment, the X-ray diffraction patterns were confirmed for each of the precursor fine particles P of the present invention examples 1 to 4 shown in Experiment 1 above, when ferric oxide fine particles were produced under heat treatment conditions of "before heating", "150°C", "200°C", "300°C", and "500°C".

[0090] The heating conditions involved setting the furnace temperature to 150°C, 200°C, 300°C, and 500°C in an atmospheric environment, and heating for 4 hours in each case. The heating method used was a muffle furnace "KDF-S100" manufactured by Tokyo Rikakikai Co., Ltd.

[0091] For the evaluation method, after heating using a heating method, the sample was placed on a silicon non-reflector plate, fixed by dropping a few drops of 10% collodion solution onto it and drying, and then X-ray diffraction measurements were performed. The X-ray diffraction measurement conditions were the same as those for Experiment 1 described above.

[0092] The results of this experiment are shown in Figures 5 to 8. Specifically, Figure 5 shows the results of Example 1 of the present invention, Figure 6 shows the results of Example 2 of the present invention, Figure 7 shows the results of Example 3 of the present invention, and Figure 8 shows the results of Example 4 of the present invention. In Figures 5 to 8, the vertical axis represents the intensity in an arbitrary unit [a.u.], and the horizontal axis represents the scanning range of 10° to 80° at the diffraction angle 2θ.

[0093] In Example 1 of the present invention, as shown in Figure 5, diffraction peaks were obtained at approximately 27°, 36°, 55°, and 60° in the "before heating" stage, which corresponds to the "ε-FeOOH" pattern. Furthermore, at "150°C" and "200°C," diffraction peaks were obtained at approximately 36°, 40°, 46°, 54°, and 64°. This corresponds to the "ε-Fe2O3" pattern shown in FIG 6 (a) on page 100 of "Structural and Magnetic Characterization of e-Fe2O3 E. Tronc C. Chaneac, and JP Jolivet JOURNAL OF SOLID STATE CHEMISTRY 139, 93D104 (1998)". Furthermore, at 300°C and 500°C, diffraction peaks were obtained at approximately 33°, 36°, 41°, 49°, 54°, 62°, and 64°. These correspond to the diffraction pattern of "α-Fe2O3" among the diffraction patterns of each substance shown in Figure 4.

[0094] In the case of Example 2 of the present invention, as shown in Figure 6, a similar trend to that of Example 1 of the present invention shown in Figure 5 was observed. Specifically, the "before heating" corresponds to the "ε-FeOOH" pattern, the "150°C" and "200°C" correspond to the "ε-Fe2O3" pattern, and the "300°C" and "500°C" correspond to the "α-Fe2O3" pattern.

[0095] In the case of Example 3 of the present invention, as shown in Figure 7, a similar trend to that of Example 1 of the present invention shown in Figure 5 was observed. Specifically, the "before heating" corresponds to the "ε-FeOOH" pattern, the "150°C" and "200°C" correspond to the "ε-Fe2O3" pattern, and the "300°C" and "500°C" correspond to the "α-Fe2O3" pattern.

[0096] In Example 4 of the present invention, as shown in Figure 8, diffraction peaks were obtained at approximately 35°, 40°, 53°, and 63° in the "before heating" stage, corresponding to the "ferrihydrite" pattern. Furthermore, at "150°C" and "200°C," diffraction peaks were obtained at approximately 36°, 40°, 46°, 54°, and 64°. This corresponds to the "ε-Fe2O3" pattern. Additionally, at "300°C" and "500°C," diffraction peaks were obtained at approximately 33°, 36°, 41°, 49°, 54°, 62°, and 64°. This corresponds to the "α-Fe2O3" pattern among the diffraction patterns of each substance shown in Figure 4.

[0097] Based on the above, it can be said that all of the present invention examples 1 to 4 can produce ε-type ferric oxide fine particles by heating at a temperature of 150°C to 200°C.

[0098] <Experiment 3: Comparative Experiment on Magnetism> In this experiment, the magnetism of ferric oxide nanoparticles was confirmed by checking whether or not the nanoparticles obtained from multiple examples with different compositions or crystal structures of precursor nanoparticles P flowed when a permanent magnet was brought near them. The same conditions as in the above experiment will not be explained.

[0099] Table 2 shows the conditions for each particle used in this experiment.

[0100]

[0101] Example 5 of the present invention is an ε-type ferric oxide fine particle produced by heating the precursor fine particle P of Example 1 of the present invention.

[0102] Example 6 of the present invention is an ε-type ferric oxide fine particle produced by heating the precursor fine particle P of Example 2 of the present invention.

[0103] Example 7 of the present invention is an ε-type ferric oxide fine particle produced by heating the precursor fine particle P of Example 3 of the present invention.

[0104] Example 8 of the present invention is an ε-type ferric oxide fine particle produced by heating the precursor fine particle P of Example 4 of the present invention.

[0105] Example 9 of the present invention is an ε-type ferric oxide fine particle produced by heating a precursor fine particle P prepared using a solution 4 which is a mixture of solvent 5, which is a mixture of 285 ml of water and 15 ml of methanol, and a total of 0.003 mol of solute in a ratio of ferric nitrate to calcium nitrate of 99:1 (at% ratio).

[0106] Example 10 of the present invention is an ε-type ferric oxide fine particle produced by heating a precursor fine particle P prepared using a solution 4 which is a mixture of solvent 5, which is a mixture of 285 ml of water and 15 ml of methanol, and a solute totaling 0.003 mol in a ratio of ferric nitrate to strontium nitrate of 99:1.

[0107] For the heating conditions, first, an appropriate amount of solution 4 was taken from container 3 and concentrated to about 1 / 10 of its original volume using a rotary evaporator. Then, it was heated and dried at 100°C in an air atmosphere using a hot plate for 1 hour. After that, approximately 10 mg of each dried sample was weighed onto an alumina board and heated on a hot plate until the surface temperature of the alumina board reached approximately 200°C. The heating of the dried samples was carried out continuously for 4 hours.

[0108] The evaluation method involved sealing each dried powder sample in a resin container with air, bringing a neodymium magnet with a diameter of φ12 mm and a thickness of 2 mm close to each sample in the resin container, and then inverting the resin container once to check whether the powder sample detached from the neodymium magnet and fell.

[0109] The results of this experiment are shown in Figures 9 to 10.

[0110] In Examples 5 to 7 of the present invention, as shown in Figure 9, the powder samples did not fall completely. This suggests that the powder material contains an ε-phase exhibiting ferromagnetism or superparamagnetism. Similarly, in Example 8 of the present invention, although the majority of the sample fell, some did not, suggesting that it also contains an ε-phase. Based on the above, it can be concluded that Examples 5 to 8 of the present invention all contain ε-type ferric oxide.

[0111] As shown in Figure 10, in Examples 9 and 10 of the present invention, similar to Examples 5 and 7, the powder sample did not fall completely, so it is considered to contain the ε phase. Therefore, it can be said that all of Examples 9 and 10 of the present invention contain ε-type ferric oxide. In addition, Example 1 of the present invention is precursor fine particles P before heat treatment, but when the magnetism was checked as a precaution, the sample fell completely, so it is considered to be before it has changed into ferric oxide fine particles.

[0112] <Experiment 4: Comparison of Phase Transition Temperatures> In this experiment, the phase transition temperatures at which precursor fine particles P of the above-mentioned Examples 1 to 4 transition to the ε phase or α phase were confirmed by differential scanning calorimetry (DSC). The same conditions as in the above-mentioned experiments will not be explained.

[0113] The heating conditions involved using a heating furnace, heating to 150°C in an air atmosphere for 4 hours, then raising the temperature to 200°C and continuing heating at 200°C for 4 hours. After that, the temperature was raised again to 300°C and continued heating for 4 hours.

[0114] For the evaluation method, the precursor fine particle P of Examples 1 to 4 of the present invention and a reference material were placed in the same space inside a heating furnace. The temperature was raised from room temperature to 1100°C at a rate of 10°C / min, and the correlation between the heat flow [mW] and temperature [°C] inside the heating furnace was measured based on the results of calibration using the temperature difference with the reference material. Alumina was used as the reference material.

[0115] The results of this experiment are shown in Figures 11 and 12. In Figures 11 and 12, the vertical axis represents heat flow [mW], and the horizontal axis represents the temperature inside the heating furnace [°C]. Figure 12 is a magnified view of a portion of Figure 11.

[0116] In Examples 1 to 4 of the present invention, as shown in Figure 11, a large exothermic peak was observed in the temperature range of 225°C to 300°C. This requires consideration of the effects of combustion of alcohol, nitrate ions, and their decomposition products. However, based on the results of Experiment 2 described above, it is considered that a phase transition temperature to the α-phase exists in the range of 225°C to 300°C, and that the effects related to this phase transition are also included.

[0117] Furthermore, as shown in Figure 12, for Examples 1 to 4 of the present invention, peak temperatures T1 to T4 corresponding to the exothermic peak were confirmed in the temperature range of 150°C to 200°C. Specifically, for Example 1, a peak temperature T1 ≈ 182°C was confirmed, for Example 2, a peak temperature T2 ≈ 180°C was confirmed, for Example 3, a peak temperature T3 ≈ 175°C was confirmed, and for Example 4, a peak temperature T4 ≈ 203°C was confirmed. Based on the results of Experiment 2 described above, it is considered that these peak temperatures were influenced by the phase transition at the phase transition temperature to the ε phase present in the range of 150°C to 200°C. Examples 1 to 3 of the present invention are precursor fine particles P containing ε-type iron oxyhydroxide, and Example 4 of the present invention is a precursor fine particles P containing ferrihydrite.

[0118] Based on the above, it is considered that the precursor fine particles P containing ε-type iron oxyhydroxide have a first phase transition temperature to the ε phase of 150°C to 200°C and a second phase transition temperature to the α phase of 300°C or higher than the first phase transition temperature. In this case, ε-type ferric oxide fine particles can be produced by low-temperature heat treatment at around 200°C, making it easier to maintain the stable performance of the manufacturing equipment and improving the manufacturability of ε-type ferric oxide fine particles.

[0119] <Experiment 5: Comparative experiment with the presence or absence of alcohol in solvent 5> In this experiment, it was confirmed that the precursor fine particles P obtained with and without alcohol in solvent 5 contained iron oxyhydroxide. The same conditions as in the above experiment will not be explained.

[0120] Table 3 shows the conditions for each particle used in this experiment.

[0121]

[0122] Example 11 of the present invention is a precursor fine particle P produced using a solution 4 which is a combination of a solvent 5 of 3 ml of water and a solute of 0.03 mmol of ferric nitrate.

[0123] Example 12 of the present invention is a precursor fine particle P produced using a solution 4 which is a mixture of solvent 5, obtained by mixing 2.85 ml of water and 0.15 ml (5 vol%) of methanol, and a solute of 0.03 mmol of ferric nitrate. Since the combination of solvent 5 and solute used in Example 12 of the present invention is the same as in Example 1 of the present invention in Experiment 1 described above, it is considered to be a precursor fine particle P containing ε-type iron oxyhydroxide.

[0124] For this experiment, the laser irradiation conditions were as follows: Laser device 1 was set to a femtosecond pulsed laser with a pulse width of 100 fs, pulse energy of 7 mJ, and repetition frequency of 1000 Hz, with an irradiation time of 30 minutes.

[0125] For the evaluation method, for each of the present invention examples 11 to 12, a 3 ml colloidal solution containing suspended precursor microparticles P was taken out into a quartz cell, and the absorbance spectrum was measured using a spectrophotometer.

[0126] The results of this experiment are shown in Figure 13. In Figure 13, the vertical axis represents absorbance [abs] and the horizontal axis represents the wavelength of the irradiated light [nm].

[0127] According to Figure 13, the absorbance spectra of Invention Example 11 and Invention Example 12 are very similar and are considered to be the same substance. Therefore, Invention Example 11 is a precursor fine particle P produced using a solvent 5 that does not contain alcohol and is considered to contain ε-type iron oxyhydroxide.

[0128] Based on the above, it can be said that the precursor fine particle manufacturing method S1 can produce precursor fine particles P containing iron oxyhydroxide, regardless of whether or not the solvent 5 contains alcohol.

[0129] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0130] 100 Manufacturing equipment 1 Laser device 2 Lens 3 Container 4 Solution 5 Solvent P Precursor microparticles S1 Method for producing precursor microparticles S10 Irradiation step S2 Method for producing ε-type ferric oxide microparticles S20 Heating step

Claims

1. A method for producing precursor nanoparticles that can be used for the production of ε-type ferric oxide nanoparticles, characterized by comprising an irradiation step of irradiating a ferric salt in a solvent with a femtosecond pulse laser to produce precursor nanoparticles containing iron oxyhydroxide.

2. The method for producing precursor fine particles according to claim 1, characterized in that the irradiation step produces precursor fine particles containing ε-type iron oxyhydroxide.

3. The method for producing precursor fine particles according to claim 2, characterized in that the irradiation step involves irradiating the ferric salt in the solvent containing alcohol and water with the femtosecond pulse laser.

4. A method for producing ε-type ferric oxide fine particles using precursor fine particles according to any one of claims 1 to 3, further comprising a heating step of heating the precursor fine particles generated in the irradiation step at a temperature of 150°C or higher and 200°C or lower.

5. Precursor microparticles usable for the production of ε-type ferric oxide microparticles, characterized in that the precursor microparticles contain ε-type iron oxyhydroxide.

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