Coating device and coating method for coating metal particles with metal oxide

Abstract

A coating device (10) for coating metal particles with a metal oxide comprises: a spray drying device (30) that sprays a solution, in which metal particles are dispersed, into a heating atmosphere in a mist state to obtain coated particles; and a heating furnace (40) that fires the coated particles. The solution contains a coordination compound in which the metal ion is stabilized by a ligand that forms a coordination bond with a metal ion. The coordination compound contains an oxygen atom. The spray drying device (30) generates the coated particles in which the metal particles are coated with the coordination compound. The heating furnace (40) converts the coordination compound in the coated particles into the metal oxide.

Description

Coating device and coating method for coating metal particles with metal oxide

[0001] The present invention relates to a coating apparatus and a coating method for coating metal particles with a metal oxide.

[0002] The applicant of the present application has proposed a method and apparatus for forming a film on the surface of powder by atomic layer deposition (ALD), for example, coating powder with a metal oxide (Patent Document 1).

[0003] Patent Document 2 discloses a method for producing a metal pigment composition. This production method involves forming a silicon compound-containing layer on the surface of the metal particles by hydrolysis / (partial) condensation of the organosilicon compound in a mixed solution containing (a) metal particles, (b) a silicon-containing raw material containing an organosilicon compound such as a silane compound or silicon oxide, and (c) a solvent (water and / or a hydrophilic solvent) (paragraph 0056). It also discloses that, to disperse the metal particles in the solvent, the solvent containing the metal particles is stirred or ultrasonically irradiated (paragraphs 0084-0090).

[0004] Japanese Patent No. 6787621 Japanese Patent Application Laid-Open No. 2022-163850

[0005] The purpose of coating particles varies depending on the application, but methods other than the ALD method described in Patent Document 1, such as the method described in Patent Document 2, are limited to applications of metal pigment compositions in which the coating layer on the particles is a silicon compound-containing layer.

[0006] An object of the present invention is to provide a coating apparatus and a coating method for coating the surfaces of metal particles with a metal oxide derived from a coordination compound.

[0007] (1) One aspect of the present invention relates to a coating apparatus for coating metal particles with a metal oxide, comprising: a spray dryer that sprays a solution in which metal particles are dispersed into a heated atmosphere in the form of a mist to obtain coated particles; and a heating furnace that bakes the coated particles, wherein the solution contains a coordination compound in which metal ions are stabilized by ligands that form coordinate bonds with the metal ions, and the coordination compound contains oxygen atoms; the spray dryer produces the coated particles in which the metal particles are coated with the coordination compound; and the heating furnace converts the coordination compound of the coated particles into a metal oxide.

[0008] According to one aspect of the present invention, a raw material containing dispersed metal particles in a solution is sprayed in a mist form in a heated atmosphere using a spray dryer. In this way, according to the principles of spray drying, the raw material is atomized by spraying and continuously contacted with hot air while increasing its surface area. When the atomized solution comes into contact with the hot air, the water contained in the solution instantly evaporates, resulting in coated particles in which the metal particles are coated with a coordination compound that stabilizes the metal ions. The coated particles are then calcined, converting the coordination compound into a metal oxide and forming an oxide with a uniform metal composition. In this way, the metal particles are coated with the metal oxide derived from the coordination compound.

[0009] (2) The coating apparatus according to aspect (1) of the present invention may further include a dispersing device for dispersing the metal particles in the solution.

[0010] (3) In the coating apparatus according to aspect (2) of the present invention, the dispersing device can supply the metal particles into the solution at a high pressure of 100 MPa or more. In this way, the speed of the raw material in the dispersing device exceeds the speed of sound. The strong shear force applied to the raw material exceeding the speed of sound and the energy generated by collisions between the raw materials disperse the metal particles in the solution and can also be atomized to nano-level particles. In this way, the dispersing device uniformly disperses metal particles to nano-level sizes in the solution.

[0011] (4) In the coating apparatus according to any one of aspects (1) to (3) of the present invention, the coordination compound contains Ti and Ba as the metal ions, and the metal particles can be coated with barium titanate. In this case, the coordination compound on the surfaces of the metal particles is thermally decomposed to form barium titanate, and the surfaces of the metal particles are coated with barium titanate.

[0012] (5) In the coating apparatus according to any one of aspects (1) to (3) of the present invention, the coordination compound contains Al as the metal ion, and the metal particles can be coated with aluminum oxide. In this case, the coordination compound on the surfaces of the metal particles is thermally decomposed to form aluminum oxide, and the surfaces of the metal particles are coated with aluminum oxide.

[0013] (6) Another aspect of the present invention relates to a coating method, comprising: preparing a solution containing a coordination compound containing oxygen atoms and stabilizing metal ions with ligands that form coordinate bonds with the metal ions, and dispersing metal particles in the solution; spraying the solution containing the dispersed metal particles in a mist form in a heated atmosphere to obtain coated particles in which the metal particles are coated with the coordination compound; and calcining the coated particles to convert the coordination compound into a metal oxide, thereby coating the metal particles with the metal oxide derived from the coordination compound.

[0014] According to another aspect (6) of the present invention, a raw material containing dispersed metal particles in a solution is sprayed in a mist in a heated atmosphere. In this way, according to the principle of spray drying, the raw material is atomized by spraying and continuously contacted with hot air while increasing its surface area. When the atomized solution comes into contact with the hot air, the water instantly evaporates, resulting in coated particles in which the metal particles are coated with a coordination compound that stabilizes the metal ions. The coated particles are then calcined, converting the coordination compound into a metal oxide and forming an oxide with a uniform metal composition. In this way, the metal particles are coated with the metal oxide derived from the coordination compound.

[0015] FIG. 1 is a schematic block diagram of a coating apparatus according to one embodiment of the present invention. FIG. 2 is a diagram showing an example of a dispersion apparatus and a spray-drying apparatus in FIG. 1. FIG. 3 is a cross-sectional view showing an example of an atomization chamber in FIG. 2. FIG. 4(A) to FIG. 4(E) are micrographs of coated particles in which the surfaces of metal particles Ni are coated with barium titanate BaTiO3 and their constituent components. FIG. 5(A) shows Ni particles before coating, and FIG. 5(B) is a micrograph showing coated particles with Ni as a core. ３ 7A to 7D are characteristic diagrams showing X-ray diffraction intensities of particles coated with aluminum oxide (Al) and particles coated with aluminum oxide (Al). ２ O ３ 1 is a micrograph of a coated particle and its constituent components, which is a metal particle Cu and a metal particle whose surface is coated with aluminum oxide Al. ２ O ３ 1 is a characteristic diagram showing X-ray diffraction intensity of coated particles coated with a coating material.

[0016] An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, metal particles, such as Ni or Cu, are coated with a metal oxide film, such as a barium titanate film or an aluminum oxide film. A common purpose of coating metal particles with a metal oxide film is to make the coated particles electrically insulating.

[0017] 1. Coating Apparatus As shown in FIG. 1 , the coating apparatus 10 of this embodiment includes a dispersing apparatus 20, a spray drying apparatus 30, and a heating furnace 40. The dispersing apparatus 20 is not necessarily required; a solution containing dispersed metal particles to be supplied to the spray drying apparatus 30 may be prepared in advance. The dispersing apparatus 20, the spray drying apparatus 30, and the heating furnace 40 may be connected inline or offline. The dispersing apparatus 20 disperses metal particles in a solution containing a coordination compound in which metal ions are stabilized by ligands that form coordinate bonds with the metal ions, the coordination compound containing oxygen atoms. The spray drying apparatus 30 sprays the solution containing dispersed metal particles in a mist form into a heated atmosphere in a chamber to obtain coated particles in which the metal particles are coated with the coordination compound. The heating furnace, such as an open-air furnace 40, calcines the resulting coated particles to convert the coordination compound into metal oxide.

[0018] In this embodiment, a solution containing a coordination compound is used in which metal ions are stabilized by ligands that form coordinate bonds with the metal ions. The metal ions that can be contained in this solution are metal ions other than lithium, sodium, potassium, and cesium. The ligand is a chemical species that forms a coordinate bond with the metal ion by donating an unshared electron pair to the metal ion.

[0019] Coordination compounds contain at least one coordinating atom in a ligand that forms a coordinate bond with a metal ion by donating an unshared electron pair to the metal ion. A ligand with one coordinating atom is called a monodentate ligand, a ligand with two coordinating atoms is called a bidentate ligand, and a ligand with two or more coordinating atoms is generally called a multidentate ligand. Specific examples of coordination compounds include metal complexes and chelate complexes in which bidentate or higher ligands sandwich a metal ion.

[0020] The coordination compound of this embodiment contains an oxygen atom. In this case, at least one coordination atom in the ligand may be an oxygen atom. For example, when the ligand is a carboxylic acid, a carboxylate ion RCOO － The coordinating atom O in the ligand bonds to the metal. Alternatively, an atom other than the coordinating atom in the ligand may be an oxygen atom. Alternatively, an atom in the coordination compound other than the ligand may be an oxygen atom.

[0021] Preferred coordination agents for use in the present invention include water-soluble aminocarboxylic acid chelating agents such as ethylenediaminetetraacetic acid, 1,2-cyclohexanediaminetetraacetic acid, dihydroxyethylglycine, diaminopropanoltetraacetic acid, diethylenetriaminepentaacetic acid, ethylenediaminediacetic acid, ethylenediaminedipropionic acid, hydroxyethylenediaminetriacetic acid, glycol ether diaminetetraacetic acid, hexamethylenediaminetetraacetic acid, ethylenediaminedi(o-hydroxyphenyl)acetic acid, hydroxyethyliminodiacetic acid, iminodiacetic acid, 1,3-diaminopropanetetraacetic acid, 1,2-diaminopropanetetraacetic acid, nitrilotriacetic acid, nitrilotripropionic acid, triethylenetetraminehexaacetic acid, ethylenediaminedisuccinic acid, 1,3-diaminopropanedisuccinic acid, glutamic acid-N,N-diacetic acid, and aspartic acid-N,N-diacetic acid. Any of these monomers, oligomers, or polymers can be used. Other coordination agents include hydroxycarboxylic acids such as gluconic acid, citric acid, tartaric acid, and malic acid, but in the present invention, aminocarboxylic acid chelating agents can be preferably used.

[0022] The dispersion device 20 disperses metal particles, which are the target of film formation, in the above-mentioned solution. In this embodiment, the metal particles are dispersed under high pressure, but this is not limiting. The dispersion device 20 shown in Figure 2 includes, for example, a raw material tank 21, a liquid supply pump 22, two branched liquid paths 23, 23, two pressurizing units 24, 24, a high-pressure filter 25, and an atomization chamber 26. The raw material tank 21 stores the above-mentioned raw material. The liquid supply pump 22 supplies the raw material in the raw material tank 21 to the branched liquid paths 23, 23. The two pressurizing units 24, 24 pressurize the raw material flowing through the branched liquid paths 23, 23. The pressurized raw material is supplied to the atomization chamber 26 via the high-pressure filter 25.

[0023] 3, the atomization chamber 26 has two branched inlet pipes 26A connected to the high-pressure filter 25, two nozzles 26B communicating with the two branched inlet pipes 26A, a chamber main body 26C communicating with the two nozzles 26B, and an outlet pipe 26D communicating with the chamber main body 26C. As such a dispersing device 20, for example, a wet atomization device (product name: Starburst) manufactured by Sugino Machine Ltd. can be suitably used.

[0024] As shown in Figure 2, the spray drying apparatus 30 has a drying chamber 31, a blower 32, a heater 33, a nozzle 34, an exhaust pipe 35, an exhaust pump 36, and a recovery unit 37. The blower 32 takes in outside air, and the heater 33 heats the taken-in outside air to turn it into hot air. Hot air H is introduced into the drying chamber 31 from the heater 33, and raw material M, which is a solution in which metal particles have been dispersed by the dispersing device 20, is sprayed in the form of a mist into the hot air through the nozzle 34. The drying chamber 31 is evacuated by the exhaust pump 36 through the exhaust pipe 35, and the coated particles in the drying chamber 31 are recovered in the recovery unit 37.

[0025] The heating furnace 40 is a furnace that sinters the coated particles taken out from the recovery section 37. As the heating furnace 40, an open-air furnace that sinters the particles in the atmosphere (in air) is generally used.

[0026] 2. Coating Method The solution used in this embodiment contains a Ba complex and a Ti complex as coordination compounds containing oxygen atoms, and a raw material is prepared by mixing this solution with metal particles of Ni.

[0027] In the dispersion device 20, the raw material in the raw material tank 21 is supplied to branched liquid paths 23, 23 by a liquid supply pump, for example, a diaphragm pump 22. The raw material branched and supplied by the branched liquid paths 23, 23 is pressurized by two pressurizing units 24, 24. Each of the two pressurizing units 24 has, for example, a piston-cylinder mechanism, and is driven so that when the piston of one pressurizing unit 24 is at top dead center, the piston of the other pressurizing unit 24 is at bottom dead center. The raw material is pressurized to, for example, 100 MPa or more, preferably 200 MPa or more, for example, 245 MPa. The pressurized raw material is supplied to an atomization chamber 26 via a high-pressure filter 25.

[0028] In the atomization chamber 26, the speed of the raw material supplied to the two branched introduction pipes 26A, 26A at a high pressure of, for example, 245 MPa and sprayed from the two nozzles 26B, 26B exceeds the speed of sound. The strong shear force acting on the raw material exceeding the speed of sound and the energy generated by collisions between the raw materials within the chamber main body 26C cause the metal particles to be dispersed in the solution and further atomized to nano-level particles. In this way, in the dispersing device 20, the metal particles, which have been made uniform in size to the nano-level, are evenly dispersed in the solution.

[0029] Hot air H is introduced into the drying chamber 31 of the spray dryer 30 from a heater 33, and raw material M, which is a solution in which metal particles have been dispersed by the disperser 20, is sprayed in the form of a mist into the hot air H through a nozzle 34. In this way, according to the principle of spray drying, raw material M is atomized by being sprayed from the nozzle 34, and is continuously brought into contact with the hot air H while increasing its surface area within the drying chamber 31. In this way, the water in the solution instantly evaporates, and coated particles in which the metal particles are coated with a Ba complex and a Ti complex can be obtained. The dried coated particles obtained in this way are collected in a collection section 37.

[0030] Next, the coated particles removed from the recovery section 37 are placed in the heating furnace 40 shown in FIG. 1. In the heating furnace 40, the coated particles are fired, for example, in an atmosphere open to the atmosphere. By firing the coated particles, the coordination compound is converted into a metal oxide, and an oxide with a uniform metal composition can be formed. In this way, the metal oxide derived from the coordination compound coats the metal particles.

[0031] The deposited structure of the metal oxides BaO and TiO is thermally stable and becomes barium titanate BaTiO ３ The surface of the metal particles Ni is barium titanate BaTiO ３ It is coated with

[0032] Similarly, the surface of the metal particles Cu is coated with aluminum oxide Al ２ O ３The solution in this case is a solution containing a coordination compound in which the metal ion Al is stabilized by a ligand that forms a coordinate bond with the metal ion Al, and the coordination compound contains oxygen atoms.

[0033] 3. Coated particles Figures 4(A) to 4(E) show the surface of metal particles Ni coated with barium titanate BaTiO ３ 4(A) and 4(B) are micrographs of a coated particle coated with Ba and its constituent components. The outer shape of the coated particle shown in Fig. 4(A) is reflected in Fig. 4(B), which shows the Ba component in the coating, Fig. 4(D), which shows the Ti component in the coating, and Fig. 4(E), which shows the oxygen component in the coating. However, the outer shape cannot be identified in Fig. 4(C), which shows the Ni component of the metal particle that is the core of the coated particle. In other words, the Ni core metal particle shown in Fig. 5(A) is composed of barium titanate BaTiO as shown in Fig. 5(B). ３ 6 shows the results of the comparison between the metal particles Ni and the metal particles whose surfaces are coated with barium titanate BaTiO. ３ The X-ray diffraction intensity of the metal particles Ni and the X-ray diffraction intensity of the metal particles coated with barium titanate BaTiO are shown. ３ The X-ray diffraction intensity of the coated particles was clearly different from that of the coated particles, and the latter X-ray diffraction intensity was specific to barium titanate. This also indicates that the core metal particles Ni are barium titanate BaTiO ３ It is clear that it is coated with

[0034] 7(A) to 7(D) show the results of the surface of the metal particles Cu being aluminum oxide Al ２ O ３ 7(A) and 7(B) are micrographs of coated particles and their constituent components. The outer shape of the coated particle shown in Fig. 7(A) is reflected in Fig. 7(B), which shows the Ba component in the coating, and Fig. 7(D), which shows the oxygen component in the coating. However, in Fig. 7(C), which shows the metal particle Cu component that is the core of the coated particle, the outer shape is hardly discernible. In other words, the metal particle Cu that is the core is aluminum oxide Al. ２ O ３ 8 shows the results of the comparison between the metal particles Cu and the metal particles whose surfaces are coated with aluminum oxide Al. ２ O ３The X-ray diffraction intensity of the metal particles Cu and the X-ray diffraction intensity of the metal particles Al coated with aluminum oxide are shown. ２ O ３ The X-ray diffraction intensity of the particles coated with aluminum oxide was clearly different from that of the particles coated with aluminum oxide, and the X-ray diffraction intensity of the latter was specific to aluminum oxide. ２ O ３ It is clear that it is coated with

[0035] A feature of such coated particles is that the metal oxide coating on the surface of the metal particle is a metal oxide derived from a coordination compound. Furthermore, by coating the core metal particle with a metal oxide, the coated particle is ensured to have electrical insulation.

[0036] 10...coating device, 20...dispersing device, 21...raw material tank, 22...liquid supply pump, 23...branched liquid passage, 24...pressurizing section, 25...high-pressure filter, 26...atomization chamber, 26A...branched inlet pipe, 26B...nozzle, 26C...chamber body, 26C...outlet pipe, 30...spray drying device, 31...drying chamber, 32...blower, 33...heater, 34...nozzle, 35...exhaust pipe, 36...exhaust pump, 37...recovery section, 40...heating furnace

Claims

1. A coating apparatus for coating metal particles with a metal oxide, comprising: a spray dryer that sprays a solution in which metal particles are dispersed into a heated atmosphere in the form of a mist to obtain coated particles; and a heating furnace that bakes the coated particles, wherein the solution contains a coordination compound in which metal ions are stabilized by ligands that form coordinate bonds with the metal ions, and the coordination compound contains oxygen atoms; the spray dryer produces the coated particles in which the metal particles are coated with the coordination compound; and the heating furnace converts the coordination compound of the coated particles into a metal oxide.

2. The coating apparatus according to claim 1, further comprising a dispersing device for dispersing the metal particles in the solution.

3. A coating apparatus according to claim 2, wherein the dispersion device supplies the metal particles into the solution at a high pressure of 100 MPa or more.

4. A coating apparatus according to any one of claims 1 to 3, wherein the coordination compound contains Ti and Ba as the metal ions, and the metal particles are coated with barium titanate.

5. A coating apparatus according to any one of claims 1 to 3, wherein the coordination compound contains Al as the metal ion, and the metal particles are coated with aluminum oxide.

6. A coating method comprising: preparing a solution containing a coordination compound containing oxygen atoms and stabilizing metal ions with ligands that form coordinate bonds with the metal ions, and dispersing metal particles in the solution; spraying the solution containing the dispersed metal particles in a mist form in a heated atmosphere to obtain coated particles in which the metal particles are coated with the coordination compound; and calcining the coated particles to convert the coordination compound into a metal oxide, thereby coating the metal particles with the metal oxide derived from the coordination compound.

7. A coating method according to claim 6, wherein the metal particles are supplied into the solution at a high pressure of 100 MPa or more to prepare the solution in which the metal particles are dispersed.

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