Tantalum oxide particles and method for producing tantalum oxide particles

Abstract

This invention relates to molybdenum-containing tantalum oxide particles. The tantalum oxide particles preferably have a polyhedral shape, and the grain size of the tantalum oxide particles at 2θ = 22.8° is preferably 160 nm or larger. A method for manufacturing the tantalum oxide particles is also disclosed, comprising calcining a tantalum compound in the presence of a molybdenum compound.

Description

Technical Field

[0001] This invention relates to tantalum oxide particles and a method for manufacturing tantalum oxide particles. Background Technology

[0002] Tantalum oxide possesses excellent dielectric properties, a high refractive index (2.16) in the visible light region, and exhibits very high stability against high temperatures and chemicals. Therefore, it is widely used as an electronic ceramic material, optical material, catalyst material, and electronic material, such as capacitors, dielectric materials, piezoelectric materials, etc.

[0003] For example, PTL 1 discloses the addition of an aqueous alcohol solution to an alcohol solution of tantalum alkoxide, thereby generating 1.0–1.5 μm tantalum pentoxide particles by hydrolysis of tantalum alkoxide (claims, examples, etc.).

[0004] PTL 2 discloses a method of dissolving tantalum pentoxide in alcohol, directly evaporating the solvent or evaporating the solvent after heating and reflux, and then heating the residue at 600°C to 800°C to generate tantalum pentoxide particles with an average dispersed particle size of 80 nm (claim 1, Example 7, etc.).

[0005] PTL 3 discloses a method of mixing a solution containing tantalum raw material and a surfactant with a mixed solvent of water and alcohol, reacting the tantalum raw material in the mixed solvent to form tantalum oxide / surfactant composite microparticles containing a surfactant introduced into tantalum oxide, hydrothermally treating the tantalum oxide / surfactant composite microparticles to form porous precursor microparticles, and removing the surfactant from the porous precursor microparticles, thereby generating tantalum oxide mesoporous microparticles as amorphous particles.

[0006] [List of Citations]

[0007] [Patent Literature]

[0008] [Patent Document 1]

[0009] Japanese Unexamined Patent Application Publication No. 62-91422

[0010] [Patent Document 2]

[0011] Japanese Unexamined Patent Application Publication No. 2004-311315

[0012] [Patent Document 3]

[0013] Japanese Unexamined Patent Application Publication No. 2011-136897 Summary of the Invention

[0014] The problem the invention aims to solve

[0015] However, it is difficult to synthesize tantalum oxide particles with stable control over their shape using any conventional method for manufacturing tantalum oxide microparticles.

[0016] Therefore, the object of the present invention is to provide tantalum oxide particles whose shape can be stably controlled and to provide a method for manufacturing them.

[0017] Solution for solving the problem

[0018] The present invention includes the following aspects.

[0019] [1] A tantalum oxide particle containing molybdenum.

[0020] [2] The tantalum oxide particles described in [1] above, wherein the tantalum oxide particles contain particles with a polyhedral shape.

[0021] [3] The tantalum oxide particles described in [1] or [2] above, wherein the MoO3 content (M1) relative to 100% by mass of the tantalum oxide particles, as determined by XRF analysis of the tantalum oxide particles, is 0.1% to 10.0% by mass.

[0022] [4] The tantalum oxide particles described in any one of [1] to [3] above, wherein the Ta2O5 content (T1) relative to 100% by mass of the tantalum oxide particles, as determined by XRF analysis of the tantalum oxide particles, is 85.0% to 99.9% by mass.

[0023] [5] The tantalum oxide particles described in any one of [1] to [4] above, wherein the grain size of the tantalum oxide particles at 2θ = 22.8° is 160 nm or more.

[0024] [6] The tantalum oxide particles described in any one of [1] to [5] above, wherein the grain size of the tantalum oxide particles at 2θ = 36.6° is 100 nm or more.

[0025] [7] The tantalum oxide particles described in any one of [1] to [6] above, wherein the Ta2O5 content (T2) relative to 100% by mass of the surface layer of the tantalum oxide particles, as determined by XPS surface analysis of the tantalum oxide particles, is 70.0% to 99.5% by mass, and the MoO3 content (M2) relative to 100% by mass of the surface layer of the tantalum oxide particles, as determined by XPS surface analysis of the tantalum oxide particles, is 0.5% to 30.0% by mass.

[0026] [8] The tantalum oxide particles described in any one of [1] to [7] above, wherein the surface layer of the tantalum oxide particles is selectively enriched with molybdenum.

[0027] [9] The tantalum oxide particles described in any one of [1] to [8] above, wherein the specific surface area obtained by the BET method is 10 m². 2 / g or less.

[0028]

[10] A method for manufacturing tantalum oxide particles, comprising calcining a tantalum compound in the presence of a molybdenum compound.

[0029]

[11] The method for manufacturing tantalum oxide particles described in

[10] above, wherein the molybdenum compound is molybdenum oxide.

[0030]

[12] The method for manufacturing tantalum oxide particles described in

[10] or

[11] above, wherein the maximum calcination temperature of the tantalum compound is 800℃~1600℃.

[0031]

[13] The method for manufacturing tantalum oxide particles according to any one of

[10] to

[12] above, wherein the molar ratio of molybdenum atoms in the molybdenum compound to tantalum atoms in the tantalum compound is Mo / Ta = 0.2 or more.

[0032] The effects of the invention

[0033] The present invention provides tantalum oxide particles with stable shape control and a method for manufacturing them. Attached Figure Description

[0034] [ Figure 1 ]

[0035] Figure 1 This is a SEM image of the tantalum oxide particles from Example 1.

[0036] [ Figure 2 ]

[0037] Figure 2 This is a SEM image of the tantalum oxide particles from Example 2.

[0038] [ Figure 3 ]

[0039] Figure 3 This is a SEM image of the tantalum oxide particles from Example 3.

[0040] [ Figure 4 ]

[0041] Figure 4 SEM images of tantalum oxide particles from Comparative Example 1.

[0042] [ Figure 5 ]

[0043] Figure 5 SEM images of tantalum oxide particles from Comparative Example 2.

[0044] [ Figure 6 ]

[0045] Figure 6This is a diagram showing the X-ray diffraction (XRD) patterns of tantalum oxide particles in the examples and comparative examples. Detailed Implementation

[0046] [Tantalum oxide particles]

[0047] The tantalum oxide particles according to an embodiment of the present invention are molybdenum-containing tantalum oxide particles.

[0048] The tantalum oxide particles according to embodiments of the present invention contain molybdenum. In the manufacturing method described later, by controlling the mixing amount and state of molybdenum, the particle shape can be stably controlled into a polyhedral shape, and thus the physical properties and performance of the tantalum oxide particles, such as optical properties like hue and transparency, can be arbitrarily adjusted according to the application.

[0049] In this specification, the phrase "controlling the particle shape of tantalum oxide particles" means that the manufactured tantalum oxide particles are not shapeless. The phrase "tantalum oxide particles with a controllable shape" means tantalum oxide particles with a well-defined shape.

[0050] Tantalum oxide particles according to one embodiment of the invention, manufactured by the manufacturing method according to an embodiment of the invention, as shown in the examples described below, have characteristic euhedral shapes such as cubic, prismatic, or other polyhedral shapes.

[0051] The tantalum oxide particles preferably comprise polyhedral particles. The tantalum oxide particles according to this embodiment contain molybdenum, and by controlling the amount and state of molybdenum in the manufacturing method described later, the particle shape can be stably controlled to be polyhedral.

[0052] In this specification, the term "polyhedral shape" refers to a polyhedron of six or more hexahedrons, preferably an octahedron or more, and more preferably a decahedron to an icosahedron. Polyhedral shapes include cubic shapes and prism shapes.

[0053] The MoO3 content (M1) of the tantalum oxide particles according to this embodiment, determined by XRF analysis of the tantalum oxide particles relative to 100% by mass, is preferably 0.1% to 10.0% by mass.

[0054] The MoO3 content (M1) is more preferably 0.3% to 8.0% by mass, and even more preferably 0.5% to 6.0% by mass.

[0055] The MoO3 content (M1) is a value obtained by pre-forming a MoO3 calibration curve and performing XRF (X-ray fluorescence) analysis on tantalum oxide particles to determine the MoO3 content, and is taken as the MoO3 content relative to 100% by mass of tantalum oxide particles.

[0056] The Ta₂O₅ content (T₁) of the tantalum oxide particles according to this embodiment, determined by XRF analysis of the tantalum oxide particles, is preferably 85.0% to 99.9% by mass relative to 100% by mass of the tantalum oxide particles.

[0057] The Ta2O5 content (T1) is more preferably 87.0% to 99.7% by mass, and even more preferably 89.0% to 99.5% by mass.

[0058] The Ta2O5 content (T1) is a value obtained by pre-forming a Ta2O5 calibration curve and performing XRF (X-ray fluorescence) analysis on tantalum oxide particles to determine the Ta2O5 content, which is taken as the Ta2O5 content relative to 100% by mass of tantalum oxide particles.

[0059] The tantalum oxide particles according to this embodiment preferably have a grain size of 160 nm or more at 2θ = 22.8°. The polyhedral tantalum oxide particles according to this embodiment have a grain size of 160 nm or more at 2θ = 22.8°, thus maintaining high crystallinity and allowing for easy control of the average grain size and narrow grain size distribution.

[0060] In this specification, the grain size of tantalum oxide particles at 2θ = 22.8° is calculated using the Scherrer equation from the half-width of the peak appearing at 2θ = 22.8° ± 0.2° in X-ray diffraction (XRD) measurements.

[0061] The tantalum oxide particles according to this embodiment have a grain size of 180 nm or more at 2θ = 22.8°, more preferably 200 nm or more, and particularly preferably 210 nm or more. The tantalum oxide particles according to this embodiment may have a grain size of 800 nm or less, 600 nm or less, 500 nm or less, or 400 nm or less. The tantalum oxide particles according to this embodiment may have a grain size of 160 nm or more and 800 nm or less, preferably 180 nm or more and 600 nm or less, more preferably 200 nm or more and 500 nm or less, and even more preferably 210 nm or more and 400 nm or less.

[0062] The grain size of the tantalum oxide particles according to this embodiment at 2θ = 36.6° is preferably 100 nm or more, more preferably 120 nm or more, and even more preferably 140 nm or more. The grain size of the tantalum oxide particles according to this embodiment at 2θ = 36.6° can be 600 nm or less, 550 nm or less, or 500 nm or less. The grain size of the tantalum oxide particles according to this embodiment at 2θ = 36.6° is preferably 100 nm or more and 600 nm or less, more preferably 120 nm or more and 550 nm or less, and even more preferably 140 nm or more and 500 nm or less.

[0063] In this specification, the grain size of tantalum oxide particles at 2θ = 36.6° is calculated using the Scherrer equation from the half-width of the peak appearing at 2θ = 36.6° ± 0.2° in X-ray diffraction (XRD) measurements.

[0064] According to this embodiment, the polyhedral tantalum oxide particles have a grain size of more than 160 nm at 2θ = 22.8° and a grain size of more than 100 nm at 2θ = 36.6°, thereby maintaining high crystallinity, making it easy to control the average particle size, and making it easy to control the particle size distribution to be narrow.

[0065] According to this embodiment, the Ta2O5 content (T2) of the tantalum oxide particles, determined by XPS surface analysis of the tantalum oxide particles relative to 100% by mass of the surface layer of the tantalum oxide particles, is preferably 70.0% to 99.5% by mass, and the MoO3 content (M2) of the tantalum oxide particles, determined by XPS surface analysis of the tantalum oxide particles relative to 100% by mass of the surface layer of the tantalum oxide particles, is 0.5% to 30.0% by mass.

[0066] The Ta2O5 content (T2) represents the Ta2O5 content obtained by XPS surface analysis of tantalum oxide particles using X-ray photoelectron spectroscopy (XPS) to determine the presence ratio (atomic %) of each element and calculating the tantalum content as oxide, which is the value obtained as the Ta2O5 content relative to 100 mass% of the surface layer of the tantalum oxide particles.

[0067] The MoO3 content (M2) represents the MoO3 content obtained by XPS surface analysis of tantalum oxide particles using X-ray photoelectron spectroscopy (XPS) to obtain the presence ratio (atomic %) of each element and calculating the molybdenum content as oxide, which is the value obtained as the MoO3 content relative to 100 mass% of the surface layer of the tantalum oxide particles.

[0068] Here, the term "surface" refers to a distance of within 10 nm from the surface of each tantalum oxide particle according to this embodiment. This distance corresponds to the detection depth of the XPS measured in the examples.

[0069] Here, the expression "surface rich" indicates a state in which the mass of molybdenum or molybdenum compound per unit volume in the surface layer is greater than the mass of molybdenum or molybdenum compound per unit volume in the parts other than the surface layer.

[0070] The tantalum oxide particles according to this embodiment contain molybdenum selectively enriched in the surface layer of the tantalum oxide particles. When the MoO3 content (M2) relative to the surface layer of the tantalum oxide particles, obtained by XPS surface analysis of the tantalum oxide particles, is higher than the MoO3 content (M1) relative to the surface layer of the tantalum oxide particles, obtained by XRF analysis of the tantalum oxide particles, it can be confirmed that the surface layer of the tantalum oxide particles is selectively enriched with molybdenum.

[0071] The surface enrichment ratio (M2 / M1) of the MoO3 content (M2) relative to 100% by mass of the surface layer of tantalum oxide particles, obtained by XPS surface analysis of tantalum oxide particles, relative to the MoO3 content (M1) relative to 100% by mass of tantalum oxide particles, obtained by XRF analysis of tantalum oxide particles, is preferably greater than 1, more preferably 1.01 to 8.0, even more preferably 1.03 to 6.0, and particularly preferably 1.05 to 4.0.

[0072] According to this embodiment, the specific surface area of ​​the tantalum oxide particles, calculated by the BET method, can be 10 m². 2 / g or less, 5m 2 / g or less, 1m 2 / g or less or 0.6m 2 / g or less.

[0073] The specific surface area of ​​the tantalum oxide particles according to this embodiment, determined by the BET method, can range from 0.01 to 10 m². 2 / g, 0.03~5m 2 / g, 0.06~1m 2 / g or 0.1~0.6m 2 Within the range of / g.

[0074] According to this embodiment, the average particle size of the primary particles of tantalum oxide particles can be 2–1000 μm, 3–500 μm, 4–400 μm, or 5–200 μm.

[0075] The average primary particle size of tantalum oxide particles is represented by the average primary particle size of at least 50 primary particles when tantalum oxide particles are photographed by scanning electron microscopy (SEM). The major axis (Ferret diameter of the longest observed portion) and minor axis (short Ferret diameter in the direction perpendicular to the Ferret diameter of the longest portion) of the smallest unit particle constituting the aggregate (i.e., the primary particle) are determined in a two-dimensional image, and their average is taken as the primary particle size.

[0076] The tantalum oxide particles according to this embodiment can be provided as aggregates of tantalum oxide particles, and the values ​​obtained by using the aggregates as samples can be used as values ​​for MoO3 content, Ta2O5 content, and specific surface area.

[0077] The tantalum oxide particles according to this embodiment can be manufactured, for example, by the "method for manufacturing tantalum oxide particles" described later.

[0078] The tantalum oxide particles of the present invention are not limited to those manufactured by the method for manufacturing tantalum oxide particles according to the embodiments described below.

[0079] The tantalum oxide particles according to this embodiment can provide properties that combine those of tantalum oxide and molybdenum, which is very useful.

[0080] [Manufacturing method of tantalum oxide particles]

[0081] The manufacturing method according to this embodiment is a method for manufacturing the above-mentioned tantalum oxide particles, and includes calcining the tantalum compound in the presence of a molybdenum compound.

[0082] The method for manufacturing tantalum oxide particles according to this embodiment can manufacture molybdenum-containing tantalum oxide particles according to the above-described embodiment of the present invention.

[0083] The method for manufacturing tantalum oxide particles according to this embodiment includes calcining a tantalum compound in the presence of a molybdenum compound. Therefore, this method can stably control the particle shape, increase the grain size of the tantalum oxide particles, allow the tantalum oxide particles to have a polyhedral shape, reduce the aggregation of the tantalum oxide particles, and improve the dispersibility of the tantalum oxide particles.

[0084] A preferred method for manufacturing tantalum oxide particles includes the steps of mixing a tantalum compound with a molybdenum compound to form a mixture (mixing step) and calcining the mixture (calcination step).

[0085] [Mixed Steps]

[0086] The mixing step involves mixing a tantalum compound with a molybdenum compound to form a mixture. The contents of the mixture are described below.

[0087] [Tantalum compound]

[0088] The tantalum compound is not limited, as long as it can be converted into tantalum oxide by calcination. The tantalum compound can be tantalum oxide (α-Ta₂O₅, β-Ta₂O₅, γ-Ta₂O₅, δ-Ta₂O₅, TaO₂, TaO, etc.), tantalum hydroxide (Ta(OH)₅), or tantalum halide (TaCl₅, TaBr₅, etc.), but is not limited to these. Tantalum oxide is preferred.

[0089] [Molybdenum compounds]

[0090] Examples of molybdenum compounds include molybdenum oxide, molybdenum sulfide, molybdic acid, etc.

[0091] Examples of molybdenum oxides include molybdenum dioxide, molybdenum trioxide, etc., with molybdenum trioxide being preferred.

[0092] The method for manufacturing tantalum oxide particles according to this embodiment uses a molybdenum compound as a flux. In this specification, the manufacturing method using a molybdenum compound as a flux can be simply referred to as the "flux method." Furthermore, the molybdenum compound reacts with a tantalum compound at high temperature through calcination to form tantalum molybdate. Then, when the tantalum molybdate further decomposes into tantalum oxide and molybdenum oxide at an even higher temperature, it is believed that the molybdenum compound is absorbed into the tantalum oxide particles. The molybdenum oxide is removed from the system by sublimation, and during this process, it is believed that the molybdenum compound reacts with the tantalum compound to form a molybdenum compound on the surface of the tantalum oxide particles. More specifically, regarding the mechanism of the formation of the molybdenum compound contained in the tantalum oxide particles, it is believed that Mo-O-Ta is formed through the reaction of molybdenum with Ta atoms in the surface of the tantalum oxide particles. High-temperature calcination causes Mo desorption, and simultaneously, molybdenum oxide or compounds with Mo-O-Ta bonds are formed on the surface of the tantalum oxide particles.

[0093] Molybdenum oxide that is not absorbed into tantalum oxide particles can be recovered through sublimation or reused. This reduces the amount of molybdenum oxide adhering to the surface of tantalum oxide particles and maximizes the original properties of the tantalum oxide particles.

[0094] In this invention, the material that has sublimation properties in the manufacturing method described later is called a "flux".

[0095] In the method for manufacturing tantalum oxide particles according to this embodiment, the molar ratio of molybdenum atoms in the molybdenum compound to tantalum atoms in the tantalum compound is preferably Mo / Ta = 0.2 or more, more preferably 0.4 or more, even more preferably 0.6 or more, and particularly preferably 0.8 or more.

[0096] The upper limit of the molar ratio of molybdenum atoms in a molybdenum compound to tantalum atoms in a tantalum compound can be appropriately determined. From the viewpoint of reducing the amount of molybdenum compound used and improving production efficiency, this molar ratio can be, for example, Mo / Ta = 14 or less, 12 or less, 10 or less, or 9 or less.

[0097] Examples of numerical ranges for the molar ratio of molybdenum atoms in a molybdenum compound to tantalum atoms in a tantalum compound include, for example, Mo / Ta = 0.2 to 14, more preferably 0.4 to 12, even more preferably 0.6 to 10, and particularly preferably 0.8 to 9.

[0098] With increasing molybdenum content relative to tantalum, the average particle size of the primary tantalum oxide particles tends to increase.

[0099] In the method for manufacturing tantalum oxide particles according to this embodiment, the mixing amounts of tantalum compound and molybdenum compound are not particularly limited. However, preferably, the mixture can be prepared by mixing 35% or more of tantalum compound with 65% or less of molybdenum compound relative to 100% by mass of the mixture, and then the mixture can be calcined. More preferably, the mixture can be prepared by mixing 40% or more and 99% or less of tantalum compound with 1% or more and 60% or less of molybdenum compound relative to 100% by mass of the mixture, and then the mixture can be calcined. Even more preferably, the mixture can be prepared by mixing 45% or more and 98% or less of tantalum compound with 2% or more and 55% or less of molybdenum compound relative to 100% by mass of the mixture, and then the mixture can be calcined.

[0100] By using the compounds within the above range, the amount of molybdenum compound contained in the obtained tantalum oxide particles can be made more suitable, a polyhedral shape can be formed well, and tantalum oxide particles with a grain size of 160 nm or more at 2θ = 22.8° can be manufactured.

[0101] [Calcination Steps]

[0102] The calcination step is the step of calcining the mixture. Tantalum oxide particles according to embodiments of the present invention can be manufactured by calcining this mixture. As described above, this manufacturing method is called the "flux method".

[0103] Flux methods are classified as solution methods. More specifically, flux methods are crystal growth methods that utilize a crystal-flux binary phase diagram representing the eutectic form. The mechanism of flux methods is based on the following assumptions: when a mixture of solute and flux is heated, both the solute and flux become liquid phases. In this case, the flux acts as a fusing agent; in other words, the solute-flux binary phase diagram indicates a eutectic form, thus the solute melts at a temperature below its melting point, forming a liquid phase. In this state, the evaporation of the flux lowers its concentration, thus reducing the effect of lowering the melting point of the solute by the flux, and crystal growth of the solute occurs driven by the evaporation of the flux (flux evaporation method). Crystal growth of the solute can also be induced by cooling the liquid phase of the solute and flux (slow cooling method).

[0104] The advantages of the flux method are that crystal growth can be carried out at temperatures far below the melting point, the crystal structure can be precisely controlled, and polyhedral crystals with euhedral shapes can be formed.

[0105] The mechanism for manufacturing tantalum oxide particles using a fluxing method with molybdenum compounds as fluxes is not entirely clear, but a hypothetical mechanism is as follows: When tantalum compounds are calcined in the presence of molybdenum compounds, tantalum molybdate is first formed. In this case, as described above, tantalum molybdate induces crystal growth of tantalum oxide at temperatures below its melting point. Then, tantalum molybdate is decomposed, for example, by evaporating the flux, and tantalum oxide particles can be manufactured through crystal growth. That is, the molybdenum compound acts as a flux, and tantalum oxide particles are manufactured through tantalum molybdate as an intermediate.

[0106] The flux method can produce tantalum oxide particles with a polyhedral shape containing molybdenum.

[0107] The calcination method is not particularly limited and can be carried out using well-known and commonly used methods. When the calcination temperature exceeds 650°C, the tantalum compound reacts with the molybdenum compound to form tantalum molybdate. Furthermore, when the calcination temperature becomes above 800°C, tantalum molybdate decomposes to form tantalum oxide particles. Additionally, within the tantalum oxide particles, when tantalum molybdate decomposes into tantalum oxide and molybdenum oxide, it is believed that molybdenum compounds are absorbed into the tantalum oxide particles.

[0108] Furthermore, the state of the tantalum and molybdenum compounds during calcination is not particularly limited, as long as the molybdenum and tantalum compounds exist in the same space that allows for their reaction. Specifically, the powders of the molybdenum and tantalum compounds can be simply mixed together, either mechanically using a pulverizer or by using a mortar and pestle, and can be mixed in either a dry or moist state.

[0109] The calcination temperature is not particularly limited and is appropriately determined based on the expected average particle size of the tantalum oxide particles, the formation and dispersibility of molybdenum compounds in the tantalum oxide particles, etc. Regarding the calcination temperature, the highest calcination temperature is close to the decomposition temperature of tantalum molybdate, preferably 800°C or higher, and more preferably 900°C or higher.

[0110] Generally, in order to control the shape of tantalum oxide obtained after calcination, it is necessary to calcine at a high temperature of over 1500°C, close to the melting point of tantalum oxide. However, from the perspective of the load on the combustion furnace and fuel cost, this poses a significant problem for industrial use.

[0111] The manufacturing method of the present invention can be carried out even at high temperatures such as above 1500°C, but even at temperatures below 1300°C, which are far below the melting point of tantalum oxide, and can form polyhedral tantalum oxide particles with large grain sizes at 2θ = 22.8° and 2θ = 36.6°, regardless of the shape of the precursor.

[0112] According to embodiments of the present invention, even at the highest calcination temperature of 800°C to 1600°C, polyhedral tantalum oxide particles with large grain sizes at 2θ = 22.8° and 2θ = 36.6° can be formed efficiently and at low cost. More preferably, calcination is carried out at a highest calcination temperature of 850°C to 1500°C, and most preferably at a highest calcination temperature in the range of 900°C to 1400°C.

[0113] From the viewpoint of production efficiency and from the viewpoint of avoiding damage to the loading container (crucible or sagger) due to rapid thermal expansion, the heating rate is preferably 1 to 30°C / min, more preferably 2 to 20°C / min, and even more preferably 3 to 10°C / min.

[0114] Regarding the calcination time, preferably, the time for the temperature to rise to the predetermined maximum calcination temperature is in the range of 15 minutes to 10 hours, and the holding time after reaching the predetermined maximum calcination temperature is in the range of 1 to 30 hours. In order to effectively form tantalum oxide particles, the holding time at the maximum calcination temperature is more preferably about 2 to 15 hours.

[0115] By selecting conditions including a maximum calcination temperature of 800℃ to 1600℃ and a holding time of the maximum calcination temperature of 2 to 15 hours, it is possible to easily manufacture molybdenum-containing polyhedral tantalum oxide particles that are difficult to aggregate.

[0116] The calcination atmosphere is not particularly limited, as long as it can achieve the effect of the present invention. For example, an oxygen-containing atmosphere such as air or oxygen is preferred, or an inert atmosphere such as nitrogen, argon, or carbon dioxide is preferred. Considering cost, an air atmosphere is preferred.

[0117] There are no inherent limitations on the equipment used for calcination; a so-called calcination furnace can be used. The calcination furnace is preferably constructed of a material that does not react with sublimated molybdenum oxide. Furthermore, for the efficient use of molybdenum oxide, a calcination furnace with high sealing performance is preferred.

[0118] This reduces the amount of molybdenum compounds adhering to the surface of tantalum oxide particles and maximizes the original properties of the tantalum oxide particles.

[0119] [Molybdenum Removal Steps]

[0120] The method for manufacturing tantalum oxide particles according to this embodiment may further include a molybdenum removal step after the calcination step, whereby at least a portion of the molybdenum is removed as needed.

[0121] As mentioned above, molybdenum is related to sublimation during calcination. Therefore, by controlling the calcination time, calcination temperature, etc., the amount of molybdenum oxide present on the surface of tantalum oxide particles can be controlled, as well as the content and state of molybdenum oxide present in the part other than the surface of tantalum oxide particles (inner layer).

[0122] Molybdenum can adhere to the surface of tantalum oxide particles. As a method other than sublimation, molybdenum can be removed by washing with water, ammonia solution, sodium hydroxide solution, or acid solution. Alternatively, while it is possible not to remove molybdenum from the tantalum oxide particles, it is preferable to remove it at least from the surface, because in cases such as when used by dispersing in a dispersion medium based on any type of binder, the original properties of tantalum oxide can be fully exhibited, and the presence of molybdenum on the surface does not cause inconvenience.

[0123] In this case, the molybdenum oxide content can be controlled by appropriately changing the concentration and amount of water, ammonia solution, sodium hydroxide solution or acid solution used, the washing process, washing time, etc.

[0124] [Grinding Steps]

[0125] Due to the aggregation of tantalum oxide particles, the calcined product produced by the calcination step may not meet the preferred particle size range of the present invention. Therefore, if necessary, the tantalum oxide particles can be ground to meet the preferred particle size range of the present invention.

[0126] There are no particular limitations on the grinding method for calcined products. Commonly known grinding methods such as ball mills, jaw crushers, jet mills, disc mills, spectro mills, grinding mills, and mixer mills can be used.

[0127] [Grading Steps]

[0128] To improve powder flowability by adjusting the average particle size, or to suppress viscosity increase when mixed with binders used to form the matrix, it is preferable to classify tantalum oxide particles. "Classification" refers to the operation of grouping particles according to particle size.

[0129] Classification can be wet or dry, but dry classification is preferred from a productivity standpoint. Examples of dry classification include classification using sieves and airflow classification based on the difference between centrifugal force and fluid resistance. From the perspective of classification accuracy, airflow classification is preferred and can be performed using classifiers such as airflow classifiers, vortex airflow classifiers, forced vortex centrifugal classifiers, and semi-free vortex centrifugal classifiers.

[0130] The grinding and classification steps can be performed at necessary stages. For example, the average particle size of the resulting tantalum oxide particles can be adjusted by the presence or absence of grinding and classification and by selecting their conditions.

[0131] From the viewpoint that the tantalum oxide particles of the present invention, or the tantalum oxide particles manufactured by the manufacturing method of the present invention, can easily exhibit their original properties when used in a dispersion medium, have excellent operability, and superior dispersibility, they are preferably less or non-agglomerated. The manufacturing method of the tantalum oxide particles is preferably one that produces tantalum oxide particles with less or no agglomeration without performing grinding and classification steps. Because the aforementioned grinding and classification steps are unnecessary, tantalum oxide particles with the desired superior properties can be manufactured with high productivity.

[0132] [Example]

[0133] The present invention will be further described in detail below with reference to illustrated embodiments, but the present invention is not limited to these embodiments.

[0134] (Comparative Example 1)

[0135] Tantalum oxide (manufactured by Aladdin Co., Ltd. (China), Ta2O5) was used in the tantalum oxide particles of Comparative Example 1. Figure 4 SEM images of tantalum oxide particles from Comparative Example 1 are shown. The particles are amorphous.

[0136] (Comparative Example 2)

[0137] [Manufacturing of tantalum oxide particles]

[0138] Take 10.0g of tantalum oxide (manufactured by Aladdin Co., Ltd. (China), Ta2O5) from the container, place it in an alumina-based oven, and then heat-treat it under the following conditions.

[0139] [Heat Treatment]

[0140] Using a heating furnace SC-2045D-SP manufactured by Motoyama Co., Ltd., the temperature was increased from room temperature to 1100°C at a rate of approximately 5°C / minute, held at 1100°C for 24 hours, and then cooled.

[0141] Figure 5 SEM images of the tantalum oxide particles obtained in Comparative Example 2 are shown. It can be confirmed that the particle size of the tantalum oxide particles in Comparative Example 2 increases due to particle growth compared to those in Comparative Example 1. Furthermore, poor dispersibility and aggregation were observed. The shape of the amorphous particles remained unchanged.

[0142] [Example 1]

[0143] [Manufacturing of tantalum oxide particles]

[0144] In a mortar, 10.0 g of tantalum oxide (manufactured by Aladdin Co., Ltd. (China), Ta₂O₅) and 0.5 g of molybdenum trioxide (Chengdu Hongbo Industrial Co., Ltd. (China), MoO₃) were mixed to prepare a mixture. The resulting mixture was placed in a crucible and calcined in a ceramic furnace at 1100 °C for 24 hours. After cooling, the crucible was removed from the ceramic furnace, yielding 10.2 g of light pink powder.

[0145] Then, 9.5 g of the obtained powder was dispersed in 100 mL of 0.5% ammonia water, and the dispersion was stirred at room temperature (25℃~30℃) for 3 hours, and then filtered to remove the ammonia water. The residue was washed with water and dried to remove the molybdenum residue on the particle surface, thereby producing a light pink powder of 9.4 g of tantalum oxide particles.

[0146] Figure 1 SEM images of the tantalum oxide particles obtained in Example 1 are shown. The tantalum oxide particles exhibit a polyhedral shape approaching a cubic shape. No significant aggregation was observed in the tantalum oxide particles of Example 1, and the dispersion of the tantalum oxide particles was good compared to Comparative Examples 1 and 2.

[0147] [Example 2]

[0148] [Manufacturing of tantalum oxide particles]

[0149] Except that the reagent amounts of the raw materials were changed to 10.0 g of tantalum oxide (manufactured by Aladdin Co., Ltd. (China), Ta2O5) and 2.0 g of molybdenum trioxide (Chengdu Hongbo Industrial Co., Ltd. (China), MoO3) in Example 1, a light pink powder of tantalum oxide particles was produced by the same method as in Example 1.

[0150] Figure 2 SEM images of the tantalum oxide particles obtained in Example 2 are shown. The tantalum oxide particles exhibit a polyhedral shape. No significant aggregation was observed in the tantalum oxide particles of Example 2, and the dispersion of the tantalum oxide particles was good compared to Comparative Examples 1 and 2.

[0151] [Example 3]

[0152] [Manufacturing of tantalum oxide particles]

[0153] Except that the reagent amounts of the raw materials were changed to 10.0 g of tantalum oxide (manufactured by Aladdin Co., Ltd. (China), Ta2O5) and 10.0 g of molybdenum trioxide (Chengdu Hongbo Industrial Co., Ltd. (China), MoO3) in Example 1, a light pink powder of tantalum oxide particles was produced by the same method as in Example 1.

[0154] Figure 3 SEM images of the tantalum oxide particles obtained in Example 3 are shown. The tantalum oxide particles exhibit a polyhedral shape approaching a prism shape. No significant aggregation was observed in the tantalum oxide particles of Example 3, and the dispersion of the tantalum oxide particles was good compared to Comparative Examples 1 and 2.

[0155] [Determination of the average particle size of primary tantalum oxide particles]

[0156] Tantalum oxide particles were photographed using a scanning electron microscope (SEM). The major axis (Ferret diameter of the longest observed portion) and minor axis (short Ferret diameter in the direction perpendicular to the Ferret diameter of the longest portion) of the smallest unit particles constituting the aggregates (i.e., primary particles) were measured in the two-dimensional images, and their average value was considered the primary particle size. The same procedure was performed on 50 primary particles with measurable major and minor axes, and the average particle size of the primary particles was calculated from the average of the primary particle sizes. The results are shown in Table 1.

[0157] [Grain size determination]

[0158] Powder X-ray diffraction (2θ / θ method) measurements were performed using an X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation) equipped with a high-intensity, high-resolution crystallography (CALSA) detector under the following measurement conditions. Analysis was performed using the CALSA function of analysis software (PDXL) manufactured by Rigaku Corporation, and the grain size at 2θ = 22.8° was calculated using the Scherrer equation from the half-width of the peak appearing at 2θ = 22.8°, and the grain size at 2θ = 36.6° was calculated using the Scherrer equation from the half-width of the peak appearing at 2θ = 36.6°. However, in Example 3, no peaks with a definite half-width were detected at 2θ = 22.8° and 2θ = 36.6°. The results are shown in Table 1.

[0159] [Determination conditions for powder X-ray diffraction]

[0160] Tube voltage: 45kV

[0161] Tube current: 200mA

[0162] Scanning speed: 0.05° / min

[0163] Scanning range: 10°~70°

[0164] Step: 0.002°

[0165] βs: 20 rpm

[0166] Standard width of the device: 0.026° calculated using standard silicon powder (NIST, 640d) prepared by the National Institute of Standards and Technology (NIST).

[0167] [Crystal Structure Analysis: XRD (X-ray Diffraction) Method]

[0168] Samples of tantalum oxide particles from Examples 1-3 and Comparative Examples 1 and 2 were filled into a sample holder with a depth of 0.5 mm and placed in a wide-angle X-ray diffractometer (XRD) (manufactured by Rigaku Corporation, Ultima IV). XRD measurements were performed under conditions including Cu / Kα lines, 40 kV / 40 mA, a scan rate of 2° / min, and a scan range of 10° to 70°. The MoO3 and Ta2O5 contents were determined as the MoO3 and Ta2O5 contents relative to 100% by mass of the tantalum oxide particles using previously established MoO3 and Ta2O5 calibration curves. Figure 6 The XRD results of tantalum oxide particles from Examples 1-3 and Comparative Examples 1 and 2 are shown.

[0169] For the tantalum oxide particles of Examples 1 and 2 and Comparative Examples 1 and 2, crystallization peaks originating from tantalum oxide were observed at 2θ = 22.8° and 2θ = 36.6°. For the tantalum oxide particles of Example 3, crystallization peaks originating from tantalum oxide were observed near 2θ = 17.5° and 2θ = 25.3°.

[0170] [Determination of the specific surface area of ​​tantalum oxide particles]

[0171] The specific surface area of ​​tantalum oxide particles was determined using a specific surface area meter (BELSORP-mini, manufactured by MicrotracBEL Corp.). The surface area per 1g of sample, as determined by the nitrogen adsorption capacity using the BET method, was calculated as the specific surface area (m²). 2 / g). The results are shown in Table 1.

[0172] [Determination of purity of tantalum oxide particles: XRF (X-ray fluorescence) analysis]

[0173] Approximately 70 mg of tantalum oxide particles were placed on filter paper, covered with a PP film, and analyzed by XRF (X-ray fluorescence) using a Primus IV X-ray fluorescence analyzer (manufactured by Rigaku Corporation) under the following conditions.

[0174] Measurement conditions

[0175] EZ scan mode

[0176] Measuring elements: F~U

[0177] Measurement time: standard

[0178] Diameter measured: 10mm

[0179] Balance (Balance Components): None

[0180] Table 1 shows the results of XRF analysis for the Ta2O5 content (T1) and MoO3 content (M1) relative to 100% by mass of tantalum oxide particles.

[0181] [XPS Surface Analysis]

[0182] In the surface elemental analysis of tantalum oxide particles, a QUANTERA SXM and monochromatic Al-Kα line manufactured by ULVAC-PHI, Inc. were used as the X-ray source. The atomic content of each element in the surface layer was determined by X-ray photoelectron spectroscopy (XPS) under the following conditions.

[0183] X-ray source: monochromatic Al-Kα, beam diameter 100μmφ, output 25W

[0184] Measurement: Area measurement (1000 μm square), n = 3

[0185] Charge correction: C1s = 284.8 eV

[0186] To facilitate comparison with XRF results, the Ta₂O₅ content (T₂) (mass%) relative to 100% mass of the surface layer of tantalum oxide particles and the MoO₃ content (M₂) (mass%) relative to 100% mass of the surface layer of tantalum oxide particles were determined by measuring the tantalum and molybdenum content in the surface layer of the tantalum oxide particles as oxides. The results are shown in Table 1.

[0187] Therefore, the surface enrichment ratio (M2 / M1) of the MoO3 content (M2) obtained by XPS surface analysis of tantalum oxide particles and the MoO3 content (M1) obtained by XRF analysis of tantalum oxide particles was determined. The results are shown in Table 1.

[0188] The tantalum oxide particles in Examples 1-3 are polyhedral tantalum oxide particles containing molybdenum, which have a controlled shape that differs from that of ordinary tantalum oxide particles, and have lower aggregation and relatively larger grain size compared to those of ordinary tantalum oxide particles.

[0189] For the tantalum oxide particles of Examples 1-3, the MoO3 content (M2) relative to the surface layer of the tantalum oxide particles, obtained by XPS surface analysis, is higher than the MoO3 content (M1) relative to the surface layer of the tantalum oxide particles, obtained by XRF analysis. Therefore, it can be confirmed that the surface layer of the tantalum oxide particles is selectively enriched with molybdenum.

[0190] The tantalum oxide particles in Examples 1-3 contain molybdenum on their surface, and therefore can be expected to perform various functions of molybdenum.

[0191] Each configuration and combination thereof according to each embodiment is merely an example, and configurations may be added, deleted, substituted, and other changes may be made without departing from the spirit of the invention. Furthermore, the invention is not limited to the embodiments, but only to the scope of the claims.

[0192] Industrial availability

[0193] The tantalum oxide particles of the present invention are intended to be used as electronic ceramic materials such as capacitors, dielectric materials, piezoelectric materials, optical materials, catalyst materials, electronic materials, and functional fillers.

[0194] [Table 1]

[0195]

Claims

1. A tantalum oxide particle comprising molybdenum, The MoO3 content M1, determined by XRF analysis of the tantalum oxide particles, is 0.1% to 10.0% by mass relative to 100% by mass of the tantalum oxide particles. The average particle size of the primary particles of the tantalum oxide particles is 2–1000 μm. The tantalum oxide particles contain polyhedral particles.

2. The tantalum oxide particles according to claim 1, wherein the Ta₂O₅ content T₁ relative to 100% by mass of the tantalum oxide particles, as determined by XRF analysis of the tantalum oxide particles, is 85.0% to 99.9% by mass.

3. The tantalum oxide particles according to claim 1, wherein the grain size of the tantalum oxide particles is greater than 160 nm, calculated by using the Scherrer equation from the half-width of the peak appearing at 2θ = 22.8° ± 0.2° in X-ray diffraction.

4. The tantalum oxide particles according to claim 1, wherein the grain size of the tantalum oxide particles is greater than 100 nm, calculated by using the Scherrer equation from the half-width of the peak appearing at 2θ = 36.6° ± 0.2° in X-ray diffraction.

5. The tantalum oxide particles according to claim 1, wherein the Ta2O5 content T2 relative to 100% by mass of the surface layer of the tantalum oxide particles, as determined by XPS surface analysis of the tantalum oxide particles, is 70.0% to 99.5% by mass, and the MoO3 content M2 relative to 100% by mass of the surface layer of the tantalum oxide particles, as determined by XPS surface analysis of the tantalum oxide particles, is 0.5% to 30.0% by mass.

6. The tantalum oxide particles according to claim 1, wherein the surface richness ratio M2 / M1, which is the surface richness of 100% by mass of the surface layer of the tantalum oxide particles as determined by XPS surface analysis of the tantalum oxide particles, is greater than 1 relative to the surface richness of 100% by mass of the tantalum oxide particles as determined by XRF analysis of the tantalum oxide particles.

7. The tantalum oxide particle according to claim 1, wherein the specific surface area is 10 m2 / g or less as measured by the BET method. 2 / g or less as measured by the BET method.

8. A method for manufacturing tantalum oxide particles, comprising calcining a tantalum compound in the presence of a molybdenum compound. The average particle size of the primary particles of the tantalum oxide particles is 2–1000 μm. The MoO3 content M1, relative to 100% by mass of the tantalum oxide particles, determined by XRF analysis, is 0.1% to 10.0% by mass.

9. The method for manufacturing tantalum oxide particles according to claim 8, wherein the molybdenum compound is molybdenum oxide.

10. The method for manufacturing tantalum oxide particles according to claim 8, wherein the calcination temperature of the tantalum compound is 800°C to 1600°C.

11. The method for manufacturing tantalum oxide particles according to claim 8, wherein the molar ratio of molybdenum atoms in the molybdenum compound to tantalum atoms in the tantalum compound is Mo / Ta = 0.2 or higher.

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