Niobium oxide particles and method for producing niobium oxide particles

Abstract

Provided are niobium oxide particles having a controllable crystal shape and exhibiting excellent properties. The niobium oxide particles contain molybdenum. The niobium oxide particles preferably have a polyhedral, columnar or needle-like shape. The MoO3 content (M1) of the niobium oxide particles, relative to 100 mass% of the niobium oxide particles, as determined by XRF analysis, is preferably 0.1 to 40 mass%. The method for producing the above-described niobium oxide particles includes calcining a niobium compound in the presence of a molybdenum compound.

Description

Technical Field

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

[0002] Niobium oxide possesses excellent properties, such as dielectric properties, solid acidity, and high refractive index, and also exhibits very high stability to chemicals and other materials. Therefore, it has been found to have a wide range of applications, such as as electronic ceramic materials, heat-resistant alloy materials, optical glass materials, catalyst materials, and electronic materials, including capacitors, dielectric materials, and piezoelectric materials.

[0003] PTL 1 discloses a method for manufacturing niobium oxide microparticles, wherein niobium chloride is volatilized at a temperature of 170–240°C, and water vapor is added to the raw material gas stream of the resulting niobium chloride vapor to hydrolyze the niobium chloride, thereby obtaining niobium oxide microparticles with a particle size of no more than 1.0 μm in the gas stream.

[0004] PTL 2 discloses a method for manufacturing niobium oxide sol, wherein citric acid is added to niobium oxide sol stabilized by oxalic acid, then an aqueous ammonia solution is added to adjust the pH to 7-10, and then the oxalic acid is removed.

[0005] PTL 3 discloses a method for manufacturing tantalum oxide and / or niobium oxide, wherein an alkaline aqueous solution is added to an aqueous solution of tantalum fluoride salt and / or niobium fluoride salt to form tantalum hydroxide and / or niobium hydroxide, and then the tantalum hydroxide and / or niobium hydroxide are calcined to form tantalum oxide and / or niobium oxide having a needle-like or columnar crystal shape.

[0006] [List of Citations]

[0007] [Patent Literature]

[0008] [PTL 1]

[0009] Japanese Unexamined Patent Application Publication No. 2003-267728

[0010] [PTL 2]

[0011] Japanese Unexamined Patent Application Publication No. 2005-200235

[0012] [PTL 3]

[0013] Japanese Unexamined Patent Application Publication No. 2005-255454 Summary of the Invention

[0014] The problem the invention aims to solve

[0015] Controlling the crystal shape of niobium oxide particles broadens their versatility, making it a particularly important technique. Unfortunately, the methods disclosed in PTL 2 and PTL 3 are specialized solution methods that are complex to implement. The method disclosed in PTL 1 may be difficult to control the particle shape.

[0016] This invention was made to overcome the aforementioned problems. Therefore, the object of this invention is to provide niobium oxide particles with a controllable crystal shape and exhibiting excellent properties.

[0017] Solution for solving the problem

[0018] The inventors conducted extensive research to achieve the above objectives, and thus discovered that using a molybdenum compound as a flux helps control the crystal shape of the produced niobium oxide particles, and further discovered that the niobium oxide particles produced in this way contain molybdenum. Based on these findings, the present invention has been completed.

[0019] Specifically, aspects of the present invention include the following.

[0020] (1) A niobium oxide particle containing molybdenum.

[0021] (2) Niobium oxide particles as described in (1), wherein the major diameter is 0.1 to 300 μm.

[0022] (3) Niobium oxide particles as described in (1) or (2) having a polyhedral, columnar or needle-like shape.

[0023] (4) Niobium oxide particles as described in any one of (1) to (3), wherein the aspect ratio expressed as major diameter / minor diameter is not less than 2.

[0024] (5) Niobium oxide particles as described in any one of (1) to (4), wherein the MoO3 content (M1) of the niobium oxide particles, as determined by XRF analysis, is 0.1 to 40% by mass relative to 100% by mass of the niobium oxide particles.

[0025] (6) Niobium oxide particles as described in any one of (1) to (5), wherein the surface layer of the niobium oxide particles is selectively enriched with molybdenum.

[0026] (7) Niobium oxide particles as described in any one of (1) to (6), wherein the MoO3 content (M2) of the niobium oxide particles, as determined by XPS surface analysis, is 0.5 to 45% by mass relative to 100% by mass of the surface layer of the niobium oxide particles.

[0027] (8) Niobium oxide particles as described in any one of (1) to (7), wherein the specific surface area determined by the BET method is less than 10 m². 2 / g.

[0028] (9) A method for manufacturing niobium oxide particles as described in any one of (1) to (8), comprising:

[0029] Niobium compounds were calcined in the presence of molybdenum compounds.

[0030] (10) The method for manufacturing niobium oxide particles as described in (9), wherein the niobium compound is calcined at a calcination temperature of 800 to 1500 °C.

[0031] (11) The method for manufacturing niobium oxide particles as described in (9) or (10), wherein the molar ratio of molybdenum atoms in the molybdenum compound to niobium atoms in the niobium compound is not less than 0.01.

[0032] The effects of the invention

[0033] The niobium oxide particles provided by the present invention have excellent properties derived from molybdenum and have a controllable crystal shape. Attached Figure Description

[0034] [ Figure 1 ]

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

[0036] [ Figure 2 ]

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

[0038] [ Figure 3 ]

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

[0040] [ Figure 4 ]

[0041] Figure 4 This is a SEM image of the niobium oxide particles from Example 4.

[0042] [ Figure 5 ]

[0043] Figure 5 This is a SEM image of the niobium oxide particles from Example 5.

[0044] [ Figure 6 ]

[0045] Figure 6 This is a SEM image of the niobium oxide particles from Example 7.

[0046] [ Figure 7 ]

[0047] Figure 7 This is a SEM image of the niobium oxide particles from Comparative Example 1.

[0048] [ Figure 8 ]

[0049] Figure 8 This is a SEM image of the niobium oxide particles from Comparative Example 2.

[0050] [ Figure 9 ]

[0051] Figure 9 The X-ray diffraction (XRD) patterns of niobium oxide particles of the examples and comparative examples are shown.

[0052] [ Figure 10 ]

[0053] Figure 10 The X-ray diffraction (XRD) patterns of niobium oxide particles of the examples and comparative examples are shown.

[0054] [ Figure 11 ]

[0055] Figure 11 The X-ray diffraction (XRD) patterns of niobium oxide particles of the examples and comparative examples are shown. Detailed Implementation

[0056] In the following, embodiments of the niobium oxide particles and the method for manufacturing niobium oxide particles according to the present invention will be described.

[0057] [Niobium oxide particles]

[0058] According to one embodiment, the niobium oxide particles contain molybdenum.

[0059] The niobium oxide particles according to this embodiment contain molybdenum and have excellent properties derived from molybdenum, such as catalytic activity.

[0060] According to this embodiment, niobium oxide particles can be manufactured in a controllable crystal shape by means of a manufacturing method described later, while adjusting the content and state of molybdenum, so as to adjust the properties and performance of the niobium oxide particles, such as optical properties like hue and transparency, according to the application requirements.

[0061] In this specification, phrases such as "the crystal shape of the niobium oxide particles is controlled" mean that the produced niobium oxide particles have a shapeless crystal structure. In this specification, phrases such as "the niobium oxide particles have a controllable crystal shape" mean that the niobium oxide particles have a shapeless crystal structure.

[0062] In one embodiment, niobium oxide particles manufactured by a manufacturing method according to an embodiment may have a specific idiomorphic shape, such as a polyhedron, columnar, or needle-like shape, as will be described in later embodiments.

[0063] The niobium oxide particles according to this embodiment can have a polyhedral, columnar, or needle-like shape. Niobium oxide particles with such shapes can be manufactured by the manufacturing methods described later. Compared to niobium, as the amount of molybdenum increases, the obtained niobium oxide particles are more likely to be columnar or needle-like.

[0064] In this specification, the term "polyhedron" means any shape that is more than tetrahedral. Shapes that are more than hexahedral are preferred, shapes that are more than octahedral are more preferred, and shapes that are decahedral to triacontahedral are even more preferred. The faces constituting a polyhedron can be planes or curved surfaces.

[0065] In this specification, the term "columnar" means prism shape, cylindrical shape, rod shape, etc. There are no particular limitations on the shape of the base of columnar niobium oxide particles, and they can be, for example, circular, elliptical, or polygonal. For example, the column can extend straight in the longitudinal direction, can extend obliquely, can be curved, or can branch.

[0066] In this specification, the term "needle-like" means that at least one end of a niobium oxide particle tapers like a needle.

[0067] In the niobium oxide particles according to this embodiment, the major diameter is preferably 0.1 to 300 μm, more preferably 1.5 to 200 μm, even more preferably 2 to 100 μm, and particularly preferably 5 to 50 μm.

[0068] In the niobium oxide particles according to this embodiment, the short diameter is preferably 0.01 to 50 μm, more preferably 0.2 to 40 μm, and even more preferably 0.05 to 10 μm.

[0069] In this specification, the "major axis" of a niobium oxide particle is the length of the longer side of the rectangle circumscribed around the niobium oxide particle in a two-dimensional image captured by a scanning electron microscope (SEM) (the circumscribed rectangle is drawn to minimize its area). In this specification, the "minor axis" of a niobium oxide particle is the length of the straight line connecting the two furthest points on the outer periphery of the photographed particle in a direction perpendicular to the major axis.

[0070] In the case of columnar or needle-shaped niobium oxide particles, the particles can be roughly approximated as fibers, with the major axis corresponding to the fiber length and the minor axis corresponding to the fiber diameter. Depending on the orientation of the particles in the image, the true major and minor axes of the particles can differ significantly from the values ​​measured with respect to a two-dimensional image. Therefore, when the niobium oxide particles in the sample are primarily columnar or needle-shaped, it is appropriate to select those particles that are directly shown in the image with a plane parallel to the longitudinal direction for dimensional determination.

[0071] The major and minor diameters are the arithmetic mean of at least 50 randomly selected niobium oxide particles, determined in the manner described above.

[0072] According to the manufacturing method described later, relative to niobium, with the increase of molybdenum content and with the increase of calcination temperature, the obtained niobium oxide particles tend to have a larger major diameter and a larger minor diameter.

[0073] In the niobium oxide particles according to this embodiment, the aspect ratio, expressed as major axis to minor axis, is preferably not less than 2, more preferably 5 to 50, and even more preferably 7 to 30. For example, columnar or needle-shaped niobium oxide particles have such an aspect ratio.

[0074] The major and minor axes of the aspect ratio can be determined using the values ​​of the major and minor axes described above.

[0075] According to the manufacturing method described later, the obtained niobium oxide particles are more likely to be columnar or needle-shaped, and tend to have a higher aspect ratio relative to niobium as the amount of molybdenum increases. Furthermore, when the calcination temperature is lower than a certain level, the obtained niobium oxide particles are more likely to be columnar or needle-shaped, and tend to have a higher aspect ratio.

[0076] The niobium oxide particles according to this embodiment can be provided as aggregates of niobium oxide particles. Such aggregates of niobium oxide particles according to this embodiment preferably include at least 50, more preferably at least 70, and even more preferably at least 90% of particles that satisfy at least one of the above-mentioned major diameter, minor diameter, and aspect ratio.

[0077] In the niobium oxide particles according to this embodiment, the MoO3 content (M1) of the niobium oxide particles, as determined by XRF analysis, is preferably not less than 0.1% by mass relative to 100% by mass of the niobium oxide particles, and preferably 0.1 to 40% by mass relative to 100% by mass of the niobium oxide particles, more preferably 1 to 35% by mass, and even more preferably 5 to 30% by mass.

[0078] Niobium oxide particles containing molybdenum within the above-mentioned numerical range can effectively exhibit the superior properties derived from molybdenum.

[0079] The MoO3 content (M1) of the niobium oxide particles, as determined by XRF analysis relative to 100% by mass of the niobium oxide particles, can be not less than 5% by mass, preferably not less than 7% by mass. Such niobium oxide particles are advantageously more likely to be columnar or needle-shaped particles with a high aspect ratio.

[0080] The MoO3 content (M1) is determined by XRF (X-ray fluorescence) analysis of niobium oxide particles with reference to a pre-prepared MoO3 calibration curve, and the MoO3 content is expressed as a percentage of MoO3 relative to 100% by mass of niobium oxide particles.

[0081] From a similar perspective, the niobium oxide particles according to this embodiment preferably have a MoO3 content (M2) of not less than 0.5% by mass relative to 100% by mass of the surface layer of the niobium oxide particles, as determined by XPS surface analysis. The MoO3 content (M2) relative to 100% by mass of the surface layer of the niobium oxide particles is preferably 0.5 to 45% by mass, more preferably 10 to 43% by mass, and even more preferably 15 to 40% by mass.

[0082] Niobium oxide particles containing molybdenum within the above-mentioned numerical range can effectively exhibit the superior properties derived from molybdenum.

[0083] Niobium oxide particles may have, for example, a MoO3 content (M2) of not less than 10% by mass relative to 100% by mass of the surface layer of the niobium oxide particles, as determined by XPS surface analysis. Such niobium oxide particles are advantageously more likely to be columnar or needle-like particles with a high aspect ratio.

[0084] The MoO3 content (M2) is determined by analyzing the surface of niobium oxide particles using X-ray photoelectron spectroscopy (XPS) to determine the amount of the element (atomic %), and the amount of molybdenum is converted into the MoO3 oxide content relative to 100% by mass of the surface layer of the niobium oxide particles.

[0085] In the niobium oxide particles according to this embodiment, it is preferable that the surface layer of the niobium oxide particles is selectively enriched with molybdenum.

[0086] Here, "surface" refers to the region extending from the surface of the niobium oxide particles according to this embodiment to a depth of 10 nm. This distance corresponds to the detection depth of the XPS used in the measurements of the embodiments.

[0087] Here, the phrase “selectively rich in the surface” means that the mass of molybdenum or molybdenum compound per unit volume of the surface is greater than the mass of molybdenum or molybdenum compound per unit volume of the region outside the surface.

[0088] In the niobium oxide particles according to this embodiment, as will be described in the following examples, the surface enrichment of molybdenum in the surface layer of the niobium oxide particles can be confirmed by confirming that the Mo content (M2) of the niobium oxide particles relative to 100% by mass of the surface layer of the niobium oxide particles, as determined by XPS surface analysis, is greater than the Mo content (M1) of the niobium oxide particles relative to 100% by mass of the niobium oxide particles, as determined by XRF analysis.

[0089] The surface enrichment rate, expressed by the ratio (M2 / M1) of the MoO3 content (M2) of niobium oxide particles as determined by XPS surface analysis to the MoO3 content (M1) of niobium oxide particles as determined by XRF analysis, is preferably greater than 1, more preferably 1.01 to 8.0, even more preferably 1.03 to 6.0, and particularly preferably 1.10 to 4.0.

[0090] When molybdenum or molybdenum compounds are uniformly distributed in the surface layer and in the interior region outside the surface layer, the superior properties derived from molybdenum can be effectively exhibited when the surface layer is selectively rich in molybdenum or molybdenum compounds.

[0091] Examples of niobium oxide contained in the niobium oxide particles according to this embodiment include niobium pentoxide (Nb₂O₅), niobium dioxide (NbO₂), and niobium monoxide (NbO). The niobium oxide particles may also include niobium oxide having any valence state other than the oxidation states described above. Among the above, the niobium oxide particles according to this embodiment preferably include niobium pentoxide (Nb₂O₅).

[0092] In the niobium oxide particles according to this embodiment, the Nb2O5 content may be not less than 50% by mass relative to 100% by mass of the niobium oxide particles, and may be 60-99.9% by mass, 65-99% by mass, or 70-95% by mass relative to 100% by mass of the niobium oxide particles.

[0093] Many polymorphs of niobium pentoxide, such as the T phase (T-Nb2O5), M phase (M-Nb2O5) and H phase (H-Nb2O5), have been reported and are known (for XRD patterns of these phases, see, for example, J. Therm. Anal. Calorim. (2017) 130:77-83).

[0094] As will be described in later embodiments, the niobium oxide particles tend to comprise niobium pentoxide having both an M phase (M-Nb₂O₅) and an H phase (H-Nb₂O₅). To ensure the provision of niobium oxide particles with a high aspect ratio, the niobium oxide particles according to this embodiment preferably comprise M-phase niobium pentoxide.

[0095] In the XRD analysis of niobium oxide particles according to this embodiment, the ratio (Mp / Hp) of the intensity of the peak at 2θ = 25.4° belonging to the M phase niobium pentoxide to the intensity of the peak at 2θ = 24.5° belonging to the H phase niobium pentoxide to the intensity of the peak at 2θ = 25.4° can be not less than 0.1, not less than 0.3, or not less than 0.6.

[0096] Columnar or needle-shaped niobium oxide particles that meet the above ratio Mp / Hp can have a higher aspect ratio.

[0097] In the niobium oxide particles according to this embodiment, the Nb2O5 content (N1) of the niobium oxide particles, as determined by XRF analysis, relative to 100% by mass of the niobium oxide particles, may be not less than 50% by mass, and may be 60-99.9% by mass, 65-99% by mass, or 70-95% by mass relative to 100% by mass of the niobium oxide particles.

[0098] The Nb2O5 content (N1) is determined by XRF (X-ray fluorescence) analysis of niobium oxide particles with reference to a pre-prepared Nb2O5 calibration curve, and the Nb2O5 content is expressed as a percentage of Nb2O5 relative to 100% by mass of niobium oxide particles.

[0099] In the niobium oxide particles according to this embodiment, the Nb2O5 content (N2) of the niobium oxide particles, as determined by XPS surface analysis, is preferably not less than 50% by mass relative to 100% by mass of the surface layer of the niobium oxide particles, and may be 55-99.5% by mass, 57-90% by mass, or 60-88% by mass relative to 100% by mass of the surface layer of the niobium oxide particles.

[0100] The Nb2O5 content (N2) is determined by analyzing the surface of niobium oxide particles using X-ray photoelectron spectroscopy (XPS) to determine the amount of the element (atomic %), and the amount of niobium is converted into the Nb2O5 oxide content relative to 100% by mass of the surface layer of the niobium oxide particles.

[0101] In the niobium oxide particles according to this embodiment, the specific surface area, as determined by the BET method, is preferably less than 10 m². 2 / g, more preferably not greater than 9m 2 / g, or more preferably no more than 5m 2 / g, or even more preferably no more than 4m 2 / g.

[0102] The advantage of niobium oxide particles having a specific surface area less than or not greater than the above upper limit is that the particle size is large and / or the particles are dense.

[0103] In the niobium oxide particles according to this embodiment, there is no particular limitation on the lower limit of the specific surface area determined by the BET method, but it can be, for example, not less than 0.01 m². 2 / g and less than 10m 2 / g can be 0.1 to 9m 2 / g, can be 0.2~5m 2 / g, or it can be 0.2~4m 2 / g.

[0104] According to this embodiment, niobium oxide particles can be provided as aggregates of niobium oxide particles, and the values ​​of molybdenum content, niobium content, and specific surface area can be values ​​determined for aggregates as samples.

[0105] For example, the niobium oxide particles according to this embodiment can be manufactured by the method described later in [Method for Manufacturing Niobium Oxide Particles].

[0106] Furthermore, the niobium oxide particles of the present invention are not limited to those manufactured by the niobium oxide particle manufacturing method according to the embodiments described below.

[0107] The niobium oxide particles according to this embodiment are very useful because they exhibit the properties of both niobium oxide and molybdenum.

[0108] [Method for manufacturing niobium oxide particles]

[0109] The method for manufacturing niobium oxide particles according to one embodiment is a method for manufacturing the aforementioned niobium oxide particles, and includes calcining a niobium compound in the presence of a molybdenum compound.

[0110] The method for manufacturing niobium oxide particles according to this embodiment can be used to manufacture molybdenum-containing niobium oxide particles as described in one of the embodiments of the present invention.

[0111] In the method for manufacturing niobium oxide particles according to this embodiment, the crystal shape of the manufactured niobium oxide particles can be easily controlled by calcining the niobium compound in the presence of a molybdenum compound.

[0112] The method for manufacturing niobium oxide particles preferably includes a step of mixing a niobium compound and a molybdenum compound together to form a mixture (mixing step) and a step of calcining the mixture (calcination step).

[0113] [Mixed Steps]

[0114] In the mixing step, the niobium compound and the molybdenum compound are mixed together to form a mixture. The mixed materials will be described below.

[0115] [Niobium compounds]

[0116] There are no particular limitations on the niobium compound, as long as it can be calcined to niobium oxide. Examples include niobium oxide, niobium hydroxide, niobium sulfide, niobium nitride, and niobium halides and niobium alkoxides such as niobium fluoride, niobium chloride, niobium bromide, and niobium iodide. Niobium hydroxide and niobium oxide are preferred, with niobium oxide being more preferred.

[0117] Examples of niobium oxide include niobium pentoxide (Nb₂O₅), niobium dioxide (NbO₂), and niobium monoxide (NbO). Niobium oxide with any oxidation state other than those mentioned above can be used.

[0118] There are no particular restrictions on the physical properties of niobium compounds used as precursors, such as shape, particle size, and specific surface area.

[0119] After calcination, the niobium compound used as a raw material essentially does not retain its shape before calcination. Therefore, compounds of any form can be advantageously used, such as spherical shapes, amorphous shapes, aspect structures (e.g., threads, fibers, belts, and tubes), and sheets.

[0120] [Molybdenum compounds]

[0121] Examples of molybdenum compounds include molybdenum oxide, molybdic acid, and molybdenum sulfide. Molybdenum oxide is preferred.

[0122] Examples of molybdenum oxide include molybdenum dioxide (MoO2) and molybdenum trioxide (MoO3), with molybdenum trioxide being preferred.

[0123] In the method for manufacturing niobium oxide particles according to this embodiment, a molybdenum compound is used as a flux. In this specification, the manufacturing method using a molybdenum compound as a flux is sometimes abbreviated as "flux method" below. During calcination, the molybdenum compound reacts with a niobium compound at high temperature to form niobium molybdate, and possibly in such a manner as to introduce the molybdenum compound into the niobium oxide particles, whereby the niobium molybdate decomposes into niobium oxide and molybdenum oxide at an even higher temperature. The molybdenum oxide sublimates and is removed from the system, and in this process, the molybdenum compound and the niobium compound react with each other, most likely forming a molybdenum compound on the surface of the niobium oxide particles. More specifically, the molybdenum compound contained in the niobium oxide particles may be formed through a mechanism in which molybdenum reacts with Nb atoms to form Mo-O-Nb on the surface of the niobium oxide particles, and through high-temperature calcination, Mo is released, while molybdenum oxide or, for example, a compound having Mo-O-Nb bonds is formed on the surface of the niobium oxide particles.

[0124] Molybdenum oxide not introduced into the niobium oxide particles can be sublimated and recycled for reuse. In this way, the amount of molybdenum oxide adhering to the surface of the niobium oxide particles can be reduced, allowing the niobium oxide particles to fully exhibit their inherent properties.

[0125] In the method for manufacturing niobium oxide particles according to this embodiment, there are no particular limitations on the amount of niobium compound and molybdenum compound added. Preferably, the mixture can be prepared by mixing at least 35% by mass of niobium compound and less than 65% by mass of molybdenum compound relative to 100% by mass of the mixture, and then calcining the mixture. More preferably, the mixture can be prepared by mixing at least 40% by mass and at least 99% by mass of niobium compound and at least 0.5% by mass and at least 60% by mass of molybdenum compound relative to 100% by mass of the mixture, and then calcining the mixture. Even more preferably, the mixture can be prepared by mixing at least 50% by mass and at least 90% by mass of niobium compound and at least 2% by mass and at least 50% by mass of molybdenum compound relative to 100% by mass of the mixture, and then calcining the mixture.

[0126] In the method for manufacturing niobium oxide particles according to this embodiment, the molar ratio of molybdenum atoms in the molybdenum compound to niobium atoms in the niobium compound, molybdenum / niobium, is preferably not less than 0.01, more preferably not less than 0.03, even more preferably not less than 0.05, and particularly preferably not less than 0.1.

[0127] An upper limit can be appropriately determined for the molar ratio of molybdenum atoms in a molybdenum compound to niobium atoms in a niobium compound. From the perspective of saving molybdenum compound usage and improving production efficiency, for example, the molybdenum / niobium ratio can be no greater than 5, no greater than 3, no greater than 1, or no greater than 0.5.

[0128] For example, the molar ratio of molybdenum atoms in the molybdenum compound to niobium atoms in the niobium compound is preferably in the range of 0.01 to 5, more preferably 0.03 to 3, even more preferably 0.05 to 1, and particularly preferably 0.1 to 0.5.

[0129] The obtained niobium oxide particles are more likely to be columnar or needle-shaped, and tend to have larger minor and major diameters relative to niobium as the amount of molybdenum increases. Furthermore, when the molar ratio of molybdenum atoms in the molybdenum compound to niobium atoms in the niobium compound does not exceed the aforementioned upper limit, the obtained niobium oxide particles tend to have a higher aspect ratio.

[0130] When the molar ratio of molybdenum atoms in a molybdenum compound to niobium atoms in a niobium compound is greater than 0.05, columnar or needle-shaped niobium oxide particles are readily obtained.

[0131] By using compounds within the aforementioned range, the obtained niobium oxide particles contain a more suitable amount of molybdenum compound and are easier to obtain with a controllable crystal shape.

[0132] [Calcination Steps]

[0133] In the calcination step, the mixture is calcined. Niobium oxide particles according to the aforementioned embodiment can be obtained by calcining the mixture. As previously stated, this manufacturing method is called the flux method.

[0134] Flux methods are classified as solution methods. More specifically, flux methods are crystal growth methods that utilize the fact that the crystal-flux binary phase diagram is eutectic. The mechanism of flux methods is likely as follows: When a mixture of solute and flux is heated, the solute and flux form a liquid phase. Because the flux acts as a fusing agent in this process, in other words, the solute-flux binary phase diagram is eutectic, the solute melts at a temperature below its melting point, forming a liquid phase. When the flux evaporates in this state, the flux concentration is reduced, in other words, the effect of the flux in lowering the melting point of the solute is reduced, and the evaporation of the flux drives the growth of solute crystals (flux evaporation method). Alternatively, the growth of solute crystals can also be induced by cooling the solute-flux liquid phase (slow cooling method).

[0135] Flux methods offer several advantages, such as the ability to grow crystals at temperatures far below the melting point, precise control over the crystal structure, and the formation of euhedral crystals.

[0136] The mechanism of the fluxing process in the manufacture of niobium oxide particles using molybdenum compounds as fluxes is not fully understood, but it may be, for example, as described below. When the niobium compound is calcined in the presence of a molybdenum compound, niobium molybdate is first formed. In this process, as can be understood from the above description, niobium molybdate grows into niobium oxide crystals at a temperature below the melting point of niobium oxide. For example, when the flux evaporates, niobium molybdate decomposes and undergoes crystal growth to form niobium oxide particles. That is, the molybdenum compound acts as a flux and participates in the manufacture of niobium oxide particles in an intermediate form of niobium molybdate.

[0137] Calcination can be carried out by any known method without limitation. The reaction between niobium and molybdenum compounds to form niobium molybdate will occur at calcination temperatures above 650°C. When the calcination temperature is further increased to above 800°C, niobium molybdate will decompose to form niobium oxide particles. During the decomposition of niobium molybdate into niobium oxide and molybdenum oxide, molybdenum compounds will be introduced into the niobium oxide particles.

[0138] During calcination, the niobium and molybdenum compounds can be in any state without restriction, as long as the compounds are in the same space, allowing the molybdenum compound to act on the niobium compound. Specifically, the molybdenum and niobium compounds can be in the form of a simple mixture of their respective powders, or in the form of a mixture obtained by mechanical mixing such as a crusher, or by mixing in a mortar, etc. The mixture can be a dry mixture or a wet mixture.

[0139] There are no particular restrictions on the calcination temperature, and it can be appropriately determined based on factors such as the particle size of the target niobium oxide particles, the formation of molybdenum compounds in the niobium oxide particles, and the shape of the niobium oxide particles. The calcination temperature can be close to the decomposition temperature of niobium molybdate, specifically, it can be no less than 800℃, no less than 850℃, no less than 900℃, no less than 950℃, or no less than 1000℃.

[0140] The obtained niobium oxide particles are more likely to be columnar or needle-shaped, and tend to have a higher aspect ratio as the calcination temperature increases. In order to effectively produce columnar or needle-shaped niobium oxide particles with a high aspect ratio, the calcination temperature is preferably not lower than 950°C, and more preferably not lower than 1000°C.

[0141] Typically, the shape of niobium oxide obtained after calcination is controlled by calcining at temperatures above 1500°C, close to the melting point of niobium oxide. This requirement presents a significant challenge for industrial applications in terms of the burden on the calcination furnace and fuel costs.

[0142] According to one embodiment of the invention, niobium oxide particles can be formed efficiently and at low cost even under conditions where, for example, the maximum calcination temperature during the calcination of niobium compounds is below 1500°C.

[0143] Furthermore, even when the calcination temperature is as low as 1300°C or below, which is far below the melting point of niobium oxide, the niobium oxide particle manufacturing method according to this embodiment can form euhedral niobium oxide particles regardless of the shape of the precursor. In order to effectively manufacture columnar or needle-shaped niobium oxide particles with a high aspect ratio, the calcination temperature is preferably not greater than 1200°C, and more preferably not greater than 1100°C.

[0144] For example, the calcination temperature of the niobium compound in the calcination step can be in the range of 850–1500℃, 900–1400℃, 950–1300℃, 950–1200℃, or 950–1100℃.

[0145] From the perspective of production efficiency, the heating rate can be 20-600℃ / h, 40-500℃ / h, or 80-400℃ / h.

[0146] The preferred calcination time is such that the temperature rises to the predetermined calcination temperature within 15 minutes to 10 hours, and is maintained at that calcination temperature for 5 minutes to 30 hours. For effective formation of niobium oxide particles, the holding time at this calcination temperature is more preferably 2 to 15 hours.

[0147] By selecting a calcination temperature of 800–1600 °C and a holding time of 2–15 hours at that calcination temperature, molybdenum-containing euhedral niobium oxide particles can be easily obtained.

[0148] By selecting a calcination temperature of 900–1600 °C and a holding time of 2–15 hours at that calcination temperature, molybdenum-containing columnar or needle-shaped niobium oxide particles can be easily obtained.

[0149] The calcination atmosphere is not particularly limited, as long as the advantageous effects of the present invention are obtained. For example, an oxygen-containing atmosphere such as air or oxygen, or an inert atmosphere such as nitrogen, argon, or carbon dioxide is preferred. Considering cost, an air atmosphere is more preferred.

[0150] The calcination equipment is not limited and can be a so-called calcination furnace. The calcination furnace is preferably made of a material that does not react with the sublimations of molybdenum oxide. To ensure the efficient use of molybdenum oxide, a highly sealed calcination furnace is preferred.

[0151] [Molybdenum Removal Steps]

[0152] The method for manufacturing niobium oxide particles according to this embodiment may further include a molybdenum removal step as needed, wherein at least a portion of the molybdenum is removed after the calcination step.

[0153] As mentioned above, molybdenum sublimates during calcination. Therefore, the molybdenum content in the surface layer of niobium oxide particles, as well as the content and state of molybdenum present in the niobium oxide particles outside the surface (inside), can be controlled by conditions such as calcination time and calcination temperature.

[0154] Molybdenum can adhere to the surface of niobium oxide particles. Besides sublimation as described above, this molybdenum can also be removed by washing with water, ammonia solution, sodium hydroxide solution, or acidic aqueous solution.

[0155] In this process, the molybdenum content in the niobium oxide particles can be controlled by appropriately changing the conditions, such as the concentration and amount of water, ammonia solution, sodium hydroxide solution or acidic solution used, the washing portion and the washing time.

[0156] [Grinding Step]

[0157] The calcined product obtained through the calcination step is sometimes an aggregate of niobium oxide particles that does not have a particle size suitable for the intended application. Therefore, the niobium oxide particles can be pulverized as needed to meet a preferred range of particle sizes.

[0158] The calcined products can be pulverized by any method without limitation. Known crushing devices can be used, such as ball mills, jaw crushers, jet mills, disc mills, Spectromills, grinding mills, and mixer mills.

[0159] [Grading Steps]

[0160] The calcined product, including niobium oxide particles, obtained through the calcination step can be appropriately graded to control the range of particle size. The term "grading" means the operation of separating the particles into groups according to their size.

[0161] Grading can be done by wet grading or dry grading. From a production point of view, dry grading is preferred.

[0162] Dry classification techniques include sieving and air classification, which utilizes the difference between centrifugal force and fluid resistance. From the viewpoint of classification accuracy, air classification is preferred. Classifiers utilizing the Coanda effect can be used, such as air classifiers, vortex air classifiers, forced vortex centrifugal classifiers, and semi-free vortex centrifugal classifiers.

[0163] The aforementioned crushing and grading steps can be performed at any appropriate stage. By selecting whether and how to perform crushing and grading, for example, the average particle size of the obtained niobium oxide particles can be controlled.

[0164] The niobium oxide particles according to this embodiment, or the niobium oxide particles obtained by the manufacturing method according to this embodiment, preferably have less or no aggregation, because such particles can suitably exhibit inherent properties and are easier to handle, and can also be dispersed more effectively when used as a dispersion in a dispersion medium.

[0165] Furthermore, the niobium oxide particle manufacturing method according to this embodiment can easily produce niobium oxide particles with less aggregation or no aggregation. Therefore, it is advantageous that the desired niobium oxide particles with excellent properties can be manufactured with high productivity even without a crushing or classification step.

[0166] [Example]

[0167] The invention will now be described in more detail by way of examples. However, it should be understood that the scope of the invention is not limited to such examples.

[0168] (Comparative Example 1)

[0169] Commercial niobium oxide (Nb2O5, a reagent manufactured by KANTO CHEMICAL CO.,INC.) was used as the niobium oxide powder in Comparative Example 1.

[0170] [Example 1]

[0171] A mixture was obtained by mixing 10 g of niobium oxide (Nb₂O₅, a reagent manufactured by KANTO CHEMICAL CO., INC.) and 0.5 g of molybdenum trioxide (manufactured by TAIYO KOKO CO., LTD.) in a mortar. The obtained mixture was added to a crucible and calcined in an electric ceramic furnace at 1100 °C for 24 hours. After cooling, the crucible was recovered. Thus, a powder weighing 10.4 g was obtained.

[0172] The obtained 10.4 g powder was then dispersed in 100 mL of 0.5% ammonia solution. The dispersion was stirred at room temperature (25–30 °C) for 3 hours, and then filtered to remove the ammonia solution. The filter cake was washed with water and dried. The molybdenum remaining on the particle surface was thus removed. In this way, 9.8 g of the powder from Example 1 was obtained.

[0173] The synthesis conditions are recorded in Table 1.

[0174] (Examples 2 and 3)

[0175] Except for changing the amount of molybdenum trioxide used in Example 1 as described in Table 1, the powders of Examples 2 and 3 were obtained in the same manner as in Example 1.

[0176] (Examples 4-7 and Comparative Example 2)

[0177] Except for changing the amount of molybdenum trioxide used in Example 1 as described in Table 1, and changing the calcination temperature and calcination time as described in Table 1, the powders of Examples 4 to 7 and Comparative Example 2 were obtained in the same manner as in Example 1.

[0178] [evaluate]

[0179] The powders used as samples in the examples and comparative examples were tested using the following measurements.

[0180] [Particle size measurement]

[0181] The sample powder was photographed using a scanning electron microscope (SEM). The major and minor axes were determined relative to the smallest unit of particle captured in the two-dimensional image (i.e., the primary particle). The major axis was defined as the length of the longer side of the rectangle circumscribed around the photographed particle (the rectangle was drawn such that its area would be minimized). The minor axis was defined as the length of the straight line connecting the two farthest points on the outer periphery of the photographed particle in a direction perpendicular to the major axis.

[0182] When the sample particles are mainly columnar or needle-shaped, appropriately select those particles that are shown in the image with a surface parallel to the longitudinal direction for size measurement.

[0183] As described above, 50 primary particles were measured, and the results were averaged arithmetically.

[0184] In addition, the ratio of the major diameter to the minor diameter (major diameter / minor diameter) is calculated as the aspect ratio of the primary particle.

[0185] [Crystal Structure Analysis: XRD (X-ray Diffraction)]

[0186] The sample powder was loaded into a sample holder with a depth of 0.5 mm. The sample was then placed on a wide-angle X-ray diffractometer (XRD) (Ultima IV, manufactured by Rigaku Corporation) and analyzed using Cu / Kα radiation at 40 kV / 40 mA, a scan rate of 2° / min, and a scan range of 10–70°.

[0187] XRF (X-ray fluorescence) analysis

[0188] Approximately 70 mg of sample powder was placed on filter paper and covered with a PP film. The sample powder was then analyzed by XRF (X-ray fluorescence) analysis on a Primus IV X-ray fluorescence analyzer (manufactured by Rigaku Corporation) under the following conditions.

[0189] Measurement conditions:

[0190] EZ scan mode

[0191] Detection element: F to U

[0192] Measurement time: standard

[0193] Diameter measured: 10mm

[0194] Remaining (balanced): None

[0195] The Nb₂O₅ content (N₁) relative to 100% by mass of the niobium oxide sample powder and the MoO₃ content (M₁) relative to 100% by mass of the niobium oxide particles were determined from the results of XRF analysis.

[0196] [XPS Surface Analysis]

[0197] XPS (X-ray photoelectron spectroscopy) was performed using a monochromatic Al-Kα X-ray source under the following conditions, with a QUANTERA SXM manufactured by ULVAC-PHI, INCORPORATED. The elemental content in the surface layer was determined in atomic percent.

[0198] ●X-ray source: Monochromatic Al Kα, beam diameter: 100μm, output: 25W

[0199] ● Measurement: Area measurement (1000μm square), n=3

[0200] ● Charge correction: C1s = 284.8 eV

[0201] To facilitate comparison with XRF results, the niobium and molybdenum contents in the surface layer of niobium oxide particles were converted to oxide contents. Specifically, the Nb₂O₅ content (N₂) (mass%) and the MoO₃ content (M₂) (mass%) relative to 100% mass of the surface layer of niobium oxide particles were calculated.

[0202] The surface enrichment rate was determined by calculating the ratio (M2 / M1) of the MoO3 content (M2) of niobium oxide particles as determined by XPS surface analysis to the MoO3 content (M1) of niobium oxide particles as determined by XRF analysis.

[0203] [Determination of specific surface area]

[0204] The specific surface area of ​​the niobium oxide sample powder was determined using a specific surface area meter (BELSORP-mini, manufactured by MicrotracBEL). The specific surface area (m²) was calculated from the surface area per g of sample determined by nitrogen absorption using the BET method. 2 / g).

[0205] [result]

[0206] The results of the XRD analysis are shown in Figures 9-11 The samples from the examples show peaks attributable to niobium oxide (niobium pentoxide) (see the peaks of niobium pentoxide in the case of the raw material in Comparative Example 1).

[0207] Compared to Example 7 (calcination temperature: 1300°C), the niobium oxide particles of Examples 1–6 (calcination temperatures: 900°C or 1100°C) obtained at relatively lower calcination temperatures showed a clear peak belonging to the M-phase niobium pentoxide near 2θ = 25.4°. This confirms the ease of producing niobium oxide particles with controllable columnar or needle-like shapes.

[0208] In the columnar or needle-shaped niobium oxide particles of Examples 2-5, the ratio (Mp / Hp) of the peak intensity (Mp) of niobium pentoxide belonging to the M phase near 2θ = 25.4° to the peak intensity (Hp) of niobium pentoxide belonging to the H phase near 2θ = 24.5° tends to be higher with increasing aspect ratio.

[0209] The evaluation results are recorded in Table 1.

[0210] In addition, "ND" is an abbreviation for "Not Detected," indicating that no data was detected.

[0211] [Table 1]

[0212]

[0213] exist Figures 1-8 SEM images of the powders obtained in the examples and comparative examples are shown.

[0214] The particle shapes of the embodiments and comparative examples, determined from SEM images, are described in Table 1. When the particles are a mixture of different shapes, the dominant shape (the most common shape) is used. Particles without a specific shape are classified as amorphous.

[0215] The particles in Example 1 may include columnar or needle-shaped particles, but are described as polyhedral as the primary shape.

[0216] The results of SEM observation and XRD analysis indicate that the powders obtained in the examples and comparative examples are niobium oxide particles including niobium oxide.

[0217] The results of the examples show that molybdenum-containing niobium oxide particles can be produced by calcining niobium compounds in the presence of molybdenum compounds, even at relatively low calcination temperatures of 900°C or 1100°C.

[0218] Furthermore, it has been shown that the shape of the produced niobium oxide particles can be easily controlled by calcining niobium compounds in the presence of molybdenum compounds.

[0219] In the comparison of Examples 1 to 3, the obtained particles tend to be columnar or needle-shaped, and have larger particle size and higher aspect ratio with increasing molybdenum content.

[0220] Similarly, the comparison between Example 2 and Example 5, and between Examples 3, 4 and 7, shows that columnar or needle-like particles with a high aspect ratio tend to be obtained at a calcination temperature of about 900 to 1100°C.

[0221] The niobium oxide particles in Examples 1-7 contain molybdenum on their surface and are therefore expected to exhibit various effects, such as catalytic activity derived from molybdenum.

[0222] In the niobium oxide particles of Examples 1-7, the molybdenum oxide content in the surface layer of the niobium oxide particles, as determined by XPS surface analysis, was higher than the molybdenum oxide content determined by XRF analysis. This indicates that the surface of the niobium oxide particles is selectively enriched with molybdenum, and various molybdenum-derived effects are expected to be effectively generated.

[0223] The constructions and combinations thereof described in the embodiments, as well as other features, are merely illustrative and may be combined with other constructions, or omitted, substituted, and modified, without departing from the spirit of the invention. Furthermore, the scope of the invention is not limited to the embodiments listed above, but only to the claims.

Claims

1. A type of niobium oxide particle, characterized in that, It is selectively rich in molybdenum in its surface layer. The MoO3 content (M1) of the niobium oxide particles, as determined by XRF analysis, is 3.2–20.4% by mass relative to 100% of the niobium oxide particles. The surface richness, expressed by the ratio M2 / M1 of the MoO3 content M2 relative to the surface 100% by mass of the niobium oxide particles as determined by XPS surface analysis, is greater than 1 and less than 4.

0.

2. The niobium oxide particles according to claim 1, characterized in that, The major diameter is 0.1~300μm.

3. The niobium oxide particles according to claim 1, characterized in that, It has a polyhedral, columnar, or needle-like shape.

4. The niobium oxide particles according to claim 1, characterized in that, The aspect ratio, expressed as major axis / minor axis, is not less than 2.

5. The niobium oxide particles according to claim 1, characterized in that, The MoO3 content M2 of the niobium oxide particles, as determined by XPS surface analysis, is 10-45% by mass relative to 100% by mass of the surface layer of the niobium oxide particles.

6. The niobium oxide particles according to claim 1, characterized in that, The specific surface area, measured by the BET method, is less than 10 m 2 / g.

7. A method for manufacturing niobium oxide particles according to any one of claims 1 to 6, characterized in that, The method includes: calcining a niobium compound in the presence of a molybdenum compound. The molybdenum compound is molybdenum oxide, molybdic acid, or molybdenum sulfide, and the calcination temperature is 900~1300℃, and the calcination time is 10~24 hours.

8. The method for manufacturing niobium oxide particles according to claim 7, characterized in that, The molar ratio of molybdenum atoms in the molybdenum compound to niobium atoms in the niobium compound is not less than 0.01.

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