Gadolinium oxide particles and methods for producing gadolinium oxide particles

Abstract

The present invention provides gadolinium oxide particles containing molybdenum and a method for producing the gadolinium oxide particles. The method for producing the gadolinium oxide particles provided by the present invention comprises calcining a gadolinium compound in the presence of a molybdenum compound.

Description

Technical Field

[0001] The present invention relates to gadolinium oxide particles and a method for producing the same. Background Art

[0002] Gadolinium oxide (ie, gadolinia) has been used and studied in optical applications such as fluorescent host materials, optical glasses, optical isolation substrates, laser elements, and photonic crystals, and in a wide range of applications such as memory materials.

[0003] For example, PTL 1 discloses the use of gadolinia-doped cerium oxide (GDC) powder and gadolinia (Gd 2 O 3 ) powder to produce gadolinia-doped cerium oxide (GDC) / gadolinia (Gd 2 O 3 ) particles.

[0004] Reference List

[0005] Patent Literature

[0006] PTL 1: JP-T-2014-511260 (As used herein, the term "JP-T" means a published Japanese translation of a PCT patent application) Summary of the Invention

[0007] Technical difficulties

[0008] However, PTL 1 discloses a method for producing the aforementioned particles, rather than a method for producing gadolinium oxide particles, wherein the gadolinium oxide particles themselves are synthesized from raw materials. As described above, knowledge of gadolinium oxide particles and methods for producing gadolinium oxide particles is limited, and there is still room for research.

[0009] Therefore, one object of the present invention is to provide gadolinium oxide particles having excellent properties and a method for producing the same.

[0010] Solutions to Problems

[0011] The present invention includes the following aspects.

[0012] (1) Gadolinium oxide particles containing molybdenum.

[0013] (2) The gadolinium oxide particles according to (1) above, wherein the median diameter D of the gadolinium oxide particles calculated by a laser diffraction / scattering method is 50 0.1μm to 1000μm.

[0014] (3) The gadolinium oxide particles according to any one of (1) or (2) above, wherein the Gd2O3 content (G1) relative to 100% by mass of the gadolinium oxide particles as measured by XRF analysis of the gadolinium oxide particles is from 60% by mass to 99.95% by mass; and the MoO3 content (M1) relative to 100% by mass of the gadolinium oxide particles as measured by XRF analysis of the gadolinium oxide particles is from 0.05% by mass to 40% by mass.

[0015] (4) The gadolinium oxide particles according to any one of (1) to (3) above, wherein the Gd2O3 content (G2) relative to 100% by mass of the surface layer of the gadolinium oxide particles measured by XPS surface analysis of the gadolinium oxide particles is 10% by mass to 98% by mass; and the MoO3 content (M2) relative to 100% by mass of the surface layer of the gadolinium oxide particles measured by XPS surface analysis of the gadolinium oxide particles is 2% by mass to 40% by mass.

[0016] (5) A method for producing the gadolinium oxide particles according to any one of (1) to (4) above, comprising calcining a gadolinium compound in the presence of a molybdenum compound.

[0017] (6) The method for producing gadolinium oxide particles according to (5) above, wherein the molybdenum compound is at least one compound selected from the group consisting of molybdenum trioxide, lithium molybdate, potassium molybdate, and sodium molybdate.

[0018] (7) The method for producing gadolinium oxide particles according to (5) or (6) above, wherein a calcination temperature for the calcination is 900°C to 1600°C.

[0019] Advantageous Effects of the Invention

[0020] According to the present invention, it is possible to provide gadolinium oxide particles having excellent characteristics and a method for producing the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a SEM photograph of the gadolinium oxide particles of Example 1.

[0022] Figure 2 This is an SEM photograph of the gadolinium oxide particles of Example 2.

[0023] Figure 3 This is an SEM photograph of the gadolinium oxide particles of Example 3.

[0024] Figure 4 This is an SEM photograph of the gadolinium oxide particles of Example 4.

[0025] Figure 5 is a SEM photograph of the gadolinium oxide particles of Comparative Example 1.

[0026] Figure 6 is a SEM photograph of the gadolinium oxide particles of Comparative Example 2.

[0027] Figure 7 Graphs showing the results of XRD measurements of gadolinium oxide particles of Examples and Comparative Examples. DETAILED DESCRIPTION

[0028] Hereinafter, an embodiment of a gadolinium oxide particle and a method for manufacturing the gadolinium oxide particle according to the present invention will be described.

[0029] <<Gadolinium Oxide Particles>>

[0030] The gadolinium oxide particles of the embodiment contain molybdenum. The gadolinium oxide particles of the embodiment contain molybdenum and have excellent properties such as catalytic activity and shape derived from molybdenum.

[0031] The gadolinium oxide particles of the embodiment manufactured by the manufacturing method of the embodiment may have a unique self-shaped shape, such as a granular or columnar shape, as shown in the examples described below.

[0032] In this specification, "columnar shape" includes prisms, columnar shapes, rod-like shapes, and the like. The shape of the bottom surface of the columnar body of the columnar gadolinium oxide particles is not particularly limited, and examples thereof include circular shapes, elliptical shapes, and polygonal shapes. The columnar body includes a body extending straight in its longitudinal direction, a body extending obliquely, a body extending while bending, a body branching in a branched shape, and the like.

[0033] In the gadolinium oxide particles of the embodiment, the particle size, aggregation degree, molybdenum content, etc. of the obtained gadolinium oxide particles can be controlled by controlling the amount and type of the molybdenum compound used in the production method described below.

[0034] The median diameter D of the gadolinium oxide particles of the embodiment calculated by the laser diffraction / scattering method is 50 It is preferably 0.1 μm to 1000 μm, more preferably 3 μm to 100 μm, and even more preferably 0.5 μm to 20 μm.

[0035] From the viewpoint of providing gadolinium oxide particles having a larger size, the median diameter D of the gadolinium oxide particles of the embodiment calculated by the laser diffraction / scattering method is 50 It is preferably 25 μm to 200 μm, more preferably 30 μm to 100 μm, and even more preferably 40 μm to 80 μm.

[0036] The median diameter D of the gadolinium oxide particle sample calculated by the laser diffraction / scattering method 50It can be determined as a particle diameter where the ratio of cumulative volume % in particle diameter distribution is 50%, as measured by a dry method using a laser diffraction type particle size distribution analyzer.

[0037] The particle diameter D of the gadolinium oxide particles of the embodiment calculated by the laser diffraction / scattering method is 10 It is preferably 0.05 μm to 100 μm, more preferably 0.08 μm to 50 μm, and even more preferably 0.1 μm to 5 μm.

[0038] From the viewpoint of providing gadolinium oxide particles having a larger size, the particle diameter D of the gadolinium oxide particles of the embodiment calculated by the laser diffraction / scattering method is 10 It is preferably 6 μm to 80 μm, more preferably 8 μm to 50 μm, and even more preferably 10 μm to 30 μm.

[0039] Particle diameter D of gadolinium oxide particle sample calculated by laser diffraction / scattering method 10 It can be determined as a particle diameter in which the ratio of cumulative volume % from the small particle side in the particle diameter distribution is 10%, as measured by a dry method using a laser diffraction type particle size distribution analyzer.

[0040] The particle diameter D of the gadolinium oxide particles of the embodiment calculated by the laser diffraction / scattering method is 90 It is preferably 1 μm to 1500 μm, more preferably 2 μm to 500 μm, and even more preferably 8 μm to 50 μm.

[0041] From the viewpoint of providing gadolinium oxide particles having a larger size, the particle diameter D of the gadolinium oxide particles of the embodiment calculated by the laser diffraction / scattering method is 90 It is preferably 60 μm to 800 μm, more preferably 80 μm to 500 μm, and even more preferably 100 μm to 200 μm.

[0042] Particle diameter D of gadolinium oxide particle sample calculated by laser diffraction / scattering method 90 It can be determined as a particle diameter in which the ratio of cumulative volume % from the small particle side in the particle diameter distribution is 90%, as measured by a dry method using a laser diffraction type particle size distribution analyzer.

[0043] The gadolinium oxide particles of the embodiment contain gadolinium oxide (i.e., gadolinia). Examples of gadolinium oxide that may be contained in the gadolinium oxide particles of the embodiment include Gd2O3 and GdO2.

[0044] The gadolinium oxide particles of the embodiment preferably contain 60 to 99.95 mass%, more preferably 65 to 99.5 mass%, and even more preferably 80 to 98 mass% of Gd2O3 relative to 100 mass% of the gadolinium oxide particles.

[0045] The gadolinium oxide content in the gadolinium oxide particles can be measured by XRF analysis. In the gadolinium oxide particles of the embodiment, the Gd2O3 content (G1) relative to 100% by mass of the gadolinium oxide particles, as measured by XRF analysis of the gadolinium oxide particles, is preferably 60% to 99.95% by mass, more preferably 65% ​​to 99.5% by mass, and even more preferably 70% to 98% by mass.

[0046] The gadolinium oxide particles of the embodiment contain molybdenum. In the gadolinium oxide particles of the embodiment, the MoO3 content (M1) relative to 100% by mass of the gadolinium oxide particles, as measured by XRF analysis of the gadolinium oxide particles, is preferably 0.05% by mass to 40% by mass, more preferably 0.1% by mass to 35% by mass, and even more preferably 1% by mass to 30% by mass.

[0047] The upper and lower limits of the Gd2O3 content (G1) and MoO3 content (M1) in the gadolinium oxide particles of the embodiment can be freely combined. In addition, the numerical values ​​of the Gd2O3 content (G1) and MoO3 content (M1) can be freely combined.

[0048] As an example of the gadolinium oxide particles of the embodiment, gadolinium oxide particles having a Gd2O3 content (G1) of 60% by mass to 99.95% by mass and a MoO3 content (M1) of 0.05% by mass to 40% by mass can be exemplified.

[0049] The above Gd 2 O 3 content (G1) and MoO 3 content (M1) can be measured by XRF analysis, for example, using a fluorescent X-ray analyzer (Primus IV) manufactured by Rigaku Corporation.

[0050] The gadolinium oxide content contained in the surface layer of the gadolinium oxide particles can be measured by X-ray photoelectron spectroscopy (XPS) surface analysis. In the gadolinium oxide particles of the embodiment, the Gd2O3 content (G2) relative to 100% by mass of the surface layer of the gadolinium oxide particles, as measured by XPS surface analysis of the gadolinium oxide particles, is preferably 10% to 98% by mass, more preferably 20% to 80% by mass, and even more preferably 30% to 65% by mass.

[0051] In the gadolinium oxide particles of the embodiment, the MoO3 content (M2) relative to 100% by mass of the surface layer of the gadolinium oxide particles, as measured by XPS surface analysis of the gadolinium oxide particles, is preferably 2% by mass to 40% by mass, more preferably 3% by mass to 35% by mass, and even more preferably 8% by mass to 30% by mass.

[0052] The upper and lower limits of the Gd2O3 content (G2) and MoO3 content (M2) in the gadolinium oxide particles of the embodiment can be freely combined. In addition, the numerical values ​​of the Gd2O3 content (G2) and MoO3 content (M2) can be freely combined.

[0053] As an example of the gadolinium oxide particles of the embodiment, gadolinium oxide particles having a Gd2O3 content (G2) of 10 to 98 mass% and a MoO3 content (M2) of 2 to 40 mass% can be exemplified.

[0054] The above Gd2O3 content (G2) refers to the abundance ratio (atomic %) of each element obtained by performing XPS surface analysis on a sample of gadolinium oxide particles using X-ray photoelectron spectroscopy (XPS), and is measured as the value of the Gd2O3 content relative to 100% by mass of the surface layer of the gadolinium oxide particles by converting the gadolinium content into oxide.

[0055] The above MoO3 content (M2) refers to the abundance ratio (atomic %) of each element obtained by performing XPS surface analysis on gadolinium oxide particles using X-ray photoelectron spectroscopy (XPS), and is measured as the value of the MoO3 content relative to 100% by mass of the surface layer of the gadolinium oxide particles by converting the molybdenum content into oxide.

[0056] In the gadolinium oxide particles of the embodiment, molybdenum is preferably distributed unevenly in the surface layer of the gadolinium oxide particles.

[0057] Here, the "surface layer" in this specification means within 10 nm from the surface of the gadolinium oxide particles of the embodiment. This distance corresponds to the detection depth of XPS used for measurement in the examples.

[0058] Herein, "non-uniformly distributed in the surface layer" means that the mass of molybdenum or the molybdenum compound per unit volume in the surface layer is greater than the mass of molybdenum or the molybdenum compound per unit volume outside the surface layer.

[0059] In the gadolinium oxide particles of the examples, the fact that molybdenum is unevenly distributed in the surface layer of the gadolinium oxide particles is confirmed by the fact that the MoO3 content (M2) relative to 100 mass % of the surface layer of the gadolinium oxide particles, as measured by XPS surface analysis of the gadolinium oxide particles, is greater than the MoO3 content (M1) relative to 100 mass % of the gadolinium oxide particles, as measured by fluorescent X-ray (XRF) analysis of the gadolinium oxide particles, as described in the examples described below.

[0060] In the gadolinium oxide particles of the embodiment, as an indicator that molybdenum is unevenly distributed in the surface layer of the gadolinium oxide particles, the surface layer uneven distribution ratio (M2 / M1) of the MoO3 content (M2) to the MoO3 content (M1) of the gadolinium oxide particles of the embodiment is preferably more than 1 and not more than 20, more preferably 1.1 to 10, and even more preferably 1.5 to 5.

[0061] By unevenly distributing molybdenum or a molybdenum compound in the surface layer, excellent characteristics such as catalytic activity can be effectively imparted compared to the case where molybdenum or a molybdenum compound exists uniformly not only in the surface layer but also outside the surface layer (inner layer).

[0062] In addition to molybdenum, the gadolinium oxide particles of the embodiment may further contain lithium, potassium, or sodium.

[0063] <Method for producing gadolinium oxide particles>

[0064] The method for producing gadolinium oxide particles of the embodiment includes a step of calcining a gadolinium compound in the presence of a molybdenum compound. More specifically, the method of the embodiment is a method for producing gadolinium oxide particles, which may include mixing a gadolinium compound and a molybdenum compound to form a mixture, and calcining the mixture.

[0065] According to the method for manufacturing gadolinium oxide particles of the embodiment, the gadolinium oxide particles of the embodiment described above can be manufactured.

[0066] A preferred method for producing gadolinium oxide particles comprises the steps of mixing a gadolinium compound and a molybdenum compound to form a mixture (mixing step) and calcining the mixture (calcining step).

[0067] [Mixing step]

[0068] The mixing step is a step of mixing the gadolinium compound and the molybdenum compound to form a mixture. The contents of the mixture will be described below.

[0069] (Gadolinium Compounds)

[0070] The gadolinium compound is not limited as long as it is a compound that can be calcined into gadolinium oxide (ie, gadolinium oxide). Examples of the gadolinium compound include gadolinium oxide, gadolinium hydroxide, gadolinium carbonate, gadolinium chloride, gadolinium nitrate, and the like, and gadolinium oxide is preferred.

[0071] Since the shape of gadolinium oxide particles after calcination hardly reflects the shape of the raw material gadolinium compound, any shape such as spheres, amorphous shapes, structures having one planar shape (wires, fibers, ribbons, tubes, etc.) or flakes may be suitable as the gadolinium compound.

[0072] (Molybdenum compounds)

[0073] Examples of the molybdenum compound include molybdenum oxide and molybdate compounds.

[0074] Examples of the molybdenum oxide include molybdenum dioxide and molybdenum trioxide, and molybdenum trioxide is preferred.

[0075] The molybdate compound is not limited as long as it is a salt compound of a molybdenum oxyanion such as MoO4 2- 、Mo2O7 2- 、Mo3O 10 2- 、Mo4O 13 2- 、Mo5O 16 2- 、Mo6O 19 2- 、Mo7O 24 6- or Mo8O 26 4- It may be an alkali metal salt, alkaline earth metal salt or ammonium salt of a molybdenum oxyanion.

[0076] As the molybdate compound, an alkali metal salt of a molybdenum oxyanion is preferable, lithium molybdate, potassium molybdate, or sodium molybdate is more preferable, and potassium molybdate or sodium molybdate is further preferable.

[0077] In the method for producing gadolinium oxide particles of the embodiment, the molybdate compound may be a hydrate.

[0078] The molybdate compound is preferably at least one compound selected from the group consisting of molybdenum trioxide, lithium molybdate, potassium molybdate, and sodium molybdate, and more preferably at least one compound selected from the group consisting of molybdenum trioxide, potassium molybdate, and sodium molybdate.

[0079] The method for producing gadolinium oxide particles of the embodiment may include the step of calcining the gadolinium compound in the presence of a molybdenum compound and a potassium compound.

[0080] The method for producing gadolinium oxide particles of the embodiment may include a step of mixing a gadolinium compound, a molybdenum compound, and a potassium compound to form a mixture before the calcining step (mixing step), and may include a step of calcining the mixture (calcining step).

[0081] The method for producing gadolinium oxide particles of the embodiment may include mixing a gadolinium compound and a compound containing molybdenum and potassium to form a mixture before the calcination step (mixing step), and may include calcining the mixture (calcination step).

[0082] For example, relatively inexpensive and more readily available molybdenum and potassium compounds can be used as raw materials in the calcination step to produce a compound containing molybdenum and potassium that is suitable for use as a flux agent. Herein, both the case where the molybdenum and potassium compounds are used as flux agents and the case where the compound containing molybdenum and potassium is used as flux agents are combined, and are considered to be in the presence of the molybdenum and potassium compounds when the molybdenum and potassium compounds are used as flux agents.

[0083] The method for producing gadolinium oxide particles of the embodiment may include a step of calcining the gadolinium compound in the presence of a molybdenum compound and a sodium compound.

[0084] The method for producing gadolinium oxide particles of the embodiment may include a step of mixing a gadolinium compound, a molybdenum compound, and a sodium compound to form a mixture before the calcining step (mixing step), and may include a step of calcining the mixture (calcining step).

[0085] Alternatively, the method for producing gadolinium oxide particles of the embodiment may include mixing a gadolinium compound and a compound containing molybdenum and sodium to form a mixture before the calcination step (mixing step), and may include calcining the mixture (calcination step).

[0086] For example, relatively inexpensive and readily available molybdenum and sodium compounds can be used as raw materials in the calcination step to produce a compound containing molybdenum and sodium that is suitable for use as a flux. Herein, the use of a molybdenum compound and a sodium compound as a flux and the use of a compound containing molybdenum and sodium as a flux are combined, and are considered to be in the presence of a molybdenum compound and a sodium compound when the molybdenum compound and the sodium compound are used as flux.

[0087] By calcining a gadolinium compound in the presence of a molybdenum compound and a potassium compound, or in the presence of a molybdenum compound and a sodium compound, the particle diameter of the produced gadolinium oxide particles can be easily adjusted, and for example, gadolinium oxide particles with a large particle size can be easily obtained. The reason for this is unclear, but the following are considered. For example, because K2MoO4 and Na2MoO4 are stable compounds and are difficult to vaporize during the calcination step, they are less likely to undergo rapid reactions during the vaporization step, and the growth of the gadolinium oxide particles can be easily controlled. Furthermore, it is believed that the molten K2MoO4 and Na2MoO4 function similarly to a solvent, allowing the particle diameter to be increased.

[0088] In the method for producing gadolinium oxide particles in the described embodiment, a molybdenum compound is used as a flux. Hereinafter, the production method using a molybdenum compound as a flux may be referred to simply as the "flux method." It should be noted that after the molybdenum compound reacts with the gadolinium compound at high temperature to form gadolinium molybdate through this type of calcination, the molybdenum compound is believed to be incorporated into the gadolinium oxide particles when the gadolinium molybdate further decomposes into gadolinium and molybdenum oxide at higher temperatures. The molybdenum oxide is believed to be sublimated and removed from the system, and during this step, the molybdenum compound and the gadolinium compound react to form a molybdenum compound in the surface layer of the gadolinium oxide particles. Regarding the formation mechanism of the molybdenum compound contained in the gadolinium oxide particles, it is believed that Mo—O—Gd is formed in the surface layer of the gadolinium oxide particles through the reaction of molybdenum and Gd atoms. High-temperature calcination desorbs Mo, and molybdenum oxide, a compound having a Mo—O—Gd bond, or the like is formed in the surface layer of the gadolinium oxide particles.

[0089] Molybdenum oxide that is not incorporated into the gadolinium oxide particles can also be recovered by sublimation and reused. In this way, the amount of molybdenum oxide adhering to the surface of the gadolinium oxide particles can be reduced, and the initial properties of the gadolinium oxide particles can be maximized.

[0090] On the other hand, the alkali metal salt of the molybdenum oxyanion does not vaporize even within the calcination temperature range and can be easily recovered by washing after calcination, so that the amount of molybdenum compound released to the outside of the calcining furnace is also reduced, and the production cost can also be significantly reduced.

[0091] In the above flux method, for example, when a molybdenum compound and a potassium compound are used in combination, it is believed that the molybdenum compound and the potassium compound first react to form potassium molybdate. Simultaneously, it is believed that the molybdenum compound reacts with the gadolinium compound to form gadolinium molybdate. Subsequently, for example, it is believed that gadolinium molybdate decomposes in the presence of liquid potassium molybdate to grow crystals, making it possible to easily obtain gadolinium oxide particles having a large particle size while suppressing the flux evaporation (sublimation of MoO3) described above.

[0092] The above mechanism is the same when a molybdenum compound and a potassium compound are used in combination (for example, a compound containing molybdenum and sodium is used), and it is believed that gadolinium molybdate is decomposed in the liquid phase in the presence of sodium molybdate, and gadolinium oxide particles with a large particle size and a high molybdenum content can be easily obtained by growing crystals.

[0093] (Metal Compound)

[0094] If necessary, a metal compound may be used during calcination. The method for producing gadolinium oxide particles of the embodiment may include a step of mixing a gadolinium compound, a molybdenum compound, a potassium compound, and a metal compound to form a mixture before the calcination step (mixing step), and may include a step of calcining the mixture (calcining step).

[0095] The metal compound is not particularly limited, but preferably contains at least one selected from the group consisting of a Group II metal compound and a Group III metal compound.

[0096] Examples of the Group II metal compound include magnesium compounds, calcium compounds, strontium compounds, barium compounds and the like.

[0097] Examples of the Group III metal compound include scandium compounds, yttrium compounds, lanthanum compounds, cerium compounds and the like.

[0098] It should be noted that the metal compounds mentioned above refer to oxides, hydroxides, carbonates, or chlorides of metal elements. For example, in the case of yttrium compounds, yttrium oxide (Y2O3), yttrium hydroxide, and yttrium carbonate can be mentioned. The metal compound is preferably an oxide of the metal element. It should be noted that the metal compound contains isomers.

[0099] Among them, metal compounds of period 3 elements, period 4 elements, period 5 elements, and period 6 elements are preferred, metal compounds of period 4 elements and period 5 elements are more preferred, and metal compounds of period 5 elements are further preferred. Specifically, magnesium compounds, calcium compounds, yttrium compounds, and lanthanum compounds are preferably used, more preferably magnesium compounds, calcium compounds, and yttrium compounds are used, and particularly preferably yttrium compounds are used.

[0100] It is preferable to use the metal compound in a proportion of, for example, 0 mass % to 1.2 mass % (eg, 0 mol % to 1 mol %) relative to the total amount of the gadolinium compound used in the mixing step.

[0101] In the method for producing gadolinium oxide particles of the embodiment, the blending amounts of the gadolinium compound and the molybdenum compound are not particularly limited, but preferably, 35% by mass or more of the gadolinium compound and 65% by mass or less of the molybdenum compound are mixed to form a mixture, relative to 100% by mass of the mixture, and the mixture may be calcined. More preferably, 40% by mass or more and 99% by mass or less of the gadolinium compound and 0.5% by mass or more and 60% by mass or less of the molybdenum compound are mixed to form a mixture, relative to 100% by mass of the mixture, and the mixture may be calcined. Even more preferably, 40% by mass or more and 90% by mass or less of the gadolinium compound and 10% by mass or more and 60% by mass or less of the molybdenum compound are mixed to form a mixture, relative to 100% by mass of the mixture, and the mixture may be calcined.

[0102] In the method for producing gadolinium oxide particles of the embodiment, the molar ratio of molybdenum atoms in the molybdenum compound to gadolinium atoms in the gadolinium compound (Mo / Gd) is preferably 0.01 or higher, more preferably 0.03 or higher, and even more preferably 0.1 or higher. From the perspective of obtaining gadolinium oxide particles having a larger size, the Mo / Gd ratio is preferably 0.5 or higher.

[0103] The upper limit of the above molar ratio of molybdenum atoms in the molybdenum compound to gadolinium atoms in the gadolinium compound can be determined appropriately, but from the viewpoint of reducing the amount of the molybdenum compound used and improving production efficiency, for example, the value of the above molar ratio (molybdenum / gadolinium) may be 5 or less, 3 or less, or 2 or less. From the viewpoint of obtaining gadolinium oxide particles having a smaller size, the molybdenum / gadolinium value is preferably less than 0.5.

[0104] As an example of the numerical range of the above molar ratio (Mo / Gd), for example, the values ​​of Mo / Gd may be 0.01 to 5, 0.03 to 3, and 0.1 to 2.

[0105] As the amount of molybdenum used together with gadolinium increases, gadolinium oxide particles having a large particle size shown in the above particle size distribution tend to be obtained.

[0106] Furthermore, as the amount of molybdenum used with respect to gadolinium increases, gadolinium particles with less aggregation tend to be obtained.

[0107] By using various compounds within the above range, the amount of the molybdenum compound contained in the obtained gadolinium oxide particles becomes more appropriate, and gadolinium oxide particles having a controlled particle size can be easily obtained.

[0108] By using various compounds within the above range, the amount of the molybdenum compound contained in the obtained gadolinium oxide particles becomes more appropriate, and gadolinium oxide particles having a controlled degree of aggregation can be easily obtained.

[0109] [Calcination step]

[0110] The calcination step is a step of calcining the mixture. The gadolinium oxide particles according to the embodiment can be obtained by calcining the mixture. As described above, the manufacturing method is called a flux method.

[0111] The flux method is classified as a solution method. More specifically, the flux method is a crystal growth method that utilizes the fact that the crystal-flux two-component phase diagram shows the eutectic type. It is assumed that the mechanism of the flux method is as follows. That is, when the mixture of solute and flux is heated, the solute and flux become liquid phase. At this time, because the flux is a melting agent, in other words, because the solute-flux two-component phase diagram shows the eutectic type, the solute melts at a temperature below its melting point to form a liquid phase. If the flux evaporates in this state, the concentration of the flux decreases, in other words, the effect of reducing the melting point of the solute by the flux is reduced, and the evaporation of the flux is used as a driving force to cause the crystal growth of the solute (flux evaporation method). It should be noted that the solute and flux can also cause the crystal growth of the solute by cooling the liquid phase (slow cooling method).

[0112] The flux method has advantages such as being able to grow crystals at a temperature much lower than the melting point, being able to precisely control the crystal structure, and being able to form a crystal having an automorphic shape.

[0113] While the mechanism of producing gadolinium oxide particles using a flux method using a molybdenum compound as a flux is not always clear, it is hypothesized, for example, to be as follows. Specifically, when the gadolinium compound is calcined in the presence of a molybdenum compound, gadolinium molybdate is first formed. As can be understood from the above description, the gadolinium molybdate then grows into gadolinium oxide crystals at a temperature below the melting point of gadolinium oxide. Subsequently, for example, by evaporating the flux, the gadolinium molybdate decomposes to grow crystals, resulting in gadolinium oxide particles. In other words, the molybdenum compound acts as a flux, and gadolinium oxide particles are produced via an intermediate product called gadolinium molybdate.

[0114] By the above flux method, gadolinium oxide particles containing molybdenum can be produced.

[0115] The calcination method is not particularly limited, and calcination can be performed by a known and commonly used method. When the calcination temperature exceeds 800°C, it is believed that the gadolinium compound and the molybdenum compound react to form gadolinium molybdate. Furthermore, when the calcination temperature reaches 900°C or higher, it is believed that gadolinium molybdate decomposes to form gadolinium oxide particles. Furthermore, in the gadolinium oxide particles, it is believed that when gadolinium molybdate decomposes into gadolinium oxide and molybdenum oxide, the molybdenum compound is incorporated into the gadolinium oxide particles.

[0116] The state of the gadolinium compound and the molybdenum compound during calcination is not particularly limited, and the molybdenum compound may be present in the same space where the molybdenum compound can act on the gadolinium compound. Specifically, the state may be simple mixing in which a molybdenum compound powder and a gadolinium compound powder are mixed, mechanical mixing using a crusher or the like, a mixture using a mortar, or the like, and the mixture may be dry or wet.

[0117] The calcination temperature conditions are not particularly limited and are appropriately determined in consideration of the target particle size of the gadolinium oxide particles, the formation of the molybdenum compound in the gadolinium oxide particles, the shape of the gadolinium oxide particles, etc. The calcination temperature may be 900° C. or higher (which is close to the decomposition temperature of gadolinium molybdate), 1000° C. or higher, or 1300° C. or higher.

[0118] Since the calcination temperature is high, gadolinium oxide particles having a controlled particle shape and a large particle size tend to be easily obtained. From the perspective of efficiently producing such gadolinium oxide particles, the calcination temperature is preferably 1100°C or higher, more preferably 1200°C or higher, and even more preferably 1300°C or higher.

[0119] Generally, when attempting to control the shape of the obtained gadolinium oxide particles after calcination, it is necessary to perform high-temperature calcination at a temperature higher than 2000° C., where the reaction of gadolinium oxide easily proceeds, but in industrial applications, there are huge problems in terms of the load on the calcination furnace and fuel costs.

[0120] According to embodiments of the present invention, for example, even if the maximum calcination temperature for calcining the gadolinium compound is 1600° C. or lower, gadolinium oxide particles can be efficiently formed at low cost.

[0121] Furthermore, according to the method for producing gadolinium oxide particles of the embodiment, even when the calcination temperature is 1600° C. or lower (which is much lower than the melting point of gadolinium oxide), gadolinium oxide particles having their own shape can be formed, regardless of the shape of the precursor. Furthermore, from this viewpoint, the calcination temperature is preferably 1500° C. or lower, more preferably 1400° C. or lower, and even more preferably 1300° C. or lower.

[0122] As an example, the calcination temperature of the gadolinium compound in the calcination step may have a numerical range of 900°C to 1600°C, 1000°C to 1500°C, 1100°C to 1400°C, or 1200°C to 1300°C.

[0123] From the viewpoint of production efficiency, the heating rate may be 20° C. / hour to 600° C. / hour, 40° C. / hour to 500° C. / hour, and 80° C. / hour to 400° C. / hour.

[0124] Regarding the calcination time, calcination is preferably performed so that the ramp-up time to the predetermined calcination temperature is in the range of 15 minutes to 10 hours. The holding time at the calcination temperature may be 5 minutes or longer, preferably in the range of 5 minutes to 1000 hours, and more preferably in the range of 1 hour to 100 hours. To effectively form gadolinium oxide particles, the holding time at the calcination temperature is more preferably 2 hours or longer, more preferably 2 hours to 100 hours, and even more preferably 2 hours to 48 hours.

[0125] As an example, the gadolinium oxide particles containing molybdenum of the embodiment can be easily obtained by selecting the conditions of a calcination temperature of 900° C. to 1600° C. and a holding time at the calcination temperature of 2 hours to 100 hours.

[0126] The calcination atmosphere is not particularly limited as long as the effects of the present invention can be obtained, but for example, an oxygen-containing atmosphere such as air or oxygen or an inert atmosphere such as nitrogen, argon or carbon dioxide is preferred, and an air atmosphere is more preferred when cost is taken into consideration.

[0127] The equipment used for calcination is not necessarily limited, and a so-called calciner can be used. The calciner is preferably made of a material that does not react with the sublimated molybdenum oxide, and a highly sealed calciner is preferably used so that the molybdenum oxide can be used efficiently.

[0128] [Molybdenum removal step]

[0129] The method for producing gadolinium oxide particles of the embodiment may further include a molybdenum removing step of removing at least a portion of the molybdenum after the calcining step, if necessary.

[0130] As described above, since molybdenum sublimes during calcination, it is possible to control the molybdenum content present in the surface layer of the gadolinium oxide particles, as well as the molybdenum content and its presence state in the inner layer other than the surface layer of the gadolinium oxide particles, by controlling the calcination time, calcination temperature, etc.

[0131] Molybdenum can adhere to the surface of gadolinium oxide particles. As a means other than sublimation, molybdenum can be removed by washing with water, aqueous ammonia solution, aqueous sodium hydroxide solution, etc.

[0132] At this time, the molybdenum content in the gadolinium oxide particles can be controlled by appropriately changing the concentration and amount of water, ammonia solution or sodium hydroxide solution used, as well as the washing location and washing time.

[0133] [Crushing step]

[0134] In the calcined product obtained by the calcination step, gadolinium oxide particles may aggregate, and the calcined product may not meet the range of particle diameters suitable for the application under consideration. Therefore, the gadolinium oxide particles may be pulverized as necessary to meet the range of suitable particle diameters.

[0135] The method for pulverizing the calcined product is not particularly limited, and conventionally known pulverization methods such as a ball mill, a jaw crusher, a jet mill, a disc mill, a spectromill, a grinder, and a mixer mill can be used.

[0136] [Classification steps]

[0137] The calcined product containing gadolinium oxide particles obtained in the calcining step may be appropriately classified in order to adjust the range of particle size. The "classification process" refers to an operation of grouping particles based on their size.

[0138] Classification can be wet or dry, but from the perspective of productivity, dry classification is preferred. Dry classification includes classification by sieving, wind classification by the difference between centrifugal force and fluid resistance, etc., but from the perspective of classification accuracy, wind classification is preferred and can be performed by using a classifier using the Coanda effect, such as an airflow classifier, a vortex airflow classifier, a forced vortex centrifugal classifier, and a semi-free vortex centrifugal classifier.

[0139] The above-mentioned pulverization step and classification step can be performed at a necessary stage. For example, the average particle diameter of the gadolinium oxide particles to be obtained can be adjusted by the presence or absence of pulverization and classification and the selection of the conditions thereof.

[0140] Among the gadolinium oxide particles of the embodiment or the gadolinium oxide particles obtained by the production method of the embodiment, gadolinium oxide particles with little or no aggregation are likely to exhibit their initial characteristics and be excellent in their own handleability, and when the gadolinium oxide particles are used by dispersing them in a medium to be dispersed, they are preferred from the viewpoint of more excellent dispersibility.

[0141] It should be noted that the method for producing gadolinium oxide particles according to the embodiment described above has an excellent advantage in that gadolinium oxide particles with little or no aggregation can be easily produced, and gadolinium oxide particles with excellent desired properties can be produced with high productivity without performing the above-mentioned pulverization step or classification step.

[0142] [Example]

[0143] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

[0144] <Manufacturing of Gadolinium Oxide Particles>

[0145] [Comparative Example 1]

[0146] 3.0 g of commercially available gadolinium oxide Gd2O3 (manufactured by Aladdin (China)) was placed in a crucible and calcined in a ceramic electric furnace at 1100° C. for 24 hours. After lowering the temperature, the crucible was taken out to obtain 3.0 g of white powder.

[0147] [Comparative Example 2]

[0148] In Comparative Example 1, 3.0 g of a white powder was obtained by the same operation as in Comparative Example 1, except that the calcination conditions were changed to 1300° C. for 24 hours.

[0149] [Example 1]

[0150] 3.0 g of gadolinium oxide Gd2O3 (manufactured by Aladdin (China)) and 0.15 g of molybdenum trioxide (manufactured by Chengdu Hongbo Industrial Co., Ltd. (China)) were mixed in a mortar to obtain a mixture. The obtained mixture was placed in a crucible and calcined in a ceramic electric furnace at 1100°C for 24 hours, and then at 1500°C for 24 hours. After lowering the temperature, the crucible was removed to obtain 3.15 g of white powder. Subsequently, 3.15 g of the obtained white powder was suspended in 9 g of ion-exchanged water, precipitated at 3000 rpm for 15 minutes using a centrifuge, and the supernatant was discarded. This operation was repeated six times to wash the white powder, obtaining 3.07 g of white powder.

[0151] [Example 2]

[0152] In Example 1, the powder of Example 2 was obtained by the same operation as in Example 1, except that the amount of molybdenum trioxide used was changed as shown in Table 1.

[0153] [Example 3]

[0154] 3.0 g of gadolinium oxide Gd2O3 (manufactured by Aladdin (China)), 2.7 g of molybdenum trioxide (manufactured by Chengdu Hongbo Industrial Co., Ltd. (China)), 1.3 g of potassium carbonate (manufactured by Aladdin (China)), and 0.015 g of yttrium oxide (manufactured by Aladdin (China)) were mixed in a mortar to obtain a mixture. The obtained mixture was placed in a crucible and calcined in a ceramic electric furnace at 1300°C for 24 hours, and then at 1500°C for 24 hours. After lowering the temperature, the crucible was removed to obtain 5.355 g of white powder. Subsequently, 5.355 g of the obtained white powder was suspended in 16 g of ion-exchanged water, precipitated at 3000 rpm for 15 minutes using a centrifuge, and the supernatant was discarded. This operation was repeated six times to wash the white powder, obtaining 3.297 g of white powder.

[0155] [Example 4]

[0156] 3.0 g of gadolinium oxide Gd2O3 (manufactured by Aladdin (China)) and 3.6 g of sodium molybdate dihydrate (manufactured by Aladdin (China)) were mixed in a mortar to obtain a mixture. The resulting mixture was placed in a crucible and calcined in a ceramic electric furnace at 1300°C for 24 hours. After lowering the temperature, the crucible was removed to obtain 6.6 g of a white powder. Subsequently, 6.55 g of the obtained white powder was suspended in 16 g of ion-exchanged water, precipitated at 3000 rpm for 15 minutes using a centrifuge, and the supernatant was discarded. This operation was repeated six times to wash the white powder, obtaining 2.93 g of white powder.

[0157] <Assessment>

[0158] The washed powders obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were used as sample powders and evaluated as follows.

[0159] [Crystal structure analysis: X-ray diffraction (XRD) method]

[0160] The sample powder was filled in a holder for a sample with a measurement depth of 0.5 mm placed in a wide-angle X-ray diffraction (XRD) apparatus (Ultima IV manufactured by Rigaku Corporation), and measurement was performed under the conditions of Cu / Kα radiation, 40 kV / 40 mA, a scanning speed of 2° / min, and a scanning range of 10° to 70°.

[0161] [Measurement of particle size distribution]

[0162] The particle diameter distribution of the sample powder was measured by a dry method using a laser diffraction type dry particle size distribution analyzer (HELOS (H3355) and RODOS manufactured by Japan Laser Corporation) under the conditions of a dispersion pressure of 3 bar and a pulling pressure of 90 mbar. The particle diameter at the point where the distribution curve of cumulative volume % intersects the horizontal axis of 10% from the small particle side is defined as D 10 The particle diameter at the point where the cumulative volume % distribution curve intersects the horizontal axis at 50% is defined as D 50 , and the particle diameter at the point where the distribution curve of cumulative volume % intersects the horizontal axis of 90% from the small particle side is defined as D 90 , and measure the diameters of these particles.

[0163] [X-ray fluorescence (XRF) analysis]

[0164] Using a fluorescent X-ray analyzer Primus IV (manufactured by Rigaku Corporation), about 70 mg of the sample powder was placed on filter paper, covered with a PP film, and X-ray fluorescence (XRF) analysis was performed under the following conditions.

[0165] Measurement conditions

[0166] EZ Scan Mode

[0167] Elements to be measured: F to U

[0168] Measuring time: Standard

[0169] Measuring diameter: 10mm

[0170] Remaining (balance components): None

[0171] Results of the Gd 2 O 3 content (G1) relative to 100 mass % of the gadolinium oxide particles and the MoO 3 content (M1) relative to 100 mass % of the gadolinium oxide particles were obtained by XRF analysis.

[0172] [XPS surface analysis]

[0173] For surface elemental analysis of the sample powder, X-ray photoelectron spectroscopy (XPS) was performed using a QUANTERA SXM manufactured by ULVAC-PHI, Inc. and a monochromatic Al-Kα X-ray source. The average value of n = 3 measurements of each element in atomic % was obtained in a 1000 μm square range.

[0174] By converting the gadolinium content in the surface layer of the gadolinium oxide particles and the molybdenum content in the surface layer obtained by XPS analysis into oxides, the Gd2O3 content (G2) (mass %) relative to 100 mass % of the surface layer of the gadolinium oxide particles and the MoO3 content (M2) (mass %) relative to 100 mass % of the surface layer of the gadolinium oxide particles were determined.

[0175] <Results>

[0176] Table 1 shows the respective values ​​obtained by the above evaluation. Note that "ND" is an abbreviation for not detected, and indicates that it was not detected.

[0177] [Table 1]

[0178]

[0179] The SEM images of the powders of the above examples and comparative examples obtained by photographing with a scanning electron microscope (SEM) are shown in FIG. Figures 1 to 6 Granular or columnar particles were observed in each of the Examples and Comparative Examples.

[0180] The results of XRD analysis are shown in Figure 7 In each sample of Examples and Comparative Examples, peaks (unlabeled peaks) derived from gadolinium oxide (Gd2O3) were observed.

[0181] Based on the results of the above SEM observation and XRD analysis, it was confirmed that the powders obtained in Examples and Comparative Examples were gadolinium oxide particles containing gadolinium oxide (gadolinium oxide).

[0182] According to the results of the respective examples, it was shown that it is possible to calcine gadolinium oxide particles containing molybdenum even at relatively low calcination temperatures of 1100° C. and 1500° C. by calcining the gadolinium compound in the presence of the molybdenum compound.

[0183] From the SEM observation images of each of the gadolinium oxide particles, the aggregation degree of the particles was evaluated according to the following criteria.

[0184] +: Particle aggregation was observed.

[0185] -: No obvious particle aggregation was observed.

[0186] In the gadolinium oxide particles of Comparative Examples 1 and 2, aggregation and fusion of the particles were observed (aggregation degree +), whereas no significant aggregation was observed in the gadolinium oxide particles of Examples 2 to 4 (aggregation degree -). Furthermore, in a comparison of Examples 1 and 2, aggregation and fusion of the particles were observed in the gadolinium oxide particles of Example 1, whereas no significant aggregation was observed in the gadolinium oxide particles of Example 2.

[0187] From these facts, it was shown that gadolinium oxide particles having low aggregation characteristics can be produced by calcining a gadolinium compound in the presence of a molybdenum compound, and that particles having a low degree of aggregation or no aggregation tend to be obtained as the amount of molybdenum used increases.

[0188] Furthermore, gadolinium oxide particles having a large particle size were obtained in Examples 3 and 4. This fact indicates that gadolinium oxide particles having a large particle size can be easily obtained by using an alkali metal salt of a molybdenum oxyanion as a flux.

[0189] Table 1 shows the values ​​of the above Gd2O3 content (G1), MoO3 content (M1), Gd2O3 content (G2), and MoO3 content (M2).

[0190] Based on the results of the MoO 3 content (M1) and the MoO 3 content (M2), the gadolinium oxide particles of Examples 1 to 4 contain molybdenum on the surface and are expected to exert various effects of molybdenum, such as catalytic activity.

[0191] In addition, Table 1 shows the calculation results of the surface layer uneven distribution ratio (M2 / M1) of the MoO3 content (M2) to the MoO3 content (M1).

[0192] According to the results of the surface layer uneven distribution ratio (M2 / M1) in the gadolinium oxide particles of Examples 1 and 4, the molybdenum oxide content in the surface layer of the gadolinium oxide particles measured by XPS surface analysis was greater than the molybdenum oxide content measured by XRF analysis. Therefore, it was confirmed that molybdenum was unevenly distributed in the surface layer of the gadolinium oxide particles, and it can be expected that the various effects of molybdenum will be effectively exerted.

[0193] The various configurations in the various embodiments, their combinations, etc. are examples, and configurations may be added, omitted, replaced, and other changes may be made without departing from the spirit of the invention. In addition, the present invention is not limited by the various embodiments, but only by the scope of the claims.

Claims

1. A gadolinium oxide particle comprising molybdenum, The gadolinium oxide Gd2O3 content G1 relative to 100% by mass of the gadolinium oxide particles as measured by XRF analysis of the gadolinium oxide particles is 70% by mass to 98% by mass, and The molybdenum trioxide MoO 3 content M1 relative to 100 mass % of the gadolinium oxide particles, as measured by XRF analysis of the gadolinium oxide particles, is 1 mass % to 30 mass %.

2. The gadolinium oxide particles according to claim 1, wherein the median diameter D of the gadolinium oxide particles calculated by the laser diffraction / scattering method is 50 0.1μm to 1000μm.

3. The gadolinium oxide particles according to claim 1 or 2, wherein The gadolinium oxide content G2 relative to 100% by mass of the surface layer of the gadolinium oxide particles, as measured by XPS surface analysis of the gadolinium oxide particles, is 10% by mass to 98% by mass, and The molybdenum trioxide content M2 relative to 100% by mass of the surface layer of the gadolinium oxide particles, as measured by XPS surface analysis of the gadolinium oxide particles, is 2% by mass to 40% by mass.

4. A method for producing the gadolinium oxide particles according to claim 1 or 2, comprising: The calcination step comprises: using a molybdenum compound as a flux and calcining gadolinium oxide in the presence of the molybdenum compound to form gadolinium molybdate; The gadolinium molybdate grows gadolinium oxide crystals at a temperature lower than the melting point of gadolinium oxide; By evaporating the flux, the gadolinium molybdate is decomposed to grow crystals, thereby obtaining the gadolinium oxide particles; and The molybdenum removal step comprises controlling the molybdenum content in the surface layer of the gadolinium oxide particles by controlling the calcination time or temperature, or removing the molybdenum adhering to the surface of the gadolinium oxide particles by washing with water, an aqueous ammonia solution, or an aqueous sodium hydroxide solution, thereby producing the gadolinium oxide particles according to claim 1 or 2. 5 . The method for producing gadolinium oxide particles according to claim 4 , wherein the molybdenum compound is at least one compound selected from the group consisting of molybdenum trioxide, lithium molybdate, potassium molybdate, and sodium molybdate.

6. The method for producing gadolinium oxide particles according to claim 4 or 5, wherein the temperature for the calcination is 900°C to 1600°C.

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