Patent Application
20240367991
The present invention relates to gadolinia particles and a method for producing the gadolinia particles.
Gadolinium oxide (that is, gadolinia) has been used and researched in optical applications such as fluorescent host materials, optical glasses, optical isolator substrates, laser elements, and photonic crystals, and in a wide range of applications such as memory materials.
For example, PTL 1 discloses that gadolinia doped ceria (GDC) powders and gadolinia (Gd2O3) powders were used to produce gadolinia doped ceria (GDC)/gadolinia (Gd2O3) granules.
However, what is disclosed in PTL 1 is a method for producing the above-mentioned granules, not a method for producing the gadolinia particles in which the gadolinia particles themselves are synthesized from raw materials. As described above, knowledge about the gadolinia particles and the method for producing the gadolinia particles is limited, and there is still room for study.
Therefore, an object of the present invention is to provide gadolinia particles having excellent properties and a method for producing the gadolinia particles.
The present invention includes the following aspects.
According to the present invention, it is possible to provide gadolinia particles having excellent properties and a method for producing the gadolinia particles.
Hereinafter, an embodiment of gadolinia particles and a method for producing the gadolinia particles of the present invention will be described.
The gadolinia particles of the embodiment contain molybdenum. The gadolinia particles of the embodiment contain molybdenum and have excellent properties such as catalytic activity and shape derived from molybdenum.
The gadolinia particles of the embodiment produced by a production method of the embodiment can have a peculiar automorphic shape such as granular or columnar shape as shown in Examples described below.
In this specification, “columnar shape” includes a prismatic shape, a columnar shape, a rod shape, and the like. A shape of a bottom surface of a columnar body of columnar gadolinia particles is not particularly limited, and examples thereof include a circular shape, an elliptical shape, and a polygonal shape. The columnar body includes a body that extends straight in a length direction thereof, a body that extends in an inclined manner, a body that extends while bending, a shape that branches in a branch shape, and the like.
In the gadolinia particles of the embodiment, a particle size, degree of aggregation, molybdenum content, and the like of the gadolinia particles obtained can be controlled by controlling a used amount and type of the molybdenum compound in the production method described below.
A median diameter D50 of the gadolinia particles of the embodiment calculated by a laser diffraction/scattering method is preferably 0.1 to 1000 μm, more preferably 3 to 100 μm, and even more preferably 0.5 to 20 μm.
From a viewpoint of providing the gadolinia particles having a larger size, the median diameter D50 of the gadolinia particles of the embodiment calculated by the laser diffraction/scattering method is preferably 25 to 200 μm, more preferably 30 to 100 μm, and even more preferably 40 to 80 μm.
The median diameter D50 of a sample of the gadolinia particles calculated by the laser diffraction/scattering method can be determined as a particle diameter in which a ratio of cumulative volume % is 50% in a particle diameter distribution measured by a dry method using a laser diffraction type particle size distribution meter.
A particle diameter D10 of the gadolinia particles of the embodiment calculated by the laser diffraction/scattering method is preferably 0.05 to 100 μm, more preferably 0.08 to 50 μm, and even more preferably 0.1 to 5 am.
From the viewpoint of providing the gadolinia particles having a larger size, the particle diameter D10 of the gadolinia particles of the embodiment calculated by the laser diffraction/scattering method is preferably 6 to 80 μm, more preferably 8 to 50 m, and even more preferably 10 to 30 μm.
The particle diameter D10 of the sample of the gadolinia particles calculated by the laser diffraction/scattering method can be determined as a particle diameter in which the ratio of cumulative volume % from a small particle side is 10% in the particle diameter distribution measured by the dry method using the laser diffraction type particle size distribution meter.
A particle diameter D90 of the gadolinia particles of the embodiment calculated by the laser diffraction/scattering method is preferably 1 to 1500 μm, more preferably 2 to 500 μm, and even more preferably 8 to 50 μm.
From the viewpoint of providing the gadolinia particles having a larger size, the particle diameter D90 of the gadolinia particles of the embodiment calculated by the laser diffraction/scattering method is preferably 60 to 800 μm, more preferably 80 to 500 μm, and even more preferably 100 to 200 μm.
The particle diameter D90 of the sample of the gadolinia particles calculated by the laser diffraction/scattering method can be determined as a particle diameter in which the ratio of cumulative volume % from the small particle side is 90% in the particle diameter distribution measured by the dry method using the laser diffraction type particle size distribution meter.
The gadolinia particles of the embodiment contain gadolinium oxide (that is gadolinia). Examples of gadolinium oxide that the gadolinia particles of the embodiment may contain include Gd2O3 and GdO2.
The gadolinia 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 with respect to 100 mass % of the gadolinia particles.
Gadolinia content in the gadolinia particles can be measured by XRF analysis. In the gadolinia particles of the embodiment, Gd2O3 content (G1) with respect to 100 mass % of the gadolinia particles determined by XRF analysis of the gadolinia particles is preferably 60 to 99.95 mass %, more preferably 65 to 99.5 mass %, and even more preferably 70 to 98 mass %.
The gadolinia particles of the embodiment contain molybdenum. In the gadolinia particles of the embodiment, MoO3 content (M1) with respect to 100 mass % of the gadolinia particles determined by XRF analysis of the gadolinia particles is preferably 0.05 to 40 mass %, more preferably 0.1 to 35 mass %, and even more preferably 1 to 30 mass %.
Upper limit values and lower limit values of the Gd2O3 content (G1) and the MoO3 content (M1) exemplified above in the gadolinia particles of the embodiment can be freely combined. Further, numerical values of the Gd2O3 content (G1) and the MoO3 content (M1) can be freely combined.
As an example of the gadolinia particles of the embodiment, the gadolinia particles having the Gd2O3 content (G1) of 60 to 99.95 mass %, and the MoO3 content (M1) of 0.05 to 40 mass % can be exemplified.
The above Gd2O3 content (G1) and the MoO3 content (M1) can be measured by XRF analysis, for example, using a fluorescent X-ray analyzer (PrimusIV) manufactured by Rigaku Corporation.
The gadolinia content contained in the surface layer of the gadolinia particles can be measured by X-ray photoelectron spectroscopy (XPS) surface analysis. In the gadolinia particles of the embodiment, Gd2O3 content (G2) with respect to 100 mass % of the surface layer of the gadolinia particles determined by XPS surface analysis of the gadolinia particles is preferably 10 to 98 mass %, more preferably 20 to 80 mass %, and even more preferably 30 to 65 mass %.
In the gadolinia particles of the embodiment, MoO3 content (M2) with respect to 100 mass % of the surface layer of the gadolinia particles determined by XPS surface analysis of the gadolinia particles is preferably 2 to 40 mass %, more preferably 3 to 35 mass %, and even more preferably 8 to 30 mass %.
Upper limit values and lower limit values of the Gd2O3 content (G2) and the MoO3 content (M2) exemplified above in the gadolinia particles of the embodiment can be freely combined. Further, numerical values of the Gd2O3 content (G2) and the MoO3 content (M2) can be freely combined.
As an example of the gadolinia particles of the embodiment, the gadolinia particles having the Gd2O3 content (G2) of 10 to 98 mass %, and the MoO3 content (M2) of 2 to 40 mass % can be exemplified.
The above Gd2O3 content (G2) refers to a value determined as the content of Gd2O3 with respect to 100 mass % of the surface layer of the gadolinia particles by obtaining an abundance ratio (atom %) for each element by XPS surface analysis of the sample of the gadolinia particles by X-ray photoelectron spectroscopy (XPS) and by converting the gadolinium content to oxide.
The above MoO3 content (M2) refers to a value determined as the content of MoO3 with respect to 100 mass % of the surface layer of the gadolinia particles by obtaining an abundance ratio (atom %) for each element by XPS surface analysis of the gadolinia particles by X-ray photoelectron spectroscopy (XPS) and by converting the molybdenum content to oxide.
In the gadolinia particles of the embodiment, the molybdenum is preferably unevenly distributed in a surface layer of the gadolinia particles.
Here, the “surface layer” in this specification means within 10 nm from a surface of the gadolinia particles of the embodiment. This distance corresponds to a detection depth of XPS used for measurement in Examples.
Here, “unevenly distributed in the surface layer” means that a mass of molybdenum or the molybdenum compound per unit volume in the surface layer is greater than that of molybdenum or the molybdenum compound per unit volume in other than the surface layer.
In the gadolinia particles of the embodiment, the fact that molybdenum is unevenly distributed in the surface layer of the gadolinia particles is confirmed by the fact that the MoO3 content (M2) with respect to 100 mass % of the surface layer of the gadolinia particles determined by XPS surface analysis of the gadolinia particles is greater than the MoO3 content (M1) with respect to 100 mass % of the gadolinia particles determined by XRF (fluorescent X-ray) analysis of the gadolinia particles as described in Examples described below.
In the gadolinia particles of the embodiment, as an index that molybdenum is unevenly distributed in the surface layer of the gadolinia particles, a surface layer uneven distribution ratio (M2/M1) of the MoO3 content (M2) to the MoO3 content (M1) of the gadolinia 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.
By unevenly distributing molybdenum or the molybdenum compound in the surface layer, excellent properties such as catalytic activity can be efficiently imparted as compared with a case where molybdenum or the molybdenum compound is uniformly present not only in the surface layer but also in other than the surface layer (inner layer).
The gadolinia particles of the embodiment may further contain lithium, potassium, or sodium in addition to molybdenum.
The method for producing the gadolinia particles of the embodiment includes calcining a gadolinium compound in presence of the molybdenum compound. More specifically, the production method of the embodiment is the method for producing the gadolinia particles, which may include mixing the gadolinium compound and the molybdenum compound to form a mixture, and calcining the mixture.
According to the method for producing the gadolinia particles of the embodiment, the gadolinia particles of the embodiment described above can be produced.
A preferred method for producing the gadolinia particles includes a step (mixing step) of mixing the gadolinium compound and the molybdenum compound to form the mixture, and a step (calcination step) of calcining the mixture.
The mixing step is a step of mixing the gadolinium compound and the molybdenum compound to form the mixture. The contents of the mixture will be described below.
The gadolinium compound is not limited as long as it is a compound that can be calcined to the gadolinium oxide (that is gadolinia). Examples of the gadolinium compound include gadolinium oxide, gadolinium hydroxide, gadolinium carbonate, gadolinium chloride, gadolinium nitrate and the like, and the gadolinium oxide is preferable.
Since a shape of the gadolinia particles after calcination hardly reflects a shape of a raw material gadolinium compound, any shape such as a sphere, an amorphous shape, a structure having an aspect (a wire, a fiber, a ribbon, a tube, or the like), or a sheet can be suitably used as the gadolinium compound.
Examples of the molybdenum compound include molybdenum oxide and molybdate compounds.
Examples of the molybdenum oxide include molybdenum dioxide and molybdenum trioxide, and the molybdenum trioxide is preferable.
The molybdate compound is not limited as long as it is a salt compound of molybdenum oxoanion such as MoO42, Mo2O72−, Mo3O102−, Mo4O132−, Mo5O162−, Mo6O192−, Mo7O246−, or Mo8O264−. It may be an alkali metal salt of the molybdenum oxoanion, an alkaline earth metal salt, or an ammonium salt.
As the molybdate compound, the alkali metal salt of the molybdenum oxoanion is preferable, lithium molybdate, potassium molybdate or sodium molybdate is more preferable, and potassium molybdate or sodium molybdate is further preferable.
In the method for producing the gadolinia particles of the embodiment, the molybdate compound may be a hydrate.
The molybdate compound is preferably at least one compound selected from a group including molybdenum trioxide, lithium molybdate, potassium molybdate, and sodium molybdate, and more preferably at least one compound selected from a group including molybdenum trioxide, potassium molybdate, and sodium molybdate.
The method for producing the gadolinia particles of the embodiment may include a step of calcining the gadolinium compound in the presence of the molybdenum compound and a potassium compound.
The method for producing the gadolinia particles of the embodiment can include the step (mixing step) of mixing the gadolinium compound, the molybdenum compound, and the potassium compound to form the mixture prior to the calcination step, and can include the step (calcination step) of calcining the mixture.
The method for producing the gadolinia particles of the embodiment can include the step (mixing step) of mixing the gadolinium compound and a compound containing molybdenum and potassium to form the mixture prior to the calcination step, and can include the step (calcination step) of calcining the mixture.
The compound containing molybdenum and potassium, which is suitable as a flux agent, can be produced, for example, using a molybdenum compound and a potassium compound, which are cheaper and more easily available, as raw materials in the calcination step. Here, both when the molybdenum compound and the potassium compound are used as the flux agent and when the compound containing molybdenum and potassium is used as the flux agent are combined and regarded as when the molybdenum compound and the potassium compound are used as the flux agent, that is, in the presence of the molybdenum compound and the potassium compound.
The method for producing the gadolinia particles of the embodiment may include a step of calcining the gadolinium compound in the presence of the molybdenum compound and a sodium compound.
The method for producing the gadolinia particles of the embodiment can include a step (mixing step) of mixing the gadolinium compound, the molybdenum compound, and the sodium compound to form the mixture prior to the calcination step, and can include a step (calcination step) of calcining the mixture.
Alternatively, the method for producing the gadolinia particles of the embodiment can include a step (mixing step) of mixing the gadolinium compound and a compound containing molybdenum and sodium to form the mixture prior to the calcination step, and can include a step (calcination step) of calcining the mixture.
The compound containing molybdenum and sodium, which is suitable as the flux agent, can be produced, for example, using the molybdenum compound and the sodium compound, which are cheaper and more easily available, as raw materials in the calcination step. Here, both when the molybdenum compound and the sodium compound are used as the flux agent and when the compound containing molybdenum and sodium is used as the flux agent are combined and regarded as when the molybdenum compound and the sodium compound are used as the flux agent, that is, in the presence of the molybdenum compound and the sodium compound.
By calcining the gadolinium compound in the presence of the molybdenum compound and the potassium compound, or in the presence of the molybdenum compound and the sodium compound, the particle diameter of the gadolinia particles to be produced can be easily adjusted, and for example, the gadolinia particles having a large particle size can be easily produced. The reason is not clear, but the following reasons can be considered. For example, since K2MoO4 and Na2MoO4 are stable compounds and are difficult to volatilize in the calcination step, they are unlikely to be accompanied by a rapid reaction in a volatilization step, and growth of the gadolinia particles can be easily controlled. Further, it is considered that the molten K2MoO4 and Na2MoO4 exert a function like a solvent, so that a value of the particle diameter can be increased.
In the method for producing the gadolinia particles of the embodiment, the molybdenum compound is used as the flux agent. Hereinafter, in this specification, the production method using the molybdenum compound as the flux agent may be simply referred to as the “flux method”. Note that after the molybdenum compound reacts with the gadolinium compound at a high temperature to form gadolinium molybdate by such calcination, when the gadolinium molybdate is further decomposed into gadolinium and molybdenum oxide at a higher temperature, it is considered that the molybdenum compound is incorporated into the gadolinia particles. It is considered that the molybdenum oxide is sublimated and removed from the system, and in this step, the molybdenum compound and the gadolinium compound react to form the molybdenum compound in the surface layer of the gadolinia particles. Regarding formation mechanism of the molybdenum compound contained in the gadolinia particles, more specifically, it is considered that Mo—O—Gd is formed in the surface layer of the gadolinia particles by reaction of molybdenum and Gd atoms, Mo is desorbed by high-temperature calcination, and the molybdenum oxide, a compound having a Mo—O—Gd bond, or the like is formed in the surface layer of the gadolinia particles.
The molybdenum oxide that is not incorporated into the gadolinia particles can also be recovered by sublimation and reused. In this way, an amount of the molybdenum oxide adhering to the surface of the gadolinia particles can be reduced, and original properties of the gadolinia particles can be maximized.
On the other hand, the alkali metal salt of the molybdenum oxoanion does not vaporize even in a calcination temperature range and can be easily recovered by washing after calcination, so that an amount of the molybdenum compound released to outside a calcining furnace is also reduced, and production cost can also be significantly reduced.
In the above flux method, for example, when the molybdenum compound and the potassium compound are used in combination, it is considered that the molybdenum compound and the potassium compound first react to form the potassium molybdate. At the same time, it is considered that the molybdenum compound reacts with the gadolinium compound to form the gadolinium molybdate. Then, for example, it is considered that the gadolinium molybdate is decomposed in the presence of potassium molybdate in a liquid phase to grow crystals, so that the gadolinia particles having a large particle size can be easily obtained while suppressing evaporation of flux (sublimation of MoO3) described above.
The above mechanism is the same when the molybdenum compound and the potassium compound are used in combination (for example, a compound containing molybdenum and sodium is used), and it is considered that the gadolinium molybdate is decomposed in the presence of sodium molybdate in the liquid phase, and the gadolinia particles having a large particle size and a high molybdenum content can be easily obtained by growing crystals.
A metal compound can be used at a time of calcination if desired. The method for producing the gadolinia particles of the embodiment can include a step (mixing step) of mixing the gadolinium compound, the molybdenum compound, the potassium compound, and the metal compound to form the mixture prior to the calcination step, and can include a step (calcination step) of calcining the mixture.
The metal compound is not particularly limited, but preferably contains at least one selected from a group including Group II metal compounds and Group III metal compounds.
Examples of the Group II metal compounds include magnesium compounds, calcium compounds, strontium compounds, barium compounds and the like.
Examples of the Group III metal compounds include scandium compounds, yttrium compounds, lanthanum compounds, cerium compounds and the like.
Note that the above-mentioned metal compound means an oxide, a hydroxide, a carbonate, or a chloride of a metal element. For example, in the case of the yttrium compound, yttrium oxide (Y2O3), yttrium hydroxide, and yttrium carbonate can be mentioned. Of these, the metal compound is preferably an oxide of the metal element. Note that the metal compound contains an isomer.
Of these, the metal compound of period 3 element, the metal compound of period 4 element, the metal compound of period 5 element, and the metal compound of period 6 element are preferable, the metal compound of period 4 element and the metal compound of period 5 element are more preferable, and the metal compound of period 5 element is further preferable. Specifically, the magnesium compound, the calcium compound, the yttrium compound, and the lanthanum compound are preferably used, the magnesium compound, the calcium compound, and the yttrium compound are more preferably used, and the yttrium compound is particularly preferably used.
The metal compound is preferably used in a proportion of, for example, 0 to 1.2 mass % (for example, 0 to 1 mol %) with respect to a total amount of the gadolinium compounds used in the mixing step.
In the method for producing the gadolinia particles of the embodiment, blending amounts of the gadolinium compound and the molybdenum compound are not particularly limited, but preferably 35 mass % or more of the gadolinium compound and 65 mass % or less of the molybdenum compound are mixed with respect to 100 mass % of the mixture to form the mixture, and the mixture can be calcined. More preferably, 40 mass % or more and 99 mass % or less of the gadolinium compound and 0.5 mass % or more and 60 mass % or less of the molybdenum compound are mixed with respect to 100 mass % of the mixture to form the mixture, and the mixture can be calcined. Even more preferably, 40 mass % or more and 90 mass % or less of the gadolinium compound and 10 mass % or more and 60 mass % or less of the molybdenum compound are mixed with respect to 100 mass % of the mixture to form the mixture, and the mixture can be calcined.
In the method for producing the gadolinia particles of the embodiment, a value of a molar ratio (molybdenum/gadolinium) of molybdenum atom in the molybdenum compound and gadolinium atom in the gadolinium compound is preferably 0.01 or more, more preferably 0.03 or more, and even more preferably 0.1 or more. From the viewpoint of obtaining the gadolinia particles having a larger size, the value of molybdenum/gadolinium is preferably 0.5 or more.
An upper limit value of the above molar ratio of the molybdenum atom in the molybdenum compound and the gadolinium atom in the gadolinium compound may be appropriately determined, but from a 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 the gadolinia particles having a smaller size, the value of molybdenum/gadolinium is preferably less than 0.5.
As an example of a numerical range of the above molar ratio (molybdenum/gadolinium), for example, the value of molybdenum/gadolinium may be 0.01 to 5, 0.03 to 3, and 0.1 to 2.
As an amount of molybdenum used with respect to gadolinium is increased, the gadolinia particles having a large particle size shown in the above particle size distribution tend to be obtained.
Further, as the amount of molybdenum used with respect to gadolinium is increased, the gadolinium particles with less aggregation tend to be obtained.
By using various compounds in the above range, the amount of the molybdenum compound contained in the gadolinia particles obtained becomes more appropriate, and the gadolinia particles having a controlled particle size can be easily obtained.
By using various compounds in the above range, the amount of the molybdenum compound contained in the obtained gadolinia particles obtained becomes more appropriate, and the gadolinia particles having a controlled degree of aggregation can be easily obtained.
The calcination step is a step of calcining the mixture. The gadolinia particles according to the embodiment can be obtained by calcining the mixture. As described above, the production method is called the flux method.
The flux method is classified as a solution method. More specifically, the flux method is a method of crystal growth utilizing the fact that a crystal-flux two-component phase diagram shows a eutectic type. A mechanism of the flux method is presumed to be as follows. That is, when a mixture of solute and the flux is heated, the solute and the flux become a liquid phase. At this time, since the flux is a fusing agent, in other words, since a solute-flux two-component phase diagram shows a eutectic type, the solute melts at a temperature lower than its melting point to form the liquid phase. If the flux is evaporated in this state, concentration of the flux is reduced, in other words, an effect on lowering the melting point of the solute by the flux is reduced, and the evaporation of the flux acts as a driving force to cause crystal growth of the solute (flux evaporation method). Note that the solute and the flux can also cause the crystal growth of the solute by cooling the liquid phase (slow cooling method).
The flux method has merits such as being able to grow the crystals at a temperature much lower than the melting point, being able to precisely control a crystal structure, and being able to form a crystalline body having an automorphic shape.
In production of the gadolinia particles by the flux method using the molybdenum compound as the flux, the mechanism is not always clear, but for example, it is presumed that the mechanism is as follows. That is, when the gadolinium compound is calcined in the presence of the molybdenum compound, the gadolinium molybdate is first formed. At this time, as can be understood from the above description, the gadolinium molybdate grows gadolinia crystals at a temperature lower than the melting point of the gadolinia. Then, for example, by evaporating the flux, the gadolinium molybdate is decomposed to grow the crystals, so that the gadolinia particles can be obtained. That is, the molybdenum compound functions as the flux, and the gadolinia particles are produced via an intermediate called the gadolinium molybdate.
By the above flux method, the gadolinia particles containing molybdenum can be produced.
A method of calcination is not particularly limited, and the calcination can be performed by a known and commonly used method. When the calcination temperature exceeds 800° C., it is considered that the gadolinium compound and the molybdenum compound react to form the gadolinium molybdate. Further, it is considered that when the calcination temperature becomes 900° C. or higher, the gadolinium molybdate is decomposed to form the gadolinia particles. Further, in the gadolinia particles, it is considered that the molybdenum compound is incorporated into the gadolinia particles when the gadolinium molybdate is decomposed into the gadolinia and the molybdenum oxide.
Further, a state of the gadolinium compound and the molybdenum compound at the time of 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 powders of the molybdenum compound and powders of the gadolinium compound are mixed, mechanical mixing using a crusher or the like, a mixture using a mortar or the like, and may be mixing in a dry state or in a wet state.
Conditions of the calcination temperature are not particularly limited, and are appropriately determined in consideration of a target particle size of the gadolinia particles, formation of the molybdenum compound in the gadolinia particles, the shape of the gadolinia particles, and the like. The calcination temperature may be 900° C. or higher, which is close to a decomposition temperature of the gadolinium molybdate, 1000° C. or higher, or 1300° C. or higher.
As the calcination temperature is higher, the gadolinia particles having a controlled particle shape and a large particle size tend to be easily obtained. From a viewpoint of efficiently producing such gadolinia particles, the calcination temperature is preferably 1100° C. or higher, more preferably 1200° C. or higher, and even more preferably 1300° C. or higher.
Generally, when trying to control the shape of the gadolinia particles obtained after calcination, it is necessary to perform the high-temperature calcination at a temperature of over 2000° C. in which reaction of the gadolinia easily proceeds, but there is a big problem in industrial applications from viewpoints of load on the calcining furnace and fuel cost.
According to the embodiment of the present invention, for example, even if the maximum calcination temperature for calcining the gadolinium compound is 1600° C. or lower, the gadolinia particles can be efficiently formed at low cost.
Further, according to the method for producing the gadolinia particles of the embodiment, even if the calcination temperature is 1600° C. or lower, which is much lower than the melting point of the gadolinia, the gadolinia particles having an automorphic shape can be formed regardless of a shape of a precursor. Further, from this point of view, the calcination temperature is preferably 1500° C. or lower, more preferably 1400° C. or lower, and even more preferably 1300° C. or lower.
As an example, a numerical range of the calcination temperature at which the gadolinium compound is calcined in the calcination step may be 900° C. to 1600° C., 1000° C. to 1500° C., 1100° C. to 1400° C., or 1200° C. to 1300° C.
From a viewpoint of the production efficiency, a 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.
Regarding a calcination time, the calcination is preferably performed such that a raising time to a predetermined calcination temperature is in a range of 15 minutes to 10 hours. A holding time at the calcination temperature can be 5 minutes or more, preferably in the range of 5 minutes to 1000 hours, and more preferably in the range of 1 to 100 hours. In order to efficiently form the gadolinia particles, the holding time at the calcination temperature is preferably 2 hours or more, more preferably 2 to 100 hours, and even more preferably 2 to 48 hours.
As an example, by selecting the conditions of the calcination temperature of 900° C. to 1600° C. and the holding time at the calcination temperature of 2 to 100 hours, the gadolinia particles of the embodiment containing molybdenum can be easily obtained.
Calcination atmosphere is not particularly limited as long as an effect of the present invention can be obtained, but for example, oxygen-containing atmosphere such as air or oxygen or an inert atmosphere such as nitrogen, argon or carbon dioxide is preferable, and air atmosphere is more preferable when considering the cost.
An apparatus for calcination is also not necessarily limited, and a so-called calcining furnace can be used. The calcining furnace is preferably made of a material that does not react with sublimated molybdenum oxide, and it is preferable to use a highly airtight calcining furnace so that the molybdenum oxide can be used efficiently.
The method for producing the gadolinia particles of the embodiment may further include a molybdenum removal step of removing at least a part of molybdenum after the calcination step, if necessary.
As described above, since the molybdenum is sublimated during calcination, it is possible to control the molybdenum content present in the surface layer of the gadolinia particles, and to control the molybdenum content and its existence state in other than the surface layer (inner layer) of the gadolinia particles, by controlling the calcination time, the calcination temperature, and the like.
The molybdenum can adhere to the surface of the gadolinia particles. As a means other than the above sublimation, the molybdenum can be removed by washing with water, an aqueous ammonia solution, an aqueous sodium hydroxide solution or the like.
At this time, the molybdenum content in the gadolinia particles can be controlled by appropriately changing concentration and used amount of the water, the aqueous ammonia solution, or the aqueous sodium hydroxide solution used, and a washing site, a washing time or the like.
In a calcined product obtained through the calcination step, the gadolinia particles may aggregate, and the calcined product may not meet a range of particle diameter suitable for applications to be considered. Therefore, the gadolinia particles may be pulverized to satisfy the range of suitable particle diameter, if necessary.
A method for pulverizing the calcined product is not particularly limited, and conventionally known pulverizing methods such as ball mill, jaw crusher, jet mill, disc mill, Spectromill, grinder, and mixer mill can be used.
The calcined product containing the gadolinia particles obtained in the calcination step may be appropriately classified in order to adjust a range of the particle size. A “classification process” refers to an operation of grouping particles based on the size of the particles.
The classification may be either wet or dry, but from a viewpoint of productivity, the dry classification is preferable. The dry classification includes classification by sieving, wind classification by a difference between centrifugal force and fluid drag, and the like, but from a viewpoint of classification accuracy, the wind classification is preferable, and can be performed by using a classifier using Coanda effect, such as an airflow classifier, a swirling airflow classifier, a forced vortex centrifugal classifier, and a semi-free vortex centrifugal classifier.
The above-mentioned pulverizing step and classification step can be performed at a necessary stage. For example, the average particle diameter of the gadolinia particles to be obtained can be adjusted by the presence or absence of pulverizing and classification, and selection of their conditions.
In the gadolinia particles of the embodiment or the gadolinia particles obtained by the production method of the embodiment, the gadolinia particles having little or no aggregation are likely to exhibit their original properties and are superior in their own handleability, and when they are used by being dispersed in a medium to be dispersed, they are preferable from the viewpoint of being more excellent in dispersibility.
Note that according to the method for producing the gadolinia particles of the above-described embodiment, since the gadolinia particles having little or no aggregation can be easily produced, it has an excellent advantage that the gadolinia particles having excellent desired properties can be produced with high productivity without performing the above-mentioned pulverizing step or classification step.
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.
3.0 g of commercially available gadolinium oxide Gd2O3 (produced by Aladdin (China)) was placed in a crucible and calcined in a ceramic electric furnace at 1100° C. for 24 hours. After the temperature was lowered, the crucible was taken out to obtain 3.0 g of white powders.
In Comparative Example 1, 3.0 g of white powders were obtained by the same operation as in Comparative Example 1 except that a calcination condition was changed to at 1300° C. for 24 hours.
3.0 g of gadolinium oxide Gd2O3 (produced by Aladdin (China)) and 0.15 g of molybdenum trioxide (produced by Chengdu Hongbo Industrial Co., Ltd. (China)) were mixed in a mortar to obtain a mixture. The obtained mixture was placed in the crucible and calcined in the ceramic electric furnace at 1100° C. for 24 hours, and then at 1500° C. for 24 hours. After the temperature was lowered, the crucible was taken out to obtain 3.15 g of white powders. Subsequently, 3.15 g of the obtained white powders were suspended in 9 g of ion-exchanged water, precipitated with a centrifuge at 3000 rpm for 15 minutes, and supernatant liquid was discarded. This operation was repeated six times to wash the white powders to obtain 3.07 g of white powders.
The powders of Example 2 were obtained by the same operation as in Example 1 except that a used amount of molybdenum trioxide was changed as shown in Table 1, in Example 1.
3.0 g of gadolinium oxide Ga2O3 (produced by Aladdin (China)), 2.7 g of molybdenum trioxide (produced by Chengdu Hongbo Industrial Co., Ltd. (China)), 1.3 g of potassium carbonate (produced by Aladdin (China)), and 0.015 g of yttrium oxide (produced by Aladdin (China)) were mixed in the mortar to obtain a mixture. The obtained mixture was placed in the crucible and calcined in the ceramic electric furnace at 1300° C. for 24 hours, and then at 1500° C. for 24 hours. After the temperature was lowered, the crucible was taken out to obtain 5.355 g of white powders. Subsequently, 5.355 g of the obtained white powders were suspended in 16 g of ion-exchanged water, precipitated with the centrifuge at 3000 rpm for 15 minutes, and the supernatant liquid was discarded. This operation was repeated six times to wash the white powders to obtain 32.97 g of white powders.
3.0 g of gadolinium oxide Ga2O3 (produced by Aladdin (China)) and 3.6 g of sodium molybdate dihydrate (produced by Aladdin (China)) were mixed in the mortar to obtain the mixture. The obtained mixture was placed in the crucible and calcined in the ceramic electric furnace at 1300° C. for 24 hours. After the temperature was lowered, the crucible was taken out to obtain 6.6 g of white powders. Subsequently, 6.55 g of the obtained white powders were suspended in 16 g of ion-exchanged water, precipitated with the centrifuge at 3000 rpm for 15 minutes, and the supernatant liquid was discarded. This operation was repeated six times to wash the white powders to obtain 2.93 g of white powders.
The washed powders obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were used as sample powders and evaluated as follows.
The sample powders were filled in a holder for a measurement sample having a depth of 0.5 mm, set in a wide-angle X-ray diffraction (XRD) apparatus (Ultima IV manufactured by Rigaku Corporation), and the measurement was performed under conditions of Cu/Kα ray, 40 kV/40 mA, scanning speed 2°/min, and scanning range of 100 to 70°.
Using a laser diffraction type dry particle size distribution meter (HELOS (H3355) & RODOS manufactured by Japan Laser Corporation), the particle diameter distribution of the sample powders was measured by the dry method under conditions of a dispersion pressure of 3 bar and a pulling pressure of 90 mbar. The particle diameter at a point where a distribution curve of cumulative volume % intersects a horizontal axis of 10% from the small particle side was defined as D10, the particle diameter at a point where the distribution curve intersects the horizontal axis of 50% was defined as D50, and the particle diameter at a point where the distribution curve intersects the horizontal axis of 90% from the small particle side was defined as D90, and they were determined.
Using a fluorescent X-ray analyzer Primus IV (manufactured by Rigaku Corporation), about 70 mg of the sample powders were placed on a filter paper, were covered with a PP film, and the X-ray fluorescence (XRF) analysis was performed under the following conditions.
Measurement conditions
EZ scan mode
Elements to be measured: F to U
Measurement time: standard
Measurement diameter: 10 mm
Residual (Balance component): None
The results of the Gd2O3 content (G1) with respect to 100 mass % of the gadolinia particles and the MoO3 content (M1) with respect to 100 mass % of the gadolinia particles were obtained by XRF analysis.
For surface element analysis of the sample powders, X-ray Photoelectron spectroscopy (XPS) measurement was performed using QUANTERA SXM manufactured by ULVAC-PHI, Inc. and monochromatic Al-Kα as an X-ray source. In an area measurement of 1000 μm square, an average value of n=3 measurement was obtained in atom % for each element.
By converting the gadolinium content in the surface layer and the molybdenum content in the surface layer of the gadolinia particles obtained by XPS analysis into oxides, the Gd2O3 content (G2) (mass %) with respect to 100 mass % of the surface layer of the gadolinia particles and the MoO3 content (M2) (mass %) with respect to 100 mass % of the surface layer of the gadolinia particles were determined.
Table 1 shows each value obtained by the above evaluation. Note that “N.D.” is an abbreviation for not detected, and indicates that it is not detected.
SEM images of the powders of the above Examples and Comparative Examples obtained by photographing with a scanning electron microscope (SEM) are shown in
Results of XRD analysis are shown in
From the results of the above SEM observation and XRD analysis, it was confirmed that the powders obtained in Examples and Comparative Examples were the gadolinia particles containing gadolinium oxide (gadolinia).
From the results of each Example, it was shown that it is possible to calcine the gadolinium oxide particles containing molybdenum even at a relatively low calcination temperature of 1300° C. and 1500° C. by calcining the gadolinium compound in the presence of the molybdenum compound.
From an SEM observation image of each of the gadolinia particles, the degree of aggregation of the particles was evaluated according to the following criteria.
+: Aggregation of particles is observed.
−: No noticeable aggregation of particles is observed.
In the gadolinia particles of Comparative Examples 1 and 2, aggregation and fusion of the particles was observed (degree of aggregation +), whereas in the gadolinia particles of Examples 2 to 4, no noticeable aggregation was observed (degree of aggregation −). Further, in the comparison of Examples 1 and 2, the aggregation and fusion of the particles was observed in the gadolinia particles of Example 1, whereas no noticeable aggregation was observed in the gadolinia particles of Example 2.
From these facts, it was shown that the gadolinia particles having low aggregation properties can be produced by calcining the gadolinium compound in the presence of the molybdenum compound, and as the amount of molybdenum used is increased, the particles with a low degree of aggregation or no aggregation tend to be obtained.
Further, in the gadolinia particles of Examples 3 and 4, the gadolinia particles having a large particle size were obtained. From this fact, it was shown that the gadolinia particles having a large particle size can be easily obtained by using the alkali metal salt of the molybdenum oxoanion as the flux agent.
Table 1 shows the values of the above Gd2O3 content (G1), MoO3 content (M1), Gd2O3 content (G2), and MoO3 content (M2).
From the results of the MoO3 content (M1) and the MoO3 content (M2), the gadolinia particles of Examples 1 to 4 contain molybdenum on the surface, and it is expected that various actions of molybdenum, such as catalytic activity will be exerted.
Further, Table 1 shows calculation results of the surface layer uneven distribution ratio (M2/M1) of the MoO3 content (M2) to the MoO3 content (M1).
From the results of the surface layer uneven distribution ratio (M2/M1), in the gadolinia particles of Examples 1 and 4, the molybdenum oxide content in the surface layer of the gadolinia particles determined by XPS surface analysis is greater than the molybdenum oxide content determined by XRF analysis. Therefore, it was confirmed that molybdenum was unevenly distributed in the surface layer of the gadolinia particles, and it can be expected that various actions of molybdenum will be effectively exerted.
Each configuration in each embodiment, a combination thereof, and the like are examples, and the configuration can be added, omitted, replaced, and other changes can be made without departing from the spirit of the present invention. Further, the present invention is not limited by each embodiment, but is limited only by the scope of the claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2021/099881 | 6/11/2021 | WO |
