Method of producing rare earth composite oxide particles

Abstract

SOLUTION: An aqueous solution including ions of one or more species of rare earth elements selected from the group consisting of Sc, Y, Nd, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, an Al ion and / or a Ga ion, an organic compound comprising a carboxy group, and urea, is heated at a temperature of 80°C or higher and lower than the boiling point of the aqueous solution, to generate particles of the rare earth composite compound by the reaction of the organic compound, a hydrolysis product of urea, the ions of the rare earth elements, and an Al ion and / or a Ga ion, to generate a rare earth composite oxide from the rare earth composite compound.EFFECT: Particles of excellent dispersibility with gelling and enlargement of the particles being more suppressed relative to a conventional method, can be obtained by adding an organic compound comprising a carboxy group to an aqueous solution in which the rare earth composite compound particles containing aluminum and / or gallium are to be precipitated, even when metal elements such as aluminum and gallium, easily gelling and easily generating enlarged particles are contained therein.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing rare earth composite oxide particles containing one or both of aluminum and gallium, which are useful as a raw material for ceramics. [Background technology]

[0002] Complex oxides containing rare earth elements are used in various functional ceramic products, contributing to the high performance of the products. Powdered raw materials of rare earth complex oxides containing aluminum or gallium are used in various ways to produce ceramics, phosphors, thin films, coatings, etc. In recent years, there is an increasing demand for finer powdered raw materials to improve the performance of functional ceramic products.

[0003] Methods for obtaining fine particles of rare earth carbonates or rare earth oxides include, for example, the method described in JP 2000-239019 A (Patent Document 1), in which urea is hydrolyzed by heating in water in the presence of hydrogen peroxide to precipitate basic carbonates of the rare earth elements from the rare earth ions as monodisperse particles, which are then separated into solid and liquid, dried and calcined to obtain rare earth oxides.

[0004] Furthermore, examples of methods for obtaining complex compounds and complex oxides of metal elements include the method described in JP 2018-095524 A (Patent Document 2), in which a metal compound containing each metal element component constituting a perovskite complex oxide and a dicarboxylic acid compound are dissolved in a solvent to obtain a solution, which is then dried and calcined to obtain a complex oxide of metal elements.

[0005] However, when rare earth element ions are precipitated with ions of metal elements other than rare earth elements, such as aluminum and gallium, which are easily hydroxylated and gelled, by the method described in JP 2000-239019 A (Patent Document 1), a composite compound containing rare earth elements, which is difficult to recover, is obtained due to gelation of hydroxides of aluminum and gallium. Furthermore, when this is fired, the particles are strongly agglomerated by dehydration condensation of the hydroxides, resulting in an enlarged rare earth composite oxide containing aluminum and gallium.

[0006] In addition, in the method described in JP 2018-095524 A (Patent Document 2), a solution in which a metal compound containing a metal element component and a dicarboxylic acid compound are dissolved in a solvent is dried using a rotary evaporator to obtain a composite compound of the metal elements, which has poor productivity in terms of mass production on an industrial scale. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2000-239019 A [Patent Document 2] JP 2018-095524 A Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above circumstances, and aims to provide a method for producing rare earth composite oxide particles containing one or both of aluminum and gallium, which suppresses gelation and does not cause the particles to become enlarged, and also aims to provide a method for producing rare earth composite oxide particles containing one or both of aluminum and gallium, which has high productivity and is advantageous for mass production. [Means for solving the problem]

[0009] In the homogeneous precipitation method, particles of rare earth compounds such as basic carbonates of rare earth elements can be precipitated by heating an aqueous solution containing urea and rare earth mineral acid salts, which are ion sources of rare earth elements, but in the case of metal elements such as aluminum and gallium, particles of metal compounds such as hydroxide salts precipitate in the low pH range, and these particles tend to bond with each other, gel, and become enlarged. In the homogeneous precipitation method in the coexistence of these metal elements and rare earth elements that tend to gel, gelled and enlarged particles are obtained.

[0010] In order to solve the above problems, the present inventors conducted extensive research into the production of rare earth composite oxide particles containing one or both of aluminum and gallium by a homogeneous precipitation method. As a result, they discovered that by adding an organic compound having a carboxy group to an aqueous solution containing a rare earth element and one or both of aluminum and gallium, and heating the aqueous solution, the gelling and enlargement of the precipitated particles are improved, and it is possible to produce rare earth composite oxide particles containing one or both of aluminum and gallium that are highly dispersible, thereby arriving at the present invention.

[0011] Therefore, the present invention provides the following method for producing rare earth composite oxide particles. 1. (A) a step of heating an aqueous solution containing ions of one or more rare earth elements selected from the group consisting of Sc, Y, Nd, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, one or both of Al ions and Ga ions, an organic compound having a carboxy group, and urea at a temperature of 80° C. or higher and lower than the boiling point of the aqueous solution, to generate particles of a rare earth composite compound by reaction between the organic compound, a hydrolysis product of urea, the ions of the rare earth elements, and one or both of Al ions and Ga ions; (B) producing a rare earth composite oxide from the rare earth composite compound; 2. A method for producing rare earth composite oxide particles, comprising: 2. The method according to 1, wherein the organic compound is an organic compound having one or more carboxy groups, or an organic compound in which two carboxy groups are condensed and which easily generates a carboxy group in an aqueous solution. 3. The method according to 1 or 2, characterized in that in the step (B), the particles of the rare earth composite compound obtained in the step (A) are subjected to solid-liquid separation, and the obtained solid content is fired at a temperature of 600°C or higher in an oxygen-containing atmosphere to produce the rare earth composite oxide. 4. The method according to 3, characterized in that rare earth composite oxide particles are produced having a volume-based median diameter (D50) of 0.1 μm or more and 10 μm or less in particle size distribution measured by a laser diffraction method. 5. The method according to 1, wherein the organic compound having a carboxy group is one or more compounds selected from the group consisting of maleic acid, maleic anhydride, malic acid, and citric acid. 6. The manufacturing method according to 5, characterized in that in the step (B), the particles of the rare earth composite compound obtained in the step (A) are subjected to solid-liquid separation, and the obtained solid content is fired at a temperature of 700°C or higher in an oxygen-containing atmosphere to produce the rare earth composite oxide. Effect of the Invention

[0012] According to the present invention, by adding an organic compound having a carboxyl group to an aqueous solution for precipitating rare earth composite compound particles containing one or both of aluminum and gallium, even if the aqueous solution contains metal elements such as aluminum and gallium, which are prone to gelation and to produce enlarged particles, gelation and particle enlargement are suppressed compared to conventional methods, and particles with good dispersibility are obtained. Therefore, it is possible to mass-produce fine particles with high properties that can respond to the recent trend of fine particle production of ceramic raw materials. [Brief description of the drawings]

[0013] [Figure 1] 1 is an electron microscope image of the rare earth composite oxide particles obtained in Example 1, and is an electron microscope photograph of yttrium-aluminum composite oxide particles. [Diagram 2] 3 is an electron microscope image of the rare earth composite oxide particles obtained in Example 2, and an electron microscope photograph of yttrium-aluminum composite oxide particles. [Diagram 3]3 is an electron microscope image of the rare earth composite oxide particles obtained in Example 3, and an electron microscope photograph of yttrium-aluminum composite oxide particles. [Figure 4] 3 is an electron microscope image of the rare earth composite oxide particles obtained in Example 4, and is an electron microscope photograph of yttrium-aluminum gallium composite oxide particles. [Diagram 5] 1 is an electron microscope image of the rare earth composite oxide particles obtained in Example 5, and is an electron microscope photograph of lutetium-aluminum composite oxide particles. [Figure 6] 1 is an electron microscope image of the rare earth composite oxide particles obtained in Example 6, and is an electron microscope photograph of gadolinium-gallium composite oxide particles. [Figure 7] 1 is an electron microscope image of the rare earth composite oxide particles obtained in Comparative Example 1, and is an electron microscope photograph of yttrium-aluminum composite oxide particles. [Figure 8] 2 shows the results of particle size distribution measurement by laser diffraction method for the yttrium-aluminum composite oxide particles obtained in Example 1. [Figure 9] 3 shows the results of particle size distribution measurement by laser diffraction method for the yttrium-aluminum composite oxide particles obtained in Example 2. [Figure 10] 1 shows the results of particle size distribution measurement by laser diffraction method for the yttrium-aluminum composite oxide particles obtained in Example 3. [Figure 11] 1 shows the results of particle size distribution measurement by laser diffraction method for the yttrium-aluminum gallium composite oxide particles obtained in Example 4. [Figure 12] 1 shows the results of particle size distribution measurement by laser diffraction method for the lutetium-aluminum composite oxide particles obtained in Example 5. [Figure 13] 1 shows the results of particle size distribution measurement by laser diffraction method for the gadolinium-gallium composite oxide particles obtained in Example 6. [Figure 14] 2 shows the results of particle size distribution measurement by laser diffraction method for the yttrium-aluminum composite oxide particles obtained in Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention will be described in detail below. In the present invention, the rare earth composite oxide particles are (A) heating an aqueous solution containing ions of one or more rare earth elements selected from the group consisting of Sc, Y, Nd, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, one or both of Al ions and Ga ions, an organic compound having a carboxy group, and urea at a temperature of 80° C. or higher and lower than the boiling point of the aqueous solution to generate particles of a rare earth composite compound through reactions between the organic compound, a hydrolysis product of urea, the rare earth element ions, and one or both of Al ions and Ga ions; (B) producing a rare earth composite oxide from the rare earth composite compound; The method comprises the steps of:

[0015] In the present invention, an aqueous solution containing ions of a rare earth element, ions of one or both of aluminum (Al) and gallium (Ga) ions which are prone to gelation, an organic compound having a carboxy group, and urea is heated to produce a rare earth composite compound containing one or both of aluminum and gallium through reaction between the organic compound, the hydrolysis product of urea, the rare earth element ions, and one or both of aluminum ions and gallium ions, thereby producing fine particles of a rare earth composite compound containing one or both of aluminum and gallium.

[0016] By preparing an aqueous solution of a water-soluble rare earth mineral acid salt, one or both of the mineral acid salts of aluminum and gallium, and the mineral acid salts of other metal elements described below as required, an aqueous solution containing ions of rare earth elements, one or both of the aluminum ions and the gallium ions, and further containing ions of other metal elements described below as required can be prepared. Examples of the mineral acid salt include nitrates and chlorides. In particular, when metals such as iron and SUS are used in the parts of the manufacturing equipment that come into contact with the aqueous solution, it is more preferable to use nitrates that are less likely to increase impurities derived from the metals in the contact parts in the product.

[0017] The rare earth element ions include ions of one or more rare earth elements (first rare earth elements) selected from the group consisting of Sc, Y, Nd, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. The concentration of the first rare earth element ions in the aqueous solution is preferably 0.01 mol / L or more, particularly 0.05 mol / L or more, and 0.3 mol / L or less, particularly 0.2 mol / L or less. From the viewpoint of particle productivity, a higher concentration of the rare earth element ions is preferable, but a concentration exceeding 0.3 mol / L may cause strong particle aggregation.

[0018] In addition to the ions of the first rare earth element, the ions of a rare earth element (second rare earth element) other than the first rare earth element may be included as the ions of the rare earth element. The second rare earth element may be ions of one or more rare earth elements selected from the group consisting of La, Ce, Pr, Sm and Eu. When the second rare earth element is included, the total concentration of the ions of the first rare earth element and the ions of the second rare earth element in the aqueous solution is preferably 0.01 mol / L or more, particularly 0.05 mol / L or more, and 0.3 mol / L or less, particularly 0.2 mol / L or less. Of the ions of the first rare earth element and the ions of the second rare earth element, the content of the ions of the second rare earth element is preferably 50 mol% or less, particularly 30 mol% or less, based on the total of the ions of the first rare earth element and the ions of the second rare earth element.

[0019] The total concentration of aluminum and gallium in the aqueous solution is preferably 0.01 mol / L or more, particularly 0.05 mol / L or more, and 0.3 mol / L or less, particularly 0.2 mol / L or less. Considering particle productivity, it is preferable that the concentration of aluminum and gallium ions is high, but if the concentration exceeds 0.3 mol / L, the aggregation of particles may become strong. When the aqueous solution contains both aluminum ions and gallium ions, the ratio of aluminum ions to gallium ions is not particularly limited, but it is preferable that the content of gallium is 50 mol% or less, particularly 40 mol% or less, based on the total of aluminum ions and gallium ions.

[0020] In addition, the aqueous solution containing ions of rare earth elements and either or both of aluminum ions and gallium ions may further contain ions of metal elements other than the first rare earth element, the second rare earth element, aluminum and gallium (ions of other metal elements) in addition to either or both of aluminum ions and gallium ions. Examples of ions of other metal elements include iron ions. When ions of other metal elements are contained, the total concentration of aluminum ions, gallium ions and ions of other metal elements in the aqueous solution is preferably 0.01 mol / L or more, particularly 0.05 mol / L or more, and 0.3 mol / L or less, particularly 0.2 mol / L or less. Among the ions of aluminum ions, gallium ions and ions of other metal elements, the content of the ions of other metal elements is preferably 50 mol% or less, particularly 40 mol% or less, based on the total of the ions of aluminum ions, gallium ions and ions of other metal elements.

[0021] The total concentration of rare earth element ions, gallium ions and aluminum ions in the aqueous solution, and further, when other metal ions are contained, the total concentration of rare earth element ions, aluminum ions, gallium ions and other metal ions is preferably 0.02 mol / L or more, particularly 0.1 mol / L or more, and 0.6 mol / L or less, particularly 0.3 mol / L or less. Considering the productivity of particles, it is preferable that the total concentration of rare earth element ions, aluminum ions, gallium ions and other metal ions contained as necessary is high, but if the concentration exceeds 0.3 mol / L, there is a risk that the aggregation of particles will become strong.

[0022] The aqueous solution contains an organic compound having a carboxy group. The organic compound having a carboxy group may be an organic compound having one or more carboxy groups, or an organic compound in which two carboxy groups are condensed and which easily generates a carboxy group in an aqueous solution. The organic compound having a carboxy group is preferably one or more selected from the group consisting of maleic acid, maleic anhydride, malic acid, and citric acid.

[0023] The amount of the organic compound having a carboxy group in the aqueous solution is preferably 0.1 times or more, particularly 0.2 times or more, and 1 times or less, particularly 0.5 times or less, in terms of molar ratio, relative to the total amount of the rare earth element ion, aluminum ion, gallium ion, and other metal ion contained as necessary. If the amount of the organic compound having a carboxy group is less than the above range, gelation may be insufficiently suppressed. If the amount of the organic compound having a carboxy group exceeds the above range, the rare earth element ion, one or both of the aluminum ion and the gallium ion, and the other metal ion contained as necessary may form a highly water-soluble compound together with the organic compound having a carboxy group, and the recovery amount (yield) of the rare earth complex compound that becomes a precipitate may decrease.

[0024] The aqueous solution contains urea. The amount of urea in the aqueous solution is preferably 5 times or more, particularly 10 times or more, and 30 times or less, particularly 20 times or less, in terms of molar ratio, relative to the total amount of rare earth element ions, aluminum ions, gallium ions, and ions of other metals contained as necessary. If the amount of urea is less than the above range, it may take too much time to produce the rare earth complex compound, and the recovery amount (yield) of the rare earth complex compound may decrease. In addition, if the amount of urea exceeds the above range, it may be disadvantageous in terms of economic efficiency.

[0025] The organic compound having a carboxy group and urea may be mixed with the rare earth element ions, one or both of the aluminum ions and the gallium ions, and ions of other metals contained as necessary, either before or after the start of heating, i.e., during heating (while the temperature is rising or after a predetermined temperature is reached).

[0026] In the production of a rare earth complex compound containing one or both of aluminum and gallium ions, an aqueous solution (mixed aqueous solution) containing each component is heated to hydrolyze urea, and the hydrolysis products such as carbonate ions and ammonium ions produced by the hydrolysis and an organic compound having a carboxyl group are reacted with ions of a rare earth element to produce a precipitate of a rare earth complex compound containing one or both of aluminum and gallium ions. The heating temperature is preferably 80°C or higher, particularly 90°C or higher, and is preferably below the boiling point of the mixed aqueous solution, particularly below the boiling point, and more preferably, for example, 100°C or lower. The heating time may be shorter as the amount of urea added increases and the heating temperature increases, but is usually 60 to 300 minutes.

[0027] The precipitate (solid content) formed is in the form of a slurry, but can be separated into solid and liquid by a method such as filtration, decantation, centrifugation, and other sedimentation methods. The precipitate obtained is a very small particle, so that there is a high possibility that the particles will pass through the filter in normal filtration, and therefore it is preferable to separate the solid and liquid by centrifugal sedimentation. When removing unreacted urea and residual anions contained in the solid content, the solid content obtained after solid-liquid separation may be washed with pure water or the like. The solid content may be further dried under an oxygen-containing atmosphere such as air or under an inert gas atmosphere, as necessary. The particles of the rare earth complex compound containing one or both of aluminum and gallium ions thus obtained contain carbonates, basic carbonates, hydroxides, and the like, depending on the type of rare earth element.

[0028] The rare earth composite compound particles containing one or both of aluminum and gallium ions obtained as a solid content can be used as it is, but can be further fired to generate a rare earth composite oxide from the rare earth composite compound to obtain rare earth composite oxide particles containing one or both of aluminum and gallium ions such as garnet, monoclinic, and perovskite. If the rare earth composite compound containing one or both of aluminum and gallium ions recovered as a solid content after solid-liquid separation is fired as it is, it often becomes agglomerated due to aggregation and sintering, so in order to recover the rare earth composite oxide obtained after firing as particles with good dispersibility, it is preferable to dry and then fire after solid-liquid separation. The drying temperature is preferably 150°C or less, particularly 80°C or less, and especially 60°C or less. Depending on the type of rare earth element, if the drying temperature is too high, recrystallization of the rare earth composite compound may occur, which may impair the properties of the particles. The drying time is preferably 1 day (24 hours) or more, and is not particularly limited, but is usually preferably 7 days (168 hours) or less. The drying atmosphere is not particularly limited, and may be an oxygen-containing atmosphere such as the air, or an inert gas atmosphere.

[0029] The dried rare earth complex compound containing one or both of aluminum and gallium ions can be crushed using a crusher or the like. The dried rare earth complex compound containing one or both of aluminum and gallium ions is considered to be bonded to each other by very weak forces such as hydrogen bonds, so that the particles can be easily separated by dissolving with a relatively weak force. The crusher can be a jet mill, a roll mill, a hammer mill, a bead mill, a ball mill, or the like, and can be appropriately selected depending on the state of the particles to be obtained by crushing.

[0030] Calcination to obtain a rare earth composite oxide containing one or both of aluminum and gallium ions is preferably carried out in an oxygen-containing atmosphere such as air or oxygen gas at a temperature of 600° C. or higher, particularly 700° C. or higher, and especially 800° C. or higher, and 1500° C. or lower, particularly 1300° C. or lower. The calcination time is preferably 2 hours or longer, and usually 8 hours or shorter.

[0031] The manufacturing method of the present invention makes it possible to obtain rare earth composite oxide particles containing one or both of aluminum and gallium ions and having a median diameter (D50) of 0.1 μm or more and 10 μm or less in the particle size distribution measured by a laser diffraction method. EXAMPLES

[0032] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0033] [Example 1] An aqueous yttrium nitrate solution and an aqueous aluminum nitrate solution were added so that the yttrium ion concentration in 100 L of the aqueous solution was 0.06 mol / L and the aluminum ion concentration was 0.10 mol / L, and maleic anhydride was added in an amount 0.4 times the total ion concentration of yttrium ions and aluminum ions, and the mixture was stirred. Next, the aqueous solution was heated to 98°C, and urea was added to the mixture so that the concentration was 2.4 mol / L. The mixture was then heated at 98°C for 150 minutes, at which point a solid precipitated.

[0034] Next, the precipitate was subjected to solid-liquid separation using a centrifuge, and the recovered solid was washed with about 20 L of pure water. It was confirmed by X-ray diffraction that the obtained solid (composite compound particles) was amorphous.

[0035] Next, the obtained composite compound particles were calcined in air at 700°C for 4 hours. The calcined product obtained was crushed in a hammer mill and then calcined in air at 1100°C for 2 hours, resulting in particles of yttrium-aluminum composite oxide. When observed under an electron microscope, it was confirmed that the particles were connected to each other, but that the particles were very little enlarged and had a primary particle diameter of 0.1 μm or less. An electron microscope image of this particle is shown in Figure 1. In addition, X-ray diffraction confirmed that the particles were yttrium aluminum garnet. Furthermore, the obtained particles were dispersed in pure water using a homogenizer (40 W, 3 minutes), and then the particle size distribution was measured by a laser diffraction method using a laser diffraction / scattering particle size distribution measuring device (Microtrack Bell Co., Ltd., MT3300). The results are shown in Figure 8. The median diameter (D50) was 2.05 μm.

[0036] [Example 2] An aqueous yttrium nitrate solution and an aqueous aluminum nitrate solution were added so that the yttrium ion concentration in 100 L of the aqueous solution was 0.06 mol / L and the aluminum ion concentration was 0.10 mol / L, and then citric acid was added in an amount 0.2 times the total ion concentration of yttrium ions and aluminum ions, and the mixture was stirred. Next, the aqueous solution was heated to 98°C, and urea was added to the mixture so that the concentration was 2.4 mol / L. The mixture was heated at 98°C for 150 minutes, and a solid precipitated.

[0037] Next, the precipitate was subjected to solid-liquid separation using a centrifuge, and the recovered solid was washed with about 20 L of pure water. It was confirmed by X-ray diffraction that the obtained solid (composite compound particles) was amorphous.

[0038] Next, the obtained composite compound particles were calcined in air at 700°C for 4 hours. The calcined product obtained was crushed with a hammer mill and then calcined in air at 1100°C for 2 hours, resulting in particles of yttrium-aluminum composite oxide. When observed with an electron microscope, it was confirmed that the particles had a primary particle diameter of about 0.3 to 1 μm, with very little particle enlargement, although the particles were connected to each other. An electron microscope image of this particle is shown in Figure 2. In addition, it was confirmed by X-ray diffraction that the particles were yttrium aluminum garnet. Furthermore, the obtained particles were dispersed in pure water using a homogenizer (40 W, 3 minutes), and then the particle size distribution was measured by the laser diffraction method using a laser diffraction / scattering particle size distribution measuring device MT3300. The results are shown in Figure 9. The median diameter (D50) was 5.70 μm.

[0039] [Example 3] An aqueous solution of yttrium nitrate and an aqueous solution of aluminum nitrate were added so that the yttrium ion concentration in 100 L of the aqueous solution was 0.10 mol / L and the aluminum ion concentration was 0.05 mol / L, and maleic anhydride was added in an amount 0.5 times the total ion concentration of yttrium ions and aluminum ions, and the mixture was stirred. Next, the aqueous solution was heated to 98°C, and urea was added to the mixture so that the concentration was 2.4 mol / L. The mixture was heated at 98°C for 150 minutes, and a solid precipitated.

[0040] Next, the precipitate was subjected to solid-liquid separation using a centrifuge, and the recovered solid was washed with about 20 L of pure water. It was confirmed by X-ray diffraction that the obtained solid (composite compound particles) was amorphous.

[0041] Next, the obtained composite compound particles were calcined in air at 700°C for 4 hours. The calcined product obtained was crushed in a hammer mill and then calcined in air at 1000°C for 2 hours, resulting in particles of yttrium-aluminum composite oxide. When observed under an electron microscope, it was confirmed that the particles were connected to each other, but that the particles were very little enlarged and had a primary particle diameter of 0.2 μm or less. An electron microscope image of this particle is shown in FIG. 3. In addition, X-ray diffraction confirmed that the particles were yttrium aluminum monoclinic. Furthermore, the obtained particles were dispersed in pure water using a homogenizer (40 W, 3 minutes), and then the particle size distribution was measured by the laser diffraction method using a laser diffraction / scattering particle size distribution measuring device MT3300. The results are shown in FIG. 10. The median diameter (D50) was 4.54 μm.

[0042] [Example 4] An aqueous yttrium nitrate solution, an aqueous aluminum nitrate solution, and an aqueous gallium nitrate solution were added so that the yttrium ion concentration in 100L of the aqueous solution was 0.06mol / L, the aluminum ion concentration was 0.06mol / L, and the gallium ion concentration was 0.04mol / L, and further, malic acid was added in an amount of 0.4 times the total ion concentration of yttrium ion, aluminum ion, and gallium ion, and stirred. Next, this aqueous solution was heated to 98°C, and then urea was added to the aqueous solution so that the total ion concentration was 2.4mol / L. When the aqueous solution was heated at 98°C for 165 minutes, a solid precipitated.

[0043] Next, the precipitate was subjected to solid-liquid separation using a centrifuge, and the recovered solid was washed with about 20 L of pure water. It was confirmed by X-ray diffraction that the obtained solid (composite compound particles) was amorphous.

[0044] Next, the obtained composite compound particles were calcined in air at 700°C for 4 hours. The calcined product obtained was crushed in a hammer mill and then calcined in air at 1100°C for 2 hours, resulting in particles of yttrium-aluminum gallium composite oxide. When observed under an electron microscope, it was confirmed that the particles had a primary particle diameter of about 0.5 to 1.5 μm, with very little particle enlargement, although connections between the particles were observed. An electron microscope image of the particles is shown in FIG. 4. Furthermore, it was confirmed by X-ray diffraction that the particles were yttrium (aluminum, gallium) garnet. Furthermore, the obtained particles were dispersed in pure water using a homogenizer (40 W, 3 minutes), and then the particle size distribution was measured by the laser diffraction method using a laser diffraction / scattering particle size distribution measuring device MT3300. The results are shown in FIG. 11. The median diameter (D50) was 8.58 μm.

[0045] [Example 5] A lutetium nitrate aqueous solution and an aluminum nitrate aqueous solution were added so that the lutetium ion concentration in 100 L of the aqueous solution was 0.06 mol / L and the aluminum ion concentration was 0.10 mol / L, and malic acid was added in an amount 0.4 times the total ion concentration of the lutetium ion and the aluminum ion, and the mixture was stirred. Next, the aqueous solution was heated to 98°C, and urea was added to the aqueous solution so that the concentration was 2.4 mol / L. The mixture was heated at 98°C for 165 minutes, and a solid precipitated.

[0046] Next, the precipitate was subjected to solid-liquid separation using a centrifuge, and the recovered solid was washed with about 20 L of pure water. It was confirmed by X-ray diffraction that the obtained solid (composite compound particles) was amorphous.

[0047] Next, the obtained composite compound particles were calcined in air at 700°C for 4 hours. The calcined product obtained was crushed with a hammer mill and then calcined in air at 1100°C for 2 hours, resulting in particles of lutetium-aluminum composite oxide. When observed with an electron microscope, it was confirmed that the particles were connected to each other, but that the particles were very little enlarged, and that the primary particle diameter was about 0.5 to 1.5 μm. An electron microscope image of this particle is shown in FIG. 5. In addition, it was confirmed by X-ray diffraction that the particles were lutetium aluminum garnet. Furthermore, the obtained particles were dispersed in pure water using a homogenizer (40 W, 3 minutes), and then the particle size distribution was measured by the laser diffraction method using a laser diffraction / scattering particle size distribution measuring device MT3300. The results are shown in FIG. 12. The median diameter (D50) was 7.59 μm.

[0048] [Example 6] A gadolinium nitrate aqueous solution and a gallium nitrate aqueous solution were added so that the gadolinium ion concentration in 100L of the aqueous solution was 0.06mol / L and the gallium ion concentration was 0.10mol / L, and further, maleic anhydride was added in an amount of 0.3 times the total ion concentration of gadolinium ion and gallium ion, and malic acid was added in an amount of 0.1 times the total ion concentration of gadolinium ion and gallium ion, respectively, and stirred. Next, this aqueous solution was heated to 98℃, and then urea was added to the solution to make the concentration 2.4mol / L. The solution was heated at 98℃ for 180 minutes, and a solid precipitated.

[0049] Next, the precipitate was subjected to solid-liquid separation using a centrifuge, and the recovered solid was washed with about 20 L of pure water. It was confirmed by X-ray diffraction that the obtained solid (composite compound particles) was amorphous.

[0050] Next, the obtained composite compound particles were calcined in air at 700°C for 4 hours. The calcined product obtained was crushed in a hammer mill and then calcined in air at 1100°C for 2 hours, resulting in gadolinium-gallium composite oxide particles. When observed under an electron microscope, it was confirmed that the particles were connected to each other, but that the particles were very little enlarged, and that the primary particle diameter was about 0.1 to 0.3 μm. An electron microscope image of this particle is shown in FIG. 6. In addition, it was confirmed by X-ray diffraction that the particles were gadolinium gallium garnet. Furthermore, the obtained particles were dispersed in pure water using a homogenizer (40 W, 3 minutes), and then the particle size distribution was measured by the laser diffraction method using a laser diffraction / scattering particle size distribution measuring device MT3300. The results are shown in FIG. 13. The median diameter (D50) was 1.92 μm.

[0051] [Comparative Example 1] An aqueous yttrium nitrate solution and an aqueous aluminum nitrate solution were added and stirred so that the yttrium ion concentration in 100 L of the aqueous solution was 0.06 mol / L and the aluminum ion concentration was 0.10 mol / L. Next, this aqueous solution was heated to 98°C, and urea was added to the aqueous solution so that the concentration was 2.4 mol / L. When the aqueous solution was heated at 98°C for 150 minutes, a gel-like solid was precipitated.

[0052] Next, the precipitate was subjected to solid-liquid separation using a centrifuge, and the recovered solid was washed with about 20 L of pure water. It was confirmed by X-ray diffraction that the obtained solid (composite compound particles) was amorphous.

[0053] Next, the obtained composite compound particles were sintered in air at 700°C for 4 hours. The obtained lumps of sintered material were too hard to be easily crushed by hand, and the hammer mill crushing would have to be scraped off, which would have caused contamination, so the particles were crushed in a mortar. The particles were sintered in air at 1100°C for 2 hours, and particles of yttrium-aluminum composite oxide were obtained. When observed with an electron microscope, it was confirmed that the particles had enlarged and had a primary particle diameter of 10 μm or more. An electron microscope image of the particles is shown in FIG. 7. In addition, X-ray diffraction confirmed that the particles were yttrium aluminum garnet. Furthermore, the obtained particles were dispersed in pure water using a homogenizer (40 W, 3 minutes), and then the particle size distribution was measured by the laser diffraction method using a laser diffraction / scattering particle size distribution measuring device MT3300. The results are shown in FIG. 14. The median diameter (D50) was 96.66 μm.

Claims

1. (A) heating an aqueous solution containing ions of one or more rare earth elements selected from the group consisting of Sc, Y, Nd, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, one or both of Al ions and Ga ions, an organic compound having a carboxy group, and urea at a temperature of 80° C. or higher and lower than the boiling point of the aqueous solution, to generate particles of a rare earth composite compound by reaction between the organic compound, a hydrolysis product of urea, the ions of the rare earth elements, and one or both of Al ions and Ga ions; (B) producing a rare earth composite oxide from the rare earth composite compound; 2. A method for producing rare earth composite oxide particles, comprising:

2. The method according to claim 1, wherein the organic compound is an organic compound having one or more carboxy groups, or an organic compound in which two carboxy groups are condensed and which easily generates a carboxy group in an aqueous solution.

3. 3. The method according to claim 1, wherein in the step (B), the particles of the rare earth composite compound obtained in the step (A) are subjected to solid-liquid separation, and the obtained solid content is fired at a temperature of 600° C. or higher in an oxygen-containing atmosphere to produce the rare earth composite oxide.

4. 4. The method according to claim 3, wherein rare earth composite oxide particles having a volume-based median diameter (D50) of 0.1 μm or more and 10 μm or less in particle size distribution measured by a laser diffraction method are produced.

5. 2. The method according to claim 1, wherein the organic compound having a carboxy group is at least one selected from the group consisting of maleic acid, maleic anhydride, malic acid, and citric acid.

6. 6. The method according to claim 5, wherein in the step (B), the particles of the rare earth composite compound obtained in the step (A) are subjected to solid-liquid separation, and the obtained solid content is fired at a temperature of 700° C. or higher in an oxygen-containing atmosphere to produce the rare earth composite oxide.

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