Rare earth oxide powder

Abstract

To provide a rare earth oxide fine powder capable of: being easily dispersed without an intense crushing process; forming a thin coating film; or obtaining a highly dispersed slurry without the use of a dispersing agent, thereby maintaining a stable transparency.SOLUTION: The present invention relates to powder of oxides of a rare earth element other than Ce, which satisfies (a) or (b). (a) A primary particle diameter is 10 to 60 nm, satisfying (I) or (II). (I) D100 measured by ultrasonic dispersion is 1 to 10 μm. (II) When the true density is ρ, a difference between porosity PAD(%) calculated from the initial bulk density AD and porosity PTD(%) calculated from the tapped bulk density TD is 2.0 to 5.0%. PAD=(1-AD / ρ)×100 PTD=(1-TD / ρ)×100 (b). A primary particle size is 10 nm or larger and smaller than 100 nm, satisfying (III) and (IV). (III) A value obtained by multiplying a pore volume of 0.005 to 100 μm in pore diameter by the true density is 3 to 14. (IV) A value obtained by multiplying a pore volume of 5 to 50 nm in pore diameter by the true density is 0 to 2.0.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to rare earth oxide powder.

Background Art

[0002] Rare earth oxides are used in dielectrics or internal electrodes for capacitors, phosphors, refractive index adjusters for optical glass, oxygen sensors, sintering aids for ceramics, catalysts, refractories, etc. Their usage forms are various, including coating (coating film), trace addition, molded bodies (including sintered bodies), etc.

[0003] When coating a slurry containing rare earth oxide powder and there is a firing process after coating, the heat diffusivity can be enhanced by increasing the specific surface area of the rare earth oxide powder or reducing the primary particles. Also, when using rare earth oxide as an additive for firing, smaller primary particles may be more likely to undergo heat diffusion. From these viewpoints, various fine powders of rare earth oxides are known. In Patent Document 1, it is described that ultrafine yttrium oxide particles with an average primary particle size of 80 Å were obtained (Example 1 of Patent Document 1). In Patent Document 2, it is described that "when observed with a scanning electron microscope (SEM), (omitted) spherical particle groups with a uniform particle size of approximately 100 nm without aggregation" of yttrium oxide fine powder were obtained (Example 1 of Patent Document 2). In Non-Patent Document 1, a TEM image of Dy 2 O 3 fine powder crystallized as a result of long-term exposure to the electron beam of TEM is shown (Fig. 1a b of Non-Patent Document 1)

[0004] On the other hand, in the case of powders with a small primary particle size, for example, in the range of several tens of nm, aggregates are easily formed, and these aggregated particles become hard aggregates in the case of fine nano-powders with a small average particle size (see, for example, paragraph

[0014] of Japanese Patent No. 6119528). Therefore, in order to coat particles with small primary particles, it is necessary to use media or the like to crush them with high energy.

[0005] Patent Document 3 describes that the median particle diameter D50 measured by dispersing yttrium oxide powder in a slurry using a dispersant was 5.3 nm (Example 1 of Patent Document 3).

[0006] The slurry of fine rare earth oxide powder can be highly dispersed by using an appropriate dispersant (see, for example, paragraphs

[0020] and

[0029] of JP-A-2007-126349). However, depending on the formulation components, the dispersant may not work, and depending on the application, the dispersant may become an impurity.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0008]

Non-Patent Document 1

Summary of the Invention

[0009] The applicant has found that rare earth oxide powders produced by the methods described in Patent Documents 1 and 2 and Non-Patent Document 1, although they may appear not to be aggregated when observed with a scanning electron microscope (SEM), large coarse particles are measured when the aggregation diameter is measured by a macroscopic measurement method (laser scattering method). When the aggregation diameter is large, it becomes difficult to coat a thin film in the case of a coating solution. Also, even if an attempt is made to reduce the aggregation diameter by pulverization, since the primary particles are small, the aggregation force becomes strong, so strength dispersion is required and contamination derived from the pulverization media increases. In addition, when dried after wet pulverization, aggregation occurs during drying and the particle size increases. In particular, CeO2 Fine powders of rare earth oxides other than this were difficult to suppress aggregation.

[0010] Therefore, an object of the first invention is to provide rare earth oxide fine powders that can be easily dispersed without a crushing treatment of high strength and can form a thin film coating.

[0011] As a result of intensive studies, the present inventors have found that, surprisingly, the above problems can be solved by having a specific primary particle diameter (SSA conversion diameter) and setting the aggregation diameter in a specific range when a predetermined ultrasonic treatment is applied, or by having a specific primary particle diameter (SSA conversion diameter) and setting the difference in porosity calculated from the initial bulk density AD and the tapped bulk density TD within a predetermined range.

[0012] The first invention is based on the above findings and provides the following [a1] to [a9]. [a1] A powder of an oxide of at least one rare earth element other than Ce, having a primary particle diameter of 10 nm or more and 60 nm or less, and satisfying the following (I) or (II), rare earth oxide powder. (I) The volume cumulative particle diameter D at 100% by volume in the cumulative volume measured by laser diffraction / scattering particle size distribution measurement method after ultrasonic dispersion treatment at 40 W for 5 minutes 100 is 1 μm or more and 10 μm or less. (II) When the true density of the rare earth oxide is ρ (g / cm 3 ), the porosity P AD (%) calculated by the following formula 1 from the initial bulk density AD and the porosity P TD (%) calculated by the following formula 2 from the tapped bulk density TD, the difference (P AD - P TD ) is 2.0% or more and 5.0% or less. Formula 1: P AD = (1 - AD / ρ) × 100 (%) Formula 2: P TD = (1 - TD / ρ) × 100 (%) [a2] The rare earth oxide powder according to claim 1, which corresponds to the above (I). [a3] When the true density of the rare earth oxide is ρ (g / cm3 ) when it is, the porosity P calculated by the following formula 1 from the initial bulk density AD AD (%) is 90.0% or more and 99.0% or less, the rare earth oxide powder according to [a1] or [a2]. Formula 1: P AD =(1 - AD / ρ) × 100 (%) [a4] The rare earth oxide powder according to any one of [a1] to [a3], wherein the primary particle diameter is 35 nm or less. [a5] The rare earth oxide powder according to any one of [a1] to [a4], wherein the Zr content is 100 mass ppm or less. [a6] The rare earth oxide powder according to any one of [a1] to [a5], wherein the carbon content is 2 mass% or less. [a7] The rare earth oxide powder according to [a1], which corresponds to the above (II). [a8] The above porosity P AD (%) is 90.0% or more and 99.0% or less, the rare earth oxide powder according to [a7]. [a9] The volume cumulative particle diameter D at 100% by volume of the cumulative volume measured by the laser diffraction scattering particle size distribution measurement method after ultrasonic dispersion treatment for 40 W for 5 minutes 100 is 1 μm or more and 10 μm or less, and the D 100 measured by ultrasonic dispersion treatment and the volume cumulative particle diameter D 50 at 50% by volume of the cumulative volume measured by the above measurement method 100 Ratio of D 50 is 3.0 or more and 11.0 or less, the rare earth oxide powder according to [a7] or [a8].

[0013] Even for rare earth oxide fine powders that seem to have little aggregation visually in observations by a scanning electron microscope (SEM) as shown in Patent Documents 1 to 3, Non-Patent Document 1, etc., when the primary particles become as small as several tens of nm, the aggregation force becomes strong, and it is necessary to use a dispersant for wet pulverization in order to disperse it in the slurry. Also, due to the above circumstances, it is preferable that the slurry of the rare earth oxide fine powder can be in a highly dispersed state without using a dispersant. However, conventionally, it has been difficult to highly disperse rare earth oxide fine powder in a slurry without using a dispersant, and furthermore, it has been even more difficult to stably maintain the dispersed state. In particular, it has been difficult to obtain a highly dispersed slurry of fine powder of an oxide of a rare earth element other than Ce without using a dispersant.

[0014] Therefore, an object of the second invention is to provide an oxide powder of a rare earth element other than Ce that can form a highly dispersed slurry without using a dispersant and can stably maintain the transparency of the slurry.

[0015] As a result of intensive studies, the present inventors have surprisingly found that the above problems can be solved by having a specific primary particle size and setting the product of the pore volume / pore capacity and the true density within a specific range.

[0016] The second invention is based on the above findings and provides the following [b1] to [b7].

[0017] [b1] A powder of an oxide of at least one rare earth element other than Ce, having a primary particle size of 10 nm or more and less than 100 nm, and satisfying the following (III) and (IV). (III) The value obtained by multiplying the pore volume (cm 3 / g) of pores having a pore diameter of 0.005 μm or more and 100 μm or less by the true density (g / cm 3 ) is 3 or more and 14 or less. (IV) The value obtained by multiplying the pore volume (cm 3 / g) of pores having a pore diameter of 5 nm or more and 50 nm or less by the true density (g / cm 3 ) is 0 or more and 2.0 or less. [b2] The rare earth oxide powder according to [b1], having a Na content of 10 mass ppm or less. [b3] The rare earth oxide powder according to [b1] or [b2], having a crystallite size of 6 nm or more and 25 nm or less. After mixing the rare earth oxide powder with ethanol to obtain an ethanol slurry containing 10% by mass of the rare earth oxide powder, when the operation of (A) below is repeatedly performed until the average particle size becomes larger than the previous measured value, the minimum average particle size is 10 nm or more and 150 nm or less, and the rare earth oxide powder according to any one of [b1] to [b3]. (A): Using zirconia beads with a diameter of 0.1 mm, the slurry is subjected to bead mill treatment for 10 minutes, and then the average particle size is measured. (However, when the average particle size becomes larger than the previous measured value, the bead mill treatment is terminated at that point. Even if (A) is repeated 20 times and the average particle size does not become larger than the previous measured value in each of the second to twentieth times, the process is terminated when (A) is repeated 20 times. Here, the minimum average particle size means the minimum value of the average particle size measured by the dynamic light scattering method sampled for each treatment of (A).). [b5] The rare earth oxide powder according to [b4], wherein the calculated value of the following formula is -15% or more and 25% or less. [b6] The rare earth oxide powder according to [b4] or [b5], which is subjected to the bead mill treatment and has a minimum average particle size of 50 nm or more and 90 nm or less. [b7] A method for producing a slurry in which the rare earth oxide powder according to any one of [b1] to [b6] is wet pulverized using a solvent.

BEST MODE FOR CARRYING OUT THE INVENTION

[0018] Hereinafter, in this specification, "oxide of rare earth element" may be described as "rare earth oxide". Hereinafter, the first invention will be described in detail based on its preferred embodiments. The first invention relates to a powder of an oxide of a rare earth element other than Ce. CeO, which is an oxide of Ce 2 is obtained uncalcined by adding an oxidizing agent (H 2 O 2 ) to cerium hydroxide in water, and can also be easily obtained by calcining the precursor at a low temperature because Ce is easily oxidized. From this, CeO 2is less susceptible to agglomeration caused by firing during production, and even powders with primary particles of several tens of nanometers can be easily crushed. On the other hand, rare earth elements other than Ce do not become oxides like Ce when not fired, even if an oxidizing agent is added to the hydroxide. In addition, the precursor usually needs to be fired at a relatively high temperature for production, and high-temperature firing is one of the causes of necking. Therefore, with conventional rare earth element powders other than Ce, it has been very difficult to suppress the aggregation of the powder when the primary particles are several tens of nm in size.

[0019] In the first invention, the oxide of the rare earth element may be at least one oxide selected from Sc, Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Specifically, the oxide of the rare earth element other than Ce may be Sc. 2 O 3 , Y 2 O 3 , La 2 O 3 ,Pr 6 O 11 , Nd 2 O 3 , Sm 2 O 3 ,EU 2 O 3 , Gd 2 O 3 , Tb 4 O 7 , Dy 2 O 3 , Ho 2 O 3 , Er 2 O 3 , Tm 2 O 3 , Yb 2 O 3 and Lu 2 O 3include. From the viewpoint of the significance of the effect of the first invention being superior to the difficulty of conventional aggregation inhibition, as the oxide of the rare earth element, preferably, it is at least one oxide selected from Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, more preferably at least one oxide selected from Y, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, still more preferably at least one oxide selected from Y, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and particularly preferably at least one oxide selected from Y, Dy, Ho, Er, and Yb.

[0020] The primary particle size of the rare earth oxide powder preferably falls within a predetermined range. In the oxide powder of the rare earth element, the smaller the primary particle size, the better the heat diffusion. However, if it is too small, the aggregation becomes strong and it cannot be easily crushed. On the other hand, if the primary particle size is too large, necking occurs and the aggregation diameter becomes large. In addition, when the rare earth oxide powder is crushed by a bead mill or the like, the particles are crushed and the active surface increases, resulting in an unstable slurry. From these points, in the first invention, the primary particle size of the rare earth oxide powder is preferably 10 nm or more and 60 nm or less, more preferably 15 nm or more and 60 nm or less, and still more preferably 15 nm or more and 35 nm or less. The fact that the primary particle size of the rare earth oxide powder is 35 nm or less is particularly preferable in terms of improving the coating film property when used as a coating liquid and the large heat diffusion of the rare earth oxide powder.

[0021] In the first invention, the primary particle size of the oxide powder of the rare earth element is the primary particle size in terms of specific surface area. Specifically, it is the particle size obtained from the specific surface area s (m 2 / g) measured by the BET one-point method. For example, the primary particle size d (nm) is d = 6000 / (ρs). (ρ is the true density (g / cm 3 ).

[0022] The specific surface area of the oxide powder of the rare earth element of the first invention is, for example, preferably 10 m 2 / g or more and 160 m 2 / g or less, more preferably 15 m 2 / g or more and 110 m 2More preferably, it is below 20 m / g, and 2 more preferably, it is 80 m / g or less and 2 particularly preferably, it is below 40 m / g.

[0023] In the first invention, after ultrasonic irradiation, D based on volume measured by the laser diffraction scattering method for particle size distribution 100 (volume cumulative particle size at 100% by volume of cumulative volume) being within a specific range is preferable from the viewpoint of enabling the thin film to be coated. For example, from the viewpoint of coatability, D after ultrasonic irradiation 100 is particularly preferably 10 μm or less, more preferably 9 μm or less, and even more preferably 7 μm or less. To produce a thin film, if there are large coarse particles, it cannot be coated. Also, if the dispersibility of the slurry is too good, the stability of the slurry is poor and it may aggregate. Then, physical properties such as viscosity also change, and the coating conditions also change. From the viewpoint of stability, the above-mentioned D 100 is preferably 1 μm or more, and more preferably 2 μm or more.

[0024] The above-mentioned ultrasonic irradiation is more specifically a treatment of dispersing with 40 W of ultrasonic waves at a frequency of 40 kHz for 5 minutes. Examples of the irradiation device include those attached to a laser diffraction scattering particle size measuring device. For example, it irradiates a sample in which rare earth oxide powder is added to a 0.2 mass% aqueous solution of sodium hexametaphosphate. The concentration of the rare earth oxide powder in the dispersion liquid during ultrasonic irradiation is preferably the concentration determined by the particle size measuring device to be an appropriate concentration for particle size measurement, and is usually within the range of 0.002 to 0.2 mass%. Ultrasonic irradiation is specifically performed by the method described in the examples. However, if it is an equivalent irradiation device, irradiation may be performed with a device other than the one attached to the laser diffraction scattering particle size measuring device used for measurement. However, when irradiation is performed using a device other than the one attached to the laser diffraction scattering particle size measuring device used for measurement, 0.2 g of the sample is put into about 100 ml of a 0.2 mass% aqueous solution of sodium hexametaphosphate. After ultrasonic irradiation, the slurry after ultrasonic irradiation is added to the sample circulation device until the particle size measuring device determines that it is an appropriate concentration for particle size measurement, and then the measurement is performed.

[0025] From the viewpoint of further improving the film-forming property and the ease of coating, the particles of the first invention have a volume-based D measured by the laser diffraction scattering particle size distribution measurement method after the above ultrasonic irradiation 90 (volume cumulative particle size at a cumulative volume of 90% by volume) is preferably 0.1 μm or more and 2.5 μm or less, more preferably 0.3 μm or more and 2.3 μm or less, and particularly preferably 0.5 μm or more and 2.0 μm or less.

[0026] Furthermore, from the viewpoint of further improving the film-forming property and the ease of coating, the particles of the first invention have a volume-based D measured by the laser diffraction scattering particle size distribution measurement method after the above ultrasonic irradiation 50 (volume cumulative particle size at a cumulative volume of 50% by volume) is preferably 0.3 μm or more and 1.2 μm or less, more preferably 0.5 μm or more and 1.0 μm or less, and even more preferably 0.5 μm or more and 0.7 μm or less.

[0027] From the viewpoint of film-forming property, D 100 / D 50 is particularly preferably a particle size distribution within a specific range. Specifically, D 100 / D 50 is preferably 3.0 or more and 11.0 or less, and more preferably 3.0 or more and 8.5 or less.

[0028] The amount of impurities in the rare earth oxide powder is preferably small. In particular, if grinding media such as beads of a bead mill are used, D 100It can be easily crushed to 1 to 20 μm, more preferably up to 10 μm, but the media becomes an impurity and causes contamination. In the first invention, since rare earth oxide powder can be produced without using the above media, it is possible to reduce the Zr element, which is generally used as a constituent element of the grinding media, to 100 mass ppm or less. Furthermore, it is easy to reduce it to 10 mass ppm or less, and it can also be reduced to 2 mass ppm or less. Such rare earth oxide powder is preferable in terms of reducing the risk of contamination, and is also suitable for applications such as electronic components and corrosion-resistant materials for semiconductor manufacturing equipment. The content of the Zr element can be measured by ICP emission spectrometry and can be measured by the method described in the examples below. The measurement sample can be prepared by a conventional method, for example, by dissolving rare earth oxide powder in nitric acid or sulfuric acid.

[0029] It is preferable that the carbon content of the rare earth oxide powder is low. Rare earth elements and their compounds are also frequently used as additives for the purpose of solid solution. If there is a carbon component, mass loss (volume change) occurs during firing, resulting in cracks in the film. Therefore, the carbon content is preferably 2 mass% or less. More preferably, it is 1 mass% or less, and particularly preferably 0.7 mass% or less. The carbon content can be measured by the method described in the examples below. Note that the rare earth oxide powder preferably has a purity of usually 99 mass% or more. For example, the total content of Zr and carbon is preferably 1 mass% or less.

[0030] For the ease of dispersion of rare earth oxide powder with a primary particle size in a predetermined range in terms of SSA conversion, the present inventor found that the porosity P AD (%) obtained from the initial bulk density (AD) by Equation 1 and the porosity P TD (%) obtained from the tapped bulk density (TD) by Equation 2, and the difference (P AD -P TD )(%) being in a predetermined range is particularly preferable. ρ is the true density. Equation 1: P AD =(1 - AD / ρ) × 100 (%) Equation 2: P TD =(1 - TD / ρ) × 100 (%)

[0031] (P AD -P TD )(%) having a large value means that voids are likely to be clogged by tapping in the tapped bulk density measurement. (P AD -P TD )(%) particles having too large a value, that is, powders that can be compressed too much, become powders with strong aggregation. On the other hand, (P AD -P TD )(%) powders having too small a value are in a state where there is a lot of air between particles, which means that they are relatively fluffy powders that are difficult to compress easily in that state. Such powders tend to entrap air between particles and have a large aggregation diameter. Based on the speculation that the balance of the degree of compression affects the ease of aggregation of rare earth oxide fine powders, the present inventors conducted studies and as a result, found that the parameter affects the ease of dispersion of rare earth oxide powders. Specifically, the difference in (P AD -P TD )(%) is preferably 2.0% or more and 5.0% or less. (P AD -P TD )(%) being 2.0% or more and 5.0% or less makes the compressibility appropriate, is excellent in dispersibility compared to powders outside the range, and is excellent in coatability when used as a coating liquid. From this viewpoint, (P AD -P TD )(%) being 3.0% or more and 5.0% or less is more preferable, and 3.0% or more and 4.5% or less is even more preferable.

[0032] Furthermore, in view of the balance between aggregation suppression and handleability, the porosity P AD (%) calculated from the initial bulk density is preferably 90.0% or more and 99.0% or less, and more preferably 92.0% or more and 98.0% or less. Having the above (P AD -P TD )(%) and P AD (%) being 92.0% or more and 98.0% or less is preferable in terms of being particularly moderately aggregative and thus easy to disperse. Also, from the same viewpoint, P TDIt is preferably 88.0% or more and 95.5% or less, more preferably 88.5% or more and 92.0% or less.

[0033] The specific surface area (m 2 / g), primary particle diameter (nm), particle size distribution, initial bulk density (AD) and tapped bulk density (TD), Zr content, carbon content, P AD , P TD and P AD -P TD In order to obtain the above, a suitable method for producing rare earth oxide powder described below may be adopted, and the conditions for mixing, washing or firing may be adjusted.

[0034] Next, a suitable method for producing the rare earth oxide powder of the first invention will be described. In this production method, an aqueous carbonate solution (hereinafter also referred to as "solution A") and an aqueous solution of a water-soluble salt of a rare earth element (hereinafter also referred to as "solution B") are simultaneously charged into a reaction tank, and the pH of the mixed solution is 6.5 to 7.0, preferably 6.5 to 6.9, and mixed under high-speed stirring so that a reaction between the carbonate and the water-soluble salt of the rare earth element occurs. Solid-liquid separation is started within 5 minutes from the start of mixing of solution A and solution B. The method includes a reaction·solid-liquid separation step, a washing step of washing the residue obtained in the reaction·solid-liquid separation step with alcohol, and a firing step of firing the washed residue. From the viewpoint of successfully obtaining the rare earth oxide powder of the first invention, preferably, the concentration of the water-soluble salt in terms of oxide in the aqueous solution of the water-soluble salt of the rare earth element, which is solution B, is 10 to 400 g / L in terms of oxide, more preferably 50 to 350 g / L, particularly preferably 80 to 300 g / L, and most preferably more than 100 g / L and 300 g / L or less.

[0035] (Reaction·solid-liquid separation step) In solution A, which is an aqueous carbonate solution, the carbonate includes ammonium bicarbonate, ammonium carbonate, sodium carbonate, sodium bicarbonate, etc. The carbonate as used herein includes not only the normal salt but also the acidic salt, ammonium bicarbonate. Ammonium bicarbonate is preferred from the viewpoints of easy adjustment of the pH of the mixed solution and reduction of the sodium content. In the solution B which is an aqueous solution of a water-soluble salt of a rare earth element, examples of the water-soluble salt of the rare earth element include nitrates, acetates, amine complexes, and chlorides. Nitrates are preferred from the viewpoints of ease of adjusting the pH of the mixed solution and productivity.

[0036] In this production method, the solution A which is an aqueous solution of a carbonate and the solution B which is an aqueous solution of a water-soluble salt of a rare earth element are simultaneously introduced into the reaction tank so that the pH of the mixed solution of the two is 6.5 to 7.0, preferably 6.5 to 6.9. The pH mentioned here is the pH of the mixed solution at the temperature. When the pH of the mixed solution exceeds 7.0, the primary particles will become large. Also, setting the pH to 6.5 or more has the advantage that almost all of the rare earth ions in the solution A will precipitate. It is preferable that neither the solution A nor the solution B is heated at the time of introduction. It is suitable that the solution A and the solution B are at 5 to 50°C at the time of introduction into the reaction tank, and it is suitable that the temperature of the mixed solution is 5 to 40°C. In order to keep the primary particle size within a suitable range, it is preferable to carry out the reaction in an extremely short time and immediately filter. For this purpose, the pH of the mixed solution is adjusted so that it is in the range of 6.5 to 7.0 from the start point of introduction of the solution A and the solution B into the reaction tank (the start point of mixing of the solution A and the solution B) to the point when the reaction product is formed (more specifically, the start point of solid-liquid separation), and it is preferable to keep the pH constant within the above range by adjusting the timing and the introduction rate of the two solutions. When the pH is within the above range, the reaction proceeds smoothly.

[0037] The fact that the solution A and the solution B are added simultaneously means that the time when the solution A is introduced into the reaction tank and the time when the solution B is introduced into the reaction tank are at least partially simultaneous. As described above, in order for the pH of the mixed solution to be in the range of 6.5 to 7.0 from the start point of introduction of the solution A and the solution B into the reaction tank (the start point of mixing of the solution A and the solution B) to the point when the reaction product is formed (more specifically, the start point of solid-liquid separation), it is preferable to start the introduction of each of them almost simultaneously and keep the introduction rate constant. Also, the introduction rates of the solution A and the solution B are adjusted so that solid-liquid separation can be started within 5 minutes, more preferably within 3 minutes, from the start of mixing of the solution A and the solution B.

[0038] In this manufacturing method, in the reaction tank, the mixed solution of liquid A and liquid B is simultaneously introduced as described above and rapidly stirred under a predetermined pH condition. In such a manner, powders having the primary particle diameter, the aggregated diameter D after ultrasonic irradiation 100 , and the porosity difference within the above-specified range are preferably easily obtained. Examples of the rapid stirring include stirring at a rotational speed of 10,000 to 25,000 rpm, with 18,000 to 21,000 rpm being more preferable. When the stirrer in the reaction tank of the mixed solution performs the above rotation for these stirrings, the capacity of the reaction tank is preferably 50 ml to 1 L, and more preferably 100 ml to 500 ml. The inventor of the present invention does not add liquid B to liquid A previously placed in the reaction tank or introduce liquid A into liquid B previously placed in the reaction tank, but simultaneously introduces liquid A and liquid B and rapidly stirs under the condition of maintaining a predetermined pH, whereby the reaction can be completed in a short time. When this is subjected to a predetermined post-treatment, it has been found that a rare earth oxide powder of the first invention having a small primary particle diameter and being easily dispersible with low-intensity pulverization can be obtained.

[0039] Regarding the above primary particle diameter, the aggregated diameter D after ultrasonic irradiation 100 , and the porosity difference, from the viewpoint of easier obtainment, the concentration of carbonate in liquid A is preferably 5 to 25% by mass, and more preferably 10 to 15% by mass. Also, the concentration of the water-soluble salt of the rare earth element in liquid B is as described above.

[0040] (Washing step) The residue (also referred to as "solid matter") obtained in the above solid-liquid separation step is washed with alcohol. As the alcohol used in this manufacturing method, for example, a high-purity alcohol having an alcohol purity of 99.5 vol% or more is preferably used. Examples of the alcohol include methanol, ethanol, isopropanol, etc., with ethanol being preferable from the viewpoint of usability. The amount of alcohol used for washing is preferably 0.1 L to 50 L, more preferably 0.5 L to 20 L, and even more preferably 1 L to 10 L per 1 g of the rare earth oxide used. The amount referred to here is the total amount when the alcohol is passed through the residue several times for washing.

[0041] (Firing process) The firing temperature is preferably 1000 °C or lower from the viewpoints of suppressing aggregation and suppressing crystal growth, and more preferably 800 °C or lower. The firing temperature is preferably 500 °C or higher from the viewpoint of reducing the carbon content. From this viewpoint, the firing temperature is more preferably 500 °C or higher and 1000 °C or lower, and even more preferably 500 °C or higher and 800 °C or lower. The firing can be carried out in an oxygen gas-containing atmosphere such as an air atmosphere and in an inert atmosphere such as argon or nitrogen, but it is preferable to carry out the firing in an oxygen gas-containing atmosphere, particularly in an air atmosphere, from the viewpoints of reducing the carbon content and cost.

[0042] (Crushing process) It is preferable to crush the coarse particles of the rare earth oxide powder obtained by firing. A dry pulverizer can be used for crushing, for example, a pulverizer (trade name: Force Mill, manufactured by Osaka Chemical) can be used.

[0043] Next, the rare earth oxide powder obtained as described above can be used for various applications by taking advantage of its easy dispersibility. For example, dielectrics or internal electrodes for capacitors, phosphors, refractive index adjusters for optical glasses, oxygen sensors, sintering aids for ceramics, additives to alloys, catalysts, refractories, laser crystal raw materials, corrosion-resistant materials for semiconductor manufacturing equipment, etc. can be mentioned. The usage method at that time is various, and it can be applied to various forms such as coating (film formation), trace addition, and molded bodies (including sintered bodies). In particular, since the rare earth oxide powder of the first invention has good film-forming properties, it can be suitably used for its coating applications (including film formation applications).

[0044] Hereinafter, the second invention will be described in detail based on its preferred embodiments. The second invention relates to a powder of an oxide of a rare earth element other than Ce. CeO, which is an oxide of Ce 2 is obtained by adding an oxidizing agent (H 2 O 2) can be added to the precursor to obtain the ceramic without the need for a firing process, and since Ce is easily oxidized, it can be easily obtained by firing the precursor at a low temperature. 2 is less susceptible to agglomeration caused by firing during production, and even powders with primary particles of several tens of nanometers can be easily crushed. On the other hand, for rare earth elements other than Ce, oxides cannot be obtained even if an oxidizing agent is added to the hydroxide, and therefore, in general, firing at relatively high temperatures is essential for production, and high-temperature firing is one of the causes of necking. Therefore, in conventional rare earth element powders other than Ce, it has been very difficult to suppress the aggregation of powder when the primary particles are several tens of nm in size.

[0045] In the second invention, the oxide of the rare earth element other than Ce may be at least one oxide selected from Sc, Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Specifically, the oxide of the rare earth element other than Ce may be Sc 2 O 3 , Y 2 O 3 , La 2 O 3 ,Pr 6 O 11 , Nd 2 O 3 , Sm 2 O 3 ,EU 2 O 3 , Gd 2 O 3 , Tb 4 O 7 , Dy 2 O 3 , Ho 2 O 3 , Er 2 O 3 , Tm 2 O 3 , Yb 2 O 3 and Lu 2 O 3include. From the viewpoint of the significance of the effect of the second invention being superior to the difficulties of conventional aggregation inhibition, as the oxide of the rare earth element, preferably, it is at least one oxide selected from Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, more preferably at least one oxide selected from Y, La, Pr, Nd, Eu, Gd, Dy, Ho, Er, and Yb, and particularly preferably at least one oxide selected from Y, La, Eu, Gd, Dy, Ho, and Yb.

[0046] In the oxide powder of the rare earth element, the smaller the primary particles, the more difficult it is to be pulverized, and the active surface area decreases. In the absence of a dispersant, the smaller the active surface area, the more stable the slurry becomes. However, if the primary particles are too small, aggregation becomes stronger and it becomes impossible to disintegrate. Even if it can be disintegrated, when the strongly aggregated part is separated, the activity of that part increases and an unstable slurry is formed. From this viewpoint, the primary particle diameter needs to be within a predetermined range. Specifically, the primary particles are 10 nm or more and less than 100 nm, preferably 12 nm or more and 60 nm or less, more preferably 15 nm or more and 50 nm or less, and particularly preferably 15 nm or more and 35 nm or less. In the second invention, the primary particle diameter of the oxide powder of the rare earth element is the primary particle diameter in terms of specific surface area, specifically, the particle diameter obtained from the specific surface area s (m 2 / g) measured by the BET one-point method. For example, the primary particle diameter d (nm) is d = 6000 / (ρs). (ρ is the true density (g / cm 3 ).

[0047] Furthermore, in the second invention, the numerical value obtained by multiplying the pore volume (cm 3 / g) with pore diameters of 0.005 μm or more and 100 μm or less by the true density (g / cm 3 ) is a specific value. Here, the reason for defining the value obtained by multiplying the true density by the pore volume instead of the pore volume in the second invention will be explained below. The pore volume (cm 3 / g) depends on the volume per weight of the sample to be measured. Therefore, the pore volume per volume (cm 3) is the same, but when the pore volume per unit weight (cm 3 / g) is considered, the value of the compound with a higher true density becomes smaller. Therefore, in the second invention, as a value of the pore volume independent of the compound species, a value obtained by multiplying the pore volume per gram (cm 3 / g) by the true density is defined. When the pore volume (cm 3 / g) obtained from a mercury porosimeter is multiplied by the true density (mass per 1 cm 3 ), it becomes the pore volume per unit volume.

[0048] The value obtained by multiplying the true density by the pore volume with a pore diameter of 0.005 μm or more and 100 μm or less (hereinafter also referred to as "first pore volume") represents the total pore volume derived from the voids between primary particles and the gaps between aggregated particles, and is a parameter indicating the degree of aggregation. A small first pore volume per unit indicates strong aggregation, and a large first pore volume indicates a large or numerous voids and a large aggregation diameter. Therefore, an appropriate first pore volume leads to ease of comminution.

[0049] Specifically, the first pore volume, which is the value obtained by multiplying the true density by the pore volume with a pore diameter of 0.005 μm or more and 100 μm or less, is 3 or more and 14 or less. When the value of the first pore volume is low, aggregation is strong with no voids between particles. Also, when it exceeds 14, the number of voids increases and the initial aggregation diameter becomes large. Also, it is expected that the presence of many voids makes it easier to absorb impacts, making comminution with a bead mill difficult. From these viewpoints, 4 or more and 12 or less is more preferable, and 5.5 or more and 12 or less is particularly preferable.

[0050] In the second invention, another feature is that the numerical value obtained by multiplying the true density (g / cm 3 / g) by the pore volume with a pore diameter of 5 nm or more and 50 nm or less (cm 3 / g) (hereinafter also referred to as "second pore volume") is also a specific value. At a pore diameter, it is known that pores having a size of about 1 / 3 to 1 / 4 of the particle diameter are formed between particles (see Japanese Patent Laid-Open No. 7-237982). Pores with a pore diameter of 5 nm or more and 50 nm or less correspond to pores of aggregates with an aggregate diameter of about 15 nm or more and 200 nm or less. The achievable aggregate diameter by crushing depends on the bead diameter. However, as will be described later, the bead diameter cannot be made too small in consideration of the crushing energy. If there are many particles with an aggregate diameter of about 15 nm or more and 200 nm or less, they are likely to overlap with the achievable particle diameter of bead crushing. Particles with an aggregate diameter relatively close to the achievable particle diameter of bead crushing are difficult to crush even if they are larger than the achievable particle diameter of bead crushing, and even if they are smaller than the achievable particle diameter, the force for aggregating these aggregates becomes stronger, and it is easy to form aggregates of aggregates (tertiary aggregates). From these facts, a powder with a large pore volume with a pore diameter of 5 nm or more and 50 nm or less is likely to form a slurry with a large particle diameter of the dispersed substance. Therefore, in the second invention, the second pore volume, which is the value obtained by multiplying the pore volume with a pore diameter of 5 nm or more and 50 nm or less by the true density, is 2.0 or less, more preferably 1.5 or less, particularly preferably 1.2 or less, still more preferably 1.0 or less, even more preferably 0.8 or less, and particularly preferably 0.7 or less. Also, the lower limit value of the second pore volume is not particularly limited as long as it is 0 or more, but from the viewpoint of ease of production, it is preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.05 or more.

[0051] Also, the specific surface area of the oxide powder of the rare earth element of the second invention is, for example, 10 m 2 / g or more and 160 m 2 / g or less, which is preferable in terms of easily providing the above primary particle diameter, more preferably 15 m 2 / g or more and 110 m 2 / g or less, and still more preferably 20 m 2 / g or more and 80 m 2 / g or less.

[0052] Furthermore, the impurity content of the rare earth oxide powder should preferably be low. If Na ions or the like are present during synthesis, particle growth can be suppressed, but Na is difficult to decompose. Since there are certain electronic materials that do not prefer Na, it is better to have less Na ions. From this perspective, the Na content of the rare earth oxide powder is preferably 100 mass ppm or less, and particularly preferably 10 mass ppm or less. The Na content can be measured by the method described in the examples below.

[0053] The rare earth oxide powder preferably has a crystallite size within a predetermined range. Specifically, the crystallite size of the rare earth oxide powder is preferably 6 nm or more and 25 nm or less. When the crystallite size of the rare earth oxide powder is equal to or greater than the predetermined value, it is easier to make the primary particle size equal to or greater than a certain value, and the cohesive force of the primary particles can be reduced. Also, when the crystallite size is equal to or less than the predetermined value, it is easier to make the primary particle size equal to or less than a certain value, and necking between particles can be prevented. Considering these points, the crystallite size of the rare earth oxide powder is more preferably 8 nm or more and 20 nm or less. The crystallite size can be measured by the method described in the examples below.

[0054] The rare earth oxide powder of the second invention can be made into a slurry by wet grinding. The rare earth oxide powder of the second invention preferably has an agglomerated particle size within a specific range in a specific grinding process. Specifically, after mixing the rare earth oxide powder with ethanol to form an ethanol slurry containing 10% by mass of the rare earth oxide powder, when the operation of (A) is repeated until the average particle size becomes larger than the previous measured value, the minimum average particle size (Dm) is preferably 10 nm or more and 150 nm or less. As a method of making an ethanol slurry containing 10% by mass of the rare earth oxide powder, a method of mixing 40.5 g of ethanol with a purity of 99% by mass or more and 4.5 g of the rare earth oxide powder to form a slurry can be mentioned. No dispersant is used in the slurry for measuring the agglomerated particle size. Examples of the dispersant include various dispersants described below. (A): Using zirconia beads with a diameter of 0.1 mm, perform bead milling on the slurry for 10 minutes, and then measure the average particle size by the dynamic light scattering method. (A) shall be specifically carried out as follows (a). (a): Using zirconia beads with a diameter of 0.1 mm, with a mass ratio of slurry:beads of 45:240, in a bead mill with an effective volume of 80 cc of the vessel, perform bead mill treatment for 10 minutes under the condition of a peripheral speed of 4 m / s or more and 6 m / s or less, and then measure the average particle diameter by the dynamic light scattering method. (However, when the average particle diameter becomes larger than the previous measurement value, the bead mill treatment is terminated at that time. Also, if the average particle diameter does not become larger than the previous measurement value in each of the second to twentieth repetitions of 20 times of (A), it is terminated when 20 times of (A) are repeated.) However, the minimum average particle diameter (Dm) here means the minimum value of the average particle diameter by the dynamic light scattering method measured by sampling every 10 minutes during the bead mill treatment. In addition, when the average particle diameter is expressed in nm units and there are numerical values after the decimal point, the magnitude is judged by the value obtained by rounding the first digit after the decimal point to an integer.

[0055] The minimum average particle diameter (Dm) obtained by the above measurement indicates the minimum aggregation diameter by bead crushing treatment, which is a general crushing treatment in the technical field related to oxide fine powder slurries. The minimum average particle diameter (Dm) is preferably 150 nm or less, more preferably 140 nm or less, still more preferably 105 nm or less, and particularly preferably 90 nm or less. This is because the transparency can be improved by making the minimum average particle diameter (Dm) below a predetermined value. Further, the minimum average particle diameter (Dm) is preferably 10 nm or more, more preferably 15 nm or more, still more preferably 20 nm or more, and most preferably 50 nm or more. This is because the dispersion stability of the slurry can be enhanced by setting this lower limit above a predetermined value.

[0056] Also, the polydispersity index (PI) during the measurement of the minimum average particle diameter (Dm) is preferably 0.3 or less because the particle size distribution is sharp, and it is easier to maintain the high dispersibility and visible light transmittance when made into a slurry. More preferably, it is 0.25 or less. The polydispersity index (PI) is a dimensionless index indicating the spread of the particle size distribution.

[0057] The effective volume of the vessel refers to the internal volume of the container (vessel) in which the beads and the slurry are accommodated. Also, for the peripheral speed of the bead mill, any peripheral speed of 4 m / s or more and 6 m / s or less may be adopted, but more preferably it is 4 m / s or more and 5 m / s or less, and still more preferably it is 4 m / s.

[0058] For the measurement of the average particle size and the polydispersity index (PI) by the dynamic light scattering method (photon correlation method), the measurement sample is filled into a dynamic light scattering photometer for measurement. The measurement sample is a sample obtained by taking out a part of the above slurry and not subjecting it to ultrasonic treatment using the solvent used during wet grinding as the dispersion medium. The concentration of the measurement sample is set to the dilution ratio determined by the dynamic light scattering photometer to be an appropriate concentration in the range of 1000 to 10000 volume times. As the dynamic light scattering photometer, an apparatus that adopts a method of obtaining the average particle size and the polydispersity index (PI) by cumulant method analysis from the autocorrelation function obtained by the photon correlation method can be adopted. For example, ELSZ-2000ZS manufactured by Otsuka Electronics can be used. Note that the cumulant method is described in "9.2.1 Cumulant method" of JIS Z 8828:2019 "Particle size analysis - Dynamic light scattering method" and "A.1.2 Cumulant method" in Annex A of the same JIS.

[0059] The slurry after crushing obtained by crushing the rare earth oxide powder of the second invention as described above to obtain the minimum average particle size (Dm) preferably has a calculated value within a predetermined range when it is allowed to stand at room temperature (15 to 25 °C). The following formula shows the particle size variation when allowed to stand for 7 days. The value of the following formula is preferably 25% or less, more preferably 20% or less, and still more preferably 15% or less. If it is below this upper limit, it can be easily returned to a particle size equivalent to or close to that immediately after crushing by applying ultrasonic waves or the like. Since the average particle size of the slurry is a measurement of fine particles, it is necessary to consider the variation in measurement. When there is no substantial change in the particle size, it may be measured as if the particle size has become smaller. Therefore, the calculated value is preferably -15% or more, and more preferably -10% or more. In the following formula, the "average particle diameter immediately after comminution (D0)" means that when the operation of (A) above is repeated until the average particle diameter becomes larger than the previous measurement value, if the average particle diameter does not become larger than the previous measurement value until the 20th time, it becomes the same value as the minimum average particle diameter (Dm). On the other hand, if during the repetition up to the 20th time, the average particle diameter becomes larger than the previous measurement value and the bead mill treatment ends, the last measurement value becomes the "average particle diameter immediately after comminution (D0)". Also, in the following formula, the "average particle diameter 7 days after comminution (D7)" refers to the average particle diameter measured by the dynamic light scattering method (photon correlation method) again when the slurry after the bead mill treatment is allowed to stand for 7 days under the above conditions. Formula: (Average particle diameter 7 days after comminution (D7) - Average particle diameter immediately after comminution (D0)) / Average particle diameter immediately after comminution (D0) × 100 (%)

[0060] For the rare earth oxide powder of the second invention, the average particle diameter immediately after comminution (D0) is preferably 210 nm or less, more preferably 150 nm or less, and particularly preferably 120 nm or less. This is because the transmittance after standing can be increased. Also, the average particle diameter immediately after comminution (D0) is preferably 25 nm or more, more preferably 50 nm or more. This is because the dispersibility of the slurry can be increased.

[0061] For the rare earth oxide powder of the second invention, the average particle diameter 7 days after comminution (D7) is preferably 150 nm or less, more preferably 120 nm or less, and particularly preferably 100 nm or less. This is because the transmittance after standing can be increased. Also, the average particle diameter 7 days after comminution (D7) is preferably 25 nm or more, more preferably 50 nm or more. This is because the dispersibility of the slurry can be increased.

[0062] In the rare earth oxide powder of the second invention, it is preferable that the average particle diameter (D7S) after irradiating 20 ml of the slurry with 40 W of ultrasonic waves (frequency: 40 kHz) for 5 minutes 7 days after crushing is 150 nm or less, more preferably 120 nm or less, and particularly preferably 100 nm or less. This is because the transmittance after standing can be increased. Further, the average particle diameter (D7S) is preferably 25 nm or more, and more preferably 50 nm or more. This is because the dispersibility of the slurry can be increased.

[0063] For obtaining the specific surface area (m 2 / g), primary particle diameter (nm), first pore volume, second pore volume, Na content, Dm (nm), D0 (nm), D7 (nm), ((D7 - D0) / D0) (%), D7S (nm) described above, a suitable production method of the rare earth oxide powder described below may be adopted, and the conditions of mixing, washing, or firing may be adjusted.

[0064] Next, a suitable production method of the rare earth oxide powder of the second invention will be described. This production method simultaneously feeds an aqueous carbonate solution (hereinafter also referred to as "solution A") and an aqueous solution of a water-soluble salt of a rare earth element (hereinafter also referred to as "solution B") into a reaction tank, and mixes them so that the pH of the mixed solution becomes 6.5 to 7.0, preferably 6.5 to 6.9, to react the carbonate with the water-soluble salt of the rare earth element, and starts solid-liquid separation within 5 minutes from the start of mixing of solution A and solution B, a reaction · solid-liquid separation step, and a washing step of washing the residue obtained in the reaction · solid-liquid separation step with alcohol or hydrous alcohol, and includes a firing step of firing the washed residue. From the viewpoint of successfully obtaining the rare earth oxide powder of the second invention, preferably, the concentration of the water-soluble salt in terms of oxide in the aqueous solution of the water-soluble salt of the rare earth element as solution B is 10 to 400 g / L, more preferably 20 to 300 g / L, particularly preferably 20 to 200 g / L, and most preferably more than 20 g / L and less than 100 g / L. This manufacturing method is different from the manufacturing method of the rare earth oxide powder of the first invention in that the mixed solution of liquid A and liquid B does not necessarily need to be stirred at a high speed, the residue obtained in the reaction and solid-liquid separation step may be washed not only with alcohol but also with hydrous alcohol, and the preferable concentration range of the water-soluble salt aqueous solution of the rare earth element in liquid B is different.

[0065] (Reaction and solid-liquid separation step) In liquid A which is an aqueous carbonate solution, examples of the carbonate include ammonium bicarbonate, ammonium carbonate, sodium carbonate, sodium bicarbonate, etc. The carbonate referred to in this specification includes not only the normal salt but also the acidic salt, ammonium bicarbonate. Ammonium bicarbonate is preferable from the viewpoints of easy adjustment of the pH of the mixed solution and reduction of the sodium content. In liquid B which is an aqueous solution of a water-soluble salt of a rare earth element, examples of the water-soluble salt of the rare earth element include nitrates, acetates, ammine complexes, and chlorides. Nitrates are preferable from the viewpoints of easy adjustment of the pH of the mixed solution and productivity.

[0066] When adopting this manufacturing method, it is also preferable that the concentrations of liquid A and liquid B are within a predetermined range from the viewpoint of successfully setting the primary particle diameter, the first pore volume, and the second pore volume within a predetermined range. Specifically, the concentration of the carbonate in liquid A is preferably 5 to 25% by mass, and more preferably 10 to 15% by mass. The concentration of the water-soluble salt of the rare earth element in liquid B is as described above.

[0067] In this manufacturing method, liquid A, which is an aqueous carbonate solution, and liquid B, which is an aqueous solution of a water-soluble salt of a rare earth element, are simultaneously introduced into a reaction tank such that the pH of the mixed solution of the two is 6.5 to 7.0, preferably 6.5 to 6.9. The pH referred to here is the pH of the mixed solution at the temperature of the mixed solution. When the pH of the mixed solution exceeds 7.0, the primary particles become large. Also, setting the pH to 6.5 or higher has the advantage that almost all of the rare earth ions in liquid A precipitate. It is preferable that neither liquid A nor liquid B is heated at the time of introduction. It is suitable that liquid A and liquid B are at 5 to 50°C at the time of introduction into the reaction tank, and it is suitable that the temperature of the mixed solution is 5 to 40°C. In order to keep the primary particle size within a suitable range, it is preferable to carry out the reaction in an extremely short time and immediately filter. For this purpose, it is suitable to adjust the timing and feeding rate of the two liquids so that the pH of the mixed solution is in the range of 6.5 to 7.0, preferably 6.5 to 6.9, from the start time of introduction of liquid A and liquid B into the reaction tank (the start time of mixing of liquid A and liquid B) to the time when the reaction product is formed (more specifically, the start time of solid-liquid separation), and to keep the pH constant within the above range. When the pH is within the above range, the reaction proceeds smoothly.

[0068] The simultaneous addition of liquid A and liquid B means that the time when liquid A is introduced into the reaction tank and the time when liquid B is introduced into the reaction tank are at least partially simultaneous. As described above, in order for the pH of the mixed solution to continuously be in the range of 6.5 to 7.0, preferably 6.5 to 6.9, from the start time of introduction of liquid A and liquid B into the reaction tank (the start time of mixing of liquid A and liquid B) to the time when the reaction product is formed (more specifically, the start time of solid-liquid separation), for liquid A and liquid B with the above concentrations, it is preferable that the start of each introduction is almost simultaneous and the feeding rate is constant. Also, the feeding rates of liquid A and liquid B are adjusted so that solid-liquid separation can be started within 5 minutes, more preferably within 3 minutes, from the start of mixing of liquid A and liquid B. Instead of adding liquid B to liquid A pre-placed in the reaction tank or introducing liquid A into liquid B pre-placed in the reaction tank, the inventor simultaneously introduces liquid A and liquid B at a predetermined concentration and mixes them under the condition of maintaining a predetermined pH, so that the reaction can be completed in a short time. When this is subjected to a predetermined post-treatment, rare earth oxide powder of the second invention can be obtained, which is a slurry having a small primary particle size, good dispersibility, and excellent transparency.

[0069] In the reaction tank, it is preferable that the mixed solution of liquid A and liquid B is stirred in that the rare earth oxide powder of the second invention can be successfully obtained. It may be high-speed stirring, low-speed stirring, or medium-speed stirring. The stirring speed is preferably 100 rpm or more and 25000 rpm or less, and more preferably 200 rpm or more and 21000 rpm or less. Examples of low-speed stirring include stirring at 100 rpm or more and less than 1000 rpm, and more preferably 200 rpm or more. Examples of medium-speed stirring include stirring at 1000 rpm or more and less than 10000 rpm. Examples of high-speed stirring include stirring at 10000 rpm or more and 25000 rpm or less. In the case of high-speed stirring, 18000 rpm or more and 21000 rpm are particularly preferable. High-speed stirring is preferable because the primary particle size can be particularly preferably reduced. As for the reaction tank, as long as it is equipped with a stirring device (including those integrated with the reaction tank) capable of stirring at a predetermined rotation speed, the capacity of the reaction tank may be appropriately determined according to the production volume and the like. However, due to the limitation of the size of the high-speed stirring device, the capacity of the reaction tank equipped with the high-speed stirring device is preferably 50 mL to 5 L, more preferably 100 mL to 2 L, and even more preferably 100 mL to 1 L.

[0070] (Washing step) The residue obtained in the above solid-liquid separation step (also referred to as "solid matter") is also importantly washed with alcohol or hydrous alcohol. Examples of the alcohol include methanol, ethanol, isopropanol, etc., but ethanol is preferred from the viewpoint of usability. When using hydrous alcohol, the alcohol concentration in the hydrous alcohol is preferably 10% by volume or more, and more preferably 50% by volume or more. The amount of alcohol used for washing is preferably 0.1 L to 50 L, more preferably 0.5 L to 20 L, and even more preferably 1 L to 10 L with respect to 1 g of the oxide conversion amount of the solid matter to be washed. The amount referred to here is the total amount when the alcohol is passed through the residue several times for washing.

[0071] (Firing step) The firing temperature is preferably 1000 °C or lower from the viewpoints of aggregation suppression and crystal growth suppression, and more preferably 800 °C or lower. The firing temperature is preferably 500 °C or higher from the viewpoint of carbon content reduction. From this viewpoint, the firing temperature is more preferably 500 °C or higher and 1000 °C or lower, and even more preferably 500 °C or higher and 800 °C or lower. The firing can be carried out in an active gas atmosphere such as an air atmosphere or an inert atmosphere such as argon or nitrogen, but it is preferably carried out in an active gas atmosphere, particularly in an air atmosphere.

[0072] (Crushing step) The rare earth oxide powder obtained by firing is preferably crushed to remove coarse particles. A dry pulverizer can be used for crushing. For example, a pulverizer (trade name: Force Mill, manufactured by Osaka Chemical) can be used.

[0073] Next, a method for producing a slurry in which the rare earth oxide powder obtained as described above is wet-crushed to form a slurry will be described.

[0074] Wet pulverization is preferably carried out by a bead mill in terms of enabling high dispersion. The beads of the bead mill are usually spherical. Examples of the bead material include zirconia, alumina, silicon nitride, silicon carbide, tungsten carbide, wear-resistant steel, stainless steel, etc., and zirconia is preferred. The zirconia mentioned here includes stabilized zirconia such as YSZ and PSZ.

[0075] The bead diameter during pulverization is preferably 0.01 to 0.3 mm. Since the particle size reached by pulverization is, for example, about 1 / 1000 of the bead diameter based on the bead diameter, it is better for the bead diameter to be smaller. However, if it is too small, the pulverization energy becomes small, and aggregation may not be dispersed. From this viewpoint, a bead diameter of 0.05 to 0.15 mm during pulverization is more preferable.

[0076] The solvent for dispersing the rare earth oxide powder is preferably a monohydric alcohol in terms of having better dispersibility than water, particularly a primary alcohol, and especially ethanol. Examples of the monohydric alcohol solvent include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol. Monohydric alcohols are frequently used as laboratory cleaning materials, etc., and are easily available. In addition, ethanol and 1-propanol are not subject to the Poisonous Organic Solvents Prevention Regulations, so they are easy to handle. Note that the monohydric alcohol preferably has a purity of 99% by volume or more.

[0077] Moreover, the proportion of the rare earth oxide powder in the slurry obtained by the production method of the second invention is preferably 1 to 50% by mass from the viewpoint of obtaining a desired visible light transmittance, and more preferably 5 to 20% by mass.

[0078] In the production method of the slurry of the second invention, it is preferable that the average particle size of the obtained slurry is pulverized to 200 nm or less, more preferably pulverized until it becomes 10 nm or more and 150 nm or less, still more preferably 15 nm or more and 140 nm or less, and particularly preferably 20 nm or more and 105 nm or less. By being below the above upper limit, particularly within the above range, it has excellent permeability and stability.

[0079] In the method for producing the slurry of the second invention, the polydispersity index (PI) of the resulting slurry is preferably 0.3 or less, more preferably 0.25 or less. The lower the polydispersity index (PI), the more preferable it is, but from the viewpoint of ease of production, it is preferably 0.1 or more.

[0080] The method for producing the slurry of the second invention is preferably a method in which the visible light transmittance of the slurry left standing 7 days after pulverization is 40 to 95%, more preferably 50 to 80%. The visible light transmittance can be measured by the method described in the examples below.

[0081] In the method for producing the slurry of the second invention, it is preferable not to use a dispersant. Examples of the dispersant include ionic surfactants, nonionic surfactants, pH adjusters, and soluble salts. For example, ether types such as polyoxyethylene alkyl ether, polyoxyethylene secondary alcohol ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene, polyoxypropylene block copolymer, and polyoxyethylene polyoxypropylene alkyl ether, and ester ether types such as polyoxyethylene glycerin fatty acid ester, polyoxyethylene castor oil and hydrogenated castor oil, and polyoxyethylene sorbitan fatty acid ester. Also, polyglycerin fatty acid esters such as diglycerin laurate can be mentioned. Further, nitric acid, hydrochloric acid, acetic acid, sodium chloride, potassium chloride, magnesium chloride, and calcium chloride can also be mentioned. Also, β-diketones described in JP-A-2007-126349 can be mentioned. In addition, those whose dispersibility is improved by adding additives can also be used as dispersants. Not using a dispersant preferably means that the amount of the dispersant is 10,000 mass ppm or less in the slurry, more preferably 1,000 mass ppm or less, still more preferably 100 mass ppm or less, even more preferably 10 mass ppm or less, and particularly preferably not using it.

Examples

[0082] <Examples and Comparative Examples for Explaining the First Invention> Hereinafter, the first invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[0083] (Example a1) 10 kg of an aqueous ammonium bicarbonate solution (25 °C) in which 13.0 mass% of ammonium bicarbonate was dissolved and 40 L of an aqueous yttrium nitrate solution (25 °C) with a concentration of 300 g / L in terms of oxide were prepared. The aqueous ammonium bicarbonate solution was also used in Examples a2 to 9 described later, and the aqueous yttrium nitrate solution was also used in Examples a2 to 4 described later. The aqueous yttrium nitrate solution was simultaneously introduced into the same reaction layer at a rate of 100 mL / min, and the aqueous ammonium bicarbonate solution was introduced at a flow rate such that the pH of the mixed solution of the two liquids became 6.8 and mixed. When introducing, the mixed solution in the container was stirred at 20,000 rpm. The suspension overflowing from the container was sequentially filtered for 20 seconds, then the introduction and stirring of the two liquids were stopped, and the residue, which was the filtrate, was washed with running water using 10 L of ethanol. This running water washing operation was repeated 5 times. The time from the start of mixing of the two liquids to the start of filtration was 60 seconds to 120 seconds. The residue after washing was calcined at 600 °C in an air atmosphere to obtain about 10 g of Y 2 O 3 was obtained. Also, the internal volume of the reaction vessel was 100 ml. The yield of the obtained Y 2 O 3 was approximately 99% when converted based on the filtration for 20 seconds. The above operation was repeated 10 times, and the Y 2 O 3 samples obtained in the 10 operations were mixed. The obtained Y 2 O 3 was crushed in a force mill (manufactured by Osaka Chemical Co., Ltd.) for 30 seconds to obtain fine powder. Regarding the obtained Y 2 O 3 fine powder, the specific surface area (m 2 / g), primary particle diameter (nm), agglomeration diameter, initial bulk density (AD) and tapped bulk density (TD), Zr content, and carbon content were measured by the following method. From the initial bulk density (AD) and tapped bulk density (TD), PAD , P TD and P AD -P TD In addition to calculating the values of P and -P, the film-forming property was evaluated. The results are shown in Table 1.

[0084] (Method for measuring specific surface area) Measurement was carried out by the BET one-point method using a fully automatic specific surface area meter Macsorb model-1201 manufactured by Mountech Co., Ltd. The gas used was a nitrogen-helium mixed gas (nitrogen 30 vol%). As a pretreatment for the measurement, powder was put into a glass cell, the device was set, and nitrogen gas was passed through the set glass cell and degassed at 300 °C for 60 minutes.

[0085] (Method for calculating primary particle diameter) The particle diameter obtained from the specific surface area s (m 2 / g) measured by the BET one-point method was determined by the following formula. The primary particle diameter d (nm) is d = 6000 / (ρs) (ρ is the true density (g / cm 3 )). Regarding the true density, Y 2 O 3 is 5.03 (g / cm 3 ), Nd 2 O 3 is 7.33 (g / cm 3 ), Gd 2 O 3 is 7.62 (g / cm 3 ), Eu 2 O 3 is 7.4 (g / cm 3 ), Dy 2 O 3 is 7.81 (g / cm 3 ), Yb 2 O 3 is 9.22 (g / cm 3 ).

[0086] (Agglomeration diameter (D 100 , D 50 , D 90 )) Measured with the Microtrac MT3300EXII manufactured by Nikkiso Co., Ltd. During the measurement, a sample in powder form was added to the chamber of a sample circulator filled with an aqueous solution in which 0.2% by mass of sodium hexaphosphate was dissolved, and dispersed for 5 minutes with ultrasonic waves of 40 W and a frequency of 40 kHz using the ultrasonic irradiation device equipped in the apparatus. After the apparatus determined that the concentration was appropriate, D 100 D 50 D 90 was measured.

[0087] (Method for Measuring Initial Bulk Density and Tap Bulk Density) 1. Pretreatment of sample: The rare earth oxide powder (Y 2 O 3 fine powder in Example a1) was pulverized for 30 seconds with a Force Mill manufactured by Osaka Chemical Co., Ltd. immediately before measurement. 2. Measurement (1) The mass (W 3 (g)) of a measuring container made of SUS304 with an inner diameter of 10 mm, an outer diameter of 12 mm, a height of 51 mm, and an inner surface height of 50 mm (inner volume 3.93 cm C ) was measured. (2) The pretreated sample was put into the measuring container through a sieve with a mesh size of 2 mm until it overflowed. (3) The powder bulging above the upper end face of the measuring container was leveled off using a spatula. (4) The mass (W 0 (g)) of the measuring container together with the sample was measured, and the mass (W c (g)) of the measuring container was subtracted to calculate the mass (W A (g)) of the sample. (5) An auxiliary cylinder (made of SUS304 with an inner diameter of 12 mm at the lower part, 10 mm at the upper part, an outer diameter of 14 mm, and a height of 50 mm (10 mm at the lower part and 40 mm at the upper part)) was added on top of the measuring container containing the sample, and the sample was further filled through a sieve with a mesh size of 2 mm. (6) With the auxiliary cylinder attached, the measuring container containing the sample was tapped 600 times by hitting it against a table covered with a rubber sheet by hand at a tapping height of about 10 mm. During that time, the sample was added so that the height of the sample was always 20 to 30 mm higher than the upper end face of the measuring container. (7) The auxiliary cylinder was removed, and the sample overflowing on the measuring container was ground with a grinding plate. (8) After grinding the sample, the mass (W 1 (g)) of the entire measuring container was measured, and the mass (W c (g)) of the measuring container was subtracted to obtain the mass (W T1 (g)) of the sample. (9) The auxiliary cylinder was attached to the measuring container again, and the sample was further filled through a sieve with a mesh size of 2 mm, and 100 taps were performed by hand shaking at a tapping height of about 10 mm. (10) The auxiliary cylinder was removed, and the sample overflowing on the measuring container was ground with a grinding plate. (11) After grinding the sample, the mass (W 2 (g)) of the entire measuring container was measured, and the mass (W c (g)) of the measuring container was subtracted to calculate the mass (W T2 (g)) of the sample. The difference between this value (W T2 (g)) and the previous value (W T1 (g)) was confirmed to be within 0.3% of W T1 . If it exceeded 0.3%, the operations after (9) were repeated until the difference from the previous time was within 0.3%. (12) The initial bulk density and the tapped bulk density were calculated by the following formulas. Initial bulk density (g / cm 3 ) = W A (g) / 3.93 (cm 3 ) Tapped bulk density (g / cm 3 ) = W T2 (g) / 3.93 (cm 3 ) (13) The above measurements were performed three times. The initial bulk density and the tapped bulk density were the average values of the three times.

[0088] (Porosity) Assuming that the measured initial bulk density and tapped bulk density are ρ 0 , the porosity P (%) was obtained from P = (1 - ρ 0 / ρ) × 100. (ρ is the true density (g / cm 3 ).)

[0089] (Carbon content) Measurement was carried out by the combustion infrared absorption method in an oxygen stream using the carbon and sulfur analyzer EMIA-320V manufactured by Horiba, Ltd.

[0090] (Zr content) Measurement was carried out using the ICP emission spectroscopic analyzer SPS-3520V-DD manufactured by Hitachi High-Technologies Corporation.

[0091] (Evaluation of film-forming property) The obtained Y 2 O 3 Using 3 g of the fine powder and ethanol, a 30 mass% ethanol slurry of Y 2 O 3 was prepared, dispersed for 5 minutes with 40 W ultrasonic waves (frequency 40 kHz), and then coated on a PET film using an applicator (manufactured by BEVS Industrial) with a gap of 10 μm. The film-forming property was evaluated according to the following evaluation criteria. A: Coating is possible. B: Uncoated parts occur. C: Coating is impossible because the dispersed substance does not come out from the gap.

[0092] (Example a2) The content was the same as that described in Example a1 except that it was fired at 800 °C.

[0093] (Example a3) The content was the same as that described in Example a1 except that it was fired at 900 °C.

[0094] (Example a4) The content was the same as that described in Example a1 except that it was fired at 500 °C.

[0095] (Example a5) In the content described in Example 1, an aqueous neodymium nitrate solution with an oxide conversion concentration of 400 g / L was used instead of the aqueous yttrium nitrate solution. Also, the firing temperature was 900 °C. Otherwise, it was the same as Example a1.

[0096] (Example a6) In the content described in Example 1, an aqueous gadolinium nitrate solution with an oxide-equivalent concentration of 250 g / L was used instead of the aqueous yttrium nitrate solution. Also, the firing temperature was set at 650 °C. Otherwise, it was the same as Example a1.

[0097] (Example a7) In the content described in Example 1, an aqueous europium nitrate solution with an oxide-equivalent concentration of 300 g / L was used instead of the aqueous yttrium nitrate solution. Also, the firing temperature was set at 650 °C. Otherwise, it was the same as Example a1.

[0098] (Example a8) In the content described in Example 1, an aqueous dysprosium nitrate solution with an oxide-equivalent concentration of 300 g / L was used instead of the aqueous yttrium nitrate solution. Also, the firing temperature was set at 600 °C. Otherwise, it was the same as Example a1.

[0099] (Example a9) In the content described in Example a1, an aqueous ytterbium nitrate solution with an oxide-equivalent concentration of 300 g / L was used instead of the aqueous yttrium nitrate solution. Also, the firing temperature was set at 600 °C. Otherwise, it was the same as Example a1.

[0100] (Comparative Example a1) This comparative example corresponds to Example 1 of JP-A-2014-218384. 100 mL of a 1.0 mol / L aqueous solution of yttrium nitrate was added with 5 g of sodium oleate and stirred for 2 hours. Next, 1000 mL of cyclohexane and 1.0 g of a nonionic surfactant Span80 (sorbitan monooleate, manufactured by Kanto Chemical Co., Inc.) were added to the aqueous solution and vigorously stirred (at 10,000 rpm), and a W / O type emulsion solution composed of minute droplets was obtained. Next, 13 g of ammonium bicarbonate was dissolved in 50 mL of pure water to form an aqueous solution, and this aqueous ammonium bicarbonate solution was added dropwise while vigorously stirring the emulsion solution. White precipitates occurred with the dropwise addition of the aqueous ammonium bicarbonate solution. After completion of the dropwise addition, aging was carried out at room temperature (25°C) for 1 hour while continuing stirring. Thereafter, the resulting precipitate was filtered off from the aqueous solution with a Buchner funnel, and the obtained precipitate was dried in an oven at 75°C for 12 hours and then placed in an alumina crucible and fired in an 800°C air atmosphere. Thus, 8 g of yttrium oxide fine powder was obtained. Thereafter, it was coated by the method described in Example a1. When this powder was observed with a scanning electron microscope (SEM), it was a group of spherical particles with a uniform particle size of approximately 100 nm without aggregation. The primary particle size determined from the specific surface area was also 100 nm or more.

[0101] (Comparative Example a2) This comparative example corresponds to an example in which the firing temperature in Example 1 of JP-A-2014-218384 was changed. It was prepared in the same manner as in Comparative Example 1 except that the firing temperature was set to 600°C. When this powder was observed with a scanning electron microscope (SEM), particles with SEM diameters of approximately 100 nm and 10 nm were mixed, and particles with a uniform SEM diameter could not be obtained by low-temperature firing. The primary particle size determined from the specific surface area was also 100 nm or more.

[0102] (Comparative Example a3) This comparative example corresponds to the example in J Nanopart Res (2013) 15:1438. As the yttrium element, 2 L of a 50 mmol / L aqueous solution of yttrium chloride (pH = 5.0) was added with 50 mmol / L of Na 2 CO 3It was instantaneously added to 2 L of an aqueous solution. The resulting suspension was immediately filtered, and the filtrate was washed with 10 L of ethanol and then calcined at 600 °C to obtain 5 g of Y 2 O 3 was obtained. Thereafter, a coating film was formed by the method described in Example 1a.

[0103] (Comparative Example a4) This comparative example corresponds to the example described in JP-A-4-310516. 18.0 g of Y 2 O 3 was dissolved in 900 mL of dilute hydrochloric acid, and this solution was added dropwise to 9 L of dilute aqueous ammonia (containing 0.2 mol of ammonia) at 40 °C. The addition was carried out over 30 minutes, and after completion of the addition, the mixture was aged for 30 minutes. Then, an aqueous solution prepared by dissolving 144 g of ammonium hydrogen carbonate in 900 mL of water was added to precipitate yttrium carbonate. After aging for 2 hours, the precipitate was filtered and washed with water. Then, 900 mL of octanol was added to the obtained yttrium carbonate, and water was evaporated while stirring at 100 °C for 3 hours. Thereafter, the precipitate was filtered to obtain yttrium carbonate, which was dried under reduced pressure at 13.3 Pa (0.1 Torr) and 160 °C. Then, it was calcined at 650 °C for 2 hours to obtain 10 g of Y 2 O 3 was obtained. The crystallite diameter of this Y 2 O 3 was 80 Å.

[0104]

Table 1

[0105] As shown in Table 1 above, powders of oxides of at least one rare earth element other than Ce, having a predetermined primary particle diameter of 10 nm or more and 60 nm or less, and having a D 100 measured by ultrasonic dispersion treatment at 40 W of 1 μm or more and 10 μm or less, or a difference in porosity (P AD -P TD ) of 2.0% or more and 5.0% or less had good coatability. On the other hand, when the primary particle diameter is outside the range of 10 nm or more and 60 nm or less, or (P AD -P TD) In Comparative Examples a1 to a4 where it is outside the range of 2.0% or more and 5.0% or less, the aggregate diameter after ultrasonic treatment at 40 W all increased, indicating that film formability could not be obtained. From the above, it can be seen that with the configuration of the present invention, in rare earth oxides other than Ce, rare earth oxide powders with a primary particle diameter (SSA conversion diameter) of several tens of nm can be easily pulverized and film formation is possible.

[0106] Hereinafter, the second invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. In the following examples, the internal volume of the reaction tank was 2 L for low-speed stirring and 100 mL for high-speed stirring.

[0107] (Example b1) 10 kg of an aqueous ammonium bicarbonate solution (25 °C) in which 13.0 mass% of ammonium bicarbonate was dissolved and 40 L of an aqueous yttrium nitrate solution (25 °C) at 50 g / L in terms of oxide were prepared. The aqueous ammonium bicarbonate solution was also used in Examples b2 to b6 described later, and the aqueous yttrium nitrate solution was also used in Examples b2 to b4 and b6 described later. The aqueous yttrium nitrate solution was introduced into the same container at a rate of 600 mL / min, and the aqueous ammonium bicarbonate solution was introduced into the same container at a flow rate such that the pH of the mixed solution of the two liquids became 6.8 (temperature of the mixed solution: 20 to 30 °C) and mixed. The mixed solution in the container was vigorously stirred at 20,000 rpm during the introduction. The suspension overflowing from the container was sequentially filtered for 20 seconds, then the introduction and stirring of the two liquids were stopped, and the residue, which was the filtrate, was washed with 10 L of ethanol. This washing operation was repeated 5 times. The washed filtered powder was calcined at 700 °C in an air atmosphere to obtain 10 g of Y 2 O 3 was obtained. The obtained Y 2 O 3 was pulverized in a force mill (manufactured by Osaka Chemical Co., Ltd.) for 30 seconds to obtain fine powder. Regarding the obtained Y 2 O 3 The specific surface area (m 2 / g), primary particle diameter (nm), pore volume * true density of pores with a pore diameter of 0.005 μm or more and 100 μm or less, pore volume * true density of pores with a pore diameter of 5 nm or more and 50 nm or less, Na content (mass ppm), crystallite diameter (nm) were measured, and the following crushing evaluation was also performed. The results are shown in Table 2.

[0108] (Specific surface area (m 2 / g)) It was measured by the same method as in the example of the first invention.

[0109] (Calculation method of primary particle diameter) It was calculated by the same method as in the example of the first invention.

[0110] (Pore volume * true density of pores with a pore diameter of 0.005 μm to 100 μm and pore volume * true density of pores with a pore diameter of 5 nm to 50 nm) The pore volume was measured using Autopore IV manufactured by Micromeritics. The cumulative volume in the range where the pore diameter is 0.005 μm or more and 100 μm or less was taken as the pore volume with a pore diameter of 0.005 μm or more and 100 μm or more. Also, the cumulative volume in the range where the pore diameter is 5 nm or more and 50 nm or less was taken as the pore volume with a pore diameter of 5 nm or more and 50 nm or less. By multiplying the obtained pore volume by the true density of the rare earth oxide, the value of pore volume * true density was obtained. The value of the true density used was the same as that used for the calculation of the primary particle diameter.

[0111] (Na content (mass ppm)) Atomic absorption analysis was performed using CE3300FL manufactured by Thermo Fisher Scientific.

[0112] (Crystallite diameter (nm)) The crystallite diameter was determined using the Halder-Wagner method from the profile obtained under the following X-ray diffraction conditions. (X-ray diffraction measurement conditions) · Apparatus: UltimaIV (manufactured by Rigaku Corporation) · Radiation source: CuKα ray · Tube voltage: 40 kV · Tube current: 40 mA · Scan speed: 2 degrees / min · Step: 0.02 degrees · Scan range: 2θ = 20° to 90°

[0113] (Fragmentation evaluation: Measurement of average particle size) Y obtained above 2 O 3 Using the fine powder, 45 g of a 10 mass% slurry (dispersion medium: 99.5 vol% ethanol) was prepared, and it was fragmented with 240 g of zirconia beads with a diameter of 0.1 mm, a peripheral speed of 4 m / s, and a bead mill (Apex LABO / A-LABO manufactured by Hiroshima Metal & Machinery Co., Ltd., effective capacity 80 cc). Fragmentation was stopped at 10-minute intervals, and the average particle size was measured by the following method. However, when the average particle size became larger than the previous measured value, the bead mill treatment was terminated at that time. Even if the average particle size did not become larger than the previous measured value in each of the 2nd to 20th times when repeating 20 times (A), it was terminated when repeating 20 times (A). The particle size that became the minimum with a maximum of 20 repetitions was taken as the minimum average particle size (Dm). Also, the data immediately after fragmentation was taken as the particle size when the bead mill treatment was completed ("D0" in Table 2).

[0114] (Measurement method of average particle size and polydispersity index) Using a Otsuka Electronics ELSZ-2000ZS, the average particle size was measured after the device determined that it was at an appropriate concentration. The slurry was diluted at the above dilution ratio using 99.5 vol% ethanol as the solvent. The average particle size and polydispersity index obtained by the dynamic light scattering method (photon correlation method), measured in accordance with JIS Z 8828:2019, were adopted. The measurement was performed by measuring the same sample three times, and the average value of the three times was taken as the average particle size. However, if the absolute value of the difference between each measured value and the average value of the three times exceeded 2% for any of the three times, that measurement result was not adopted, and new three-time remeasurements were performed. The measurement was carried out at 25°C. The polydispersity index shown in Table 2 is for the measurement of the minimum average particle size (Dm) in the fragmentation evaluation.

[0115] (Evaluation 7 days after fragmentation) The slurry subjected to the crushing evaluation as described above was allowed to stand at room temperature (20 °C) for 7 days. The average particle diameter (D7) after standing for 7 days was measured by the above method, and the value of "formula: (average particle diameter after 7 days after crushing (D7) - average particle diameter immediately after crushing (D0)) / average particle diameter immediately after crushing (D0) × 100 (%)" was calculated. The results are shown in Table 2 as "(D7 - D0) / D0 × 100 (%)". Also, the average particle diameter after irradiating 20 ml of the slurry after one week with 40 W of ultrasonic waves (frequency 40 kHz) for 5 minutes was also measured ("D7S" in Table 2).

[0116] Also, the sedimentation property after standing for 7 days was evaluated according to the following criteria. Present: A lump of particles can be visually confirmed at the bottom of the container. Absent: A lump of particles cannot be visually confirmed at the bottom of the container.

[0117] Furthermore, the visible light transmittance (%) after standing for 7 days was measured by the following method. (Transmittance) Using a visible light absorption photometer (U-3100 manufactured by Hitachi, Ltd.), the transmission spectrum from 350 nm to 800 nm was measured. The transmittance indicates the minimum value among the transmission spectra from 350 nm to 800 nm. The sample was prepared by dropping 0.2 ml of the slurry obtained by crushing (after 1 week after crushing) into 30 ml of the solvent used during crushing.

[0118] (Example b2) The stirring during the mixing of the ammonium bicarbonate aqueous solution and the yttrium nitrate aqueous solution was set to low-speed stirring at a rotation speed of 400 rpm. Also, instead of 10 L of ethanol, the residue was washed with 10 L of 90 vol% ethanol (10 vol% pure water). Otherwise, it was the same as in Example b1.

[0119] (Example b3) Instead of 10 L of 90 vol% ethanol, the residue was washed with 10 L of 80 vol% ethanol (20 vol% pure water). Otherwise, it was the same as in Example b2.

[0120] (Example b4) Instead of using 10 L of 90 vol% ethanol, the residue was washed with 10 L of 50 vol% ethanol (50 vol% pure water). Otherwise, it was the same as Example b2.

[0121] (Example b5) Instead of using an aqueous solution of yttrium nitrate (25 °C) with a concentration of 50 g / L in terms of oxide, an aqueous solution of ytterbium nitrate (25 °C) with a concentration of 50 g / L in terms of oxide was used. Otherwise, it was the same as Example b1.

[0122] (Example b6) 〔Crushing evaluation〕The concentration of the slurry to be subjected to bead mill crushing was changed from 10% by mass to 4% by mass, and the dispersion medium was changed from ethanol to methanol. Otherwise, it was the same as Example b1.

[0123] (Example b7) Instead of using an aqueous solution of yttrium nitrate (25 °C) with a concentration of 50 g / L in terms of oxide, an aqueous solution of dysprosium nitrate (25 °C) with a concentration of 50 g / L in terms of oxide was used. Otherwise, it was the same as Example b1.

[0124] (Comparative Example b1) The yttrium oxide fine powder obtained in Comparative Example a1 was used as the yttrium oxide fine powder of Comparative Example b1. As described above, when this powder was observed with a scanning electron microscope (SEM), it was a group of spherical particles with a uniform particle size of approximately 100 nm without aggregation. Since the primary particle size determined from the specific surface area was also 100 nm or more, some of the above evaluations were not performed.

[0125] (Comparative Example b2) The yttrium oxide fine powder prepared in Comparative Example a2 was used as the yttrium oxide fine powder of Comparative Example b2. As described above, when this powder was observed with a scanning electron microscope (SEM), particles with SEM diameters of approximately 100 nm and 10 nm were mixed, and particles with a uniform SEM diameter could not be obtained by low-temperature firing. Since the primary particle size determined from the specific surface area was also 100 nm or more, some of the above evaluations were not performed.

[0126] (Comparative Example b3) Y prepared in Comparative Example a3 2 O 3 was used as the yttrium oxide fine powder of Comparative Example b3. For this powder, various measurements were carried out by the method described in Example b1, and crushing evaluation was also performed. Since the slurry after one week from crushing had aggregated and settled, the aggregation diameter ("7D") and transmittance after one week could not be measured. Also, the measurement of the aggregation diameter "7DS" after ultrasonic irradiation after one week was not carried out.

[0127] (Comparative Example b4) The yttrium oxide fine powder prepared in Comparative Example a4 was used as the yttrium oxide fine powder of Comparative Example b4.

[0128] (Comparative Example b5) This comparative example corresponds to the example in US2020 / 0071180A. 20 L of an aqueous solution of yttrium nitrate was prepared so that the concentration of yttrium ions was 0.05 mol / L. 21.1 g of acetylene glycol-ethylene oxide adduct (Surfynol 485 manufactured by Nissin Chemical Industry Co., Ltd.) was added to the aqueous solution. And urea in an amount 15 times the molar ratio was added to the yttrium ions. In order to advance the hydrolysis reaction, it was heated to 95 °C and held for 90 minutes, and then cooled to room temperature. During heating, the aqueous solution was slowly stirred by a stirring blade so that the temperature distribution of the aqueous solution in the container became uniform. Next, the precipitate was separated from the liquid after the reaction by using a centrifuge. Further, in order to remove unreacted urea, residual nitrate ions, etc., the recovered solid content was washed with water. Next, the obtained rare earth compound particles were dried at 55 °C for 5 days and then dry-crushed with a bead mill. The crushed rare earth compound particles were calcined at 600 °C for 4 hours to obtain yttrium oxide particles. Since the obtained yttrium oxide had a primary particle diameter of 100 nm or more, some of the above evaluations were not carried out.

[0129]

Table 2

[0130] As shown in Table 2 above, it is a powder of an oxide of at least one rare earth element other than Ce, The primary particle size is 10 nm or more and less than 100 nm, and the pore volume (cm 3 / g) multiplied by the true density (g / cm 3 ) gives a value of 3 or more and 14, The pore volume (cm 3 / g) of pores with a pore diameter of 5 nm or more and 50 nm or less multiplied by the true density (g / cm 3 ) gives a value of 0 or more and 2.0 or less. The rare earth oxide powder of each example had a small particle size after crushing and a high transmittance after standing for 7 days. On the other hand, in Comparative Examples b1, b2, and b5 where the primary particle size was outside the range of 10 nm or more and less than 100 nm, the average particle size after crushing became large and the visible light transmittance after 7 days was low. Also, in Comparative Example b4 where the value obtained by multiplying the pore volume (cm 3 / g) of pores with a pore diameter of 0.005 μm or more and 100 μm or less by the true density (g / cm 3 ) exceeded 14, the average particle size after crushing became large and the transmittance after 7 days was low. Furthermore, in Comparative Example 3 where the value obtained by multiplying the pore volume (cm 3 / g) of pores with a pore diameter of 5 nm or more and 50 nm or less by the true density (g / cm 3 ) exceeded 2.0, the dispersoid settled over time and the visible light transmittance could not be measured. From the above, it can be seen that the rare earth oxide powder of the present invention can be made into a highly dispersed slurry without using a dispersant, and it is possible to provide a fine oxide powder of a rare earth element other than Ce that can stably maintain the transparency of the slurry.

Industrial Applicability

[0131] According to the first invention, in rare earth oxides other than Ce, a rare earth oxide powder that can be easily dispersed by a simple dispersion treatment such as ultrasonic treatment and can form a thin film coating is provided.

[0132] According to the second invention, fine powders of oxides of rare earth elements other than Ce are provided which can form a highly dispersed slurry without using a dispersant and can maintain the dispersed state. By pulverizing such rare earth oxide fine powders, a highly dispersed slurry can be obtained, and the slurry can be made to have enhanced visible light transmittance based on its dispersibility. By enhancing the visible light transmittance, it becomes possible to expand to materials that require transparency while taking advantage of the effect of adding rare earth oxides. In addition, it becomes possible to provide a slurry that absorbs only a narrow wavelength range characteristic of rare earth ions. Furthermore, according to the rare earth oxide powder of the present invention, since the dispersed state in the slurry can be maintained, the transparency of the slurry can be stably maintained.

Claims

[Claim 1] A powder of an oxide of at least one rare earth element other than Ce, The primary particle size is 10 nm or more and less than 100 nm, A rare earth oxide powder in which, when a rare earth oxide powder is mixed with ethanol to prepare an ethanol slurry containing 10% by mass of the rare earth oxide powder, the following operation (A) is repeatedly performed until the average particle diameter becomes larger than the previous measurement value, the smallest average particle diameter is 10 nm or more and 105 nm or less. (A): The slurry is subjected to a bead mill treatment for 10 minutes using zirconia beads having a diameter of 0.1 mm, and then the average particle size is measured by a dynamic light scattering method. (However, when the average particle size becomes larger than the previous measurement value, the bead mill treatment is terminated without performing the next operation (A), and even if (A) is repeated 20 times and the average particle size does not become larger than the previous measurement value in each of the second to twentieth operations, (A) is also terminated when it has been repeated 20 times. The minimum average particle size here means the minimum value of the average particle size measured by a dynamic light scattering method by sampling after each treatment of (A).

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