Rare earth oxide powder

Abstract

A powder, which is an oxide of at least one rare earth element other than Ce, satisfies (a) or (b). (a) The primary particle size is 10–60 nm, satisfying (I) or (II). (I) The particle size distribution obtained by ultrasonic dispersion and measured using laser diffraction-scattering particle size distribution method. 100 The value is 1–10 μm. (II) The true density of rare earth oxides is set to ρ (g / cm³). 3 When the initial bulk density AD is reached, the porosity P is calculated from the initial bulk density AD. AD (%) and porosity P calculated from tapped bulk density TD TD The difference (%) (P) AD -P TD The percentage was 2.0% to 5.0%. AD = (1 - AD / ρ) × 100 (%)P TD = (1-TD / ρ)×100(%) (b) Primary particle size is greater than 10nm and less than 100nm, satisfying (III) and (IV). (III) Pore volume (cm³) with a pore diameter of 0.005~100μm. 3 / g) multiplied by true density (g / cm³) 3 The values ​​obtained are 3 to 14. (IV) The pore volume (cm³) of pores with a diameter of 5 to 50 nm. 3 / g) multiplied by true density (g / cm³) 3 The resulting value ranges from 0 to 2.0.

Description

Technical Field

[0001] This invention relates to rare earth oxide powders. Background Technology

[0002] Rare earth oxides are used in dielectrics or internal electrodes for capacitors, phosphors, refractive index modifiers for optical glass, oxygen sensors, sintering aids for ceramics, catalysts, and refractories. They are used in various forms, including coatings (films), trace additions, and molded bodies (including sintered bodies).

[0003] When a slurry containing rare earth oxide powder is coated and a firing process is performed after coating, thermal diffusivity can be improved by increasing the specific surface area of ​​the rare earth oxide powder or reducing the primary particle size. Furthermore, when rare earth oxides are used as additives and firing is performed, thermal diffusivity sometimes becomes easier if the primary particle size is small. Based on these points, various micronized powders of rare earth oxides are known. Patent Document 1 describes obtaining a primary particle size of average... Ultrafine yttrium oxide particles (Example 1 of Patent Document 1). Patent Document 2 describes obtaining yttrium oxide micropowder that "when observed with a scanning electron microscope (SEM), the result (omitted) shows a group of non-agglomerated, uniformly spherical particles with a particle size of approximately 100 nm" (Example 1 of Patent Document 2). Non-Patent Document 1 also shows TEM images of Dy2O3 micropowder crystallized as a result of long-term exposure to an electron beam in a TEM (Fig. 1a b of Non-Patent Document 1).

[0004] On the other hand, in the case of powders with small primary particle sizes, such as those at the tens of nm level, aggregates are easily formed. These aggregated particles, in the case of fine nanoparticles with small average particle sizes, become hard aggregates (see, for example, paragraph

[0014] of Japanese Patent No. 6119528). Therefore, in order to coat particles with small primary particle sizes, it is necessary to use a medium or the like to break them down with high energy.

[0005] Patent Document 3 describes a central particle size D50 of 5.3 nm obtained by dispersing yttrium oxide powder in a slurry using a dispersant (Example 1 of Patent Document 3).

[0006] A slurry of particulate rare earth oxide powder can be highly dispersed if a suitable dispersant is used to disperse it (see, for example, paragraphs

[0020] and

[0029] of Japanese Patent Application Publication No. 2007-126349). However, depending on the formulation, there may be cases where the dispersant does not function properly, and furthermore, depending on the application, the dispersant may become an impurity.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 4-310516

[0010] Patent Document 2: Japanese Patent Application Publication No. 2014-218384

[0011] Patent Document 3: US2020 / 0071180A

[0012] Non-patent literature

[0013] Non-patent literature 1: J Nanopart Res (2013) 15: 1438 Summary of the Invention

[0014] The applicant observed that rare earth oxide powders manufactured using the methods described in Patent Documents 1-2 and Non-Patent Document 1, while initially appearing to lack agglomeration when observed with a scanning electron microscope (SEM), revealed large, coarse particles when the agglomeration size was measured using a macroscopic method (laser scattering). Large agglomeration sizes make film coating difficult in the presence of a coating solution. Furthermore, even when attempting to reduce agglomeration size through crushing, the small primary particles result in stronger agglomeration, requiring more vigorous dispersion and increasing contamination from the crushing medium. Additionally, when wet crushing is followed by drying, agglomeration occurs during drying, leading to larger particle sizes. In particular, it is difficult to suppress agglomeration in micro-powders of rare earth oxides other than CeO2.

[0015] Therefore, the objective of the first invention is to provide rare earth oxide micro powders that can be easily dispersed even without intense crushing processes and can form thin films.

[0016] The inventors conducted in-depth research and discovered that the above-mentioned problems can be surprisingly solved by having a specific primary particle size (SSA equivalent diameter) and setting the coagulation diameter to a specific range for providing a specified ultrasonic treatment, or by having a specific primary particle size (SSA equivalent diameter) and setting the porosity difference calculated from the initial bulk density AD and the tapped bulk density TD to a specified range.

[0017] Based on the above understanding, the first invention provides the following [a1] to [a9].

[0018] [a1] A rare earth oxide powder, which is a powder of an oxide of at least one rare earth element other than Ce.

[0019] The primary particle size is greater than 10 nm and less than 60 nm, satisfying either (I) or (II) below.

[0020] (I) The cumulative particle size D at 100% capacity, obtained by ultrasonic dispersion at 40W for 5 minutes and measured using laser diffraction-scattering particle size distribution method. 100 It is between 1μm and 10μm.

[0021] (II) The true density of the above rare earth oxides is set to ρ (g / cm³). 3 When the initial bulk density AD is 0, the porosity P is calculated from the initial bulk density AD using the following equation 1. AD (%) and the porosity P calculated from the tapped bulk density TD using the following formula 2. TD The difference (%) (P) AD -P TD The percentage is between 2.0% and 5.0%.

[0022] Formula 1: P AD = (1-AD / ρ)×100(%)

[0023] Equation 2: P TD = (1-TD / ρ)×100(%)

[0024] [a2] The rare earth oxide powder according to claim 1 conforms to (I) above.

[0025] [a3] According to the rare earth oxide powder described in [a1] or [a2], wherein the true density of the rare earth oxide is set to ρ (g / cm³). 3 When the initial bulk density AD is 0, the porosity P is calculated from the initial bulk density AD using the following equation 1. AD (%) is above 90.0% and below 99.0%.

[0026] Formula 1: P AD = (1-AD / ρ)×100(%)

[0027] [a4] Rare earth oxide powder according to any one of [a1] to [a3], wherein the primary particle size is 35 nm or less.

[0028] [a5] A rare earth oxide powder according to any one of [a1] to [a4], wherein the Zr content is less than 100 ppm by mass.

[0029] [a6] A rare earth oxide powder according to any one of [a1] to [a5], wherein the carbon content is 2% by mass or less.

[0030] [a7] The rare earth oxide powder according to [a1] conforms to (II) above.

[0031] [a8] According to the rare earth oxide powder described in [a7], wherein the porosity P is... AD (%) is above 90.0% and below 99.0%.

[0032] [a9] The rare earth oxide powder according to [a7] or [a8], wherein the cumulative volumetric particle size D at 100% capacity, determined by laser diffraction scattering particle size distribution method, is obtained by ultrasonic dispersion treatment at 40 W for 5 minutes. 100 The D is between 1μm and 10μm. 100 The cumulative particle size D at 50% of the cumulative volume, determined by the above-described method, was obtained by ultrasonic dispersion treatment. 50 The ratio is D 100 / D 50 It is between 3.0 and 11.0.

[0033] Even rare earth oxide micropowders that appear to have little aggregation when observed using a scanning electron microscope (SEM), as shown in Patent Documents 1-3 and Non-Patent Document 1, have strong aggregation if the primary particles are reduced to tens of nm. In order to disperse them in a slurry, wet crushing with a dispersant is required.

[0034] Furthermore, due to the above circumstances, it is preferable that the slurry of rare earth oxide micro powders can be made into a highly dispersed state even without the use of a dispersant.

[0035] However, in the past, it has been difficult to set rare earth oxide micro powders in slurry into a highly dispersed state without the use of dispersants, and it is even more difficult to maintain the dispersion state stably.

[0036] In particular, it is difficult to prepare highly dispersed slurries from the fine powders of oxides of rare earth elements other than Ce without the use of dispersants.

[0037] Therefore, the objective of the second invention is to provide oxide powders of rare earth elements other than Ce that are capable of producing highly dispersed slurries without the use of dispersants and that can stably maintain the transparency of the slurry.

[0038] The inventors conducted in-depth research and discovered that, surprisingly, the above-mentioned problems could be solved by having a specific primary particle size and setting the product of pore capacity / pore volume and true density to a specific range.

[0039] Based on the above insights, the second invention provides the following [b1] to [b7].

[0040] [b1] It is a powder of an oxide of at least one rare earth element other than Ce.

[0041] The primary particle size is greater than 10 nm and less than 100 nm, satisfying (III) and (IV) below.

[0042] (III) Pore volume (cm³) with a pore diameter of 0.005 μm or more and 100 μm or less. 3 / g) multiplied by true density (g / cm³) 3 The resulting value is 3 or higher and 14 or lower.

[0043] (IV) Pore volume (cm³) of pores with a diameter of 5 nm or more and 50 nm or less. 3 / g) multiplied by true density (g / cm³) 3 The resulting value is above 0 and below 2.0.

[0044] [b2] The rare earth oxide powder according to [b1], wherein the Na content is less than 10 ppm by mass.

[0045] [b3] The rare earth oxide powder according to [b1] or [b2], wherein the crystallite diameter is 6 nm or more and 25 nm or less.

[0046] [b4] The rare earth oxide powder according to any one of [b1] to [b3], wherein after mixing the rare earth oxide powder with ethanol to prepare an ethanol slurry containing 10% by mass of rare earth oxide powder, the following operation (A) is repeated until the average particle size becomes larger than the previous measurement value, and the minimum average particle size becomes 10 nm or more and 150 nm or less.

[0047] (A): Zirconia beads with a diameter of 0.1 mm were used to make beads. The slurry was bead-milled for 10 minutes, and then the average particle size was measured.

[0048] (Among them, the bead milling process ends at the moment when the average particle size becomes larger than the previous measurement value, and the process ends at the moment when the average particle size does not become larger than the previous measurement value in each of the 20 repetitions (A). The so-called minimum average particle size here means the minimum value of the average particle size measured by sampling at each of the above (A) processes using the dynamic light scattering method.)

[0049] [b5] According to the rare earth oxide powder described in [b4], wherein the calculated value of the following formula is more than -15% and less than 25%.

[0050] [b6] The rare earth oxide powder according to [b4] or [b5], wherein the average particle size that is minimized by the above-described bead milling process is 50 nm or more and 90 nm or less.

[0051] [b7] A method for manufacturing a slurry, wherein the rare earth oxide powder described in any one of [b1] to [b6] is wet-crushed using a solvent. Detailed Implementation

[0052] In this specification, “oxides of rare earth elements” will sometimes be referred to as “rare earth oxides”.

[0053] The first invention will now be described in detail based on its preferred embodiments.

[0054] The first invention relates to powders of oxides of rare earth elements other than Ce.

[0055] Ce oxide, namely CeO2, is obtained without sintering by adding an oxidant (H2O2) to cerium hydroxide in water. Furthermore, since Ce is easily oxidized, it is also easy to obtain by sintering the precursor at low temperatures. As a result, CeO2 is less affected by agglomeration during manufacturing due to sintering, and even powders with primary particles of tens of nm can be easily broken down.

[0056] On the other hand, rare earth elements other than Ce do not form oxides like Ce even when oxidizing agents are added to hydroxides without firing. Furthermore, manufacturing typically requires firing the precursors at relatively high temperatures, which contributes to necking. Therefore, for conventional rare earth element powders other than Ce, suppressing powder agglomeration is extremely difficult when primary particles are tens of nm in size.

[0057] In the first invention, oxides of rare earth elements include at least one selected from Sc, Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Specifically, oxides of rare earth elements other than Ce include Sc₂O₃, Y₂O₃, La₂O₃, and Pr₆O₃. 11The rare earth elements are Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₄O₇, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, and Lu₂O₃. From the perspective of the superior effect of the first invention, which addresses the difficulty of suppressing aggregation in the past, the oxides of rare earth elements are preferably oxides selected from at least one of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; more preferably oxides selected from at least one of Y, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; even more preferably oxides selected from at least one of Y, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; and particularly preferably oxides selected from at least one of Y, Dy, Ho, Er, and Yb.

[0058] The primary particle size of rare earth oxide powder is preferably within a specified range. For rare earth oxide powders, a smaller primary particle size improves thermal diffusion, but if it is too small, agglomeration becomes stronger, making it difficult to break down. On the other hand, even if the primary particle size is too large, necking occurs, increasing the agglomeration diameter. Furthermore, when rare earth oxide powder is crushed using a bead mill or similar device, the particles are pulverized, increasing the active surface area and forming an unstable slurry. Based on 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 even more preferably 15 nm or more and 35 nm or less. A primary particle size of 35 nm or less is particularly preferred from the perspectives of improved film-forming properties when preparing a coating liquid and high thermal diffusion of the rare earth oxide powder.

[0059] In the first invention, the primary particle size of the rare earth element oxide powder is the primary particle size calculated from the specific surface area, specifically, it is the specific surface area s(m) determined by the BET1 point method. 2 The particle size is calculated using the density ρs (g / cm³). For example, the primary particle size d (nm) is d = 6000 / (ρs). (ρ is the true density (g / cm³)). 3 )).

[0060] The specific surface area of ​​the rare earth element oxide powder of the first invention is preferably, for example, 10 m². 2 / g or more and 160m 2 / g or less, more preferably 15m 2 / g or more and 110m 2 / g or less, especially preferably 20m 2 / g or more and 80m 2 / g or less.

[0061] In the first invention, the volume standard D is measured by laser diffraction scattering particle size distribution determination method after ultrasonic irradiation. 100 (The cumulative particle size at 100% capacity) is a specific range preferred from the perspective of enabling thin film coating. For example, from the viewpoint of coating properties, D after ultrasonic irradiation 100 Particularly preferred is 10 μm or less, more preferably 9 μm or less, and even more preferably 7 μm or less. For film fabrication, the presence of large, coarse particles prevents coating. Furthermore, if the slurry's dispersibility is too good, its stability is poor, and it may sometimes agglomerate. This alters physical properties such as viscosity, changing the coating conditions. From a stability perspective, the aforementioned D... 100 Preferably, it is 1 μm or more, and more preferably 2 μm or more.

[0062] More specifically, the aforementioned ultrasonic irradiation involves dispersion for 5 minutes using 40W ultrasound at a frequency of 40kHz. Examples of irradiation devices include those associated with laser diffraction scattering particle size analyzers, such as devices for irradiating samples containing rare earth oxide powder added to a 0.2% by mass sodium hexametaphosphate aqueous solution. The concentration of the rare earth oxide powder in the dispersion during ultrasonic irradiation is preferably an appropriate concentration determined by the particle size analyzer for particle size determination, typically in the range of 0.002 to 0.2% by mass. While ultrasonic irradiation is specifically performed using the method described in the examples, irradiation can also be performed using devices other than those associated with the laser diffraction scattering particle size analyzer used for measurement, provided the irradiation device is equivalent. However, when using a device other than the one attached to the laser diffraction scattering particle size analyzer for irradiation, 0.2 g of sample is added to approximately 100 ml of a 0.2% by mass sodium hexametaphosphate aqueous solution. After ultrasonic irradiation, the ultrasonically irradiated slurry is added to the sample circulation device until the particle size analyzer determines that it is the appropriate concentration for particle size determination, and then the determination is carried out.

[0063] From the perspective of further improving coating properties and ease of application, the particle size distribution of the particles in the first invention is measured using the aforementioned laser diffraction scattering particle size distribution determination method after ultrasonic irradiation, with a volume reference D. 90 The cumulative particle size (at 90% of the cumulative 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.

[0064] Furthermore, from the perspective of further improving the film-forming properties and ease of application, the volume D of the particles of the first invention, measured by the aforementioned laser diffraction scattering particle size distribution determination method after ultrasonic irradiation, is...50 The cumulative particle size (at 50% of the cumulative 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.

[0065] From the perspective of coating properties, D is particularly preferred. 100 / D 50 For a specific range of granularity distribution. Specifically, D 100 / D 50 Preferably, the value is 3.0 or higher and 11.0 or lower, and more preferably 3.0 or higher and 8.5 or lower.

[0066] Rare earth oxide powders preferably have fewer impurities. Especially when using grinding media such as beads in a bead mill, it is possible to reduce the impurities in D... 100 It is easily broken down to 1-20 μm, more preferably 10 μm, but the medium becomes an impurity and becomes contaminated. In the first invention, since rare earth oxide powder can be manufactured without using the aforementioned medium, the Zr element, which is generally used as a constituent element of the pulverizing medium, can be set to 100 ppm by mass or less. Furthermore, it is easy to set it to 10 ppm by mass or less, and even more readily to 2 ppm by mass or less. Such rare earth oxide powder is preferred from the perspective of reducing the risk of contamination, and is also suitable for applications such as electronic components, corrosion-resistant materials for semiconductor manufacturing equipment, etc. The Zr content can be determined by ICP-luminescence analysis, and can be determined by the method described in the examples described later. The sample for testing can be prepared by conventional methods, for example, by dissolving the rare earth oxide powder in nitric acid or sulfuric acid.

[0067] The carbon content of rare earth oxide powder is preferably low. Rare earth elements and their compounds are frequently used as additives for solid solution purposes. If carbon is present, mass reduction (volume change) occurs during firing, leading to cracks in the film, etc. Therefore, the carbon content is preferably 2% by mass or less. More preferably, it is 1% by mass or less, and particularly preferably 0.7% by mass or less. The carbon content can be determined by the method described in the examples below.

[0068] It should be noted that the rare earth oxide powder is preferably a powder with a purity of 99% by mass or higher. For example, the combined content of Zr and carbon is preferably less than 1% by mass.

[0069] The inventors have discovered that, regarding the dispersibility of rare earth oxide powders with a primary particle size within a specified range as calculated by SSA, the porosity P obtained from the initial bulk density (AD) using Equation 1 is... AD (%) and the porosity P obtained from the tapped bulk density (TD) using Equation 2 TD The difference (%) (P)AD -P TD (%) is particularly preferred within the specified range. ρ is the true density.

[0070] Formula 1: P AD = (1-AD / ρ)×100(%)

[0071] Equation 2: P TD = (1-TD / ρ)×100(%)

[0072] (P AD -P TD A high value of (%) indicates that the voids are easily blocked, as measured by tapping the bulk density. (P) AD -P TD Particles with excessively high (%) values, or overly compressed powders, become powders with strong cohesion. On the other hand, (P) AD -P TD A value of )(%) that is too small indicates a state with a high amount of air between particles, making it a relatively soft powder that is difficult to compress easily. Such powders tend to absorb air between particles, resulting in larger agglomeration diameters. Based on the assumption that the balance of compression level affects the agglomeration of rare earth oxide micropowders, the inventors conducted research and found that this parameter affects the dispersibility of rare earth oxide powders.

[0073] Specifically, (P) AD -P TD The difference between (%) and (%) is preferably 2.0% or more and 5.0% or less. (P) AD -P TD When the concentration (%) is 2.0% or higher and 5.0% or lower, the compressibility becomes moderate, the dispersibility is excellent compared to powders outside this range, and the film-forming properties are excellent when formulated into a coating liquid. From this perspective, (P) AD -P TD (%) is more preferably 3.0% or more and 5.0% or less, and even more preferably 3.0% or more and 4.5% or less.

[0074] Furthermore, considering the balance between condensation suppression and operability, the porosity P calculated from the initial bulk density... AD The percentage (%) is preferably 90.0% or more and 99.0% or less, more preferably 92.0% or more and 98.0% or less. Having the above-mentioned (P) AD -P TD (%), and P AD A concentration of 92.0% or higher and 98.0% or lower is preferred due to its particularly moderate cohesiveness, making it easy to disperse.

[0075] Furthermore, from the same perspective, P calculated from the tapped bulk density TD Preferably, it is 88.0% or more and 95.5% or less, more preferably 88.5% or more and 92.0% or less.

[0076] To obtain the above specific surface area (m²) 2 / g), primary particle size (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 The preferred method for manufacturing rare earth oxide powders described later can be used, and the mixing, washing, or firing conditions can be adjusted.

[0077] Next, a preferred method for manufacturing the rare earth oxide powder of the first invention will be described.

[0078] This manufacturing method includes: simultaneously adding an aqueous solution of carbonate (hereinafter also referred to as "Liquid A") and an aqueous solution of water-soluble salts of rare earth elements (hereinafter also referred to as "Liquid B") into a reaction tank, mixing the mixture under high-speed stirring to allow the carbonate to react with the water-soluble salts of rare earth elements, with the pH of the mixture being 6.5 to 7.0, preferably 6.5 to 6.9; initiating a reaction-solid-liquid separation process within 5 minutes from the start of mixing Liquid A and Liquid B; a washing process of washing the residue obtained in the reaction-solid-liquid separation process with alcohol; and a calcination process of calcining the washed residue.

[0079] From the perspective of successfully obtaining the rare earth oxide powder of the first invention, it is preferable that the concentration of water-soluble salt in the water-soluble salt aqueous solution of the rare earth element as liquid B, converted from oxide, is 10 to 400 g / L, more preferably 50 to 350 g / L, particularly preferably 80 to 300 g / L, and most preferably more than 100 g / L and less than 300 g / L.

[0080] (Reaction-solid-liquid separation process)

[0081] In the carbonate aqueous solution, i.e., solution A, the carbonates can include ammonium bicarbonate, ammonium carbonate, sodium carbonate, sodium bicarbonate, etc. The carbonates referred to in this specification include not only normal salts but also acidic salts, i.e., bicarbonates. From the perspectives of ease of pH adjustment of the mixture and reducing sodium content, ammonium bicarbonate is preferred.

[0082] In the aqueous solution of rare earth elements, i.e., solution B, the water-soluble salts of rare earth elements can be nitrates, acetates, ammonium complexes, and chlorides. From the perspective of ease of pH adjustment of the mixed solution and productivity, nitrates are preferred.

[0083] In this manufacturing method, an aqueous carbonate solution (solution A) and an aqueous solution of water-soluble rare earth elements (solution B) are simultaneously added to a reaction tank such that the pH of the mixture is 6.5–7.0, preferably 6.5–6.9. Here, pH refers to the pH at the temperature of the mixture. If the pH of the mixture exceeds 7.0, it becomes a mixture with large primary particles. Furthermore, setting the pH to 6.5 or higher has the advantage that almost all rare earth ions in solution A precipitate. It is preferable that neither solution A nor solution B is heated at the time of addition. The temperature of solution A and solution B is preferably 5–50°C when added to the reaction tank, and the temperature of the mixture is preferably 5–40°C. To set the primary particle size within the preferred range, it is preferable to react for a very short time and filter immediately. Therefore, it is preferable to adjust the timing and rate of addition of the two liquids so that the pH of the mixture is within the range of 6.5 to 7.0 from the start of addition of liquid A and liquid B to the reaction tank (the start of mixing of liquid A and liquid B) until the time of production of reaction products (more specifically, the start of solid-liquid separation), thereby maintaining the pH constant within the above range. By ensuring the pH is within the above range, the reaction proceeds smoothly.

[0084] The simultaneous addition of solution A and solution B means that the timing of adding solution A to the reaction tank and the timing of adding solution B, even partially, become simultaneous. As described above, in order to keep the pH of the mixture within the range of 6.5 to 7.0 from the start of adding solution A and solution B to the reaction tank (the start of mixing solution A and solution B) to the time when reaction products are generated (more specifically, the start of solid-liquid separation), it is preferable to set the start of each addition to be almost simultaneous and to set the addition rate to be constant. Furthermore, the addition rate of solution A and solution B is adjusted in such a way that solid-liquid separation can begin within 5 minutes, more preferably within 3 minutes, from the start of mixing solution A and solution B.

[0085] In this manufacturing method, a mixture of liquid A and liquid B is simultaneously added to the reaction tank as described above and stirred at high speed under specified pH conditions. This approach readily and appropriately yields the aforementioned primary particle size and the agglomeration diameter D after ultrasonic irradiation. 100 The powder has a porosity difference within the range specified above. Examples of high-speed stirring include stirring at speeds of 10,000 to 25,000 rpm, more preferably 18,000 to 21,000 rpm. When the stir bar in the reaction tank of the mixture rotates as described above, the capacity of the reaction tank is preferably 50 ml to 1 L, more preferably 100 ml to 500 ml.

[0086] The inventors discovered that instead of adding liquid B to liquid A pre-added to the reaction tank, or adding liquid A to liquid B pre-added to the reaction tank, by simultaneously adding liquid A and liquid B and stirring at high speed while maintaining a specified pH, the reaction can be completed in a short time. If the mixture is then subjected to a specified post-processing, a first-invention rare earth oxide powder with a small particle size that can be easily dispersed by low-intensity crushing can be obtained.

[0087] The above-mentioned primary particle size and the agglomeration diameter D after ultrasonic irradiation are easier to obtain. 100 From the perspective of reducing porosity, the concentration of carbonate in solution A is preferably 5-25% by mass, more preferably 10-15% by mass. Furthermore, the concentration of water-soluble salts of rare earth elements in solution B is as described above.

[0088] (Washing process)

[0089] The residue (also called "solid matter") obtained in the above-described solid-liquid separation process is washed with alcohol. For example, a high-purity alcohol with a purity of 99.5 vol% or higher is preferably used as the alcohol used in this manufacturing method. Examples of alcohols include methanol, ethanol, and isopropanol, with ethanol being preferred from a usability perspective. The amount of alcohol used in the washing process 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, relative to 1 g of the rare earth oxide used. The amount referred to here is the total amount obtained by repeatedly flushing the residue with the alcohol.

[0090] (Firing process)

[0091] A firing temperature of 1000°C or below is preferred from the perspective of suppressing agglomeration and crystal growth, and more preferably 800°C or below. A firing temperature of 500°C or above is preferred from the perspective of reducing carbon content. From this point of view, a firing temperature of 500°C or above and 1000°C is more preferred, and 500°C or above and 800°C is even more preferred. Firing can be carried out in an atmosphere containing oxygen, such as atmospheric atmosphere, or in an inert atmosphere, such as argon or nitrogen, but it is preferred to carry out the firing in an atmosphere containing oxygen, especially an atmospheric atmosphere, from the perspective of reducing carbon content and cost.

[0092] (Crushing process)

[0093] The rare earth oxide powder obtained by calcination is preferably crushed into coarse particles. For crushing, a dry pulverizer can be used, such as a pulverizer (trade name: Forcemill, manufactured by OSAKA CHEMICAL).

[0094] Next, the rare earth oxide powder obtained by the above-described operation can be used for various applications due to its ease of dispersion. Examples include dielectrics or internal electrodes for capacitors, phosphors, refractive index modifiers for optical glass, oxygen sensors, sintering aids for ceramics, additives in alloys, catalysts, refractories, laser crystallization raw materials, and corrosion-resistant materials for semiconductor manufacturing equipment. Various methods of application are available, including coating (film formation), micro-addition, and molding (including sintered bodies). In particular, the rare earth oxide powder of the first invention is suitable for coating applications (including film formation applications) due to its excellent coating properties.

[0095] The second invention will now be described in detail based on its preferred embodiments.

[0096] The second invention relates to powders of oxides of rare earth elements other than Ce.

[0097] Ce oxide, namely CeO2, is obtained by adding an oxidant (H2O2) to cerium hydroxide in water without a sintering process. Furthermore, since Ce is easily oxidized, it is also easy to obtain the precursor by sintering at low temperatures. As a result, CeO2 is less affected by agglomeration during manufacturing due to sintering, and even powders with primary particles of tens of nm can be easily broken down.

[0098] On the other hand, rare earth elements other than Ce do not produce oxides even when oxidizing agents are added to hydroxides, so they usually require high-temperature firing during manufacturing, which is one cause of necking. Therefore, for rare earth element powders other than Ce, it is very difficult to suppress powder agglomeration when the primary particle size is tens of nm.

[0099] In the second invention, oxides of rare earth elements other than Ce can be listed as oxides selected from at least one of Sc, Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Specifically, oxides of rare earth elements other than Ce can be listed as Sc2O3, Y2O3, La2O3, and Pr6O3. 11The rare earth elements are Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₄O₇, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, and Lu₂O₃. From the perspective of the superior effect of the second invention, which addresses the difficulty of suppressing aggregation in the past, the oxides of the aforementioned rare earth elements are preferably oxides selected from at least one of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; more preferably oxides selected from at least one of Y, La, Pr, Nd, Eu, Gd, Dy, Ho, Er, and Yb; and particularly preferably oxides selected from at least one of Y, La, Eu, Gd, Dy, Ho, and Yb.

[0100] For rare earth element oxide powders, the smaller the primary particles, the more difficult they are to pulverize, and the fewer active surfaces they contain. In the absence of a dispersant, fewer active surfaces result in a more stable slurry. However, if the primary particles are too small, agglomeration becomes strong, making them impossible to break down. Even if they can be broken down, the activity of the strongly agglomerated portions increases when they are disintegrated, resulting in an unstable slurry. From this perspective, the primary particle size must be within a specified range. Specifically, the primary particle size is 10 nm or more and less than 100 nm, preferably 12 nm or more and less than 60 nm, more preferably 15 nm or more and less than 50 nm, and particularly preferably 15 nm or more and less than 35 nm.

[0101] In the second invention, the primary particle size of the rare earth element oxide powder is the primary particle size calculated from the specific surface area, specifically, it is the particle size s(m) determined by the specific surface area s(m) using the BET1 point method. 2 The particle size is calculated using the density ρs (g / cm³). For example, the primary particle size d (nm) is d = 6000 / (ρs). (ρ is the true density (g / cm³)). 3 )).

[0102] Furthermore, in the second invention, the pore diameter is 0.005 μm or more and 100 μm or less, and the pore volume (cm³) is... 3 / g) multiplied by true density (g / cm³) 3 The resulting value is a specific value.

[0103] Here, the reason why the second invention specifies the value of the product of the pore volume and the true density instead of the pore volume is explained as follows.

[0104] Pore ​​volume (cm³) 3 / g) depends on the volume per unit weight of the sample being measured. Therefore, even the pore volume per unit volume (cm³) 3 The same applies if the pore volume per unit weight (cm³) is set. 3 If the true density is / g), then the value of the compound with the higher true density will also become smaller.

[0105] Therefore, in the second invention, the value of the pore volume, which is independent of the compound species, is set as a specified pore volume (cm³) per 1g. 3 The value of (g) multiplied by the true density. If the pore volume (cm³) obtained from the mercury porosimeter is... 3 / g) multiplied by true density (per 1cm³) 3 The mass of the pores becomes the pore volume per unit volume.

[0106] The value obtained by multiplying the pore volume (with a pore diameter of 0.005 μm or more but less than 100 μm) by the true density (hereinafter also referred to as "first pore capacity") represents the total pore volume originating from the gaps between primary particles and the gaps between aggregated particles, and is a parameter indicating the degree of aggregation. If the pore volume per unit, i.e., the first pore capacity, is low, it indicates strong aggregation; if the first pore capacity is high, it indicates that there are large or numerous gaps through which the aggregated particles pass, resulting in a large aggregate diameter. Therefore, an appropriate first pore capacity is related to fragility.

[0107] Specifically, the first pore capacity, obtained by multiplying the pore volume (with a pore diameter of 0.005 μm or more and 100 μm or less) by the true density, is 3 or more and 14 or less. A low first pore capacity results in strong cohesion even when there are no voids between particles. Furthermore, if the value exceeds 14, there are more voids, and the initial cohesion diameter increases. Additionally, it is anticipated that more voids make it easier to absorb impacts, making crushing using a bead mill more difficult. From these perspectives, a value of 4 or more and 12 or less is more preferred, and a value of 5.5 or more and 12 or less is particularly preferred.

[0108] Furthermore, in the second invention, one of its features is that the pore diameter is 5 nm or more and 50 nm or less, and the pore volume (cm³) is... 3 / g) multiplied by true density (g / cm³) 3 The resulting value (hereinafter also referred to as "second pore capacity") is also a specific value.

[0109] Regarding pore size, it is known that pores with a size of approximately 1 / 3 to 1 / 4 of the particle size are formed between particles (see Japanese Patent Application Publication No. 7-237982). Pores with a diameter of 5 nm or more and less than 50 nm become equivalent to the pores of aggregates with agglomeration diameters of approximately 15 nm or more and less than 200 nm. The limiting agglomeration diameter for breakage depends on the bead diameter, but as will be discussed later, the bead diameter cannot be excessively reduced due to considerations of breakage energy. If there are many particles with agglomeration diameters of approximately 15 nm or more and less than 200 nm, it is easy to overlap with the limiting particle size for bead breakage. Particles with agglomeration diameters relatively close to the limiting particle size for bead breakage are difficult to break even if they are larger than the limiting particle size for bead breakage, and even if they are smaller than the limiting particle size, their aggregate aggregation force becomes stronger, and they are prone to agglomerate (tertiary agglomerates). For these reasons, powders with a pore volume of 5 nm or more and less than 50 nm are prone to becoming slurries with large dispersed particle sizes. Therefore, in the second invention, the product of the pore volume and true density (i.e., the pore diameter being 5 nm or more and 50 nm or less) is 2.0 or less, more preferably 1.5 or less, particularly preferably 1.2 or less, even more preferably 1.0 or less, and still more preferably 0.8 or less, particularly preferably 0.7 or less. Furthermore, the lower limit of the second pore capacity is not particularly limited as long as it is 0 or more, but from the viewpoint of ease of manufacture, it is preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.05 or more.

[0110] Furthermore, the specific surface area of ​​the rare earth element oxide powder of the second invention is, for example, 10 m². 2 / g or more and 160m 2 The size of 15 μm or less is preferred from the perspective of easily achieving the aforementioned primary particle size. 2 / g or more and 110m 2 / g or less, more preferably 20m 2 / g or more and 80m 2 / g or less.

[0111] Furthermore, it is preferable for rare earth oxide powders to have low impurity content. If Na ions are present during synthesis, particle growth can be inhibited, but Na is difficult to decompose. Since electronic materials containing Na are not preferred, low Na ion content is preferable. From this perspective, the Na content of rare earth oxide powders is preferably 100 ppm by mass or less, and particularly preferably 10 ppm by mass or less. The Na content can be determined using the method described in the examples below.

[0112] The crystallite diameter of rare earth oxide powder is preferably within a specified range. Specifically, the crystallite diameter of rare earth oxide powder is preferably 6 nm or more and 25 nm or less. By having a crystallite diameter of 6 nm or more, it is easy to set the primary particle size to a certain value, which can reduce the cohesion of primary particles. Furthermore, by having a crystallite diameter of 6 nm or less, it is easy to set the primary particle size to a certain value, and it can prevent the necking of particles. Considering these aspects, the crystallite diameter of rare earth oxide powder is more preferably 8 nm or more and 20 nm or less.

[0113] The crystallite diameter can be determined by the method described in the examples below.

[0114] The rare earth oxide powder of the second invention can be made into a slurry by wet crushing.

[0115] The rare earth oxide powder of the second invention preferably has a specific range of aggregated particle size during a specific crushing process. Specifically, the rare earth oxide powder of the second invention preferably has an average particle size (Dm) of 10 nm or more and 150 nm or less after being mixed with ethanol to prepare an ethanol slurry containing 10% by mass of rare earth oxide powder, and the operation (A) is repeated until the average particle size becomes larger than the previous measurement value. As a method for preparing the ethanol slurry containing 10% by mass of rare earth oxide powder, a method of mixing 40.5 g of ethanol with a purity of 99% by mass or more with 4.5 g of rare earth oxide powder to prepare the slurry can be cited. No dispersant is used in the slurry in which the aggregated particle size is measured. Examples of various dispersants described later can be cited as dispersants.

[0116] (A): Zirconia beads with a diameter of 0.1 mm were used to mill the slurry for 10 minutes. The average particle size was then determined by dynamic light scattering.

[0117] The operation of (A) is specifically set as follows (a).

[0118] (a): Zirconia beads with a diameter of 0.1 mm were made. The mass ratio of slurry to beads was set to 45:240. The beads were milled for 10 minutes in a bead mill with an effective volume of 80 cc at a circumferential speed of 4 m / s or more and 6 m / s or less. The average particle size was then determined by dynamic light scattering method.

[0119] (Among them, the bead milling process ends at the moment when the average particle size becomes larger than the previous measurement value, and the process also ends at the moment when the average particle size does not become larger than the previous measurement value in each of the 20 repetitions (A).)

[0120] Here, the minimum average particle size (Dm) refers to the minimum value of the average particle size measured using dynamic light scattering method, sampled every 10 minutes during the aforementioned bead milling process. It should be noted that the average particle size, when expressed in nm and containing decimal values, is determined by rounding the first decimal place to the nearest integer.

[0121] The minimum average particle size (Dm) obtained by the above-described measurement represents the minimum agglomeration diameter obtained by a typical crushing process, i.e., bead crushing process, in the technical field involving slurries made from oxide micropowders. The minimum average particle size (Dm) is preferably 150 nm or less, more preferably 140 nm or less, even more preferably 105 nm or less, and particularly preferably 90 nm or less. This is because setting this minimum average particle size (Dm) to a predetermined value or less improves transparency. Furthermore, the minimum average particle size (Dm) is preferably 10 nm or more, more preferably 15 nm or more, even more preferably 20 nm or more, and most preferably 50 nm or more. This is because setting this lower limit to a predetermined value or more improves the dispersion stability of the slurry.

[0122] Furthermore, a polydispersity index (PI) of 0.3 or less is preferred for determining the minimum average particle size (Dm), considering factors such as sharp particle size distribution, easier maintenance of high dispersibility when preparing slurry, and visible light transmittance; more preferably, it is 0.25 or less. It should be noted that the polydispersity index (PI) is a dimensionless index that represents the extent of particle size distribution.

[0123] The effective volume of the container refers to the internal volume of the container (container) that holds the beads and slurry. In addition, the circumferential speed of the bead mill can be any circumferential speed of 4 m / s or more and 6 m / s or less, but it is more preferable to have a circumferential speed of 4 m / s or more and 5 m / s or less, and even more preferably a circumferential speed of 4 m / s.

[0124] For the determination of average particle size and polydispersity index (PI) using dynamic light scattering (photon correlation method), the test sample is filled into a dynamic light scattering spectrophotometer. The test sample is prepared by taking a portion of the aforementioned slurry, using the solvent used in wet crushing as the dispersion medium, and without ultrasonic treatment. The concentration of the test sample is set to a dilution factor within the range of 1000 to 10000 times the capacity, which the dynamic light scattering spectrophotometer determines to be the appropriate concentration. As the dynamic light scattering spectrophotometer, an apparatus employing a method that uses the autocorrelation function obtained by photon correlation and analyzes it using the cumulant method to determine the average particle size and polydispersity index (PI) can be used; for example, the Otsuka Electronics ELSZ-2000ZS can be used.

[0125] It should be noted that the cumulative method is described in "9.2.1 Cumulative Method" of JIS Z 8828:2019 "Particle Size Analysis - Dynamic Light Scattering Method" and "A.1.2 Cumulative Method" of Appendix A of the same JIS.

[0126] The rare earth oxide powder of the second invention is crushed as described above, and the minimum average particle size (Dm) is determined. When the crushed slurry is left to stand at room temperature (15–25°C), the calculated value of the following formula is preferably within a specified range. The following formula represents the particle size change after standing for 7 days. The value of the following formula is preferably 25% or less, more preferably 20% or less, and even more preferably 15% or less. If it is below this upper limit, the particle size can be easily restored to the same or close to that immediately after crushing by applying ultrasound or the like. Since the average particle size of the slurry is measured as microparticles, the inhomogeneity of the measurement must also be considered. In the absence of substantial particle size change, it is sometimes measured as if the particle size has decreased; therefore, the calculated value is preferably -15% or more, and even more preferably -10% or more.

[0127] In the following formula, the "average particle size immediately after crushing (D0)" refers to the value that is the same as the minimum average particle size (Dm) when the operation (A) above is repeated until the average particle size becomes larger than the previous measurement value, and the average particle size does not increase compared to the previous measurement value up to the 20th iteration. On the other hand, if the average particle size increases compared to the previous measurement value during the 20th iteration and the bead milling process ends, this final measurement value is called the "average particle size immediately after crushing (D0)". Furthermore, in the following formula, "average particle size 7 days after crushing (D7)" refers to the average particle size measured again using the dynamic light scattering method (photon correlation method) after the slurry after bead milling has been left to stand for 7 days under the above conditions. Formula: (average particle size 7 days after crushing (D7) - average particle size immediately after crushing (D0)) / average particle size immediately after crushing (D0) × 100 (%)

[0128] The rare earth oxide powder of the second invention preferably has an average particle size (D0) of 210 nm or less immediately after crushing, more preferably 150 nm or less, and particularly preferably 120 nm or less. This is because it can improve the transmittance after settling. Furthermore, the average particle size (D0) immediately after crushing is preferably 25 nm or more, more preferably 50 nm or more. This is because it can improve the dispersibility of the slurry.

[0129] The rare earth oxide powder of the second invention preferably has an average particle size (D7) of 150 nm or less after crushing for 7 days, more preferably 120 nm or less, and particularly preferably 100 nm or less. This is because it can improve the transmittance after standing. Furthermore, the average particle size (D7) after crushing for 7 days is preferably 25 nm or more, more preferably 50 nm or more. This is because it can improve the dispersibility of the slurry.

[0130] The average particle size (D7S) of the rare earth oxide powder of the second invention, after being crushed for 7 days and then irradiated with 20 ml of slurry with 40W ultrasound (frequency 40kHz) for 5 minutes, is preferably 150 nm or less, more preferably 120 nm or less, and particularly preferably 100 nm or less. This is because it can improve the transmittance after standing. Furthermore, this average particle size (D7S) is preferably 25 nm or more, more preferably 50 nm or more, because it can improve the dispersibility of the slurry.

[0131] To obtain the above specific surface area (m²) 2 The following parameters can be used: primary particle size (nm), first pore volume, second pore volume, Na content, Dm (nm), D0 (nm), D7 (nm), (D7-D0 / D0) (%), and D7S (nm). As long as the preferred rare earth oxide powder manufacturing method described later is adopted, the mixing, washing, or firing conditions can be adjusted.

[0132] Next, a preferred method for manufacturing the rare earth oxide powder of the second invention will be described.

[0133] This manufacturing method includes the following steps: simultaneously adding a carbonate aqueous solution (hereinafter also referred to as "A solution") and a water-soluble salt aqueous solution of rare earth elements (hereinafter also referred to as "B solution") into a reaction tank, mixing the mixture in such a way that the pH of the mixture is 6.5 to 7.0, preferably 6.5 to 6.9, so that the carbonate reacts with the water-soluble salt of rare earth elements, and starting the solid-liquid separation reaction - solid-liquid separation step within 5 minutes from the start of mixing A solution and B solution;

[0134] A washing process in which the residue obtained from the reaction-solid-liquid separation process is washed with alcohol or aqueous alcohol; and

[0135] The firing process involves firing the residue after washing.

[0136] From the perspective of successfully obtaining the rare earth oxide powder of the second invention, it is preferred that the concentration of water-soluble salt converted from oxide in solution B, i.e., the water-soluble salt solution of rare earth elements, is 10 to 400 g / L, more preferably 20 to 300 g / L, particularly preferably 20 to 200 g / L, and most preferably 20 g / L or more but less than 100 g / L.

[0137] This manufacturing method differs from the method for manufacturing rare earth oxide powder of the first invention in that the mixture of liquid A and liquid B is not necessarily subjected to high-speed stirring, the residue obtained in the reaction-solid-liquid separation process is preferably washed not only with alcohol but also with aqueous alcohol, and the preferred concentration range of the water-soluble salt solution of rare earth elements in liquid B is different.

[0138] (Reaction-solid-liquid separation process)

[0139] In the carbonate aqueous solution, i.e., solution A, the carbonates can include ammonium bicarbonate, ammonium carbonate, sodium carbonate, sodium bicarbonate, etc. The carbonates referred to in this specification include not only normal salts but also acidic salts, i.e., bicarbonates. From the perspectives of ease of pH adjustment of the mixture and reducing sodium content, ammonium bicarbonate is preferred.

[0140] In the aqueous solution of rare earth elements, i.e., solution B, the water-soluble salts of rare earth elements can be nitrates, acetates, ammonium complexes, and chlorides. From the perspective of ease of pH adjustment of the mixed solution and productivity, nitrates are preferred.

[0141] When using this manufacturing method, it is preferable that the concentrations of liquid A and liquid B are within a specified range, from the perspective of smoothly setting the primary particle size, the first pore volume, and the second pore volume within the specified range. Specifically, the concentration of carbonate in liquid A is preferably 5 to 25% by mass, more preferably 10 to 15% by mass. Regarding the concentration of water-soluble salts of rare earth elements in liquid B, as described above.

[0142] In this manufacturing method, an aqueous carbonate solution (solution A) and an aqueous solution of water-soluble rare earth elements (solution B) are simultaneously added to a reaction tank such that the pH of the mixture is 6.5–7.0, preferably 6.5–6.9. Here, pH refers to the pH at the temperature of the mixture. If the pH of the mixture exceeds 7.0, it becomes a mixture with large primary particles. Furthermore, setting the pH to 6.5 or higher has the advantage of almost completely precipitating the rare earth ions in solution A. It is preferable that neither solution A nor solution B is heated at the time of addition. The temperature of solution A and solution B is preferably 5–50°C when added to the reaction tank, and the temperature of the mixture is preferably 5–40°C. To set the primary particle size within the preferred range, it is preferable to react for a very short time and filter immediately. Therefore, it is preferable to adjust the timing and rate of adding the two liquids so that the pH of the mixture is within the range of 6.5 to 7.0, preferably 6.5 to 6.9, from the start of adding liquid A and liquid B to the reaction tank (the start of mixing of liquid A and liquid B) until the time of reaction product formation (more specifically, the start of solid-liquid separation), thereby maintaining the pH constant within the above range. By ensuring the pH is within the above range, the reaction proceeds smoothly.

[0143] The simultaneous addition of solution A and solution B means that the timing of adding solution A to the reaction tank and the timing of adding solution B are at least partially simultaneous. As described above, in order to ensure that the pH of the mixture remains within the range of 6.5 to 7.0, preferably 6.5 to 6.9, from the start of adding solution A and solution B to the reaction tank (the start of mixing solution A and solution B) until the time of generating reaction products (more specifically, the start of solid-liquid separation), it is preferable to set the start of adding solution A and solution B of the above concentrations to be almost simultaneous, and to set the addition rate to be constant. Furthermore, the addition rate of solution A and solution B is adjusted in such a way that solid-liquid separation can begin within 5 minutes, more preferably within 3 minutes, from the start of mixing solution A and solution B.

[0144] The inventors discovered that instead of adding liquid B to liquid A pre-added to the reaction tank, or adding liquid A to liquid B pre-added to the reaction tank, by simultaneously adding liquid A and liquid B of a specified concentration and mixing them under conditions that maintain a specified pH, the reaction can be completed in a short time. If the mixture is then subjected to a specified post-processing, a rare earth oxide powder of the second invention can be obtained, which produces a slurry with small particle size, good dispersibility, and excellent transparency.

[0145] In the reaction tank, the mixture of liquid A and liquid B is stirred. From the viewpoint of successfully obtaining the rare earth oxide powder of the second invention, it is preferable that the stirring can be high speed, low speed, or medium speed.

[0146] The stirring speed is preferably 100 rpm or more and 25,000 rpm or less, more preferably 200 rpm or more and 21,000 rpm or less.

[0147] As a low-speed mixing, mixing speeds of 100 rpm or higher and below 1000 rpm can be listed, with 200 rpm or higher being more preferred.

[0148] As a medium-speed mixer, mixers with speeds above 1000 rpm and below 10000 rpm can be listed.

[0149] Examples of high-speed mixing include mixing speeds of 10,000 rpm and above, but less than 25,000 rpm. In the case of high-speed mixing, speeds of 18,000 rpm and above, but less than 21,000 rpm, are particularly preferred.

[0150] From the perspective of particularly optimizing the reduction of primary particle size, high-speed stirring is preferred.

[0151] As for the reaction tank, as long as it is equipped with a stirring device capable of stirring at a specified speed (including a stirring device integrated with the reaction tank), the capacity of the reaction tank can be appropriately determined according to the production volume, etc. However, the capacity of the reaction tank equipped with a high-speed stirring device is also limited by the size of the high-speed stirring device, which is preferably 50mL to 5L, more preferably 100mL to 2L, and even more preferably 100mL to 1L.

[0152] (Washing process)

[0153] It is also important to wash the residue (also called "solid matter") obtained in the above-mentioned solid-liquid separation process with alcohol or aqueous alcohol. Examples of alcohols include methanol, ethanol, and isopropanol, with ethanol being preferred from a usability perspective. When using aqueous alcohol, the alcohol concentration is preferably 10% by volume or more, more preferably 50% by volume or more. The amount of alcohol used in the washing process, relative to 1g of the oxide of the solid matter to be washed, is preferably 0.1L to 50L, more preferably 0.5L to 20L, and even more preferably 1L to 10L. The amount referred to here is the total amount when the alcohol is repeatedly passed through the residue for washing.

[0154] (Firing process)

[0155] A firing temperature of 1000°C or below is preferred from the perspective of suppressing agglomeration and crystal growth, and more preferably 800°C or below. A firing temperature of 500°C or above is preferred from the perspective of reducing carbon content. From this point of view, a firing temperature of 500°C or above and 1000°C is more preferred, and 500°C or above and 800°C is even more preferred. Firing can be carried out in an atmosphere of active gas such as the atmosphere, or in an atmosphere of inert gas such as argon or nitrogen, but it is preferred to carry out it in an atmosphere of active gas, especially an atmosphere of the atmosphere.

[0156] (Crushing process)

[0157] The rare earth oxide powder obtained by calcination is preferably crushed into coarse particles. For crushing, a dry pulverizer can be used, such as a pulverizer (trade name: Forcemill, manufactured by OSAKA CHEMICAL).

[0158] Next, a method for manufacturing a slurry by wet crushing rare earth oxide powder obtained as described above will be explained.

[0159] Wet crushing is preferably performed using a bead mill, which is preferred for its ability to achieve high dispersion. The beads produced by the bead mill are typically spherical. Materials for the beads include zirconium oxide, alumina, silicon nitride, silicon carbide, tungsten carbide, wear-resistant steel, and stainless steel, with zirconium oxide being the preferred material. The zirconium oxide referred to here includes stabilized zirconium oxides such as YSZ and PSZ.

[0160] The bead diameter during crushing is preferably 0.01–0.3 mm. Since the limiting particle size for crushing is based on the bead diameter, for example, approximately 1 / 1000 of the bead diameter, a smaller bead diameter is preferable. However, if the diameter is too small, the crushing energy decreases, and therefore, the beads may sometimes remain aggregated without being broken up. From this perspective, the bead diameter during crushing is more preferably 0.05–0.15 mm.

[0161] Considering that the solvent for dispersing rare earth oxide powders has better dispersibility than water, monohydric alcohols are preferred, especially primary alcohols, and particularly ethanol. Examples of monohydric alcohol solvents include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol. Monohydric alcohols are frequently used in laboratory detergents and are readily available. Furthermore, ethanol and 1-propanol are easy to handle as they are not subject to organic solvent poisoning prevention regulations. It should be noted that the monohydric alcohol preferably has a purity of 99% by volume or higher.

[0162] Furthermore, the proportion of rare earth oxide powder in the slurry obtained by the manufacturing method of the second invention is preferably 1 to 50% by mass from the viewpoint of obtaining the desired visible light transmittance, and more preferably 5 to 20% by mass.

[0163] The method for manufacturing the slurry of the second invention preferably involves reducing the average particle size of the obtained slurry to below 200 nm, more preferably to below 10 nm and 150 nm, even more preferably to below 15 nm and 140 nm, and particularly preferably to below 20 nm and 105 nm. By achieving the above-mentioned upper limits, and especially the above-mentioned ranges, excellent transmittance and stability are obtained.

[0164] The method for manufacturing the slurry of the second invention preferably produces a slurry with a polydispersity index (PI) of 0.3 or less, more preferably 0.25 or less. A lower polydispersity index (PI) is more preferred, but from the perspective of ease of manufacturing, a PI of 0.1 or more is preferred.

[0165] The preferred method for manufacturing the slurry of the second invention is a method in which the visible light transmittance of the slurry, after being crushed and allowed to stand for 7 days, is 40-95%, and more preferably 50-80%. The visible light transmittance can be measured by the method described in the examples described later.

[0166] The method for manufacturing the slurry of the second invention preferably does not use a dispersant. Examples of dispersants include ionic surfactants, nonionic surfactants, pH adjusters, and soluble salts, such as ether types like polyoxyethylene alkyl ethers, polyoxyethylene secondary alcohol ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene, polyoxypropylene block copolymers, and polyoxyethylene polyoxypropylene alkyl ethers; ester types like polyoxyethylene glycerol fatty acid esters, polyoxyethylene castor oil and hydrogenated castor oil, and polyoxyethylene sorbitan fatty acid esters. Polyglycerol fatty acid esters such as diglycerol laurate can also be listed. Furthermore, nitric acid, hydrochloric acid, acetic acid, sodium chloride, potassium chloride, magnesium chloride, and calcium chloride can also be listed. β-diketones described in Japanese Patent Application Publication No. 2007-126349 can also be listed. In addition, substances whose dispersibility is improved by adding additives are also considered dispersants. Not using a dispersant preferably means that the amount of dispersant in the slurry is less than 10,000 ppm by mass, more preferably less than 1,000 ppm by mass, even more preferably less than 100 ppm by mass, even more preferably less than 10 ppm by mass, and especially preferably not used.

[0167] Example

[0168] <Description of embodiments and comparative examples of the first invention>

[0169] The first invention will now be described in more detail through embodiments. However, the scope of the invention is not limited to the embodiments described.

[0170] (Example a1)

[0171] Prepare 10 kg of an aqueous solution of ammonium bicarbonate (25°C) containing 13.0% by mass of ammonium bicarbonate and 40 L of an aqueous solution of yttrium nitrate (25°C) with a concentration of 300 g / L (based on oxide conversion). The ammonium bicarbonate aqueous solution was also used in Examples a2-9 described later, and the yttrium nitrate aqueous solution was also used in Examples a2-4 described later. The yttrium nitrate aqueous solution was simultaneously added to the same reaction layer at a flow rate of 100 mL / min, and the ammonium bicarbonate aqueous solution was added at a pH of 6.8 for the mixture of the two solutions, and the mixture was stirred at 20,000 rpm during the addition. After filtering the suspension overflowing from the container for 20 seconds each time, the addition of both solutions and stirring were stopped, and the residue, which was the filter material, was washed with 10 L of ethanol. This washing operation was repeated 5 times. The time from the start of mixing the two solutions to the start of filtration was 60 to 120 seconds. Approximately 10 g of Y₂O₃ was obtained by calcining the washed residue at 600°C under atmospheric conditions. The reaction vessel had a volume of 100 ml. The yield of the obtained Y₂O₃ was approximately 99% after filtration for 20 seconds.

[0172] The above process was repeated 10 times, and the Y2O3 samples obtained from the 10 processes were mixed. The resulting Y2O3 was then crushed using a Forcemill (manufactured by OSAKA CHEMICAL) for 30 seconds to obtain a fine powder.

[0173] The specific surface area (m²) of the obtained Y₂O₃ micro powder was determined by the following method. 2 / g), primary particle size (nm), aggregate diameter, initial bulk density (AD) and tap bulk density (TD), Zr content, carbon content, and P is calculated from the initial bulk density (AD) and tap bulk density (TD). AD P TD and P AD -P TD The values ​​were also used to evaluate the coating properties. The results are shown in Table 1.

[0174] (Methods for determining specific surface area)

[0175] The determination was performed using the BET 1-point method with a fully automated surface area meter (Macsorbmodel-1201, Mounttech). The gas used was a nitrogen-helium mixture (nitrogen 30 vol%). As a pretreatment, the powder was placed in a glass cell and placed in the apparatus. Nitrogen gas was circulated through the glass cell, and degassing was performed at 300°C for 60 minutes.

[0176] (Method for calculating primary particle size)

[0177] The specific surface area s (m²) measured by the BET1 point method is calculated using the following formula. 2 The particle size is calculated from the density (ρs). The primary particle size d (nm) is d = 6000 / (ρs) (ρ is the true density (g / cm³)). 3 Regarding the true density, Y₂O₃ is set to 5.03 g / cm³. 3 Nd2O3 was set at 7.33 g / cm³. 3 The Gd2O3 content was set at 7.62 g / cm³. 3 Eu2O3 was set at 7.4 g / cm³. 3 The Dy2O3 concentration was set at 7.81 g / cm³. 3 Yb₂O₃ was set at 9.22 g / cm³. 3 ).

[0178] (condensation path (D) 100 D 50 D 90 ))

[0179] The determination was performed using a Microtrac MT3300EXII manufactured by Nikkiso Corporation. During the determination, a powdered sample was added to the chamber of a sample circulator filled with a 0.2% by mass aqueous solution of sodium hexametaphosphate. The sample was then dispersed for 5 minutes using the ultrasonic irradiation device of the apparatus at 40W and 40kHz. D was measured after the apparatus determined the concentration to be appropriate. 100 D 50 D 90 .

[0180] (Methods for determining initial bulk density and tapped bulk density)

[0181] 1. Sample pretreatment: Rare earth oxide powder (Y2O3 micro powder in Example a1) was crushed for 30 seconds using OSAKA CHEMICAL Co., Ltd. Forcemill just before the determination.

[0182] 2. Measurement

[0183] (1) Measured inner diameter 10mm, outer diameter 12mm, height 51mm, inner surface height 50mm (internal volume 3.93cm). 3 The mass (W) of the container made of SUS304 was determined. C (g)).

[0184] (2) Add the pretreated sample into the measuring container through a sieve with a mesh size of 2 mm until it overflows.

[0185] (3) Use a scraper to level the powder that has risen from the top surface of the measuring container.

[0186] (4) Measure the mass of the measuring container together (W0(g)) and subtract the mass of the measuring container (W). c (g) and calculate the mass (W) of the sample. A (g)).

[0187] (5) Attach an auxiliary cylinder (made of SUS304 with an inner diameter of 12 mm at the bottom and 10 mm at the top, an outer diameter of 14 mm, and a height of 50 mm (10 mm at the bottom and 40 mm at the top) to the measuring container containing the sample, and further fill the sample through a sieve with a sieve opening of 2 mm.

[0188] (6) The test container, which contains the sample and has an auxiliary cylinder, is vibrated 600 times by hand by colliding the container with a rubber sheet to a height of about 10 mm. During this process, additional samples are added, with the height of the sample increasing by 20 to 30 mm from the top of the test container.

[0189] (7) Remove the auxiliary cylinder and scrape the overflowing sample on the measuring container with a scraper.

[0190] (8) After leveling the sample, measure the mass of the sample along with the measuring container (W1(g)), and subtract the mass of the measuring container (W). c (g) to determine the mass (W) of the sample. T1 (g)).

[0191] (9) Install the auxiliary cylinder on the measuring container again, and fill the sample further through a sieve with a sieve hole of 2 mm. Vibrate the sample 100 times by hand to a compaction height of about 10 mm.

[0192] (10) Remove the auxiliary cylinder and scrape the overflowing sample on the measuring container with a scraper.

[0193] (11) After leveling the sample, measure the mass of the sample along with the measuring container (W2(g)), and subtract the mass of the measuring container (W). c (g) and calculate the mass (W) of the sample. T2 (g)). Confirm this value (W) T2 (g) and the previous value (W) T1 (g) difference relative to W T1 Within 0.3%. If it exceeds 0.3%, repeat (9) until the difference with the previous one is within 0.3%.

[0194] (12) The initial bulk density and the tapped bulk density are calculated using the following formula.

[0195] Initial bulk density (g / cm³) 3 ) = W A (g) / 3.93(cm 3 )

[0196] Tapped bulk density (g / cm³) 3 ) = W T2 (g) / 3.93(cm 3 )

[0197] (13) Perform at least three measurements. The initial bulk density and tapped bulk density are the average of the three measurements.

[0198] (Porosity)

[0199] The initial bulk density and tapped bulk density are set as ρ0, then the porosity P (%) is calculated by P = (1 - ρ0 / ρ) × 100. (ρ is the true density (g / cm³) 3 )).

[0200] (Carbon content)

[0201] The carbon and sulfur analysis apparatus EMIA-320V manufactured by Horiba Corporation was used to determine the carbon and sulfur content using the infrared absorption method of combustion in an oxygen stream.

[0202] (Zr content)

[0203] The measurements were performed using an ICP luminescence spectrophotometer SPS-3520V-DD manufactured by Hitachi High-Tech Science Co., Ltd.

[0204] (Evaluation of coating properties)

[0205] Using 3g of the obtained Y2O3 micro powder and ethanol, an ethanol slurry with a Y2O3 concentration of 30% by mass was prepared. After dispersion using 40W ultrasound (40kHz frequency) for 5 minutes, the slurry was coated onto a PET film using a 10μm gap applicator (BEVS Industrial). The coating properties were evaluated according to the following evaluation criteria.

[0206] A: Yes, it can be painted.

[0207] B: Parts that cannot be painted are produced.

[0208] C: Because the dispersed phase does not come out of the gap, it cannot be coated.

[0209] (Example a2)

[0210] Except for firing at 800°C, the settings are the same as those described in Example a1.

[0211] (Example a3)

[0212] Except for firing at 900°C, the settings are the same as those described in Example a1.

[0213] (Example a4)

[0214] Except for firing at 500°C, the settings are the same as those described in Example a1.

[0215] (Example a5)

[0216] In Example 1, instead of using an aqueous solution of yttrium nitrate, an aqueous solution of neodymium nitrate with an oxide conversion concentration of 400 g / L was used. Furthermore, the firing temperature was set to 900°C. Apart from these points, everything else was the same as in Example a1.

[0217] (Example a6)

[0218] In Example 1, instead of using an aqueous solution of yttrium nitrate, an aqueous solution of gadolinium nitrate with an oxide conversion concentration of 250 g / L was used. Furthermore, the firing temperature was set to 650°C. Apart from these points, everything else was the same as in Example a1.

[0219] (Example a7)

[0220] In Example 1, instead of using an aqueous solution of yttrium nitrate, an aqueous solution of europium nitrate with an oxide conversion concentration of 300 g / L was used. Furthermore, the firing temperature was set to 650°C. Apart from these points, everything else was the same as in Example a1.

[0221] (Example a8)

[0222] In Example 1, instead of using an aqueous solution of yttrium nitrate, an aqueous solution of dysprosium nitrate with an oxide equivalent concentration of 300 g / L was used. Furthermore, the firing temperature was set to 600°C. Apart from these points, everything else was the same as in Example a1.

[0223] (Example a9)

[0224] In Example a1, instead of using an aqueous solution of yttrium nitrate, an aqueous solution of ytterbium nitrate with an oxide conversion concentration of 300 g / L was used. Furthermore, the firing temperature was set to 600°C. Apart from these points, everything else was the same as in Example a1.

[0225] (Comparative Example a1)

[0226] This comparative example is an example equivalent to Example 1 of Japanese Patent Application Publication No. 2014-218384.

[0227] 5 g of sodium oleate was added to 100 mL of a 1.0 mol / L yttrium nitrate aqueous solution, and the mixture was stirred for 2 hours. Next, 1000 mL of cyclohexane and 1.0 g of the nonionic surfactant Span80 (sorbitan monooleate, manufactured by Kanto Chemical Co., Ltd.) were added to the aqueous solution and stirred vigorously (at 10000 rpm) to obtain a W / O emulsion solution consisting of tiny droplets. Then, 13 g of ammonium bicarbonate was dissolved in 50 mL of pure water to prepare an aqueous solution, which was added dropwise while the emulsion solution was stirred vigorously. A white precipitate formed with the addition of the ammonium bicarbonate solution. After the addition was complete, the mixture was aged at room temperature (25°C) for 1 hour while continuing to stir. The resulting precipitate was then filtered from the aqueous solution using a Buchner funnel, dried in an oven at 75°C for 12 hours, and then calcined in an alumina crucible at 800°C under atmospheric atmosphere. This process yielded 8 g of yttrium oxide micropowder. Then, the coating is applied using the method described in Example a1.

[0228] The powder was observed using a scanning electron microscope (SEM), and the results showed that it consisted of non-agglomerated, uniformly sized spherical particles with a diameter of approximately 100 nm. The primary particle size, calculated from the specific surface area, was also greater than 100 nm.

[0229] (Comparative Example a2)

[0230] This comparative example is an example equivalent to Example 1 of Japanese Patent Application Publication No. 2014-218384, with a modified firing temperature.

[0231] Except for setting the firing temperature to 600°C, the powder was prepared in the same manner as Comparative Example 1. The powder was observed using a scanning electron microscope (SEM), and the results showed a mixture of particles with SEM diameters of approximately 100 nm and 10 nm. Particles with uniform SEM diameters were not obtained through low-temperature firing. The primary particle size, calculated from the specific surface area, was also greater than 100 nm.

[0232] (Comparative Example a3)

[0233] This comparative example is equivalent to the example in J Nanopart Res (2013) 15: 1438.

[0234] As yttrium, 2 L of a 50 mmol / L yttrium chloride aqueous solution (pH = 5.0) was instantaneously added to 2 L of a 50 mmol / L Na₂CO₃ 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 Y₂O₃. Subsequently, a coating was prepared using the method described in Example 1a.

[0235] (Comparative Example a4)

[0236] This comparative example is equivalent to Japanese Patent Application Publication No. 4-310516.

[0237] 18.0 g of Y₂O₃ was dissolved in 900 mL of diluted hydrochloric acid. This solution was then added dropwise to 9 L of diluted ammonia water (containing 0.2 mol of ammonia) at 40 °C. The addition was done dropwise over 30 minutes. After the addition was complete, the mixture was allowed to mature for 30 minutes. Then, an aqueous solution obtained by dissolving 144 g of ammonium bicarbonate in 900 mL of water was added to precipitate yttrium carbonate. After maturation for 2 hours, the mixture was filtered, washed with water, and then 900 mL of octanol was added to the resulting yttrium carbonate. The mixture was stirred at 100 °C for 3 hours while the water was evaporated. The yttrium carbonate was then filtered and dried under reduced pressure at 13.3 Pa (0.1 Torr) and 160 °C. Finally, it was calcined at 650 °C for 2 hours to obtain 10 g of Y₂O₃. The crystallite diameter of this Y₂O₃ was [missing information].

[0238]

[0239] As shown in Table 1 above, D is measured by ultrasonic dispersion at 40W on powders containing oxides of at least one rare earth element other than Ce, with a specified primary particle size of 10 nm or more and 60 nm or less. 100 For particles larger than 1 μm and smaller than 10 μm, or the difference in porosity (P) AD -P TD The powders in each embodiment with a content of 2.0% or more and 5.0% or less exhibit good coating properties.

[0240] On the other hand, for particles with a primary diameter of 10 nm or more but less than 60 nm, or (P AD -P TD For comparative examples a1 to a4, which are outside the range of 2.0% to 5.0%, it was shown that the coagulation diameter increased after ultrasonic treatment with 40W, and no coating properties were obtained.

[0241] Based on the above, the present invention provides rare earth oxide powders that can be easily broken down and form coatings even when the primary particle size (SSA equivalent diameter) is tens of nm, except for Ce.

[0242] The second invention will now be described in more detail through examples. However, the scope of the invention is not limited to these examples. It should be noted that in the following examples, the internal volume of the reaction vessel is 2 L when stirred at low speed and 100 mL when stirred at high speed.

[0243] (Example b1)

[0244] Prepare 10 kg of an aqueous solution of ammonium bicarbonate (25°C) containing 13.0% by mass of ammonium bicarbonate and 40 L of an aqueous solution of yttrium nitrate (25°C) with an oxide concentration of 50 g / L. The ammonium bicarbonate solution was also used in Examples b2-6 described later, and the yttrium nitrate solution was also used in Examples b2-b4 and b6 described later. The yttrium nitrate solution was simultaneously added to the same container at a flow rate of 600 mL / min, and the ammonium bicarbonate solution was added at a pH of 6.8 (temperature of the mixture: 20-30°C) to mix the solutions. The mixture in the container was stirred at a high speed of 20,000 rpm during the addition. The suspension overflowing from the container was filtered sequentially for 20 seconds each time. The addition of both solutions and stirring were then stopped, and the residue was washed with 10 L of ethanol. This washing process was repeated 5 times. The washed filter powder was calcined at 700°C under atmospheric conditions to obtain 10 g of Y₂O₃. The obtained Y₂O₃ was crushed using a Forcemill (manufactured by OSAKA CHEMICAL) for 30 seconds to obtain micro powder. The specific surface area (m²) of the obtained Y₂O₃ micro powder was determined using the following method. 2 The following parameters were also considered: particle size (g), primary particle size (nm), pore volume * true density for particles with a pore diameter of 0.005 μm or more and 100 μm or less, pore volume * true density for particles with a pore diameter of 5 nm or more and 50 nm or less, Na content (ppm by mass), and crystallite diameter (nm). In addition, the following fragmentation evaluation was performed. The results are shown in Table 2.

[0245] Specific surface area (m²) 2 / g))

[0246] The determination was performed using the same method as in the embodiment of the first invention described above.

[0247] (Method for calculating primary particle size)

[0248] It is calculated using the same method as in the embodiments of the first invention described above.

[0249] (Volume and true density of pores with diameters from 0.005μm to 100μm and volume and true density of pores from 5nm to 50nm)

[0250] The pore volume was determined using the AutoPore IV from Micromeritics.

[0251] The cumulative volume for pore diameters of 0.005 μm to 100 μm is defined as the pore volume for pore diameters of 0.005 μm to 100 μm. Similarly, the cumulative volume for pore diameters of 5 nm to 50 nm is defined as the pore volume for pore diameters of 5 nm to 50 nm. The pore volume * true density value is obtained by multiplying the calculated pore volume by the true density of the rare earth oxide. The true density value used is the same as that used in the calculation of the primary particle size.

[0252] (Na content (ppm by mass))

[0253] Atomic absorption spectrometry was performed using a Thermo Fisher Scientific CE3300FL.

[0254] (Crystal diameter (nm))

[0255] The crystallite diameter was determined using the Halder-Wagner method based on the distribution pattern obtained under the following X-ray diffraction conditions.

[0256] (X-ray diffraction measurement conditions)

[0257] ·Device: Ultima IV (manufactured by Rigaku Co., Ltd.)

[0258] • Radiation source: CuKα rays

[0259] • Tube voltage: 40kV

[0260] Tube current: 40mA

[0261] • Scanning speed: 2 degrees / min • Step: 0.02 degrees

[0262] • Scanning range: 2θ = 20°~90°

[0263] (Fragmentation evaluation: determination of average particle size)

[0264] Using the Y₂O₃ micropowder obtained above, 45 g of a 10% by mass slurry (dispersion medium: 99.5 vol% ethanol) was prepared and crushed using 240 g of zirconia beads with a diameter of 0.1 mm, at a circumferential speed of 4 m / s, in a bead mill (Apex LABO / A-LABO, effective capacity 80 cc, manufactured by HIROSHIMA METAL & MACHINER). Crushing was stopped at 10-minute intervals, and the average particle size was determined using the following method. The bead milling process ended at the point where the average particle size became larger than the previous measurement value, and also ended at the point of 20 repetitions (A) where the average particle size did not become larger than the previous measurement value in each of the 20th repetitions up to the 20th repetition. The particle size that became smallest due to a maximum of 20 repetitions was set as the minimum average particle size (Dm). Furthermore, the data immediately after crushing was set as the particle size at the end of the bead milling process ("D0" in Table 2).

[0265] (Methods for determining average particle size and polydispersity index)

[0266] The average particle size was measured using an Otsuka Electronics ELSZ-2000ZS instrument after the device determined the concentration to be appropriate. The slurry was diluted with 99.5 vol% ethanol at the dilution ratio described above. The average particle size and polydispersity index were determined according to JIS Z 8828:2019 using the dynamic light scattering method (photon correlation method). The same sample was measured three times, and the average of the three measurements was set as the average particle size. However, if the absolute value of the difference between any measurement and the average of the three measurements exceeded 2% of the average of the three measurements, the result was not used, and three more measurements were performed. The measurements were conducted at 25°C. It should be noted that the polydispersity index shown in Table 2 is the value used for measuring the minimum average particle size (Dm) in the crushing evaluation.

[0267] (Evaluation 7 days after the breakage)

[0268] The slurry, which underwent crushing evaluation as described above, was allowed to stand at room temperature (20°C) for 7 days. The average particle size (D7) after 7 days of standing was determined using the method described above, and the value of "(average particle size after 7 days of crushing (D7) - average particle size immediately after crushing (D0)) / average particle size immediately after crushing (D0) × 100 (%)" was calculated. The results are recorded in Table 2 as "(D7-D0) / D0×100 (%)". In addition, for 20 ml of slurry after 1 week, the average particle size ("D7S" in Table 2) was also measured after irradiation with 40W ultrasound (frequency 40kHz) for 5 minutes.

[0269] In addition, the settling properties after standing for 7 days were evaluated using the following criteria.

[0270] There is a block of particles that can be visually identified at the bottom of the container.

[0271] None: A block at the bottom of the container where particles cannot be visually identified.

[0272] Furthermore, the visible light transmittance (%) after standing for 7 days was determined using the following method.

[0273] (transmittance)

[0274] The transmission spectrum from 350 nm to 800 nm was measured using a visible absorbance spectrophotometer (Hitachi, Ltd. U-3100). Transmittance represents the minimum value within the transmission spectrum from 350 nm to 800 nm. The sample was prepared by adding 0.2 ml of the slurry obtained from the crushing process to 30 ml of the solvent used during crushing (slurry one week after crushing).

[0275] (Example b2)

[0276] The stirring during the mixing of the ammonium bicarbonate aqueous solution and the yttrium nitrate aqueous solution was set to a low stirring speed of 400 rpm. Furthermore, instead of using 10 L of ethanol, the residue was washed with 10 L of 90 vol% ethanol (10 vol% pure water). All other settings were the same as in Example b1.

[0277] (Example b3)

[0278] Instead of using 10L of 90 vol% ethanol, the residue was washed with 10L of 80 vol% ethanol (20 vol% pure water). All other settings were the same as in Example b2.

[0279] (Example b4)

[0280] Instead of using 10L of 90 vol% ethanol, the residue was washed with 10L of 50 vol% ethanol (50 vol% pure water). All other things being equal, the setup was the same as in Example b2.

[0281] (Example b5)

[0282] Instead of a yttrium nitrate aqueous solution (25°C) with a concentration of 50 g / L based on oxides, a ytterbium nitrate aqueous solution (25°C) with a concentration of 50 g / L based on oxides was used. All other settings were the same as in Example b1.

[0283] (Example b6)

[0284] The concentration of the slurry crushed by the bead mill for the [crushing evaluation] was changed from 10% by mass to 4% by mass, and the dispersion medium was changed from ethanol to methanol. Except for these points, the settings were the same as in Example b1.

[0285] (Example b7)

[0286] Instead of a yttrium nitrate aqueous solution (25°C) with a concentration of 50 g / L based on oxides, a dysprosium nitrate aqueous solution (25°C) with a concentration of 50 g / L based on oxides was used. Except for this, the settings were the same as in Example b1.

[0287] (Comparative Example b1)

[0288] The yttrium oxide micro powder obtained in Comparative Example a1 was set as the yttrium oxide micro powder of Comparative Example b1.

[0289] As described above, the powder was observed using a scanning electron microscope (SEM), and the results showed a group of non-agglomerated, uniformly sized spherical particles with a diameter of approximately 100 nm. The primary particle size, calculated from the specific surface area, was also greater than 100 nm, therefore, some of the aforementioned evaluations were not performed.

[0290] (Comparative Example b2)

[0291] The yttrium oxide micropowder prepared in Comparative Example a2 was used as the yttrium oxide micropowder of Comparative Example b2. As described above, the powder was observed using a scanning electron microscope (SEM). The results showed that particles with SEM diameters of approximately 100 nm and 10 nm were mixed together, and particles with uniform SEM diameters were not obtained through low-temperature sintering. The primary particle size calculated from the specific surface area was also greater than 100 nm; therefore, the aforementioned evaluation was not performed.

[0292] (Comparative Example b3)

[0293] The Y₂O₃ prepared in Comparative Example a3 was used as the yttrium oxide micropowder of Comparative Example b3. Various measurements were performed on this powder using the method described in Example b1, and a crushing evaluation was also conducted. The slurry settled due to agglomeration one week after crushing, therefore the agglomeration diameter (“7D”) and transmittance after one week could not be measured. Furthermore, the agglomeration diameter “7DS” after ultrasonic irradiation one week later was not measured.

[0294] (Comparative Example b4)

[0295] The yttrium oxide micropowder prepared in Comparative Example a4 was set as the yttrium oxide micropowder of Comparative Example b4.

[0296] (Comparative Example b5)

[0297] This comparative example is equivalent to US2020 / 0071180A.

[0298] Prepare 20 L of yttrium nitrate aqueous solution with a yttrium ion concentration of 0.05 mol / L. Add 21.1 g of acetylenol-ethylene oxide adduct (SURFYNOL 485, manufactured by Nissin Chemical Industry) to this aqueous solution. Then, add urea in a molar ratio of 15 to the yttrium ions. To carry out the hydrolysis reaction, heat to 95°C and maintain for 90 minutes, then cool to room temperature. During heating, slowly stir the aqueous solution with a stir bar to homogenize the temperature distribution within the container.

[0299] Next, the precipitate was separated from the reaction solution using a centrifuge. Then, to remove undecomposed urea and residual nitrate ions, the recovered solid components were washed with water. The obtained rare earth compound particles were then dried at 55°C for 5 days and subsequently crushed using a dry bead mill. The crushed rare earth compound particles were then calcined at 600°C for 4 hours to obtain yttrium oxide particles. Since the obtained yttrium oxide had a primary particle size of over 100 nm, the aforementioned evaluation was not performed.

[0300]

[0301] As shown in Table 2 above, these are powders containing oxides of at least one rare earth element other than Ce.

[0302] Furthermore, the primary particle size is greater than 10 nm and less than 100 nm, and the pore diameter is greater than 0.005 μm and less than 100 μm, with a pore volume (cm³). 3 / g) multiplied by true density (g / cm³) 3 The obtained value is 3 or higher and 14 or lower.

[0303] The volume (cm³) of a pore with a diameter of 5 nm or more but less than 50 nm. 3 / g) multiplied by true density (g / cm³) 3 The rare earth oxide powders of the embodiments with values ​​of 0 or higher and 2.0 or lower have small particle sizes after crushing and high transmittance after standing for 7 days.

[0304] In contrast, for comparative examples b1, b2, and b5, which are outside the range of initial particle size of 10 nm or more but less than 100 nm, the average particle size after fragmentation increased, resulting in low visible light transmittance after 7 days. Furthermore, the pore volume (cm³) was also higher than 0.005 μm but less than 100 μm. 3 / g) multiplied by true density (g / cm³) 3 Comparative example b4, with a value exceeding 14, also showed an increased average particle size after fragmentation and low transmittance after 7 days. Furthermore, the pore volume (cm³) was determined to be between 5 nm and 50 nm in diameter. 3 / g) multiplied by true density (g / cm³) 3 Comparative Example 3, whose value exceeded 2.0, could not be measured for visible light transmittance due to the sedimentation of the dispersed particles over time.

[0305] Based on the above, the rare earth oxide powder of the present invention can provide oxide powders of rare earth elements other than Ce that can be used to form highly dispersed slurries without the use of dispersants and can stably maintain the transparency of the slurry.

[0306] Industrial availability

[0307] According to the first invention, for rare earth oxides other than Ce, rare earth oxide powders that can be easily dispersed by simple dispersion treatments such as ultrasonic treatment and can form thin films can be provided.

[0308] According to the second invention, micronized powders of oxides of rare earth elements other than Ce can be provided, which can be formulated into highly dispersed slurries and maintain their dispersed state even without the use of dispersants. Such rare earth oxide micronized powders can be crushed to obtain highly dispersed slurries, which, based on their dispersibility, can improve the transmittance of visible light. By improving the transmittance of visible light, the effects of adding rare earth oxides can be utilized and the slurry can be spread in materials requiring transparency. Furthermore, slurries that absorb only the narrow wavelength range characteristic of rare earth ions can be provided. Moreover, if the rare earth oxide powder of the present invention is used, the dispersed state in the slurry can be maintained, thus stably maintaining the transparency of the slurry.

Claims

1. A rare earth oxide powder, which is a powder of an oxide of at least one rare earth element other than Ce. (a) The primary particle size is 10 nm or more and 60 nm or less, satisfying (I) or (II) below; or (b) The primary particle size is 10 nm or more and less than 100 nm, satisfying (III) and (IV) below. (I) The cumulative particle size D at 100% capacity, obtained by ultrasonic dispersion at 40W for 5 minutes and measured using laser diffraction-scattering particle size distribution method. 100 The size is greater than 1 μm and less than 10 μm. (II) The true density of the oxides of the rare earth elements is set to ρ (g / cm³). 3 When the initial bulk density AD is 0, the porosity P is calculated from the initial bulk density AD using the following equation 1. AD (%) and the porosity P calculated from the tapped bulk density TD using the following Equation 2. TD The difference (%) (P) AD -P TD The percentage is between 2.0% and 5.0%. Formula 1: P AD = (1-AD / ρ) × 100 (%) Formula 2: P TD = (1-TD / ρ) × 100 (%) (III) Pore volume (cm³) with a pore diameter of 0.005 μm or more and 100 μm or less. 3 / g) multiplied by true density (g / cm³) 3 The obtained value is 3 or higher and 14 or lower. (IV) Pore volume (cm³) with a pore diameter of 5 nm or more and 50 nm or less 3 / g) multiplied by true density (g / cm³) 3 The resulting value is above 0 and below 2.

0.

2. The rare earth oxide powder according to claim 1, wherein, (a) The primary particle size is 10 nm or more and 60 nm or less, satisfying (I) or (II) above.

3. The rare earth oxide powder according to claim 2, wherein, Satisfy (I).

4. The rare earth oxide powder according to claim 3, wherein, The true density of the rare earth oxides is set to ρ (g / cm³). 3 When the initial bulk density AD is 0, the porosity P is calculated from the initial bulk density AD using the following equation 1. AD (%) is above 90.0% and below 99.0%. Formula 1: P AD = (1-AD / ρ) × 100 (%).

5. The rare earth oxide powder according to claim 3 or 4, wherein, The primary particle size is less than 35nm.

6. The rare earth oxide powder according to claim 3 or 4, wherein, The Zr content is below 100 ppm by mass.

7. The rare earth oxide powder according to claim 3 or 4, wherein, The carbon content is less than 2% by mass.

8. The rare earth oxide powder according to claim 2, wherein, Satisfy (II).

9. The rare earth oxide powder according to claim 8, wherein, The porosity P AD (%) is above 90.0% and below 99.0%.

10. The rare earth oxide powder according to claim 8 or 9, wherein, The cumulative volumetric particle size D at 100% capacity, obtained by ultrasonic dispersion at 40W for 5 minutes and measured using laser diffraction scattering particle size distribution method. 100 The D is between 1μm and 10μm. 100 The cumulative particle size D at 50% of the cumulative volume, determined by the method described above, is compared with the cumulative particle size D obtained by ultrasonic dispersion treatment. 50 The ratio is D 100 / D 50 It must be between 3.0 and 11.

0.

11. The rare earth oxide powder according to claim 1, wherein, (b) The primary particle size is greater than 10 nm and less than 100 nm, satisfying (III) and (IV) above.

12. The rare earth oxide powder according to claim 11, wherein, The Na content is below 100 ppm by mass.

13. The rare earth oxide powder according to claim 11, wherein, The diameter of the microcrystals is greater than 6 nm and less than 25 nm.

14. The rare earth oxide powder according to claim 12, wherein, The diameter of the microcrystals is greater than 6 nm and less than 25 nm.

15. The rare earth oxide powder according to any one of claims 11 to 14, wherein, After mixing rare earth oxide powder with ethanol to prepare an ethanol slurry containing 10% by mass of rare earth oxide powder, the following operation (A) is repeated until the average particle size becomes larger than the previous measurement value, and the minimum average particle size becomes 10 nm or more and 150 nm or less. (A): Zirconia beads with a diameter of 0.1 mm were used to mill the slurry for 10 minutes. The average particle size was then determined by dynamic light scattering. The bead milling process was terminated when the average particle size became larger than the previous measurement value. It was also terminated at the 20th repetition (A) if the average particle size did not become larger than the previous measurement value in any of the repetitions from the 2nd to the 20th. The term "minimum average particle size" here refers to the minimum average particle size measured by sampling during each of the processes described in (A) using dynamic light scattering.

16. The rare earth oxide powder according to claim 15, wherein, The calculated value of the following formula is above -15% and below 25%. Formula: (Average particle size after 7 days of crushing - Average particle size immediately after crushing) / Average particle size immediately after crushing × 100 (%).

17. The rare earth oxide powder according to claim 15, wherein, The minimum average particle size obtained by the bead milling process is 50 nm or more and 90 nm or less.

18. The rare earth oxide powder according to claim 16, wherein, The minimum average particle size obtained by the bead milling process is 50 nm or more and 90 nm or less.

19. A method for manufacturing a slurry, wherein, The rare earth oxide powder described in any one of claims 11 or 12 is wet-crushed using a solvent.

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