Zirconia-based composite oxide powder, and method for producing zirconia-based composite oxide powder

Abstract

To provide a zirconia-based composite oxide powder with small particle size, small pore volume, and porous properties. [Solution] The material contains zirconia and an oxide of a rare earth element, with a zirconia content of 50% to 95% by weight, and the pore distribution calculated from the scattering curve measured by small-angle X-ray scattering has a monomodal distribution in the range of 1 nm to 15 nm, and the particle size D in the particle size distribution measured by laser diffraction-scattering is 50 The particle size is between 0.05 μm and less than 1.0 μm, and the tap density is 1.0 g / cm³. 3 More than 1.7g / cm 3 The following is a zirconia-based composite oxide powder whose crystal system, as identified by powder X-ray diffraction, is either tetragonal, cubic, or both.

Description

Technical Field

[0001] The present invention relates to a zirconia-based composite oxide powder and a method for producing the zirconia-based composite oxide powder.

Background Art

[0002] Currently, in gasoline engines, the direct injection method is the mainstream. For the collection and purification of particulate matter (PM), an exhaust gas purification catalyst in which a three-way catalyst (TWC) function is combined with a gasoline particulate filter (GPF) is used. The TWC is supported on and inside the GPF. As the TWC, a zirconia-based composite oxide supporting noble metal fine particles such as Pt, Rh, Pd, etc. is often used.

[0003] Particle diameter D 50 As zirconia-based composite oxides having a particle diameter D of 1 μm or less, Patent Documents 1 to 4 are disclosed.

[0004] Patent Document 1 discloses zirconia fine powder containing one or more of yttria, calcia, magnesia, and ceria as a stabilizer, the average particle diameter of the zirconia fine powder being less than 0.5 μm, and the proportion of particles at 1 μm in the cumulative curve of the particle size distribution being 100% (Claim 1).

[0005] Patent Document 2 discloses zirconia powder containing a stabilizer, having a specific surface area of 20 m 2 / g or more and 60 m 2 / g or less, a particle diameter D 50 being 0.1 μm or more and 0.7 μm or less, in the range of 10 nm or more and 200 nm or less in the pore distribution based on the mercury intrusion method, the peak top diameter of the pore volume distribution being 20 nm or more and 85 nm or less, the pore volume being 0.2 ml / g or more and less than 0.5 ml / g, and the pore distribution width being 40 nm or more and 105 nm or less (Claim 1).

[0006] Patent Document 3 discloses zirconia powder containing a stabilizer, the stabilizer being CaO, Y2O3, Er2O3, or Yb2O3, and having a specific surface area of 10 m2 50 m or more per g 2 is less than or equal to per g, and the particle diameter D 50 is a zirconia powder having a particle diameter of 0.1 μm or more and 0.7 μm or less (Claim 1, Claim 2).

[0007] In Patent Document 4, in the pore diameter distribution determined by the mercury intrusion method, when the pore volume in the range of pore diameter X nm or more and less than Y nm is Vp X-Y [(Vp 10-100 ) / (Vp 100-6000 )] satisfies the following formula [1], and the particle diameter D 50 after the crushing treatment is a zirconia-based powder material having a particle diameter of 0.05 μm or more and 1.5 μm or less (Claim 1, Claim 7). Formula [1] 0.4 ≤ [(Vp 10-100 ) / (Vp 100-6000 )] ≤ 1

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0009] <0000The zirconia-based composite oxide required for support within the GPF is a porous powder with small particle size and small pore volume. Reducing the particle size of the zirconia-based composite oxide makes it possible to suitably support it within the GPF. Furthermore, making the zirconia-based composite oxide a porous material increases the frequency of contact with exhaust gas. In addition, since there is an upper limit to the amount of zirconia-based composite oxide that can be supported in the GPF, reducing the pore volume of the zirconia-based composite oxide allows for the support of a larger amount of zirconia-based composite oxide in the GPF.

[0010] However, although the zirconia fine powder in Patent Document 1 is said to have 100% of its particle size distribution at 1 μm in the cumulative curve, its specific surface area is 15 m². 2 Because the value is small at / g (see Examples), it is considered that the powder contains a certain proportion of non-porous particles that do not have pores.

[0011] Furthermore, as is clear from Figure 2 of Patent Document 2, the zirconia powder described in Patent Document 2 does not have a peak in the pore distribution range of 1 nm to 15 nm, and therefore cannot be said to be porous.

[0012] Furthermore, as is clear from Figures 2 and 3 of Patent Document 3, the zirconia powder described in Patent Document 3 does not have a peak in the pore distribution range of 1 nm to 15 nm, and therefore cannot be said to be porous.

[0013] Furthermore, Patent Document 4 states that the zirconia-based powder material has excellent crushability because the pore volume derived from tertiary particle aggregates of 100 to 6000 nm is in a constant ratio to the pore volume derived from secondary particle aggregates of 10 to 100 nm (paragraph

[0010] ). In other words, the zirconia-based powder material of Patent Document 4 is a bulky powder with relatively large pores that are easily crushed starting from the pores, and therefore has a large pore volume.

[0014] The present invention has been made in view of the above-mentioned problems, and its objective is to provide a zirconia-based composite oxide powder with small particle size, small pore volume, and porous properties. Furthermore, it aims to provide a method for producing such a zirconia-based composite oxide powder. [Means for solving the problem]

[0015] The inventors of this invention conducted intensive research to address the aforementioned problem. As a result, they succeeded in producing a porous zirconia-based composite oxide powder with small particle size and small pore volume, thus completing the present invention.

[0016] In other words, the present invention provides the following: [1] Zirconia and Oxides of rare earth elements and Includes, The zirconia content is 50% by weight or more and 95% by weight or less. In the pore distribution calculated from the scattering curve measured by small-angle X-ray scattering, a monomodal distribution was found in the range of 1 nm to 15 nm. Particle size D in the particle size distribution measured by laser diffraction / scattering method 50 The particle size is 0.05 μm or more and less than 1.0 μm. Tap density is 1.0 g / cm³ 3 More than 1.7g / cm 3 The following: A zirconia-based composite oxide powder characterized in that the crystal system identified by powder X-ray diffraction is either tetragonal, cubic, or both.

[0017] According to the above configuration, it contains zirconia and an oxide of a rare earth element. Conventionally, in composite oxides of zirconia and an oxide of a rare earth element, aggregation tends to occur during manufacturing, resulting in fine particles (particle size D 50 It was difficult to manufacture (small particles). However, in the present invention, a composite oxide containing zirconia and an oxide of a rare earth element is produced, with a particle size D 50We were able to obtain a zirconia-based composite oxide powder with a particle size of less than 1.0 μm. Furthermore, the above configuration, which includes zirconia and an oxide of a rare earth element, is suitable for catalytic applications.

[0018] Furthermore, according to the above configuration, the tap density is 1.0 g / cm³. 3 Therefore, the pore volume can be said to be sufficiently small. As will be described later, although the zirconia-based composite oxide powder of the present invention is porous, the pore diameter is small (having a monomodal distribution in the range of 1 nm to 15 nm), so although it is porous, the pore volume is small.

[0019] Furthermore, according to the above configuration, the pore distribution calculated from the scattering curve measured by small-angle X-ray scattering has a monomodal distribution in the range of 1 nm to 15 nm. Particle size D 50 In particles with a diameter of less than 1.0 μm, the pore distribution has a monomodal distribution in the range of 1 nm to 15 nm. Therefore, it can be said that uniform pores exist inside the particle (secondary particle), i.e., the particle is porous. For example, as shown in Comparative Example 2 in Figure 2, if the pore distribution has two peaks in the range of 1 nm to 15 nm, that is, if it is bimodal rather than monomodal, then such a pore distribution is characteristic of wet-milled particles. The peak around 14 nm in Figure 2 originates from the pores inside the particles (secondary particles), while the peak around 3 nm in Figure 2 originates from the particles produced by wet milling (the particles themselves that do not have pores). Therefore, if the pore distribution in the range of 1 nm to 15 nm is bimodal, the pores inside the particles (secondary particles) are few, and it cannot be said that the material is porous. Furthermore, "having a monomodal distribution in the range of 1 nm to 15 nm" means that the pore distribution curve has only one peak in the range of 1 nm to 15 nm.

[0020] When zirconia contains a certain amount or more of rare earth elements, it does not contain monoclinic crystals, but only tetragonal and cubic crystals. With the above configuration, the crystal system identified by powder X-ray diffraction is either tetragonal, cubic, or both, and therefore it contains rare earth elements and is suitable for catalytic applications.

[0021] The zirconia fine powder described in Patent Document 1 is manufactured by wet grinding, and therefore, even if it has a peak in the pore distribution range of 1 nm to 15 nm, there is a high probability that it will have two peaks, and it cannot be said that it has a monomodal distribution in the range of 1 nm to 15 nm. Furthermore, the zirconia powders described in Patent Documents 2 and 3 do not have any peaks in the pore distribution range of 1 nm to 15 nm, and therefore cannot be said to be porous.

[0022] As described above, the objective is to provide a zirconia-based composite oxide powder that is porous, with small particle size and small pore volume, while being a composite oxide containing zirconia and an oxide of a rare earth element.

[0023] Furthermore, the present invention provides the following: [2] The zirconia-based composite oxide powder according to [1], having pores within a single particle.

[0024] Whether or not a single particle contains pores is determined by the following procedure a to f using HAADF-STEM imaging. In HAADF-STEM images, detected signals are converted into luminance values ​​in 256 steps from 0 to 255 per pixel, forming a single image. Empty spaces appear dark (low luminance value), while areas containing matter appear bright (high luminance value). The luminance value of areas containing matter correlates with the electron density of that area; the higher the electron density, the brighter the area appears. For materials composed of the same constituent elements, the electron density is the same as the material density. If contrast is observed within a particle, dark areas indicate areas with low material density and can be considered pores. The presence or absence of pores can be confirmed, for example, using image analysis software such as ImageJ, by following the procedure below. <Instructions> a. Capture HAADF-STEM images at magnification of 2 million or more. b. Convert to grayscale (8-bit) using image analysis software. c. The region where the brightness value, expressed in 256 levels from 0 to 255, is 80 or higher is determined to be a region where particles are present, and one spherical particle (single particle) without overlapping particles is extracted. d. Within the extracted particles, regions with a long axis of 1 nm or more where the brightness value is 40% or more lower than the surrounding area are defined as pores, and their presence or absence is confirmed. e. Repeat the process until the cumulative number of particles checked for the presence or absence of pores reaches 100. f. If it is confirmed that all particles have pores according to the procedures a to e above, it is determined that "a single particle has pores." In HAADF-STEM image observation using the above procedure, if pores are present within the particles, it means that the pores in the zirconia-based composite oxide powder are not voids (interparticle gaps) formed between particles, but rather voids inherent in the particles themselves.

[0025] Furthermore, the present invention provides the following: [3] Particle diameter D 50 The zirconia-based composite oxide powder according to [1] or [2], characterized in that the particle size is 0.08 μm or more and 0.85 μm or less.

[0026] The particle size D 50 If the particle size is 0.85 μm or less, it can be said that the particle size (the particle size of secondary particles) is smaller.

[0027] Furthermore, the present invention provides the following: [4] Specific surface area of ​​30 m 2 / g or more 90m 2 A zirconia-based composite oxide powder according to any one of the above [1] to [3], characterized in that it is less than / g.

[0028] Specific surface area is 30 m 2 A value of 90 m² or more indicates greater porousness. 2If the value is less than / g, the pore volume can be further reduced.

[0029] Furthermore, the present invention provides the following: [5] The oxide of the rare earth element is one or more selected from the group consisting of yttrium oxide, lanthanum oxide, cerium oxide, neodymium oxide, and praseodymium oxide. The zirconia-based composite oxide powder according to any one of [1] to [4] above, characterized in that the content of the oxide of the rare earth element is 5% by weight or more and 50% by weight or less.

[0030] The oxide of the rare earth element is more suitable for catalytic use if it is one or more selected from the group consisting of yttrium oxide, lanthanum oxide, cerium oxide, neodymium oxide, and praseodymium oxide, and the content of the oxide of the rare earth element is 5% by weight or more and 50% by weight or less.

[0031] Furthermore, the present invention provides the following: [6] Step 1 involves adjusting the pH of an aqueous solution of zirconium oxychloride to make a suspension, Step 2 involves lowering the pH of the suspension to a level lower than that of step 1 and heating it to obtain a hydrated ZrO2 microcrystalline nucleus slurry. Step 3 involves adding a flocculant to the hydrated ZrO2 microcrystalline nucleus slurry to obtain a hydrated ZrO2-containing basic zirconium sulfate slurry, Step 4 involves adding a surface modifier to the hydrated ZrO2-containing basic zirconium sulfate slurry, Step 5 involves adding a raw material salt containing rare earth elements, Step 6 involves neutralizing with a base to obtain a precipitate, Step 7 to obtain a zirconia-based composite oxide by heat-treating the aforementioned precipitate. A method for producing a zirconia-based composite oxide powder according to any one of the above [1] to [5], characterized by containing [1].

[0032] According to the above configuration, the pH of the suspension is made lower than that of step 1, and a hydrated ZrO2 microcrystalline nucleus slurry is obtained by heating (step 2). As a result, although porous, particles with small pore volume and peaks in the pore distribution range of 1 nm to 15 nm can be obtained.

[0033] Furthermore, according to the above configuration, a flocculant is added to the hydrated ZrO2 microcrystalline nucleus slurry to obtain a hydrated ZrO2-containing basic zirconium sulfate slurry (step 3), resulting in secondary particles with strong aggregation of primary particles.

[0034] Furthermore, according to the above configuration, a surface modifier is added to the hydrated ZrO2-containing basic zirconium sulfate slurry, and then rare earth elements are added (step 5), which suppresses the aggregation of secondary particles during firing (step 7).

[0035] As described above, the above configuration yields a zirconia-based composite oxide powder with small particle size, small pore volume, and porous structure. [Effects of the Invention]

[0036] According to the present invention, it is possible to provide a zirconia-based composite oxide powder with small particle size, small pore volume, and porous properties. Furthermore, it is possible to provide a method for producing such a zirconia-based composite oxide powder. [Brief explanation of the drawing]

[0037] [Figure 1] These are the pore distributions for Example 1 and Example 2. [Figure 2] These are the pore size distributions for Comparative Example 1 and Comparative Example 2. [Figure 3] This is a HAADF-STEM image from Example 1. [Figure 4] This is a HAADF-STEM image from Example 2. [Figure 5] This is the HAADF-STEM image of Comparative Example 1. [Modes for carrying out the invention]

[0038] Embodiments of the present invention will be described below. However, the present invention is not limited to these embodiments. In this specification, zirconia-based composite oxide powder is a general term and contains impurity metal compounds in an oxide equivalent of 10% by mass or less, including hafnium. In this specification, the expressions "contains" and "includes" include the concepts of "contains," "includes," "substantially consists of," and "consists only of."

[0039] The maximum and minimum values ​​of the content of each component shown below are, independently of the content of other components, the preferred minimum and preferred maximum values ​​of the present invention. Furthermore, the maximum and minimum values ​​of the various parameters (measured values, etc.) shown below are, independently of the content (composition) of each component, the preferred minimum and maximum values ​​of the present invention.

[0040] [Zirconia-based composite oxide powder] The zirconia-based composite oxide powder according to this embodiment is Zirconia and Oxides of rare earth elements and Includes, The zirconia content is 50% by weight or more and 95% by weight or less. In the pore distribution calculated from the scattering curve measured by small-angle X-ray scattering, a monomodal distribution was found in the range of 1 nm to 15 nm. Particle size D in the particle size distribution measured by laser diffraction / scattering method 50 The particle size is 0.05 μm or more and less than 1.0 μm. Tap density is 1.0 g / cm³ 3 More than 1.7g / cm 3 The following: The crystal system identified by powder X-ray diffraction is either tetragonal, cubic, or both.

[0041] As described above, the zirconia-based composite oxide powder according to this embodiment contains zirconia and an oxide of a rare earth element. The zirconia-based composite oxide powder may consist only of zirconia and an oxide of a rare earth element, or it may contain other components as long as it achieves the effects of the present invention (as long as it does not significantly hinder the effects of the present invention). Conventionally, composite oxides of zirconia and rare earth element oxides tend to aggregate during manufacturing, resulting in fine particles (particle size D 50 It was difficult to manufacture (small particles). However, in this embodiment, although it is a composite oxide containing zirconia and an oxide of a rare earth element, the particle size D 50 We were able to obtain a zirconia-based composite oxide powder with a particle size of less than 1.0 μm. The zirconia-based composite oxide powder according to this embodiment contains zirconia and an oxide of a rare earth element, and is therefore suitable for catalytic applications.

[0042] The zirconia content is 50% by weight or more and 95% by weight or less of the total zirconia-based composite oxide powder. Since the zirconia content is between 50% and 95% by weight, it is suitable for catalytic applications.

[0043] The zirconia content is preferably 52% by mass or more, and more preferably 54% by mass or more, relative to the total zirconia-based composite oxide powder. The zirconia content is preferably 94% by mass or less, and more preferably 93% by mass or less, relative to the total zirconia-based composite oxide powder. The zirconia content is preferably 52% by mass or more and 94% by mass or less, and more preferably 54% by mass or more and 94% by mass or less, relative to the total zirconia-based composite oxide powder.

[0044] The content of the rare earth element oxide is preferably 5% by weight or more and 50% by weight or less relative to the total zirconia-based composite oxide powder. A rare earth element oxide content of 5% by weight or more and 50% by weight or less is more suitable for catalytic applications.

[0045] The content of the rare earth element oxide is more preferably 6% by mass or more, and even more preferably 7% by mass or more, relative to the total zirconia-based composite oxide powder. The content of the rare earth element oxide is more preferably 48% by mass or less, and even more preferably 46% by mass or less, relative to the total zirconia-based composite oxide powder. The content of the rare earth element oxide is more preferably 6% by mass or more and 48% by mass or less, and even more preferably 7% by mass or more and 46% by mass or less, relative to the total zirconia-based composite oxide powder.

[0046] The zirconia-based composite oxide powder preferably contains one or more rare earth element oxides selected from the group consisting of yttrium oxide, lanthanum oxide, cerium oxide, neodymium oxide, and praseodymium oxide. The oxide of the rare earth element is more suitable for catalytic use if it is one or more selected from the group consisting of yttrium oxide, lanthanum oxide, cerium oxide, neodymium oxide, and praseodymium oxide.

[0047] The total content of zirconia and the oxide of the rare earth element is preferably 85% by mass or more relative to the total amount of the zirconia-based composite oxide powder. The material is suitable for catalytic use if the total content of zirconia and the oxide of the rare earth element is 85% by mass or more.

[0048] The total content of zirconia and the oxide of the rare earth element is more preferably 88% by mass or more, and even more preferably 90% by mass or more, relative to the zirconia-based composite oxide powder. The total content of zirconia and the oxide of the rare earth element may be 100% by mass, 99% by mass or less, or 98% by mass or less, relative to the zirconia-based composite oxide powder. The total content of zirconia and the oxide of the rare earth element is more preferably 88% by mass or more and 100% by mass or less, and even more preferably 90% by mass or more and 100% by mass or less, relative to the zirconia-based composite oxide powder.

[0049] The zirconia-based composite oxide powder may contain one or more elements selected from the group consisting of (A) oxides of at least one element selected from the group consisting of In, Si, Sn, Bi, P, and Zn, (B) transition metal oxides (excluding oxides of rare earth elements and oxides of noble metal elements), and (C) alkaline earth metal oxides. These components (A) to (C) will also be referred to as "other oxides" below.

[0050] Examples of the transition metal oxide include one or more oxides selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Ta, and W.

[0051] Examples of the alkaline earth metal oxide include one or more oxides selected from the group consisting of Mg, Ca, Sr, and Ba.

[0052] If the zirconia-based composite oxide powder contains the other oxides, the content of the other oxides is preferably 0.5% by mass or more and 25% by mass or less, relative to the total amount of the zirconia-based composite oxide powder.

[0053] The content of the aforementioned other oxides is more preferably 1% by mass or more, and even more preferably 1.5% by mass or more, relative to the total zirconia-based composite oxide powder. The content of the aforementioned other oxides is more preferably 15% by mass or less, even more preferably 10% by mass or less, and particularly preferably 5% by mass or less, relative to the total zirconia-based composite oxide powder. The content of the aforementioned other oxides is more preferably 1% by mass or more and 15% by mass or less, and even more preferably 1.5% by mass or more and 10% by mass or less, relative to the total zirconia-based composite oxide powder.

[0054] The zirconia-based composite oxide powder has a particle size D in its particle size distribution, as measured by laser diffraction and scattering. 50 The particle size is 0.05 μm or more and less than 1.0 μm. 50Since the particle size is less than 1.0 μm, it can be said that the particle size is small, making it suitable for catalytic applications.

[0055] The particle size D 50 The particle size is preferably 0.90 μm or less, and more preferably 0.85 μm or less. The particle size D 50 There are no specific restrictions, but for example, they should be 0.07 μm or larger, 0.08 μm or larger, etc. The particle size D 50 The particle size is preferably 0.07 μm or more and 0.90 μm or less, and more preferably 0.08 μm or more and 0.85 μm or less.

[0056] The zirconia-based composite oxide powder has a particle size D in its particle size distribution, as measured by laser diffraction and scattering. 90 It is preferable that the particle size is between 0.08 μm and 1.6 μm. 90 If the particle size is 1.6 μm or less, it means that there are no large particles and the overall particle size is small, making it suitable for catalytic applications.

[0057] The particle size D 90 The particle size is more preferably 1.5 μm or less, and even more preferably 1.4 μm or less. The particle size D 90 There are no specific restrictions, but for example, they could be 0.1 μm or larger, 0.11 μm or larger, etc. The particle size D 90 The particle size is more preferably 0.1 μm to 1.5 μm, and even more preferably 0.11 μm to 1.4 μm.

[0058] The particle size D 50 , the particle size D 90 This is a value obtained by the method described in the example.

[0059] The zirconia-based composite oxide powder has a monomodal pore distribution in the range of 1 nm to 15 nm, as calculated from the scattering curve measured by small-angle X-ray scattering. The zirconia-based composite oxide powder has a particle size of D 50The particles are less than 1.0 μm in diameter, and furthermore, they have a monomodal distribution of pores in the range of 1 nm to 15 nm. Therefore, uniform pores exist inside the particles (secondary particles), meaning they are porous.

[0060] Furthermore, the zirconia-based composite oxide powder only needs to have a monomodal pore distribution in the range of 1 nm to 15 nm in the scattering curve measured by small-angle X-ray scattering, and may or may not have a peak in the range of over 15 nm and up to 40 nm. From the viewpoint of further reducing the pore volume, it is preferable that there is no peak in the range of over 15 nm and up to 40 nm.

[0061] The method for determining the pore distribution is as described in the examples.

[0062] Preferably, the zirconia-based composite oxide powder does not have pores in the range exceeding 40 nm in its pore distribution.

[0063] The zirconia-based composite oxide powder has a tap density of 1.0 g / cm³. 3 More than 1.7g / cm 3 The following is the result: Tap density is 1.0 g / cm³. 3 Therefore, the pore volume can be said to be sufficiently small. Furthermore, the tap density is 1.7 g / cm³. 3 Therefore, it can be said that these are porous particles.

[0064] The tap density is preferably 1.03 g / cm³. 3 More preferably 1.05 g / cm³ 3 That's all. The tap density is preferably 1.69 g / cm³. 3 More preferably, 1.68 g / cm³ 3 The following applies: The tap density is preferably 1.03 g / cm³. 3 More than 1.69g / cm 3 More preferably, 1.05 g / cm³ 3 More than 1.68g / cm 3 The following applies:

[0065] The tap density is a value obtained by the method described in the example.

[0066] The zirconia-based composite oxide powder has a bulk density of 0.5 g / cm³. 3 More than 1.2g / cm 3 Preferably, the bulk density is 0.5 g / cm³. 3 Based on the above, the pore volume can be said to be sufficiently small. Furthermore, the bulk density is 1.2 g / cm³. 3 The following conditions indicate that the particle is a porous material.

[0067] The bulk density is more preferably 0.52 g / cm³. 3 More preferably 0.54 g / cm³ 3 That's all. The bulk density is more preferably 1.1 g / cm³. 3 More preferably, 1.0 g / cm³ 3 The following applies: The bulk density is more preferably 0.52 g / cm³. 3 More than 1.1g / cm 3 More preferably, 0.54 g / cm³ 3 More than 1.0g / cm 3 The following applies:

[0068] The bulk density is the value obtained by the method described in the example.

[0069] The zirconia-based composite oxide powder has a crystal system identified by powder X-ray diffraction as either tetragonal, cubic, or both. Zirconia, when containing a certain amount or more of rare earth elements, does not exist in monoclinic form, but only in tetragonal and cubic crystal structures. Because the crystal system identified by powder X-ray diffraction is either tetragonal, cubic, or both, it contains rare earth elements and is suitable for catalytic applications.

[0070] The zirconia-based composite oxide powder has a specific surface area of ​​30 m². 2 / g or more 90m 2It is preferable that the amount be less than / g. Specific surface area is 30 m 2 A value of 90 m² or more indicates greater porousness. 2 If the value is less than / g, the pore volume can be further reduced.

[0071] The specific surface area is more preferably 32 m². 2 / g or more, more preferably 34m 2 It is 1 / g or more. The specific surface area is more preferably 85 m². 2 / g or less, more preferably 82m 2 It is less than / g. The specific surface area is more preferably 32 m². 2 / g or more 85m 2 / g or less, more preferably 34m 2 / g or more 82m 2 It is less than / g.

[0072] The specific surface area is a value obtained by the method described in the example.

[0073] The zirconia-based composite oxide powder preferably has pores within a single particle. Whether or not a single particle has pores is determined by the following procedure a to f using HAADF-STEM imaging. <Instructions> a. Capture HAADF-STEM images at magnification of 2 million or more. b. Convert to grayscale (8-bit) using image analysis software. c. The region where the brightness value, expressed in 256 levels from 0 to 255, is 80 or higher is determined to be a region where particles are present, and one spherical particle with no overlapping particles is extracted. d. Within the extracted particles, regions with a long axis of 1 nm or more where the brightness value is 40% or more lower than the surrounding area are defined as pores, and their presence or absence is confirmed. e. Repeat the process until the cumulative number of particles checked for the presence or absence of pores reaches 100. f. If it is confirmed that all particles have pores according to the procedures a to e above, then it is determined that the particles have pores. In HAADF-STEM image observation using the above procedure, if pores are present within the particles, it means that the pores in the zirconia-based composite oxide powder are not voids (interparticle gaps) formed between particles, but rather voids inherent in the particles themselves.

[0074] When the zirconia-based composite oxide powder is used as a catalyst support for an exhaust gas purification catalyst, the metal to be supported is not particularly limited, but examples include Pt, Pd, Rh, etc.

[0075] [Method for producing zirconia-based composite oxide powder] The following describes an example of a method for producing zirconia-based composite oxide powder. However, the method for producing zirconia-based composite oxide powder according to the present invention is not limited to the following examples.

[0076] The method for producing the zirconia-based composite oxide powder according to this embodiment is as follows: Step 1 involves adjusting the pH of an aqueous zirconium oxychloride solution to form a suspension, Step 2 involves lowering the pH of the suspension to a level lower than that of step 1 and heating it to obtain a hydrated ZrO2 microcrystalline nucleus slurry. Step 3 involves adding a flocculant to the hydrated ZrO2 microcrystalline nucleus slurry to obtain a hydrated ZrO2-containing basic zirconium sulfate slurry, Step 4 involves adding a surface modifier to the hydrated ZrO2-containing basic zirconium sulfate slurry, Step 5 involves adding a raw material salt containing rare earth elements, Step 6 involves neutralizing with a base to obtain a precipitate, Step 7 to obtain a zirconia-based composite oxide by heat-treating the aforementioned precipitate. Includes.

[0077] The following describes each step in the method for producing the zirconia-based composite oxide powder according to this embodiment.

[0078] First, adjust the pH of the zirconium oxychloride aqueous solution to make a suspension (Step 1).

[0079] The concentration of the aforementioned zirconium oxychloride aqueous solution is such that the ZrO2 concentration is 2% by weight or more. Any substance within the range of 15% by weight or less should be used.

[0080] In step 1, it is preferable to adjust the pH to between 2 and 7.

[0081] Since the pH of an aqueous solution of zirconium oxychloride after dissolving zirconium oxychloride in water is usually less than 2, the pH can be adjusted to 2 or higher by adding a base to the aqueous solution of zirconium oxychloride.

[0082] In step 1, it is preferable to adjust the pH to 2.5 or higher, and even more preferably 2.7 or higher. In step 1, the pH is preferably adjusted to 6.5 or lower, and even more preferably to 6 or lower. In step 1, it is preferable to adjust the pH to more preferably 2.5 or more and 6.5 or less, and even more preferably 2.7 or more and 6 or less.

[0083] Examples of the aforementioned base include alkali hydroxides such as sodium hydroxide and potassium hydroxide, and aqueous ammonia. Among these, sodium hydroxide (aqueous solution of sodium hydroxide) is preferred from the viewpoint of its strength of basicity and ease of availability.

[0084] In step 1, by adjusting the pH to 2 or higher and 7 or lower, the zirconium salt dissolved in the aqueous solution can be suitably precipitated as zirconium hydroxide, and a suitable suspension of zirconium hydroxide can be obtained. Note that the zirconium hydroxide in the suspension is amorphous and not crystalline. If the pH is increased too much in step 1 (for example, to 8 or higher), the salt concentration may become too high when acid is added in a later step (step 2), potentially hindering the reaction. For example, if a large amount of sodium hydroxide solution is used to adjust the pH in step 1, and then a large amount of hydrochloric acid is added in step 2, the concentration of NaCl will become too high, potentially hindering the reaction.

[0085] Next, the pH of the suspension is reduced to a lower level than in step 1, and heating is performed to obtain a hydrated ZrO2 microcrystalline nucleus slurry (step 2).

[0086] In step 2, the pH of the suspension is not particularly limited as long as it is lower than that of step 1, but it is preferable to adjust it to a value between 1 and 1.5. By adjusting the pH to between 1 and 1.5, a suitable hydrated ZrO2 microcrystalline nucleus slurry can be obtained. That is, by setting the pH to a value near the boundary where zirconium hydroxide can no longer dissolve in aqueous solution, a suitable hydrated ZrO2 microcrystalline nucleus slurry can be obtained. If the pH is made too low, precipitation may occur all at once, and amorphous material may be formed instead of hydrated ZrO2 crystal nuclei.

[0087] In step 2, it is preferable to adjust the pH to 1.1 or higher, and even more preferably to 1.15 or higher. In step 2, it is preferable to adjust the pH to 1.4 or less, and even more preferably to 1.35 or less. In step 2, it is preferable to adjust the pH to more preferably 1.1 or more and 1.4 or less, and even more preferably 1.15 or more and 1.35 or less.

[0088] In step 2, the heating temperature is preferably between 90°C and 120°C. By setting the heating temperature to 90°C or higher and 120°C or lower, a suitable slurry of hydrated ZrO2 microcrystalline nuclei can be obtained.

[0089] The heating temperature in step 2 is more preferably 95°C or higher, and even more preferably 98°C or higher. The heating temperature in step 2 is more preferably 115°C or lower, and even more preferably 110°C or lower. The heating temperature in step 2 is more preferably 95°C to 115°C, and even more preferably 98°C to 110°C.

[0090] In step 2, the heating time is preferably between 140 hours and 200 hours. By setting the heating time to 140 hours or more and 200 hours or less, a suitable hydrated ZrO2 microcrystalline nucleus slurry can be obtained.

[0091] The heating time in step 2 is more preferably 150 hours or more, and even more preferably 155 hours or more. The heating time in step 2 is more preferably 190 hours or less, and even more preferably 185 hours or less. The heating time in step 2 is more preferably 150 hours or more and 190 hours or less, and even more preferably 155 hours or more and 185 hours or less.

[0092] In step 2, the pH of the suspension is made lower than in step 1, and by heating, a hydrated ZrO2 microcrystalline nucleus slurry is obtained. This allows for the production of porous particles with small pore volumes, where the pore distribution peaks in the range of 1 nm to 15 nm.

[0093] Afterward, it may be cooled as needed (for example, to room temperature (10°C to 30°C)).

[0094] Next, a flocculant is added to the hydrated ZrO2 microcrystalline nucleus slurry to obtain a hydrated ZrO2-containing basic zirconium sulfate slurry (step 3). By adding a flocculant to the aforementioned hydrated ZrO2 microcrystalline nucleus slurry, a hydrated ZrO2-containing basic zirconium sulfate slurry is obtained, resulting in secondary particles with strong aggregation of primary particles.

[0095] The aforementioned flocculant is not particularly limited as long as it has a negative charge, can neutralize and flocce positively charged particles that repel each other, and can adsorb to hydrated ZrO2. Examples include sodium sulfate, potassium sulfate, and aluminum sulfate (aluminum sulfate).

[0096] From the viewpoint of impurities, sodium sulfate is preferred as the type of flocculant. The method of addition is not particularly limited, but examples include addition in solid form or liquid form. The amount added is preferably 0.05 to 1.0 by weight relative to ZrO2, and more preferably 0.1 to 0.8 by weight.

[0097] Afterward, it may be cooled as needed (for example, to room temperature (10°C to 30°C)).

[0098] Next, a surface modifier is added to the hydrated ZrO2-containing basic zirconium sulfate slurry (step 4). By adding a surface modifier to a hydrated ZrO2-containing basic zirconium sulfate slurry, and then adding rare earth elements (step 5), the aggregation of secondary particles during calcination (step 7) can be suppressed. As a result, there are fewer aggregates of secondary particles (tertiary particles), and the material can remain almost entirely in the secondary particle state.

[0099] Examples of the surface modifiers include oxalates, citrates, succinates, and sulfates. From the viewpoint of impurities, sodium oxalate and sodium citrate are preferred.

[0100] The amount of the surface modifier added is preferably 0.1 to 0.8 by weight relative to ZrO2, and more preferably 0.2 to 0.7 by weight.

[0101] Next, raw material salts containing rare earth elements are added (step 5).

[0102] The aforementioned raw material salt is not particularly limited, but examples include nitrates, chlorides, acetates, and hydrates thereof of rare earth elements.

[0103] Next, the solution is neutralized with a base to obtain a precipitate (step 6). Neutralization generates a precursor precipitate of zirconium-containing hydroxide. The aforementioned base is not limited to caustic soda, sodium carbonate, ammonia, hydrazine ammonium bicarbonate, etc. The concentration of the base is not particularly limited, but it is usually diluted with water and a concentration of 5-30% is used.

[0104] Neutralization is carried out until the pH is preferably between 9 and 14, more preferably between 10 and 14. This allows for the suitable acquisition of a zirconium-containing hydroxide precursor (precipitate).

[0105] After neutralization, if necessary, the precursor precipitate may be separated into solid and liquid components and washed.

[0106] Next, the precursor precipitate is heat-treated to obtain a zirconia-based composite oxide (step 7).

[0107] The temperature of the heat treatment is preferably 400°C or higher, and more preferably 500°C or higher. The temperature of the heat treatment is preferably 1000°C or lower, and more preferably 900°C or lower. The temperature of the heat treatment is preferably 400°C to 1000°C, and more preferably 500°C to 900°C.

[0108] The duration of the heat treatment is preferably 2 hours or more, and more preferably 3 hours or more. The duration of the heat treatment is preferably 10 hours or less, and more preferably 9 hours or less. The duration of the heat treatment is preferably 2 hours or more and 10 hours or less, and more preferably 3 hours or more and 9 hours or less.

[0109] The atmosphere for the heat treatment is not particularly limited and may be air, an inert gas (e.g., nitrogen), etc.

[0110] The heat treatment can be carried out, for example, in an electric furnace.

[0111] As a result, a zirconia-based composite oxide can be obtained.

[0112] Furthermore, the obtained zirconia-based composite oxide may be crushed if necessary. Note that "crushing" is an operation that applies a separating force to the aggregate of particles to reduce the size of tertiary particles (an operation that separates them into secondary particles), and is an operation that does not involve changes in secondary particle size, specific surface area, or pore volume. The crushing process is not particularly limited, but can be carried out, for example, by a hammer mill.

[0113] The method for producing zirconia-based composite oxide powder according to this embodiment has been described above. [Examples]

[0114] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. In the zirconia-based composite oxide powders obtained in the examples and comparative examples, hafnium is contained as an unavoidable impurity in an oxide equivalent of 1 to 3% by mass relative to zirconium (calculated by the following formula (X)). <Formula (X)> ([Mass of hafnium] / ([Mass of zirconium]+[Mass of hafnium]))×100(%)

[0115] The maximum and minimum values ​​of the content of each component shown in the following examples should be considered as the preferred minimum and preferred maximum values ​​of the present invention, regardless of the content of other components. Furthermore, the maximum and minimum values ​​of the measurements shown in the following examples should be considered as the preferred minimum and maximum values ​​of the present invention, regardless of the content (composition) of each component.

[0116] [Preparation of zirconia-based composite oxide powder] (Example 1) Zirconium oxychloride octahydrate (Mitsuwa Chemical, reagent grade, equivalent to 70g of zirconium oxide) was dissolved in deionized water to adjust the ZrO2 concentration to 5% by weight. A 25% by mass sodium hydroxide aqueous solution was added to the aqueous solution to adjust the pH to 3, and the mixture was kept at 25°C for 24 hours to obtain a suspension (Step 1). Hydrochloric acid was added to the suspension to adjust the pH to 1.5, and the mixture was kept at 100°C for 168 hours (7 days) to obtain a slurry of hydrated ZrO2 microcrystalline nuclei (Step 2). After cooling the slurry to 25°C, 150g of 10% sodium sulfate aqueous solution was added, and the mixture was kept at 1 hour to obtain a slurry of hydrated ZrO2-containing basic zirconium sulfate (Step 3). Next, 45 g of trisodium citrate dihydrate (Wako Reagent, Reagent Grade) was added (Step 4). Then, cerium(III) nitrate hexahydrate (Wako Pure Chemical Industries, Reagent Grade, 20 g in terms of cerium oxide), lanthanum nitrate hexahydrate (Wako Pure Chemical Industries, Reagent Grade, 5 g in terms of lanthanum oxide), and yttrium(III) nitrate hexahydrate (Wako Pure Chemical Industries, Reagent Grade, 5 g in terms of yttrium oxide) were added (Step 5), and a 25% by mass sodium hydroxide aqueous solution was added until the pH reached 13 to obtain a precursor precipitate (Step 6). The precipitate was recovered by solid-liquid separation and washed. The solid was calcined in an electric furnace at 700°C in air for 5 hours to obtain the zirconia-based composite oxide powder according to Example 1 (Step 7).

[0117] (Example 2) Except for adjusting the pH to 7 instead of 3 in step 1, the zirconia-based composite oxide powder according to Example 2 was obtained in the same manner as in Example 1.

[0118] (Example 3) Except for changing the firing temperature in step 7 to 550°C, the zirconia-based composite oxide powder according to Example 3 was obtained in the same manner as in Example 2.

[0119] (Example 4) Except for changing the firing temperature in step 7 to 850°C, the zirconia-based composite oxide powder according to Example 4 was obtained in the same manner as in Example 1.

[0120] (Example 5) Except for adjusting the pH to 2.7 instead of 3 in step 1, and adjusting the composition to match that shown in Table 1, the zirconia-based composite oxide powder according to Example 5 was obtained in the same manner as in Example 1.

[0121] (Example 6) Except for adjusting the composition to match that shown in Table 1, the zirconia-based composite oxide powder according to Example 6 was obtained in the same manner as in Example 1.

[0122] (Example 7) Except for adjusting the pH to 7 instead of 3 in step 1, maintaining the temperature at 80°C for 24 hours, and adjusting the composition to match that shown in Table 1, the zirconia-based composite oxide powder according to Example 7 was obtained in the same manner as in Example 2.

[0123] (Examples 8-10) Except for adjusting the composition to match that shown in Table 1, zirconia-based composite oxide powders according to Examples 8-10 were obtained in the same manner as in Example 1.

[0124] (Comparative Example 1) 207 g of a 25% by mass sodium sulfate aqueous solution and 438 g of a zirconium oxychloride aqueous solution (acid concentration: 1N), equivalent to 16% by mass in terms of zirconium oxide, were heated separately at 95°C. Then, the SO4 of the mixed solution was heated. 2- The heated aqueous solutions were brought into contact with each other for 2 minutes so that the mass ratio of / ZrO2 was 0.50. Next, the reaction solution containing basic zirconium sulfate obtained was aged at 95°C for 4 hours to obtain basic zirconium sulfate. Next, after the matured solution was cooled to room temperature, a 10% by mass yttrium chloride aqueous solution (in terms of yttrium oxide) was added so that the Y2O3 content was 5% by weight, a 10% by mass cerium chloride aqueous solution (in terms of cerium oxide) was added so that the CeO2 content was 20% by weight, and a 10% by mass lanthanum chloride aqueous solution (in terms of lanthanum oxide) was added so that the La2O3 content was 5% by weight, and the mixture was then uniformly mixed. Next, a 25% by mass aqueous sodium hydroxide solution was added to the resulting mixed solution and neutralized until the pH reached 13 or higher, thereby generating a hydroxide precipitate. The obtained hydroxide precipitate was filtered and thoroughly washed with water, and the obtained hydroxide was dried at 105°C for 24 hours. The dried hydroxide was heat-treated (calcined) in air at 700°C for 5 hours to obtain the zirconia-based composite oxide powder according to Comparative Example 1.

[0125] (Comparative Example 2) The zirconia-based composite oxide powder of Comparative Example 1 was subjected to a particle size D 50 Wet grinding was performed to obtain a zirconia-based composite oxide powder according to Comparative Example 2, with the particle size being less than 1 μm. The conditions for wet grinding were as follows: The unground zirconia-based composite oxide powder of Comparative Example 1 was ground and mixed for 40 hours in a wet ball mill using water as the dispersion medium. Zirconia beads with a diameter of φ5 mm were used for grinding. The slurry obtained after grinding was dried at 110°C.

[0126] (Comparative Example 3) The firing temperature was changed to 1200°C, and the particle size D 50 Except for performing wet grinding to a particle size of less than 1 μm, the zirconia-based composite oxide powder according to Comparative Example 3 was obtained in the same manner as in Comparative Example 1.

[0127] (Comparative Example 4) 350 mL of zirconium oxychloride aqueous solution (Zr concentration = 1.6 M) (equivalent to 70 g of zirconium oxide) and 123 mL of sodium sulfate aqueous solution (Na2SO4 concentration = 1.6 M) were each heated to 70°C, while 875 mL of sodium hydroxide aqueous solution (NaOH concentration = 2.5 mM) was heated to 90°C. Then, the two solutions, zirconium oxychloride aqueous solution and sodium sulfate aqueous solution, were mixed using a metered delivery pump. The mixed solution was then directly transferred to the sodium hydroxide aqueous solution heated to 90°C. In this experiment, a 4mm inner diameter tube made of Tygon was used, and a glass Y-shaped tube connector was used at the junction of the two liquids for the two-liquid mixing reaction. The flow rate of the zirconium oxychloride aqueous solution was set to 10 mL / min, and the flow rate of the sodium sulfate aqueous solution was set to 3.5 mL / min. Subsequently, cerium chloride aqueous solution (equivalent to 20g of cerium oxide), lanthanum chloride aqueous solution (equivalent to 5g of lanthanum oxide), and yttrium chloride aqueous solution (equivalent to 5g of yttrium oxide) were added at room temperature (25°C). The mixture of each aqueous solution was stirred at 90°C for 30 minutes, and then sodium hydroxide aqueous solution (NaOH concentration = 0.1M) was added until the pH reached 11 or higher to obtain a slurry containing zirconium hydroxide. Next, this slurry was filtered, and the precipitate was washed with distilled water until the amount of Na and Cl in the precipitate was less than 100 ppm to obtain a cake consisting of zirconium hydroxide. The recovered zirconium hydroxide cake was heat-treated (calcined) in a box-type electric furnace at 700°C for 5 hours in air. The resulting calcined material was loosened with a hammer-type head (IKA Corporation, MF10.2 hammer-type head) to obtain the zirconia-based composite oxide powder according to Comparative Example 4. The conditions for using the hammer-type head for massage were as follows: Rotation speed: 6000 rpm Sieve mesh size: 0.5 mm

[0128] [Particle size D 50 , D 90 [Measurement] Suspensions were prepared by placing 0.15 g of the zirconia-based composite oxide powder of the examples and comparative examples into a 50 ml beaker and adding 40 ml of a 0.2% sodium hexametaphosphate aqueous solution. The suspensions were dispersed using an ultrasonic homogenizer (BRANSON DigitalSonifier 250) at an oscillation frequency of 20 kHz and an output of 6000 J, and then measured using a laser diffraction / scattering particle size distribution analyzer ("LA-950", Horiba, Ltd.). The results are shown in Table 1. Furthermore, by performing the dispersion process under the same sample volume, frequency, and output, the dispersion intensity will be equivalent regardless of the model of ultrasonic homogenizer.

[0129] [Pore distribution calculated from scattering curves measured by small-angle X-ray scattering (SAXS)] The zirconia-based composite oxide powders of the examples and comparative examples were measured under the following measurement conditions, and the pore distribution was obtained under the following analysis conditions. [Measurement conditions] Measurement device: Rigaku SmartLab X-ray diffraction analyzer Ray tube: Cu Kα Tube voltage / current: 45kV-200mA Detector: Scintillation counter Scan range: 0.06-8.00deg Scan step: 0.02deg Scan speed: 0.53 deg / min [Analysis conditions] Scattering body model: sphere Measurement method: transmission method Particle / Vacancy: Pore Matrix: CeO2 Distribution function: Gamma distribution Slit correction: High Analyzer crystal: None Analysis range: 0.1600~2.5000° Step: 0.0200° Wavelength: 1.541867Å Table 1 shows the number of peaks and peak pore diameters in the range of 1 nm to 15 nm from the obtained pore distribution (measurement range 1 nm to 40 nm). If there is one peak in the range of 1 nm to 15 nm and the pore diameter of that peak is between 1 nm and 15 nm, it is determined that there is a monomodal distribution in the range of 1 nm to 15 nm. Figure 1 shows the pore distributions of Example 1 and Example 2, and Figure 2 shows the pore distributions of Comparative Example 1 and Comparative Example 2. Although not shown, Examples 3-10 also had pore distributions similar to those of Examples 1 and 2, exhibiting a monomodal distribution in the range of 1 nm to 15 nm.

[0130] [Measurement of specific surface area] The specific surface area of ​​the zirconia-based composite oxide powders of the examples and comparative examples was measured using the BET method with a specific surface area meter ("Macsorb," manufactured by Mountec). The results are shown in Table 1.

[0131] [Measurement of tap density] A TAPDENSER KYT-3000 (manufactured by Seishin Corporation) was used as the tap density measuring device. 100g of the sample powder (zirconia-based composite oxide powder from the Examples and Comparative Examples) was filled into a tapping cell, and the spacer height was set to 3cm. The tapping cell was set on a tapping table, and the measuring device was used to tap 800 times. After tapping was completed, the cell scale was read, and the tap density was obtained by calculating [(powder weight) / (volume)]. More detailed measurement conditions were as follows. The results are shown in Table 1. <Measurement conditions for tap density> Tapping stroke: 3cm Tapping speed: 100 taps / 50 seconds

[0132] [Measurement of bulk density] For the zirconia-based composite oxide powders of the examples and comparative examples, the bulk density of the zirconia-based composite oxide powder was determined from the weight of the powder filled into 30 ml of volume, in accordance with JIS K 5101. The results are shown in Table 1.

[0133] [Identification of crystalline phases] X-ray diffraction spectra were obtained for the zirconia-based composite oxide powders of the examples and comparative examples using an X-ray diffractometer ("Ultima IV," manufactured by Rigaku). The measurement conditions were as follows. <Measurement conditions> Measurement equipment: X-ray diffractometer (Rigaku Ultima IV) Source: CuKα source Tube voltage: 50kV Tube current: 30mA Scanning speed: 2θ = 20~80°: 4° / min

[0134] Subsequently, the crystalline phase was identified from the X-ray diffraction spectrum. When zirconia-based composite oxides contain tetragonal and / or cubic phases, peaks originating from the tetragonal (101) and cubic (111) phases appear around 28.5–31°. On the other hand, when monoclinic phases are present, peaks originating from the monoclinic (-111) phase appear around 28° and around 32°. If peaks are present around 28° and 32°, it was determined that monoclinic phases are present, and if peaks are present around 28.5–31°, it was determined that tetragonal and / or cubic phases are present. The results are shown in Table 1.

[0135] [HAADF-STEM imaging using a transmission electron microscope] High-angle scattering annular dark-field scanning transmission electron microscope (HAADF-STEM) images were obtained for the zirconia-based composite oxide powders of the examples and comparative examples using a transmission electron microscope ("JEM-ARM200F," manufactured by JEOL) at an acceleration voltage of 200 kV. Figure 3 shows the HAADF-STEM image of Example 1. Figure 4 shows the HAADF-STEM image of Example 2. Figure 5 shows the HAADF-STEM image of Comparative Example 1. Although not shown, HAADF-STEM images were obtained in the same manner for the other examples and comparative examples. The obtained images were observed according to the following procedure to confirm whether or not pores were present within single particles. As a result, the zirconia-based composite oxide powders of the examples had pores within single particles. On the other hand, the zirconia-based composite oxide powders of the comparative examples did not have pores within single particles. <Instructions> a. Capture HAADF-STEM images at magnification of 2 million or more. b. Convert to grayscale (8-bit) using image analysis software. c. The region where the brightness value, expressed in 256 levels from 0 to 255, is 80 or higher is determined to be a region where particles are present, and one spherical particle with no overlapping particles is extracted. d. Within the extracted particles, regions with a long axis of 1 nm or more where the brightness value is 40% or more lower than the surrounding area are defined as pores, and their presence or absence is confirmed. e. Repeat the process until the cumulative number of particles checked for the presence or absence of pores reaches 100. f. If it is confirmed that all particles have pores according to the procedures a to e above, then it is determined that the particles have pores.

[0136] [Table 1]

Claims

1. Zirconia and Oxides of rare earth elements and Includes, The zirconia content is 50% by weight or more and 95% by weight or less. In the pore distribution calculated from the scattering curve measured by small-angle X-ray scattering, a monomodal distribution was found in the range of 1 nm to 15 nm. Particle size D in the particle size distribution measured by laser diffraction / scattering method ５０ The particle size is 0.05 μm or more and less than 1.0 μm. Tap density is 1.0 g / cm³ ３ 1.7g / cm or more ３ The following: A zirconia-based composite oxide powder characterized in that the crystal system identified by powder X-ray diffraction is either tetragonal, cubic, or both.

2. The zirconia-based composite oxide powder according to claim 1, characterized in that it has pores within a single particle.

3. The particle size D ５０ The zirconia-based composite oxide powder according to claim 1 or 2, characterized in that the particle size is 0.08 μm or more and 0.85 μm or less.

4. Specific surface area is 30 m² ２ / g or more 90m ２ The zirconia-based composite oxide powder according to claim 1 or 2, characterized in that it is less than / g.

5. The oxide of the rare earth element is one or more selected from the group consisting of yttrium oxide, lanthanum oxide, cerium oxide, neodymium oxide, and praseodymium oxide. The zirconia-based composite oxide powder according to claim 1 or 2, characterized in that the content of the oxide of the rare earth element is 5% by weight or more and 50% by weight or less.

6. Step 1 involves adjusting the pH of an aqueous zirconium oxychloride solution to form a suspension, By lowering the pH of the suspension to that of step 1 and heating it, hydrate ZrO ２ Step 2 to obtain a microcrystalline nucleus slurry, The hydrated ZrO ２ Adding a flocculant to the microcrystalline nucleus slurry to obtain a hydrated ZrO ２ Step 3 of obtaining a basic zirconium sulfate-containing slurry, The hydrated Zr ２ Step 4 involves adding a surface modifier to a basic zirconium sulfate slurry, Step 5 involves adding a raw material salt containing rare earth elements, Step 6 involves neutralizing with a base to obtain a precipitate, Step 7 to obtain a zirconia-based composite oxide by heat-treating the aforementioned precipitate. A method for producing a zirconia-based composite oxide powder according to claim 1 or 2, characterized by including the following:

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