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

Abstract

A zirconia-based composite oxide powder which contains zirconia and an oxide of a rare earth element, wherein: the content of zirconia is 50 wt% to 95 wt% inclusive; a monomodal distribution is present in the range of 1 nm to 15 nm inclusive in the pore distribution calculated from a scattering curve determined by a small-angle X-ray scattering method; the particle diameter D50 in a particle size distribution determined by a laser diffraction scattering method is not less than 0.05 µm but less than 1.0 µm; the tap density is 1.0 g / cm3 to 1.7 g / cm3 inclusive; and the crystal systems identified by powder X-ray diffraction are tetragonal systems and / or cubic systems.

Description

Zirconia-based composite oxide powder and method for producing zirconia-based composite oxide powder 【0001】 The present invention relates to a zirconia-based composite oxide powder and a method for producing the zirconia-based composite oxide powder. 【0002】 Currently, in gasoline engines, the direct injection method is the mainstream, and 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, and 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, Y ２ O ３ , Er ２ O ３ , or Yb ２ O ３ , and having a specific surface area of 10 m ２ / g or more 50m ２ / g or less, particle size D ５０ A zirconia powder having a particle size of 0.1 μm or more and 0.7 μm or less is disclosed (Claim 1, Claim 2). 【0007】 Patent Document 4 describes a pore diameter distribution obtained by the mercury intrusion method, in which the pore volume in the range of pore diameters X nm or more and less than Y nm is defined as Vp Ｘ－Ｙ When that is the case, [(Vp １０－１００ ) / (Vp １００－６０００ )] satisfies the following equation [1], and the particle size D after crushing treatment ５０ However, a zirconia-based powder material having a particle size of 0.05 μm or more and 1.5 μm or less is disclosed (Claim 1, Claim 7). Formula [1] 0.4 ≤ [(Vp １０－１００ ) / (Vp １００－６０００ ) ≤ 1 【0008】 Japanese Patent Publication No. 2006-240928, International Publication No. 2022 / 075345, International Publication No. 2022 / 075346, Japanese Patent Publication No. 2023-142376 【0009】 The zirconia-based composite oxide required for support within 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 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 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 GPF. 【0010】 However, although the zirconia fine powder in Patent Document 1 is said to have 100% of its particle size distribution in the cumulative curve, its specific surface area is 15 m². ２ Because the concentration 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. 【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] A material comprising zirconia and an oxide of a rare earth element, wherein the zirconia content is 50% by weight or more and 95% by weight or less, 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 and scattering is ５０ The particle size is 0.05 μm or more and less than 1.0 μm, and the tap density is 1.0 g / cm³. ３ 1.7g / cm or more ３The zirconia-based composite oxide powder is 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 ５０ This allowed us to obtain a zirconia-based composite oxide powder with a particle size of less than 1.0 μm. Furthermore, because the above composition contains zirconia and an oxide of a rare earth element, it 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 ５０In particles with a diameter of less than 1.0 μm, a monomodal distribution exists in the pore size range of 1 nm to 15 nm. This means that uniform pores exist inside the particle (secondary particle), i.e., it is porous. For example, as shown in Comparative Example 2 in Figure 2, if there are two peaks in the pore size range of 1 nm to 15 nm, i.e., if it is bimodal rather than monomodal, such a pore size distribution is characteristic of wet-milled particles. The peak around 14 nm in Figure 2 originates from the pores inside the particle (secondary particle), while the peak around 3 nm in Figure 2 originates from the particle produced by wet milling (the particle itself, which does not have pores). Therefore, if the pore size range of 1 nm to 15 nm is bimodal, there are few pores inside the particle (secondary particle), and it cannot be said to be 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 peaks in the pore distribution range of 1 nm to 15 nm, it is highly likely to have two peaks, and it cannot be said to have 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 a HAADF-STEM image. In a HAADF-STEM image, the detected signal is converted into a single image with 256 brightness values ​​from 0 to 255 per pixel. Empty spaces appear dark (low brightness value), and areas where matter exists appear bright (high brightness value). The brightness value of areas where matter exists correlates with the electron density of that area; the higher the electron density, the brighter it appears. In materials composed of the same constituent elements, the electron density is the same as the density of the material. 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. <Procedure> a. Take a HAADF-STEM image at magnification of 2 million or more. b. Convert to grayscale (8-bit) using image analysis software. c. d. A region with a brightness value of 80 or higher, expressed in 256 steps from 0 to 255, is determined to be a region where particles are visible, and one spherical particle (single particle) without particle overlap is extracted. e. Within the extracted particle, a region with a long axis of 1 nm or more where the brightness value is 40% or more lower than the surrounding area is defined as a pore, and its presence or absence is confirmed. e. This is repeated until the cumulative number of particles for which the presence or absence of pores has been confirmed reaches 100. f. If it is confirmed that all particles have pores using the above procedures a to e, it is determined that "a single particle has pores." In HAADF-STEM image observation using the above procedure, if a particle has pores, it means that the pores in that zirconia-based composite oxide powder are not voids (interparticle gaps) between particles, but voids inherent in the particle itself. 【0025】 Furthermore, the present invention provides the following: [3] The particle size 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 ５０If 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 m² ２ / g or more 90m ２ A zirconia-based composite oxide powder according to any one of [1] to [3] above, characterized in that it is less than / g. 【0028】 Specific surface area is 30 m² ２ A value of 90 m² or more indicates greater porosity. Furthermore, a specific surface area of ​​90 m² is also considered important. ２ If the value is less than / g, the pore volume can be further reduced. 【0029】 Furthermore, the present invention provides the following: [5] The zirconia-based composite oxide powder according to any one of [1] to [4] above, characterized in that 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, and 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: Adjusting the pH of an aqueous solution of zirconium oxychloride to make a suspension; and hydrating ZrO by lowering the pH of the suspension to a level lower than that of Step 1 and heating it. ２ Step 2 to obtain a microcrystalline nucleus slurry, and the hydrated ZrO ２ Adding a flocculant to a microcrystalline nucleus slurry to hydrate ZrO ２ Step 3 to obtain a slurry containing basic zirconium sulfate, and the hydrated ZrO ２A method for producing a zirconia-based composite oxide powder according to any one of [1] to [5] above, comprising: step 4 of adding a surface modifier to a basic zirconium sulfate slurry; step 5 of adding a raw material salt containing a rare earth element; step 6 of neutralizing with a base to obtain a precipitate; and step 7 of heat-treating the precipitate to obtain a zirconia-based composite oxide. 【0032】 According to the above configuration, the pH of the suspension is made lower than that of step 1, and heating allows hydrated ZrO ２ To obtain a microcrystalline nucleus slurry (step 2), it is possible to obtain porous particles with small pore volumes and peaks in the pore distribution range of 1 nm to 15 nm. 【0033】 Furthermore, according to the above configuration, hydrated ZrO ２ Adding a flocculant to a microcrystalline nucleus slurry to hydrate ZrO ２ In order to obtain a slurry containing basic zirconium sulfate (step 3), secondary particles with strong aggregation of primary particles are obtained. 【0034】 Furthermore, according to the above configuration, hydrated ZrO ２ Since a surface modifier is added to the basic zirconium sulfate slurry, and then rare earth elements are added (step 5), aggregation of secondary particles during calcination (step 7) can be suppressed. 【0035】 As described above, the above configuration yields a zirconia-based composite oxide powder with small particle size, small pore volume, and porous structure. 【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. 【0037】 Pore ​​distribution for Example 1 and Example 2. Pore distribution for Comparative Example 1 and Comparative Example 2. HAADF-STEM image of Example 1. HAADF-STEM image of Example 2. HAADF-STEM image of Comparative Example 1. 【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. Similarly, 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 preferred maximum values ​​of the present invention. 【0040】 [Zirconia-based composite oxide powder] The zirconia-based composite oxide powder according to this embodiment contains zirconia and an oxide of a rare earth element, the zirconia content is 50% by weight or more and 95% by weight or less, 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 and scattering is ５０ The particle size is 0.05 μm or more and less than 1.0 μm, and the tap density is 1.0 g / cm³. ３ 1.7g / cm or more ３ The following conditions apply: 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, and may contain other components as long as the effects of the present invention are achieved (as long as they do not significantly hinder the effects of the present invention). Conventionally, composite oxides of zirconia and an oxide of a rare earth element tend to aggregate during manufacturing, resulting in fine particles (particle size D ５０It was difficult to manufacture (those with small particle size D). However, in this embodiment, although it is a composite oxide containing zirconia and an oxide of a rare earth element, 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, making it 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. Because the zirconia content is 50% by weight or more and 95% by weight or less, 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 content of 5% by weight or more and 50% by weight or less of the rare earth element oxide 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. If the rare earth element oxide is one or more selected from the group consisting of yttrium oxide, lanthanum oxide, cerium oxide, neodymium oxide, and praseodymium oxide, it is more suitable for catalytic applications. 【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. When the total content of zirconia and the oxide of the rare earth element is 85% by mass or more, it is suitable for catalytic applications. 【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) an oxide of at least one element selected from the group consisting of In, Si, Sn, Bi, P, and Zn, (B) a transition metal oxide (excluding oxides of rare earth elements and oxides of noble metal elements), and (C) an alkaline earth metal oxide. 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. ５０ Since the particle size is less than 1.0 μm, it can be said that the particle size is small and is suitable for catalytic applications. 【0055】 The particle size D ５０ The particle size D is preferably 0.90 μm or less, more preferably 0.85 μm or less. ５０ There are no particular restrictions, but for example, it may 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 0.08 μm or more and 1.6 μm or less. 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 D is more preferably 1.5 μm or less, and even more preferably 1.4 μm or less. ９０ There are no particular restrictions, but for example, it may 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 D ５０ The 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 distribution in the range of 1 nm to 15 nm in the pore distribution calculated from the scattering curve measured by small-angle X-ray scattering, and may or may not have a peak in the range of greater than 15 nm and less than or equal to 40 nm. From the viewpoint of further reducing the pore volume, it is preferable that there is no peak in the range of greater than 15 nm and less than or equal 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 1.7g / cm or more ３ The following is the result: Tap density is 1.0 g / cm³. ３Therefore, 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 The above is a more preferable 1.05 g / cm³. ３ That concludes the explanation. 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 1.69g / cm or more ３ More preferably, 1.05 g / cm³ ３ 1.68g / cm or more 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 1.2g / cm or more ３ Preferably, the following: 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 is 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 1.1g / cm or more ３ More preferably, 0.54 g / cm³ ３ 1.0g / cm or more 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 that is either tetragonal, cubic, or both. Zirconia does not contain monoclinic crystals when it contains a certain amount or more of rare earth elements, and only tetragonal and cubic crystals remain. Since the crystal system identified by powder X-ray diffraction is either tetragonal, cubic, or both, it contains rare earth elements and is suitable for catalyst applications. 【0070】 The zirconia-based composite oxide powder has a specific surface area of 30 m ２ / g or more and less than 90 m ２ / g. When the specific surface area is 30 m ２ / g or more, it can be said to be more porous. Also, when the specific surface area is less than 90 m ２ / g, the pore volume can be made smaller. 【0071】 The specific surface area is more preferably 32 m ２ / g or more, and even more preferably 34 m ２ / g or more. The specific surface area is more preferably 85 m ２ / g or less, and even more preferably 82 m ２ / g or less. The specific surface area is more preferably 32 m ２ / g or more and 85 m ２ / g or less, and even more preferably 34 m ２ / g or more and 82 m ２ / g or less. 【0072】 The specific surface area is a value obtained by the method described in the examples. 【0073】The zirconia-based composite oxide powder preferably has pores within a single particle. Whether there are pores within a single particle is determined by the following <Procedure> a to f using a HAADF-STEM image. <Procedure> a. Take a HAADF-STEM image at 2 million times magnification or more. b. Convert it to grayscale (8-bit) using image analysis software. c. Determine the region where the luminance value represented by 256 levels from 0 to 255 is 80 or more as the region where the particles are reflected, and extract one spherical particle without particle overlap. d. In the extracted particle, a region having a major axis of 1 nm or more and a luminance value 40% or more lower than the surroundings is regarded as a pore, and its presence or absence is confirmed. e. Repeat until the cumulative number of particles for which the presence or absence of pores has been confirmed reaches 100. f. If it is confirmed that all particles have pores by the procedures a to e above, it is determined that the particles have pores. In the observation of the HAADF-STEM image by the above <Procedure>, when there are pores within the particles, the pores of the zirconia-based composite oxide powder mean that they are not voids (interparticle gaps) composed of particles themselves, but voids held by the particles themselves. 【0074】 When the zirconia-based composite oxide powder is used as a catalyst carrier for an exhaust gas purification catalyst, the metal to be supported is not particularly limited, and examples include Pt, Pd, Rh, and the like. 【0075】 [Manufacturing method of zirconia-based composite oxide powder] Hereinafter, an example of the manufacturing method of the zirconia-based composite oxide powder will be described. However, the manufacturing method of the zirconia-based composite oxide powder of the present invention is not limited to the following examples. 【0076】 The manufacturing method of the zirconia-based composite oxide powder according to the present embodiment includes: Step 1 of adjusting the pH of an aqueous zirconium oxychloride solution to form a suspension; Step 2 of obtaining a hydrated ZrO ２ microcrystalline nucleus slurry by making the pH of the suspension smaller than that in Step 1 and heating; ２ Step 3 of adding a flocculant to the hydrated ZrO ２ containing basic zirconium sulfate slurry to obtain a hydrated ZrO ２The process includes: step 4 of adding a surface modifier to a basic zirconium sulfate slurry; step 5 of adding a raw material salt containing a rare earth element; step 6 of neutralizing with a base to obtain a precipitate; and step 7 of heat-treating the precipitate to obtain a zirconia-based composite oxide. 【0077】 The following describes each step in the method for producing the zirconia-based composite oxide powder according to this embodiment. 【0078】 First, the pH of the zirconium oxychloride aqueous solution is adjusted to form a suspension (Step 1). 【0079】 The concentration of the aforementioned zirconium oxychloride aqueous solution is ZrO ２ Any solution with a concentration between 2% by weight and 15% by weight is acceptable. 【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 more preferably 2.5 or higher, and even more preferably 2.7 or higher. In step 1, it is preferable to adjust the pH to more preferably 6.5 or lower, and even more preferably 6 or lower. In step 1, it is preferable to adjust the pH to more preferably 2.5 or higher and 6.5 or lower, and even more preferably 2.7 or higher and 6 or lower. 【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 between 2 and 7, 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 made too high 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), which may hinder the reaction. For example, if a large amount of aqueous 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 high, which may hinder the reaction. 【0085】 Next, the pH of the suspension is made lower than that of step 1, and then heated to hydrate ZrO ２ A slurry of microcrystalline nuclei is obtained (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 of 1 or more and 1.5 or less. By adjusting the pH to 1 or more and 1.5 or less, hydrated ZrO ２ A suitable microcrystalline nucleus slurry can be obtained. Specifically, by setting the pH to near the boundary where zirconium hydroxide becomes insoluble in aqueous solution, hydrated ZrO ２ A slurry of microcrystalline nuclei can be suitably obtained. If the pH is made too low, precipitation occurs rapidly, and hydrated ZrO ２ There is a risk that amorphous material will be formed instead of crystal nuclei. 【0087】 In step 2, it is preferable to adjust the pH to more preferably 1.1 or higher, and even more preferably 1.15 or higher. In step 2, it is preferable to adjust the pH to more preferably 1.4 or lower, and even more preferably 1.35 or lower. In step 2, it is preferable to adjust the pH to more preferably 1.1 or higher and 1.4 or lower, and even more preferably 1.15 or higher and 1.35 or lower. 【0088】 In step 2, the heating temperature is preferably 90°C to 120°C. By setting the heating temperature to 90°C to 120°C, hydrated ZrO２ A slurry of microcrystalline nuclei can be suitably 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 or higher and 115°C or lower, and even more preferably 98°C or higher and 110°C or lower. 【0090】 In step 2, the heating time is preferably 140 hours or more and 200 hours or less. By setting the heating time to 140 hours or more and 200 hours or less, hydrated ZrO ２ A slurry of microcrystalline nuclei can be suitably 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 that of step 1, and by heating, hydrated ZrO ２ To obtain a microcrystalline nucleus slurry, it is possible to create particles that are porous but have a small pore volume with peaks in the pore distribution 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, the hydrated ZrO ２ Adding a flocculant to a microcrystalline nucleus slurry to hydrate ZrO ２ A slurry containing basic zirconium sulfate is obtained (step 3). The hydrated ZrO ２ Adding a flocculant to a microcrystalline nucleus slurry to hydrate ZrO ２ To obtain a slurry containing basic zirconium sulfate, secondary particles with strong aggregation between primary particles are obtained. 【0095】 The aforementioned flocculant is negatively charged and hydrated ZrO2, which can neutralize and flocce positively charged particles that repel each other. ２ The substances that adsorb to it are not particularly limited, but examples include sodium sulfate, potassium sulfate, and 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 to be added is ZrO ２ A weight ratio of 0.05 to 1.0 is preferred, and 0.1 to 0.8 is more preferred. 【0097】 Afterward, it may be cooled as needed (for example, to room temperature (10°C to 30°C)). 【0098】 Next, the hydrated ZrO ２ A surface modifier is added to the basic zirconium sulfate slurry (step 4). Hydrated ZrO ２ In step 5, a surface modifier is added to the basic zirconium sulfate slurry, followed by the addition of rare earth elements. This suppresses the aggregation of secondary particles during calcination (step 7). As a result, there are fewer aggregates of secondary particles (tertiary particles), and the mixture can remain almost entirely in the form of secondary particles. 【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 ZrO ２ A weight ratio of 0.1 to 0.8 is preferred, and 0.2 to 0.7 is more preferred. 【0101】 Next, a raw material salt containing rare earth elements is 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 mixture is neutralized with a base to obtain a precipitate (step 6). Neutralization produces a precursor precipitate of zirconium-containing hydroxide. The base is not limited and examples include caustic soda, sodium carbonate, ammonia, and hydrazine ammonium bicarbonate. 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 or higher and 1000°C or lower, and more preferably 500°C or higher and 900°C or lower. 【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 as needed. "Crushing" refers to the operation of applying a separating force to the particle aggregate to reduce the size of tertiary particles (separating them into secondary particles), and does not involve changes in secondary particle size, specific surface area, or pore volume. While the crushing is not particularly limited, it can be carried out, for example, using a hammer mill. 【0113】 The method for producing zirconia-based composite oxide powder according to this embodiment has been described above. 【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 powder 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 measured values ​​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) Dissolve zirconium oxychloride octahydrate (Mitsuwa Chemical, reagent grade, equivalent to 70 g of zirconium oxide) in deionized water and prepare ZrO ２ The concentration was adjusted 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 a suspension was obtained by keeping it at 25°C for 24 hours (Step 1). Hydrochloric acid was added to the suspension to adjust the pH to 1.5, and hydrated ZrO was obtained by keeping it at 100°C for 168 hours (7 days). ２ A slurry of microcrystalline nuclei was obtained (Step 2). After cooling the slurry to 25°C, 150 g of 10% sodium sulfate aqueous solution was added and kept for 1 hour to hydrate ZrO ２A slurry containing basic zirconium sulfate was obtained (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 that the pH was adjusted 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 that the pH was adjusted to 2.7 instead of 3 in step 1, and the composition was adjusted to be as 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) A zirconia-based composite oxide powder according to Example 6 was obtained in the same manner as in Example 1, except that the composition was adjusted to be as shown in Table 1. 【0122】 (Example 7) Except that the pH was adjusted to 7 instead of 3 in step 1 and kept at 80°C for 24 hours, and the composition was adjusted to be as 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) Zirconia-based composite oxide powders according to Examples 8-10 were obtained in the same manner as in Example 1, except that the composition was adjusted to match that shown in Table 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 to 95°C. Then, the SO2 mixture was heated. ４ ２－ / ZrO ２ The heated aqueous solutions were brought into contact with each other for 2 minutes so that the mass ratio was 0.50. Next, the reaction solution containing basic zirconium sulfate was aged at 95°C for 4 hours to obtain basic zirconium sulfate. Next, after the aged solution was cooled to room temperature, a 10% by mass aqueous solution of yttrium chloride (in terms of yttrium oxide) was added to Y ２ O ３ To make the amount 5% by weight, add a 10% by mass aqueous solution of cerium chloride in terms of cerium oxide, CeO ２ To make the amount 20% by weight, add a 10% by mass aqueous solution of lanthanum chloride in terms of lanthanum oxide, La ２ O ３ The substance was added to a total of 5% by weight and mixed uniformly. 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, 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 5 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 so that the particle size was 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 sodium sulfate aqueous solution (Na ２ SO ４ 123 mL each of the 1.6 M zirconium oxychloride solution and the sodium sulfate solution were heated to 70°C, and 875 mL of sodium hydroxide solution (NaOH concentration = 2.5 mM) was heated to 90°C. Then, the two solutions, the zirconium oxychloride solution and the sodium sulfate solution, were mixed using a metering pump, and the mixed solution was then directly transferred to the sodium hydroxide solution heated to 90°C. At this time, a 4 mm inner diameter Tygon tube was used, and a glass Y-shaped tube connector was used at the confluence of the two solutions for the mixing reaction. The flow rate of the zirconium oxychloride solution was set to 10 mL / min, and the flow rate of the sodium sulfate solution was set to 3.5 mL / min. Subsequently, cerium chloride solution (equivalent to 20 g of cerium oxide), lanthanum chloride solution (equivalent to 5 g of lanthanum oxide), and yttrium chloride solution (equivalent to 5 g 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 = 0.1 M) 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 contained in the precipitate was less than 100 ppm to obtain a cake composed of zirconium hydroxide. The recovered zirconium hydroxide cake was heat-treated (calcined) in a box-type electric furnace at 700°C in air for 5 hours. The resulting calcined product 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 loosening with the hammer-type head were as follows: Rotation speed: 6000 rpm Sieve mesh size: 0.5 mm 【0128】 [Particle size D ５０ , D ９０ [Measurement] 0.15 g of the zirconia-based composite oxide powder of the examples and comparative examples and 40 ml of a 0.2% sodium hexametaphosphate aqueous solution were placed in a 50 ml beaker to prepare a suspension. The suspension was dispersed using an ultrasonic homogenizer (DigitalSonifier 250, BRANSON) 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. Note that by performing the dispersion treatment 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)] For the zirconia-based composite oxide powders of the examples and comparative examples, measurements were performed under the following measurement conditions, and the pore distribution was obtained under the following analysis conditions. [Measurement Conditions] Measurement device: Rigaku X-ray diffraction analyzer SmartLab X-ray tube: Cu Kα Tube voltage / current: 45kV-200mA Detector: Scintillation counter Scan range: 0.06-8.00 deg Scan step: 0.02 deg Scan speed: 0.53 deg / min [Analysis Conditions] Scatterer model: Sphere Measurement method: Transmission method Particle / vacancy: Pore Matrix: CeO2 Distribution function: Γ distribution Slit correction: High Analyzer crystal: None Analysis range: 0.1600-2.5000° Step: 0.0200° Wavelength: 1.541867 Å The number of peaks in the range of 1 nm to 15 nm and the peak pore diameters of the obtained pore distribution (measurement range 1 nm to 40 nm) are shown in Table 1. 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, then 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 to 10 also had pore distributions similar to those of Examples 1 and 2, and exhibited 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. 100 g of sample powder (zirconia-based composite oxide powder of the example and comparative example) was filled into a tapping cell, and the spacer height was set to 3 cm. 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: 3 cm Tapping speed: 100 times / 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 device: X-ray diffractometer (Rigaku, Ultima IV) Radiation 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 peaks originating from the monoclinic (111) phase appear 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 Image Observation using a Transmission Electron Microscope] High-angle scattering annular dark-field scanning transmission electron microscope images (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 is the HAADF-STEM image of Example 1. Figure 4 is the HAADF-STEM image of Example 2. Figure 5 is 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. <Procedure> a. a. Capture a HAADF-STEM image at a magnification of 2 million or more. b. Convert the image to grayscale (8-bit) using image analysis software. c. Determine that areas with a brightness value of 80 or higher, expressed in 256 levels from 0 to 255, are areas where particles are present, and extract one spherical particle with no overlapping particles. d. Within the extracted particle, identify areas with a long axis of 1 nm or more where the brightness value is 40% or more lower than the surrounding area as pores, and check for their presence or absence. e. Repeat until the cumulative number of particles for which pores have been checked reaches 100. f. If it is confirmed that all particles have pores using the above procedures a to e, determine that the particle has pores. 【0136】

Claims

1. Containing zirconia and an oxide of a rare earth element, the zirconia content is 50% by weight or more and 95% by weight or less, 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 and scattering is ５０ The particle size is 0.05 μm or more and less than 1.0 μm, and the tap density is 1.0 g / cm³. ３ 1.7g / cm or more ３ The zirconia-based composite oxide powder is 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 of ​​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 zirconia-based composite oxide powder according to claim 1 or 2, characterized in that 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, and 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 of adjusting the pH of an aqueous zirconium oxychloride solution to form a suspension; reducing the pH of the suspension to be lower than that in Step 1 and heating to obtain hydrated ZrO ２ Step 2 of obtaining a microcrystalline nucleus slurry; the hydrated ZrO ２ Step 3 of adding a flocculant to the microcrystalline nucleus slurry of hydrated ZrO to obtain a slurry of basic zirconium sulfate containing hydrated ZrO ２ Step 4 of adding a surface modifier to the slurry of basic zirconium sulfate containing hydrated ZrO; Step 5 of adding a raw material salt containing a rare earth element; Step 6 of neutralizing with a base to obtain a precipitate; and Step 7 of heat-treating the precipitate to obtain a zirconia-based composite oxide, characterized in that it comprises the method for producing a zirconia-based composite oxide powder according to claim 1 or 2. ２ ​

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