Zirconia powder and its manufacturing method

Abstract

To provide at least one of the following: a zirconia powder which gives a zirconia sintered body exhibiting high electrical conductivity even when sintered at a low temperature and a method for producing the zirconia powder; and a zirconia sintered body obtained from the zirconia powder, a method for producing the zirconia sintered body, and a solid electrolyte using the same.SOLUTION: A zirconia powder comprises one or more stabilizers selected from the group of yttria, calcia, magnesia, and ceria, in which a proportion of monoclinic crystals in a crystal phase is 0.5% or less, an average particle diameter is less than 0.5 μm, and a proportion of particles of 1 μm or less in volume particle size distribution is 100%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a zirconia powder, and in particular to a zirconia powder that provides a zirconia sintered body suitable for solid electrolytes. [Background technology]

[0002] Zirconia-based solid electrolytes are used in solid oxide fuel cells (SOFCs), etc. For example, Patent Document 1 reports a solid electrolyte obtained by crushing a zirconia sintered body containing yttria (YO) and ceria (CeO), mixing this with a lanthanide oxide, manganese dioxide, or iron oxide, and sintering the mixture at 1450°C. Patent Document 2 also discloses a solid electrolyte integrated with a solid electrolyte layer made of zirconia containing 8 mol% or 10 mol% yttria and a fuel electrode obtained by co-sintering a compact having a fuel electrode and a barrier layer at 1400°C. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2012 / 105580 [Patent Document 2] Patent No. 5770400 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0004] The zirconia-based solid electrolytes of Patent Documents 1 and 2 both require a high sintering temperature of 1400° C. or higher to exhibit practical conductivity.

[0005] In response to this, the present disclosure aims to provide at least one of a zirconia powder that provides a zirconia sintered body that exhibits high electrical conductivity even when sintered at a low temperature, a method for producing the same, and a zirconia sintered body obtained from the zirconia powder, a method for producing the same, and a solid electrolyte using the same. [Means for solving the problem]

[0006] The gist of the present disclosure is as follows. [1] A zirconia powder characterized by containing one or more stabilizers selected from the group consisting of yttria, calcia, magnesia, and ceria, having a monoclinic crystal content of 0.5% or less in the crystalline phase, an average particle size of less than 0.5 μm, and a volume particle size distribution in which particles of 1 μm or less account for 100%. [2] The zirconia powder according to [1] above, wherein the proportion of particles having a size of 0.2 μm or less in the volume particle size distribution is 10% to 90%. [3] The zirconia powder according to the above [1] or [2], which has a particle size peak with a peak top at 0.3 to 0.5 μm in a volume particle size distribution. [4] The zirconia powder according to any one of [1] to [3], wherein the content of the stabilizer is more than 4 mol% and not more than 12 mol%. [5] The zirconia powder according to any one of [1] to {4} above, which is a compound containing at least one of a cation having an ionic radius smaller than that of a zirconium ion and a cation having a valence other than tetravalent. [6] The zirconia powder according to [5] above, wherein the compound contains one or more cations selected from the group consisting of aluminum, silicon, and germanium. [7] The zirconia powder according to [5] or [6] above, wherein the content of the compound is greater than 0 mass % and not more than 1 mass %. [8] Average granule particle size is 30 μm or more and 80 μm or less, and the light bulk density is 1.00 g / cm 3 More than 1.40g / cm 3 The zirconia powder according to any one of the above [1] to [7] below.

[0007] [9] A method for producing a zirconia powder according to any one of [1] to [8] above, comprising the steps of: mixing a zirconia sol having a zirconium element content of 2 mass% or less, calculated by the following formula, with one or more compounds selected from the group consisting of yttrium, calcium, magnesium, and cerium; and treating the zirconia sol at a calcination temperature of 900°C or higher and 1200°C or lower. W Zr =(m / m0)×100 In the above formula, W Zr is the amount of adsorbed zirconium (mass%). m is the mass (mg) of zirconium in the filtrate obtained by ultrafiltration of a slurry in which zirconia sol is dispersed in pure water using an ultrafiltration membrane with a molecular weight cutoff of 500 to 3,000,000, converted into zirconia (ZrO2). m o is the mass (mg) of the zirconia sol before ultrafiltration after heat treatment at 1000°C for 1 hour in an air atmosphere.

[10] A method for producing a zirconia sintered body, characterized by using the zirconia powder according to any one of [1] to [8] above.

[11] A ceramic ceramic material containing one or more stabilizers selected from the group consisting of yttria, calcia, magnesia, and ceria, and having a conductivity of 5.0×10 at 600°C. -3 A zirconia sintered body characterized by a viscosity of S / cm or more.

[12] A solid electrolyte comprising the zirconia sintered body according to

[11] above. [Effects of the Invention]

[0008] The present disclosure can provide at least one of a zirconia powder that provides a zirconia sintered body that exhibits high electrical conductivity even when sintered at a low temperature, a method for producing the same, and a zirconia sintered body obtained from the zirconia powder, a method for producing the same, and a solid electrolyte using the same. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the zirconia powder of the present disclosure will be described with reference to an example embodiment.

[0010] The "average particle size" is the particle size (median size) corresponding to a volume fraction of 50% on the cumulative volume particle size distribution curve obtained by volume particle size distribution measurement using laser diffraction method.

[0011] The "crystallite size" refers to the value calculated by the following formula 3 using the Bragg angle (θ) of the diffraction line measured by powder X-ray diffraction (XRD) and the half-width (β) of the diffraction line corrected for mechanical broadening. Dx = κλ / (β cosθ) In the above formula, κ is the Scherrer constant (κ=1), λ is the measurement wavelength, and β is The crystallite diameter of the zirconia fine powder is determined from the diffraction line with the strongest intensity.

[0012] The "BET specific surface area" is a value determined by the BET single-point method in accordance with JIS R 1626-1996, using nitrogen (N2) as the adsorbed substance.

[0013] The "stabilizer content" is the molar ratio of the stabilizer to zirconia and the stabilizer calculated as an oxide.

[0014] The "monoclinic fraction of the crystalline phase" (hereinafter also referred to as the "monoclinic fraction") is the fraction of the monoclinic phase in the crystalline phase of zirconia. For powders, the powder X-ray diffraction (hereinafter also referred to as "XRD") pattern of the powder is used, while for sintered bodies, the XRD pattern of the surface of the sintered body after mirror polishing is used, and it can be calculated from the following formula.

[0015] f m ={I m (111)+I m (11-1)} / [I m (111) +I m (11-1)+I t (111)+I c (111)] × 100

[0016] In the above equation, f m is the monoclinic fraction (%), I m(111) and I m (11-1) are the area intensities of the XRD peaks corresponding to the monoclinic (111) and (11-1) planes, respectively, and I t (111) is the area intensity of the XRD peak corresponding to the (111) plane of the tetragonal crystal, and I c (111) is the area intensity of the XRD peak corresponding to the (111) plane of the cubic crystal.

[0017] The conditions for measuring the XRD pattern include the following. Radiation source: CuKα radiation (λ=0.15418nm) Measurement mode: Continuous scan Scan speed: 4° / min Step width: 0.02° Measurement range: 2θ=26°~33°

[0018] In the above-mentioned XRD pattern measurement, preferably, the XRD peaks corresponding to the respective crystal planes of zirconia are measured as peaks having peak tops at the following 2θ angles.

[0019] XRD peak corresponding to the monoclinic (111) plane: 2θ=31±0.5° XRD peak corresponding to the monoclinic (11-1) plane: 2θ=28±0.5° The RD peaks corresponding to the (111) planes of the tetragonal and cubic crystals were measured in duplicate, and their 2θ angles were 2θ=30±0.5°.

[0020] The area intensity of the XRD peak of each crystal plane can be determined by separating each XRD peak using the calculation program "PRO-FIT" according to the method described in H. Toraya, J. Appl. Crystallogr., 19, 440-447 (1986).

[0021] The "ionic radius" is a value described in Acta. Crystallogr., A32, 751-67 (1976) (hereinafter also referred to as "reference document").

[0022] "Additive content" refers to the ratio of additive / (ZrO2 + stabilizer + additive) expressed as mass %. Here, the additive is expressed as a value converted into oxide.

[0023] The "average sol particle size" is the sol size (median size) corresponding to a volume ratio of 50% on the cumulative volume particle size distribution curve obtained by dynamic light scattering particle size distribution measurement.

[0024] The "measured density of the sintered body" can be measured using the Archimedes method.

[0025] The zirconia powder of this embodiment contains one or more stabilizers selected from the group consisting of yttria, calcia, magnesia, and ceria. The stabilizer is preferably at least one of yttria and ceria. The stabilizer is more preferably yttria, since this results in a zirconia sintered body having properties suitable for a solid electrolyte.

[0026] The type and content of the stabilizer may be appropriately changed depending on the desired properties of the zirconia sintered body. For example, when the stabilizer is yttria, the content of yttria is preferably more than 4 mol% and not more than 12 mol%, and more preferably 6 mol% or more and not more than 10 mol%.

[0027] The zirconia powder of this embodiment has a monoclinic fraction of the crystalline phase of 0.5% or less (hereinafter also referred to as the "monoclinic fraction"), and preferably 0% to 0.2%. If the monoclinic fraction exceeds this range, the sintering temperature required for densification increases, and coarse pores tend to remain even after densification has progressed. If the monoclinic fraction is 0.5% or less, the other crystalline phases may be any, including tetragonal and cubic, preferably cubic. The crystalline phase of the zirconia powder of this embodiment is preferably composed of cubic and monoclinic.

[0028] The zirconia powder of this embodiment has an average particle size of less than 0.5 μm. If the average particle size is outside this range, the amount of hard, coarse aggregated particles increases, resulting in poor moldability and sinterability of the zirconia powder. Because moldability and sinterability tend to be high, the average particle size is preferably 0.05 μm or more and 0.4 μm or less, more preferably 0.05 μm or more and 0.35 μm or less, and even more preferably 0.1 μm or more and 0.3 μm or less.

[0029] For the same reason, the zirconia powder of this embodiment is a powder in which the proportion of particles of 1 μm or less in the volume particle size distribution (hereinafter also referred to as the "particle ratio") is 100%, and does not contain particles exceeding 1 μm in the volume particle size distribution. Therefore, the zirconia powder of this embodiment can also be considered as a fine zirconia powder.

[0030] Since moldability tends to be improved, the zirconia powder of this embodiment preferably has a ratio of particles of 0.2 μm or less in the volume particle size distribution (hereinafter also referred to as the "microparticle ratio") of 10% or more and 90% or less, more preferably 20% or more and 80% or less, and even more preferably 30% or more and 70% or less.

[0031] Since a dense sintered body can be easily obtained even at a lower sintering temperature, the zirconia powder of this embodiment preferably has a particle size peak with a top at 0.3 to 0.5 μm in its volume particle size distribution, and the width of the particle size peak is preferably 0.05 μm or more and 0.2 μm or less.

[0032] The particle ratio and fine particle ratio are the proportions of particles of each particle size relative to a cumulative value of 100% in a cumulative volume particle size distribution curve obtained by measuring volume particle size distribution by laser diffraction, and the particle size peak is the peak in the particle size distribution obtained by measuring volume particle size distribution by laser diffraction.

[0033] Other physical properties of the zirconia powder of this embodiment are optional, but for example, the BET specific surface area is preferably 11 m 2 / g or more 20m 2 / g or less, more preferably 13m 2 / g or more 19m 2 / g or less, and the average crystallite size is 26 nm or more and 50 nm or less, preferably 30 nm or more and 45 nm or less, and more preferably 35 nm or more and 40 nm or less.

[0034] The zirconia powder of this embodiment may contain a stabilizer with the remainder being zirconia. However, to improve sinterability by accelerating the densification rate, the zirconia powder of this embodiment preferably contains a compound (hereinafter also referred to as "additive") containing at least one of a cation with an ionic radius smaller than that of the zirconium ion and a cation with a valence other than tetravalent. This facilitates the production of a high-density zirconia sintered body even at lower sintering temperatures. The additive is preferably a compound containing one or more cations selected from the group consisting of aluminum, silicon, and germanium, more preferably a compound containing at least one of aluminum and germanium cations, and even more preferably a compound containing aluminum cations and germanium cations. Specific examples of the additive include one or more selected from the group consisting of alumina (Al2O3), silica (SiO2), and germania (Ge2O3), preferably at least one of alumina and germania. The zirconia powder of this embodiment preferably does not contain a cation with an ionic radius equal to or larger than that of the zirconium ion and a valence of tetravalent.

[0035] In the reference, the zirconium cation has an ionic radius of 0.86 Å and a valence of 4, the aluminum cation has an ionic radius of 0.68 Å and a valence of 3, the silicon cation has an ionic radius of 0.54 Å and a valence of 4, and the germanium cation has an ionic radius of 0.67 Å and a valence of 4.

[0036] The content of the additives can be, for example, 0% by mass or more and 1% by mass or less in terms of the mass ratio of the additives converted into oxides relative to the mass of the zirconia powder.If additives are contained, the content can be, for example, more than 0% by mass and 1% by mass or less, or even 0.05% by mass or more and 0.8% by mass or less.

[0037] The zirconia powder of this embodiment may be in the form of slowly agglomerated particles, so-called granules. When the zirconia powder of this embodiment is in the form of granules, the average granule size is 30 μm or more and 80 μm or less, and the bulk density is 1.10 g / cm 3 More than 1.40g / cm 3 The following can be exemplified.

[0038] The zirconia powder of this embodiment is preferably used as a zirconia powder for a solid electrolyte to obtain a zirconia sintered body for a solid electrolyte.

[0039] The zirconia powder of this embodiment can be obtained by a production method characterized by comprising a step of mixing a zirconia sol having an amount of zirconium element calculated by the following formula of 2 mass % or less with one or more compounds selected from the group consisting of yttrium, calcium, magnesium, and cerium. W Zr =(m / m0)×100

[0040] In the above formula, W Zr is the amount of adsorbed zirconium (mass%). m is the mass (mg) of zirconium in the filtrate obtained by ultrafiltration of a slurry in which zirconia sol is dispersed in pure water using an ultrafiltration membrane with a molecular weight cutoff of 500 to 3,000,000, converted into zirconia (ZrO2). m o is the mass (mg) of the zirconia sol before ultrafiltration after heat treatment at 1000°C for 1 hour in an air atmosphere. The amount of zirconium in the filtrate can be measured by ICP analysis.

[0041] The zirconia sol subjected to the step of mixing the zirconia sol with a compound such as yttrium (hereinafter also referred to as the "mixing step") has an amount of zirconium element calculated by the following formula (hereinafter also referred to as the "adsorbed zirconium amount") of 2 mass% or less, preferably 0 mass% or more and 1 mass% or less, more preferably 0 mass% or more and 0.5 mass% or less, and even more preferably 0 mass% or more and 0.01 mass% or less. WZr =(m / m0)×100

[0042] In the above formula, W Zr is the amount of adsorbed zirconium (mass%). m is the mass (mg) of zirconium in the filtrate obtained by ultrafiltration of a slurry in which zirconia sol is dispersed in pure water using an ultrafiltration membrane with a molecular weight cutoff of 500 to 3 million, converted into zirconia (ZrO2). The amount of zirconium in the filtrate can be measured by ICP analysis. m o m and m are the mass (mg) of the zirconia sol before ultrafiltration after heat treatment at 1000°C for 1 hour in an air atmosphere. o The measurements of (a) and (b) can be carried out by preparing the same amount of zirconia sol before ultrafiltration.

[0043] If the amount of adsorbed zirconium exceeds 2 mass %, the powder particles are strongly sintered together during calcination, resulting in an increase in coarse particles including hard agglomerates, which results in poor compactibility and sinterability.

[0044] The zirconia sol preferably has an average sol particle size of 0.05 μm or more and 0.2 μm or less, as this improves moldability.

[0045] The zirconia sol may be produced by any method as long as it has the above-mentioned characteristics. Examples of methods for producing the zirconia sol include at least one of a hydrothermal synthesis method and a hydrolysis method. In the hydrothermal synthesis method, a coprecipitate obtained by mixing a zirconium salt with an alkali or the like in the presence of a solvent is heat-treated at 100 to 200°C to obtain the zirconia sol. In the hydrolysis method, the zirconium salt is heated in the presence of a solvent to hydrolyze the zirconium salt, thereby obtaining the zirconia sol. Thus, examples of the zirconia sol include a zirconia sol obtained by a hydrothermal synthesis method or a hydrolysis method, and a zirconia sol obtained by a hydrolysis method is preferred.

[0046] When obtaining a zirconia sol by hydrolysis, it is preferable to control the pH at the end of the reaction. This makes it easier to control the average sol particle size of the zirconia sol. For example, to obtain a hydrated zirconia sol with an average sol particle size of 0.05 to 0.2 μm, it is preferable to make the pH at the end of the reaction at least either acidic or basic, specifically at least either 0.3 to 0.6 or 0.8 to 1.4.

[0047] The zirconium salt used in producing the zirconia sol may be one or more selected from the group consisting of zirconium oxychloride, zirconyl nitrate, zirconium chloride, and zirconium sulfate. At least one of zirconium chloride and zirconium oxychloride is preferred, and zirconium oxychloride is more preferred. In another embodiment, the zirconium salt may be a mixture of zirconium hydroxide and an acid. The acid may be at least one of an inorganic acid and an organic acid, preferably one or more selected from the group consisting of acetic acid, citric acid, hydrochloric acid, nitric acid, and sulfuric acid, more preferably one or more selected from the group consisting of hydrochloric acid, nitric acid, and sulfuric acid.

[0048] The alkali used in the production of the zirconia sol can be at least one selected from the group consisting of ammonia, sodium hydroxide, and potassium hydroxide. In another embodiment, the alkali is a compound that decomposes to become basic, such as urea.

[0049] The one or more compounds selected from the group consisting of yttrium, calcium, magnesium, and cerium (hereinafter also referred to as "stabilizer source") used in the production method of this embodiment can be exemplified by one or more selected from the group consisting of chlorides, fluorides, nitrates, carbonates, sulfates, acetates, oxides, and hydroxides containing one or more selected from the group consisting of yttrium, calcium, magnesium, and cerium, preferably one or more selected from the group consisting of chlorides, fluorides, oxides, and hydroxides, and more preferably at least one of chlorides and oxides.

[0050] The zirconia sol and the stabilizer source may be mixed uniformly by any method, for example, by adding the stabilizer source to an aqueous solution of zirconia sol.

[0051] The concentration of the stabilizer source to be mixed with the zirconia sol may be adjusted so that the amount of the stabilizer source, calculated as an oxide relative to the amount of zirconia in the zirconia sol, is the desired stabilizer content in the zirconia powder. For example, when the stabilizer source is an yttria source, the amount may be more than 4 mol% to 12 mol%, preferably 6 mol% to 10 mol%.

[0052] The manufacturing method of this embodiment preferably includes a step of drying the zirconia sol after mixing with the stabilizer source (hereinafter also referred to as a "drying step"). The drying method may be any method that can remove the solvent, hydration water of the zirconia sol, and adsorbed water, and examples thereof include treatment in the air at 120 to 200°C.

[0053] The manufacturing method of this embodiment includes a step of treating the zirconia sol at a calcination temperature of 900°C or higher and 1200°C or lower (hereinafter also referred to as the "calcination step"), which results in the production of the zirconia powder of this embodiment. When the calcination temperature is within this range, the zirconia powder particles do not strongly agglomerate with each other, or the formation of strongly agglomerated coarse particles is unlikely. This makes it easier to control the average particle size of the zirconia powder of this embodiment by pulverization or the like. Preferred calcination conditions include 900°C or higher and 1100°C or lower.

[0054] When producing a zirconia powder containing an additive, the additive may be mixed with the zirconia sol in at least one of the mixing step and the calcination step. The additive to be mixed with the zirconia sol is optional, but examples thereof include one or more selected from the group consisting of alumina, hydrated alumina, alumina sol, aluminum hydroxide, aluminum chloride, aluminum nitrate, aluminum sulfate, silica, silica sol, silicic acid, germanium oxide, and germanium hydroxide. The additive is preferably one or more selected from the group consisting of alumina, hydrated alumina, alumina sol, aluminum hydroxide, aluminum chloride, aluminum nitrate, aluminum sulfate, germanium oxide, and germanium hydroxide. The additive is more preferably one or more selected from the group consisting of alumina, hydrated alumina, alumina sol, germanium oxide, and germanium hydroxide. The additive is further preferably at least one of alumina and germanium oxide.

[0055] In order to achieve the average particle size and particle size ratio of the zirconia powder of this embodiment, a step of pulverizing the zirconia powder (hereinafter also referred to as a "pulverizing step") may be included. The pulverization method may be either dry pulverization or wet pulverization, with wet pulverization being preferred. A particularly preferred pulverization method is wet pulverization using zirconia balls as the pulverization medium, preferably zirconia balls with a diameter of 3 mm or less, more preferably zirconia balls with a diameter of 2 mm or less. Specific examples of wet pulverization include pulverization using one or more selected from the group consisting of a vibration mill, a continuous media stirring mill, and a ball mill.

[0056] In the manufacturing method of this embodiment, when the zirconia powder is to be made into granules, it can be granulated by a known method, for example, spray granulation.

[0057] The zirconia powder of this embodiment can be used in a method for producing a sintered body using the zirconia powder of this embodiment. Any method for producing a sintered body using the zirconia powder of this embodiment can be used, and examples include a method of molding the zirconia powder of this embodiment and sintering the resulting molded body, and a method of molding the zirconia powder of this embodiment, calcining the resulting molded body, and sintering the resulting calcined body.

[0058] Any molding method may be used, including at least one selected from the group consisting of mold press molding, sheet molding, doctor blade molding, calendar roll molding, injection molding, and cold isostatic pressing (CIP). Specific molding methods include, for example, mold press molding at a pressure of 20 MPa to 100 MPa, preferably 30 MPa to 80 MPa, and CIP at a pressure of 30 MPa to 250 MPa, preferably 50 MPa to 200 MPa. The zirconia powder used for molding may be zirconia powder or a composition containing zirconia powder.

[0059] The sintering method can be one or more selected from the group consisting of atmospheric sintering, pressure sintering, and vacuum sintering, with at least one of atmospheric sintering and pressure sintering being preferred. Because of its simplicity, atmospheric sintering is preferred, with atmospheric sintering in an air atmosphere being particularly preferred. Conditions for atmospheric sintering include a sintering temperature of 1200°C to 1600°C, preferably 1250°C to 1500°C, and a sintering time of 1 hour to 24 hours, preferably 2 hours to 20 hours. However, since the zirconia powder of this embodiment can produce a zirconia sintered body with high conductivity even at a sintering temperature lower than conventional temperatures, the sintering temperature is more preferably 1200°C to 1400°C, and particularly preferably 1200°C to 1325°C.

[0060] The zirconia sintered body obtained from the zirconia powder of this embodiment (hereinafter also referred to as "the zirconia sintered body of this embodiment") contains one or more stabilizers selected from the group consisting of yttria, calcia, magnesia, and ceria. The stabilizer is preferably at least one of yttria and ceria, and more preferably yttria.

[0061] The type and content of the stabilizer may be appropriately changed depending on the desired properties of the zirconia sintered body. For example, when the stabilizer is yttria, the content of yttria is preferably more than 4 mol% and not more than 12 mol%, and more preferably 6 mol% or more and not more than 10 mol%.

[0062] The zirconia sintered body of the present embodiment may contain a stabilizer, with the remainder being zirconia, but may also contain one or more selected from the group consisting of alumina (Al2O3), silica (SiO2), and germania (Ge2O3), preferably at least one of alumina and germania.

[0063] The zirconia sintered body of this embodiment preferably contains at least cubic crystals in the crystalline phase, with cubic crystals being the main phase, and more preferably is made up of only cubic crystals. This tends to increase electrical conductivity. In the zirconia sintered body of this embodiment, "cubic crystals being the main phase" means that the proportion of cubic crystals in the zirconia crystalline phase is the highest.

[0064] The zirconia sintered body of this embodiment has a measured density of 5.76 g / cm 3 and preferably 5.82 g / cm 3 More preferably, 5.94 g / cm 3 That's all.

[0065] The upper limit of the actually measured density is the theoretical density. When the zirconia sintered body of this embodiment is a sintered body obtained by atmospheric sintering (atmospheric sintered body), the actually measured density is 6.02 g / cm 3 Below that, 6.01g / cm 3 The following points can be mentioned.

[0066] The zirconia sintered body of this embodiment may have a three-point bending strength of 350 MPa or more, preferably 380 MPa or more, and more preferably 400 MPa or more, measured by a method in accordance with JIS R 1601. When the zirconia sintered body of this embodiment is a sintered body obtained by atmospheric sintering (atmospheric sintered body), the three-point bending strength may be 600 MPa or less, or even 500 MPa or less.

[0067] The zirconia sintered body of the present embodiment preferably has a conductivity suitable for a solid electrolyte, particularly a low-temperature solid electrolyte that operates at temperatures below 800°C. Specifically, the conductivity at 600°C is 5.0 × 10 -3 S / cm or more, and 6.5 x 10 -3 When the zirconia sintered body of the present embodiment is a sintered body obtained by atmospheric sintering (atmospheric sintered body), the electrical conductivity is preferably 1.0 × 10 -2 S / cm or less.

[0068] The zirconia sintered body of this embodiment exhibits high electrical conductivity and can therefore be used as a solid electrolyte, and further as a solid electrolyte for solid oxide fuel cells (SOFCs).

[0069] The SOFC including the zirconia sintered body of this embodiment may be any SOFC including a fuel electrode, an air electrode, and the zirconia sintered body of this embodiment.

[0070] The fuel electrode may be made of any known material, such as a Ni-zirconia cermet material composed of 60 mass % nickel and 40 mass % zirconia.

[0071] The air electrode may be made of any known material, such as lanthanum strontium manganate (La(Sr)MnO3).

[0072] Any method can be used to manufacture an SOFC including the zirconia sintered body of this embodiment. For example, one surface of the zirconia sintered body of this embodiment is coated with at least one of an anode and its precursor compound, and the other surface is coated with at least one of an air electrode and its precursor compound, and then the resulting body is sintered as a single unit. Furthermore, the zirconia powder of this embodiment provides a zirconia sintered body that exhibits high electrical conductivity even at sintering temperatures similar to those of the anode and air electrode. Therefore, by stacking at least one of an anode and its precursor compound, the zirconia powder of this embodiment, and at least one of an air electrode and its precursor compound, and molding and sintering the resulting body as a single unit, an SOFC in which the anode, solid electrolyte, and air electrode are integrated can be obtained by a single sintering process. [Example]

[0073] The present embodiment will be specifically described below using examples, but the present disclosure is not limited to these examples. (average sol particle size) The average sol particle size of the zirconia sol was measured using a dynamic light scattering particle size distribution analyzer (apparatus name: UPA The measurement was performed using a zirconia sol-containing solution (UT151, manufactured by Microtrack Bell Co., Ltd.). As a pretreatment for the sample, the solution containing the zirconia sol was suspended in pure water and dispersed for 3 minutes using an ultrasonic homogenizer. (Amount of adsorbed zirconium) A portion of the slurry containing the hydrolyzed zirconia sol was recovered, and half of it was subjected to ultrafiltration using an ultrafiltration membrane with a molecular weight cutoff of 5 to 3 million to obtain a filtrate. The remaining half of the slurry was heat-treated in air at 1000°C for 1 hour, and the mass (mg) was measured. The zirconium content of each was measured by ICP analysis to determine m and m0. The amount of adsorbed zirconium was calculated using the following formula: W Zr =(m / m0)×100

[0074] (Particle size distribution measurement) The volumetric particle size distribution curve and cumulative volumetric particle size distribution curve of the powder sample were obtained using the HRA mode of a Microtrac particle size distribution analyzer (product name: MT3000II, Microtrac Bell Co., Ltd.), and the average particle size, particle ratio, fine particle ratio, particle size peak, and particle size peak width were measured using the attached analysis software. Prior to measurement, the powder sample was suspended in pure water and dispersed for 10 minutes using an ultrasonic homogenizer as pretreatment. (monoclinic phase ratio) An XRD pattern of the powder sample was obtained using a general X-ray diffractometer (trade name: Ultima II V, manufactured by Rigaku Corporation). The conditions for the XRD measurement were as follows: Radiation source: CuKα radiation (λ=0.15418nm) Measurement mode: Continuous scan Scan speed: 4° / min Step width: 0.02° Measurement range: 2θ=26°~33° Using the obtained XRD pattern and the calculation program "PRO-FIT", the monoclinic fraction was calculated according to the above formula.

[0075] (BET specific surface area) The BET specific surface area of ​​the powder samples was measured using a general flow-type automatic specific surface area measuring device (Device name: FlowSorb III2305, manufactured by Shimadzu Corporation) and nitrogen as the adsorption gas. Prior to the measurement, the powder samples were pretreated by degassing in air at 250°C for 30 minutes. (Average particle size) The average particle size of the zirconia granules was determined by a sieving test method. (Molded object density) The mass of the compact sample was measured with a balance, and the volume was measured with a vernier caliper to determine the dimensions. The actual density was calculated from the obtained mass and volume. (sintered body density) The actual density of the sintered body sample was measured by the Archimedes method. Prior to the measurement, the mass of the sintered body after drying was measured, and then the sintered body was placed in water and boiled for 1 hour as a pretreatment. (three-point bending strength) The bending strength of the sintered body samples was measured by a three-point bending test in accordance with JIS R 1601. The measurement was carried out using a columnar sintered body sample with a width of 4 mm and a thickness of 3 mm, with a support distance of 30 mm, and the bending strength was calculated as the average value of 10 measurements. (conductivity) The conductivity was measured by an AC impedance method using a frequency response analyzer (device name: 1260, manufactured by Solartron) and a potentiostat (device name: 1286A, manufactured by Solartron) as the measuring equipment. The measurement conditions are shown below. Measurement sample: rectangular sintered body, 4mm long x 3mm wide, 35mm long Measurement atmosphere: Air Measurement temperature: 600℃ Measurement method: Four-probe method Electrode terminal: Pt wire (diameter 0.2mm) Distance between voltage terminals: 15mm Measurement frequency: 1MHz~0.1Hz Applied current: 1mA

[0076] Example 1 A 2 mol / L aqueous solution of zirconium oxychloride was mixed with 2 mol / L aqueous ammonia and pure water to obtain an aqueous solution of zirconium oxychloride with a zirconia-equivalent concentration of 0.8 mol / L. The resulting aqueous solution was hydrolyzed at boiling temperature for 200 hours with stirring to obtain a zirconia sol. The resulting zirconia sol had an adsorbed zirconium content of 0.5% by mass and an average sol particle size of 0.1 μm.

[0077] Yttrium chloride was added to and mixed with the zirconia sol so that the yttria concentration was 8 mol %, and the sol was dried in air at 160°C, and then calcined in air at 980°C for 2 hours to obtain zirconia powder.

[0078] The obtained zirconia powder was washed with a sufficient amount of pure water, then formed into a slurry, which was then pulverized for 24 hours in a vibration mill equipped with zirconia balls having a diameter of 2 mm as a pulverizing medium, and then dried at 130°C in the air to obtain the zirconia powder of this example.

[0079] The zirconia powder of this embodiment was molded under a pressure of 70 MPa by press molding, and then sintered under atmospheric pressure at 1300°C for 2 hours in the air to obtain a zirconia sintered body of this example.

[0080] Example 2 After washing with pure water, the zirconia powder of this example was obtained under the same conditions as in Example 1, except that alumina sol was added to the zirconia powder so that the alumina content was 0.25% by mass.

[0081] The zirconia sintered body of this example was obtained in the same manner as in Example 1, except that the sintering temperature was 1250°C.

[0082] Example 3 After washing with pure water, the zirconia powder of this example was obtained under the same conditions as in Example 1, except that alumina sol was added to the zirconia powder so that the alumina content was 0.25 mass% and germania was added to the zirconia powder so that the germania content was 0.25 mass%.

[0083] The zirconia sintered body of this example was obtained in the same manner as in Example 1, except that the sintering temperature was 1200°C.

[0084] Example 4 Zirconia powder and pure water were mixed to form a slurry in the same manner as in Example 1, and then this was spray-granulated to form a granular powder. The average granule diameter of the zirconia granules was 55 μm, and the loose bulk density was 1.29 g / cm. 3 It was.

[0085] A zirconia sintered body of this example was obtained in the same manner as in Example 1, except that the obtained zirconia granules were used.

[0086] Example 5 The zirconia powder of this example was obtained in the same manner as in Example 1, except that yttrium chloride was added to the zirconia sol so that the yttria concentration was 10 mol %, that alumina sol was added to the zirconia powder after washing with pure water so that the alumina content was 0.25 mass %, and that the zirconia powder was calcined in air at 970°C for 2 hours.

[0087] The zirconia sintered body of this example was obtained in the same manner as in Example 1, except that the obtained zirconia powder was used and the sintering temperature was set to 1250°C.

[0088] Comparative Example 1 A 0.37 mol / L aqueous solution of zirconium oxychloride was hydrolyzed at boiling temperature for 160 hours with stirring to obtain a zirconia sol with an adsorbed zirconium content of 12 mass% and an average sol particle size of 0.1 μm.

[0089] Yttrium chloride was added to and mixed with the zirconia sol so that the yttria concentration was 8 mol %, and the sol was dried at 160°C in the air, and then calcined at 1030°C for 2 hours in the air to obtain zirconia powder.

[0090] The obtained zirconia powder was washed with a sufficient amount of pure water, then formed into a slurry, which was then pulverized for 30 hours in a vibration mill equipped with zirconia balls having a diameter of 10 mm as a pulverizing medium, and then dried at 130°C in the air to obtain the zirconia powder of this comparative example.

[0091] The zirconia powder of this comparative example was molded under a pressure of 70 MPa by press molding, and then sintered under atmospheric pressure at 1300°C for 2 hours to obtain a zirconia sintered body of this comparative example.

[0092] Comparative Example 2 A zirconia powder of this comparative example was obtained in the same manner as in Example 1, except that yttrium chloride was added to the zirconia sol so that the yttria concentration was 4 mol %.

[0093] A zirconia sintered body was obtained in the same manner as in Example 1, except that the sintering temperature was 1350°C.

[0094] Comparative Example 3 A zirconia sol was obtained in the same manner as in Example 1. The obtained zirconia sol was washed with a sufficient amount of water, and the obtained zirconia sol had an adsorbed zirconium amount of 0.5 mass % and an average sol particle size of 0.1 μm.

[0095] Yttrium chloride was added to and mixed with the zirconia sol so that the yttria concentration was 8 mol %, and the sol was dried at 160°C in air, and then calcined at 990°C in air for 2 hours to obtain zirconia powder.

[0096] The obtained zirconia powder was washed with a sufficient amount of pure water, then formed into a slurry, which was then pulverized for 24 hours in a vibration mill equipped with 10 mm diameter zirconia balls as a pulverization medium, and then dried at 130°C in the air to obtain the zirconia powder of this comparative example.

[0097] A zirconia sintered body was obtained in the same manner as in Example 1, except that the sintering temperature was 1350°C.

[0098] The evaluation results of the zirconia powders obtained in the Examples and Comparative Examples are shown in the table below. In the volume particle size distribution, all of the zirconia powders of the Examples had a particle size peak with a peak top at 0.3 to 0.5 μm, and the width of the particle size peak was 0.1 μm. It was also confirmed that Comparative Example 1 had an average particle size exceeding 0.5 μm and a particle ratio of 80% or less, and that Comparative Examples 2 and 3 had a monoclinic fraction of 1% or more.

[0099] [Table 1]

[0100] The evaluation results of the zirconia sintered bodies obtained in the Examples and Comparative Examples are shown in the table below. Although the zirconia sintered bodies of the Examples and Comparative Example 1 were both obtained by low-temperature sintering at 1300°C or less, the zirconia sintered body of Comparative Example 1 had an electrical conductivity of 5.0 × 10 at 600°C. -3 S / cm, whereas the zirconia sintered body of the example has a conductivity of 8.0 × 10 -3It can be confirmed that the material has high electrical conductivity of S / cm or more.

[0101] Furthermore, the zirconia sintered bodies of Comparative Examples 2 and 3 were sintered at a relatively high temperature of 1350°C, but their electrical conductivity was 5.0 × 10 -3 It can be confirmed that the electrical conductivity is low, at less than S / cm.

[0102] The measured density of the compact of Comparative Example 1 was 2.55 g / cm 3 In contrast, the measured densities of the compacts of Examples 1 and 5, which had the same composition, were both 2.76 g / cm 3 It can be confirmed that these zirconia powders exhibit high moldability.

[0103] [Table 2]

Claims

1. Contains 6 mol% or more and 10 mol% or less of yttria, and has a measured density of 5.76 g / cm ３ 6.01g / cm or more ３ and the electrical conductivity at 600°C is 5.0 × 10 －３ A zirconia sintered body characterized in that the zirconia sintered body has a three-point bending strength of 353 MPa or more and 600 MPa or less, as measured by a method in accordance with JIS R 1601.

2. The zirconia sintered body according to claim 1, wherein the crystalline phase contains at least cubic crystals.

3. Alumina (Al ２ O ３ ), silica (SiO ２ ) and germania (Ge ２ O ３ The zirconia sintered body according to claim 1 or 2, comprising one or more selected from the group consisting of:

4. The zirconia sintered body according to any one of claims 1 to 3, which is for use in a solid electrolyte.

5. A solid electrolyte comprising the zirconia sintered body according to any one of claims 1 to 4.

6. A method for producing a solid electrolyte, which uses the zirconia sintered body according to any one of claims 1 to 4.

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