JP2023171832A - Zirconia powder and its production method - Google Patents

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

The present disclosure relates to zirconia powder, particularly zirconia powder that provides a zirconia sintered body suitable for solid electrolytes.

Zirconia-based solid electrolytes are used in solid oxide fuel cells (SOFC) and the like. For example, in Patent Document 1, after pulverizing a zirconia sintered body containing yttria (Y ₂ O ₃ ) and ceria (CeO ₂ ), a mixture of lanthanide oxide, manganese dioxide, and iron oxide is heated at 1450°C. A solid electrolyte obtained by sintering has been reported. Furthermore, in Patent Document 2, a solid electrolyte layer made of 8 mol% or 10 mol% yttria-containing zirconia is integrated with a fuel electrode obtained by co-sintering a molded body including a fuel electrode and a barrier layer at 1400°C. A solid electrolyte is disclosed.

International Publication 2012/105580 Patent No. 5770400

Both of the zirconia-based solid electrolytes of Patent Documents 1 and 2 require a high sintering temperature of 1400° C. or higher in order to develop practical conductivity.

In contrast, the present disclosure provides a zirconia powder that provides a zirconia sintered body that exhibits high electrical conductivity even when sintered at low temperatures, a method for producing the same, a zirconia sintered body obtained from the zirconia powder, and a zirconia sintered body obtained from the zirconia powder. The present invention aims to provide at least one of a manufacturing method and a solid electrolyte using the same.

The gist of the present disclosure is as follows.
[1] Contains one or more stabilizers selected from the group of yttria, calcia, magnesia, and ceria, the proportion of monoclinic crystals in the crystal phase is 0.5% or less, and the average particle diameter is less than 0.5 μm A zirconia powder characterized in that the proportion of particles of 1 μm or less in the volume particle size distribution is 100%.
[2] The zirconia powder according to the above [1], wherein the proportion of particles of 0.2 μm or less in the volume particle size distribution is 10% or more and 90% or less.
[3] The zirconia powder according to [1] or [2] above, which has a particle size peak with a peak top at 0.3 to 0.5 μm in the 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 12 mol% or less.
[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 the above [5], wherein the compound contains one or more cations selected from the group of aluminum, silicon, and germanium.
[7] The zirconia powder according to [5] or [6] above, wherein the content of the compound is more than 0% by mass and not more than 1% by mass.
[8] The zirconia powder according to any one of [1] to [7] above, having an average granule diameter of 30 μm or more and 80 μm or less, and a light bulk density of 1.00 g/cm ^{3 or} more and 1.40 g/cm 3 or less.

[9] A step of mixing a zirconia sol with a zirconium element content of 2% by mass or less as determined by the following formula and one or more compounds selected from the group of yttrium, calcium, magnesium, and cerium, and a zirconia sol The method for producing zirconia powder according to any one of items [1] to [8] above, comprising the step of treating at a calcination temperature of 900° C. or more and 1200° C. or less.
W _Zr = (m/m ₀ )×100
In the above formula, _WZr is the amount of adsorbed zirconium (% by mass). m is the amount of zirconium in the filtrate obtained by ultrafiltration of a slurry prepared by dispersing zirconia sol in pure water using an ultrafiltration membrane with a molecular weight cutoff of 500 to 3 million, converted to zirconia (ZrO ₂ ). The mass (mg). m _o is the mass (mg) after heat-treating the zirconia sol before ultrafiltration at 1000° C. for 1 hour in the air atmosphere.
[10] A method for producing a zirconia sintered body, which uses the zirconia powder described in any one of [1] to [8] above.
[11] A zirconia sintered product containing one or more stabilizers selected from the group of yttria, calcia, magnesia and ceria, and having an electrical conductivity of 5.0×10 ⁻³ S/cm or more at 600°C. Concretion.
[12] A solid electrolyte comprising the zirconia sintered body according to [11] above.

The present disclosure provides a zirconia powder that provides a zirconia sintered body that exhibits high electrical conductivity even when sintered at low temperatures, a method for producing the same, a zirconia sintered body obtained from the zirconia powder, a method for producing the same, and a method for producing the same. A solid electrolyte using a solid electrolyte can be provided.

Hereinafter, an example of an embodiment of the zirconia powder of the present disclosure will be described.

The "average particle diameter" is a particle diameter (median diameter) corresponding to a volume ratio of 50% in a cumulative volume particle diameter distribution curve obtained by volume particle diameter distribution measurement using a laser diffraction method.

"Crystallite diameter" is calculated by calculating the Bragg angle (θ) of the diffraction line measured by powder X-ray diffraction (XRD) method and the half-width (β) of the diffraction line corrected for the mechanical broadening width. This is the value calculated using Equation 3.
Dx = κλ/(β・cosθ)
In the above equation, κ is the Scheler constant (κ=1), λ is the measurement wavelength, and β is. The crystallite diameter of the zirconia fine powder is determined by the most intense diffraction line.

The "BET specific surface area" is a value determined by the BET one-point method using nitrogen (N ₂ ) as the adsorbent in accordance with JIS R 1626-1996.

"Stabilizer content" is the molar ratio of stabilizer to zirconia and stabilizer in terms of oxide.

"Ratio of monoclinic crystal in the crystal phase" (hereinafter also referred to as "monoclinic phase ratio") is the ratio of monoclinic crystal in the crystal phase of zirconia. For the powder, the powder X-ray diffraction (hereinafter also referred to as "XRD") pattern is used, while for the sintered body, the XRD pattern of the surface of the sintered body after mirror polishing is used. It can be obtained from the formula.

f _m ={I _m (111)+I _m (11-1)}/[I _m (111)
+I _m (11-1)+I _t (111)+I _c (111)]×100

In the above formula, f _m is the monoclinic phase ratio (%), I _m (111) and I _m (11-1) correspond to the (111) plane and (11-1) plane of the monoclinic crystal, respectively. 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 of the XRD peak corresponding to the (111) plane of the cubic crystal. It is strength.

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

In the above-mentioned XRD pattern measurement, preferably, the XRD peak corresponding to each crystal plane of zirconia is measured as a peak having a peak top at the following 2θ.

XRD peak corresponding to monoclinic (111) plane: 2θ=31±0.5°
XRD peak corresponding to 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 the 2θ thereof was 2θ=30±0.5°.

The area intensity of the XRD peak of each crystal plane was determined using the calculation program "PRO-FIT" and the H. Toraya, J. Appl. Crystallogr. , 19, 440-447 (1986), each XRD peak can be separated and determined.

"Ionic radius" is Acta. Crystallogr. , A32, 751-67 (1976). (hereinafter also referred to as "references").

"Additive content" refers to the ratio of additive/(ZrO ₂ + stabilizer + additive) expressed as mass %. Here, the additives are values converted to oxides.

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

The "actually measured density of the sintered body" can be measured using the Archimedes method.

The zirconia powder of this embodiment contains one or more stabilizers selected from the group of yttria, calcia, magnesia, and ceria. The stabilizer is preferably at least one of yttria and ceria. The stabilizer is more preferably yttria, since a zirconia sintered body having properties suitable as a solid electrolyte can be obtained.

The type and content of the stabilizer may be changed as appropriate depending on the desired characteristics of the zirconia sintered body. For example, when the stabilizer is yttria, the content of yttria is preferably more than 4 mol% and no more than 12 mol%, more preferably 6 mol% or more and no more than 10 mol%.

In the zirconia powder of this embodiment, the proportion of monoclinic crystal in the crystal phase (hereinafter also referred to as "monoclinic phase ratio") is 0.5% or less, and is 0% or more and 0.2% or less. It is preferable. When the monoclinic phase ratio exceeds this range, the sintering temperature required for densification becomes high, and coarse pores are likely to remain even if densification progresses. As long as the monoclinic phase ratio is 0.5% or less, other crystal phases are optional, and include tetragonal and cubic, preferably cubic. The crystal phase of the zirconia powder of this embodiment is preferably composed of cubic crystals and monoclinic crystals.

The zirconia powder of this embodiment has an average particle diameter of less than 0.5 μm. If the average particle diameter is outside this range, there will be many hard and coarse agglomerated particles, and the formability and sinterability of the zirconia powder will decrease. Since moldability and sinterability tend to be high, the average particle diameter 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. .3 μm or less.

For the same reason, in the zirconia powder of this embodiment, the ratio of particles of 1 μm or less in the volume particle size distribution (hereinafter also referred to as "particle ratio") is 100%, and the proportion of particles larger than 1 μm in the volume particle size distribution is 100%. It is a powder containing no particles. Therefore, the zirconia powder of this embodiment can also be considered as a zirconia fine powder.

Since moldability tends to improve, the zirconia powder of this embodiment preferably has a volume particle size distribution in which the ratio of particles of 0.2 μm or less (hereinafter also referred to as "fine particle ratio") is 10% or more. It is 90% or less, more preferably 20% or more and 80% or less, and still more preferably 30% or more and 70% or less.

Since a dense sintered body can be easily obtained even at a lower sintering temperature, the zirconia powder of this embodiment has particles having a peak top at 0.3 to 0.5 μm in the volume particle size distribution. It is preferable to have a diameter peak. Moreover, it is preferable that the width of the particle size peak is 0.05 μm or more and 0.2 μm or less.

Particle ratio and fine particle ratio are the ratios of particles of each particle size to 100% of the cumulative value in the cumulative volume particle size distribution curve obtained by volume particle size distribution measurement using laser diffraction method. This is a peak in the particle size distribution obtained by volume particle size distribution measurement using the method.

Although other physical properties of the zirconia powder of this embodiment are arbitrary, for example, the BET specific surface area is preferably 11 m ² /g or more and 20 m ² /g or less, more preferably 13 m ² /g or more and 19 m ² /g or less. The average crystallite diameter 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.

It is sufficient that the zirconia powder of this embodiment contains a stabilizer and the remainder is zirconia, but since the sinterability is improved by accelerating the densification rate, the zirconia powder of this embodiment has an ionic radius. It is preferable to include a compound (hereinafter also referred to as "additive") containing at least one of a cation smaller than a zirconium ion and a cation having a valence other than tetravalent. This makes it easier to obtain a high-density zirconia sintered body even at a lower sintering temperature. The additive is preferably a compound containing one or more cations selected from the group of aluminum, silicon, and germanium, and more preferably a compound containing at least one cation of aluminum and germanium. More preferably, it is a compound containing a cation. Specific additives include one or more selected from the group of alumina (Al ₂ O ₃ ), silica (SiO ₂ ), and germania (Ge ₂ O ₃ ), preferably at least one of alumina and germania. It is preferable that the zirconia powder of this embodiment has an ionic radius equal to or larger than a zirconium ion and does not contain a cation having a valence of 4.

In addition, in the reference literature, zirconium cations have an ionic radius of 0.86 Å and a valence of 4, aluminum cations have an ionic radius of 0.68 Å and a valence of 3, and silicon cations have 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.

The content of the additive can be exemplified as 0% by mass or more and 1% by mass or less as the mass ratio of the additive calculated as an oxide with respect to the mass of the zirconia powder. Examples include 0.05% by mass or more and 0.8% by mass or less.

The zirconia powder of this embodiment may be slowly agglomerated particles, so-called granules.
When the zirconia powder of this embodiment is a granule, the average granule diameter is 30 μm or more and 80 μm or less, and the contented bulk density is 1.10 g/cm ³ or more and 1.40 g/cm ³ .

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

The zirconia powder of this embodiment is produced by mixing a zirconia sol having a zirconium element content of 2% by mass or less as determined by the following formula, and one or more compounds selected from the group of yttrium, calcium, magnesium, and cerium. It can be obtained by a manufacturing method characterized by having.
W _Zr = (m/m ₀ )×100

In the above formula, _WZr is the amount of adsorbed zirconium (% by mass). m is the amount of zirconium in the filtrate obtained by ultrafiltration of a slurry prepared by dispersing zirconia sol in pure water using an ultrafiltration membrane with a molecular weight cutoff of 500 to 3 million, converted to zirconia (ZrO ₂ ). The mass (mg). m _o is the mass (mg) after heat-treating the zirconia sol before ultrafiltration at 1000° C. for 1 hour in the air atmosphere. The amount of zirconium in the filtrate may be measured by ICP analysis.

The zirconia sol to be subjected to the process of mixing zirconia sol and a compound such as yttrium (hereinafter also referred to as "mixing process") has an amount of zirconium element (hereinafter also referred to as "adsorbed zirconium amount") determined by the following formula. 2% by mass or less, preferably 0% by mass or more and 1% by mass or less, more preferably 0% by mass or more and 0.5% by mass or less, and 0% by mass or more and 0.01% by mass or less. More preferably.
W _Zr = (m/m ₀ )×100

In the above formula, _WZr is the amount of adsorbed zirconium (% by mass). m is the amount of zirconium in the filtrate obtained by ultrafiltrating a slurry in which zirconia sol is dispersed in pure water using an ultrafiltration membrane with a molecular weight cut-off of 500 to 3 million _. ) is the converted mass (mg). The amount of zirconium in the filtrate may be measured by ICP analysis. m _o is the mass (mg) after heat-treating the zirconia sol before ultrafiltration at 1000° C. for 1 hour in the air atmosphere. The measurements of m and m _o can be carried out by preparing the same amount of zirconia sol before ultrafiltration.

When the amount of adsorbed zirconium exceeds 2% by mass, powder particles are strongly sintered together during calcination, and coarse particles including hard aggregated particles increase. As a result, both formability and sinterability become low.

In order to improve moldability, it is preferable that the average sol particle size of the zirconia sol is 0.05 μm or more and 0.2 μm or less.

The zirconia sol only needs to have the above-mentioned characteristics, and its manufacturing method is arbitrary. Examples of methods for producing zirconia sol include at least one of a hydrothermal synthesis method and a hydrolysis method. In the hydrothermal synthesis method, a zirconia sol is obtained by heat-treating a coprecipitate obtained by mixing a zirconium salt and an alkali etc. in the presence of a solvent at 100 to 200°C. Furthermore, in the hydrolysis method, the zirconium salt is hydrolyzed by heating it in the presence of a solvent to obtain a zirconia sol. As described above, the zirconia sol can be exemplified by a zirconia sol obtained by a hydrothermal synthesis method or a hydrolysis method, and is preferably a zirconia sol obtained by a hydrolysis method.

In addition, when obtaining 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, in order to obtain a hydrated zirconia sol with an average sol particle size of 0.05 to 0.2 μm, the pH at the end of the reaction is preferably at least one of acidic and basic, specifically 0.3 to 0.0. It is preferably at least one of 6 or less and 0.8 or more and 1.4 or less.

The zirconium salt used in the production of zirconia sol includes one or more salts selected from the group of zirconium oxychloride, zirconyl nitrate, zirconium chloride, and zirconium sulfate, preferably at least one of zirconium chloride and zirconium oxychloride, and zirconium oxychloride is more preferable. In another embodiment, the zirconium salt is a mixture of zirconium hydroxide and an acid. The acid is at least one of an inorganic acid and an organic acid, preferably one or more selected from the group of acetic acid, citric acid, hydrochloric acid, nitric acid, and sulfuric acid, more preferably one or more selected from the group of hydrochloric acid, nitric acid, and sulfuric acid. preferable.

Examples of the alkali used for producing the zirconia sol include one or more selected from the group of ammonia, sodium hydroxide, and potassium hydroxide. In another embodiment, the alkali is a compound that decomposes to become basic, such as urea.

One or more compounds selected from the group of yttrium, calcium, magnesium, and cerium (hereinafter also referred to as "stabilizer source") used in the production method of the present embodiment are selected from the group of yttrium, calcium, magnesium, and cerium. Examples include one or more selected from the group of chlorides, fluorides, nitrates, carbonates, sulfates, acetates, oxides, and hydroxides, including one or more of chlorides, fluorides, oxides, and hydroxides. One or more selected from the group of oxides is preferred, and at least one of chlorides and oxides is more preferred.

The zirconia sol and the stabilizer source may be mixed uniformly. Although the mixing method is arbitrary, for example, a method of adding a stabilizer source to an aqueous zirconia sol solution can be mentioned.

The concentration of the stabilizer source to be mixed with the zirconia sol may be such that the stabilizer source in terms of oxide relative to zirconia in the zirconia sol has the desired stabilizer content of the zirconia powder. For example, when the stabilizer source is an yttria source, it may be more than 4 mol% and less than 12 mol%, preferably more than 6 mol% and less than 10 mol%.

The manufacturing method of the present embodiment preferably includes a step of drying the zirconia sol after mixing with the stabilizer source (hereinafter also referred to as "drying step"). The drying method may be any method as long as it can remove the solvent, hydration water and adsorbed water of the zirconia sol, and for example, treatment in the air at 120 to 200° C. may be used.

The manufacturing method of this embodiment includes a step of treating zirconia sol at a calcination temperature of 900°C or more and 1200°C or less (hereinafter also referred to as "calcination step"), whereby the zirconia powder of this embodiment is obtained. . When the calcination temperature is within this range, the aggregation of zirconia powder particles does not become strong, or it becomes difficult to form strongly agglomerated coarse particles. This makes it easier to control the average particle diameter, etc. of the zirconia powder of this embodiment by pulverization or the like. Preferred calcination conditions include 900°C or more and 1100°C or less.

When producing zirconia powder containing additives, the additives may be mixed with zirconia sol in at least one of the mixing step and the calcination step. Additives to be mixed with the zirconia sol are optional, but are from the group of alumina, hydrated alumina, alumina sol, aluminum hydroxide, aluminum chloride, aluminum nitrate, aluminum sulfate, silica, silica sol, silicic acid, germanium oxide and germanium hydroxide. Examples include 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. It is more preferably one or more selected from the group of hydrated alumina, alumina sol, germanium oxide, and germanium hydroxide, and even more preferably at least one of alumina and germanium oxide.

In order to obtain the average particle diameter and particle diameter ratio of the zirconia powder of this embodiment, the process may include a step of pulverizing the zirconia powder (hereinafter also referred to as a "pulverization step"). The pulverization method may be dry pulverization or wet pulverization, and wet pulverization is preferred. A particularly preferred pulverization method includes wet pulverization using zirconia balls, preferably zirconia balls with a diameter of 3 mm or less, more preferably zirconia balls with a diameter of 2 mm or less, as the pulverization medium. A specific example of wet pulverization is pulverization using one or more selected from the group of a vibration mill, a continuous medium stirring mill, and a ball mill.

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

The zirconia powder of this embodiment can be used in a method for manufacturing a sintered body using the zirconia powder. The method for producing a sintered body using the zirconia powder of this embodiment is arbitrary, and examples include a method of molding the zirconia powder of this embodiment and sintering the obtained molded body, and a method of manufacturing the sintered body using the zirconia powder of this embodiment. Examples include a method of molding, calcining the obtained molded body, and sintering the obtained calcined body.

The molding method is arbitrary, but examples include one or more selected from the group of die press molding, sheet molding, doctor blade method, calendar roll method, injection molding, and cold isostatic pressing (CIP). Specific molding methods include, for example, at least one of mold press molding at 20 MPa or more and 100 MPa or less, preferably 30 MPa or more and 80 MPa or less, and CIP method at 30 MPa or more and 250 MPa or less, preferably 50 MPa or more and 200 MPa or less. . The zirconia powder used for molding may be zirconia powder or a composition containing zirconia powder.

Examples of the sintering method include one or more selected from the group of normal pressure sintering, pressure sintering, and vacuum sintering, and at least one of normal pressure sintering and pressure sintering is preferred. Since it is simple, pressureless sintering is preferred, and pressureless sintering in an atmospheric atmosphere is particularly preferred. Conditions for pressureless sintering include a sintering temperature of 1200°C or more and 1600°C or less, further 1250°C or more and 1500°C or less, and a sintering time of 1 hour or more and 24 hours or less, preferably 2 hours or more and 20 hours or less. Can be mentioned. However, with the zirconia powder of this embodiment, a zirconia sintered body with high conductivity can be obtained even at a lower sintering temperature than conventional ones, so the sintering temperature is more preferably 1200°C or more and less than 1400°C, and 1200°C or more and less than 1400°C. Particularly preferred is 1325°C or higher.

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

The type and content of the stabilizer may be changed as appropriate depending on the desired characteristics of the zirconia sintered body. For example, when the stabilizer is yttria, the content of yttria is preferably more than 4 mol% and no more than 12 mol%, more preferably 6 mol% or more and no more than 10 mol%.

The zirconia sintered body of this embodiment may contain a stabilizer, and the remainder may be zirconia, but may be selected from the group of alumina (Al ₂ O ₃ ), silica (SiO ₂ ), and germania (Ge ₂ O ₃ ). It may contain at least one of alumina and germania, preferably alumina and germania.

The zirconia sintered body of this embodiment preferably contains at least cubic crystals in its crystal phase, preferably has cubic crystals as its main phase, and more preferably only cubic crystals. This tends to increase conductivity. In the zirconia sintered body of this embodiment, "having cubic crystal as the main phase" means that the proportion of cubic crystal in the crystal phase of zirconia is the largest.

The zirconia sintered body of this embodiment has an actual density of 5.76 g/cm ³ or more, preferably 5.82 g/cm ³ or more, more preferably 5.94 g/cm ³ or more.

The upper limit of the measured density is the theoretical density, but if the zirconia sintered body of this embodiment is a sintered body obtained by pressureless sintering (pressureless sintered body), the measured density is 6.02 g/cm. ³ or less, more preferably 6.01 g/cm ³ or less.

The zirconia sintered body of this embodiment has a three-point bending strength of 350 MPa or more, preferably 380 MPa or more, and more preferably 400 MPa or more, as measured by a method according to JIS R 1601. preferable. When the zirconia sintered body of this embodiment is a sintered body obtained by pressureless sintering (pressureless sintered body), the three-point bending strength is 600 MPa or less, and further preferably 500 MPa or less.

The zirconia sintered body of this embodiment preferably has a conductivity suitable as a solid electrolyte, particularly a conductivity suitable as a low-temperature solid electrolyte that operates at less than 800°C. Specifically, the conductivity at 600° C. is 5.0×10 ⁻³ S/cm or more, preferably 6.5×10 ⁻³ S/cm or more. When the zirconia sintered body of this embodiment is a sintered body obtained by pressureless sintering (atmospheric pressure sintered body), the electrical conductivity is 1.0×10 ⁻² S/cm or less.

Since the zirconia sintered body of this embodiment exhibits high electrical conductivity, it can be used as a solid electrolyte, and further as a solid electrolyte for solid oxide fuel cells (SOFC).

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

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

The air electrode may be any air electrode made of a known material, such as lanthanum strontium manganate (La(Sr)MnO ₃ ).

The method for manufacturing the SOFC including the zirconia sintered body of this embodiment is arbitrary. For example, after applying at least one of the fuel electrode and its precursor compound to one surface of the zirconia sintered body of this embodiment and applying at least one of the air electrode and its precursor compound to the other surface, One method is to sinter this as one piece. Furthermore, the zirconia powder of this embodiment provides a zirconia sintered body that exhibits high electrical conductivity even at a sintering temperature comparable to that of the fuel electrode and the air electrode. Therefore, a method of laminating at least one of the fuel electrode and its precursor compound, the zirconia powder of this embodiment, and the air electrode and at least one of its precursor compound, and molding and sintering them as one body; Accordingly, a SOFC in which a fuel electrode, a solid electrolyte, and an air electrode are integrated can be obtained by sintering once.

Hereinafter, this embodiment will be specifically described with reference to Examples. However, 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 measuring device (device name: UPA-UT151, manufactured by Microtrac Bell Co., Ltd.). As pretreatment of the sample, a solution containing hydrated 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 zirconia sol after hydrolysis was collected, and half of it was subjected to ultrafiltration using an ultrafiltration membrane having a molecular weight cutoff of 5 million to 3 million to obtain a filtrate. The mass (mg) of the remaining half of the slurry is after heat treatment at 1000° C. for 1 hour in an air atmosphere. By ICP analysis, the amount of zirconium was measured to determine m and m ₀ , and the amount of adsorbed zirconium was determined from the following formula.
W _Zr = (m/m ₀ )×100

(Particle size distribution measurement)
The volume particle size distribution curve and the cumulative volume particle size distribution curve of the powder sample were obtained using the HRA mode of the Microtrac particle size distribution meter (trade name: MT3000II, manufactured by Microtrac Bell Co., Ltd.), and the average particle size was calculated using the attached analysis software. , particle ratio, fine particle ratio, particle size peak, and width of particle size peak were measured. Prior to the measurement, the powder sample was suspended in pure water and dispersed for 10 minutes using an ultrasonic homogenizer to perform pretreatment.
(monoclinic phase ratio)
An XRD pattern of the powder sample was obtained using a general X-ray diffraction device (trade name: Ultima IIV, manufactured by Rigaku Corporation). The conditions for XRD measurement are 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 "PRO-FIT" as a calculation program, the monoclinic phase ratio was determined according to the above formula.

(BET specific surface area)
The BET specific surface area of the powder sample was measured using a general fluid type automatic specific surface area measuring device (device name: Flowsorb III 2305, manufactured by Shimadzu Corporation) and nitrogen as an adsorption gas.
Prior to the measurement, the powder sample was subjected to deaeration treatment at 250° C. for 30 minutes in the air as a pretreatment.
(Average granule diameter)
The average particle size of the zirconia granules was determined by the sieving test method.
(Molded body density)
The mass of the molded body sample was measured with a balance, and the volume was measured with a caliper and determined from the dimensions. The measured density was determined 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, after measuring the mass of the sintered body after drying, the sintered body was placed in water and boiled for 1 hour to perform pretreatment.
(Three-point bending strength)
The bending strength of the sintered sample was measured by a three-point bending test according to JIS R1601. The measurement was performed using a column-shaped sintered body sample with a distance between fulcrums of 30 mm, a width of 4 mm, and a thickness of 3 mm, and the average value of 10 measurements was taken as the bending strength.
(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 measurement devices. The measurement conditions are shown below.
Measurement sample: Rectangular parallelepiped sintered body measuring 4 mm long x 3 mm wide and 35 mm long Measurement atmosphere: Air atmosphere Measurement temperature: 600°C
Measurement method: Four-terminal method Electrode terminal: Pt wire (diameter 0.2 mm)
Distance between voltage terminals: 15mm
Measurement frequency: 1MHz to 0.1Hz
Applied current: 1mA

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

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

The obtained zirconia powder was washed with a sufficient amount of pure water, made into a slurry, and ground for 24 hours in a vibrating mill equipped with zirconia balls having a diameter of 2 mm as a grinding medium. After pulverization, it was dried in the air at 130°C to obtain the zirconia powder of this example.

The zirconia powder of this embodiment was press-molded with a mold at a pressure of 70 MPa, and then sintered under normal pressure at 1300° C. for 2 hours in the atmosphere to obtain a zirconia sintered body of this embodiment.

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

A zirconia sintered body of this example was obtained in the same manner as in Example 1 except that the sintering temperature was 1250°C.

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

A zirconia sintered body of this example was obtained in the same manner as in Example 1 except that the sintering temperature was 1200°C.

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 sprayed and granulated to obtain granulated powder. The average particle diameter of the zirconia granules was 55 μm, and the light bulk density was 1.29 g/cm ³ .

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.

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

A 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 1250°C.

Comparative example 1
A 0.37 mol/L zirconium oxychloride aqueous solution was hydrolyzed at boiling temperature for 160 hours while stirring to obtain a zirconia sol. The obtained zirconia sol had an adsorbed zirconium amount of 12% by mass and an average sol particle size of 0.1 μm.

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

After washing the obtained zirconia powder with a sufficient amount of pure water, it was made into a slurry and ground for 30 hours in a vibrating mill equipped with zirconia balls having a diameter of 10 mm as a grinding medium. After pulverization, it was dried in the air at 130°C to obtain zirconia powder of this comparative example.

The zirconia powder of this comparative example was press-molded with a mold at a pressure of 70 MPa, and then sintered under normal pressure at 1300° C. for 2 hours in the atmosphere to obtain a zirconia sintered body of this comparative example.

Comparative example 2
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 %.

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

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 amount of adsorbed zirconium in the obtained zirconia sol was 0.5% by mass, and the average sol particle size was 0.1 μm.

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

After washing the obtained zirconia powder with a sufficient amount of pure water, it was made into a slurry and ground for 24 hours in a vibrating mill equipped with zirconia balls having a diameter of 10 mm as a grinding medium. After pulverization, it was dried in the air at 130°C to obtain zirconia powder of this comparative example.

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

The evaluation results of the zirconia powders obtained in Examples and Comparative Examples are shown in the table below. All of the zirconia powders of Examples had a particle size peak having a peak top at 0.3 to 0.5 μm in the volume particle size distribution, and the width of the particle size peak was 0.1 μm. In addition, it can be confirmed that Comparative Example 1 has an average particle diameter exceeding 0.5 μm and a particle ratio of 80% or less, and Comparative Examples 2 and 3 have a monoclinic phase ratio of 1% or more. .

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

Furthermore, although the zirconia sintered bodies of Comparative Examples 2 and 3 were sintered at a relatively high temperature of 1350°C, they had low electrical conductivity of 5.0 × 10 ^-3 S/cm or less. This can be confirmed.

Note that the actual density of the compact of Comparative Example 1 was 2.55 g/cm ³ , whereas the actual density of the compacts of Examples 1 and 5 having the same composition was 2.76 g/cm ³ . It can be confirmed that these zirconia powders exhibit high moldability.

Claims (8)

A zirconia sintered body containing one or more stabilizers selected from the group of yttria, calcia, magnesia, and ceria, and having an electrical conductivity of 5.0×10 ⁻³ S/cm or more at 600° C. The zirconia sintered body according to claim 1, wherein the stabilizer is yttria and contains more than 4 mol% and 12 mol% or less of yttria. The zirconia sintered body according to claim 1 or 2, wherein the crystal phase includes at least cubic crystals. The zirconia sintered body according to any one of claims 1 to 3, having an actual density of 5.76 g/cm ³ or more and 6.02 g/cm ³ or less. The zirconia sintered body according to any one of claims 1 to 4, having a three-point bending strength of 350 MPa or more and 600 MPa or less, as measured by a method according to JIS R 1601. The zirconia sintering method according to any one of claims 1 to 5, comprising sintering zirconia powder in an air atmosphere at a sintering temperature of 1200°C or more and 1600°C or less, and for a sintering time of 1 hour or more and 24 hours or less. Method for producing solids. A solid electrolyte comprising the zirconia sintered body according to any one of claims 1 to 5. A method for producing a solid electrolyte, using the zirconia sintered body according to any one of claims 1 to 5.