JP5689100B2 - Raw material zirconia powder for solid oxide fuel cell, zirconia sintered body, electrolyte for solid oxide fuel cell, and solid oxide fuel cell - Google Patents

Description

The present invention, the raw material zirconia powder for a solid oxide fuel cell, the zirconia sintered body, a solid oxide fuel cell electrolyte and relates to a solid oxide fuel cell.

  Many technologies related to zirconia sintered bodies using zirconia powder have been proposed (Patent Literature 1, Patent Literature 2, Non-Patent Literature 1, etc.), but pulverized zirconia sintered bodies are ceramics obtained by firing the precursor. Therefore, it is difficult to maintain the dimensional accuracy because the size changes greatly due to firing shrinkage during firing, and as a result, the production yield of the sintered body tends to be lowered. In particular, a thin film zirconia sheet having flatness requires a large amount of binder for molding because it uses fine zirconia powder of submicron grade as a raw material, and its firing shrinkage is large, and it has high flatness and flatness after firing. It is difficult to maintain the characteristics, and the low yield is remarkable.

  Moreover, since it is a thin film, it cannot be said that handling strength is sufficient, and many sheets may be damaged during manufacturing or handling. Since the defective zirconia sintered body sheet and the defective fragments and fragments generated after the above-mentioned sintering accumulate, disposal problems and effective utilization of resources are desired. On the other hand, once sintered, the zirconia sintered body is chemically stable and resistant to chemicals, and has higher hardness, strength, and toughness than other ceramics. Is very difficult.

  Among them, with regard to the recycling of zirconia, the zirconia sintered body is converted into zirconia particles having a specific crystal system and an average particle diameter of 0.5 μm to 1.5 μm by heat treatment, and this is again used as a sintered body. The technique used as a raw material is disclosed (Patent Document 3). However, the zirconia sintered body related to this technology is substantially tetragonal zirconia, and it is necessary to further pulverize after heat treatment in an autoclave using the hydrothermal deterioration characteristics of tetragonal zirconia. The zirconia particles having the same particle diameter as the above-mentioned particles are expensive, and there are few advantages of using recycled powder.

JP 58-55373 A JP-A-60-191056 JP 10-218662 A

Journal of Materials Science Volume 20 p. 1407-1418 (1985)

  The present invention obtains a recycled zirconia powder by reusing the pulverized zirconia sintered body as a raw material, and reusing the recycled zirconia powder to improve the quality of the zirconia sintered body, in particular, the zirconia sintered body sheet. The technology that can be obtained is provided.

The present invention provides a raw material zirconia powder for a solid oxide fuel cell, comprising 2 to 98% by mass of recycled zirconia powder and 98 to 2% by mass of unused zirconia powder.

The present invention further provides a zirconia sintered body obtained by molding and firing the raw material zirconia powder for the solid oxide fuel cell of the present invention.

The present invention further provides an electrolyte for a solid oxide fuel cell comprising the zirconia sintered body of the present invention.

The present invention further provides a solid oxide fuel cell comprising the zirconia sintered body of the present invention or the electrolyte for a solid oxide fuel cell of the present invention.

  The present invention provides a zirconia sintered body by using a recycled zirconia powder obtained by pulverizing and dissolving a zirconia sintered body for grinding once, so that resources can be used effectively, and the strength and toughness of the zirconia sintered body can be obtained. Can be improved. In particular, by using recycled zirconia powder and unused zirconia powder as raw material zirconia powder, the effect is further improved in the case of a zirconia sintered body, particularly a zirconia sintered body sheet.

  The present invention is described in detail below, but is not limited to the following unless it is contrary to the gist of the present invention.

  1st invention concerning this invention is a manufacturing method of recycled zirconia powder, and the manufacturing method consists of a grinding | pulverization process, a melt | dissolution process, a dilution process, a precursor preparation process, and a calcination process. Hereinafter, each process will be described in detail.

(Crushing process)
This is a step of pulverizing a zirconia sintered body for pulverization in order to produce the recycled zirconia powder of the present invention. The pulverized zirconia sintered body includes a flat plate shape, a flat plate shape with dimples, a cylindrical shape, a flat plate cylindrical shape, a ring shape, a block shape, a spherical shape, or a damaged or partially damaged product thereof. Can do. However, a zirconia sintered body having a three-dimensional shape having a size or thickness of 1 mm or more consumes a lot of energy for pulverization, resulting in poor pulverization efficiency and a problem of contamination due to pulverization. Therefore, as the zirconia sintered body for pulverization, a plate-like or sheet-like zirconia sintered body having a thickness of less than 1 mm, particularly 0.5 mm or less is preferable. Specific examples include non-standard zirconia sintered body sheets such as dimensions, broken pieces of zirconia sintered body sheets, and the like.

The material of the pulverized zirconia sintered body may be any material as long as it is zirconia, but alkaline earth metal oxides such as MgO, CaO, SrO, BaO; Y ₂ O ₃ , La ₂ O ₃ , _{CeO 2, Pr 2 O 3,} Nd 2 O 3, Sm 2 O 3, Eu 2 O 3, Gd 2 O 3, Tb 2 O 3, Dy 2 O 3, Ho 2 O 3, Er 2 O 3, Yb 2 Zirconia added as a stabilizer such as rare earth metal oxides such as O ₃ ; other metal oxides such as Sc ₂ O ₃ , Bi ₂ O ₃ and In ₂ O ₃ is preferred. One or a mixture selected from one or more of them may be used. Among these, when used as a solid electrolyte for a fuel cell, the composition is, for example, 90 to 97 mol% zirconia stabilized with ₃ to 10 mol% Y ₂ O ₃ , and 4 to 12 mol% Sc _2. Preference is given to 88-96 mol% zirconia stabilized with O ₃ or 85-96 mol% zirconia stabilized with 4-15 mol% Yb ₂ O ₃ , in particular 8-10 mol% Y ₂ O. ₃ , cubic zirconia stabilized with 8-12 mol% Sc ₂ O ₃ or 8-15 mol% Yb ₂ O ₃ is preferred. Furthermore, an additive such as Al ₂ O ₃ , Ga ₂ O ₃ , SiO ₂ , Bi ₂ O ₃ , TiO ₂ , CeO _{2 and the} like with respect to the total mass of the stabilizer and zirconia is included. The added zirconia can be illustrated. Further, the impurities contained in the pulverized zirconia sintered body from the beginning include components such as Al ₂ O ₃ , SiO ₂ , TiO ₂ , Fe ₂ O ₃ , NaO, KO, and SO _{3 in} terms of oxides. , Both are less than 0.3 mass%, preferably less than 0.1 mass%, particularly preferably less than 0.01 mass%. It is also possible to add zirconia sand and / or badelite to the zirconia sintered body for pulverization and pulverize them together.

  As the pulverization method, the pulverized zirconia fired body is made of jaw crusher, hammer crusher, shredder, roll crusher, hammer mill, cutting mill, rod mill, roller mill, rotor mill, impact pulverizer, jet pulverizer, ball mill, mortar, etc. These dry pulverizers can be obtained by pulverization by ordinary means combining one or more dry pulverizers. In this pulverization, it is necessary to efficiently obtain as fine a pulverized zirconia powder as possible with a small proportion of coarse particles in order to allow the subsequent dissolution process to proceed smoothly. Specifically, the average particle diameter of the pulverized zirconia powder obtained by pulverizing the zirconia sintered body for pulverization is 2.0 to 2000 μm, more preferably 3.0 to 1000 μm, still more preferably 3.0 to 500 μm, Particularly preferably, the particle diameter is 5.0 to 100 μm, and the 95% by volume particle diameter is preferably 4.0 to 4000 μm, more preferably 5.0 to 3000 μm, still more preferably 5.0 to 2000 μm, and particularly preferably 6 0.0 to 300 μm. Furthermore, the maximum particle size is preferably 3.0 to 5000 μm, more preferably 3.0 to 4000 μm, still more preferably 3.0 to 3000 μm, and particularly preferably 3.0 to 500 μm. When the average particle size of the pulverized zirconia powder is less than 2.0 μm, the 95% by volume particle size is less than 4.0 μm, and the maximum particle size is less than 3.0 μm, dissolution of the pulverized zirconia powder is promoted in the subsequent dissolution step. Although it can be carried out simply and efficiently, it requires a great deal of energy, labor, and time for the grinding and becomes impractical. In addition, when the average particle diameter exceeds 2000 μm, the 95 volume% particle diameter exceeds 4000 μm, and the maximum particle diameter exceeds 5000 μm, it takes time to dissolve in the subsequent dissolution step, and high pressure is required for complete dissolution. Since severe dissolution conditions such as heating are required, a great deal of energy, labor, and time are required, making it impractical.

  The average particle size and the maximum particle size are measured with a laser diffraction / scattering particle size distribution measuring device (trade name “LA-920” manufactured by Horiba, Ltd.), and the particle volume is integrated from the smaller particle size. Then, the particle diameter is 50% by volume with respect to the total particle volume, and the particle diameter is 100% by volume when the particle volume is integrated from the smaller particle diameter. The 95% volume diameter is a particle diameter that is 95 volume% with respect to the total particle volume by integrating the particle volume from the smaller particle diameter.

In actual measurement, an aqueous solution to which 0.2% by mass of sodium metaphosphate was added as a dispersant in distilled water was used as a dispersion medium, and 0.01 to 1% by mass of the pulverized zirconia powder was added to about 100 cm ^{3 of the} dispersion medium. Sonicate for 5 minutes to disperse and measure. When the pulverized zirconia powder settles without being dispersed by the above method, a particle image is captured using an ultra-deep color 3D shape measurement laser light microscope (manufactured by Keyence, trade name “VK-9500”). Then, the printed particles are measured with a caliper, the average value thereof is calculated as the average particle size, and the maximum value among the measured particles is set as the maximum particle size.

  For the pulverization, a normal pulverization means using a dry pulverizer as described above can be used without using a dispersion medium such as water or alcohol. As mentioned above, the zirconia sintered sheet for grinding has high hardness, high strength, and high toughness, so the rotating blade (pulverizing blade), rotating rotor (pulverizing rotor), etc. of the dry grinding machine can be rotated at high speed for efficiency. Therefore, it is necessary to grind in a short time. For that purpose, it is preferable to select an apparatus capable of rotating in the range of 2000 to 30000 rpm, preferably 3000 to 20000 rpm.

  In particular, rather than pulverizing a zirconia sintered body for pulverization using only one of the dry pulverizers, primary pulverization and secondary pulverization may be performed using two or more dry pulverizers having different rotational speeds. Furthermore, it is preferable for obtaining a pulverized zirconia powder with a smaller proportion of coarse particles efficiently in a short time. Specifically, as the primary pulverization, the cutting blade is rotated in the range of 2000 to 5000 rpm with a cutting mill and the primary pulverization is performed to obtain primary pulverized zirconia powder having an average particle diameter of 100 to 3000 μm. At this time, as a particle size adjusting screen for avoiding the mixing of coarse particles, for example, sorting what passes through a sieve of 0.05 to 1.5 mm, preferably 0.08 to 0.2 mm. Is preferred. The sieve shape at that time can be selected from a round hole shape, a ladder shape, a herringbone shape, and the like.

  Next, the primary pulverized zirconia powder is pulverized by rotating the rotor in a range of 5000 to 30000 rpm, which is higher than that of the primary pulverization using a rotor mill or the like, and 2 of the powder having an average particle size of 2.0 to 2000 μm. Next, a ground zirconia powder is obtained. Also at this time, as a particle size adjusting screen for avoiding the mixing of coarse particles, for example, it is preferable to collect what passes through a sieve of 0.05 to 1.5 mm in order to increase the grinding efficiency. In these pulverizations, especially in the secondary pulverization, the rotating blades and the rotating rotor rotate at high speed, so they are worn by the pulverized zirconia powder and cause contamination of the pulverized zirconia powder such as iron, chromium, etc. Sometimes. In order to avoid this, it is preferable to use a rotary blade or a rotary rotor made of zirconia. When the dry pulverized zirconia powder is colored gray or the like due to contamination, the contamination component is removed by magnet or acid cleaning.

  In order to further promote the dissolution of zirconia in the next dissolution step, the pulverized zirconia powder obtained as described above can be further wet pulverized to make coarse particles finer.

  The wet pulverization can be performed by means used as a normal wet pulverization using a dispersion medium such as water or alcohol. Examples of the apparatus for this purpose include a ball mill, a bead mill, a planetary mill, a wet jet mill, a colloid mill, and a homogenizer. Specifically, the pulverized zirconia powder obtained by the dry pulverizer is pulverized by stirring and rotating together with a dispersion medium such as water and alcohol, and a grinding medium such as balls and beads made of zirconia, and then the dispersion medium is removed. And dried to obtain a pulverized zirconia powder suitable for dissolution used in the present invention. The average particle size of the pulverized zirconia powder at this time is in the range of 2.0 to 1000 μm, the maximum particle size is in the range of 3 to 3000 μm, and the average of the pulverized zirconia powder obtained compared to the case where only the dry pulverizer is used. The upper limit value of the particle diameter and the upper limit value of the maximum particle diameter become 1/2 to 3/5, and the coarse particles can be miniaturized.

  The pulverized zirconia powder is obtained by pulverizing a zirconia sintered body in which the powder has already been baked, so that the obtained powder has almost no pores and a very small specific surface area. In addition, it is present in a state of almost agglomeration with little aggregation, which is very different from an unused powder such as a commercially available zirconia powder. Accordingly, the smaller the particle size of the pulverized zirconia powder, the easier the subsequent dissolution step.

(Dissolution process)
It is a step of dissolving the pulverized zirconia powder obtained in the above pulverization step with an acid, and it is possible to obtain a zirconia solution or a paste-like zirconia melt by a known method such as an acid decomposition method, a pressure decomposition method, or a melting method. it can.

  The acid decomposition method is a method in which hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, phosphoric acid, hydrofluoric acid and mixed acid thereof are put in an open container together with the pulverized zirconia powder and heated to 100 to 400 ° C. to dissolve. It is. In the pressure decomposition method, these acids and pulverized zirconia powder are put in a pressure decomposition vessel made of polytetrafluoroethylene resin, and this vessel is further put in a metal pressure vessel to dissolve the zirconia powder under heating and pressure. Is the method. The melting method is sodium carbonate, sodium hydroxide, sodium peroxide, sodium borate, sodium metaborate, ammonium sulfate, potassium pyrosulfate, sodium carbonate + boric acid, lithium carbonate + boric acid, ammonium sulfate + sulfuric acid, etc. This is a method of dissolving the above-mentioned hydrochloric acid, nitric acid, sulfuric acid and the like in a melt obtained by mixing well with the pulverized zirconia powder, heating in an electric furnace or the like for 1 to 10 hours at 200 to 1200 ° C. and igniting with high heat.

  In the present invention, in order to perform dissolution more simply and efficiently, an acid decomposition method and a melting method in which an acid and a flux are added to the pulverized zirconia powder and decomposed at 150 to 350 ° C., preferably 200 to 300 ° C. under normal pressure. A combination of these is preferred. The concentration of the acid at that time is 10 to 98%, preferably 30 to 97%, and 1 kg of acid is added to 1 kg of the pulverized zirconia powder, preferably 1 to 10 L, and 1 to 10 kg of flux is added. It is preferable to add 2 to 8 kg and dissolve these mixtures for 20 to 180 minutes, preferably 30 to 120 minutes. When the temperature is lower than 150 ° C. or when the concentration of the acid used is lower than 10%, the pulverized zirconia powder cannot be completely dissolved and becomes a residue as an undissolved pulverized zirconia powder, and the recovery rate decreases. On the other hand, when the temperature is higher than 350 ° C. or the acid concentration is higher than 98%, the dissolution efficiency does not become much higher for the setting conditions to be very strict, but is an excessive condition. Similarly, when the amount of acid used is less than 1 L, the amount of flux is less than 1 kg, and the dissolution time is less than 20 minutes, similarly, the pulverized zirconia powder cannot be completely dissolved and the undissolved pulverized zirconia powder As a residue, the recovery rate decreases. On the other hand, when the amount of acid exceeds 20 L, the amount of flux exceeds 10 kg, and the dissolution time exceeds 180 minutes, the dissolution efficiency does not become much worse but is an excessive condition. Among the acids used, sulfuric acid is preferable, and among the fluxes, ammonium sulfate and sodium carbonate are preferable, and ammonium sulfate is particularly preferable. Note that the pulverized zirconia powder remaining undissolved in the main dissolution step is removed by filtration or the like.

(Dilution process)
In this step, the solution obtained in the dissolution step is diluted with water. Since the obtained solution or melt is a strong acid having a pH of 2 or less, and in many cases a pH of 1 or less, the pH is 4.0 to 7.0 so that it can be easily handled in the next precursor preparation step by the dilution. This is a diluted solution. The preferred pH of the diluent is 5.0 to 7.0, more preferably 6.0 to 7.0. In dilution, it is preferable to gradually drop the solution while stirring the solution in water in order to avoid sudden heat generation due to dilution.

In addition, in the dilution process, it is possible to dilute using an aqueous solution of zirconium salt, zirconia sol, or zirconia dispersion instead of water in order to prevent the decrease in zirconia concentration due to dilution and increase the productivity of recycled zirconia powder. It is. Furthermore, after diluting with water, it is also possible to add unused zirconia powder, zirconia hydroxide, and hydrated zirconia as defined below. At this time, Sc ₂ O ₃ , Yb ₂ O ₃ , Y ₂ O _{3 as described above} is stabilized in the composition of the zirconium salt, zirconia sol, and unused zirconia powder so as to be the same as the composition of the pulverizing zirconia material. It is preferable to add a stabilizer added alone or as a stabilizer separately.

(Precursor preparation step)
In the step of preparing the zirconia powder precursor by a known method such as neutralization method, uniform precipitation method, coprecipitation method, hydrolysis method, hydrothermal synthesis method, spray drying method, etc. is there. The neutralization method is a method of synthesizing a powder by adding an acid or an alkali solution (in the present invention, an alkali solution) to a pH region where a hydroxide is generated and precipitating it as a hydroxide. The homogeneous precipitation method is a method of synthesizing a powder by gradually forming a precipitating agent in a solution and eliminating a local non-uniformity of the precipitating agent to generate a precipitate. The coprecipitation method is a method of synthesizing powder by simultaneously producing and precipitating two kinds of products in a liquid phase, and the hydrolysis method is a solution containing a metal salt, a metal ion or a metal alkoxide. In this method, water is added to synthesize a hydroxide or a coordination compound with H ⁺ or OH ⁻ . The hydrothermal synthesis method is a method of synthesizing powder in the atmosphere of a hermetic container or a pressurizing apparatus using the reactivity of a dissolved solution in which oxide is dissolved in an atmosphere of hot water or high-pressure steam. The drying method is a method of obtaining a powder by spraying a solution containing a powder raw material into a high temperature and instantaneously performing a thermal decomposition reaction.

In the present invention, since the diluting solution is acidic, a neutralization method using an alkaline solution such as aqueous ammonia, a coprecipitation method, a uniform precipitation method using urea or the like is preferably selected, and particularly disclosed in Japanese Patent No. 1613619. It is preferable to form a precipitate by continuously performing a precipitation product of ammonia water as described above by a flow reaction method while keeping the pH during the reaction constant. A precipitate such as zirconia hydroxide is produced by these methods, and the precipitate is separated and recovered by dehydration with a filter press or the like by normal filtration or ultrafiltration, and further dried at 60 to 100 ° C. Thus, a recycled zirconia powder precursor is obtained. The precipitate contains ions such as Cl ⁻ , NO ₃ ⁻ , SO ₄ ^{2− of} the acid used in the dissolution process, Na ⁺ , K ⁺ , NH ₄ ^{− of the} flux, and the like as impurities. In order to sufficiently wash and remove, ultrafiltration is preferable.

(Calcination process)
In this step, the precursor obtained in the precursor preparation step is calcined. The calcining conditions, especially the temperature, is determined by the specific surface area of the recycled zirconia powder to be obtained. In general, in order to adjust to 500 to 1100 ° C., the specific surface area suitable for handling is 3 to 30 m ² / g. Preferably it is 600-1000 degreeC. The calcining time is 1 to 20 hours, preferably 2 to 10 hours. The calcination atmosphere is an oxidizing gas atmosphere having an oxygen concentration of 1 to 21%, preferably an air atmosphere.

  The recycled zirconia powder can be obtained by sequentially performing the above steps, but other steps may be appropriately added between the respective steps. For example, it is preferable that the recycled zirconia powder after calcination is spray-dried into a spherically weakly agglomerated powder in order to further facilitate subsequent handling.

A second invention of the present invention is a recycled zirconia powder characterized by having an average particle diameter of 0.01 to 1 μm and a specific surface area of 3 to 30 m ² / g produced by the method of the first invention. The average particle size of the recycled zirconia powder is more preferably 0.1 to 0.8 μm, particularly preferably 0.2 to 0.7 μm. The specific surface area of the recycled zirconia powder are those measured by a known BET method, more preferably ^{5~20m 2 / g, 7~15m 2 /} g is particularly preferred.

The composition / composition ratio of the recycled zirconia powder is preferably the same composition / composition ratio as that of the pulverized zirconia sintered body used as the raw material. In that case, as described above, MgO, CaO, SrO Alkaline earth metal oxides such as BaO; Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , Pr ₂ O ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Tb Rare earth metal oxides such as ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Yb ₂ O ₃ ; Other metal oxides such as Sc ₂ O ₃ , Bi ₂ O ₃ , In ₂ O ₃ Zirconia added as a stabilizer is preferred. One or a mixture selected from one or more of them may be used. Among these, the composition when used as a solid electrolyte for a fuel cell is, for example, 3 to 10 mol% Y ₂ O ₃ , 4 to 12 mol% Sc ₂ O _3, or 4 to 15 mol% Yb _2. Zirconia stabilized with O ₃ is preferred, especially stabilized with 8-10 mol% Y ₂ O ₃ , 8-12 mol% Sc ₂ O ₃ or 8-15 mol% Yb ₂ O ₃ . Cubic zirconia is preferred. Can be exemplified further Al ₂ O ₃ of 0.01 to 5 _{wt%, Ga 2 O 3, SiO} 2, Bi 2 O 3, zirconia TiO _2, CeO ₂ or the like is added. Incidentally, the impurities contained in the recycled zirconia of the present invention include Al ₂ O ₃ , SiO ₂ , TiO ₂ , Fe ₂ O ₃ , NaO, etc. in the form of oxides contained in the pulverized zirconia sintered body from the beginning. And components such as SO ₃ , Cl, WO ₃ , CoO, Fe ₂ O ₃ , Cr ₂ O ₃ , NaO, and KO mixed in the pulverization step, all of which are less than 0.3% by mass, Preferably it is less than 0.1% by weight, particularly preferably less than 0.01% by weight.

In addition, in the dilution process, in the case of a diluted solution obtained by adding an aqueous solution of zirconium salt, zirconia sol, zirconia dispersion, or after dilution with water, add unused zirconia powder, zirconia hydroxide, zirconia hydrate In this case, the composition ratio of the obtained recycled zirconia powder may deviate from the composition ratio of the pulverized zirconia sintered body. There is no problem even if the composition ratio of the zirconia sintered body for pulverization deviates from that of the recycled zirconia powder, but the zirconia sintered body for pulverization was used as an electrolyte for solid oxide fuel cells. When using recycled zirconia powder obtained by recycling it as a raw material powder for electrolytes for solid oxide fuel cells, adjust the composition ratio to meet the zirconia sintered compact for grinding. There is a need. In this case, Sc ₂ O ₃ , Yb ₂ O ₃ , and Y ₂ O ₃ as described above are separately added separately as stabilizers, or an aqueous solution, sol, or dispersion of these salts is added to the above-mentioned zirconium salt aqueous solution, zirconia sol. It is preferable to add to the zirconia dispersion.

  The third invention of the present invention is to produce a zirconia sintered body using the recycled zirconia powder obtained by the second invention as a raw material zirconia powder, or using a powder comprising the recycled zirconia powder and an unused zirconia powder as a raw material zirconia powder. It is. Preferably, it is a method for producing a zirconia sintered body sheet obtained by forming a raw material zirconia powder into a sheet by a doctor blade method or an extrusion method.

The unused zirconia powder referred to in the present invention is not used as a powder for producing the zirconia sintered body, and any zirconia-containing powder may be used, not only zirconia, A hydrated product, a hydroxide, or the like may be dried or fired to form a zirconia powder, but a zirconia powder is preferable. The composition and composition ratio of the unused zirconia powder is preferably the same as that of the pulverized zirconia sintered body. Commercially available zirconia powder, hydrated zirconia, zirconia hydroxide and the like can be used. The unused zirconia powder has an average particle diameter of 0.01 to 2 μm, preferably 0.1 to 1 μm, and a specific surface area of 3 to 30 m ² / g, preferably 5 to ²⁰ m ² / g. When the raw material zirconia powder is composed of the recycled zirconia powder and the unused zirconia powder, the ratio is not particularly limited, but the recycled zirconia powder in the raw material powder is 2 to 98% by mass, and the unused zirconia powder is 98 to 2% by mass. %, Preferably 5 to 50% by weight of recycled zirconia powder, 95 to 50% by weight of unused zirconia powder, particularly preferably 10 to 30% by weight of recycled zirconia powder, and 90 to 70% by weight of unused zirconia powder .

  Hereinafter, the process is demonstrated in detail about the manufacturing method of a zirconia sheet as a zirconia sintered compact.

(1) Preparation of raw material slurry or raw material kneaded material First, the raw material zirconia powder, a solvent, a binder, a plasticizer and the like are mixed to prepare a raw material slurry or a raw material kneaded material. There is no particular limitation on the type of binder used in the raw material slurry or the raw material kneaded material, and conventionally known organic binders can be appropriately selected and used. Examples of organic binders include ethylene copolymers, styrene copolymers, acrylate and methacrylate copolymers, vinyl acetate copolymers, maleic acid copolymers, vinyl butyral resins, and vinyl acetal resins. And vinyl formal resins, vinyl alcohol resins, waxes, celluloses such as ethyl cellulose, and the like. Among these, from the viewpoint of suppressing the moldability, punching workability, strength, and shrinkage ratio variation during firing of the zirconia green sheet, it is thermoplastic and has a number average molecular weight of 20,000 to 250,000, more preferably 50. 1,000 to 200,000 (meth) acrylate copolymers are recommended as preferred.

  The use ratio of the raw material zirconia powder and the binder is preferably 5 to 30 parts by mass, more preferably 10 to 20 parts by mass with respect to the former 100 parts by mass. When the amount of the binder used is insufficient, the moldability of the zirconia green sheet is lowered, and the strength and flexibility are insufficient. On the other hand, if the amount is too large, not only will it be difficult to adjust the viscosity of the slurry, but the decomposition and release of the binder component during degreasing and sintering will increase and become severe, resulting in large variations in shrinkage ratio, resulting in a sheet with small dimensional variations. Further, the thermal decomposition of the binder becomes insufficient, and a part of the binder component tends to remain as residual carbon.

  Solvents used include water; alcohols such as methanol, ethanol, 2-propanol, 1-butanol and 1-hexanol; ketones such as acetone and 2-butanone; aliphatic hydrocarbons such as pentane, hexane and heptane. Aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; and acetates such as methyl acetate, ethyl acetate, and butyl acetate, and the like. These solvents can also be used alone, or two or more of them can be appropriately mixed and used. The amount of these solvents used should be appropriately adjusted in consideration of the viscosity of the slurry at the time of forming the zirconia green sheet, and preferably the slurry viscosity is in the range of 1 to 50 Pa · s, more preferably 2 to 20 Pa · s. It is better to adjust as follows.

  In preparing the raw slurry or raw material kneaded material, polymer electrolytes such as polyacrylic acid and ammonium polyacrylate; organic acids such as citric acid and tartaric acid; isobutylene or styrene are used to promote peptization and dispersion of the zirconia raw material powder. Copolymer of styrene and maleic anhydride and ammonium salt or amine salt thereof; Dispersant comprising copolymer of butadiene and maleic anhydride and ammonium salt thereof; phthalic acid for imparting flexibility to ceramic green sheet Phthalic acid esters such as dibutyl and dioctyl phthalate; Glycols such as propylene glycol and glycol ethers; Plasticizers made of polyester such as phthalic polyester, adipic acid polyester, and sebacic acid polyester; Activators and antifoams It can be added as needed.

  The raw material slurry or the raw material kneaded material is prepared by mixing an appropriate amount of the above components. At that time, in order to make each particle fine and uniform the particle diameter, the particles may be mixed while being pulverized by a ball mill or the like. Moreover, the order of addition of each component is not particularly limited, and may be according to a conventional method.

(2) Production of zirconia green sheet Next, the raw material slurry or raw material kneaded material obtained as described above is molded. Although a shaping | molding method is not restrict | limited in particular, It is preferable to set it as a sheet | seat of appropriate thickness using a doctor blade method or an extrusion molding method. Then, it is set as a zirconia green sheet by drying. Drying conditions are not particularly limited, and for example, drying may be performed at a constant temperature of room temperature to 150 ° C., or heating may be performed by successively raising the temperature in the order of 50 ° C., 80 ° C., and 120 ° C.

  The obtained zirconia green sheet may be punched or cut into an appropriate size by any method. The green sheet may have any shape such as a circle, an ellipse, a square, or a square with R (R), and a similar circle, ellipse, square, or square with an R in the sheet. One or two or more may be included. Also, the thickness of the green sheet is not particularly limited, but can be about 35 to 1000 μm, for example.

The surface roughness of the zirconia green sheet depends on the particle size distribution of the raw material zirconia powder, raw material slurry, raw material kneaded material, etc., but it can be adjusted relatively easily if necessary in the case of tape casting by the doctor blade method. can do. For example, casting or the like on a roughened PET film, or a roughening sheet or mold whose surface is roughened after casting may be pressed against the green sheet. The same applies when a ceramic green sheet is obtained by an extrusion method. As the surface roughness of the ceramic green sheet, in general, the range of 0.01~6μm by R _a are suitable.

(3) Firing of green sheets When firing zirconia green sheets, the green sheets can be placed and fired on a shelf board one by one. For mass production, the zirconia green sheets It is preferable to fire as a laminated body in which porous spacer sheets are alternately stacked. Usually, a spacer sheet is placed on the lower stage, and zirconia green sheets and spacer sheets are alternately stacked thereon, and a spacer sheet is placed on the upper stage. The lower-stage spacer sheet prevents the zirconia green sheet and the shelf from being joined, and the upper-stage spacer sheet serves as a weight to reduce the occurrence of warpage and undulation of the zirconia green sheet.

Specific firing conditions are not particularly limited, and may be based on a conventional method. For example, in order to remove organic components such as a binder and a plasticizer from the zirconia green sheet, the treatment is performed at 150 to 600 ° C., preferably 250 to 500 ° C. for about 5 to 80 hours. Next, the zirconia powder is sintered by holding and firing at 1000 to 1600 ° C., preferably 1200 to 1500 ° C. for 2 to 10 hours, and the zirconia sintered body sheet of the present invention having a thickness of 0.03 to 0.5 mm is obtained. obtain. The total area is 5 to 2000 cm ² , preferably 50 to 1000 cm ² , more preferably 100 to 500 cm ² .

  The zirconia sintered body sheet of the present invention thus obtained has a thickness of 0.03 to 0.5 mm, and the relative density of the density measured by the Archimedes method with respect to the theoretical density is 93% or more, preferably 95% or more. The three-point bending strength is 800 MPa or more, preferably 900 MPa or more, particularly preferably 1000 MPa or more when the crystal structure of zirconia is a tetragonal system, and 300 MPa or more, preferably 350 MPa or more, for a cubic system. Particularly preferably, it is 400 MPa or more, and has a strength equivalent to that of a zirconia sintered body sheet produced by using unused zirconia powder.

In a fifth aspect of the present invention, the zirconia sintered body obtained in the fourth aspect is used as an electrolyte for a solid oxide fuel cell. When the electrolyte for a solid oxide fuel cell is in the form of a sheet, the thickness is 0.03 to 0.5 mm, and the total area is 5 to 2000 cm ² , preferably 50 to 1000 cm ² , more preferably. 100-500 cm ² . When used as an electrolyte for a solid oxide fuel cell, a fuel electrode is formed on one surface of the electrolyte, and an air electrode is formed on the other surface, and an electrolyte material and a fuel electrode material or an electrolyte material as necessary In general, an intermediate layer is formed on one surface or both surfaces of the electrolyte in order to prevent the reaction between the electrode material and the air electrode material. Therefore, in order to increase the bonding force between the electrolyte, the fuel electrode, the air electrode, and the intermediate layer and prevent the separation from the electrolyte, the surface roughness that gives an anchor effect to the surface of the solid oxide fuel cell electrolyte is set. Preferably, the roughness is Ra in the range of 0.1 to 3 μm, preferably 0.3 to 2 μm, and more preferably 0.5 to 1.5 μm.

A sixth invention of the present invention is a solid oxide fuel cell using the zirconia sintered body according to the fourth invention or the electrolyte for a solid oxide fuel cell according to the fifth invention. A general means for forming a fuel cell by using the zirconia sintered body or the solid oxide fuel cell electrolyte can be used. Preferably, the zirconia sintered sheet or the solid oxide fuel cell electrolyte is used. On the other hand, a cermet of ceria oxide doped with Ni, Co, Ru or the like as a fuel electrode material and the above-mentioned stabilized zirconia and / or yttria, samaria, gadria or the like is preferably used. Particularly preferred is a cermet comprising Ni and 9-12 mol% Sc ₂ O ₃ stabilized zirconia. These fuel electrode materials are kneaded with a binder such as ethyl cellulose and a solvent such as α-terpineol to prepare a fuel electrode paste, or milling to prepare a fuel electrode slurry, which is coated, dried, screened, coated, etc. A fuel electrode can be obtained by baking. Next, lanthanum manganite, lanthanum cobaltite and lanthanum ferrite lanthanum, which are air electrode materials, are formed on the surface opposite to the anode of the zirconia sintered body or the solid oxide fuel cell electrolyte. Perovskite structure substituted with other rare earth elements such as praseodymium, alkaline earth elements such as strontium, calcium, barium, magnesium, etc. and / or partially substituted with manganese, cobalt, iron, etc. An oxide, and a ceria-based oxide containing 10 to 35 mol% of at least one oxide selected from Gd ₂ O ₃ , Y ₂ O ₃ and Sm ₂ O _{3 in the} perovskite oxide, or , 8-10 mol% of Y ₂ O ₃ and comprises yttria stabilized zirconia or a 9-12 mole% c mixture was added scandia-stabilized zirconia containing ₂ O ₃ is preferably used. As in the case of the fuel electrode, an air electrode can be obtained by preparing an air electrode paste or an air electrode slurry, and coating, drying, and baking it by a screen printing method, a coating method, or the like. A solid oxide fuel cell is formed by the zirconia sintered body or the solid oxide fuel cell electrolyte, the air electrode, and the fuel electrode. The order of manufacturing the fuel electrode and the air electrode is not particularly limited. In addition, the ceria-based oxide may be present as an intermediate layer between the solid electrolyte and the air electrode in order to prevent these solid phase reactions. Furthermore, Ni powder, Ni alloy powder are used for the purpose of filling the gap generated between the fuel electrode and the separator to improve the adhesion between them, thereby reducing the contact resistance and improving the current collecting efficiency. Body, Pt powder, Pt alloy powder, Ag powder, Ag alloy powder, Au powder, Au alloy powder, etc., and the gap formed between the air electrode and the separator is also filled An air electrode made of Ag powder or Ag alloy powder and / or the perovskite oxide for the purpose of improving the adhesion between the two, thereby reducing contact resistance and improving current collection efficiency. A contact layer or may be formed.

  As described above, a solid oxide fuel cell is formed by the zirconia sintered body sheet or the solid oxide fuel cell electrolyte, the air electrode, and the fuel electrode. The order of manufacturing the fuel electrode and the air electrode is not particularly limited.

  Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following Examples unless it is contrary to the gist of the present invention.

<Reference Example 1>
Production of Zirconia Sintered Sheet for Grinding Commercial 8 mol% yttria stabilized zirconia powder (trade name “TZ-8YS”, manufactured by Tosoh Corporation, average particle size: 0.52 μm, specific surface area: 8.5 m ² / g , Hereinafter referred to as 8YSZ), 100 parts by mass, 50 parts by mass of a toluene / isopropanol mixed solution (toluene / isopropanol mass ratio = 3/2) as a solvent, and 2 parts by mass of a sorbitan fatty acid ester surfactant as a dispersant. The mixture was mixed while being pulverized using a ball mill. A methacrylate copolymer (number average molecular weight: 100,000, glass transition temperature: −8 ° C., solid content concentration: 50%) as a binder and 15 parts by mass in terms of solid content and dibutyl as a plasticizer are added to the mixture. 3 parts by mass of phthalate was added and further mixed by a ball mill to form a slurry. The obtained slurry was concentrated and degassed, and the viscosity at 25 ° C. was adjusted to 3 Pa · s to obtain a slurry for coating.

  This coating slurry is applied onto a PET film by the doctor blade method, and is passed through a dryer (3 zones of 50 ° C., 80 ° C. and 110 ° C.) following the coating portion at a speed of 0.2 m / min. And dried with a slitter to obtain a long zirconia green sheet having a width of 150 mm, a length of 200 m, and a thickness of 320 μm. This long green sheet was cut into 120 mm squares to obtain 1800 120 mm square zirconia green sheets.

  Next, one piece of the zirconia green sheet obtained above was placed on a baking shelf on which two alumina porous sheets (porosity: 45%, thickness: 0.2 mm, dimensions: 15 cm square) were placed and placed. Stack a porous sheet as a spacer on top of it, and then stack 9 sheets of zirconia green sheets and porous sheets alternately in the same way, and finally use a mullite / alumina weight over the top spacer. A jig (porosity 60%, bulk specific gravity: 1.3) was placed. A total of 1800 zirconia green sheets stacked in this way were fired at 1425 ° C. for 3 hours in an air atmosphere to obtain an 8YSZ sintered body sheet of about 90 mm square and a thickness of 270 μm.

  For reference, when the physical properties of the 8YSZ sintered body sheet were measured, the porosity determined from the density by the Archimedes method with respect to the sheet theoretical density was 97.2%, and the three-point bending strength test of the sintered body sheet in accordance with JIS-1601 The average value of the strength of 20 sheets was 348 MPa.

<Example 1>
a) Grinding step The 8YSZ sintered body sheet obtained in the above Reference Example 1 is sequentially put into a cutting mill (model “P-25”, sieve mesh: 0.75 mm trapezoidal mesh, manufactured by Fritsch), and the rotational speed is 2800 rpm. Then, the rotor with a rotary blade was rotated for primary pulverization, and zirconia powder was recovered in a tray. The recovery rate at this time was 98%. The average particle size, 95 volume% particle size, and maximum particle size of the obtained primary pulverized zirconia powder were measured using a laser diffraction / scattering particle size distribution measuring device (Horiba Seisakusho: Model “LA-920”).

  Next, the primary pulverized zirconia powder was continuously charged from a vibrating sample supply device into a high-speed rotor mill (manufactured by Fritsch, model “P-14”, sieve mesh: 0.12 mm trapezoidal mesh) at a rotational speed of 20000 rpm. A 12-blade rotor was rotated and pulverized to recover zirconia powder. The recovery rate at this time was 96%. The obtained secondary pulverized zirconia powder had an average particle size of 6.9 μm, a 95 volume% particle size of 15.7 μm, and a maximum particle size of 30 μm.

b) Dissolution Step 100 g of the pulverized zirconia powder obtained in the above pulverization step was placed in a flat bottom platinum dish, and then 500 mL of commercially available sulfuric acid (98%) and 200 g of commercially available ammonium sulfate were added. This was covered with an upper lid and heated at 250 ° C. for 1 hour to obtain a paste-like melt. This was washed with 10% sulfuric acid to obtain a solution. The zirconia solid content concentration in this solution was 10%, and its pH was 1 or less.

c) Dilution process Distilled water was put into a reaction tank equipped with a stirrer and circulated through an overflow pipe by a sealless pump. The solution obtained in the dissolution step was gradually added dropwise to the reaction layer to dilute the concentration as zirconia to 0.5 mol / L.

d) Precursor preparation step Distilled water was put into a reaction vessel with a stirrer different from the reaction vessel used in the dilution step, and was circulated through an overflow pipe by a sealless pump. Sulfuric acid was added to adjust the pH to 5.5. Reaction from the overflow pipe while injecting the diluted solution obtained in the above dilution step at a rate of 50 mL / min and ammonia water (28 mass% aqueous solution) at a rate of 40 mL / min with a metering pump into the stirring reaction tank. The neutralization precipitation reaction was carried out while maintaining the pH in the reaction tank at 5.5 ± 0.5 by a flow system in which a part of the liquid was allowed to flow out. After removing the ammonium sulfate and the like by filtering and washing the hydroxide in the effluent with an ultrafiltration machine and washing with water, the moisture is removed with a rotary filter press machine and dried at 120 ° C. for 20 hours to obtain a zirconia precursor. Prepared.

e) Calcination Step The zirconia precursor obtained in the precursor preparation step is calcined at 800 ° C. for 5 hours to obtain a specific surface area of 12 m 2 / g, an average particle diameter of 0.3 μm, and a 95 volume% diameter of 1. An 8YSZ recycled zirconia powder having 0 μm and a maximum particle size of 1.5 μm was obtained.

<Reference example 2>
Production of zirconia sintered sheet for grinding Commercially available scandia-stabilized zirconia powder (manufactured by Daiichi Elemental Chemical Co., Ltd., trade name “10Sc1CeSZ”, average particle size: 0.60 μm, specific surface area: 10.8 m ² / g, below 1800 sheets of 10Sc1CeSZ sintered sheets having a size of about 90 mm square and a thickness of about 240 μm were produced in the same manner as in Example 1 except that the amount of the binder was 16 parts by mass using 10Sc1CeSZ.
For reference, when the physical properties of the 10Sc1CeSZ sintered body sheet were measured, the porosity determined from the density by Archimedes method with respect to the sheet theoretical density was 97.9%, and the three-point bending strength test of the sintered body sheet according to JIS-1601 The average value of the strength by 20 sheets was 381 MPa.

<Example 2>
a) Grinding step The obtained sheet is sequentially put into a cutting mill (model “P-25” manufactured by Fritsch, sieve mesh: 0.75 mm trapezoidal), and the rotor with a rotating blade is rotated at a rotational speed of 2800 rpm. After grinding, primary ground zirconia powder was collected in a saucer. The recovery rate at this time was 94%. The average particle diameter, 95 volume% particle diameter, and maximum particle diameter of this zirconia powder were measured.
Further, the recovered primary pulverized zirconia powder is continuously fed from a vibrating sample supply device to a high-speed rotor mill (manufactured by Fritsch, model “P-14”, sieve mesh: 0.12 mm trapezoidal mesh) and rotated at 20000 rpm. Then, a 12-blade rotor was rotated and ground to recover zirconia powder. The recovery rate at this time was 93%. The average particle diameter, 95 volume% particle diameter, and maximum particle diameter of the obtained secondary pulverized zirconia powder were measured in the same manner.

Next, 100 g of the secondary pulverized zirconia powder was put into a 500 mL zirconia pot containing 5 mmφ zirconia beads, 150 g of distilled water was further added, and mounted on a planetary mill (model “P-5” manufactured by Fritsch). The mixture was rotated at 300 rpm for 30 minutes and subjected to primary wet pulverization. Further, the 5 mmφ zirconia beads were replaced with 1 mmφ zirconia beads, and the mixture was similarly rotated at 300 rpm for 30 minutes to perform secondary wet grinding. After pulverization, the pulverized zirconia powder was separated and collected through a glass filter, and further dried at 80 ° C. for 5 hours to obtain recycled zirconia powder. The average particle size of the obtained powder was 0.9 μm, the 95% by volume particle size was 6.1 μm, the maximum particle size was 10 μm, and the specific surface area was 2.3 m ² / g.

b) Dissolution Step 200 g of the pulverized zirconia powder obtained in the above pulverization step was placed in a flat bottom platinum dish, and then 500 mL of commercially available sulfuric acid (98%) and 200 g of commercially available ammonium sulfate were added. This was covered with an upper lid and heated at 250 ° C. for 1 hour to obtain a paste-like melt. This was washed with 10% sulfuric acid to obtain a solution. The zirconia solid content concentration in this solution was 10%, and its pH was 1 or less.

c) Dilution step to e) Calcination step The dilution step to the precursor preparation step were performed in the same manner as in Example 1. The calcination step is a calcination of the zirconia precursor obtained in the precursor preparation step at 950 ° C. for 2 hours, and the calcined powder is spray-dried with a spray dryer to form a weakly agglomerated spherical shape with a specific surface area. A 10Sc1CeSZ recycled zirconia powder having 8.8 m ² / g, an average particle diameter of 0.6 μm, a 95 volume% diameter of 1.1 μm, and a maximum particle diameter of 1.4 μm was obtained.

<Example 3>
200 sheets of 8YSZ sintered body sheets were manufactured in exactly the same manner as the method for producing a zirconia sintered body sheet for grinding in Reference Example 1 except that the 8YSZ recycled zirconia powder obtained in Example 1 was used as a raw material zirconia powder. When the physical properties of the 8YSZ sintered body sheet were measured, the porosity determined from the density by Archimedes method with respect to the sheet theoretical density was 96.6%, and the strength of the sintered body sheet according to JIS-1601 was determined by the three-point bending strength test. The average value of 20 sheets was 335 MPa, which was almost the same performance as that of a sintered body sheet using unused zirconia powder of Reference Example 1 as a raw material powder.

<Example 4>
As the raw material zirconia powder, 200 10Sc1CeSZ sintered body sheets were produced in exactly the same manner as in the method for producing the pulverized zirconia sintered body sheet of Reference Example 2 except that the 10Sc1CeSZ recycled zirconia powder obtained in Example 2 was used. When the physical properties of the 10Sc1CeSZ sintered body sheet were measured, the porosity determined from the density by the Archimedes method with respect to the sheet theoretical density was 98.2%, and the strength was determined by the three-point bending strength test of the sintered body sheet according to JIS-1601. The average value of 20 sheets was 401 MPa, which was almost the same performance as that of a sintered body sheet made from the unused zirconia powder of Reference Example 2 as a raw material powder.

<Example 5>
Reference Example, except that 50% by mass of recycled zirconia powder obtained in Example 1 and 50% by mass of unused 8YSZ powder used in the production of the pulverized zirconia sintered body sheet of Reference Example 1 were used as raw material zirconia powder. In the same manner as in No. 1, 200 sheets of 8YSZ sintered body were produced. The porosity determined from the density by the Archimedes method with respect to the sheet theoretical density was 97.1%, and the average value of 20 sheets of the strength by the three-point bending strength test of the sintered body sheet according to JIS-1601 was 347 MPa.

<Example 6>
As raw material zirconia powder, except that 10% by weight of recycled zirconia powder of Example 2 and 90% by weight of unused 10Sc1CeSZ powder used in the production of the pulverized zirconia sintered body sheet of Reference Example 2 were used as raw material zirconia powder, In the same manner as in Reference Example 2, 200 10Sc1CeSZ sintered sheets were produced. The relative density calculated | required from the density by the Archimedes method with respect to a sheet | seat theoretical density was 98.4%, and the average value of 20 sheets of the intensity | strength by the three-point bending strength test of the sintered compact sheet | seat based on JIS-1601 was 410 MPa.

  The present invention relates to the production of a zirconia sintered body by reusing the zirconia sintered body produced after the production of the zirconia sintered body.

Claims (5)

Ri Do from 10 to 30 mass% of recycled zirconia powder and 90 to 70% by weight of virgin zirconia powder,
The recycled zirconia powder is
(1) A step of crushing a zirconia sintered body for crushing into zirconia particles (crushing step)
(2) Step of dissolving zirconia particles obtained in the pulverization step with an acid (dissolution step)
(3) Step of diluting the solution obtained in the dissolution step with water (dilution step)
(4) A step of preparing a zirconia powder precursor by a coprecipitation method, a hydrolysis method, a hydrothermal synthesis method or a spray drying method using the diluted solution obtained in the dilution step (precursor preparation step)
(5) Step of drying and calcining the precursor obtained in the precursor preparation step to make recycled zirconia powder (calcination step)
Der those produced by the manufacturing method using a Ru raw material zirconia powder for a solid oxide fuel cell. The recycled zirconia powder has an average particle size of 0.01 to 1 μm and a specific surface area of 3 to ²⁰ m ² / g,
The unused zirconia powder has an average particle size of 0.01 to ² μm and a specific surface area of 3 to 30 m ² / g.
The raw material zirconia powder for a solid oxide fuel cell according to claim 1. A zirconia sintered body formed by molding and firing the raw material zirconia powder for a solid oxide fuel cell according to claim 1. An electrolyte for a solid oxide fuel cell, comprising the zirconia sintered body according to claim 3. A solid oxide fuel cell comprising the zirconia sintered body according to claim 3 or the electrolyte for a solid oxide fuel cell according to claim 4.