JP4855599B2 - Scandia stabilized zirconia electrolyte - Google Patents

Description

【００９２】
【表２】

【００９３】
【発明の効果】
本発明は以上の様に構成されており、スカンジア安定化ジルコニア電解質に特定の酸化物を少量含有させることによって、この種のジルコニア系セラミックスに欠けていたイオン導電性の長期安定性を改善すると共に、強度持続性にも優れた燃料電池用のスカンジア安定化ジルコニア電解質を提供し得ることになった。
【００９４】
そして、この燃料電池用スカンジア安定化ジルコニア電解質は、その優れたイオン導電性とその安定性、および強度持続性を活かし、燃料電池用の酸化物形固体電解質膜として有効に活用できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a scandia-stabilized zirconia electrolyte, and in particular, scandia which has stable and excellent oxygen ion conductivity, has sufficient mechanical strength for handling, and has excellent performance as a solid electrolyte membrane for fuel cells. The present invention relates to a stabilized zirconia electrolyte.
[0002]
[Prior art]
Cubic zirconia ceramics and tetragonal zirconia ceramics have been widely studied as electrolytes for solid oxide fuel cells, and yttria is generally used as a stabilizer to stabilize the crystal structure of the ceramics. Has been used.
[0003]
However, the oxygen ion conductivity of zirconia-based ceramics depends on the radius and amount of metal ions added, and zirconia in which scandia is dissolved may have higher conductivity than zirconia in which yttria is dissolved. It is shown. In addition, in order to put the solid oxide fuel cell power generation system into practical use, in addition to the economic efficiency and superior power generation performance comparable to other power generation systems, etc., long-term high-temperature durability of at least 40,000 hours or more Sex is required.
[0004]
Therefore, various researches have been carried out to realize excellent power generation performance at a lower cost than yttria-stabilized zirconia (YSZ) as a solid electrolyte membrane of a fuel cell, which has higher oxygen ion conductivity than yttria-stabilized zirconia. The scandia-stabilized zirconia ceramics that have been attracting attention.
[0005]
For example, a ceramic oxygen ion conductor made of a ternary metal oxide obtained by adding alumina to scandia-stabilized zirconia (ScSZ) is known. This ceramic is stabilized by adding a specific ratio of alumina as a sub-dopant and does not cause structural transformation between room temperature and high operating temperature, and has higher ionic conductivity than yttria-stabilized zirconia. It is considered that the oxygen ion conductor can be used as a solid electrolyte for a fuel cell.
[0006]
In addition, scandia-stabilized zirconia (ScSZ) has a valence of 2 or 3 and is a stable sub-dopant. ₂ O _Three An oxygen ion conductor made of a ternary metal oxide to which (M represents a metal element) is also known.
[0007]
The sub-dopant is one of the metals M selected from In, Ga, Ti, V, Cr, Fe, Co, Mg, Ca, Zn, Sr, and Ba, and by adding these, While maintaining the characteristics of Sc, the crystal structure is stabilized with cubic crystals, crystal transformations at high temperatures do not appear, high ionic conductivity, and excellent strength sustainability when subjected to thermal cycling. Become.
[0008]
However, none of them describes the change over time in oxygen ion conductivity, which is one of the important requirements for sustaining power generation characteristics over the long term.
[0009]
On the other hand, Volume 72, pages 271-275 (1994), volume 79, pages 137-142 (1995), volume 132, pages 235-239 (2000) of “Solid State Ionics” contain 2 scandia amounts. Scandia-stabilized zirconia (2.9-12ScSZ) varied in the range of 0.9-12 mol%, 8-11 mol% scandia-stabilized zirconia (8-11ScSZ20A) to which 20% by mass of alumina was added Changes over time have been studied. Among them, 11-12ScSZ and 11ScSZ20A having a rhombohedral crystal structure show almost no change over time even after long-term exposure at 1000 ° C. for 4000-6000 hours.
[0010]
However, it has been reported that 8ScSZ having a cubic structure has a conductivity reduced from 0.32 S / cm to 0.14 S / cm after exposure at 1000 ° C. for 1300 hours. In addition, 2.9ScSZ, which is a tetragonal structure, has been reported to decrease in conductivity from 0.09 S / cm to 0.063 S / cm after 1000 hours of exposure at 1000 ° C. In other words, the conductivity is greatly reduced by 30 to 60% after 1000 to 1300 hours of exposure.
[0011]
As described above, alumina has excellent properties as a dispersion strengthening agent. However, since alumina is highly reactive, when alumina is present in the surface layer of the zirconia electrolyte sheet, it is exposed to high temperatures for a long time. In addition, a solid-phase reaction may occur between transition metals and rare earth elements contained in the electrode component, and a new alumina-based composite oxide may be generated. For example, when Ni component is present in the anode, NiAl ₂ O _Four (Spinel crystal system) is easily generated. Further, when a Mn component is present in the cathode, MnAlO _Three (Perovskite crystal system) is easily generated. When these exist in the surface layer part of a zirconia electrolyte sheet, it becomes a foreign substance and becomes a starting point of a crack of a zirconia electrolyte sheet by a thermal expansion difference with a zirconia, and causes strength deterioration. For this reason, it is difficult to say that alumina is preferable as a dispersion strengthener for zirconia for electrolyte.
[0012]
Further, as a solid electrolyte used in a fuel cell power generation system, it is important to stably maintain the high oxygen ion conductivity for a long period of time, for example, 40,000 hours, in addition to high oxygen ion conductivity. Therefore, it is desired to improve such that the rate of decrease in the temperature can be kept small and a high level of electrical characteristics can be maintained for a long time.
[0013]
In other words, there is room for further study, including the type of oxide, contained in the scandia-stabilized zirconia used in the fuel cell system, and the crystal structure and strength of the obtained scandia-stabilized zirconia for fuel cells. Furthermore, there is still room for study on the change over time of the conductivity of the scandia-stabilized zirconia electrolyte for a fuel cell using the same.
[0014]
[Problems to be solved by the invention]
The present invention has been made by paying attention to the above-described circumstances, and its purpose is to reduce the time-dependent change in oxygen ion conductivity during high-temperature and long-time use of the scandia-stabilized zirconia electrolyte, thereby stably providing high conductivity. In particular, it is intended to provide a scandia-stabilized zirconia electrolyte having excellent high-temperature strength and strength sustainability, while reducing the degree of deterioration of the initial conductivity until 2000 hours.
[0015]
In addition, as a development goal of “Research and Development of Solid Oxide Fuel Cells” from FY 2001 by the New Energy and Industrial Technology Development Organization (NEDO), the target performance of the thermal self-sustaining module is the same as the initial characteristic evaluation. The voltage drop rate after 3000 hours of power generation is less than “0.25% / 1000 hours” (2000 “High Temperature Fuel Cell Power Generation Technology” R & D Report Summary (NEDO, Fuel and Storage Technology) In order to provide a scandia-stabilized zirconia electrolyte in which the deterioration of oxygen ion conductivity over time does not significantly affect the voltage drop rate as a solid electrolyte. is there.
[0016]
[Means for Solving the Problems]
Under the above-mentioned problems, the present inventors have determined the type of oxide to be blended with scandia-stabilized zirconia and the crystal structure and conductivity of scandia-stabilized zirconia electrolyte for fuel cells, which is the resulting blend. As a result of investigations focusing on changes, we succeeded in obtaining a scandia electrolyte for fuel cells that satisfies both of these characteristics.
[0017]
That is, the scandia-stabilized zirconia electrolyte for a fuel cell according to the present invention that has solved the above-mentioned problems is stabilized by scandia, and from oxides of 4A group, 5A group, 7A group, and 4B group elements. The gist of the invention is that it contains 0.01 to 5% by mass of at least one selected from the group consisting of scandia-stabilized zirconia.
[0018]
More specifically, the scandia-stabilized zirconia for a fuel cell is stabilized with 3 to 15 mol% of scandia and TiO, which is an oxide of an element having a valence of 4 or 5. ₂ , Nb ₂ O _Five , Ta ₂ O _Five And MnO ₂ What contains 0.01-5 mass% of at least 1 sort (s) selected from the group which consists of scandia stabilization zirconia is preferable.
[0019]
In the electrolyte of the present invention, the content of silicon oxide and / or oxides of alkali metals such as Na, K, Rb and Cs is desirably minimized, and preferably 0.1% by mass or less. More preferably, it is desirable to suppress the content to 0.05% by mass or less.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Under the problems as described above, the present inventors have focused on scandia-stabilized zirconia electrolytes, and in order to obtain a more durable electrolyte by reducing the change over time in the conductivity of the electrolyte. I have been researching from this angle.
[0021]
As a result, the change in conductivity over time is greatly influenced by the change in crystal structure and the stability of the grain particle size, and if a specific amount of a specific oxide in scandia-stabilized zirconia is contained, the initial conductivity is slightly reduced. Thus, the inventors have found that the subsequent change in conductivity with time can be suppressed to a small extent, and have arrived at the present invention.
[0022]
It has also been found that the above specific oxide also acts as a dispersion strengthening agent for scandia-stabilized zirconia ceramics, resulting in excellent high-temperature strength and strength sustainability.
[0023]
First, the present invention is directed to zirconia stabilized with scandia, and a general scandia addition amount is 3 mol% or more and 15 mol% or less. That is, if the scandia content is less than 3 mol%, the proportion of monoclinic crystals in the ceramic crystal structure increases, and the stabilization of zirconia becomes insufficient, making it difficult to obtain satisfactory strength. On the other hand, the stabilizing effect of scandia saturates at about 15 mol%, and the inclusion of more expensive scandia is only an economic disadvantage.
[0024]
In order to increase the high temperature endurance strength and the handling strength at room temperature, it is preferable to have a crystal structure mainly composed of a tetragonal system, and the preferable amount of scandia for that purpose is 3 mol% or more, 9 mol% or less, Preferably it is 3.5 mol% or more and 6 mol% or less, More preferably, it is 5 mol% or less.
[0025]
Further, in the present invention, at least one selected from the group consisting of oxides of 4A group, 5A group, 7A group and 4B group elements is used as a scandia-stabilized zirconia in order to suppress change in electrical conductivity as well as mechanical strength. It is necessary to make it contain 0.01 mass% or more and 5 mass% or less with respect to it.
[0026]
Here, 4A group, 5A group, 7A group and 4B group element are, for example, the periodic table of elements described in the RIKEN Dictionary 5th edition (Iwanami Shoten: issued on April 24, 1998) (short period type) ), Specifically, the oxide of the 4A group element is TiO. ₂ ; V as an oxide of 5A group element ₂ O _Five , Nb ₂ O _Five , Ta ₂ O _Five ; MnO as an oxide of 7A group element ₂ ; GeO as a group 4B element oxide ₂ Is preferred.
[0027]
In particular, in order to suppress the initial deterioration of the conductivity of scandia-stabilized zirconia and to enhance the sinterability and stabilize its crystal structure, TiO ₂ , Nb ₂ O _Five , Ta ₂ O _Five And MnO ₂ It is desirable to select at least one selected from the group consisting of:
[0028]
In order to effectively exhibit the effect of the metal oxide, the total amount of zirconia stabilized with scandia, specifically, 0.01% by mass or more, 5.0% with respect to the total amount of zirconia and scandia. It is good to contain in the range of less than mass%, More preferably, it is 0.1 mass% or more and 3.0 mass% or less, More preferably, it is the range of 0.3 mass% or more and 2.0 mass% or less.
[0029]
When the content of the metal oxide is less than 0.01% by mass, the above-described effects are not effectively exhibited. On the other hand, when the content is more than 5% by mass, the initial conductivity is preferably decreased. Absent.
[0030]
Furthermore, in the present invention, it is desirable to suppress the content of silicon oxide that may be mixed as impurities and / or alkali metal oxides such as Na, K, Rb, and Cs as much as possible. It is preferable to suppress the content to 0.1% by mass or less, more preferably 0.05% by mass or less.
[0031]
The silicon oxides and alkali metal oxides are low melting melting oxides compared to zirconia and the oxides, and segregate near the grain boundaries in scandia-stabilized zirconia when exposed to high temperatures for a long time. This is because there is a risk of decreasing the electrical conductivity.
[0032]
Therefore, it is desirable that the scandia-stabilized zirconia electrolyte for a fuel cell of the present invention is substantially free of silicon oxide and / or alkali metal oxide, but both are inevitably mixed in the zirconia raw material powder. More preferably, the content of silicon oxide is 0.03% by mass or less, and the total content of alkali metal oxides is preferably 0.01% by mass or less.
[0033]
Here, the total amount of alkali metal oxide is Na ₂ O, K ₂ O, Rb ₂ O, Cs ₂ The total amount of each oxide when O is used.
[0034]
The conductivity referred to in the present invention is a DC four-terminal method using a test piece partially cut with a diamond cutter as a sample for measuring conductivity from a ceramic used as an electrolyte membrane for a solid oxide fuel cell. It refers to the measured value, not the value using the test piece that was produced from the beginning as a sample for measuring conductivity. The size of the test piece used for this measurement was 50 mm long, 5 mm wide, and 0.01-0.6 mm thick.
[0035]
Next, in the scandia-stabilized zirconia electrolyte for fuel cells of the present invention, when the crystal structure is mainly composed of cubic crystals, the average particle size is 1 μm or more and 3 μm or less and the maximum diameter is 4 μm. As described above, it is preferable that the coefficient of variation is 8 μm or less and the variation coefficient is 35% or less in order to suppress the temporal change of the conductivity and ensure a high level of strength.
[0036]
Further, when the crystal structure is mainly composed of tetragonal crystals, the average particle diameter is 0.1 μm or more and 0.5 μm or less, and the maximum diameter is 0.5 μm or more and 1.0 μm or less, and the variation It is preferable that the coefficient is 30% or less in order to suppress the change in conductivity over time and to ensure high temperature strength durability.
[0037]
When the variation coefficient of the grain particle diameter exceeds 35% in the case of cubic crystals or exceeds 30% in the case of tetragonal crystals, the change in conductivity with time tends to increase and the Weibull coefficient tends to decrease to 10 or less. Will arise. The Weibull coefficient is regarded as a material constant that reflects the degree of strength variation, and in order to be used as a solid electrolyte for a fuel cell, the Weibull coefficient is 10 or more, more preferably 12 or more, and even more preferably 15 or more. As a result, the reliability as a material is enhanced and the design of the power generation system is facilitated. On the other hand, when the value is 10 or less, the strength variation is large, the reliability as a material is lacking, and it is not suitable for practical use.
[0038]
Here, the grain diameter of the above scandia-stabilized zirconia ceramics is photographed with a scanning electron microscope (10,000 to 20,000 times) on the surface, and the size of all grain particles in the photographic field of view is determined with calipers. The average diameter, maximum diameter, and coefficient of variation obtained by summing up individual data based on the measured values. When measuring the grain particle size with calipers, the grain particles located at the edge of the photographic field that do not appear as a whole are excluded from the object of measurement, and the grain particles with different vertical and horizontal dimensions are excluded. Used the average value of the major axis and minor axis as the particle diameter.
[0039]
The strength referred to in the present invention refers to a three-point bending strength measured using a test piece prepared in the same manner as a test piece for measuring conductivity in accordance with the provisions of JlS R1601, and the high temperature durability is This refers to a material having a small change over time in strength measured after being held at 950 ° C. for 1000 hours or more.
[0040]
Thus, the scandia-stabilized zirconia electrolyte for a fuel cell of the present invention comprises at least one selected from the group consisting of oxides of 4A group, 5A group, 7A group and 4B group elements as an additive. The addition of 0.01 to 5% by mass with respect to the amount suppresses the change over time in the conductivity of the scandia-stabilized zirconia electrolyte, and further improves the normal temperature strength, high temperature strength and durability thereof. This is extremely useful as a solid electrolyte for a physical fuel cell.
[0041]
Among them, TiO as the oxide ₂ , Nb ₂ O _Three , Ta ₂ O _Five And MnO ₂ The scandia-stabilized zirconia electrolyte of the present invention using at least one selected from the above has an extremely low decrease in initial conductivity compared to those not containing those oxides, and the stability of conductivity over time Therefore, for example, by forming a thin film sheet having a thickness of about 0.01 to 0.6 mm, extremely excellent performance is exhibited as a solid electrolyte membrane of a fuel cell.
[0042]
The powder used as the raw material for the scandia-stabilized zirconia electrolyte for fuel cells according to the present invention having such excellent characteristics may be obtained by adding and mixing the oxide powder of the specific element as it is to a commercially available scandia-stabilized zirconia powder. It can be added to commercially available zirconia powder in the form of an aqueous solution of alkoxide, nitrate, carbonate, etc., and if necessary, it can be further blended with other additives, etc., for hydrolysis, filtration, washing, calcining, mixed grinding, etc. It is good also as a raw material powder by processing.
[0043]
The preferred particle size of the raw material powder is an average particle size of 0.3 to 3 μm, preferably 0.5 to 1.5 μm and a specific surface area of 3 to 30 m. ² / G, preferably 5-15m ² / G.
[0044]
In particular, the raw material powder, which is granulated after spray-drying after mixing and pulverization, and having a granular shape of about 10 to 100 μm, has a density of 97% or more, preferably 98% of the theoretical density as a ceramic that has been molded and fired thereafter. It is suitable for increasing the above.
[0045]
In the case of spray drying, the pulverized and mixed zirconia powder may be spray dried by spray drying or the like as it is. However, the binder component (A) is added at the time of spray drying, and the granules containing the binder are spray dried. It is preferable to use the powdered material as a raw material powder because the moldability and sinterability can be further improved.
[0046]
The type of the binder (A) used here is not particularly limited, but is preferably water-soluble, and conventionally known organic or inorganic binders can be appropriately selected and used. Specific examples of the organic binder in the binder (A) include, for example, ethylene copolymers, styrene copolymers, acrylate and methacrylate copolymers, vinyl acetate copolymers, maleic acid copolymers. Examples thereof include cellulose such as coalescence, vinyl butyral resin, vinyl acetal resin, vinyl formal resin, vinyl alcohol resin, waxes, and ethyl cellulose. Specific examples of the inorganic binder include zirconia sol and titania sol. These binders can be used alone or, of course, can be used in combination of two or more if necessary.
[0047]
A preferable blending amount of the binder (A) is more preferably 0.5 parts by mass or more and 10 parts by mass or less in terms of solid content of the binder with respect to 100 parts by mass in total of the scandia-stabilized zirconia powder and the additive oxide. Is 1 part by mass or more and 5 parts by mass or less. The granular raw material powder containing the zirconia powder thus prepared is preferably used as a raw material for press molding.
[0048]
The production method of the scandia-stabilized zirconia electrolyte for a fuel cell according to the present invention is not particularly limited, and the scandia-stabilized zirconia powder prepared as described above is used, and a press molding method or extrusion molding using a mold or rubber. For example, a film forming method using a doctor blade, a sheet forming method using a doctor blade, a slurry coating method or a vapor deposition method on a supporting substrate, and a method of firing are employed.
[0049]
In particular, in order to produce a thin film sheet having a thickness of 10 to 200 μm, sheet forming by a doctor blade method is suitable, and the scandia-stabilized zirconia raw material powder, binder (B), and dispersion medium in which the specific oxide described above is blended. If a slurry is made on a carrier film and formed into a sheet shape, this is dried and the dispersion medium is volatilized to obtain a green sheet. Good.
[0050]
Firing is carried out by placing a green sheet or slurry-coated body formed by the above-described method on a shelf board or a porous setter, and 1300-1600 ° C., preferably about 1350-1500 ° C., most commonly 1400 It is performed by heating at 1450 ° C. for about 1 to 5 hours.
[0051]
The sheet-like zirconia ceramics have a high degree of thermal, mechanical, electrical, and chemical characteristics. When put into practical use for a solid electrolyte membrane of a fuel cell, the current loss is satisfied while satisfying the required strength. In order to suppress as much as possible, the sheet thickness should be 0.01 mm or more, more preferably 0.02 mm or more, 0.6 mm or less, more preferably 0.3 mm or less, and further preferably 0.2 mm or less. .
[0052]
The size is not particularly limited, but in order to obtain a fuel cell system with sufficient power generation capacity on a practical scale, it is 50 cm. ² Above, preferably 100cm ² The above dimensions are desirable.
[0053]
The sheet is generally square, rectangular, disc-shaped, or donut-shaped with a hole in the center, but there is no reason to limit it, and any other polygonal shape or hole Any shape such as a polygonal shape may be used. In addition to the sheet shape, a three-dimensional shape such as a cylindrical shape, a cylindrical shape with one side sealed, a honeycomb shape, a corrugated shape, or a dimple shape can also be used effectively.
[0054]
There is no particular limitation on the type of binder (B) blended in the slurry, and conventionally known organic or inorganic 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.
[0055]
Among these, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, isobutyl acrylate, cyclohexyl acrylate, 2-ethylhexyl are preferred from the viewpoints of moldability and strength when obtaining an unfired zirconia-based molded product, and thermal decomposition during firing. Alkyl acrylates having an alkyl group having 10 or less carbon atoms such as acrylate; carbons such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate, dodecyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate Alkyl methacrylates having an alkyl group of several 20 or less; hydroxyethyl acrylate, hydroxy Hydroxyalkyl acrylates or hydroxyalkyl methacrylates having a hydroxyalkyl group such as propyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate; aminoalkyl acrylates or aminoalkyl methacrylates such as dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate; (meth) acrylic A number average molecular weight of 20,000 to 200,000 obtained by polymerizing or copolymerizing at least one of a carboxyl group-containing monomer such as maleic acid half ester such as acid, maleic acid and monoisopropylmalate; More preferably, 50,000 to 100,000 (meth) acrylate copolymer is recommended.
[0056]
These organic binders can be used alone or in combination of two or more as necessary. Particularly preferred is a monomer polymer containing 60% by mass or more of isobutyl methacrylate and / or 2-ethylhexyl methacrylate.
[0057]
As the inorganic binder, zirconia sol, silica sol, titania sol and the like can be used alone or in combination of two or more.
[0058]
The use ratio of the zirconia-based raw material powder and the binder is preferably in the range of 5 to 30 parts by mass, more preferably 10 to 20 parts by mass in terms of solid content with respect to the former 100 parts by mass, and the amount of binder used is If the amount is insufficient, the strength and flexibility of the molded product will be 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 there will be a lot of decomposition and release of the binder component during firing, and it will become homogeneous. It becomes difficult to obtain a sintered body.
[0059]
The slurry containing the zirconia powder thus obtained can be suitably formed into a sheet by a doctor blade method.
[0060]
Moreover, as a solvent used for manufacture of a non-baking zirconia molded object, water; alcohols, such as methanol, ethanol, 2-propanol, 1-butanol, and 1-hexanol; ketones, such as acetone and 2-butanone; pentane, Aliphatic hydrocarbons such as hexane and heptane; aromatic hydrocarbons such as benzene, toluene, xylene and ethylbenzene; acetates such as methyl acetate, ethyl acetate and butyl acetate are appropriately selected and used. These solvents can also be used alone, or two or more of them can be appropriately mixed and used. The amount of the solvent used may be appropriately adjusted in consideration of the viscosity of the slurry at the time of forming the green sheet, but the slurry viscosity is preferably in the range of 1 to 10 Pa · s, more preferably 2 to 5 Pa · s. It is better to make adjustments.
[0061]
In the preparation of the slurry, in order to promote peptization and dispersion of the zirconia-based raw material powder, polymer electrolytes such as polyacrylic acid and ammonium polyacrylate; organic acids such as citric acid and tartaric acid; isobutylene or styrene and maleic anhydride Dispersants such as copolymers with acids and ammonium salts or amine salts thereof, copolymers of butadiene and maleic anhydride and ammonium salts thereof; phthalates for imparting flexibility to green bodies (green sheets) Plasticizers such as phthalates such as dibutyl acid and dioctyl phthalate, glycols such as propylene glycol and glycol ethers; and surfactants and antifoaming agents can be added as necessary.
[0062]
A slurry composed of the above raw material blend is formed by the method as described above, dried to obtain a zirconia green body, and then heated and fired to obtain the scandia-stabilized zirconia electrolyte of the present invention.
[0063]
In this firing step, as a means for obtaining a thin sheet-like sintered body having a high flatness without causing deformation such as warpage and undulation, it has an area larger than that of the green sheet and is defined by JIS K7125 (1987). Between a porous sheet having a static friction coefficient of 1.5 or less and a breathability of 0.0005 m / s · kPa or more, measured according to the “Friction Coefficient Test Method for Plastic Films and Sheets”, It is desirable that the green sheet is sandwiched and fired so that the periphery of the green sheet does not protrude, or is fired after the porous sheet is placed so that the periphery of the green sheet does not protrude.
[0064]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. It is also possible to implement them, and they are all included in the technical scope of the present invention.
[0065]
Example 1
4.5 mol% scandia partially stabilized zirconia powder (Daiichi Rare Elemental Chemical Co., Ltd .: trade name “4.5ScSZ”) 100 parts by mass, isopropyl alcohol 60 parts by mass, titanium isopropoxide in terms of titanium oxide. 3. The mixture added to 3 parts by mass was added, and isopropyl alcohol was distilled off under reduced pressure using a rotary evaporator, followed by drying under reduced pressure, followed by calcination at 800 ° C. to disperse 0.3% by mass of titanium oxide. 5 mol% scandia partially stabilized zirconia powder (A) was obtained. The silica content in the powder was 0.004% by mass, and the sodium oxide content was 0.001% by mass.
[0066]
To 100 parts by mass of this powder (A), 70 parts by mass of water and a water-soluble binder (molecular weight: 50,000, glass transition temperature: -14 ° C.) made of an acrylate copolymer mainly composed of ethyl acrylate are solidified. After adding 5 parts by mass and dispersing and mixing with a ball mill for 20 hours, the resulting slurry is spray-dried by spray drying, and 0.3% by mass of titanium oxide dispersed 4.5 mol% scandia partially stabilized zirconia powder is added. (B) was obtained.
[0067]
Using this zirconia powder (B), 1000 kg / cm by rubber press method ² After being formed into a plate shape at a pressure of 4.5 mm for a fuel cell containing 0.3% by mass of titanium oxide having a square of about 50 mm square on one side and a thickness of 0.5 mm, fired at 1400 ° C. for 3 hours. A mol% scandia partially stabilized zirconia sheet (I) was obtained. When the density of this sheet fired body was determined by the Archimedes method, it was 98.8% of the theoretical density.
[0068]
In addition, 100 parts by mass of the zirconia powder (A) obtained above was replaced with 14 parts by mass of a binder (molecular weight: 30,000, glass transition temperature: −8 ° C.) made of a methacrylic acid ester copolymer, and plastic. 2 parts by weight of dibutyl phthalate as an agent, 50 parts by weight of a mixed solvent of toluene / isopropyl alcohol (mass ratio: 3/2) as a dispersion medium, and placed in a nylon pot charged with a zirconia ball having a diameter of 5 mm. % Was kneaded at about 60 rpm for 40 hours to prepare a slurry.
[0069]
A part of this slurry was sampled, diluted with a mixed solvent of toluene / isopropyl alcohol (mass ratio: 3/2), and then in the slurry using a laser diffraction particle size distribution analyzer “SALD-1000” manufactured by Shimadzu Corporation. When the particle size distribution of the solid component was measured, the average particle diameter (50 volume% diameter) was 0.49 μm, the 90 volume% diameter was 1.18 μm, and the critical particle diameter (100 volume% diameter) was 2.88 μm. .
[0070]
The slurry was concentrated and defoamed, the viscosity was adjusted to 3 Pa · s (23 ° C.), and finally passed through a 200 mesh filter, and then coated on a polyethylene terephthalate (PET) film by the doctor blade method. A green sheet having a thickness of about 0.18 mm was obtained. This green sheet was cut into a square of about 125 mm on one side, degreased by sandwiching the top and bottom with a 99.5% alumina porous plate with a maximum height of 10 μm, fired at 1400 ° C. for 3 hours, Is a square of about 100 mm square, and a 4.5 mol% scandia partially stabilized zirconia sheet (II) for fuel cells containing 0.3% by mass of titanium oxide having a thickness of 0.15 mm was obtained.
[0071]
The zirconia sheets (I) and (II) are cut into strips having a width of 5 mm and a length of 50 mm with a diamond cutter to obtain test pieces for conductivity measurement and three-point bending strength measurement. And after exposure in an electric furnace maintained at 750 ° C. for 500 hours, 1000 hours, 2000 hours and 3000 hours, the conductivity and the three-point bending strength were measured.
[0072]
The electrical conductivity is measured by winding the test piece exposed to the above high temperature at four intervals at 1 cm intervals with a 0.2 mm diameter platinum wire, applying a platinum paste, drying and fixing at 100 ° C., and a current / voltage terminal. With both ends of the test piece wound with platinum wire sandwiched between alumina plates so that the platinum wire is in close contact with the test piece, a constant load of 0.1 mA is applied to the outer two terminals with a load of about 500 g applied from above. A current was passed, and the voltage at the inner two terminals was measured by a DC multi-terminal method using a digital multimeter (manufactured by Advantest Corporation: trade name “TR6845 type”).
[0073]
The durability stability of the conductivity was determined by the following formula from the initial conductivity and the change over time in the conductivity after a predetermined time.
Degradation rate of conductivity = [(initial conductivity−conductivity after holding for a predetermined time) / (initial conductivity)] × 100 (%)
The bending strength was measured in accordance with JIS R1601, a test piece exposed at high temperature was measured at room temperature, and the bending strength was determined from the ratio between the initial bending strength and the bending strength after a predetermined time by the following formula.
Strength deterioration rate = [(initial strength−strength after holding for a predetermined time) / (initial strength)] × 100 (%)
Furthermore, the composition of the obtained zirconia sheets (I) and (II) for fuel cells was measured by ICP emission spectrometry. The results are shown in Table 1.
[0074]
Example 2
4.0 parts by mass of scandia partially stabilized zirconia powder (Daiichi Rare Elemental Chemical Co., Ltd .: trade name “4ScSZ”) with 100 parts by mass of water, 1.0 part by mass of niobium chloride in terms of niobium oxide was added to 60 parts by mass of water. Niobium hydroxide obtained by decomposition and 1 part by mass of a water-soluble binder composed of the same acrylate copolymer as used in Example 1 above are added and dispersed and mixed for 20 minutes by a ball mill. Subsequently, spray drying was performed by a spray drying method to obtain a binder-added 1.0% niobium oxide dispersion 4.0 mol% scandia partially stabilized zirconia powder (C) for the fuel cell according to the present invention. The silica content in the powder was 0.005% by mass, and the sodium oxide content was 0.001% by mass.
[0075]
Using this powder (C), it was molded by a rubber press method in the same manner as in Example 1, and then fired. A niobium oxide of 1.0 mass having a square of about 50 mm square and a thickness of 0.5 mm was 1.0 mass. A 4.0 mol% scandia partially stabilized zirconia sheet (III) for a fuel cell was obtained. When the density of this sheet fired body was determined by the Archimedes method, it was 98.1% of the theoretical density.
[0076]
A test piece was prepared from this sheet in the same manner as in Example 1, and the durability and durability of the electrical conductivity and the three-point bending strength were determined. The results are shown in Table 1.
[0077]
Example 3
The scandium oxide powder (Wako Pure Chemical Industries, Ltd .: Reagent 99.9%) is 8 mol% with respect to the zirconia powder (Sumitomo Osaka Cement Co., Ltd .: brand name "OZC-0") which is not stabilized by Scandia. A total of 2 kg obtained by adding 1.5% by mass of tantalum oxide powder (Wako Pure Chemical Industries, Ltd .: Reagent 99.8%) to 100 parts by mass of these mixed powders. Was put in a bead mill (manufactured by Kotobuki Giken Kogyo Co., Ltd .: trade name “Apex Mill AM-1”) containing 3 kg of water and zirconia balls having a diameter of 0.5 mm, and the rotor tip circumferential speed was 7 m / sec for 1 hour. Wet crushed.
[0078]
The obtained slurry was put in a rotary evaporator, and an equal amount of octanol was further added and heated under reduced pressure to discharge water to obtain an octanol-substituted slurry. The slurry was further heated under reduced pressure to allow octanol to flow out, and then dried under reduced pressure, whereby a 1.5% tantalum oxide dispersion 8.0 mol% scandia-stabilized zirconia powder for fuel cells according to the present invention ( D) was obtained. The silica content in the powder was 0.004% by mass, and the sodium oxide content was 0.001% by mass.
[0079]
Using this powder (D), 1250 Kg / cm ² In the same manner as in Example 1 at a pressure of, after being molded by a rubber press method, it is fired at 1450 ° C. and includes 1.5% by mass of tantalum oxide having a square of about 50 mm square and a thickness of 0.5 mm. An 8.0 mol% scandia-stabilized zirconia sheet (IV) for a fuel cell was obtained. The density of the sheet fired body was 97.2% of the theoretical density.
[0080]
Using this sheet (IV), a test piece was prepared in the same manner as in Example 1, and the durability and stability of conductivity and three-point bending strength were determined. The results shown in Table 1 were obtained.
[0081]
Example 4
Water 60 in which 0.8 parts by mass of manganese nitrate in terms of manganese oxide was dissolved in 100 parts by mass of 4.5 mol% scandia partially stabilized zirconia powder (Daiichi Rare Element Chemical Co., Ltd .: trade name “4.5ScSZ”). 1 part by weight of the same water-soluble binder as used in Example 1 was added and dispersed for 20 hours by a ball mill, followed by spray drying by a spray drying method, and 0.8 mass% manganese oxide dispersion 4 added with a binder. 0.0 mol% scandia partially stabilized zirconia powder (E) was obtained. The silica content in the powder was 0.004% by mass, and the sodium oxide content was 0.001% by mass.
[0082]
Using this powder (E), in the same manner as in Example 1, it was molded into a plate shape by a rubber press method and then fired, and then a manganese oxide having a square of about 50 mm square and a thickness of 0.5 mm. A 4.5 mol% scandia partially stabilized zirconia sheet (V) for a fuel cell containing 0.8 mass% was obtained. The density of this sheet was 98.4% of the theoretical density.
[0083]
A test piece was prepared from this sheet in the same manner as in Example 1, and the durability and durability of the electrical conductivity and the three-point bending strength were determined. The results are shown in Table 1.
[0084]
Comparative Example 1
4.5 parts by weight of scandia partially stabilized zirconia powder (Daiichi Rare Elemental Chemical Co., Ltd .: trade name “4.5ScSZ”) 70 parts by weight of water and water-soluble acrylate mainly composed of ethyl acrylate After adding 5 parts by mass of a binder composed of a copolymer and dispersing and mixing with a ball mill for 20 hours, the resulting slurry is spray-dried by a spray drying method to add 4.5 mol% scandia partially stable. Zirconia powder (a) was obtained.
[0085]
Using this zirconia powder (a), 1000 kg / cm by rubber press method ² After being molded into a plate shape at a pressure of 1400 ° C., it is heated and fired at 1400 ° C. for 3 hours, and a 4.5 mol% scandia partial stability for a fuel cell with a side of about 50 mm square and a thickness of 0.5 mm Zirconia sheet (i) was obtained. The density of this sheet fired body was 96.8% of the theoretical density.
[0086]
A test piece was prepared from this sheet in the same manner as in Example 1, and the durability and durability of the electrical conductivity and the three-point bending strength were determined. The results are shown in Table 2.
[0087]
Comparative Example 2
4.5 parts by mass of scandia partially stabilized zirconia powder (Daiichi Rare Elemental Chemical Co., Ltd .: trade name “4.5ScSZ”), 100 parts by mass of isopropyl alcohol and titanium isopropoxide in terms of titanium oxide After adding the mixture added so that it becomes 8.0 mass%, isopropanol was depressurizingly distilled with a rotary evaporator, and after further drying under reduced pressure, it calcined at 800 degreeC, and 8.0 mass% titanium oxide was disperse | distributed. Thus, 4.5 mol% scandia partially stabilized zirconia powder (b) for a fuel cell was obtained. The silica content in the powder was 0.004% by mass, and the sodium oxide content was 0.001% by mass.
[0088]
For 100 parts by mass of this zirconia powder (b), 70 parts by mass of water and a binder (manufactured by Nippon Shokubai Co., Ltd .: trade name “AT-502”) comprising a water-soluble acrylate copolymer containing ethyl acrylate as a main component are solidified. After adding 5 mass% in terms of minutes and dispersing and mixing with a ball mill for 20 hours, the resulting slurry is spray-dried by a spray drying method to add a binder to 8.0 mass% titanium oxide dispersion 4.5 mol% scandia partially stable Zirconia powder (c) was obtained.
[0089]
Using the obtained zirconia powder (c), 1000 kg / cm by rubber press method ² For a fuel cell containing 8.0% by mass of titanium oxide having a square of about 50 mm square and a thickness of 0.5 mm by heating and baking at 1400 ° C. for 3 hours. Of 4.5 mol% scandia partially stabilized zirconia sheet (ii) was obtained. The density of the sheet fired body was 95.0% of the theoretical density.
[0090]
A test piece was prepared from this sheet in the same manner as in Example 1, and the durability and durability of the electrical conductivity and the three-point bending strength were determined. The results are shown in Table 2.
[0091]
[Table 1]

[0092]
[Table 2]

[0093]
【The invention's effect】
The present invention is configured as described above, and improves the long-term stability of ionic conductivity lacking in this kind of zirconia-based ceramics by containing a small amount of a specific oxide in a scandia-stabilized zirconia electrolyte. Thus, it was possible to provide a scandia-stabilized zirconia electrolyte for a fuel cell having excellent strength sustainability.
[0094]
The scandia-stabilized zirconia electrolyte for a fuel cell can be effectively used as an oxide solid electrolyte membrane for a fuel cell by utilizing its excellent ionic conductivity, its stability, and strength sustainability.

Claims (3)

In scandia stabilized zirconia,
Stabilized with 3-15 mol% scandia,
The solid oxide fuel further comprises 0.01 to 5% by mass of at least one selected from the group consisting of Nb ₂ O ₅ , Ta ₂ O ₅ and MnO ₂ with respect to scandia-stabilized zirconia. Scandia-stabilized zirconia electrolyte for batteries. The scandia-stabilized zirconia electrolyte according to claim 1, wherein the content of silicon oxide and / or alkali metal oxide is 0.1% by mass or less. The scandia-stabilized zirconia electrolyte according to claim 1 or 2, wherein the scandia-stabilized zirconia electrolyte has a sheet shape having a thickness of 0.01 mm or more and 0.6 mm or less.