JP2003020272A - Method for producing dense scandia stabilized zirconia sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a scandia stabilized zirconia sheet which exhibits stable, excellent ion electrical conductivity, further has sufficient strength and high temperature durability on handling, and has excellent performance as the one for a solid electrolytic membrane of a fuel battery, an oxygen generator, an oxygen sensor, or the like. SOLUTION: In the method for producing the dense zirconia sheet stabilized by scandia, slurry for producing a green sheet in which the mean grain size (50 vol.% size) of solid components is 0.15 to 0.5 μm, and the 90 volume % size is 0.6 to 1.5 μm is used, and this slurry is formed into a sheet shape, and is then sintered, so that the dense scandia stabilized zirconia sheet in which the mean value of the grain size is 0.1 to 0.6 μm, and the coefficient of the variation thereof is <=50% can be obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a scandia-stabilized zirconia sheet, and particularly shows stable and excellent ionic conductivity, has sufficient mechanical strength for handling, and is excellent in high-temperature durability, and is suitable for fuel cells and Oxygen generator,
The present invention relates to a method for producing a dense scandia-stabilized zirconia sheet having excellent performance for a solid electrolyte membrane such as an oxygen sensor.

[0002]

2. Description of the Related Art Yttria-stabilized zirconia, which is an oxygen ion conductor, has been widely studied as a solid electrolyte membrane for solid oxide fuel cells and the like. However, yttria-stabilized zirconia has a drawback that it must be kept at a high temperature to obtain a high level of oxygen ion conductivity, and the operating temperature must be increased. Therefore, zirconia stabilized with scandium oxide (scandia) has been investigated as a solid electrolyte material exhibiting excellent ionic conductivity even at a relatively low temperature.

However, the mechanical strength of scandia-stabilized zirconia is almost the same as or slightly inferior to that of yttria-stabilized zirconia. Therefore, in order to effectively exhibit the characteristics of high conductivity, the film is a expensive raw material. It must be thick.

On the other hand, in order to use such scandia-stabilized zirconia as a solid electrolyte membrane, it is necessary to reduce the film thickness, and practically, tape molding is desirable. However, scandia-stabilized zirconia is 1
It is necessary to fire and sinter at a high temperature of 700 ° C or higher,
Not only the production cost becomes high, but when the tape molded body is fired at such a high temperature, there arises a problem that the strength is lowered and the durability at high temperature is deteriorated as compared with the bulk body.

Further, like the yttria-stabilized zirconia, it is said that if a raw material having a large specific surface area prepared by the sol-gel method or the like is used, it can be densified even at a relatively low temperature. For example, JP-A-7-69721 and Same as 7-7
Japanese Patent No. 3891 discloses a press-molded body using the powder obtained by such a method. However, although such a high surface area powder raw material can be formed by the press forming method, it is extremely difficult to form a flat and dense sheet by the tape forming method. Moreover, even if the methods disclosed in these publications are adopted, the temperature cannot be lowered as in the case of yttria-stabilized zirconia, so that
It must be fired at a high temperature such as 0 ° C. this is,
This is because scandia-stabilized zirconia is more likely to agglomerate than yttria-stabilized zirconia, and in order to obtain a dense body by a sheet forming method from a raw material powder that is easily agglomerated, high temperature firing is required contrary to the spirit thereof.

Further, Japanese Patent Laid-Open No. 6-107462 discloses that
An oxygen ion conductor composed of a ternary metal oxide of ZrO ₂ —Sc ₂ O ₃ —Al ₂ O ₃ is disclosed. This ceramic is a solid crystal for a fuel cell that does not undergo structural transformation between room temperature and operating temperature by adding a specific ratio of Al ₂ O ₃ as a subdopant and stabilizing the crystal structure by cubic crystal. It gives an oxygen ion conductor that can be used as an electrolyte membrane. However, in order to obtain a dense body by this method, for example,
It is necessary to perform baking at a high temperature of about 620 ° C. for a high temperature and a long time of 60 hours, and when tape molding is performed, the same problem as described above occurs.

Further, in Japanese Patent Laid-Open No. 7-69720, as a means for providing a composite dispersion-strengthened solid electrolyte material having high electrical conductivity and excellent mechanical strength as a sheet-shaped solid electrolyte material, scandia is used. A technique is disclosed in which stabilized zirconia is used as a main component and alumina, mullite, or the like is dispersed as a reinforced composite material. However, the ceramic sheet obtained by tape molding using this raw material is not always satisfactory in strength and high temperature durability, and in order to obtain a dense ceramic sheet, high temperature such as 1500 to 1700 ° C. is required for firing. Must be adopted, and it is hard to say that it is satisfactory in industrial productivity.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its purpose is to improve the mechanical strength and durability at high temperature of a scandia-stabilized zirconia sheet, and to improve stability. Another object of the present invention is to provide a method by which a scandia-stabilized zirconia sheet exhibiting high oxygen ion conductivity can be efficiently formed by a tape forming method and can be produced industrially advantageously at a relatively low firing temperature.

[0009]

The manufacturing method of the present invention which has been able to solve the above-mentioned problems is a method for manufacturing a dense zirconia sheet stabilized with scandia, wherein the average particle size of solid components (50 Volume% diameter) is 0.15-0.5
By using a slurry for producing a green sheet having a diameter of 0.6 μm and a volume ratio of 90% by volume of 0.6 to 1.5 μm, and forming the same into a sheet and then sintering the slurry, the average grain size is 0.1 to 0.1 μm. The main point is to obtain a dense scandia-stabilized zirconia sheet having a coefficient of variation of 0.6 μm and a variation coefficient of 50% or less.

As a powder which is a raw material of a dense scandia-stabilized zirconia sheet produced by this method,
It is preferable to use the one having a specific surface area of 4 to ²⁰ m ² / g because it is possible to surely obtain a more dense and stable performance.

Further, as a ceramic component, TiO ₂ , N
one or more oxides selected from b ₂ O ₅ , Ta ₂ O ₅ and MnO ₂ , or LaAlO ₃ and MgAl
Those having a composition containing one or more kinds of oxides selected from ₂ O ₄ and Al ₂ TiO ₅ are preferable because higher levels of strength and high temperature durability can be obtained as described later.

The dense scandia-stabilized zirconia sheet produced according to the present invention has a thickness of 0 in order to effectively utilize its excellent characteristics for solid electrolyte membranes such as fuel cells, oxygen generators and oxygen sensors. .01 to 0.5
A thin film sheet having a size of 25 mm ² and an area of 25 cm ² is desirable.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the inventors of the present invention are directed to scandia-stabilized zirconia sheets, and improve the mechanical strength and durability at high temperature of the scandia-stabilized zirconia sheets. We have been conducting research from various angles. As a result, the strength and durability at high temperature have a large relationship with the grain size of the zirconia sheet after sintering, the average value of the grain size in the dense material is in a suitable range, and the coefficient of variation is Those that are as small as possible
I learned that it will be extremely excellent in room temperature strength and high temperature durability. Then, in order to obtain a scandia-stabilized zirconia sheet satisfying such a grain size and a coefficient of variation, an average particle diameter and a 90 volume% diameter of solid components are appropriately used as a slurry for producing a green sheet which is a raw material for manufacturing the sheet. The inventors of the present invention have come up with the present invention, knowing that control is effective.

In the present invention, the average grain size of the scandia-stabilized zirconia sheet is 0.1.
.About.0.6 .mu.m, preferably a coefficient of variation of 50% or less is important for ensuring high strength and high temperature durability. By the way, the average grain size is 0.1μ
If it is less than m, sufficient strength cannot be obtained because it is not densified due to insufficient sintering, while on the other hand, if the average value exceeds 0.6 μm, mainly strength and high temperature durability tend to be insufficient. Is. If the coefficient of variation exceeds 50%, the grain size distribution in the sintered body is wide and the strength and high temperature durability deteriorate, and the Weibull coefficient tends to decrease to 10 or less. Here, the Weibull coefficient is
It is considered to be a constant that reflects the degree of strength variation, and the one with a low value is evaluated as having a large variation and poor reliability.

A more preferable grain size in consideration of mechanical strength, high temperature durability, etc., has an average value of 0.2 to 0.5 μm, and more preferably 90% value (90% diameter). It is 1 μm or less.

The grain size in the ceramic sheet is determined by taking a photograph of the surface of the scandia-stabilized zirconia sheet with a scanning electron microscope (10,000 to 20,000 times) and measuring the size of all grains in the visual field. Based on the values measured with a caliper, individual data are aggregated to obtain the average value and 90% value of all grains and the coefficient of variation on a number basis. When measuring the grain size with a caliper, those that are located at the edge of the photographic field and do not show the entire grain are excluded from the measurement target.For grains with different vertical and horizontal dimensions, the major and minor axes are Let the average value be the grain size.

The strength as used in the present invention means JIS R1.
The three-point bending strength measured at room temperature (15 to 30 ° C) according to the regulations of 601, and the high temperature durability is 100 at 950 ° C.
It refers to one having a small change in strength over time measured after holding for 0 hour or more.

As described above, in the scandia-stabilized zirconia sheet of the present invention, by controlling the average value of the grain size in the sintered state and its variation coefficient, preferably 90% value, the room temperature strength and the high temperature durability are improved. Since it has excellent characteristics, it can be effectively used for solid electrolyte membranes such as fuel cells, oxygen generators, and oxygen sensors.

What is important in obtaining a dense scandia-stabilized zirconia sheet satisfying the above-mentioned average grain size and coefficient of variation is the particle size composition of the solid components contained in the slurry when the green sheet is produced. The average particle size (50% by volume) is 0.15 μm.
As described above, using a slurry satisfying the requirements of 0.5 μm or less and 0.6 μm or more and 1.5 μm or less at 90 volume% diameter gives a dense scandia-stabilized zirconia sheet satisfying the requirements of the preferred grain size. Will be extremely important above. A more preferable particle size constitution of the solid component contained in the slurry is 0.2 μm or more and 0.4 μm or less in average particle diameter (50 volume% diameter), and 0.
It is 8 μm or more and 1.2 μm or less.

Here, the 50% volume diameter means a particle diameter at 50% by volume in the distribution in which a cumulative volume distribution curve for the particle diameter is prepared from the smaller particle diameter. Similarly, 90 volume diameter means the particle diameter at 90 volume%.

By the way, when the average particle diameter in the slurry is out of the above range, a large amount of binder has to be blended at the time of preparing the slurry, and the sheet is warped or swelled in the degreasing step after being formed into a green sheet. If the 90% by volume diameter exceeds the above range, the particle size distribution becomes broad and gaps are easily formed between particles of the molded body, and it becomes difficult to obtain a dense scandia-stabilized zirconia sheet.

By defining the particle size composition of the solid content in these slurries and thereby ensuring a sharp particle size composition, it becomes possible to densify even when fired at a lower temperature, and to obtain a dense and appropriate grain size. A zirconia sheet can be obtained.

In the preparation of the above-mentioned slurry, a method of uniformly kneading and blending the blended raw material and the dispersion medium in a ball mill or the like is adopted, but depending on the kneading conditions (including the kind and addition amount of the dispersant), In the slurry preparation process, a part of the raw material powder undergoes secondary agglomeration or a part of the raw material powder is further pulverized, so that the particle size composition of the raw material powder does not become the same as that of the solid component in the slurry.

Then, the above-mentioned preferable particle size composition in a slurry state
In order to secure the
The specific surface area of the entire raw material powder before preparing the slurry
Is 4m ²/ G or more, 20m²/ G or less, more preferably 5
m²/ G or more, 15m²/ G or less can be used
desirable. By the way, the specific surface area of the raw material powder is 4m.²/ G
If it is less than the above, an excessive share is applied when the slurry is prepared.
If the raw material powder is not crushed further, it is suitable in a slurry state.
It becomes difficult to secure the particle size composition, and the specific surface area of the raw material powder is
15m²> / G, the raw material powder may cause secondary agglomeration.
It becomes easier to cause the particle size composition in the slurry state
This is because there is a tendency to become rough.

Here, the specific surface area of the whole raw material powder means that the raw material powder is weighed in a ratio according to the composition, put into one measuring cell, and the specific surface area of the mixed powder is determined by the BET method. It is a value measured by physically adsorbing nitrogen.

As described above, as a conventional method for sintering at a lower temperature, a powder obtained by firing a precipitate obtained by a sol-gel method or a coprecipitation method at a temperature of 800 ° C. or lower, for example, 20 m ^2. It has been practiced to use a powder having a large specific surface area of not less than / g. In fact, as described in JP-A-7-69721, for example, if powder having a high specific surface area is used, it is possible to densify by a method of applying pressure, for example, a press molding method. However, even in this case, low-temperature firing cannot sufficiently densify, and high-temperature firing at 1500 ° C. or higher is required.

As described above, powder having a large specific surface area easily forms agglomerates, and a tape molding method in which the agglomerates are not crushed causes a problem that it becomes difficult to obtain a dense green body. come.

That is, when the tape molding method is adopted, it is important to prevent agglomerates from being generated in a slurry state as much as possible and to prepare a slurry having an appropriate average particle diameter range. However, there have been few examples examined from this point of view so far, and it was surprisingly difficult to manufacture a zirconia-based sheet having a high density by a tape molding method.

This tendency is more remarkable in scandia-stabilized zirconia, which is more likely to aggregate than yttria-stabilized zirconia and whose particle diameter is difficult to control.

Therefore, in carrying out the present invention, the raw material powder before preparing the slurry has a specific surface area of 4 m ²
/ G or more and 20 m ² / g or less, more preferably,
Precipitates obtained by the sol-gel method or co-precipitation method should be used after adding an organic solvent, a dispersant or a pH adjusting agent, and then drying, so that the particles of the solid component in the slurry to be prepared later are used. It becomes easy to adjust the diameter within the above range.

When the raw material powder is mixed with a binder component, a dispersion medium, etc. to prepare a slurry, for example, a ball mill, an agitator or the like is used, and coarse particles or secondary agglomerates are crushed and uniformly dispersed. Is desirable. Further, when crushing and dispersing using a ball mill or the like, it is preferable to use a zirconia-based medium in order to avoid undesired inclusion of foreign matter as much as possible.

The particle size composition of the solid content in the slurry means the value measured by the following method. That is, a laser diffraction particle size distribution analyzer “SALD-11” manufactured by Shimadzu Corporation
“00” is used, a solvent having the same composition as the dispersion medium in the slurry is diluted as a dispersion medium, and ultrasonically treated for 1 minute to disperse the dispersion medium.

The method for molding the dense scandia-stabilized zirconia sheet according to the present invention is preferably a tape molding method, more preferably a doctor blade method or a calender method. That is, a slurry comprising the above-mentioned ceramic raw material powder, a binder, an additive and a dispersion medium is spread on a support plate or a carrier film and formed into a sheet, which is dried to volatilize the dispersion medium to obtain a green sheet. After this is cut, punched or the like to have an appropriate size, it is placed on a porous setter on a shelf plate and placed at 1200 to 1500 ° C., preferably 1250 to 142.
A method of heating and firing at a temperature of about 5 ° C. for about 1 to 5 hours is adopted.

When the temperature at the time of firing exceeds 1500 ° C.,
Not only is it difficult to secure the proper grain size intended by the present invention because the grain size of the fired sheet becomes large, but also rhombohedral and monoclinic crystals are formed in the sintered body, resulting in strength at room temperature and high temperature durability. Both sex become worse. On the other hand, the firing temperature is 1
If the temperature is lower than 200 ° C., it becomes difficult to obtain a dense sheet due to insufficient sintering, resulting in insufficient strength and gas permeation. However, if the firing is carried out in the above-mentioned preferable temperature range, the formation of monoclinic crystals and rhombohedra is suppressed, and the density of the fired sheet becomes 97% or more, more preferably 99% or more of the theoretical density, which is excellent in room temperature strength. The sintered body sheet has excellent high temperature durability.

In any case, in the present invention, by defining the particle size in the slurry as described above, it is possible to easily densify even at a firing temperature considerably lower than in the prior art, and to obtain the obtained zirconia. It is possible to reduce the grain size of the sheet and control it appropriately. This stabilizes the crystal structure and contributes not only to improvement of room temperature strength and high temperature durability and further improvement of oxygen ion conductivity, but also reduction of equipment cost and thermal energy required for firing. .

In this firing step, as a means for obtaining a thin-walled sheet-shaped sintered body having a high degree of flatness without causing deformation such as warping or waviness, for example, air permeability is 0.0005.
Between the porous sheets of m / s · kPa or more, the green sheet is sandwiched and baked so that the peripheral edge thereof does not protrude, and fired.
Alternatively, it is desirable that the porous sheet is placed so that the peripheral edge of the green sheet does not protrude, and then firing is performed.

The thus obtained dense scandia-stabilized zirconia sheet according to the present invention has a high degree of thermal, mechanical, electrical and chemical properties, for example, for fuel cells, oxygen generators and oxygen sensors. It is used as a solid electrolyte membrane, but especially when it is put to practical use for a solid electrolyte membrane of a fuel cell, while satisfying the required strength, the internal resistance value is suppressed as much as possible to improve power generation efficiency. The thickness is preferably 0.01 mm or more, more preferably 0.02 mm or more and 0.5 mm or less, more preferably 0.2 mm or less, and further preferably 0.1 mm or less.

The size is not particularly limited, but in order to obtain a fuel cell having a sufficient power generation capacity on a practical scale, 25 cm ²
It is desirable that the size is about the same or larger. In the present invention,
It is more effective in producing a large-area sheet having a size of 60 cm ² or more, further 100 cm ² or more. The most common sheet shape is a square, rectangle, disk shape, or donut shape with a hole formed in the center, but any other polygonal shape, such as a perforated polygonal shape, can be used. It goes without saying that things are not excluded.

There are no particular restrictions on the type of binder used when preparing the slurry, and conventionally known organic or inorganic binders can be appropriately selected and used. Examples of the organic binder include ethylene-based copolymers, styrene-based copolymers, acrylate-based and methacrylate-based copolymers, vinyl acetate-based copolymers, maleic acid-based copolymers, vinyl butyral-based resins, vinyl acetal-based resins. , Vinyl formal resin, vinyl alcohol resin, waxes, celluloses such as ethyl cellulose, and the like.

Among these, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, isobutyl acrylate, cyclohexyl acrylate, and 2-ethylhexyl acrylate are preferable from the viewpoints of moldability and strength when obtaining a green sheet, thermal decomposability during firing, and the like. Alkyl acrylates having an alkyl group having 10 or less carbon atoms such as; methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate, dodecyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, etc. Alkyl methacrylates having 20 or less alkyl groups; hydroxyethyl acrylate, hydro Hydroxyalkyl acrylates or hydroxyalkylmethacrylates having hydroxyalkyl groups such as cypropylacrylate, hydroxyethylmethacrylate, hydroxypropylmethacrylate; aminoalkylacrylates or aminoalkylmethacrylates such as dimethylaminoethylacrylate, dimethylaminoethylmethacrylate; (meth) A number average molecular weight of 20,000, obtained by polymerizing or copolymerizing at least one kind of a carboxyl group-containing monomer such as acrylic acid, maleic acid, maleic acid half ester such as monoisopropyl maleate;
0 to 200,000, more preferably 50,000 to 1
A 0,000 (meth) acrylate-based copolymer is recommended as preferred. These organic binders may be used alone or in combination of two or more kinds, if necessary. Particularly preferred is a polymer of a monomer containing 60% by mass or more of isobutyl methacrylate and / or 2-ethylhexyl methacrylate.

As the inorganic binder, zirconia sol, silica sol, alumina sol, titania sol or the like can be used alone or in combination of two or more kinds.

The ratio of the raw material powder to the binder used is preferably in the range of 5 to 30 parts by mass, more preferably 10 to 20 parts by mass with respect to 100 parts by mass of the former, and when the amount of binder used is insufficient. However, if the strength and flexibility of the green sheet are insufficient and, on the contrary, too much, it becomes difficult to control the viscosity of the slurry, and the decomposition and release of the binder component during firing become large and violent, resulting in a homogeneous and flat firing. It becomes difficult to obtain a united sheet.

As the solvent used for preparing the slurry, water; methanol, ethanol, 2-propanol,
Alcohols such as 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; acetic acid esters such as methyl acetate, ethyl acetate and butyl acetate Classes are appropriately selected and used. These solvents may be used alone, or two or more kinds may be appropriately mixed and used. The amount of these solvents used may be appropriately adjusted in consideration of the viscosity of the slurry at the time of forming the green sheet. The preferable slurry viscosity at the time of molding is 0.5 to 10
Pa · s, more preferably 1 to 5 Pa · s.

In the preparation of the above-mentioned slurry, polyacrylic acid, a polymer electrolyte such as ammonium polyacrylate, citric acid
Organic acid such as tartaric acid, copolymer of isobutylene or styrene and maleic anhydride and its ammonium salt or amine salt, dispersant of copolymer of butadiene and maleic anhydride and its ammonium salt; Dibutyl phthalate for imparting flexibility,
Phthalates such as dioctyl phthalate, plasticizers such as glycols such as propylene glycol and glycol ethers; and surfactants and defoamers can be added as required.

The present invention is directed to scandia-stabilized zirconia sheets, but in order to ensure high strength, the tetragonal crystal structure is preferable and it is stabilized with about 2 to 6 mol% scandia. It is a zirconia-based ceramic. That is, if the scandia content is less than 2 mol%, the proportion of the monoclinic system in the crystal structure of the sintered body is large, the stabilization of zirconia is insufficient, and the strength at room temperature and the high temperature durability are improved. I feel like I'm running short. On the other hand, those containing 6 mol% or more show higher conductivity, but the proportion of tetragonal crystals decreases and the strength decreases, so the sheet thickness must be increased.

In order to effectively exert the high temperature stabilization effect by an appropriate amount of scandia, and to minimize the grain size and its distribution of the sintered body to ensure high strength and high temperature durability, it is more preferable to have a crystal structure. In those containing mainly tetragonal crystals, the scandia content is 3.5 mol% or more and 5.0 mol% or less.

Further, in the present invention, in order to stabilize the crystal system, further enhance the room temperature strength and the high temperature durability, or enhance the sinterability to improve the densification, the TiO 2 content in the raw material powder is increased.
₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , MnO ₂ , Al ₂ O ₃ , LaAl
It is also effective to contain an appropriate amount of O ₃ , MgAl ₂ O ₄ , Al ₂ TiO _{5, and the} like. These may be blended alone, or may be used in combination of two or more kinds if necessary. By including these in the raw material powder, it is possible to produce a scandia-stabilized zirconia sheet in which the oxide is more uniformly dispersed.

That is, it is predicted that these oxides act as a sintering aid to lower the sintering temperature of the scandia-stabilized zirconia-based ceramic, and as a result, suppress the growth of grain particles in the sintering process. It These oxides are present near grain boundaries in scandia-stabilized zirconia-based ceramics, and prevent grains from coarsening due to sintering of grains even when exposed to high temperature for a long time, and the crystal phase is also tetragonal. It also suppresses the transition from to monoclinic crystals and contributes to the improvement of high temperature durability.

In order to exert such an effect effectively, 0.05 mass% or more and 2.0 mass% or less based on the total mass of 100 mol% of [zirconia + scandia] in scandia-stabilized zirconia, It is desirable that the content be 0.5% by mass or less.

[0050]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited by the following Examples, and is within a range applicable to the gist of the preceding and the following. It is also possible to carry out by appropriately changing the above, and all of them are included in the technical scope of the present invention.

The methods for evaluating the density, the proportion of tetragonal crystals and the high temperature durability of the sintered sheets used in the following Examples and Comparative Examples are as follows.

Density: The ratio of the density obtained by the Archimedes method to the theoretical density. If the density is less than 92%, the strength is insufficient and there is a possibility of gas permeation.
Those having 97% or more, particularly 99% or more, have high strength and no gas permeation defect is observed. ⊚: 97% or more of theoretical density, ◯: 92% or more and less than 97%, ×: less than 92%.

Proportion of tetragonal crystal: Estimated from peak intensity ratios of tetragonal (111) plane, cubic (111) plane and monoclinic (11-1) plane from X-ray diffraction pattern. ⊚: 95% or more of tetragonal crystals, ◯: 80 to 95% of tetragonal crystals,
X: Tetragonal crystal is less than 80%.

High temperature durability: 5 × 50 m from each test sheet
Cut out an m-square test piece and measure the 3-point bending strength at room temperature with J
Measured in accordance with IS R1601 and further in an electric furnace 95
Similarly, the strength after holding at 0 ° C. for 500 hours or more is measured at room temperature, and the high temperature durability is calculated by the following formula from the ratio of the initial strength and the strength after a predetermined time. High temperature durability = [(strength after holding at 950 ° C. for a predetermined time) / (initial strength)] × 100 (%) ⊚: 97% or more, ◯: 95 to 97%, x: less than 95%.

Example 1 A predetermined amount of scandium nitrate was mixed with an aqueous solution of zirconyl nitrate 0.1 mol / liter to prepare a mixed solution of scandium and zirconium nitrate. This mixed solution is dropped into aqueous ammonia while stirring, and the generated precipitate is taken out by decantation. 3. The same volume of butanol was added to this precipitate for redispersion, the solvent was distilled off under reduced pressure with an evaporator, and then the precipitate was baked at 950 ° C.
A 0 mol% scandia-stabilized zirconia powder (A ₀ ) was obtained. The specific surface area of this powder was measured with a fully automatic surface area measuring device "U2S" manufactured by Yuasa Ionics Co., Ltd.
It was ² / g.

100 parts by mass of the obtained 4.0 mol% scandia-stabilized zirconia powder, 14 parts by mass of a methacrylic ester binder (number average molecular weight: 30,000, glass transition temperature: -8 ° C.), and dibutyl as a plasticizer. 2 parts by mass of phthalate (DBP), toluene / 2- as a dispersion medium
50 parts by mass of propanol (mass ratio = 4/1) mixed solvent was put in a nylon pot mill charged with zirconia balls having a diameter of 10 mm, and kneaded at 50 rpm for 48 hours to obtain a slurry for producing a green sheet. It was

A part of this slurry was collected and
When diluted with a mixed solvent of 2-propanol (mass ratio = 4/1) and measured with a laser diffraction particle size distribution analyzer "SALD-1100" manufactured by Shimadzu Corporation, the particle size distribution of solid components in the slurry was measured, and the average value was obtained. The particle size (50% volume diameter) was 0.35 μm, and the 90% volume diameter was 1.1 μm.

The slurry was concentrated and defoamed to a viscosity of 2 Pa.
・ Adjust to s (23 ° C) and finally pass through a 200-mesh filter, then coat on a polyethylene terephthalate (PET) sheet by the doctor blade method, and apply 10
A green sheet having a thickness of about 0.2 mm was obtained by drying at 0 ° C.

One side of this green sheet is about 130 mm
Cut into squares, and the upper and lower sides of the square are 99.5% alumina porous plate with a swell height of 10 μm or less (air permeability: 0.003
m / s · kPa) for degreasing and firing. At this time, the rate of temperature increase at 1100 ° C. or higher was set to 1 deg / min or less, the maximum reached temperature was maintained at 1400 ° C. for 2 hours, and one side was a square of about 100 mm square, and the thickness was 4.0 mol of 0.15 mm. A% scandia stabilized zirconia sheet was obtained.

The surface of the obtained scandia-stabilized zirconia sheet was photographed with a scanning electron microscope to obtain 15,000.
Measure the size of all grains in the field of view of the double photograph with a caliper,
Based on these measurements, the average grain size, 90
The% value and coefficient of variation were determined. At this time, the grains located at the edges in the photographic field where all the particles did not appear were excluded from the measurement target.

A portion of the obtained sheet was sampled, the density was measured by the Archimedes method, the abundance ratio of tetragonal crystals was determined from the X-ray diffraction pattern, and the high temperature durability was determined by the above method. The results shown in are obtained.

Example 2 4.0 parts by weight of 4.0 mol% scandia-stabilized zirconia powder obtained in the same manner as in Example 1 was added to 100 parts by weight of alumina powder.
A slurry for producing a green sheet was prepared in the same manner as in Example 1 except that the mixed powder (A ₁ ) added with 25 parts by mass was used, and the formation, degreasing and firing of the green sheet were performed in the same manner. 3. A square having sides of about 100 mm and a thickness of 0.12 mm and containing 0.25% alumina.
A 0 mol% scandia-stabilized zirconia sheet was obtained.

Particle size distribution of solid components in the slurry for producing green sheets in this experiment, average value of grain size of the obtained scandia-stabilized zirconia sheet, 90
Tables 1 and 2 show the% value and coefficient of variation, the density of the sheet, the existence ratio of each crystal structure, the three-point bending strength at room temperature, and the high temperature durability.

Example 3 In Example 2, the firing temperature at the final stage was set to 125.
Except that the temperature was changed to 0 ° C., the same procedure as in Example 2 was repeated.
A scandia-stabilized zirconia sheet containing 0.25% alumina was obtained. Tables 1 and 2 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, density, crystal structure, strength and high temperature durability of the obtained zirconia sheet at this time.

Comparative Example 1 In Example 2 above, the firing temperature at the final stage was changed to 152
Except for changing the temperature to 0 ° C., in the same manner as in Example 2,
A scandia-stabilized zirconia sheet containing 0.25% alumina was obtained. Tables 1 and 2 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, density, crystal structure, strength and high temperature durability of the obtained zirconia sheet at this time.

Comparative Example 2 In the above Example 2, the firing temperature of the green sheet was set to 1
A 0.25% alumina-containing scandia-stabilized zirconia sheet was obtained in exactly the same manner as in Example 2 except that the temperature was changed to 100 ° C. Tables 1 and 2 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, density, crystal structure, strength and high temperature durability of the obtained zirconia sheet at this time.

Example 4 In the above Example 2, the concentrations of zirconyl nitrate and scandium nitrate during the production of the raw material powder were changed so that the specific surface area was 12
In the same manner as in Example 2 except that the raw material powder (C) of m ² / g was produced, the binder content was changed to 15 parts by mass, and the firing temperature of the green sheet was changed to 1250 ° C., A 6 mol% scandia-stabilized zirconia sheet containing 0.25% alumina was obtained. Tables 1 and 2 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, density, crystal structure, strength and high temperature durability of the obtained zirconia sheet at this time.

Comparative Example 3 In the above Example 2, the concentrations of zirconyl nitrate and scandium nitrate during production of the raw material powder were changed to produce a raw material powder (D) having a scandia content of 10 mol% and a specific surface area of 15 m ² / g. In addition, except that the blending amount of the binder was changed to 18 parts by mass, in exactly the same manner as in Example 2,
A scandia-stabilized zirconia sheet containing 0.25% alumina was obtained. Tables 1 and 2 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, density, crystal structure, strength and high temperature durability of the obtained zirconia sheet at this time.

Comparative Example 4 In the above-mentioned Example 2, as a raw material powder, a mixed powder of scandia and zirconia (scandia content: 4 mol%) was dry-mixed with a mill to obtain a mixed powder having a specific surface area of 5 m ² / g (E ₀ ). Was used in the same manner as in Example 2 except that the binder content was changed to 14 parts by mass.
A 4 mol% scandia-stabilized zirconia sheet containing 25% alumina was obtained. Tables 1 and 2 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, density, crystal structure, strength and high temperature durability of the obtained zirconia sheet at this time.

Comparative Example 5 In Example 2 above, the firing temperature at the final stage was set to 125.
A scandia-stabilized zirconia sheet containing 0.25% alumina was prepared in the same manner as in Example 2 except that the temperature was raised to 0 ° C. (however, the heating rate was 10 deg / min, and the holding time at the maximum temperature was 10 minutes). Obtained. Tables 1 and 2 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, density, crystal structure, strength and high temperature durability of the obtained zirconia sheet at this time.

[0071]

[Table 1]

[0072]

[Table 2]

As is clear from Tables 1 and 2, all the examples satisfying the specified requirements of the present invention have high density and excellent strength and high temperature durability.

On the other hand, in Comparative Example 1, since the final firing temperature was too high, the average grain size of the sintered sheet, the 90% value, and the coefficient of variation were all high, and the crystal structure was mainly tetragonal. However, the strength and the high temperature durability are inferior. In contrast, in Comparative Example 2, since the sintering temperature is too low, the sintering is poor and the compactness is poor and the strength is poor. The grain size is large and the proportion of tetragonal crystals is small, resulting in poor strength.

In Comparative Example 4, an appropriate amount of scandia was dry-mixed with zirconia. However, since the particle size of the solid component in the slurry state was not appropriate, the denseness was lacking and a satisfactory gas shielding property could not be expected.

Example 5 In Example 2, the firing temperature during the production of the raw material powder was set to 8
The raw material powder (A ₂ ) having a specific surface area of 18 m ² / g obtained by changing the temperature to 00 ° C. was used, and the grinding time during slurry preparation was 72
In the same manner as in Example 2, except that the final sheet firing temperature was changed to 1250 ° C. (however, the temperature rising rate was 10 deg / min and the holding time at the maximum temperature was 10 minutes). A scandia-stabilized zirconia sheet containing 25% alumina was obtained. Tables 3 and 4 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, the density, the crystal structure, the strength and the high temperature durability of the obtained zirconia sheet at this time.

Example 6 The procedure of Example 2 was repeated except that 4.0 mol% scandia-stabilized zirconia powder (A ₁ ) obtained in the same manner as in Example 2 was used, and the milling time during slurry preparation was changed to 72 hours. Example 2
A 4.0 mol% scandia-stabilized zirconia sheet was obtained in the same manner as above.

Particle size distribution of the solid component in the slurry for producing the green sheet in this experiment, the average value of the grain size of the obtained scandia-stabilized zirconia sheet, 90
Tables 3 and 4 show the% value and coefficient of variation, the density of the sheet and the proportion of tetragonal crystals present, as well as the three-point bending strength at room temperature and the high temperature durability.

Comparative Example 6 A specific surface area of 30 m ² / g produced in exactly the same manner as in Example 1 except that the precipitate produced during the production of the raw material powder was filtered off, dried in a dryer and then calcined at 800 ° C. Of 4
An experiment was conducted in the same manner as in Example 1, except that the mol% scandia-stabilized zirconia powder (B ₁ ) was used.
The obtained sheet had not only significant swelling but also insufficient sintering, and could not be put into practical use as a ceramic sheet.

Example 7 In Example 2, the firing temperature during the production of the raw material powder was set to 1
A scandia-stabilized zirconia sheet containing 0.25% alumina was prepared in exactly the same manner as in Example 2 except that the raw material powder (A ₃ ) having a specific surface area of 6 m ² / g obtained by changing to 050 ° C. was used. Obtained. Tables 3 and 4 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, the density, the crystal structure, the strength and the high temperature durability of the obtained zirconia sheet at this time.

Example 8 In Example 2, the grinding time at the time of slurry preparation was 2
Except for changing the time, exactly the same as in Example 2,
A scandia-stabilized zirconia sheet containing 0.25% alumina was obtained. Tables 3 and 4 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, the density, the crystal structure, the strength and the high temperature durability of the obtained zirconia sheet at this time.

Example 9 In Example 2, TiO ₂ was used instead of alumina powder.
A 0.4% TiO ₂ -containing scandia-stabilized zirconia sheet was obtained in exactly the same manner as in Example 2 except that 0.4% by weight of was added. Tables 3 and 4 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, the density, the crystal structure, the strength and the high temperature durability of the obtained zirconia sheet at this time.

Example 10 In Example 2, Nb ₂ O ₅ was used instead of the alumina powder.
A 0.4% Nb ₂ O ₅ -containing scandia-stabilized zirconia sheet was obtained in exactly the same manner as in Example 2 except that 0.4% by weight of was added. Tables 3 and 4 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, the density, the crystal structure, the strength and the high temperature durability of the obtained zirconia sheet at this time.

Example 11 In Example 2, Ta ₂ O ₅ was used instead of the alumina powder.
A 0.25% Ta ₂ O ₅ -containing scandia-stabilized zirconia sheet was obtained in exactly the same manner as in Example 2 except that 0.25% by mass was added. At this time, the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size of the obtained zirconia sheet, the density, the crystal structure, the strength,
The high temperature durability is shown in Tables 3 and 4.

Example 12 In Example 2, MnO ₂ was used in place of alumina powder.
A 0.25% MnO ₂ -containing scandia-stabilized zirconia sheet was obtained in exactly the same manner as in Example 2 except that 0.25% by mass was added. At this time, the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size of the obtained zirconia sheet, the density, the crystal structure, the strength,
The high temperature durability is shown in Tables 3 and 4.

Example 13 In Example 2, LaAl was used instead of alumina powder.
A scandia-stabilized zirconia sheet containing 0.25% LaAlO ₃ was obtained in exactly the same manner as in Example 2 except that 0.25% by mass of O ₃ was added. Tables 3 and 4 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, the density, the crystal structure, the strength and the high temperature durability of the obtained zirconia sheet at this time.

Example 14 In Example 2, MgAl was used instead of alumina powder.
_A scandia-stabilized zirconia sheet containing 0.25% MgAl ₂ O ₄ was obtained in exactly the same manner as in Example 2 except that 0.25% by mass of ₂ O ₄ was added. Tables 3 and 4 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, the density, the crystal structure, the strength and the high temperature durability of the obtained zirconia sheet at this time.

Example 15 In Example 2, the alumina powder was replaced with Al ₂ T.
Example 2 except that 0.25% by mass of iO ₅ was added.
A scandia-stabilized zirconia sheet containing 0.4% Al ₂ TiO ₅ was obtained in the same manner as above. Tables 3 and 4 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, the density, the crystal structure, the strength and the high temperature durability of the obtained zirconia sheet at this time.

Comparative Example 7 In the above-mentioned Comparative Example 6, the raw material powder (B having a specific surface area of 12 m ² / g obtained by filtering the precipitate produced during the production of the raw material powder, drying it with a dryer, and calcining at 900 ° C. _A 4 mol% scandia-stabilized zirconia sheet was obtained in the same manner as in Comparative Example 6 except that ₂ ) was used. Tables 3 and 4 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, the density, the crystal structure, the strength and the high temperature durability of the obtained zirconia sheet at this time.

Comparative Example 8 In the above-mentioned Example 2, the firing temperature during the production of the raw material powder was 1
A scandia-stabilized zirconia sheet containing 0.25% alumina was prepared in exactly the same manner as in Example 2 except that the raw material powder (A ₄ ) having a specific surface area of 3 m ² / g obtained by changing to 100 ° C. was used. Obtained. Tables 3 and 4 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, the density, the crystal structure, the strength and the high temperature durability of the obtained zirconia sheet at this time.

Comparative Example 9 In Example 2 above, the firing temperature during the production of the raw material powder was 1
The raw material powder (A ₃ ) having a specific surface area of 3 m ² / g obtained by changing the temperature to 100 ° C. was used, and the firing temperature of the green sheet was 15
In the same manner as in Example 2 except that the temperature was changed to 20 ° C,
A scandia-stabilized zirconia sheet containing 0.25% alumina was obtained. Tables 3 and 4 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, the density, the crystal structure, the strength and the high temperature durability of the obtained zirconia sheet at this time.

Comparative Example 10 In Comparative Example 4, TiO ₂ was used instead of the alumina powder.
A 0.4% TiO ₂ -containing scandia-stabilized zirconia sheet was obtained in exactly the same manner as in Example 2 except that 0.4% by weight of was added. Tables 3 and 4 show the particle size constitution of the solid component in the slurry for producing the green sheet, the grain size, the density, the crystal structure, the strength and the high temperature durability of the obtained zirconia sheet at this time.

[0093]

[Table 3]

[0094]

[Table 4]

[0095]

EFFECT OF THE INVENTION The present invention is constituted as described above, and when the scandia-stabilized zirconia sheet is produced, the slurry for producing the green sheet in which the average particle diameter of the solid component and the 90% by volume diameter are specified is used. By forming this into a sheet and then sintering it, and keeping the average value and coefficient of variation of the grain size of the resulting scandia-stabilized zirconia sheet within the appropriate range, it has excellent room temperature strength and high temperature durability, and gas shielding. Thus, it is possible to provide a dense scandia-stabilized zirconia sheet having excellent properties and ionic conductivity.

Therefore, the dense scandia-stabilized zirconia sheet utilizes, for example, the solid electrolyte membrane for fuel cells and the ferrule (connector) of the optical fiber by utilizing its excellent strength, high temperature durability, gas shielding property and ionic conductivity. ,
It can be effectively used as a zirconia base for various printers, media for ball mills, etc.

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Claims (5)

[Claims] 1. A method for producing a dense zirconia sheet stabilized with scandia, wherein the solid component has an average particle diameter of 0.15 to 0.5 μm and a 90 volume% diameter of 0.6.
The average grain size is 0.1 to 0.6 μm, and the coefficient of variation is 50% by using a green sheet-producing slurry having a particle size of up to 1.5 μm and sintering the green sheet-forming slurry. A process for producing a dense scandia-stabilized zirconia sheet, which is characterized in that a dense scandia-stabilized zirconia sheet as described below is obtained. 2. TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , MnO ₂
The process according to claim 1, wherein a scandia-stabilized zirconia sheet containing one or more oxides selected from the above is obtained. 3. LaAlO ₃ , MgAl ₂ O ₄ , Al ₂ Ti
The process according to claim 1 or 2, wherein a scandia-stabilized zirconia sheet containing one or more oxides selected from O ₅ is obtained. 4. The method according to claim 1, wherein a dense scandia-stabilized zirconia sheet having a thickness of 0.01 to 0.5 mm and an area of 25 cm ² or more is obtained. 5. The production method according to claim 1, wherein a raw material powder having a specific surface area of the whole raw material powder of 4 to ²⁰ m ² / g before preparing the slurry is used.