JP2830795B2 - Ceramic sheet for solid electrolyte membrane of fuel cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic sheet for a solid electrolyte membrane of a fuel cell, and more particularly to a ceramic sheet for a solid electrolyte membrane which is thin, has little undulation and warpage, and has excellent load bearing strength and bending strength. This ceramic sheet has excellent heat insulating properties and electric insulating properties, and can be effectively used as a solid electrolyte membrane for a fuel cell.

[0002] Among them, a ceramic sheet mainly composed of zirconia utilizes its excellent oxygen ion conductivity, mechanical strength, toughness, abrasion resistance, chemical resistance, corrosion resistance and the like.
It can be effectively used as a solid electrolyte membrane for fuel cells.

[0003]

2. Description of the Related Art Ceramics have excellent electrical and magnetic properties, as well as biocompatibility, in addition to mechanical properties such as heat resistance and wear resistance. Has been utilized. Among them, a ceramic sheet mainly composed of zirconia has excellent oxygen ion conductivity, heat resistance and corrosion resistance, and can be effectively used as a solid electrolyte membrane for a fuel cell. For use in these applications, it is preferable to use a dense ceramic sheet. For this reason, a so-called submicron fine powder which is easily sintered is usually used as a raw material powder. However, when the fine powder is used, it is difficult to decompose and remove the binder component, and the shrinkage accompanying sintering is large. Therefore, particularly in a thin sheet-shaped molded product, undulation or warpage is likely to occur. If these undulations or warpages occur, stress concentration occurs when a force is applied from the outside, and cracks are induced. This causes a serious problem when actually used as a solid electrolyte membrane.

[0004] Incidentally, as a method of manufacturing a sheet-like ceramic sheet, a slurry comprising a ceramic raw material powder such as zirconia, an organic binder and a dispersion medium is generally used by a doctor blade method, a calendar method, or an extrusion method. The sheet is formed into a sheet shape by drying, etc., and the dispersion medium is volatilized to obtain a green sheet. The green sheet is cut, punched, or the like, adjusted to an appropriate size, placed on a setter and baked, and the organic binder is decomposed and removed. This is a method of sintering the ceramic powder afterwards.

In general, when a green sheet is heat-treated to produce a ceramic sheet, it is extremely difficult to ensure uniform thermal atmosphere conditions (temperature distribution, type and concentration of atmosphere gas, flow of atmosphere gas, etc.) over the entire surface. Because
Warpage or undulation is likely to occur due to unevenness in each part of one sheet. For example, if there is a slight difference in the degreasing conditions and the like of each part of the green sheet, the binder is not uniformly removed and undulation occurs. Further, the green sheet shrinks during sintering during sintering, but if there is any slight difference in the thermal atmosphere in each part of the sheet, the shrinkage becomes uneven, causing undulation or cracking. In particular, a thin ceramic sheet having a thickness of 1 mm or less has a small own weight, so that the sheet itself is more likely to float and swell more easily than a conventional thick sheet.

Further, when each portion of the sheet moves from the end to the center due to shrinkage, if the setter has slight irregularities or friction occurs, the shrinkage is hindered, and undulation or cracking is likely to occur.

[0007] When sintering a sheet having a size of about 400 cm ² after sintering, a relatively thin setter with high density and high strength can be used. It is necessary to use a porous and thick setter so that the setter is heat-insulating and has an extremely large heat capacity. Cause uniformity. Furthermore, when firing green sheets in an electric furnace that heats from the side, ceiling, or hearth with a heater, the sheet is large relative to the furnace, so that even a single sheet may be near or far from the heater. As a result, thermal unevenness occurs in each part of the sheet. Alternatively, in the case of a large gas furnace, there is room in the size of the soaking zone in an empty furnace, but the large setter makes it impossible to secure a sufficient path for gas (flame). Easy to occur. These thermal non-uniformities and shrinkage inhibition have a size of 400c after sintering.
It was noticeable on sheets of m ² or more, causing undulation and warpage.

[0008] The ceramic sheet thus obtained, even if a single green sheet is placed on a one-stage setter and fired, generates a considerable amount of warpage or undulation.
If a plurality of green sheets are stacked and fired on a single-stage setter for the purpose of increasing productivity, warpage and undulation will be further increased. In particular, the tendency is remarkable in the firing of a green sheet produced using a submicron ceramic powder raw material. The warpage or undulation generated in the fired ceramic sheet causes local stress concentration when a load, a bending force, or the like is applied to the sheet, causing cracks or cracks. Such a warp or undulation can be corrected by a method such as re-firing with a load applied to the sheet.However, this correction process often causes cracks or cracks in the sheet, which is a major cause of yield reduction. It is not only preferable that firing is performed twice or more from the viewpoint of energy.

[0009] Therefore, as a technique for solving such difficulties, for example, a method disclosed in Japanese Patent Application Laid-Open No. 6-9268 has been proposed. In this method, firing is performed while a load is applied to the ceramic green sheet. If such a method is employed, warpage and undulation in the firing step are suppressed as much as possible, and the surface flatness is relatively good. A ceramic sheet can be obtained. However, the above feature is effectively exhibited when relatively small green sheets of less than 400 cm ² are placed one by one on a single-stage setter and fired.
When baking thin green sheets exceeding ² cm2, multiple sheets to be loaded are placed side by side on the green sheets, so traces are easily formed on the green sheets at the joints of the sheets, so that undulations and warpage are sufficient. It is difficult to control.

On the other hand, the ceramic sheet used for the above-mentioned applications is 400 cm ² for the above-mentioned reason.
Although it has been provided as a small-sized sheet having a thickness of less than about 500 cm ² , the demand for a thin large-sized ceramic sheet having a thickness of 500 cm ² or more, and further, about 600 cm ² and 1 mm or less has been increasing as its use has been diversified. However, it is very difficult to suppress the warpage and undulation generated at the time of sintering with such a thin large-sized ceramic sheet as described above, and the surface flatness is high and the demand for the load-bearing strength, bending characteristics and the like are satisfied. The fact is that no such thing has been obtained.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems.
For a thin large ceramic sheet with a thickness of 400 cm ² or more and 0.4 mm or less, for a solid electrolyte membrane of a fuel cell with less warpage and waviness, high surface flatness, and excellent load-bearing strength and flexural strength (hereinafter simply referred to as solid (Sometimes referred to as an electrolyte membrane).

[0012]

SUMMARY OF THE INVENTION A ceramic sheet for a solid electrolyte membrane according to the present invention which can solve the above problems has an area of 400 cm ² or more and a thickness of 0.4 mm.
Hereinafter, the maximum undulation height is 100 μm or less, and the amount of warpage is 0.
1% or less, and the frequency of occurrence of cracks and cracks when the following load test and deflection load test are sequentially performed is 10% or less based on the number of sheets. (Load load test) A ceramic sheet is sandwiched between dense alumina plates having a smooth surface, and a load of 0.1 kgf / cm ² is applied to the entire surface of the ceramic sheet. (Deflection load test) Opposite two sides of the ceramic sheet In this test, a force is applied in a direction parallel to the surface of the ceramic sheet and in a direction in which the ceramic sheet is pressed against each other, and the ceramic sheet is bent. The bending height is h [mm], and the distance between two opposing sides is d [m].
m], and when the thickness of the ceramic sheet is t [mm], h = 0.002 × d / t ² (where h ≦ 0.1 × d) The operation of bending is performed once / second. 6 alternately in front and back
Repeat several times.

[0013] The ceramic sheet according to the present invention comprises:
Preferred are those containing zirconia as a main component, and among these, Y, Ce, Ca, Mg, T
at least one selected from the group consisting of i, Si, and Al
Also preferred are those containing oxides of various metals, and particularly preferred are those containing cubic zirconia as a main component, and these ceramic sheets are effectively utilized as a solid electrolyte membrane of a fuel cell. Can be.

The powder used as a raw material of the ceramic sheet has an average particle diameter of 0.1 to 0.5 μm and 90% by volume or more of the powder has a particle diameter of 1 μm or less. By using this, a ceramic sheet for a solid electrolyte membrane that is dense and has higher surface accuracy can be obtained. The preferable density of the ceramic sheet is 90% or more of the theoretical density, and the shape of the sheet varies depending on the application. The most common for membranes are square or rectangular.

The ceramic sheet can be manufactured by a general method. However, in order to efficiently obtain the flatness as described above, when a ceramic green sheet is fired to manufacture the ceramic sheet, the ceramic sheet is theoretically manufactured. The green sheet has a bulk density of 30 to 85% with respect to the density, and has a shrinkage rate of 5% by heating up to the firing temperature of the green sheet.
% Or less so that the peripheral edge of the green sheet does not protrude, or the green sheet is sandwiched between the porous sheets so that the peripheral edge does not protrude and fired. It is desirable to do.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the ceramic sheet for a solid electrolyte membrane of the present invention has an area of 400 cm ² or more, a thickness of 0.4 mm or less, and a maximum undulation height of 100 μm.
Hereinafter, a ceramic sheet having a warpage of 0.1% or less, and a frequency of occurrence of cracks and cracks of 10% or less based on the number of sheets when the load test and the deflection load test are sequentially performed, A ceramic sheet for a solid electrolyte membrane having such properties and strength characteristics has a bulk density of 30 to 85% of the theoretical density when a ceramic green sheet is manufactured by firing a ceramic green sheet as described later. At the same time, the green sheet is sandwiched between porous sheets having a shrinkage rate of 5% or less due to heating up to the firing temperature higher than the green sheet so that the peripheral edge thereof does not protrude, and the green sheet is fired. A porous sheet similar to that described above can be obtained by placing the green sheet so that the peripheral edge of the green sheet does not protrude and firing.

That is, by adopting such a method, deformation of the sheet during firing is prevented as much as possible, and extremely excellent flatness is achieved with a maximum undulation height of 100 μm or less and a warpage of 0.1% or less. A ceramic sheet having excellent characteristics that has less cracks, cracks, and the like even in the load test and the flex load test described above. These characteristics are characteristics that are not found in conventionally known ceramic sheets for a solid electrolyte membrane of a fuel cell,
The ceramic sheet itself has the aforementioned shape characteristics (flatness).
It is clearly distinguishable from known ceramic sheets for solid electrolyte membranes used for fuel cells in terms of strength and strength characteristics (load strength and deflection strength).

The reason why the area is set to be 400 cm ² or more is that a ceramic sheet having a small size less than 400 cm ² is not suitable for the purpose of the present invention, which intends to increase the size of the ceramic sheet for a solid electrolyte membrane of a fuel cell. However, if it is not possible to exhibit the advantage over known ceramic sheets for solid electrolyte membranes, and if such a small-sized ceramic sheet for solid electrolyte membranes, the above-described unique method is adopted. This is because it is easy to obtain a material having good flatness and excellent performance in load-bearing strength and bending-proof strength. 0.4m thick
m or less because the thickness of the ceramic sheet for a solid electrolyte membrane thicker than this is relatively small in the degree of warpage or undulation that occurs during firing, and a sheet that satisfies the above flatness requirement can be easily obtained. is there.

The maximum swell height defined in the present invention is:
The height of the largest undulation generated in the ceramic sheet for a solid electrolyte membrane is referred to as the height of 100 μm or less. If the value exceeds 100 μm, the characteristic of the present invention due to the improvement in flatness (especially the resistance to This is because the improvement of the load strength cannot be effectively exhibited. In order to more effectively exhibit the features of the present invention, the particularly preferable maximum undulation height is 50 μm or less, and further preferably, the maximum height (R _max ) is 1 μm or less.

The warpage amount defined in the present invention means a percentage of a value obtained by dividing a warpage height by a sheet length, and the value of 0.1% or less is defined as a warpage exceeding this value. This is because, in the case of an amount of sheet, when an external force parallel to the sheet surface acts, a bending stress acts on the warped portion to cause a crack. The more preferable warpage is 0.06% or less for more effectively exhibiting the features of the present invention.

Further, the ceramic sheet for a solid electrolyte membrane of the present invention has a great feature in that the frequency of occurrence of cracks and cracks by the load test and the flex load test is 10% or less. When a large number of the ceramic sheets for a solid electrolyte membrane are stacked and used as a solid electrolyte membrane for a fuel cell, the load applied to the sheet or the external force applied in a bending direction causes cracks or cracks to be generated and the characteristics are impaired. This is a very important property for preventing. When the above-described flexural load test is performed, the ceramic sheet for a solid electrolyte membrane will crack if it has any cracks. Therefore, if a fine crack that cannot be visually observed in the load test is generated, it will crack in the flex load test. Therefore, in the performance evaluation test of the ceramic sheet for a solid electrolyte membrane according to the present invention, it is necessary to perform a bending load test after the load test.

Incidentally, a conventional ceramic sheet having an area of 400 cm ² or more and a thickness of 1 mm or less is:
Due to the reasons described above, it has some undulations and warpages.As a result, cracks and cracks occur when the load test and flex load test as described above are performed, and the practical value is significantly impaired or extreme. Loses practicality. However, the ceramic sheet for a solid electrolyte membrane of the present invention has a very small maximum undulation height and warpage amount as described above, and is less likely to crack or crack even when the load test or the deflection load test as described above is performed. These characteristics can also be clearly distinguished from conventional ceramic sheets for solid electrolyte membranes used for fuel cells.

The shape of the ceramic sheet for a solid electrolyte membrane according to the present invention is, of course, square, rectangular, and circular.
If necessary, it may be a polygon such as a triangle or a pentagon, an ellipse, or the like, and may have a hole or a notch in the above shape, but may be a solid electrolyte for a fuel cell. The most common one for practical use as a film or the like is a square or rectangular shape.

The constituent materials of the ceramic sheet for a solid electrolyte membrane according to the present invention include, for example, alumina, zirconia, ceria, titania, silica, mullite, cordierite, spinel, forsterite, anorthite, etc. Various materials such as celsian, enstatite, aluminum nitride, and silicon nitride can be selected, and particularly preferable are those containing zirconia as a main component (preferably at least 60% by weight, more preferably at least 80% by weight). , Or, as another component,
It contains an oxide of at least one metal selected from the group consisting of Y, Ce, Ca, Mg, Ti, Si and Al (preferably about 40% by weight or less, more preferably 20% by weight or less). . Most preferred is one containing cubic zirconia as a main component.

The preferable density of the ceramic sheet for a solid electrolyte membrane made of these materials is 90% or more (preferably 95% or more) with respect to the theoretical density. A ceramic sheet mainly composed of yttria fully stabilized zirconia (cubic zirconia) having a size of 20 cm square and 0.2 mm thick that satisfies the degree of warpage and 0.1 kgf / c in load bearing strength.
m ² or more, and withstands the above-described flexural load test, and shows a high value of 35 kgf / mm ² or more in average three-point bending strength, and is a very excellent thermal material for a solid electrolyte membrane of a fuel cell. Those exhibiting mechanical, physical, electrical and chemical properties are obtained.

The ceramic sheet for a solid electrolyte membrane of the present invention is characterized by having the above-mentioned shape characteristics and strength characteristics, and the production method is not particularly limited. If adopted, a ceramic sheet for a solid electrolyte membrane of a fuel cell having the above characteristics can be easily obtained.

That is, when a ceramic green sheet obtained by kneading the above-described ceramic material with an appropriate binder and forming a sheet is fired to produce a ceramic sheet, the temperature of firing the green sheet up to the firing temperature of the green sheet is reduced. The green sheet is sandwiched between porous sheets having a shrinkage ratio by heating of 5% or less and having a bulk density of 30 to 85% of the theoretical density so that the peripheral edge thereof does not protrude and fired. Alternatively, a porous sheet similar to the above is placed and fired so that the peripheral edge of the green sheet does not protrude.

That is, a slurry comprising a mixture of the above-mentioned ceramic raw material powder, an organic or inorganic binder and a solvent is applied to a smooth substrate at a predetermined thickness by a doctor blade method, a calendar method, an extrusion method, or the like. The green sheet is obtained by drying and evaporating and removing the solvent, and the green sheet is fired under the above conditions. The raw material of the ceramic raw material powder used in the production of the green sheet is as described above, but in the production of the green sheet, the average particle diameter is 0.1 to 0.5 μm, and the particle diameter is uniform. Specifically, it is preferable to use a powder in which 90% by volume or more of the powder has a particle size of 1 μm or less. More preferably, the average particle size is 0.2 to
0.3 μm, particles of 90% by volume or more are 0.7 μm
It is as follows. More preferably, the powder has a uniform particle diameter such that 90% by volume or more of the particles are 0.07 μm or more. Here, the particle size distribution was measured using a laser diffraction type particle size distribution analyzer SALD-1100 manufactured by Shimadzu Corporation.
This is a value measured using a 0.2% by weight aqueous solution of sodium metaphosphate as a dispersion medium.

If the average particle size of the ceramic raw material powder is too small, the sintering property of the powder itself is good and a dense ceramic sheet for a solid electrolyte membrane can be easily obtained. This tends to make it difficult for the decomposition and release of the binder to occur uniformly, resulting in an adverse effect on the homogeneity of the entire ceramic sheet for solid electrolyte membranes. Conversely, if the average particle size is too large, the decomposition and release of the binder component during firing will occur. The ceramics for solid electrolyte membranes have a density of "90% or more with respect to the theoretical density" intended in the present invention, although the sintering proceeds uniformly, but the sintering is insufficient and the density cannot be sufficiently increased. This is because it becomes difficult to obtain a sheet.
In addition, when the raw material powder has a wide particle size distribution, and particularly when particles having a large particle diameter are present, the decomposition and release of the binder component become non-uniform, and further, uneven shrinkage occurs during the sintering process, and undulation is likely to occur. These effects are remarkably exhibited in a ceramic sheet for a solid electrolyte membrane containing zirconia as a main component.

The type of the binder used in the present invention is not particularly limited, and a conventionally known organic or inorganic binder can be appropriately selected and used. Examples of the organic binder 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, and celluloses such as ethyl cellulose.

Of these, carbon dioxide such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, isobutyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, and the like, are preferred in view of the moldability and strength of the green sheet and the thermal decomposition property during firing. Alkyl acrylates having an alkyl group of tens or less, and 20 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, and cyclohexyl methacrylate. Alkyl methacrylates having an alkyl group, hydroxyethyl acrylate, hydroxy Hydroxyalkyl acrylates or hydroxyalkyl methacrylates having a hydroxyalkyl group such as propyl acrylate, hydroxyethyl methacrylate and 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 20 obtained by polymerizing or copolymerizing at least one kind of a carboxyl group-containing monomer such as an acid, maleic acid, maleic acid half ester such as monoisopropyl maleate;
0000, more preferably 50,000 to 100,0
A (meth) acrylate copolymer of 00 is recommended as a preferred one. These organic binders can be used alone or in combination of two or more as needed. Particularly preferred is a polymer of a monomer containing 60% by weight or more of isobutyl methacrylate and / or 2-ethylhexyl methacrylate.

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

The use ratio of the ceramic raw material powder and the binder is preferably in the range of 5 to 30 parts by weight, more preferably 10 to 20 parts by weight, with respect to 100 parts by weight of the former. If the strength and flexibility of the green sheet become insufficient, on the other hand, if it is too large, not only is it difficult to adjust the viscosity of the slurry, but also the decomposition and release of the binder component during firing is large and intense, and a uniform sheet is obtained. It is difficult to obtain.

Examples of the solvent used for producing the green sheet include water, alcohols such as methanol, ethanol, 2-propanol, 1-butanol and 1-hexanol, ketones such as acetone and 2-butanone, pentane, and the like. Aliphatic hydrocarbons such as hexane and heptane, aromatic hydrocarbons such as benzene, toluene, xylene and ethylbenzene, and acetates such as methyl acetate, ethyl acetate and butyl acetate are appropriately selected and used. These solvents can be used alone or in combination of two or more. The amount of these solvents to be used may be appropriately adjusted in consideration of the viscosity of the slurry at the time of forming the green sheet.
It is preferable to adjust so as to be in a range of 0 poise, more preferably 10 to 50 poise.

In preparing the above slurry, in order to promote peptization and dispersion of the ceramic raw material powder, a polymer electrolyte such as polyacrylic acid and ammonium polyacrylate, an organic acid such as citric acid and tartaric acid, isobutylene or styrene are used. A copolymer with maleic anhydride and its ammonium salt or amine salt, a dispersant comprising a copolymer of butadiene and maleic anhydride and its ammonium salt, dibutyl phthalate for imparting flexibility to the green sheet, Plasticizers such as phthalic acid esters such as dioctyl phthalate, glycols such as propylene glycol, and glycol ethers, as well as surfactants and defoamers, can be added as necessary.

The slurry comprising the above raw materials is formed into a sheet by the above-described method, dried to obtain a ceramic green sheet, and then heated and fired to obtain the ceramic sheet for a solid electrolyte membrane of the present invention. To manufacture. In the firing step, in the present invention, as a means for obtaining a ceramic sheet for a solid electrolyte membrane having high flatness without causing warpage or undulation, the green sheet has an area larger than the green sheet, and the firing temperature of the green sheet is reduced. The green sheet is sandwiched between porous sheets having a shrinkage ratio due to heating up to 5% or less and a bulk density of 30 to 85% with respect to the theoretical density so that the periphery does not protrude. It is preferable to perform firing after firing, or to place the porous sheet so that the peripheral edge of the green sheet does not protrude.

The porous sheet used here is the most important point in obtaining the ceramic sheet for a solid electrolyte membrane having high flatness according to the present invention. That is, as described above, when a ceramic sheet for a solid electrolyte membrane having a small size of less than about 400 cm ² is manufactured, the flatness of the ceramic sheet is relatively low by firing with a flat sheet-like weight applied. Although a high ceramic sheet for a solid electrolyte membrane may be rarely obtained, when a thin ceramic sheet for a solid electrolyte membrane having an area of 400 cm ² or more and a thickness of 1 mm or less is formed, a binder accompanying the firing of the ceramic green sheet is obtained. Decomposition and release and volume shrinkage become uneven, especially near the center of the sheet due to insufficient sintering due to insufficient release of binder decomposition gas, resulting in insufficient density or warpage, and volume shrinkage near the periphery. It is easy to generate waviness due to uniformity, and has a flatness and strength characteristics intended for the present invention. Bet it is difficult to obtain. In particular, in the case of a thin sheet having a small weight of 0.4 mm or less, uneven portions are easily lifted, so that undulation on the peripheral side is likely to occur.

However, as described above, the green sheet has an area equal to or larger than the green sheet, and has a shrinkage rate of 5% or less due to heating at least up to the firing temperature of the green sheet.
Moreover, a porous sheet having a bulk density of 30 to 85% of the theoretical density is used for supporting and correcting during firing, and the green sheet is sandwiched between the porous sheets so that the peripheral edge thereof does not protrude. If firing is performed after firing or after placing the porous sheet so that the peripheral edge of the green sheet does not protrude, insufficient sintering or undulation due to poor release of binder decomposition gas as described above, and even warpage, etc. Thus, a thin ceramic sheet for a solid electrolyte membrane which is remarkably suppressed and has extremely excellent flatness and strength characteristics can be obtained.

Incidentally, when the size of the porous sheet is smaller than that of the green sheet to be sintered and the periphery of the green sheet protrudes from the porous sheet during sintering, deformation of the green sheet occurs at the protruding portion. Therefore, a ceramic sheet for a solid electrolyte membrane having a high degree of flatness cannot be obtained, and when a plurality of small porous sheets are used side by side, a trace may remain on the ceramic sheet at the joint. In addition, the contraction rate of the porous sheet due to heating up to the green sheet firing temperature is 5%.
When it exceeds, not only the porous sheet cannot be used stably a plurality of times, but also the flatness correcting effect cannot be effectively exhibited due to the shrinkage of the porous sheet generated at the time of firing the green sheet. A high ceramic sheet for a solid electrolyte membrane cannot be obtained.

In firing the green sheet, it is extremely difficult to ensure a uniform thermal atmosphere condition over the entire surface. Therefore, the above-described unevenness is likely to occur and warpage and undulation are likely to occur. In the method described above, by covering the entire surface of the green sheet with the porous sheet as described above, it is possible to greatly alleviate these non-uniformities in the thermal atmosphere, and to suppress warping and undulation due to the weight effect. Therefore, firing can be performed in various furnaces such as an electric furnace, a gas furnace, a batch furnace, and a continuous furnace. Also, depending on the atmosphere of the furnace, particles such as Fe, Si, Al, and Mo oxides derived from a heat insulating material, a heater, or another object to be fired may fly and adhere to the sheet surface. In this case, since the sheet surface is protected by the porous sheet, these adhesions can be prevented.

The reason why the bulk density of the porous sheet used in the above method is specified is that the surface is made denser so that the effect of correcting the surface during firing of the green sheet is effectively exerted and that the binder is formed by the thermal decomposition of the binder during firing. This is for promoting the degreasing by promptly releasing the gas components to the outside. If the bulk density is less than 30% of the theoretical density, the release of the decomposition gas proceeds efficiently without any problem, but the strength is insufficient. In addition to the deterioration of handling properties, it becomes difficult to use multiple times, and the smoothness of the surface deteriorates, the correction effect becomes insufficient, and it becomes difficult to obtain a ceramic sheet for a solid electrolyte membrane with satisfactory surface accuracy. .
On the other hand, if a porous sheet having a bulk density of more than 85% is used, the degreasing effect and the release of decomposed gas become insufficient due to a decrease in air permeability, which causes cracks, warpage, wrinkles, and the like. Here, a simple measurement of the bulk density is obtained by dividing the weight of the porous sheet by the volume calculated from the product of the area and the thickness.

However, as described above, the green sheet has an area larger than that of the green sheet (preferably 1.0 to 1.5 times, more preferably 1.0 to 1.2 times) and at least the firing temperature of the green sheet. Is 5% or less (more preferably 0.1% or less) due to heating, and 30 to 85% (more preferably 45%) with respect to the theoretical density.
The porous sheet having a bulk density of about 65%) is used for correcting the support during firing, and the green sheet is sandwiched between the porous sheets so as not to protrude, and then fired. If the sheet is placed so that the peripheral edge of the green sheet does not protrude and then fired, the excellent surface correcting effect of the porous sheet is effectively exhibited, and the degreasing effect and the release of the decomposition gas are smoothly performed. The obtained thin ceramic sheet is very homogeneous and has a high flatness, the maximum waviness height is 100 μm or less, the amount of warpage is 0.1% or less, as defined in the present invention. It is of high quality that satisfies the characteristic that the frequency of occurrence of cracks and cracks in the test is 10% or less.

In particular, the undulation amount will be described in detail. The undulation tends to increase as the area of the ceramic sheet for a solid electrolyte membrane increases and the thickness decreases. However, when the above method is employed, [the undulation amount (μm) × thickness] (Mm) / maximum length (mm)] is 0.45 or less, preferably 0.1
The thickness can be set to 0.06 or less, more preferably 0.03 or less, and it is possible to obtain a thin ceramic sheet for a solid electrolyte membrane having very excellent strength characteristics. Here, the maximum length is a length corresponding to a diagonal line for a rectangle or a square, or a diameter for a disk.

Among the above methods, a ceramic sheet for a solid electrolyte membrane that satisfies the above-mentioned flatness and strength characteristics is most easily obtained by a method in which a green sheet is sandwiched between porous sheets and fired. As described above, when a sheet that does not satisfy the above requirements is used instead of the porous sheet, even if a single green sheet is placed on a single-stage setter and fired, considerable warpage or undulation occurs. If a plurality of green sheets are stacked and fired on a single-stage setter for the purpose of increasing productivity, even greater warpage or undulation will occur. However, such a problem does not occur in the above method, so that a large number of ceramic sheets for a solid electrolyte membrane can be produced at a time with a good yield, and the firing efficiency is significantly increased, which is preferable.

The material and manufacturing method of the porous sheet having the bulk density as described above are not particularly limited, and include the same inorganic powder, organic or inorganic binder and solvent as those exemplified as the raw material for producing the ceramic green sheet. A green sheet can be obtained by using a slurry and firing the green sheet by adjusting the firing conditions so that the green sheet has the above-mentioned preferable bulk density range. At this time, the average particle diameter of the inorganic powder is 2 to 100 μm, more preferably 30 to 8 μm.
If a powder having a thickness of 0 μm is used, a porous sheet having the preferable bulk density range can be easily obtained. The bulk density of the porous sheet can be controlled by sintering conditions, and can also be adjusted by changing the average particle size of the inorganic powder to be used and the type of binder, and further by changing the amount of the sintering aid added. It is. If a powder having an average particle size smaller than this range is used, it is difficult to control the bulk density, and if a large powder is used, the smoothness of the surface of the porous sheet will be lost, and the ceramic sheet will have irregularities.

In any case, the firing conditions during the production of the porous sheet may be adjusted to the firing temperature of the green sheet, taking into account the conditions for firing the ceramic green sheet using the porous sheet. It is desired to set the raw materials and firing conditions so that the shrinkage ratio due to heating is 5% or less. Therefore, it is desirable to set the firing temperature for obtaining the porous sheet to be equal to or higher than the firing temperature of the ceramic green sheet. For example, as a constituent material of a porous sheet used when manufacturing a ceramic sheet for a zirconia-based solid electrolyte membrane, zirconia or a ceramic powder raw material having a higher sintering temperature than zirconia, for example, alumina, titania, ceria, etc. Good to choose.

Incidentally, the porous sheet used here promotes degreasing and release of decomposed gas and exerts a surface-correcting action as described above.
2 mm, more preferably 0.1 to 1 mm, and a preferred weight (weight per unit area, the same applies hereinafter) of 0.01 to 1 g
/ Cm ² , the more preferable weight depends on the use form, and details will be described later. If the porous sheet is too thin, the handleability will be reduced due to insufficient strength, and the surface correction effect will be difficult to be effectively exhibited.If the porous sheet is too light, the function as a weight will not be effectively exhibited, and warpage and The swell prevention effect becomes insufficient. Conversely, if the sheet is too thick and heavy, or if it is too heavy, the friction between the green sheet and the porous sheet increases during firing of the green sheet, and the sheet surface is easily damaged, and the shrinkage of the green sheet is reduced. It becomes difficult to progress uniformly, and there is a risk of causing distortion or cracking.

In firing the ceramic green sheet using the porous sheet as described above, for example, as shown in FIG. 1, a ceramic green sheet 2 is superimposed on a setter 1 which also serves as shaping on the lower surface side. A method in which a porous sheet 3a also serving as a weight is placed on the upper surface and firing is performed, or as shown in FIG. 2, a porous sheet 3, a ceramic green sheet 2, and a porous material serving as a weight are placed on a heat insulating setter 1. It is of course possible to fire the ceramic green sheets one by one as in the method of firing by stacking the sheets 3a. However, in order to increase the productivity, for example, as shown in FIG. Each of the green sheets 2, 2,... Is sandwiched between the porous sheets 3 and overlapped, and a thick porous sheet 3 also serving as a weight at the top.
This is a method in which a is placed and firing is performed. If such a method is employed, a plurality of ceramic sheets for a solid electrolyte membrane can be obtained by a single firing, which is preferable. The uppermost porous sheet 3a of the firing may have the same shape as the porous sheet 3, but is preferably heavier than the porous sheet 3 in order to obtain a weighting effect. More preferably, the weight of the porous sheet 3 is 0.01 to 0.25 g / cm.
^{2. The} porous sheet 3a has a thickness of 0.2 to 1 g / cm ² .

As described above, the porous sheet used when adopting the above method has a bulk density of 30 to 50 with respect to the theoretical density.
85% and under the green sheet firing conditions, sintering hardly progresses, and excellent air permeability is secured.
Even when sintering is performed in a state where a plurality of sheets are stacked as described above, the release of the binder decomposition gas generated during firing of the green sheet proceeds smoothly, and a uniform ceramic sheet for a solid electrolyte membrane can be easily obtained. You can.

[0050]

EXAMPLES Hereinafter, the structure and operation and effect of the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the scope of the present invention is not limited thereto. It is also possible to carry out the present invention with appropriate modifications, and all of them are included in the technical scope of the present invention.

Example 1 [Preparation of zirconia green sheet] An aqueous solution of zirconium oxychloride containing 14.8 mol% of yttrium chloride was dropped into aqueous ammonia, and the precipitate obtained was washed, dried and calcined at 1000 ° C. Thus, zirconia powder was obtained. The average particle size of this powder was 1.5 μm, and 90% by volume of the particles were 3 μm or less.

Pure water is added to this powder to make up to 20% by weight.
After crushing for 2 hours using a bead mill, and drying at 500 ° C., the average particle diameter is 0.22 μm, 0.7 μm
A zirconia powder having 92% by volume of the following particles and 90% by volume of particles of 0.1 μm or more was obtained. This powder 10
Starting from 0 parts by weight, 15 parts by weight of an acrylic binder containing 60% by weight of isobutyl methacrylate unit and 20% by weight of 2-ethylhexyl methacrylate unit, 40 parts by weight of ethyl acetate as a solvent, and 2 parts by weight of dibutyl phthalate as a plasticizer. In addition, after mixing with a ball mill, the viscosity was adjusted, and 0.2
A 5 mm thick zirconia green sheet was obtained.

[Preparation of Porous Sheet] Average particle size 55 μm
m low soda alumina powder was formed into a 0.2 mm thick green sheet for a porous sheet by a doctor blade method using an acrylic binder. This green sheet was cut, degreased at 500 ° C., and fired at 1500 ° C. to obtain a porous sheet. The bulk density of this porous sheet was 50% of the theoretical density, and the weight was 0.03 g / cm ² .

[Production of porous sheet for weight] A green sheet for a porous sheet having a thickness of 0.6 mm was obtained in the same manner as the above-mentioned porous sheet, and the two green sheets were laminated and fired. The bulk density of the weighing porous sheet was 64% of the theoretical density, and the weight was 0.24 g / cm ² .

[Preparation of Zirconia Sheet for Solid Electrolyte Membrane of Fuel Cell] A porous sheet of about 42 cm square is placed on the center of a 60 cm square setter, and a zirconia green sheet and a porous sheet cut to about 40 cm are placed thereon. A total of six sheets were alternately placed one by one. Further, a porous sheet for weight was placed thereon. After degreasing at 500 ° C, baking at 1400 ° C,
A 30 cm square, 0.2 mm thick zirconia sheet for a solid electrolyte membrane was obtained. This sheet is flat and has a maximum height (R
_max ) was 0.8 μm, and no cracks were observed even when a load of 140 kg was applied to the entire surface. Also,
The three-point bending strength of a 5 × 50 mm sample cut by a diamond cutter was 42 kg / mm ² on average. The dimensions of the porous sheet were measured with a ruler before and after using the solid electrolyte membrane for zirconia sheet firing,
No contraction was observed.

Example 2 In Example 1, when a zirconia sheet for a solid electrolyte membrane was prepared, a setter of 32 cm square was used to alternately stack eight 28 cm square porous sheets and about 26 cm square zirconia green sheets. Exactly the same as above except that a porous sheet for weight was placed on top of it and fired.
A zirconia sheet for a solid electrolyte membrane having a square shape and a thickness of 0.2 mm was obtained. Table 1 shows the maximum warpage and maximum undulation height among the zirconia sheets for a solid electrolyte membrane of the obtained fuel cell.

[0057]

[0058]

[0059]

[0060]

Comparative Example 1 One zirconia green sheet produced in the same manner as in Example 1 was placed at the center of the setter. After degreasing at 500 ° C, baking at 1400 ° C in a gas furnace, 20cm
A zirconia sheet having a square and 0.2 mm thickness was obtained. This sheet had a slightly large swell. Also, several fine particles of silica / alumina adhered to the surface. In Example 1, no such adhesion was observed.

Comparative Example 2 An alumina green sheet having a thickness of 0.08 mm was formed by a doctor blade method using alumina powder and an acrylic binder. The alumina green sheet was placed on the center of a 32 cm square setter, and the zirconia green sheet of Example 1 and the alumina green sheet cut into a 28 cm square were alternately placed one by one in a total of seven sheets.
After degreasing at 500 ° C., the sheet was baked at 1400 ° C., resulting in a sheet with extremely large undulation. Note that warpage could not be measured due to large undulation on the entire surface. A heat treatment was performed again at 1400 ° C. while applying a load to correct swelling, but the material broke. The maximum undulation height, the amount of warpage, and the frequency of cracks and cracks in the load test and the flex load test of the sheets obtained in the above Examples and Comparative Examples were as shown in Table 1.

[0063]

[Table 1]

[0064]

The present invention is configured as described above.
A fuel cell that is a large plate having an area of 00 cm ² or more, has extremely small maximum waviness and warpage, and has excellent load strength and flexural strength. Can provide a ceramic sheet for a solid electrolyte membrane.

[Brief description of the drawings]

FIG. 1 is an explanatory view illustrating a method for producing a ceramic sheet for a solid electrolyte membrane of a fuel cell according to the present invention.

FIG. 2 is an explanatory view illustrating another method for producing a ceramic sheet for a solid electrolyte membrane of a fuel cell according to the present invention.

FIG. 3 is an explanatory view illustrating still another method for producing a ceramic sheet for a solid electrolyte membrane of a fuel cell according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat insulating setter 2 Ceramic green sheet 3,3a Porous sheet

──────────────────────────────────────────────────続 き Continuing on the front page (51) Int.Cl. ⁶ Identification code FI C04B 35/64 J (72) Inventor Tetsuya Yasaka 992, Nishioki, Okihama-shi, Aboshi-ku, Himeji-shi, Hyogo Prefecture Nippon Shokubai Co., Ltd. (56) Reference Document JP-A-6-132664 (JP, A) JP-A-5-4868 (JP, A) JP-A-4-325465 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C04B 35/00-35/22 C04B 35/48-35/493 C04B 35/622-35/65

Claims (8)

(57) [Claims] Claims: 1. A solid electrolyte membrane for use in a fuel cell.
Ceramic sheet with an area of 400 cm ²
Not less than 0.4 mm in thickness and maximum undulation height of 1
A fuel cell having a warpage of 0.1% or less, and a crack / crack occurrence frequency of 10% or less when the following load test and deflection load test are sequentially performed. Ceramic sheet for solid electrolyte membrane . (Loading test) A ceramic sheet is sandwiched between dense alumina plates having a smooth surface, and the entire surface of the ceramic sheet is 0.1 kgf / c.
applying a load of m ^2. (Deflection load test) This is a test in which a force is applied to two opposing sides of the ceramic sheet in a direction parallel to the surface of the ceramic sheet and in a direction in which they are pressed against each other, and the ceramic sheet is bent. The distance between two opposing sides is d [m
m], and when the thickness of the ceramic sheet is t [mm], h = 0.002 × d / t ² (where h ≦ 0.1 × d) The operation of bending is performed once / second. 6 alternately in front and back
Repeat several times. 2. The ceramic sheet for a solid electrolyte membrane according to claim 1, wherein the main component is zirconia. 3. As another component, Y, Ce, Ca, M
3. The ceramic sheet for a solid electrolyte membrane according to claim 2, wherein the ceramic sheet contains an oxide of at least one metal selected from the group consisting of g, Ti, Si, and Al. 4. The ceramic sheet for a solid electrolyte membrane according to claim 2, wherein the main component is cubic zirconia. 5. The raw material powder has an average particle size of 0.1 to 0.5.
5. The ceramic sheet for a solid electrolyte membrane according to claim 1, wherein 90% by volume or more of the powder has a particle size of 1 μm or less. 6. The method according to claim 1, wherein the shape is square or rectangular.
6. The ceramic sheet for a solid electrolyte membrane according to any one of items 5 to 5. 7. The ceramic mix sheet for a solid electrolyte membrane according to claim 1, wherein the density is 90% or more of the theoretical density. 8. A ceramic sheet for a solid electrolyte membrane obtained by firing a ceramic green sheet, wherein the firing has a bulk density of 30 to 85% with respect to a theoretical density and a green sheet of the green sheet. A porous sheet having a shrinkage rate of 5% or less due to heating up to the firing temperature is placed so that the peripheral edge of the green sheet does not protrude, or the peripheral edge of the green sheet is sandwiched between the porous sheets. 2. It is manufactured by a method of firing by sandwiching so as not to protrude.
8. The ceramic sheet for a solid electrolyte membrane according to any one of items 7 to 7.