JP2018129168A - Method for producing electrolyte sheet for solid oxide fuel cell - Google Patents

Abstract

An object of the present invention is to provide a method capable of efficiently producing an electrolyte sheet for a solid oxide fuel cell in which burrs at the periphery are further suppressed. A method for producing an electrolyte sheet for a solid oxide fuel cell according to the present invention includes a step of laminating a plurality of zirconia green sheets to form a first laminate, and performing primary firing to obtain a primary fired sheet; And a step of laminating a plurality of primary fired sheets obtained in the above step I to form a second laminate, and a secondary firing, wherein the second laminate directly laminates the plurality of primary fired sheets. A primary fired sheet group, a dense ceramic sheet placed on the uppermost primary fired sheet group so as to cover the entire surface of the uppermost primary fired sheet, and a weight on the dense ceramic sheet. The weight is arranged such that it does not exist vertically on at least a part of the peripheral area which is an area of 3 mm from the peripheral edge of the primary fired sheet toward the inside. [Selection figure] None

Description

  The present invention relates to a method capable of efficiently producing an electrolyte sheet for a solid oxide fuel cell in which burrs at the peripheral edge are suppressed.

  Fuel cells are attracting attention as a clean energy source. Improvements and practical application studies are being rapidly promoted mainly for household power generation, commercial power generation, and automobile power generation. Among such fuel cells, a solid oxide fuel cell (hereinafter sometimes abbreviated as “SOFC”) has high power generation efficiency and excellent long-term stability, and is expected as a power source for home use and business use. ing.

  In SOFC, a ceramic sheet is generally used as a solid electrolyte membrane. Ceramics are superior in electrical properties and magnetic properties in addition to mechanical properties such as heat resistance. Among them, a ceramic sheet mainly composed of zirconia is used as a solid electrolyte membrane of SOFC because it has excellent oxygen ion conductivity, heat resistance, corrosion resistance, toughness, and the like.

  In an SOFC, as an example, a plurality of SOFC single cells having a fuel electrode layer on one side and an air electrode layer on the other side are stacked in series to form a stack, so that a large load is applied to each layer. . Further, the electrode is exposed to temperature changes of high temperature during power generation and normal temperature during shutdown, and the volume of the electrode containing base metal changes during oxidation and during reduction. Therefore, in order to maintain a stable power generation performance over a long period of time, the SOFC is required to have no defects in each layer, be homogeneous, and have high strength. Therefore, various techniques for forming a high-quality solid electrolyte layer have been studied.

  For example, Patent Document 1 discloses a method of directly stacking a plurality of sheets on each other in the second stage firing in firing the zirconia green sheet in two stages in order to reduce the undulation of the electrolyte sheet for SOFC. . Further, in Patent Document 2, in order to reduce burr and undulation of the electrolyte sheet for SOFC as well, when firing in one stage, a load is applied to all the peripheral parts of the green sheet and at least a part of the parts other than the peripheral parts is applied. A method is disclosed in which there is no weight on the vertical.

JP 2012-94502 A JP2015-69694 A

  As described above, conventionally, various techniques for reducing defects such as burrs and waviness in an electrolyte sheet for a solid oxide fuel cell have been developed. However, in recent years, fuel cells have come to practical use, and demands on the surface properties of the electrolyte sheet have become increasingly strict. For example, the electrolyte sheet is required to have a high degree of flatness. Regarding the burr at the peripheral edge, the allowable range is about 50 μm at the maximum, but it tends to be required up to 30 μm, for example. ing.

  Then, an object of this invention is to provide the method which can manufacture efficiently the electrolyte sheet for solid oxide fuel cells in which the burr | flash in the peripheral part was suppressed further.

The inventors of the present invention have made extensive studies to solve the above problems. As a result, the zirconia green sheet is fired in two stages, and even if burrs are generated in the first stage firing, the burrs are corrected in the second stage firing. It was found that if the weight does not exist vertically above the peripheral edge region of the sheet, the flash of the electrolyte sheet can be surprisingly suppressed, and the present invention has been completed.
Hereinafter, the present invention will be described.

[1] A method for producing an electrolyte sheet for a solid oxide fuel cell,
Step I: A step of laminating a plurality of zirconia green sheets to form a first laminate, and primary firing to obtain a primary firing sheet; and
Step II: includes a step of laminating a plurality of primary fired sheets obtained in Step I above to form a second laminated body, followed by secondary firing.
The second laminated body is placed so as to cover the entire surface of the uppermost primary fired sheet on the uppermost primary fired sheet group, a primary fired sheet group obtained by directly laminating the plurality of primary fired sheets. A dense ceramic sheet, and a weight on the dense ceramic sheet,
The method is characterized in that the weight is arranged so as not to be present vertically on at least a part of a peripheral area which is an area of 3 mm from the peripheral edge of the primary fired sheet toward the inside.

  [2] The method according to [1] above, wherein a ratio of the area of the planar portion of the weight existing vertically on the peripheral area to the area of the peripheral area is 0% or more and 90% or less.

  [3] The method according to [1] or [2], wherein in the second laminated body, the plurality of primary fired sheet groups are laminated via a dense ceramic sheet.

[4] In the second laminate, the load applied to the top of the primary firing sheet 5.0 g / cm ² or more, in any of 80.0 g / cm ² or less is the [1] to [3] The method described.

  [5] The above [1] to [1], wherein the zirconia green sheet contains zirconia stabilized with one or more rare earth element oxides selected from the group consisting of scandia, yttria, ceria, gadolinia and ytterbia. 4].

  According to the present invention, the generation of burrs in the electrolyte sheet for a solid oxide fuel cell can be remarkably suppressed. Further, in the method of the present invention, the zirconia green sheet is fired in two stages, and the occurrence of burrs can be easily suppressed only by adjusting the position of the weight in the sheet laminate mainly in the second stage of firing. Therefore, the present invention is extremely useful industrially as a technology capable of efficiently producing a high-performance electrolyte sheet that is an essential component of a solid oxide fuel cell that is being put into practical use.

FIG. 1 is a schematic side view of a second laminate including a primary fired sheet, an alumina dense plate and a weight, and a ceramic setter. FIG. 2 is a schematic overhead view showing the positional relationship between the primary fired sheet and the weight during conventional secondary firing. FIG. 3 is a schematic overhead view showing the positional relationship between the primary fired sheet and the weight at the time of secondary firing according to the present invention. FIG. 4 is a schematic overhead view showing the positional relationship between the primary fired sheet and the weight at the time of secondary firing according to the present invention. FIG. 5 is a schematic overhead view showing the positional relationship between the primary fired sheet and the weight during the secondary firing according to the present invention. FIG. 6 is a schematic overhead view showing the positional relationship between the primary fired sheet and the weight during the secondary firing according to the present invention. FIG. 7 is a schematic overhead view showing the positional relationship between the primary fired sheet and the weight at the time of secondary firing according to the present invention. FIG. 8 is a schematic overhead view showing the positional relationship between the primary fired sheet and the weight during the secondary firing according to the present invention.

  The zirconia green sheet used by this invention can be manufactured by a conventional method. For example, as described below, a slurry containing zirconia powder may be prepared, and the slurry may be formed into a sheet shape to obtain a zirconia green sheet. Hereinafter, the method of the present invention including a general method for producing zirconia green sheets will be described.

Slurry preparation step In this step, at least zirconia powder, a solvent and a binder are mixed to prepare a slurry.

As a material for the zirconia powder, zirconia stabilized with one or more stabilizers can be used. For example, alkaline earth metal oxides such as MgO, CaO, SrO, BaO; Sc ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , Pr ₂ O ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ Rare earth element oxides such as Eu ₂ O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Yb ₂ O ₃ ; and Bi ₂ O ₃ , In Examples thereof include zirconia powder containing one or more selected from metal oxides such as ₂ O ₃ as a stabilizer. Furthermore, any other oxide selected from SiO ₂ , Ge ₂ O ₃ , B ₂ O ₃ , SnO ₂ , Ta ₂ O ₅ and Nb ₂ O ₅ may be contained as another additive. Among these, one or more rare earth elements selected from the group consisting of scandia, yttria, ceria, gadolinia, and ytterbia are preferable for ensuring a higher level of oxygen ion conductivity, strength, and toughness. Zirconia stabilized with oxide. The solid solution amount of the metal oxide may be appropriately adjusted. For example, the solid solution amount of the rare earth element oxide with respect to the whole including zirconia can be 8 mol% or more and 15 mol% or less. If the amount of the solid solution is 8 mol% or more, the proportion of cubic crystals increases, and zirconia crystals can be more reliably stabilized. On the other hand, if the amount of the solid solution is 15 mol% or less, the oxide ion conductivity is more reliably increased, and the performance as an electrolyte can be sufficiently ensured. The amount of the solid solution is preferably 9 mol% or more, more preferably 12 mol% or less, and even more preferably 11 mol% or less. In addition, the said rare earth element oxide may be only 1 type, and may use 2 or more types together. When using 2 or more types together, the said solid solution amount is made into the sum total of the molar concentration as an oxide of each element.

The zirconia powder is preferably pulverized by a ball mill, a bead mill or the like because of the ease of producing the zirconia electrolyte. The degree of pulverization may be adjusted as appropriate. For example, the average secondary particle diameter may be about 0.08 μm or more and 1.0 μm or less. By using a relatively fine solid electrolyte material having an average secondary particle diameter of 1.0 μm or less, the amount of binder used in slurry preparation can be reduced, and a solid electrolyte layer having a high density can be easily obtained. . On the other hand, if it is too fine, the necessary amount of a dispersant and the like increases, so that it is preferably 0.08 μm or more. The average secondary particle diameter is more preferably about 0.2 μm or more and 0.8 μm or less. The average secondary particle diameter is obtained as, for example, a diameter (D ₅₀ ) at ₅₀ % by volume by preparing a dispersion of a solid electrolyte material and measuring the particle size distribution using a laser diffraction particle size distribution analyzer. Can do.

  Although it does not restrict | limit especially as a solvent used for slurry preparation, For example, Alcohols, such as methanol, ethanol, 2-propanol, 1-butanol, 1-hexanol; Ketones, such as acetone and 2-butanone; Pentane, hexane, heptane Aliphatic hydrocarbons such as: aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; acetic acid esters such as methyl acetate, ethyl acetate, and butyl acetate, and the like. use. These solvents can be used alone or in combination of two or more.

  There is no restriction | limiting in particular as a binder, The organic binder conventionally known can be selected suitably and can be used. Examples of organic binders include ethylene copolymers, styrene copolymers, acrylate and / or methacrylate copolymers, vinyl acetate copolymers, maleic acid copolymers, vinyl butyral resins, and vinyl acetals. Examples thereof include cellulosic resins, vinyl formal resins, vinyl alcohol resins, waxes, and cellulose resins such as ethyl cellulose. These binders may be used independently and may use 2 or more types together. Among these, from the viewpoints of processability for forming depressions and protrusions on the surface of the green sheet, green sheet moldability, thermal decomposability during firing, etc., it is thermoplastic and has a number average molecular weight of 20,000. A (meth) acrylate copolymer having a glass transition temperature of −40 ° C. or higher and 20 ° C. or lower is recommended as a preferable value. Such a number average molecular weight can be measured by a conventional method. However, if there is a catalog value for a commercially available binder, it may be referred to.

  Components other than zirconia powder, a solvent, and a binder may be appropriately blended in the slurry. Examples of other components include a dispersant, a plasticizer, and an antifoaming agent.

  What is necessary is just to mix said each component by a conventional method. For example, when a solid electrolyte material having a desired secondary particle size is obtained in advance, a disperser or the like may be used and mixed under conditions that do not cause further pulverization. When the secondary particle diameter of the stabilized zirconia powder is not adjusted in advance, it may be pulverized and mixed until a desired secondary particle diameter is obtained using a ball mill or the like.

Step of preparing zirconia green sheet Next, the slurry is applied to a base material, formed into a tape shape or a sheet shape, and then dried to obtain a zirconia green sheet. A substrate film such as a PET film may be used as the substrate. The method for applying the slurry is not particularly limited, and conventional methods such as a doctor blade method and a calender roll method can be used. Specifically, for example, the slurry is transported to a coating dam, cast on a substrate so as to have a uniform thickness by a doctor blade, and dried to obtain a zirconia green tape having a width of about 5 cm to 100 cm. After being obtained, it may be cut into a desired shape to obtain a zirconia green sheet. The shape and size of the zirconia green sheet may be determined according to the shape and size of the target electrolyte sheet.

Step I: Primary firing step In this step, a plurality of zirconia green sheets are laminated to form a first laminate, which is then primarily fired to obtain a primary fired sheet. This step corresponds to a general firing step of zirconia green sheets.

  In the first laminate, zirconia green sheets and porous spacers are alternately used mainly for the purpose of improving the evaporation of organic components and residual solvents and suppressing defects such as undulation, warpage, and burrs. It is preferable to laminate. At this time, it is preferable to arrange both sheets so that the entire plane portion of each zirconia green sheet is covered with the zirconia green sheet, and the bottom and top of the zirconia green sheet-porous spacer laminate are respectively It is preferable to arrange a porous spacer. Furthermore, a ceramic setter may be disposed under the laminate, and a weight may be disposed on the uppermost porous spacer of the laminate.

  The number of zirconia green sheets laminated in the first laminate may be adjusted as appropriate, and may be, for example, 2 or more and 20 or less. From the viewpoint of production efficiency, it is preferable to laminate two or more zirconia green sheets. On the other hand, if the number of stacked layers is 20 or less, the first stacked body can be made sufficiently stable. The number of stacked layers is more preferably 4 or more and 15 or less.

  Examples of the material of the porous spacer that can be used in the present invention include at least one selected from the group consisting of alumina, zirconia, and mullite. The porous sheet made of these has excellent creep resistance and spalling resistance, and has an advantage of low reactivity with zirconia in a high temperature atmosphere.

The porosity of the porous spacer is preferably 30% or more and 70% or less. If the porosity is 30% or more, when firing zirconia green sheets with porous spacers and zirconia green sheets alternately stacked, gas generated by thermal decomposition of organic components is quickly released to the outside. Thus, the degreasing effect can be sufficiently promoted, and defects such as undulation, cracks and cracks in the primary fired sheet can be more reliably suppressed. On the other hand, if the porosity is 70% or less, the strength and smoothness of the porous spacer itself can be sufficiently secured, and repeated use is possible, and cracks and cracks in the primary fired sheet can be prevented. It can be further reduced. The porosity is more preferably 35% or more, still more preferably 40% or more, more preferably 65% or less, and still more preferably 60% or less. The porosity is calculated from the following formula in accordance with “Measurement method of apparent porosity of refractory brick” in JIS R2205.
P ₀ = [(W ₃ −W ₁ ) / (W ₃ −W ₂ )] × 100
[In the formula, P ₀ represents the apparent porosity of the sample, W ₁ represents the mass of the dried sample, W ₂ represents the mass of the saturated sample in water, and W ₃ represents the mass of the saturated sample. ]

  The thickness of the porous spacer is preferably 100 μm or more and 500 μm or less. If the thickness is 100 μm or more, the strength of the porous spacer can be sufficiently secured, and if it is 500 μm or less, the organic component decomposition gas at the time of firing is sufficiently diffused, and the swell of the primary fired sheet, etc. It is possible to more reliably suppress defects. The thickness is more preferably 120 μm or more, even more preferably 150 μm or more, more preferably 400 μm or less, and even more preferably 350 μm or less. Further, the area and shape of the porous spacer may be determined so as to cover the entire plane part of the zirconia green sheet. However, holes may be provided in the porous spacer as appropriate.

Since the zirconia green sheet is fired in a state where the zirconia green sheet is alternately stacked with the porous spacer, it is preferable to make the load applied to the zirconia green sheet uniform. Therefore, it is preferable that the area of the porous spacer is slightly larger than the area of the zirconia green sheet and that the zirconia green sheet does not protrude from the peripheral edge of the porous spacer. Specifically, the dimension in which the porous spacer protrudes from the periphery of the zirconia green sheet is preferably in the range of 0.5 mm to 5 mm, more preferably 1 mm to 3 mm, and even more preferably 1 mm to 2 mm. preferable. Further, the area of the porous spacer is preferably 80 cm ² or more and 500 cm ² or less, more preferably 100 cm ² or more and 400 cm ² or less. In addition, the area of a porous spacer means the area determined by the external shape, when the hole is provided in the spacer, the area of the planar portion of the porous spacer including the area of the hole.

  The ceramic setter that can be used in the present invention is generally a ceramic firing jig mainly used for firing electronic parts and glass, and is also called a shelf board or a floor board. The ceramic setter that can be used in the present invention comprises an oxide such as alumina, silica, magnesia, zirconia, and / or a composite oxide such as cordierite, zirconia, mullite, and has a thickness of about 5 mm to about 30 mm. It is preferably a flat plate having a side of about 150 mm or more and 400 mm or less and on which a porous spacer is placed.

It is preferable that a weight is placed on the top of the first laminated body in which the zirconia sheets are laminated, and the zirconia green sheet is fired with a load applied. The weight material may be selected as appropriate, and examples include mullite and / or alumina. Examples of the weight shape include a plate shape and a block shape. The weight is preferably a load applied to the uppermost zirconia green sheet in the first laminate, preferably 0.1 g / cm ² or more, 1.0 g / cm ² or less, more preferably 0.2 g / cm ² or more, 0 It may be selected so as to be 5 g / cm ² or less. As for the load, when the porous spacer is placed on the uppermost zirconia green sheet, the weight of the porous spacer may be taken into consideration, but the weight of the porous spacer relative to the weight is negligible. If it is small, the weight of the porous spacer need not be considered.

  What is necessary is just to adjust the baking conditions of a 1st laminated body suitably. For example, the primary firing temperature can be set to 1200 ° C. or higher and 1600 ° C. or lower. As the said temperature, 1250 degreeC or more is preferable, 1300 degreeC or more is further more preferable, 1550 degreeC or less is preferable and 1500 degreeC or less is more preferable. In addition, the temperature increase rate, the temperature decrease rate, the baking time, etc. at the time of primary baking are not particularly limited.

Step II: Secondary firing step In this step, the plurality of primary firing sheets obtained in Step I are laminated to form a second laminate, which is then subjected to secondary firing. By this step, even if burrs are generated in the primary fired sheet in Step I, the burrs can be corrected and reduced. Therefore, after step I, the presence or absence of burrs in the primary fired sheet may be inspected, and only the primary fired sheet having burrs of a predetermined value or more may be subjected to the secondary firing in this process. However, this inspection may not be performed, and the primary fired sheet that has undergone the above step I may be subjected to secondary firing as it is. By not carrying out the inspection, the overall production efficiency can be increased, and even if the defect is a primary fired sheet having a defect less than a predetermined value, the surface properties can be further improved.

  In the present invention, the “burr” refers to the curvature of the sheet peripheral edge, and can be expressed as a difference in height between the lowest point and the highest point in the sheet peripheral region. In the present invention, the “sheet peripheral portion” is a portion between the peripheral side of the primary fired sheet and the secondary fired sheet and a position between 3 mm from the peripheral side toward the inside, and “sheet peripheral region” Means all the areas between the peripheral edge of the primary fired sheet and the secondary fired sheet and a position of 3 mm from the peripheral edge toward the inside.

  In the present invention, the burr height is measured using a laser optical three-dimensional shape measuring apparatus, and can be obtained by irradiating the sheet surface with laser light and analyzing the reflected light in a three-dimensional shape. In other words, a laser optical three-dimensional shape measuring device is used to irradiate an electrolyte sheet surface to be measured with laser light to focus on the sheet surface, and to form an image of the reflected light evenly on the photodiode. Non-contact type micro-tertiary with a structure in which the lens is controlled so that the focal point of the objective lens is always in focus with the sheet surface by generating a signal that immediately cancels this when the image becomes uneven with respect to the displacement of the surface By detecting the amount of movement of the original shape analyzing apparatus, the unevenness of the sheet surface to be measured can be detected in a non-contact manner. The resolution is usually 1 μm or less, preferably 0.1 μm or less. In the present invention, a device having a resolution of 0.01 μm is used to accurately detect the burr height in each section.

  A laser optical three-dimensional shape measuring apparatus will be described with a specific example. The laser measuring instrument is provided with a red semiconductor laser having a wavelength of 670 nm and a spot diameter of about 2 μm as a light source, and the resolution is 0.01 μm, and the scan width can be set in six steps between 0 and 1100 μm. It is preferable that the laser measuring instrument further has a microscope function with an infrared LED having a wavelength of 870 nm as an illumination light source. As an example of a suitable measuring device, there is a double scan high precision laser measuring device LT series manufactured by Keyence Corporation. The laser measuring instrument controller has a minimum display unit of 0.01 μm, a display cycle of 10 times / second, and the control I / O is a no-voltage input and an NPN open collector output. Further, the laser measuring instrument controller is connected to the monitor by a PIN connector.

  In the present invention, the burr heights of the primary fired sheet and the secondary fired sheet are specifically determined by the above-mentioned double scan high-precision laser measuring instrument LT series manufactured by Keyence Corporation and high-speed three-dimensional shape measurement manufactured by COMMS Corporation. Using the system “EMS2002AD-3D”, a laser beam is emitted in an arbitrary cross direction at a pitch of 0.01 mm, and the length of the peripheral edge of 8 sheets is about 6 mm from the periphery toward the center of the sheet from the outside of the sheet. The height difference between the highest point and the lowest point in any of the eight peripheral areas is measured. Conventionally, the burr height of 50 μm has been an acceptable range for all four locations in any peripheral region, but the flatness of the electrolyte sheet is more important, and in the present invention, eight locations in any peripheral region are used. A fired sheet that is 30 μm or less is considered acceptable.

  The second laminate to be fired in this step includes a primary fired sheet group obtained by directly laminating a plurality of primary fired sheets. In the primary fired sheet group, the whole may be fixed with a tape or the like so that the fired sheets do not deviate from each other. The number of primary fired sheets constituting the primary fired sheet group is preferably 10 or more and 100 or less. If the number is 10 or more, good production efficiency can be ensured. On the other hand, if the number is 100 or less, the second laminate can be made sufficiently stable. In addition, if foreign matter is mixed between the fired sheets, there may be a possibility that a lot of fired sheets in the vicinity of the foreign matter leave traces of the foreign matter and become defective, and there is a possibility that the second laminate may collapse due to burrs of the primary fired sheet. Therefore, the second laminated body may be formed to have a configuration in which the primary fired sheet groups are stacked on each other via a dense ceramic sheet. The dense ceramic sheet that can be used in the present invention is preferably formed of a material containing at least one selected from the group consisting of alumina, zirconia, and mullite. These are excellent in creep resistance and spalling resistance, and have low reactivity with zirconia in a high temperature atmosphere. The number of laminated primary fired sheet groups in the second laminate may be adjusted as appropriate, and may be, for example, 1 or more and 10 or less.

The density of the dense ceramic sheet that can be used in the present invention may be adjusted as appropriate. For example, a sheet having a relative density of 90% or more is preferable. The relative density is more preferably 95% or more, still more preferably 98% or more, and particularly preferably 99% or more. The relative density is calculated by the following formula. In the following formula, the theoretical density is a density obtained by calculation from the sum of the volume of the unit cell of the crystal and the mass contained in the unit cell, and the bulk density is obtained based on JIS R1634, It is a value obtained by dividing the mass by the outer volume of the sintered body.
Relative density (%) = [bulk density (g / cm ³ ) / theoretical density (g / cm ³ )] × 100

  In the second laminate, a dense ceramic sheet is placed on the uppermost primary fired sheet group so as to cover the entire surface of the uppermost primary fired sheet. By performing the secondary firing while placing the dense ceramic sheet in this way, burrs in the primary fired sheet are remarkably suppressed. Such a dense ceramic sheet may have a hole inside as long as it can cover the entire peripheral area of the uppermost primary fired sheet.

  In the second laminate, a weight is further placed on the dense ceramic sheet placed on the uppermost primary fired sheet group. Such weights are arranged so as not to be present vertically on at least a part of the peripheral area, which is an area of 3 mm from the peripheral edge of the primary fired sheet toward the inside. That is, when the second laminate is placed on a horizontal plane, there is no weight on at least part of the peripheral area of the primary fired sheet constituting the second laminate. Usually, in order to reduce burrs, it is considered that the peripheral edge should be weighted. However, according to the knowledge of the present inventors, when the primary fired sheet is subjected to the secondary firing, the burr is reduced by arranging it so that there is no weight on the vertical part of at least a part of the peripheral area of the sheet. can do. The reason is not necessarily clear, but it is considered that the way of heat transfer to the sheet during secondary firing is involved. For example, if the reduction of burrs is caused only by the load, it may be problematic whether the surface on which burrs are generated during the secondary firing is up or down. There was no difference in the results depending on the orientation of the next fired sheet.

  In this invention, you may arrange | position a weight so that a weight may not exist at all vertically on the peripheral part area | region of the primary baking sheet | seat in a 2nd laminated body. The shape of the weight in this case can be freely determined within a range that can be accommodated in a flat portion other than the peripheral region of the primary fired sheet to be subjected to secondary firing.

  Even when it is arranged so that a weight exists on the vertical part of the peripheral area of the primary fired sheet, the shape of the weight can be appropriately determined. For example, when the planar shape of the primary fired sheet is a rectangle, the shape and arrangement of the weights are determined so that there is a portion where the weight is present and a portion where the weight is not present on each peripheral edge, or at least one side is It is preferable to determine the shape and arrangement of the weights so that there are a portion where the weight exists and a portion where the weight does not exist on the vertical side of the peripheral edge, and no weight exists on the vertical side of the other peripheral side. When the planar shape of the primary fired sheet is circular, the circumference is divided into four parts, and the shape and arrangement of the weights are similarly determined on the assumption that each arc corresponds to each peripheral edge of the square primary fired sheet. be able to.

  In addition, the shape and arrangement of the weight so that the ratio of the area of the planar portion of the weight that exists vertically on the peripheral area to the area of the peripheral area of the primary fired sheet is 0% or more and 90% or less. Is preferably determined. The area ratio is preferably 80% or less or 70% or less, and more preferably 50% or less or 40% or less.

  In addition, it is preferable to determine the shape and arrangement of the weight so that the position of the center of gravity in the planar direction of the primary fired sheet matches the position of the center of gravity in the planar direction of the weight. Specific examples of specific planar shapes of weights are shown in FIGS.

  The material of the weight is not particularly limited, and examples thereof include mullite and / or alumina. The weight may be porous.

As described above, in the present invention, the secondary firing is performed while applying a load by weighting the primary firing sheet in the second laminate. For example, it is possible to load on the top of the primary firing sheet 5.0 g / cm ² or more, adjusted to be 80.0 g / cm ² or less. More preferably 15.0 g / cm ² or more as the load, even more preferably from 20.0 g / cm ² or more, and more preferably from 50.0 g / cm ² or less, 40.0 g / cm ² or less are more and more preferable. As for the load, the weight of the uppermost dense ceramic sheet may be taken into account, but if the weight of the dense ceramic sheet relative to the weight is so small that it can be ignored, the weight of the dense ceramic sheet need not be taken into consideration. Be good.

  In the present invention, it is preferable to set the temperature of secondary firing, that is, the maximum temperature of secondary firing to the temperature of primary firing, that is, the maximum temperature of primary firing. By adjusting the firing temperature and weight, the burrs of the primary fired sheet can be more reliably corrected by secondary firing. The secondary firing temperature may be equal to or lower than the primary firing temperature. However, in order to effectively correct burrs, it is desirable that the firing temperature be close to the primary firing temperature. Accordingly, the temperature of the secondary firing is preferably between the primary firing temperature and a temperature lower by 200 ° C. than the primary firing temperature, more preferably between the primary firing temperature and a temperature lower by 100 ° C. than the primary firing temperature. More preferably, it is set between the primary firing temperature and a temperature lower by 50 ° C. than the primary firing temperature.

  The temperature increase rate and temperature decrease rate in the secondary firing are not particularly limited. However, with regard to the temperature lowering rate, it is preferable that the temperature lowering rate from the maximum temperature to a temperature lower by 100 ° C. than the maximum temperature is 5 ° C./min or less and then gradually cooled. By satisfying such a temperature lowering condition in the secondary firing, it is possible to reduce the occurrence of cracks and chips due to the secondary firing. In order to reduce such cracks and chips, the rate of temperature decrease in the temperature range from the highest temperature during secondary firing to room temperature is more preferably 10 ° C./min or less, and more preferably 8 ° C./min or less. More preferably, it is 5 ° C./min or less. In order to reduce the occurrence of cracks and chips, it is preferable to gradually cool to a lower temperature. Therefore, it is more preferable that the rate of temperature decrease from the highest temperature to 200 ° C. lower than the highest temperature, more preferably from the highest temperature to 300 ° C. lower than the highest temperature is 5 ° C./min or less. The cooling rate is more preferably 2 ° C./min or less, still more preferably 1 ° C./min or less, and particularly preferably 0.5 ° C./min or less. The temperature decreasing rate here is usually a temperature decreasing rate that is adjusted using a temperature regulator that controls the furnace temperature. Although the actual furnace temperature does not necessarily completely coincide with the temperature indicated by the temperature regulator, in the present invention, the average value of temperature changes including these errors is regarded as the temperature decrease rate.

  In addition, the temperature increase rate at the time of secondary baking is not specifically limited. In the manufacturing method of the present embodiment, for example, when the rate of temperature rise during secondary firing is 1 ° C./min, the rate of occurrence of cracks and chips and the rate of temperature rise are increased or decreased. Even when the reduction rate of occurrence of cracks and chips is compared, there is no significant difference in the results.

  The zirconia sheet that has undergone the above steps I and II is a sheet that has remarkable burrs, specifically, excellent surface characteristics reduced to 30 μm or less, and has high strength and excellent resistance. It is very useful as an electrolyte sheet for a physical fuel cell.

  For example, the zirconia sheet according to the present invention can be made into a single cell for SOFC by forming an electrode layer or the like by a conventional method. For example, when a zirconia electrolyte sheet is obtained according to the present invention, usually, a fuel electrode layer is first formed on the sheet and then an air electrode layer is formed on the sheet because of the sintering temperature. An intermediate layer for suppressing interlayer reaction may be formed between the zirconia electrolyte sheet, which is a solid electrolyte layer, and the air electrode layer. The intermediate layer may be formed before the fuel electrode layer, or may be formed by coating and drying the slurry for the intermediate layer and the slurry for the fuel electrode layer and then simultaneously sintering. .

  Since the electrolyte sheet according to the present invention has high strength, the single cell for SOFC and SOFC containing these also have high strength and show excellent durability.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Example 1 Production of Zirconia Sheet (1) Production of Zirconia Green Sheet A green sheet of scandia-stabilized zirconia was produced. First, scandia-stabilized zirconia ((ZrO ₂ ) _0.92 (Sc ₂ O ₃ ) _0.08 ) (hereinafter referred to as “8ScSZ”) powder (manufactured by Daiichi Elemental Chemical Co., Ltd., average particle size: 0.6 μm) 100 parts by mass of a binder made of a methacrylate copolymer (molecular weight: 30000, glass transition temperature: −8 ° C., solid content concentration: 50% by mass) in terms of solid content, 15 parts by mass, and sorbitan acid as a dispersant 2 parts by mass of triolate, 3 parts by mass of dibutyl phthalate as a plasticizer, and 50 parts by mass of a mixed solvent of toluene / ethyl acetate = 3/2 (mass ratio) as a solvent are placed in a nylon pot charged with zirconia balls, The 8ScSZ slurry was prepared by kneading for a time. The obtained slurry was transferred to a jacketed round bottom cylindrical vacuum degassing vessel equipped with a vertical stirrer and having a volume of 50 L. The jacket temperature was adjusted to 40 ° C. while rotating the stirrer at a speed of 30 rpm, and about 4 to 21 kPa. The slurry was concentrated and degassed under reduced pressure to adjust the viscosity to 2 Pa · s to obtain a slurry for coating. The slurry for coating is transferred to a slurry dam of a coating apparatus, coated on a polyethylene terephthalate (PET) film by a doctor blade method, and a drying section (3 zones of 50 ° C., 80 ° C. and 110 ° C.) following the coating portion. The 8ScSZ green tape having a thickness of 180 μm was obtained by passing it at a speed of 0.4 m / min and drying it. This green tape was cut to obtain a square 8ScSZ green sheet having a side of about 118 mm.

(2) Production of Alumina Porous Spacer Used for producing the above zirconia green sheet with respect to 100 parts by mass of commercially available low soda alumina powder (trade name “AL-13” manufactured by Showa Denko KK, average particle size: 55 μm). 12 parts by mass of the binder, 1 part by mass of the dispersant, 2 parts by mass of the plasticizer, and 35 parts by mass of the solvent were added, and an alumina slurry was prepared in the same manner as in the production of the zirconia green sheet. The viscosity of this alumina slurry was adjusted to 10 Pa · s in the same manner as in the preparation of the zirconia green sheet to obtain a coating slurry. This coating slurry was coated on a PET film by the same method as that for producing the green sheet, and further dried. However, the passing speed of the drying section was 0.8 m / min. As a result, an alumina green tape having a thickness of 200 μm was obtained. This alumina green tape was cut to obtain a square alumina green sheet having a side of about 130 mm.

  The cut square alumina green sheet was placed on an alumina plate having a polished surface, and corn starch was uniformly applied thereon using a brush, and the square alumina green sheet was further superimposed thereon. The same operation was repeated, and a total of 10 alumina green sheets were superposed via corn starch. In this state, degreasing was performed at 500 ° C. in an air atmosphere, and then calcined at 1580 ° C. for 2 hours to obtain an alumina porous spacer. The obtained spacer had a thickness of 180 μm, a side of 120 mm, a porosity of 45%, and a mass of 4.4 g.

(3) Primary firing (firing in step (I) in the present invention)
On the 300-mm square ceramic setter, the 1st laminated body which consists of the alumina porous spacer produced by said (2) and the zirconia green sheet produced by said (1) was arrange | positioned. Specifically, four alumina porous spacers were placed side by side on a ceramic setter, and a zirconia green sheet was placed on each. Each of these zirconia green sheets is further laminated with alumina porous spacers and zirconia green sheets alternately, and finally, six alumina porous spacers in which the alumina porous spacers are arranged in the lowermost layer and the uppermost layer. And four sets of first laminated bodies composed of five zirconia green sheets were placed on a ceramic setter. About 50 g of a porous block (porosity 58%) having a crystalline phase of mullite and alumina was placed as a weight on the alumina porous spacer located in the uppermost layer of the first laminate. A degreasing zone in which 10 ceramic setters with a total of 4 sets (40 sets in total) are placed on a conveyor belt, and the temperature can be set at a frontage of 340 mm, a height of 20 mm, and the front at about 500 ° C or less. Into the tunnel furnace type continuous heating furnace, which is a firing zone whose temperature can be set at about 1500 ° C. or less at the rear, is charged at a running speed of 0.3 m / hour, and primary firing is performed at a maximum temperature of 1400 ° C., A primary fired zirconia sheet was prepared. The temperature lowering rate in the primary firing was 1.2 ° C./min from 1400 ° C. to 1050 ° C. Here, the temperature increase / decrease rate in the continuous furnace refers to the difference between the temperatures of adjacent zones (usually the indicated value of a thermometer (thermocouple) located in the center of the zone in the length direction). It is a number divided by time.

(4) Inspection of the presence of burrs on the primary fired zirconia sheet The burr height of the fired sheet is determined by the double scan high-precision laser measuring instrument LT series manufactured by Keyence Corporation and the high-speed three-dimensional shape measurement system “EMS2002AD- Using 3D ", measurement is performed by scanning laser light in the direction of an arbitrary cross in the direction of an arbitrary cross from the outside of the sheet toward the center of the sheet at a pitch of 0.01 mm from the periphery to a length of about 5 mm using 3D". did. And the sheet | seat in which the difference of the height of the highest point and the lowest point in the distance of 3 mm from a peripheral edge and a peripheral edge is 30 micrometers or less in all eight places was made into the pass, and the sheet | seat exceeding 30 micrometers was made unacceptable.

(5) Secondary firing (firing in step (II) in the present invention)
Of the primary fired zirconia sheet, only the zirconia sheet in which burrs of more than 30 μm were generated was extracted, and a laminate was produced by the stacking method shown in Table 1. For example, the second laminate of Test Example 1 has a zirconia fired sheet group in which 20 fired sheets are stacked directly on each other as shown in FIG. 1, and these three zirconia sheet groups are made of an alumina dense plate (Nikkato). (Made by company, about 100 mm square, 1 mm thick), alumina dense plates are placed on the uppermost layer and the lowermost layer, and mullite and alumina are used as weights on the alumina dense plate located on the uppermost layer. This was formed by placing a porous block (porosity 19%) having the following crystal phase. Moreover, the bird's-eye view schematic diagram which looked at the positional relationship of the primary baking sheet | seat and weight in Test Examples 1-8 from the top is shown to FIGS. In addition, in FIGS. 2-8, in order to clarify the positional relationship with the peripheral part area | region and weight of a primary baking sheet, the dense ceramic sheet of the uppermost layer is not illustrated. Table 1 shows the ratio of the area of the planar portion of the weight existing on the vertical of the peripheral region to the area of the peripheral region of the primary fired sheet. In the secondary firing, the load based on the weight of the alumina dense plate was considerably smaller than the load due to the weight, so here the load due to the weight is a problem as the load applied to the uppermost primary fired zirconia sheet of the second laminate. There is no.

The second laminated body on which the weight was placed was put into an electric furnace having an effective volume of about 0.4 m ³ , and secondary firing was performed so that the secondary firing temperature shown in Table 1 was the maximum temperature. The heating rate of the electric furnace was 1 ° C./min. After the second laminate was held at the secondary firing temperature for 3 hours, it was cooled at a temperature drop rate shown in Table 1. The secondary fired zirconia sheet after the secondary firing was evaluated for burrs under the same conditions as the burr evaluation method for the primary fired zirconia sheet, and the number of fired sheets recovered from burrs was determined. The burr correction rate was calculated from the result and the following formula. The results are shown in Table 1.

    Burr correction rate (%) = {[number of fired sheets with corrected burr (excluding cracked sheets)] / [total number of fired sheets subjected to secondary firing]} × 100)

  As shown in Table 1, when a weight is present vertically on the entire peripheral area of the primary fired sheet at the time of secondary firing (Test Examples 1 and 2), burrs on the primary fired sheet are corrected. However, the ratio was low, and the incidence of cracks and chips was high. On the other hand, when the weight shape and arrangement are devised so that there is no weight on at least a part of the peripheral edge region of the primary fired sheet (Test Examples 3 to 8), the burr correction rate is all The electrolyte sheet was 80% or more and excellent in flatness with reduced burr. Furthermore, the incidence of cracks and cracks was as low as less than 3%, indicating that the method of the present invention is an excellent technique that can produce an electrolyte sheet with a low breakage rate.

1: Primary fired sheet (black areas at both ends are peripheral areas)
2: Dense ceramic sheet 3: Ceramic setter 4: Weight 5: Primary fired sheet group 6: Second laminate

Claims (5)

A method for producing an electrolyte sheet for a solid oxide fuel cell, comprising:
Step I: A step of laminating a plurality of zirconia green sheets to form a first laminate, and primary firing to obtain a primary firing sheet; and
Step II: includes a step of laminating a plurality of primary fired sheets obtained in Step I above to form a second laminated body, followed by secondary firing.
The second laminated body is placed so as to cover the entire surface of the uppermost primary fired sheet on the uppermost primary fired sheet group, a primary fired sheet group obtained by directly laminating the plurality of primary fired sheets. A dense ceramic sheet, and a weight on the dense ceramic sheet,
The method is characterized in that the weight is arranged so as not to be present vertically on at least a part of a peripheral area which is an area of 3 mm from the peripheral edge of the primary fired sheet toward the inside.   2. The method according to claim 1, wherein a ratio of the area of the planar portion of the weight existing vertically on the peripheral region to the area of the peripheral region is 0% or more and 90% or less.   The method according to claim 1 or 2, wherein a plurality of the primary fired sheet groups are laminated via a dense ceramic sheet in the second laminated body. In the second laminate, the load applied to the top of the primary firing sheet 5.0 g / cm ² or more, A method according to any one of claims 1 to 3 is 80.0 g / cm ² or less.   The zirconia green sheet contains zirconia stabilized with one or more rare earth element oxides selected from the group consisting of scandia, yttria, ceria, gadolinia and ytterbia. The method described.

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