JP5431808B2 - Method for producing laminated fired body - Google Patents

Description

  The present invention relates to a laminated fired body and a method for producing the laminated fired body, and in particular, a laminated fired body constituting a part of a solid oxide fuel cell (SOFC) cell, and the laminated fired body thereof. The present invention relates to a method for manufacturing a body.

  Conventionally, a porous fuel electrode electrode in which a flow path (fuel flow path) of fuel gas (for example, hydrogen) is formed and in contact with the fuel gas flowing through the fuel flow path to react with the fuel gas, And a dense electrolyte layer made of a solid electrolyte formed on at least one of the upper and lower surfaces of the fuel electrode and a gas containing oxygen (for example, air) formed on the surface of the electrolyte layer to bring oxygen into contact An SOFC cell that is a laminated fired body including a porous air electrode electrode that reacts a gas that contains the gas is known (see, for example, Patent Document 1).

  Regarding the SOFC configured using such a cell, the present applicant, for example, in Japanese Patent Application No. 2007-324508, collects and fixes a plurality of cells and a conductor (also referred to as an “interconnector”). SOFC with a stack structure consisting of In this stack structure, two adjacent cells are stacked in a state of being separated in the cell thickness direction. In addition, the connecting portion of the fuel electrode of one of the adjacent cells and the connecting portion of the air electrode of the other adjacent cell are electrically connected via a collector fixing member. Thereby, the plurality of cells are electrically connected in series.

  And the flow path (air flow path) of the gas containing oxygen is divided and formed in each space formed between two adjacent cells. The air flow path and the fuel flow path are partitioned by an electrolyte layer (and other members) so that the gas containing oxygen in the air flow path and the fuel gas in the fuel flow path are not mixed.

  In a state in which this stack structure is heated to the operating temperature of SOFC (for example, 800 ° C., hereinafter simply referred to as “operating temperature”), the fuel flow path and the air flow path contain gas containing fuel gas and oxygen, respectively. Supplied. Thereby, the fuel gas and the gas containing oxygen come into contact with the fuel electrode and the air electrode, respectively. As a result, a power generation reaction occurs in each cell. At that time, by adopting a stack structure in which a plurality of cells are electrically connected in series as described above, a larger output can be obtained as compared with the case where only one cell is used. .

  The present applicant has proposed the following manufacturing method in Patent Document 2, for example, in manufacturing the SOFC cell as the laminated fired body. That is, first, at least one of the upper and lower surfaces of the green molded body before firing that will later become the fuel electrode, one green sheet before firing (hereinafter referred to as “first green sheet”) that later becomes the electrolyte layer. .) Are laminated without interposing a bonding agent. An isotropic pressure (hydrostatic pressure by cold water) is applied to the laminate by a cold isostatic pressing method (hereinafter referred to as “CIP”) to press the laminate. In the present specification, “green” means a state before firing.

  As a result, a pressure molded body in which the green molded body and the first green sheet are integrated (bonded) can be obtained without using a bonding agent. Here, it is considered that the green molded body and the first green sheet are integrated based on the following reason. That is, due to the hydrostatic pressure, the green molded body and the first green sheet have a surface direction (a direction perpendicular to the thickness direction, a direction in which the contact surface between the green molded body and the first green sheet extends) in addition to the thickness direction. ) Also receives power. The green molded body and the first green sheet receive these forces due to the hydrostatic pressure and contract by an amount corresponding to the magnitude of the hydrostatic pressure. Hereinafter, focusing on the shrinkage in the surface direction, the shrinkage in the surface direction due to CIP is also referred to as “CIP shrinkage”. Due to the force in the surface direction due to the hydrostatic pressure, CIP contraction occurs in the green molded body and the first green sheet according to the magnitude of the hydrostatic pressure. Thus, CIP contraction occurs between the green molded body and the first green sheet, and the contact portions between the green molded body and the first green sheet are pressed by the force in the thickness direction due to the hydrostatic pressure. Due to the synergistic effect, an anchor effect caused by biting or the like acts between the contact portions. Due to the anchor effect, the green molded body and the first green sheet are integrated (joined). Since the CIP shrinkage between the green molded body and the first green sheet proceeds in the state where the integration is achieved in this way, the amount of CIP shrinkage between the green molded body and the first green sheet (in the plane direction by CIP) Dimension reduction amount) agrees.

  Next, the pressure-formed body is fired to obtain a laminated fired body composed of the fuel electrode and the electrolyte layer. The pressure-formed body (laminated fired body) shrinks even by firing. Hereinafter, the shrinkage in the surface direction due to firing is particularly referred to as “firing shrinkage”. As described above, integration has already been achieved in the pressure-formed body. Accordingly, since the firing shrinkage proceeds in a state where the integration is achieved, the amount of firing shrinkage between the green molded body (fuel electrode) and the first green sheet (electrolyte layer) (reduction in dimension in the plane direction due to firing). The amount) also agrees.

  Next, a green molded body before firing, which will later become an air electrode, is formed on the surface of the electrolyte layer of the laminated fired body by printing or the like. The green molded body is fired to obtain the SOFC cell described above.

International Publication No. 07/029860 Pamphlet International Publication No. 03/027041 Pamphlet

  By the way, in the above-described cell during the operation of the SOFC, the solid electrolyte (for example, YSZ) in the dense electrolyte layer reacts with a specific substance (for example, strontium) in the porous air electrode to react with the electrolyte layer. A phenomenon may occur in which the electrical resistance between the electrode and the air electrode increases. In order to suppress this reaction, the present applicant has proposed that a dense reaction preventing layer made of ceria is interposed between the dense electrolyte layer and the porous air electrode.

  In this case, before firing, a green molded body that will later become a fuel electrode, a first green sheet that will later become an electrolyte layer, and a second green sheet that will later become a reaction preventing layer are obtained. The laminate is preferably subjected to firing. In order to obtain a laminated body in which this integration has been achieved before firing, a method utilizing the above-described pressure-formed body can be considered.

  Specifically, a first green sheet is laminated on a green molded body (to be a fuel electrode later), and CIP (first CIP) is applied to the laminated body. Thereby, as described above, CIP shrinkage occurs in the green molded body and the first green sheet, and a pressure molded body in which the green molded body and the first green sheet are integrated is obtained. Next, a second green sheet is laminated on the surface of the first green sheet in the pressure molded body, and the second CIP is applied to the laminated body. As a result, CIP contraction occurs in the first and second green sheets (and the green molded body), and the first and second green sheets are integrated (that is, the green molded body, the first green sheet, and the second green sheet). A laminated body (pressure-molded body) integrated with a green sheet is obtained.

  In addition, when the hydrostatic pressure of the second CIP is equal to or lower than the hydrostatic pressure of the first CIP, the CIP contraction based on the first CIP has already occurred in the first green sheet. Shrinkage cannot occur. Therefore, the anchor effect described above cannot act between the contact portions of the first and second green sheets, and the first and second green sheets cannot be integrated. Therefore, the hydrostatic pressure of the second CIP needs to be set to a value larger than the hydrostatic pressure of the first CIP.

  In the second CIP, the CIP contraction of the first and second green sheets proceeds in a state where the first and second green sheets are integrated by the anchor effect. Therefore, as described above, the CIP of the first and second green sheets based on the second CIP is the same as “the amount of CIP shrinkage between the green molded body based on the first CIP and the first green sheet matches”. The amount of contraction is consistent. This is because the total amount of CIP shrinkage of the first green sheet (= sum of the amount of CIP shrinkage based on the first and second CIP) is equal to the total amount of CIP shrinkage of the second green sheet (= only the second time). This means that the amount of CIP contraction based on the first CIP increases by the amount of CIP contraction based on the first CIP. In other words, the green sheet that is laminated later, the smaller the amount of CIP shrinkage of the green sheet.

  In addition, when the above-described “pressure molded body in which the green molded body, the first green sheet, and the second green sheet are integrated” is fired, the fired shrinkage is achieved in a state where the integration is achieved as described above. Will progress. Therefore, the amount of firing shrinkage of the first and second green sheets (electrolyte layer and reaction preventing layer) matches.

  When the method in which CIP is performed twice in this way is adopted, reaction prevention is achieved with a laminated fired body (a laminated body of a fuel electrode, an electrolyte layer, and a reaction preventing layer) obtained after firing the pressure-formed body. It has been found that a relatively large tensile residual stress is likely to occur in the surface direction in the layer, and if this tensile residual stress is excessive, a crack (crack) may occur in the reaction preventing layer. As a result of various experiments and researches to cope with this problem, the present inventor has come up with the present invention.

  An object of the present invention is to provide a laminated fired body in which a substrate and a plurality of layers made of different materials are laminated, in which a large tensile residual stress is not easily generated inside the plurality of layers. .

  The laminated fired body according to the present invention includes a substrate and a plurality of adjacent layers made of different materials laminated on at least one of the upper surface and the lower surface of the substrate. Here, the substrate may not be porous, but is preferably porous. The plurality of layers may not be dense layers, but are preferably dense layers. The substrate is a fuel electrode that contacts the fuel gas and reacts with the fuel gas, the adjacent plural layers are two layers, and the layer that contacts the substrate of the two layers is an electrolyte made of a solid electrolyte. And the other of the two layers may be a reaction preventing layer made of ceria. In this case, the laminated fired body according to the present invention constitutes a part of the SOFC cell, and an SOFC cell is obtained by adding an air electrode to the laminated fired body.

  The feature of the laminated fired body according to the present invention is that this laminated fired body was obtained through the following process. That is, a laminate of pre-fired green sheets, which will be the multiple layers later, is laminated without interposing a bonding agent on at least one of the upper surface and the lower surface of the green molded body that will later become the substrate. Is done. Next, an isotropic pressure is applied to the laminate, and the laminate is press-molded to obtain a press-molded body in which the green compact and the green sheet laminate are integrated. And the laminated fired body which concerns on this invention is obtained by baking this press-molded body.

  Here, the pressure molding may be performed by a hot isostatic pressing method, but is preferably performed by a cold isostatic pressing method (CIP). Moreover, it is preferable that the pressure at the time of the pressure molding is 100 to 700 MPa.

  In the method described in the summary of the invention described above, green sheets are laminated one by one on the green molded body, and CIP is applied each time one green sheet is laminated. On the other hand, in the present invention, a green sheet laminate prepared in advance is laminated on the green molded body at a time, and the CIP is applied only once.

  According to the present invention, during pressure molding (for example, CIP), due to the anchor effect described above, CIP shrinkage of the green molded body and each green sheet in a state where the green molded body and each green sheet are integrated. Progress. Therefore, the amount of CIP shrinkage of the green sheets constituting the green sheet laminate coincides with each other in the press-formed body. According to the present invention, a laminated fired body is obtained by subjecting such a pressure-formed body to firing. And in the laminated fired body which concerns on this invention, it became clear that a big tension | pulling residual stress was hard to generate | occur | produce in a surface direction inside a some dense layer. This is considered based on the following reasons.

  That is, consider a case where firing is performed after CIP is applied to a certain green sheet. In this case, it is conceivable that the smaller the amount of CIP shrinkage, the larger the amount of firing shrinkage (more precisely, the amount of firing shrinkage in a single state). Therefore, in the method described in the summary column of the invention described above, as described above, the amount of CIP shrinkage of the second green sheet is smaller than the amount of CIP shrinkage of the first green sheet. The amount of firing shrinkage (in the single state) of the green sheet is greater than the amount of firing shrinkage (in the single state) of the first green sheet. That is, when firing, the second green sheet tends to shrink more than the first green sheet. However, as described above, since the first and second green sheets are already integrated before firing, the actual firing shrinkage amounts of the first and second green sheets are forcibly matched. As a result, after firing, a large tensile residual stress is easily generated in the surface direction on the second green sheet.

  On the other hand, in the present invention, as described above, the amount of CIP shrinkage of each green sheet constituting the laminate of green sheets matches. Therefore, a large difference is hardly generated in the amount of firing shrinkage (in a single state) of each green sheet. As a result, large tensile residual stress is unlikely to occur in the surface direction inside the plurality of dense layers in the laminated fired body according to the present invention.

  Specifically, the laminated fired body according to the present invention can be manufactured through the following first to fifth steps, for example. In the first step, each green sheet before firing to be a layer of the plurality of layers later is formed. In the second step, the formed green sheets are laminated to obtain a laminate of green sheets. In the third step, the green sheet laminate is laminated on at least one of the upper surface and the lower surface of the green molded body before firing, which will be the substrate later, without interposing a bonding agent. In the fourth step, the green molded body and the green sheet laminated body are integrated by applying isotropic pressure to the laminated body obtained after the third step and pressure-molding the laminated body. A pressed body is obtained. In the fifth step, the laminated fired body is obtained by firing the obtained pressure-molded body.

  By the way, the green sheet is usually formed on a resin sheet that is difficult to deform. As the resin sheet, for example, a polyethylene terephthalate sheet (also referred to as a PET film) is used. Thin green sheets are very deformable and easy to tear. In particular, it is very difficult to handle a green sheet having a thickness of 30 μm or less alone. Therefore, normally, the green sheet formed on the resin sheet is cut into a necessary planar shape integrally with the resin sheet, and the cut green sheet is handled with a resin sheet having the same planar shape attached thereto.

  As described above, when the green sheet is handled in a state where the resin sheet is adhered, and the dense layer laminated on the substrate in the laminated fired body is two layers, the first to fourth steps are as follows. It can proceed as follows. First, in the first step, each of the green sheets is formed on a resin sheet that is a resin sheet. In the second step, the green sheets to which the resin sheets are adhered are laminated so as to face each other to form a two-layer green sheet laminate, and on both end sides in the thickness direction of the two-layer green sheet laminate. By removing only one of the two resin sheets adhering to each other, it is possible to obtain the green sheet laminate in which the resin sheet adheres only to one end side in the thickness direction. In the third step, the green molded body is formed such that a plane of the green sheet laminate exposed by removing the one resin sheet and at least one of an upper surface and a lower surface of the green molded body face each other. And the green sheet laminate are laminated. In the fourth step, the laminate in which the resin sheet is attached to one end side in the thickness direction obtained after the third step is subjected to the pressure molding.

  Thus, in the fourth step, the resin sheet attached to the green sheet corresponding to the outermost layer of the laminated body is also subjected to pressure molding (for example, CIP) integrally with the laminated body. As described above, since the resin sheet is difficult to deform, it is difficult to shrink even when subjected to pressure molding. On the other hand, as described above, the green sheet laminate is contracted by pressure molding. Therefore, a shift occurs in the relative positional relationship between the contact portions of the green sheet and the resin sheet corresponding to the outermost layer. As a result, after pressure molding, the resin sheet can be naturally peeled from the green sheet corresponding to the outermost layer.

  In the laminated fired body according to the present invention described above, the shape of the laminated fired body when viewed from the thickness direction of the laminated fired body is a circle, an ellipse, a square, or a rectangle, It is preferable that the diameter of the circle, the major axis of the ellipse, the length of one side of the square, or the length of the long side of the rectangle is 3 cm or more. The thicknesses of the fuel electrode, the electrolyte layer, and the reaction preventing layer are preferably 500 to 3000 μm, 1 to 20 μm, and 3 to 20 μm, respectively.

1 is a perspective view of a solid oxide fuel cell according to an embodiment of the present invention. It is the figure which looked at the fuel cell shown in FIG. 1 from the y-axis direction. FIG. 3 is a cross-sectional view of the fuel cell in which the fuel cell shown in FIG. 1 is cut along a plane including the line 3-3 shown in FIG. 1 and parallel to the xz plane. FIG. 4 is a cross-sectional view of the fuel cell in which the fuel cell shown in FIG. 1 is cut along a plane including the line 4-4 shown in FIG. 1 and parallel to the xz plane. It is a perspective view of the cell shown in FIG. It is each figure which looked at the cell shown in FIG. 5 from the x, y, and z-axis directions. FIG. 7 is a perspective view of a fuel electrode layer obtained by cutting the cell shown in FIG. 5 along a plane including the line 7-7 shown in FIG. 5 and parallel to the xy plane. It is a perspective view of the interconnector shown in FIG. It is each figure which looked at the interconnector shown in FIG. 8 from the x, y, and z-axis directions. It is a figure explaining the distribution | circulation of the fuel and air in the fuel cell shown in FIG. It is a perspective view of the flow path formation member used in order to form a fuel flow path in the inside of a fuel electrode layer. It is a figure for demonstrating the mode at the time of press-molding the green compact which becomes a fuel electrode layer later. It is a perspective view of the green compact by which the flow-path formation member was embed | buried inside. FIG. 14 is a cross-sectional view of the green compact obtained by cutting the green compact shown in FIG. 13 along a plane including the line 14-14 shown in FIG. 13 and parallel to the xz plane. A laminate in which a laminate of a first green sheet that later becomes an electrolyte layer and a second green sheet that later becomes a reaction preventing layer is laminated and integrated on the upper and lower surfaces of the green compact shown in FIG. It is sectional drawing corresponding to FIG. FIG. 16 is a cross-sectional view corresponding to FIG. 14 of the fired body in which the fuel flow path is formed by burning the pressure forming body shown in FIG. FIG. 17 is a perspective view of a fired body having an air electrode layer formed on the upper and lower surfaces of the fired body shown in FIG. 16. FIG. 18 is a perspective view of a cell completed by forming conductive portions and through holes in the fired body shown in FIG. 17. It is the perspective view which showed the state by which the flow-path connection member was fixed by the part corresponding to the through-hole of the cell shown in FIG. FIG. 20 is a perspective view illustrating a state where the cell illustrated in FIG. 19 is accommodated in the interconnector. It is a perspective view of the 1st green sheet which PET film adhered. It is a perspective view of the 2nd green sheet to which the PET film adhered. FIG. 23 is a perspective view of a two-layer green sheet laminate in which PET films are attached to upper and lower ends formed by laminating the first and second green sheets shown in FIGS. 21 and 22 to face each other. FIG. 24 is a perspective view corresponding to FIG. 23 illustrating a state where one of the four corners of the PET film attached to the first green sheet in the green sheet laminate illustrated in FIG. 23 is peeled off. It is a perspective view corresponding to FIG. 23 which showed the state after the whole PET film adhering to the 1st green sheet in the green sheet laminated body shown in FIG. 23 was peeled. FIG. 26 is a perspective view of a laminate in which the green sheet laminate shown in FIG. 25 is laminated on the upper and lower surfaces of the green compact shown in FIG. 13. It is the perspective view which showed a mode that CIP was given to the laminated body shown in FIG. It is the perspective view which showed a mode that the PET film adhering to the 2nd green sheet after CIP was given peels naturally. It is a perspective view of the laminated body by which the 1st green sheet shown in FIG. 21 was laminated | stacked on the upper and lower surfaces of the compact shown in FIG. It is the perspective view which showed a mode that CIP was given to the laminated body shown in FIG. It is the perspective view which showed a mode that the PET film adhering to the 1st green sheet after CIP was given peels naturally. It is a perspective view of the laminated body by which the 2nd green sheet shown in FIG. 22 was laminated | stacked on the upper and lower surfaces of the press-molded body shown in FIG. It is the perspective view which showed a mode that CIP was given to the laminated body shown in FIG. It is the perspective view which showed a mode that the PET film adhering to the 2nd green sheet after CIP was given peels naturally. The transition of the change of the shrinkage | contraction amount of a 1st, 2nd green sheet in the case where baking is performed with respect to the press-molded body to which CIP was performed twice with the procedure of the comparative example shown in FIGS. 29-34 is shown. It is a graph. Changes in the shrinkage amount of the first and second green sheets in the case where firing is performed on the pressure-formed body that has been subjected to CIP once by the procedure of the embodiment of the present invention shown in FIGS. It is the graph which showed transition. It is the perspective view which showed a mode that CIP was given to the laminated body shown in FIG. It is the perspective view which showed a mode that the 1st, 2nd green sheet was not integrated even if CIP was given. FIG. 26 is a perspective view of a laminate in which a third green sheet to be a fuel electrode active layer is further laminated on the second green sheet in the green sheet laminate shown in FIG. 25. It is a perspective view of the laminated body by which the green sheet laminated body shown in FIG. 39 was laminated | stacked on the upper and lower surfaces of the green compact shown in FIG. Corresponding to FIG. 23 in the case where a difference is provided in the planar shape of the first and second green sheets so that the entire planar contour of the first green sheet exists inside the planar contour of the second green sheet. FIG. It is the figure which looked at the laminated body shown in FIG. 41 from the z-axis direction. FIG. 42 is a perspective view corresponding to FIG. 41 showing a state where one of the four corners of the PET film attached to the first green sheet in the green sheet laminate shown in FIG. 41 is peeled off. FIG. 42 shows a case where a difference is provided in the planar shape of the first and second green sheets so that a part of the planar shape of the first green sheet exists inside the planar profile of the second green sheet. It is a corresponding figure. Another example in the case where a difference is provided in the planar shape of the first and second green sheets so that a part of the planar profile of the first green sheet exists inside the planar profile of the second green sheet It is a figure corresponding to FIG.

  Hereinafter, a solid oxide fuel cell including a laminated fired body according to an embodiment of the present invention will be described with reference to the drawings.

(Overall structure of fuel cell)
FIG. 1 is a perspective view of a solid oxide fuel cell (hereinafter simply referred to as “fuel cell”) 10 according to an embodiment of the present invention. FIG. 2 is a partial view of the fuel cell 10 as seen from the y-axis direction. FIG. 3 is a view of the fuel cell cut along a plane parallel to the xz plane including the line 3-3 shown in FIG. 4 is a partial cross-sectional view corresponding to FIG. 2, and FIG. 4 is a partial cross-sectional view corresponding to FIG. 2 in which the fuel cell is cut along a plane parallel to the xz plane including the line 4-4 shown in FIG. is there. Note that the x axis and the y axis are orthogonal to each other, and the z axis is an axis perpendicular to the xy plane. Hereinafter, the z-axis positive direction may be referred to as an “up” direction, and the z-axis negative direction may be referred to as a “down” direction.

  As can be understood from FIGS. 1 to 4, the fuel cell 10 includes a plurality of cells 20 of the same type and a plurality of interconnectors 30 of the same shape. The cell 20 is also referred to as a “single cell” of the fuel cell 10. Each cell 20 is housed and fixed in a corresponding one interconnector 30. The fuel cell 10 is formed by stacking a plurality of interconnectors 30 in a state in which the cells 20 are accommodated. That is, the fuel cell 10 has a stack structure. Here, the laminated body of the plurality of interconnectors 30 corresponds to the “current collecting fixing member”.

  Hereinafter, first, the cell 20 will be described with reference to FIGS. 2 to 4 and FIGS. 5 to 7. The cell 20 generally has a rectangular parallelepiped shape (thin plate shape having a thickness direction in the z-axis direction) having sides along the x-, y-, and z-axis directions, and a side (long side) along the x-axis direction. ), The length (B1) of the side (short side) along the y-axis direction, and the thickness Z1 are 30 to 300 mm, 15 to 150 mm, and 0.5 to 5 mm, respectively, in this example (see FIG. 6). reference).

  The cell 20 includes a fuel electrode layer 21 (fuel electrode, anode electrode), a pair of electrolyte layers 22, a pair of reaction prevention layers 23, and a pair of air electrode layers 24 (air electrode, cathode electrodes). . The fuel electrode layer 21 has a rectangular parallelepiped shape (a thin plate shape having a thickness direction in the z-axis direction) having sides along the x-, y-, and z-axis directions. A fuel flow path 25 through which fuel gas (for example, hydrogen gas) flows is formed inside the fuel electrode layer 21 (see particularly FIG. 7).

  The pair of electrolyte layers 22 are respectively formed on the upper and lower surfaces of the fuel electrode layer 21. The pair of reaction preventing layers 23 are respectively formed on the upper surface of the electrolyte layer 22 formed on the upper surface of the fuel electrode layer 21 and the lower surface of the electrolyte layer 22 formed on the lower surface of the fuel electrode layer 21. Each of the pair of electrolyte layers 22 and the pair of reaction prevention layers 23 has a thin plate shape having a thickness direction in the z-axis direction, and the planar shape viewed from the z-axis direction is a fuel electrode layer viewed from the z-axis direction. This corresponds to the planar shape of 21.

  The pair of air electrode layers 24 are respectively formed on the upper surface of the reaction preventing layer 23 formed on the upper side of the fuel electrode layer 21 and on the lower surface of the reaction preventing layer 23 formed on the lower side of the fuel electrode layer 21. The pair of air electrode layers 24 have the same thin plate shape having a thickness direction in the z-axis direction. Each air electrode layer 24 is formed with a pair of notches 24a, 24a in order to avoid interference with a pair of through holes 27 described later. The thicknesses of the fuel electrode layer 21, each electrolyte layer 22, each reaction prevention layer 23, and each air electrode layer 24 are, for example, 500 to 3000 μm, 1 to 20 μm, 3 to 20 μm, and 3 to 50 μm, respectively.

  The side surfaces (four surfaces) of the cell 20, specifically, “the side surfaces (four surfaces) on which the respective side surfaces of the fuel electrode layer 21, the pair of electrolyte layers 22, and the pair of reaction preventing layers 23 are exposed” are: It is covered with a side wall 26 (glass layer). The side surface of the fuel electrode layer 21 may be covered with the electrolyte layer 22 instead of the side wall 26. In this case, the electrolyte layer 22 is a thin film formed on the surface of the fuel electrode layer 21 so as to surround the periphery (upper and lower surfaces and side surfaces) of the fuel electrode layer 21. In addition, as a sealing structure of the side part of a cell, the structure covered only with the electrolyte layer may be sufficient, the structure which further covered the glass layer on the electrolyte layer may be sufficient, and only a glass layer may be sufficient as it. It may be a covered structure.

  In this example, the fuel electrode layer 21 is a porous fired body made of Ni and YSZ (yttria-stabilized zirconia) (after a reduction treatment described later), and functions as a fuel electrode (anode electrode). The electrolyte layer 22 is a dense fired body made of YSZ. The reaction preventing layer 23 is a dense fired body made of ceria. Specific examples of ceria include GDC (gadolinium doped ceria) and SDC (samarium doped ceria). The air electrode layer 24 is a porous fired body made of LSCF (La0.6Sr0.4Co0.2Fe0.8O3: lanthanum strontium cobalt ferrite), and functions as an air electrode (cathode electrode).

  The reaction preventing layer 23 is formed between the electrolyte layer 22 and the air electrode layer 24 by reacting YSZ in the electrolyte layer 22 with strontium in the air electrode layer 24 in the cell 20 during operation of the fuel cell 10. Is interposed between the electrolyte layer 22 and the air electrode layer 24 in order to suppress the occurrence of the phenomenon that the electrical resistance increases.

  The cell 20 includes a pair of through holes 27. Each through hole 27 is formed in the vicinity of the corresponding short side of the cell 20 and in the central region of the side, and each through hole 27 is formed in the fuel electrode layer 21, the electrolyte layer 22, and the reaction preventing layer 23. It penetrates. The pair of through holes 27 communicate with each other through the fuel flow path 25 inside the fuel electrode layer 21 (see particularly FIG. 7).

  Conductive plates 28 made of a conductor (for example, lanthanum chromite) electrically connected to the fuel electrode layer 21 inside the cell 20 are disposed at the four corners of the upper surface of the cell 20, respectively. The upper surface of each conductive plate 28 (ie, the upper surface of the conductor) is exposed to the outside. As will be described later, in the above-described stacked state, these conductive plates 28 function as electrical connection portions to leg portions 34 (to be described later) of the interconnector 30 adjacent to the interconnector 30 that accommodates itself.

  Next, the interconnector 30 will be described with reference to FIGS. 2 to 4 and FIGS. 8 and 9. In this example, the interconnector 30 is divided into a first portion 30A and a second portion 30B having a symmetrical shape with respect to a plane parallel to the xz plane at the center in the y-axis direction. Hereinafter, for convenience of explanation, the interconnector 30 may be handled as an integrated body including the first and second portions 30A and 30B.

  The interconnector 30 is a frame (enclosure) made of a conductor having a rectangular parallelepiped shape (thin plate shape having a thickness direction in the z-axis direction) having sides substantially along the x-, y-, and z-axis directions. is there. In this example, the length A2 of the side (long side) along the x-axis direction, the length B2 of the side (short side) along the y-axis direction, and the height Z2 are 40 to 310 mm, 25 to 160 mm, 3 to 3, respectively. 8 mm (see FIG. 9). In this example, the interconnector 30 is made of a ZMG material (manufactured by Hitachi Metals, Ltd.), which is a ferritic stainless steel for fuel cells.

  Inside the interconnector 30 (that is, the frame), a space that opens (penetrates) in the y-axis direction for accommodating the cell 20 is formed. The interconnector 30 is formed with a pair of notches 31 and 31 in order to avoid interference with a pair of connecting members 40 described later in a state where the cell 20 is accommodated.

  A plurality of projecting portions 32 projecting downward and upward from the edge of the small window (through hole) are formed at portions corresponding to the upper surface and the lower surface of the frame constituting the interconnector 30. As will be described later, these protrusions 32 function as electrical connection portions with the air electrode layer 24 of the cell 20 accommodated in the interconnector 30.

  At the four corners of the portion corresponding to the upper surface of the frame constituting the interconnector 30, there is a window at a position corresponding to the position of the conductive plate 28 on the xy plane when the cell 20 is accommodated. 33 (through hole) is formed. Further, leg portions 34 projecting downward are formed at the four corners of the portion corresponding to the lower surface of the frame constituting the interconnector 30 and at the positions corresponding to the positions of the windows 33 on the xy plane. Has been. When viewed from the z-axis direction, the entire leg portion 34 is included in the window 33. As will be described later, in the above-described stacked state, these leg portions 34 function as an electrical connection portion with the conductive plate 28 of the cell 20 accommodated in the interconnector 30 adjacent below.

  The fuel cell 10 has a stack structure in which a plurality of interconnectors 30 having the above configuration in which the cells 20 having the above configuration are accommodated and fixed are stacked. In the fuel cell 10 having this stack structure, a cylindrical connection provided with through holes 41 at positions corresponding to the positions of the pair of through holes 27 on the xy plane between two adjacent cells 20. Members 40 and 40 are interposed. Thereby, two adjacent cells 20 are stacked via the connecting member 40 in a state where they are separated in the z-axis direction by a distance corresponding to the height of the connecting member 40 (see particularly FIG. 4).

  Further, the through holes 27 at the same position on the xy plane in the two adjacent cells 20 are connected and communicated with each other through the through hole 41 of the connecting member 40. As a result, as shown in FIG. 4, the through-holes 41 and the through-holes 27 are alternately connected, so that one fuel supply path continuously extending in the z-axis direction and continuously in the z-axis direction. An extending fuel exhaust passage is formed. The fuel supply path and the fuel exhaust path communicate with each other via a fuel flow path 25 in each cell 20.

  In addition, the pair of air electrode layers 24 of each cell 20 and the plurality of protrusions 32 of the interconnector 30 that accommodates the cell 20 are electrically connected and fixed by the conductive adhesive 51 (conductive paste). (See especially FIG. 3). Further, the four legs 34 of the interconnector 30 adjacent to the upper part of the interconnector 30 are inserted into the four windows 33 of the interconnector 30, respectively. Then, the conductive plate 28 (upper surface) of a certain cell 20 and the leg 34 (lower surface) of the interconnector 30 adjacent to the upper side of the interconnector 30 that accommodates the cell 20 are electrically conductive adhesive 52. It is electrically connected and fixed by (conductive paste) (see especially FIG. 3).

  Thereby, the air electrode layer 24 of the upper cell 20 and the fuel electrode layer 21 of the lower cell 20 among the two adjacent cells 20 are electrically connected via the interconnector 30 that houses the upper cell 20. Has been. That is, in the fuel cell 10 as a whole, the plurality of cells 20 are electrically connected in series.

  A space formed between two adjacent cells 20 is used as an air flow path S through which a gas (for example, air) containing oxygen flows. As described above, the upper and lower surfaces of the fuel electrode layer 21 are covered with the electrolyte layer 22, and the side surfaces of the fuel electrode layer 21 are covered with the side walls 26. Therefore, the air flow path S and the fuel flow path 24 are partitioned by the electrolyte layer 22 and the side wall 26.

As shown in FIG. 10, air is supplied from the y-axis direction (both directions) to the fuel cell 10 having the above configuration, and fuel gas is supplied from the fuel supply path. The supplied air flows through the air flow path S and contacts the pair of air electrode layers 24 of each cell 20. On the other hand, the supplied fuel gas passes through the fuel flow path 25 in each cell 20 and is exhausted from the fuel exhaust path (see the arrow in FIG. 4). Thus, the fuel cell 10 is based on the following chemical reaction formulas (1) and (2) by supplying the fuel gas to the fuel flow path 24 and supplying the air to the air flow path S. Generate electricity.
(1/2) · O ₂ +2 ^e− → O ²⁻ (in the air electrode layer 23) (1)
H ₂ + O ²⁻ → H ₂ O + 2 ^e− (in the fuel electrode layer 21) (2)

  Since the fuel cell (SOFC) 10 generates power using the oxygen conductivity of the electrolyte layer 22, the operating temperature of the fuel cell 10 is generally at least 600 ° C. or higher. For this reason, the fuel cell 10 has an external heating mechanism (for example, a resistance heater type heating mechanism or a heating mechanism that uses heat obtained by burning fuel gas) from normal temperature to an operating temperature (for example, 800 ° C.). ) Is used in a heated state.

(Example of manufacturing method)
Hereinafter, an example of a method for manufacturing the fuel cell 10 will be described. First, a method for manufacturing the cell 20 will be described. In order to form the fuel flow path 25 in the fuel electrode layer 21, a flow path forming member 61 shown in FIG. The flow path forming member 61 is formed by one of well-known methods using a pore forming agent (for example, cellulose). Further, a powder 62 that is a raw material for the fuel electrode layer 21 is prepared. The powder 62 uniformly contains particles of NiO, YSZ, and a pore-forming agent (for example, cellulose). The reason why the powder 62 contains the pore forming agent is to make the fuel electrode layer 21 porous.

  Next, as shown in FIG. 12, using a (uniaxial) press, the powder 62 is press-molded into a shape corresponding to the fuel electrode layer 21 so that the flow path forming member 61 is embedded. Thereby, as shown in FIG. 13, a rectangular parallelepiped green compact 21z in which the flow path forming member 61 is embedded is formed. 14 is a cross-sectional view of the green compact 21z cut along a plane parallel to the xz plane including the line 14-14 shown in FIG.

  Next, a laminate of a first green sheet 22z that will later become the electrolyte layer 22 and a second green sheet 23z that will later become the reaction preventing layer 23 is laminated on the upper and lower surfaces of the green compact 21z. Molded. The first green sheet 22z is a dense layer made of YSZ, and the second green sheet 23z is a dense layer made of ceria. This step will be described in detail later. As a result, as shown in FIG. 15, a laminated body (pressure formed body) is obtained in which the first and second green sheets 22z and 23z are laminated and integrated on the upper and lower surfaces of the green compact 21z.

  The pressure-molded body is fired at a predetermined temperature and a predetermined time (for example, 1400 ° C. for 1 hour). As a result, as shown in FIG. 16, the flow path forming member 61 is burned out, and the fuel electrode layer 21 in which the fuel flow path 25 is formed, and the pair of electrolytes formed on the upper and lower surfaces of the fuel electrode layer 21, respectively. A laminated fired body including the layer 22 and a pair of reaction preventing layers 23 formed on the upper surface of the upper electrolyte layer 22 and the lower surface of the lower electrolyte layer 22 is formed. In addition, the pore forming agent contained in the powder 62 is burned away, so that the fuel electrode layer 21 becomes porous.

  Next, as shown in FIG. 17, green sheets 24z to be air electrode layers 24 later are formed on the upper and lower surfaces of the laminated fired body by a printing method, respectively, and the green sheets 24z are formed at a predetermined temperature and a predetermined time (for example, Baked at 1000 ° C. for 1 hour). Thereby, a pair of air electrode layers 24 are formed on the upper and lower surfaces of the fired body.

  Then, as shown in FIG. 18, a pair of through holes 27 is formed on the fired body using one of known processing techniques. Further, four conductive plates 28 are disposed on the fired body so as to be electrically connected to the internal fuel electrode layer 21. Further, the side wall 26 is fixed to the side surface of the fired body using an adhesive or the like so as to cover the entire side surface of the fired body. The side wall 26 may be formed simultaneously by the above baking after glass application, or may be formed by applying glass after baking. Thus, the cell 20 is completed. A required number of completed cells 20 are prepared.

  Next, a method for manufacturing the interconnector 30 will be described. The interconnector 30 (actually, the first and second portions 30A and 30B) is a thin plate made of a ZMG material (manufactured by Hitachi Metals, Ltd.), which is a ferritic stainless steel for fuel cells, and a known technique (etching, It is completed by processing into the shape shown in FIGS. 8 and 9 by cutting, pressing, or the like. A necessary number of completed interconnectors 30 (actually, the first and second portions 30A and 30B) are prepared.

  Next, as shown in FIG. 19, the connection member 40 is adhesive (for example, glass paste) at positions corresponding to the positions of the pair of through holes 27 with respect to the upper surfaces of the prepared plurality of cells 20. Are bonded and fixed respectively. In addition, a conductive paste (conductive adhesive 51) is applied to the plurality of protrusions 32 of each interconnector 30 (actually, the first and second portions 30A and 30B).

  Next, as shown in FIG. 20, each cell 20 to which the connecting member 40 is bonded and fixed is connected to the interconnector 30 (actually, the first and second portions 30A and 30B) to which the conductive adhesive 51 is applied. Be contained. Thus, the pair of air electrode layers 24 of each cell 20 and the plurality of protrusions 32 of the interconnector 30 that accommodates the cell 20 are electrically connected and fixed by the conductive adhesive 51 (see FIG. 3).

  Next, a conductive paste (conductive adhesive 52) is applied to the leg 34 (the lower surface thereof) of each interconnector 30. Then, the plurality of interconnectors 30 are stacked so that the four legs 34 of the interconnector 30 adjacent above the interconnector 30 are respectively inserted into the four windows 33 of the interconnector 30. Thereby, a stack structure is formed. In addition, the conductive plate 28 (upper surface) of a certain cell 20 and the leg 34 (lower surface) of the interconnector 30 adjacent to the upper side of the interconnector 30 that accommodates the cell 20 are electrically conductive adhesive. It is electrically connected and fixed by 52 (see FIG. 3). That is, the plurality of cells 20 are electrically connected in series.

  Next, a reduction process is performed on the fuel electrode layer 21 of each cell 20 in the stack structure. In this reduction treatment, the stack structure is subjected to heat treatment, and the temperature of the stack structure is maintained at a predetermined temperature (for example, 800 ° C.) for a predetermined time. At the same time, a reducing gas (hydrogen gas in this example) is caused to flow into each fuel flow path 25 through the fuel supply path. As described above, the fuel flow path 25 and the air flow path S are partitioned by the electrolyte layer 22 and the side wall 26. Accordingly, during the reduction process, the supply of the reducing gas to the surface of the air electrode layer 24 can be prevented without performing a special treatment for preventing the supply of the reducing gas to the surface of the air electrode layer 24.

  NiO is reduced among NiO and YSZ constituting the fuel electrode layer 21 by the flow of the reducing gas. As a result, the fuel electrode layer 21 becomes a cermet of Ni—YSZ and can function as a fuel electrode (anode electrode). Thus, the assembly of the fuel cell 10 is completed.

(Manufacture of pressure molded products)
Hereinafter, a manufacturing method of “a pressure-formed body in which a green compact and a plurality of green sheets are laminated and integrated” shown in FIG. 15 before firing will be described with reference to FIGS. First, as shown in FIG. 21, “the dense first green sheet 22z made of YSZ that will later become the electrolyte layer 22” formed on the PET film A is integrated with the PET film A and is necessary for the necessary planar shape. Only cut out. The cut out first green sheet 22z is handled with the PET film A having the same planar shape attached thereto.

  Similarly, as shown in FIG. 22, the “dense second green sheet 23z made of ceria which will later become the reaction preventing layer 23” formed on the PET film B is necessary for the necessary planar shape integrally with the PET film B. Cut out as many as possible. The cut out second green sheet 23z is handled in a state where a PET film B having the same planar shape is attached.

  Next, as shown in FIG. 23, the first and second green sheets 22z and 23z are laminated so as to face each other without using a bonding agent or the like, and the PET films A and B are attached to the upper and lower ends, respectively. A two-layer green sheet laminate is formed. As a lamination | stacking method, the thermocompression bonding method and CIP (after-mentioned) are mentioned, for example. Next, as shown in FIG. 24, one of the four corners of the PET film A is picked with a predetermined jig or the like, and the PET film A is separated from the first green sheet 22z with the one of the four corners as a starting point. It is peeled off. As a result, as shown in FIG. 25, a two-layer green sheet laminate in which the upper surface of the first green sheet 22z is exposed and the PET film B is attached to the lower end is obtained. A required number of the laminated bodies shown in FIG. 25 are prepared.

  Next, as shown in FIG. 26, the first green is exposed on the upper and lower surfaces of the green compact 21z shown in FIG. 13 without using any bonding agent or the like. The plane of the sheet 22z and the upper and lower surfaces of the green compact 21z are laminated so as to face each other. As shown in FIG. 26, the green compacts 21z and the first and second green sheets 22z, 23z have the same planar shape (the shape seen from the z-axis direction). This is based on the fact that the planar shapes of the fuel electrode layer 21, the electrolyte layer 22, and the reaction preventing layer 23 after firing are the same as described above. At this stage, the green compact 21z and the first and second green sheets 22z and 23z are not yet integrated (joined).

  Next, in order to integrate the green compact 21z and the first and second green sheets 22z and 23z, the laminate shown in FIG. 26 is pressed by a cold isostatic pressing method (hereinafter referred to as “CIP”). Molded. Specifically, as shown in FIG. 27, this laminate is vacuum packed using a bag such as a waterproof plastic bag. In a state where the vacuum-packed laminate is immersed in cold water, a hydrostatic pressure (isotropic pressure) by cold water is applied to the laminate. The pressure P1 (hydrostatic pressure) at this time is, for example, 100 to 700 MPa.

  In this manner, by applying CIP to the laminate shown in FIG. 26, a pressure molded body in which the green compact 21z and the first and second green sheets 22z and 23z are integrated is obtained. Such integration is considered to be based on the following reason.

  That is, due to the hydrostatic pressure, the green compact 21z and the first and second green sheets 22z and 23z exert a force not only in the thickness direction (z-axis direction) but also in the plane direction (direction parallel to the xy plane). receive. The green compact 21z and the first and second green sheets 22z and 23z receive these forces due to the hydrostatic pressure and contract by an amount corresponding to the magnitude of the hydrostatic pressure. Hereinafter, the shrinkage in the plane direction by CIP is also referred to as “CIP shrinkage”. CIP contraction occurs in each of the green compact 21z and the first and second green sheets 22z and 23z according to the magnitude of the hydrostatic pressure due to the force in the surface direction due to the hydrostatic pressure.

  Here, due to the occurrence of CIP contraction in each of the green compact 21z and the first and second green sheets 22z and 23z in this way, and the green compact 21z and the first green by the force in the thickness direction due to the hydrostatic pressure. Anchors caused by biting or the like between the contact portions due to a synergistic effect between the contact portions with the sheet 22z and the contact portions between the first and second green sheets 22z and 23z being pressed. The effect works. By the anchor effect, the green compact 21z and the first green sheet 22z, and the first and second green sheets 22z and 23z are integrated (joined). Since the CIP contraction of each of the green compact 21z and the first and second green sheets 22z and 23z proceeds in the state where the integration is achieved in this way, the green compact 21z and the first and second green sheets The amounts of CIP shrinkage of 22z and 23z (the amount of dimension reduction in the surface direction due to CIP) coincide with each other.

  FIG. 28 shows the state of the laminate after completion of CIP. As shown in FIG. 28, after CIP, the PET film B attached to the second green sheet 23z naturally peels from the second green sheet 23z. This is because the PET film is difficult to shrink even if it is subjected to CIP, and the green sheet laminate is shrunk by CIP, so that the contact portions between the second green sheet 23z and the PET film B are in contact with each other. This is considered to be based on the fact that the relative positional relationship in the surface direction is shifted.

In addition, it has been proved through experiments that the pressure of CIP needs to be 1 ton / cm ² or more in order for the PET film to naturally peel from the green sheet by CIP. Through the experiment, when the CIP pressure is 0.5 ton / cm ² , the entire surface of the PET film does not peel from the green sheet, and when the CIP pressure is 0.8 ton / cm ² , only a part of the PET film peels from the green sheet. It turns out.

  As described above, in this example, the first and second green sheets 22z and 23z prepared in advance are laminated on the green compact 21z at a time, and the CIP is performed only once, as shown in FIG. As a result, a “green compact in which the green compact 21z and the pair of first and second green sheets 22z and 23z are integrated” is obtained.

  This press-molded body is subjected to firing to obtain a “laminated fired body comprising a fuel electrode layer 21, a pair of electrolyte layers 22, and a pair of reaction preventing layers 23” shown in FIG. The pressure-molded body (laminated fired body) also shrinks by this firing. Hereinafter, the shrinkage in the surface direction due to firing is particularly referred to as “firing shrinkage”. Here, as described above, integration has already been achieved in the press-molded body shown in FIG. Therefore, firing shrinkage proceeds in a state where integration is achieved. Therefore, the amount of firing shrinkage of each of the green compact 21z (fuel electrode layer 21) and the first and second green sheets 22z and 23z (electrolyte layer 22 and reaction preventing layer 23) (the amount of dimension reduction in the surface direction due to firing). ) Also match.

(Action / Effect)
Hereinafter, like this embodiment, the laminated body of the 1st, 2nd green sheet 22z, 23z prepared previously is laminated | stacked at once on the compact 21z, and CIP is given only once in FIG. The operation and effect of obtaining the pressure-molded body shown will be described.

  In order to describe the operation and effect of the present embodiment, as a comparative example, first, green sheets are laminated one by one on the green compact 21z, and CIP is applied every time one green sheet is laminated. The case where the press-molded body shown in FIG. 15 is obtained will be described with reference to FIGS.

  As shown in FIG. 29, in the comparative example, first, the “first green sheet 22z attached with PET film A” shown in FIG. 21 is respectively bonded to the upper and lower surfaces of the green compact 21z shown in FIG. And the like. The exposed flat surface of the first green sheet 22z and the upper and lower surfaces of the green compact 21z are stacked so as to face each other. At this stage, the green compact 21z and the first green sheet 22z are not yet integrated (joined).

  Next, as shown in FIG. 30, the first CIP (CIP1) is applied to the laminate shown in FIG. The CIP1 causes CIP contraction in the green compact 21z and the first green sheet 22z, and the pressure-molded body in which the green compact 21z and the pair of first green sheets 22z are integrated by the anchor effect described above. Is obtained. As shown in FIG. 31, after CIP1, the PET film A that has adhered to the first green sheet 22z naturally peels from the first green sheet 22z for the same reason as described above.

  In the CIP1, the CIP contraction of the green compact 21z and the first green sheet 22z proceeds in a state where the green compact 21z and the first green sheet 22z are integrated by an anchor effect. Therefore, the amount of CIP shrinkage of the green compact 21z and the first green sheet 22z based on CIP1 is the same.

  Next, as shown in FIG. 32, the “PET film B shown in FIG. 22 is formed on the upper and lower surfaces of the“ laminated body in which the green compact 21z and the pair of first green sheets 22z are integrated ”shown in FIG. The adhering second green sheet 23z ”is laminated so that the exposed plane of the second green sheet 23z and the upper and lower surfaces of the laminate shown in FIG. 31 face each other without using a bonding agent or the like. The At this stage, the first and second green sheets 22z and 23z are not yet integrated (joined).

  Next, as shown in FIG. 33, a second CIP (CIP2) is applied to the laminate shown in FIG. By this CIP2, CIP contraction occurs in the first and second green sheets 22z and 23z (and the green compact 21z), and the first and second green sheets 22z and 23z are integrated by the anchor effect described above. A pressure molded body (that is, the green compact 21z and the first and second green sheets 22z and 23z are integrated) is obtained. As shown in FIG. 34, after CIP2, the PET film B adhered to the second green sheet 23z naturally peels from the second green sheet 23z for the same reason as described above.

  In the CIP2, the CIP contraction of the first and second green sheets 22z and 23z proceeds in a state where the first and second green sheets 22z and 23z are integrated by an anchor effect. Therefore, the amount of CIP shrinkage of the first and second green sheets 22z and 23z based on CIP2 is the same.

  Here, the pressure (hydrostatic pressure) of CIP2 needs to be set to a value larger than the pressure (hydrostatic pressure) of CIP1. This is based on the following reason. That is, CIP contraction occurs according to the pressure of CIP. When the pressure of CIP2 is equal to or lower than the pressure of CIP1, no further CIP contraction can occur in CIP2 in the first green sheet 22z in which CIP contraction based on CIP1 has already occurred. In other words, CIP2 does not increase the amount of CIP contraction of the first green sheet 22z. Therefore, the anchor effect described above cannot act between the contact portions of the first and second green sheets 22z and 23z. As a result, the first and second green sheets 22z and 23z cannot be integrated.

  As described above, in the comparative example, each time the first and second green sheets 22z and 23z are stacked on the green compact 21z, the CIP is applied, so that the “green compact 21z shown in FIG. , And a pair of first and second green sheets 22z and 23z integrated with each other ”.

  This pressure-molded body is subjected to firing to obtain a “laminated fired body comprising a fuel electrode layer 21, a pair of electrolyte layers 22, and a pair of reaction preventing layers 23”. As in the case of the above-described embodiment, in this case as well, firing shrinkage proceeds in a state where the pressure-formed body is integrated. Therefore, the amount of firing shrinkage of each of the green compact 21z (fuel electrode layer 21) and the first and second green sheets 22z and 23z (electrolyte layer 22 and reaction preventing layer 23) (the amount of dimension reduction in the surface direction due to firing). ) Matches.

  Here, in the laminated fired body obtained after firing the pressure-formed body shown in FIG. 15 according to the comparative example, densification tends to be insufficient in the reaction preventing layer 23, or relatively large tensile is caused in the reaction preventing layer 23. It has been found that the residual stress is likely to occur in the surface direction, and particularly when the tensile residual stress is excessive, a crack (crack) can occur in the reaction preventing layer 23.

  Hereinafter, an experiment showing this will be described. In this experiment, a plurality of types of pressure-molded bodies shown in FIG. 15 having different side lengths, layer thicknesses, CIP pressures, and the like were prepared and prepared using the manufacturing method according to the comparative example described above. It was done. Each pressure-formed body was fired to obtain a laminated fired body. Each laminated fired body was observed. The results are shown in Table 1.

  The laminated fired body (cell) used in this experiment had a rectangular parallelepiped, and three levels (levels 1 to 3) were prepared as the cell size (after firing). The length A1 of the long side, the length B1 of the short side, and the thickness Z1 are 100 mm, 50 mm, and 1.5 mm at the level 1, and are 120 mm, 70 mm, and 1.5 mm at the level 2, respectively. 3 was 100 mm, 100 mm, and 1.5 mm (see FIG. 6). Firing was performed after degreasing treatment was performed at 600 ° C. for 2 hours. As the firing conditions, 1400 ° C. and 1 hr were employed.

  As an evaluation method, a method of observing the surface and cross section of the laminated fired body (cell) using an optical microscope and an electron microscope (SEM) after CIP and firing was adopted. In Comparative Examples 1 and 2, the second green sheet 23z is not laminated after CIP1 is completed, and therefore CIP2 is not performed.

  As shown in Table 1, in Comparative Example 1, the lamination state (bonded state) between the fuel electrode layer and the electrolyte layer was poor, while in Comparative Example 2, the lamination between the fuel electrode layer and the electrolyte layer was poor. The state (bonded state) was good. This means that the pressure of the CIP needs to be set to 100 Mpa or more in order to achieve a good lamination state (bonded state) between the fuel electrode layer and the electrolyte layer. In addition, when the pressure of CIP exceeds 700 Mpa, it will become easy to generate | occur | produce deformation | transformation by crushing etc. in a press-molded body. Therefore, it is considered that the CIP pressure is preferably in the range of 100 to 700 MPa.

  In Comparative Example 3, a peeled portion occurred at the interface between the electrolyte layer and the reaction preventing layer. As described above, this is considered to be caused by the fact that CIP contraction cannot occur in the first green sheet 22z when CIP2 is executed based on the equal pressure of CIP1 and CIP2.

  As shown in Table 1, laminated fired bodies obtained after firing of pressure-formed bodies obtained by using the production method according to the comparative example (pressure of CIP1 <pressure of CIP2) (that is, Comparative Examples 4 to 10) Then, although the peeling part does not generate | occur | produce in the interface between each layer, it turns out that the densification of the reaction prevention layer 23 is easy to generate | occur | produce and that the reaction prevention layer 23 is easy to generate | occur | produce a crack (crack).

  On the other hand, in the laminated fired body obtained after firing the pressure-formed body shown in FIG. 15 according to the present embodiment, no delamination portion is generated at the interface between the layers, and the densification is hardly insufficient in the reaction preventing layer 23. In addition, a relatively large tensile residual stress is hardly generated in the surface direction in the reaction preventing layer 23, and no crack (crack) is generated in the reaction preventing layer 23.

  Hereinafter, an experiment showing this will be described. Also in this experiment, as in the above-described experiment, a plurality of types of pressure-molded bodies shown in FIG. 15 having different side lengths, layer thicknesses, CIP pressures, and the like are used in the manufacturing method according to the above-described embodiment. Each was prepared and prepared using it. Each pressure-formed body was fired to obtain a laminated fired body. Each laminated fired body was observed. The results are shown in Table 2.

  The laminated fired body (cell) used in this experiment also has a rectangular parallelepiped shape, and the same three levels (levels 1 to 3) as described above were prepared as the cell size (after firing). In addition, the firing conditions, the evaluation method, and the like are the same as in the above-described experiment. Examples 1 and 2 shown in Table 2 are the same as Comparative Examples 1 and 2 shown in Table 1.

  As shown in Table 2, in the laminated fired body obtained after firing the pressure-formed body obtained by using the manufacturing method according to this embodiment (that is, Examples 3 to 10), peeling is performed at the interface between the layers. It can be seen that no part is generated, that the reaction preventing layer 23 is not sufficiently densified, and that the reaction preventing layer 23 is not cracked.

  Hereinafter, these results will be considered with reference to FIGS. For convenience of explanation, the pressure of CIP in the manufacturing method according to the present embodiment is P1, and the pressures of CIP1 and CIP2 in the manufacturing method according to the comparative example are P2 (<P1) and P1, respectively. The CIP shrinkage and firing shrinkage of the first green sheet 22z are A1 and B1, and the CIP shrinkage and firing shrinkage of the second green sheet 23z are A2 and B2.

  FIG. 35 shows the transition of changes in the shrinkage amounts (CIP shrinkage amount and firing shrinkage amount) in the surface direction of the first and second green sheets 22z and 23z when the manufacturing method according to the comparative example is applied. As shown in FIG. 35, it is assumed that the CIP contraction amount of the first green sheet 22z based on CIP1 is a value c, and the CIP contraction amount of the first green sheet 22z based on CIP2 is a value (ac). In this case, the (total) CIP contraction amount A1 of the first green sheet 22z is a value a.

  On the other hand, as described above, the amount of CIP contraction of the first and second green sheets 22z and 23z based on CIP2 is the same. Therefore, the CIP contraction amount of the second green sheet 23z based on CIP2 is a value (ac), and as a result, the (total) CIP contraction amount A2 of the second green sheet 23z is a value (ac).

  Further, as described above, the firing shrinkage amounts of the first and second green sheets 22z and 23z (the electrolyte layer 22 and the reaction preventing layer 23) are the same. If this firing shrinkage amount is b, both the firing shrinkage amounts B1 and B2 of the first and second green sheets 22z and 23z are the value b.

  As a result, as understood from FIG. 35, the sum of the CIP shrinkage amount A2 and the firing shrinkage amount B2 (total shrinkage = (a + b) −c) in the second green sheet 23z is the CIP shrinkage in the first green sheet 22z. The sum of the amount A1 and the firing shrinkage amount B1 (total shrinkage amount = (a + b)) is insufficient by the value c (= the CIP shrinkage amount of the first green sheet 22z based on CIP1).

  In other words, in order for the total shrinkage amount of the first and second green sheets 22z and 23z to coincide, the firing shrinkage amount B2 of the second green sheet 23z is insufficient by the value c. It is considered that the shortage of the firing shrinkage amount B2 of the second green sheet 23z may be the cause of the tensile residual stress of the reaction preventing layer 23 described above.

  That is, when firing is performed after CIP is applied to a certain green sheet, the smaller the CIP shrinkage amount, the larger the firing shrinkage amount (more precisely, the firing shrinkage amount in a single state), It is considered that the sum of the CIP shrinkage amount and the firing shrinkage amount (total shrinkage amount) becomes substantially constant. Therefore, in the comparative example, the second green sheet 23z has a CIP shrinkage amount A2 (= ac) that is smaller than the CIP shrinkage amount A1 (= a) of the first green sheet 22z. The firing shrinkage amount (in the single state) of 23z is larger than the firing shrinkage amount (in the single state) of the first green sheet 22z. As a result, at the time of firing, the second green sheet 23z tends to shrink more than the first green sheet 22z. However, as described above, the first and second green sheets 22z and 23z are already integrated before firing. Therefore, the actual firing shrinkage amounts of the first and second green sheets 22z and 23z are forcibly matched (B1 = B2 = b). As a result, it is considered that a large tensile residual stress tends to occur in the surface direction in the second green sheet 23z after firing.

  On the other hand, FIG. 36 shows changes in the shrinkage amounts (CIP shrinkage amount and firing shrinkage amount) in the surface direction of the first and second green sheets 22z and 23z when the manufacturing method according to the present embodiment is applied. Shows the transition. As shown in FIG. 36, in the present embodiment, the CIP contraction amounts A1 and A2 of the first and second green sheets 22z and 23z coincide (A1 = A2 = a). Therefore, a large difference is hardly generated in the amount of firing shrinkage (in a single state) of each green sheet. In addition, the actual total shrinkage amounts of the first and second green sheets 22z and 23z coincide (A1 + B1 = A2 + B2 = a + b). As a result, in this embodiment, it is considered that the tensile residual stress of the reaction preventing layer 23 described above hardly occurs.

  In the present embodiment, the CIP is not applied to the stacked body of the first and second green sheets 22z and 23z before being stacked on the green compact 21z. Therefore, the first and second green sheets 22z are not provided. , 23z are not integrated. On the other hand, it is considered that the first and second green sheets 22z and 23z are integrated by applying CIP to the laminated body of the first and second green sheets 22z and 23z before being stacked on the green compact 21z.

  For this reason, as shown in FIG. 37, CIP was applied to the laminate shown in FIG. However, in this case, as shown in FIG. 38, CIP contraction does not occur in the first and second green sheets 22z and 23z due to CIP (that is, the anchor effect described above does not act), and the first and second green sheets It has been found that the sheets 22z and 23z cannot be integrated. This is because, when the thickness of the object to be CIP is too small, the bag body that vacuum-packs the object is difficult to contact the side surface of the object, so that the hydrostatic pressure is not sufficiently transmitted to the side surface of the object. It is thought to be caused by.

  As described above, the laminated fired body according to the embodiment of the present invention is manufactured as follows. First, a first green sheet 22z that will later become the electrolyte layer 22 and a second green sheet 23z that will later become the reaction preventing layer 23 are laminated to obtain a green sheet laminate. Next, the green sheet laminate is laminated on the upper and lower surfaces of the green compact 21z, which will later become the fuel electrode layer 21, without interposing a bonding agent. Next, a CIP is applied to this laminate to obtain a compacted body in which the green compact 21z and the green sheet laminate are integrated. The pressure-molded body is fired to obtain a “laminated fired body including the fuel electrode layer 21, the pair of electrolyte layers 22, and the pair of reaction preventing layers 23”.

  As a result, the CIP shrinkage amounts of the first and second green sheets 22z and 23z coincide (see FIG. 36). Therefore, a large difference is hardly generated in the amount of firing shrinkage (in a single state) of each green sheet. As a result, a tensile residual stress of the reaction preventing layer 23 is hardly generated after firing.

  In the present invention, in particular, when a green substrate having a relatively small amount of firing shrinkage such as a green compact and a plurality of green films having a relatively large amount of firing shrinkage such as a green sheet are laminated and fired, This is very effective in that cracks and peeling are not likely to occur.

  In addition, this invention is not limited to the said embodiment, A various modification can be employ | adopted within the scope of the present invention. For example, in the above embodiment, in the cell 20, the electrolyte layer 22 is formed only on the upper and lower surfaces of the fuel electrode layer 21 and is not formed on the side surfaces (four surfaces) of the fuel electrode layer 21. The fuel electrode layer 21 may be formed on the surface of the fuel electrode layer 21 so as to surround the entire periphery (upper and lower surfaces and side surfaces). Thereby, the side wall 26 can be omitted. In this case, the air flow path S and the fuel flow path 24 are partitioned only by the electrolyte layer 22.

  In the above embodiment, the fuel electrode layer 21 can be composed of platinum, platinum-zirconia cermet, platinum-cerium oxide cermet, ruthenium, ruthenium-zirconia cermet, or the like.

  The air electrode layer 24 can be composed of, for example, a perovskite complex oxide containing lanthanum (for example, lanthanum manganite, lanthanum cobaltite, lanthanum ferrite in addition to the lanthanum strontium cobalt ferrite described above). These may be doped with strontium, calcium, chromium, cobalt, iron, nickel, aluminum or the like. Further, palladium, platinum, ruthenium, platinum-zirconia cermet, palladium-zirconia cermet, ruthenium-zirconia cermet, platinum-cerium oxide cermet, palladium-cerium oxide cermet, ruthenium-cerium oxide cermet may be used.

  Moreover, in the said embodiment, although xy planar shape of the cell 20 is a rectangle, square, circle, ellipse, etc. may be sufficient. In these cases, the diameter in the case of a circle, the major axis in the case of an ellipse, and the length of one side in the case of a square are preferably 3 cm or more.

  Further, in the above embodiment, the electrolyte layer 22, the reaction preventing layer 23, and the air electrode layer 24 are formed on the upper and lower surfaces of the fuel electrode layer 21, but on either one of the upper and lower surfaces of the fuel electrode layer 21. Only the electrolyte layer 22, the reaction preventing layer 23, and the air electrode layer 24 may be formed.

  Further, in the above embodiment, the electrolyte layers 22 are directly laminated on the upper and lower surfaces of the fuel electrode layer 21, but in order to increase the reaction rate represented by the above formula (2), the fuel electrode layer 21 and the electrolyte layer. An anode active layer 29 may be interposed between the anode 22 and the anode 22. The fuel electrode active layer 29 is also a porous fired body made of Ni and YSZ, as with the fuel electrode layer 21, but the YSZ content is larger than that of the fuel electrode layer 21.

In this configuration, the anode active layer 29 is mainly used to increase the speed of the reaction expressed by the above equation (2), and the fuel electrode layer 21 is obtained by the reaction expressed by the above equation (2). It is mainly used to carry (e ⁻ ) to the conductive plate 28. The fuel electrode layer 21 is also called a fuel electrode current collecting layer or a fuel electrode substrate. That is, it can be said that the fuel electrode layer is composed of two layers of the fuel electrode current collecting layer 21 and the fuel electrode active layer 29. The thickness of the anode active layer 29 is sufficiently smaller than the thickness of the anode current collecting layer 21.

  When this configuration is manufactured, for example, as shown in FIG. 39, a third green sheet 29z that will later become the anode active layer 29 is formed on the upper surface of the first green sheet 22z in the laminate shown in FIG. The The third green sheet 29z is formed by a printing method or the like. As shown in FIG. 40, the third green sheet is exposed on the upper and lower surfaces of the green compact 21z shown in FIG. 13 without using any bonding agent or the like. The 29z plane and the upper and lower surfaces of the green compact 21z are laminated so as to face each other. This laminate is subjected to CIP to obtain a pressure-molded body, and this pressure-molded body is subjected to calcination, “a fuel electrode current collecting layer 21, a pair of fuel electrode active layers 29, and a pair of electrolyte layers 22”. And a pair of reaction preventing layers 23 are obtained ”.

  Moreover, in the said embodiment, as shown in FIGS. 23-25, the planar shape (shape seen from the z-axis direction) of the 1st, 2nd green sheets 22z and 23z is the same. That is, the planar shape (the shape seen from the z-axis direction) of the PET film A attached to the first green sheet 22z and the PET film B attached to the second green sheet 23z is the same. In addition, the two-layer green sheet laminate with PET films A and B attached to the upper and lower ends is extremely thin. Therefore, the corresponding corners in the PET films A and B are very close to each other. Only the PET film A needs to be peeled from such an extremely thin green sheet laminate.

  From the above, as shown in FIG. 24, when only one of the four corners of the PET film A is picked by a predetermined jig or the like in order to peel only the PET film A from the green sheet laminate, the PET film A There is a possibility that one of the four corners of the three layers of the first and second green sheets 22z and 23z may be picked together. That is, the situation where the PET film B is erroneously peeled off from the green sheet laminate instead of the PET film A occurs.

  In order to suppress this and reliably and easily peel only the PET film A from the green sheet laminate, for example, the adhesive force of the PET film A to the first green sheet 22z and the PET film B to the second green sheet 23z It is conceivable to make a difference in adhesive strength. For this purpose, for example, a difference is made in the characteristics of the release agent (silicon resin, etc.) coated on the PET film for the purpose of ensuring the peelability of the green sheet, and a difference is made in the surface roughness of the PET film. Such a method can be considered. However, in the former, a large difference is hardly generated in the adhesive force, and in the latter, it is difficult to manage the quality (surface roughness) of the green sheet. In particular, when the thickness of the green sheet is 10 μm or less, defects such as cracks are likely to occur after the green sheet is fired.

  Therefore, as shown in FIG. 41, the first green sheet 22z to which the first resin sheet (PET film A) having the same planar shape is adhered and the second resin sheet (PET film B) having the same planar shape are adhered to the second green sheet 22z. In the two-layer green sheet laminate laminated so as to face the green sheet 23z, the entire planar outline of the first green sheet 22z (and the first resin sheet (PET film A)) is the second green sheet. It is conceivable to provide a difference in the planar shape of the first and second green sheets 22z and 23z so as to exist inside the contour of the planar shape of 23z (and the second resin sheet (PET film B)).

  In the example shown in FIG. 41, the planar shape of the second green sheet 23z and the PET film B is the first rectangle, and the planar shape of the first green sheet 22z and the PET film A is the first rectangle on all four sides. The second rectangle exists inside the contour.

  Thereby, the corresponding corners in the PET films A and B are relatively separated from each other. Accordingly, as shown in FIG. 43, when one of the four corners of the PET film A alone is picked with a predetermined jig or the like to peel only the PET film A from the green sheet laminate, the PET film A and The possibility that one of the four corners of the three layers of the first and second green sheets 22z and 23z is picked together is very low. That is, only the PET film A can be reliably and easily peeled from the green sheet laminate.

  Only a part but not all of the planar outline of the first green sheet 22z (and the first resin sheet) is present inside the planar outline of the second green sheet 23z (and the second resin sheet). Even if a difference is made in the planar shape of the first and second green sheets 22z and 23z, the same operation and effect can be obtained. 44 and 45 show an example of this case.

  In the example shown in FIG. 44, the planar shape of the second green sheet 23z and the PET film B is the first rectangle, and the planar shape of the first green sheet 22z and the PET film A is the second of the four sides. It overlaps with the outline of one rectangle, and the remaining two sides are the second rectangle existing inside the outline of the first rectangle. In the example shown in FIG. 45, the planar shape of the second green sheet 23z and the PET film B is the first rectangle, and the planar shape of the first green sheet 22z and the PET film A is the third of the four sides. It overlaps with the outline of one rectangle, and only the remaining one side is a second rectangle existing inside the outline of the first rectangle.

  DESCRIPTION OF SYMBOLS 10 ... Fuel cell, 20 ... Cell, 21 ... Fuel electrode layer, 21z ... Compact, 22 ... Electrolyte layer, 22z ... 1st green sheet, 23 ... Reaction prevention layer, 23z ... 2nd green sheet, 24 ... Air electrode Layer, 25 ... fuel flow path, 30 ... interconnector, S ... air flow path

Claims (1)

A method for producing a laminated fired body comprising a substrate and a plurality of adjacent layers made of different materials laminated on at least one of the upper surface and the lower surface of the substrate,
A first step of forming each green sheet before firing to be each of the plurality of layers later;
A second step of laminating the formed green sheets to obtain a laminate of green sheets;
A third step of laminating the green sheet laminate without interposing a bonding agent on at least one of the upper and lower surfaces of the green molded body before firing to be the substrate later;
Pressure molding in which the green molded body and the green sheet laminated body are integrated by applying isotropic pressure to the laminated body obtained after the third step and then pressure molding the laminated body. A fourth step of obtaining a body;
A fifth step of obtaining the laminated fired body by firing the obtained pressure-molded body;
Only including,
The adjacent plural layers are two layers,
In the first step, each green sheet is formed on a resin sheet that is a sheet made of resin,
In the second step, the green sheets to which the resin sheets are attached are laminated so as to face each other to form a two-layer green sheet laminate, on both ends in the thickness direction of the two-layer green sheet laminate. By removing only one of the two resin sheets adhering to each other, the green sheet laminate with the resin sheet adhering only to one end in the thickness direction is obtained,
In the third step, the green molded body is formed such that a plane of the green sheet laminate exposed by removing the one resin sheet and at least one of an upper surface and a lower surface of the green molded body face each other. And the green sheet laminate are laminated,
In the fourth step, a method for producing a laminated fired body , wherein a laminate having the resin sheet attached to one end side in the thickness direction obtained after the third step is subjected to the pressure molding .

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