Seal structures and electrochemical reaction cell stacks

Abstract

This design achieves both the maintenance of gas sealing properties through the glass seal portion and the suppression of elemental volatilization from the surface of the sealing member. [Solution] The seal structure comprises a first member to be joined, a second member to be joined, and a glass seal portion interposed between the first member to be joined and the second member to be joined, wherein the glass seal portion includes crystallized glass and has a surface region which is the area from the non-joining surface that does not come into contact with the first member to be joined and the second member to be joined to a depth of 10 μm, and a non-surface region which is the remaining area excluding the surface region, wherein the crystallinity of the surface region is higher than the crystallinity of the non-surface region.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a seal structure and an electrochemical reaction cell stack.

Background Art

[0002] As one type of fuel cell that generates electricity by utilizing the electrochemical reaction between hydrogen and oxygen, a solid oxide fuel cell (hereinafter referred to as "SOFC") including an electrolyte layer containing a solid oxide is known. SOFCs are generally used in the form of a fuel cell stack in which a plurality of constituent units (electrochemical reaction units) are arranged side by side in a predetermined direction. In order to connect two constituent units provided in the fuel cell stack, a glass part (glass seal part) is used (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above SOFC, it is required to achieve both the retention of gas sealing performance by the glass seal part and the suppression of the volatilization of elements from the surface of the seal member.

[0005]

Means for Solving the Problems

[0006] The technologies disclosed herein can be implemented, for example, in the following forms: (1) A seal structure disclosed herein comprises a first member to be joined, a second member to be joined, and a glass seal portion interposed between the first member to be joined and the second member to be joined, wherein the glass seal portion includes crystallized glass and has a surface region which is a region from the non-joining surface that does not contact the first member to be joined and the second member to a depth of 10 μm, and a non-surface region which is the remaining region excluding the surface region, wherein the degree of crystallinity of the surface region is higher than the degree of crystallinity of the non-surface region.

[0007] According to the above configuration, it is possible to achieve both the maintenance of gas sealing properties by the glass seal portion and the suppression of elemental volatilization from the surface of the glass seal portion.

[0008] (2) In the seal structure described in (1) above, the value obtained by dividing the crystallinity of the surface region by the crystallinity of the non-surface region may be 1.1 or greater.

[0009] This configuration allows for both maintaining gas sealing properties through the glass seal and suppressing elemental volatilization from the surface of the glass seal.

[0010] (3) In the seal structure described in (1) or (2) above, the degree of crystallinity of the surface region may be 45% or more.

[0011] With this configuration, the volatilization of elements contained in the glass seal from the non-bonding surface is further reduced.

[0012] (4) The seal structure described in any one of (1) to (3) above includes rod-shaped particles in an orientation adjustment region which is the region from the non-bonding surface to a depth of 80 μm, and the average orientation angle of the rod-shaped particles with respect to the non-bonding surface may be 45° or more and 90° or less.

[0013] This configuration reduces the propagation of cracks that occur in the glass seal.

[0014] (5) The electrochemical reaction cell stack disclosed in this specification includes the sealing structure described in any one of (1) to (4) above.

[0015] According to such a configuration, the generation of cracks in the glass seal portion is reduced.

[0016] The technology disclosed in this specification can be realized in various forms. For example, it can be realized in the form of an electrochemical reaction cell stack and its manufacturing method, etc.

Brief Description of the Drawings

[0017] [Figure 1] Perspective view showing the external configuration of the fuel cell stack of the embodiment [Figure 2] Cross-sectional view showing the fuel cell stack of the embodiment cut along the line II-II in FIG. 1 [Figure 3] Cross-sectional view showing the fuel cell stack of the embodiment cut along the line III-III in FIG. 1 [Figure 4] Cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the embodiment cut at the same position as the line II-II in FIG. 1 [Figure 5] Cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the embodiment cut at the same position as the line III-III in FIG. 1 [Figure 6] View showing an enlarged view of the inside of the frame F1 in FIG. 5 [Figure 7] View showing an enlarged view of the inside of the circle R1 in FIG. 6 [Figure 8] View showing an enlarged view of the inside of the frame F2 in FIG. 5 [Figure 9] View showing an enlarged view of the inside of the circle R2 in FIG. 8

Modes for Carrying Out the Invention

[0018] A. Embodiment: Embodiments will be described with reference to FIGS. 1 to 9. The fuel cell stack 10 (an example of an electrochemical reaction cell stack) of the present embodiment is used in a solid oxide type fuel cell including an electrolyte layer 112 containing a solid oxide.

[0019] (Overall configuration of fuel cell stack 10) As shown in FIGS. 1 to 3, the fuel cell stack 10 includes a power generation block 100, a terminal separator 230, a first plate 232, a second plate 260, a first terminal plate 240, a second terminal plate 250, an insulating portion 220, a first end plate 210, a second end plate 270, and four gas passage members 280. The first end plate 210, the insulating portion 220, the terminal separator 230, the first terminal plate 240, the power generation block 100, the second terminal plate 250, the second plate 260, and the second end plate 270 have substantially the same rectangular outer shape and are arranged to overlap in this order in a predetermined arrangement direction (the vertical direction in FIG. 2).

[0020] As shown in FIG. 1, the fuel cell stack 10 has bolt holes BH penetrating from the first end plate 210 to the second end plate 270 near each of the four corners. Bolts B are inserted into each bolt hole BH. Nuts N are screwed to both ends of each bolt B. These bolts B and nuts N integrally fasten the members from the first end plate 210 to the second end plate 270. As shown in FIGS. 2 and 3, the first plate 232 is supported by the terminal separator 230, and the four gas passage members 280 are connected to the second end plate 270.

[0021] As shown in FIGS. 2 and 3, the power generation block 100 is composed of a plurality (seven in the present embodiment) of electrochemical reaction units 100U (hereinafter sometimes abbreviated as "reaction units 100U") arranged side by side in a predetermined arrangement direction (the vertical direction in FIG. 2).

[0022] (Overall configuration of electrochemical reaction unit 100U) As shown in Figures 4 and 5, the electrochemical reaction unit 100U comprises a single cell 110, a single cell separator 120, an air electrode frame 130, a fuel electrode frame 140, a fuel electrode current collector 144, two interconnectors 190, two IC separators 180, a first glass seal portion 135, and a second glass seal portion 125. One IC separator 180, the air electrode frame 130, the single cell separator 120, the fuel electrode frame 140, and the other IC separator 180 are arranged in this order. The single cell 110 is supported by the single cell separator 120, the two interconnectors 190 are each supported by the two IC separators 180, and the fuel electrode current collector 144 is positioned between the single cell 110 and the interconnectors 190.

[0023] As shown in Figures 4 and 5, the IC separator 180 and interconnector 190 are shared by two adjacent reaction units 100U. However, as shown in Figure 2, one of the multiple reaction units 100U located at one end (the lower end in Figure 2) does not have an IC separator 180 and interconnector 190 adjacent to the fuel electrode frame 140, and the second terminal plate 250 is superimposed on the fuel electrode frame 140.

[0024] (Single cell 110) The single cell 110 comprises an electrolyte layer 112, an air electrode 114, and a fuel electrode 116. As shown in Figures 4 and 5, the air electrode 114, the electrolyte layer 112, and the fuel electrode 116 are arranged in this order, with a reaction prevention layer 118 interposed between the electrolyte layer 112 and the air electrode 114. The single cell 110 of this embodiment is a fuel electrode-supported single cell in which the other layers constituting the single cell 110 (electrolyte layer 112, air electrode 114, and reaction prevention layer 118) are supported by the fuel electrode 116.

[0025] The electrolyte layer 112 is a rectangular, flat member having one surface on which the air electrode 114 is located (the upper surface in Figures 4 and 5) and another surface parallel to the air electrode 116 (the lower surface in Figures 4 and 5). The electrolyte layer 112 is a layer containing a solid oxide (e.g., YSZ (yttria-stabilized zirconia)). The air electrode 114 is a layer having a rectangular shape smaller than the electrolyte layer 112 and contains, for example, a perovskite-type oxide (e.g., LSCF (lanthanum strontium cobalt iron oxide)). The fuel electrode 116 is a layer having a rectangular shape approximately the same size as the electrolyte layer 112 and contains, for example, Ni (nickel), a cermet made of Ni and ceramic particles, a Ni-based alloy, etc. The reaction prevention layer 118 is a layer having a rectangular shape approximately the same size as the air electrode 114 and contains, for example, GDC (gadolinium-doped ceria). The reaction prevention layer 118 has the function of suppressing the reaction of elements (e.g., Sr) diffused from the air electrode 114 with elements (e.g., Zr) contained in the electrolyte layer 112 to produce a highly resistive substance (e.g., SrZrO3).

[0026] (Single-cell separator 120) As shown in Figures 4 and 5, the single-cell separator 120 is a rectangular frame-shaped member having a roughly rectangular through-hole 121 near its center. The single-cell separator 120 is conductive and made of a metal such as ferritic stainless steel. The thickness of the single-cell separator 120 is, for example, 0.05 mm or more and 0.2 mm or less. The periphery of the through-hole 121 in the single-cell separator 120 is joined to the periphery of one surface of the electrolyte layer 112 (the surface on which the air electrode 114 is placed: the upper surface in Figures 4 and 5) by a joint 124. The joint 124 is made of, for example, brazing material (Ag brazing).

[0027] (Second glass seal portion 125) The second glass seal portion 125 is positioned on the single cell 110 and covers the edge of the through hole 121 in the single cell separator 120 and its surrounding area. The second glass seal portion 125 is made of crystallized glass. The second glass seal portion 125 may be made of, for example, SiO2-B2O3-MgO glass. The second glass seal portion 125 seals the gap between the single cell 110 and the single cell separator 120, effectively suppressing gas leakage (cross-leakage) from the air electrode 114 side to the fuel electrode 116 side, or from the fuel electrode 116 side to the air electrode 114 side.

[0028] (Air pole frame 130) As shown in Figures 4 and 5, the air electrode frame 130 is a rectangular frame-shaped member having a substantially rectangular through-hole 131 near the center, and is formed of, for example, an insulating ceramic (such as mica). The thickness of the air electrode frame 130 is, for example, 0.5 mm to 5 mm. The air electrode frame 130 has two sealing holes 132 located on both sides of the through-hole 131.

[0029] (First glass seal portion 135) Each air electrode frame 130 has two seal holes 132, each containing one first glass seal portion 135. The first glass seal portion 135 is a cylindrical member with openings at both ends. The first glass seal portion 135 is made of crystallized glass. The first glass seal portion 135 may be made of, for example, SiO2-B2O3-MgO glass. One end of the first glass seal portion 135 is joined to the single-cell separator 120, and the other end is joined to the IC separator 180.

[0030] (Fuel pole frame 140) As shown in Figure 5, the fuel electrode frame 140 is a rectangular frame-shaped member having a roughly rectangular through-hole 141 near its center. The fuel electrode frame 140 is conductive and is made of a metal such as ferritic stainless steel.

[0031] (IC separator 180) As shown in Figures 4 and 5, the IC separator 180 is a rectangular frame-shaped member having a through hole 181 near the center. The IC separator 180 is conductive and is made of a metal such as ferritic stainless steel. The thickness of the IC separator 180 is, for example, 0.05 mm or more and 0.2 mm or less.

[0032] (Interconnector 190, and fuel electrode current collector 144) As shown in Figures 4 and 5, the interconnector 190 comprises a rectangular flat plate portion 191, a plurality of plate-shaped air electrode current collector portions 192 protruding from one surface of the flat plate portion 191 toward the air electrode 114, and a coating layer 193. The flat plate portion 191 and the air electrode current collector portions 192 are conductive and are made of a metal such as ferritic stainless steel. The coating layer 193 is conductive and is made of a spinel-type oxide, for example. The coating layer 193 is arranged to cover the surface of the air electrode current collector portions 192 and the surface of the flat plate portion 191 on which the air electrode current collector portions 192 are arranged. The flat plate portion 191 is joined to the periphery of the through hole 181 in the IC separator 180, for example, by welding.

[0033] The fuel electrode current collector 144 is a member that connects the interconnector 190 and the fuel electrode 116, and is formed of a conductive material such as nickel, a nickel alloy, or stainless steel. As shown in Figures 4 and 5, the fuel electrode current collector 144 comprises an interconnector-facing portion 146, an electrode-facing portion 145 parallel to the interconnector-facing portion 146, and a connecting portion 147 connecting the electrode-facing portion 145 and the interconnector-facing portion 146, and is U-shaped overall. The electrode-facing portion 145 is in contact with the fuel electrode 116, and the interconnector-facing portion 146 is in contact with the flat plate portion 191 of the interconnector 190.

[0034] As described above, the interconnector 190 is shared by two adjacent reaction units 100U. More specifically, as shown in Figures 4 and 5, the air electrode current collector 192 is joined to the air electrode 114 of a single cell 110 provided in one of the two adjacent reaction units 100U via a conductive bonding material 196 made of, for example, a spinel-type oxide, thereby electrically connecting to the air electrode 114. The flat plate portion 191 is electrically connected to the fuel electrode 116 of a single cell 110 provided in the other of the two adjacent reaction units 100U via a fuel electrode current collector 144. This ensures electrical conductivity between the two adjacent reaction units 100U.

[0035] However, as described above, the reaction unit 100U located at one end (the lower end of Figure 2) of the multiple reaction units 100U does not have an interconnector 190 on the fuel electrode 116 side. The fuel electrode 116 provided in this reaction unit 100U is connected to the second terminal plate 250 via a fuel electrode current collector 144.

[0036] A spacer 149, for example made of mica, is placed between the electrode facing portion 145 and the interconnect facing portion 146. As a result, the fuel electrode current collector 144 follows the deformation of the reaction unit 100U due to temperature cycles and reaction gas pressure fluctuations, and the electrical connection between the fuel electrode 116 and the interconnect 190 (or second terminal plate 250) via the fuel electrode current collector 144 is maintained well.

[0037] (Air chamber 313 and fuel chamber 323) As shown in Figures 4 and 5, the space partitioned by the single-cell separator 120 and single cell 110, the air electrode frame 130, the IC separator 180 and interconnector 190 faces the air electrode 114 and forms an air chamber 313 through which the oxidizer gas OG flows. The air electrode frame 130 partitions the air chamber 313 from the outside space around its entire circumference and seals the space between the single-cell separator 120 and the IC separator 180, preventing gas from leaking from the air chamber 313 into the outside space.

[0038] Furthermore, the space partitioned by the single-cell separator 120 and single cell 110, the fuel electrode frame 140, the IC separator 180 and interconnector 190 faces the fuel electrode 116 and forms a fuel chamber 323 through which fuel gas FG flows. The fuel electrode frame 140 partitions the fuel chamber 323 from the outside space around its entire circumference and seals the space between the single-cell separator 120 and the IC separator 180, preventing gas from leaking from the fuel chamber 323 into the outside space.

[0039] The single-cell separator 120 separates the air chamber 313 from the fuel chamber 323, suppressing gas leakage (cross-leakage) from the air electrode 114 to the fuel electrode 116, or from the fuel electrode 116 to the air electrode 114, around the single-cell 110. In addition, the IC separator 180 and interconnector 190 suppress gas leakage between adjacent reaction units 100U.

[0040] (First end plate 210) The first end plate 210 is a member formed by press-forming (bending) a single plate-shaped member. The first end plate 210 is made of a metal such as ferritic stainless steel. The thickness of the first end plate 210 is, for example, 0.5 mm or more and 3 mm or less. As shown in Figures 1-3, the first end plate 210 comprises a rectangular frame-shaped planar portion 211 having a through hole 212 near the center, and an outer projection 213 and an inner projection 214 that protrude from the planar portion 211 in the opposite direction to the insulating portion 220 (upwards in Figure 2). The planar portion 211 has holes that constitute the bolt holes BH described above. The outer projection 213 protrudes from the outer peripheral edge of the planar portion 211. The outer projection 213 is arranged around the entire circumference of the outer peripheral portion of the planar portion 211. The inner projection 214 protrudes from the inner peripheral edge of the planar portion 211. The inner protrusion 214 is arranged around the entire circumference of the inner part of the flat part 211.

[0041] (Insulation part 220) The insulating portion 220 is a rectangular frame-shaped member with a through hole near the center, and is made of an insulating material. As shown in Figures 2 and 3, the insulating portion 220 is sandwiched between the first end plate 210 and the end separator 230, thereby ensuring insulation between the first end plate 210 and the end separator 230.

[0042] (End separator 230) As shown in Figures 2 and 3, the end separator 230 is a rectangular frame-shaped member having a through hole 231 near its center. The end separator 230 is conductive and is made of a metal such as ferritic stainless steel.

[0043] (Plate 1, No. 232) The first plate 232 is a rectangular, flat member. The first plate 232 is conductive and is made of a metal such as ferritic stainless steel. As shown in Figures 2 and 3, the first plate 232 is joined to the peripheral portion of the through hole 231 in the end separator 230, for example, by welding. The end separator 230 and the first plate 232 separate the power generation block 100 from the external space of the fuel cell stack 10.

[0044] The first plate 232 is connected to an interconnector 190 provided on a reaction unit 100U located at the other end (upper end in Figure 2) of the multiple reaction units 100U that constitute the power generation block 100, via a connecting member with the same structure as the fuel electrode current collector 144. In this way, the reaction unit 100U and the first plate 232 are electrically connected.

[0045] (Terminal 1 Plate 240) As shown in Figures 2 and 3, the first terminal plate 240 is a rectangular frame-shaped member having a through hole 241 near its center. The first terminal plate 240 is conductive and made of a metal such as ferritic stainless steel. The thickness of the first terminal plate 240 is, for example, 0.2 mm or more and 3 mm or less. The first terminal plate 240 is electrically connected to the reaction unit 100U located at the other end (upper end in Figure 2) of the multiple reaction units 100U that constitute the power generation block 100, via the first plate 232 and the end separator 230. One end of the first terminal plate 240 (right end in Figure 2) protrudes laterally from the power generation block 100, and this protruding portion functions as the positive output terminal of the fuel cell stack 10.

[0046] (Terminal 2 Plate 250) The second terminal plate 250 is a rectangular plate-shaped member. The second terminal plate 250 is conductive and is made of a metal such as ferritic stainless steel. The thickness of the second terminal plate 250 is, for example, 0.2 mm or more and 3 mm or less. As described above, the second terminal plate 250 is connected to the fuel electrode 116 provided on the reaction unit 100U located at one end (the lower end in Figure 2) of the plurality of reaction units 100U via the fuel electrode current collector 144, thereby electrically connecting this reaction unit 100U and the second terminal plate 250. One end of the second terminal plate 250 (the right end in Figure 2) protrudes laterally from the power generation block 100, and this protruding portion functions as the negative output terminal of the fuel cell stack 10.

[0047] (Plate 2, page 260) The second plate 260 is a rectangular, flat member made of an insulating material. As shown in Figures 2 and 3, the peripheral edge of the second plate 260 is sandwiched between the second terminal plate 250 and the second end plate 270, thereby ensuring insulation between the second terminal plate 250 and the second end plate 270.

[0048] (Second end plate 270) The second end plate 270 is a component formed by press-forming (bending) a single plate-shaped member. The second end plate 270 is made of a metal such as ferritic stainless steel. The thickness of the second end plate 270 is, for example, 0.5 mm or more and 3 mm or less. As shown in Figures 2 and 3, the second end plate 270 comprises a rectangular frame-shaped planar portion 271 having a through hole 272 near the center, and an outer projection 273 and an inner projection 274 projecting from the planar portion 271 in the opposite direction from the second terminal plate 250 (downward in Figure 2). The outer projection 273 protrudes from the outer peripheral edge of the planar portion 271. The outer projection 273 is arranged around the entire circumference of the outer peripheral portion of the planar portion 271. The inner projection 274 protrudes from the inner peripheral edge of the planar portion 271. The inner projection 274 is arranged around the entire circumference of the inner peripheral portion of the planar portion 271.

[0049] (Manifolds 311, 312, 321, 322) As shown in Figures 1-3, the fuel cell stack 10 has four holes that penetrate from the power generation block 100 to the second end plate 270. The four holes are the oxidizer gas supply manifold 311, the oxidizer gas discharge manifold 312, the fuel gas supply manifold 321, and the fuel gas discharge manifold 322, respectively.

[0050] As shown in Figure 2, the oxidizer gas supply manifold 311 is a gas flow path that supplies oxidizer gas OG, introduced from outside the fuel cell stack 10, to the air chamber 313 of each reaction unit 100U. The oxidizer gas discharge manifold 312 is a gas flow path that discharges oxidizer off-gas OOG, discharged from the air chamber 313 of each reaction unit 100U, to the outside of the fuel cell stack 10. For example, air is used as the oxidizer gas OG.

[0051] As shown in Figure 3, the fuel gas supply manifold 321 is a gas passage that supplies fuel gas FG introduced from outside the fuel cell stack 10 to the fuel chamber 323 of each reaction unit 100U. The fuel gas discharge manifold 322 is a gas passage that discharges fuel off-gas FOG discharged from the fuel chamber 323 of each reaction unit 100U to the outside of the fuel cell stack 10. As the fuel gas FG, for example, hydrogen-rich gas obtained by reforming city gas is used.

[0052] As shown in Figure 5, the fuel gas supply manifold 321 penetrates one of the two first glass seal portions 135 located inside each air electrode frame 130. In other words, the internal space of the first glass seal portion 135 is part of the fuel gas supply manifold 321. Similarly, the fuel gas exhaust manifold 322 penetrates the other of the two first glass seal portions 135 located inside each air electrode frame 130. In other words, the internal space of the first glass seal portion 135 is part of the fuel gas exhaust manifold 322. The first glass seal portions 135 suppress leakage of fuel gas FG or fuel off-gas FOG from the fuel gas supply manifold 321 and the fuel gas exhaust manifold 322 through the interface between the air electrode frame 130 and the single-cell separator 120, and the interface between the air electrode frame 130 and the IC separator 180.

[0053] (Gas passage member 280) Each of the four gas passage members 280 comprises a main body portion 281 and a flange portion 282, as shown in Figures 1-3. The main body portion 281 is cylindrical with open ends. The flange portion 282 is provided so as to protrude outward from one end of the main body portion 281 (the lower end in Figure 2). The flange portion 282 has a plurality of bolt holes 284. Bolts (not shown) for connecting the fuel cell stack 10 to an external device are inserted into each bolt hole 284. The other end of the main body portion 281 provided on the four gas passage members 280 (the upper end in Figures 2 and 3) is joined to the second end plate 270, for example by welding, and the internal space of the main body portion 281 communicates with the manifolds 311, 312, 321, and 322, respectively. Gas piping for gas supply or discharge is connected to each main body portion 281.

[0054] (Details of the first glass seal section 135) As shown in Figure 6, the first glass seal portion 135 is interposed between the single-cell separator 120 and the IC separator 180. One end of the first glass seal portion 135 is joined to the IC separator 180, and the other end is joined to the single-cell separator 120. The seal structure 410 is composed of the single-cell separator 120, the IC separator 180, and the first glass seal portion 135. The IC separator 180 is an example of a first joining target member, the single-cell separator 120 is an example of a second joining target member, and the first glass seal portion 135 is an example of a glass seal portion.

[0055] The first glass seal portion 135 has a first bonding surface 135S1, a second bonding surface 135S2, a first non-bonding surface 135S3 (an example of a non-bonding surface), and a second non-bonding surface 135S4 (an example of a non-bonding surface). The first bonding surface 135S1 is the surface that contacts the IC separator 180. The second bonding surface 135S2 is the surface that contacts the single-cell separator 120. In this embodiment, the first bonding surface 135S1 and the second bonding surface 135S2 are surfaces that are parallel to each other. The first non-bonding surface 135S3 and the second non-bonding surface 135S4 extend at an angle from the first bonding surface 135S1 and are surfaces that do not contact either the single-cell separator 120 or the IC separator 180. In this embodiment, the first non-bonding surface 135S3 is the outer circumferential surface of the first glass seal portion 135, and the second non-bonding surface 135S4 is the inner circumferential surface of the first glass seal portion 135. The non-bonding surfaces 135S3 and 135S4 are perpendicular to the first bonding surface 135S1 and the second bonding surface 135S2.

[0056] The first glass seal portion 135 has a first surface region As1 (an example of a surface region), a second surface region As2 (an example of a surface region), and a first non-surface region Ai1 (an example of a non-surface region). The first surface region As1 includes the first non-bonding surface 135S3 and is the region from the first non-bonding surface 135S3 to a depth of 10 μm. The second surface region As2 includes the second non-bonding surface 135S4 and is the region from the second non-bonding surface 135S4 to a depth of 10 μm. The first non-surface region Ai1 is the remaining region excluding the first surface region As1 and the second surface region As2.

[0057] The crystallinity of the first surface region As1 is higher than that of the first non-surface region Ai1. The value obtained by dividing the crystallinity of the first surface region As1 by the crystallinity of the first non-surface region Ai1 may be 1.1 or greater, or 1.2 or greater.

[0058] The crystallinity of the first surface region As1 may be 45% or more, or 50% or more. The crystallinity of the first surface region As1 may be 90% or less. The crystallinity of the first non-surface region Ai1 may be 15% to 80%, or 25% to 70%.

[0059] The degree of crystallinity of the first surface region As1 is determined as follows.

[0060] The first glass seal portion 135 is cut perpendicular to the first bonding surface 135S1, and one location of the first surface region As1 of the cross-section is imaged using a scanning electron microscope (SEM) at a magnification of 3000x and an observation range of 50 μm × 40 μm to obtain an SEM image. In the obtained SEM image, crystals are represented in light gray, amorphous regions in dark gray, and pores in black.

[0061] The obtained SEM images are analyzed using image analysis software (e.g., ImageJ). In the image analysis, first, the SEM images are binarized by setting a threshold between light gray and dark gray. In the binarized image, crystals are represented in white, and amorphous materials and pores are represented in black. The ratio Rw (%) of the area Aw of the white region within the observation range to the total area A0 of the observation range in the binarized image is calculated using the following formula (1). Next, the SEM images are binarized by setting a threshold between dark gray and black. In the binarized image, crystals and amorphous materials are represented in white, and pores are represented in black. The ratio Ab of the area of ​​the black region within the observation range to the total area A0 of the observation range in the binarized image is calculated using the following formula (2), and this is taken as the porosity Rp (%) of that observation range. From the calculated ratio Rw and porosity Rp, the crystallinity Rc (%) of that observation range is calculated using the following formula (3).

[0062] Rw = (Aw / A0) × 100 ... (1) Rp = (Ab / A0) × 100 ... (2) Rc={Rw / (100-Rp)}×100...(3)

[0063] The same process is performed on the other two locations in the first surface region As1 to calculate the degree of crystallinity Rc. The average value of the Rc data from the three locations is calculated and used as the degree of crystallinity of the first surface region As1.

[0064] The crystallinity of the first non-surface region Ai1 is determined in the same manner as the crystallinity of the first surface region As1 described above.

[0065] Similarly, the crystallinity of the second surface region As2 is higher than that of the first non-surface region Ai1. The value obtained by dividing the crystallinity of the second surface region As2 by the crystallinity of the first non-surface region Ai1 may be 1.1 or greater, or 1.2 or greater. The crystallinity of the second surface region As2 may be 45% or greater, or 50% or greater. The crystallinity of the second surface region As2 may be 90% or less. The crystallinity of the first non-surface region Ai1 may be 15% to 80%, or 25% to 70%. The crystallinity of the second surface region As2 is determined in the same manner as the crystallinity of the first surface region As1 described above.

[0066] The first glass seal portion 135 has a first orientation adjustment region Ao1 (an example of an orientation adjustment region) and a second orientation adjustment region Ao2 (an example of an orientation adjustment region). The first orientation adjustment region Ao1 includes the first non-bonding surface 135S3 and is a region from the first non-bonding surface 135S3 to a depth of 80 μm. The second orientation adjustment region Ao2 includes the second non-bonding surface 135S4 and is a region from the second non-bonding surface 135S4 to a depth of 80 μm.

[0067] The first orientation adjustment region Ao1 includes rod-shaped particles 136, as shown in Figure 7. The rod-shaped particles 136 are crystalline glass particles. The average aspect ratio of the rod-shaped particles 136 included in the first orientation adjustment region Ao1 may be 1.1 or greater, and may be 3 or greater. The average orientation angle of the rod-shaped particles 136 included in the first orientation adjustment region Ao1 with respect to the first non-bonding surface 135S3 may be 45° or greater and 90° or less.

[0068] The average aspect ratio and average orientation angle of the rod-shaped particles 136 contained in the first orientation adjustment region Ao1 are determined as follows. The cross section obtained by cutting the first glass seal portion 135 perpendicular to the first bonding surface 135S1 is photographed using an SEM (scanning electron microscope) so as to include the first non-bonding surface 135S3, and an SEM image is obtained. The first orientation adjustment region Ao1 appearing in the obtained SEM image is divided into three equal parts along the first non-bonding surface 135S3, as shown in Figure 6, and three divided regions Ao11, Ao12, and Ao13 are set. Ten rod-shaped particles 136 are randomly selected from each of the three divided regions Ao11, Ao12, and Ao13, for a total of 30 rod-shaped particles 136. For each of the selected rod-shaped particles 136, the maximum ferret diameter Dmax and the minimum ferret diameter Dmin are determined. As shown in Figure 7, the maximum ferret diameter Dmax of a certain rod-shaped particle 136 is the value of the distance between two parallel lines that maximize the distance when the contour line of the rod-shaped particle 136 appearing in the SEM image is enclosed by those two parallel lines. The minimum ferret diameter Dmin of a certain rod-shaped particle 136 is the value of the distance between two parallel lines that minimize the distance when the contour line of the rod-shaped particle 136 appearing in the SEM image is enclosed by those two parallel lines. The value obtained by dividing the maximum ferret diameter Dmax by the minimum ferret diameter Dmin (Dmax / Dmin) is the aspect ratio of the rod-shaped particle 136. Furthermore, when a straight line Lc parallel to the two parallel lines used to determine the minimum ferret diameter Dmin is set at the midpoint of these two parallel lines, the angle θ1 between that straight line Lc and the line indicating the first non-joint surface 135S3 appearing in the SEM image is the orientation angle of the rod-shaped particle 136. The average aspect ratio of 30 rod-shaped particles (136) is calculated and set as the average aspect ratio. The average orientation angle of 30 rod-shaped particles (136) is calculated and set as the average orientation angle.

[0069] Similarly, the second orientation adjustment region Ao2 includes rod-shaped particles 136. The average aspect ratio of the rod-shaped particles 136 included in the second orientation adjustment region Ao2 may be 1.1 or greater, or 3 or greater. The average orientation angle of the rod-shaped particles 136 included in the second orientation adjustment region Ao2 with respect to the second non-bonding surface 135S4 may be 45° or greater and 90° or less. The average aspect ratio and average orientation angle of the rod-shaped particles 136 included in the second orientation adjustment region Ao2 are determined in the same manner as the average aspect ratio and average orientation angle of the rod-shaped particles 136 included in the first orientation adjustment region Ao1 described above.

[0070] (Details of the second glass seal section 125) As shown in Figure 8, the second glass seal portion 125 is interposed between the single cell 110 and the single cell separator 120, joining them together. The second glass seal portion 125 is arranged in a frame shape on the surface of the electrolyte layer 112, along the edge of the through hole 121 in the single cell separator 120. The peripheral portion of the single cell separator 120 around the through hole 121 is embedded in the second glass seal portion 125 over its entire circumference. The seal structure 420 is composed of the single cell 110, the single cell separator 120, and the second glass seal portion 125. The single cell 110 is an example of a first joining target member, the single cell separator 120 is an example of a second joining target member, and the second glass seal portion 125 is an example of a glass seal portion.

[0071] The second glass seal portion 125 has a third bonding surface 125S1 and a third non-bonding surface 125S2 (an example of a non-bonding surface). The third bonding surface 125S1 is the surface that contacts the electrolyte layer 112. The third non-bonding surface 125S2 extends at an angle from the third bonding surface 125S1 and is a surface that does not contact either the single cell 110 or the single cell separator 120.

[0072] The second glass seal portion 125 has a third surface region As3 (an example of a surface region) and a second non-surface region Ai2 (an example of a non-surface region). The third surface region As3 (an example of a surface region) includes the third non-bonding surface 125S2 and is the region from the third non-bonding surface 125S2 to a depth of 10 μm. The second non-surface region Ai2 is the remaining region excluding the third surface region As3.

[0073] Similar to the first glass seal portion 135, the crystallinity of the third surface region As3 is higher than that of the second non-surface region Ai2. The value obtained by dividing the crystallinity of the third surface region As3 by the crystallinity of the second non-surface region Ai2 may be 1.1 or greater, or 1.2 or greater. The crystallinity of the third surface region As3 may be 45% or greater, or 50% or greater. The crystallinity of the third surface region As3 may be 90% or less. The crystallinity of the second non-surface region Ai2 may be 15% or greater and 80% or less, or 25% or greater and 70% or less. The crystallinity of the third surface region As3 and the crystallinity of the second non-surface region Ai2 are determined in the same manner as the crystallinity of the first surface region As1 described above.

[0074] The second glass seal portion 125 has a third orientation adjustment region Ao3 (an example of an orientation adjustment region). The third orientation adjustment region Ao3 includes the third non-bonding surface 125S2 and is a region from the third non-bonding surface 125S2 to a depth of 80 μm.

[0075] The third orientation adjustment region Ao3 contains rod-shaped particles 126. The rod-shaped particles 126 are crystalline glass particles. The average aspect ratio of the rod-shaped particles 126 contained in the third orientation adjustment region Ao3 may be 1.1 or greater, and may be 3 or greater. The average orientation angle of the rod-shaped particles 126 contained in the third orientation adjustment region Ao3 with respect to the third non-bonding surface 125S2 may be 45° or greater and 90° or less. The average aspect ratio and average orientation angle of the rod-shaped particles 126 contained in the third orientation adjustment region Ao3 are determined in the same manner as the average aspect ratio and average orientation angle of the rod-shaped particles 136 contained in the first orientation adjustment region Ao1 described above. As shown in Figure 9, in the second glass seal portion 125, the line indicating the third non-bonding surface 125S2 that appears in the SEM image is not a straight line. In such cases, the orientation angle of the rod-shaped particle 126 can be defined as the angle θ2 formed by a straight line Lc, which is set in the center of the two parallel lines used to determine the minimum Ferret diameter Dmin, and the tangent line Lt to the line indicating the third non-joint surface 125S2 at the intersection P of the third non-joint surface 125S2 and the straight line Lc.

[0076] (Manufacturing method for fuel cell stack 10) An example of a manufacturing method for the fuel cell stack 10 with the above configuration is described below.

[0077] Glass raw material powder is press-molded, and the resulting molded body is calcined at a temperature below the crystallization temperature of glass to obtain a cylindrical calcined glass body.

[0078] Glass paste is prepared by mixing glass raw material powder, binder, and solvent. Single cells 110 are placed around the through holes 121 in the single cell separator 120. Glass paste is applied to the electrolyte layer 112 by screen printing so as to overlap with the edges of the through holes 121.

[0079] An air electrode frame 130 is placed on top of a single-cell separator 120, and a glass calcined body is placed inside each of the two seal holes 132. An IC separator 180 is placed on top of the air electrode frame 130, and then the other components constituting the fuel cell stack 10 are stacked in order to assemble the fuel cell stack 10. The assembled fuel cell stack 10 is placed in a firing furnace and heated at the glass softening temperature to melt the glass calcined body and glass paste, and then heat-treated at a heat treatment temperature higher than the operating temperature. The softening temperature can be any temperature above the temperature at which glass softening begins, for example, 700°C. The heat treatment temperature can be any temperature above the temperature at which glass crystallization begins, for example, 850°C or higher. Through this heat treatment, the glass contained in the glass calcined body crystallizes, forming a first glass seal portion 135. The first glass seal portion 135 joins the adjacent single-cell separator 120 and IC separator 180. Furthermore, the glass contained in the glass paste crystallizes, forming a second glass seal portion 125. The second glass seal portion 125 joins the single cell 110 and the single cell separator 120.

[0080] The degree of crystallinity of the first glass seal portion 135 can be adjusted by adjusting the particle size of the raw material powder. Glass has the characteristic of crystallizing easily from the part that is exposed to air. Since the surface of the glass raw material powder is in contact with air inside the calcined body, the smaller the surface area of ​​the glass raw material powder, the less likely crystallinity is to proceed. If the particle size of the glass raw material powder is large, the surface area per unit volume is smaller compared to the case where the particle size is small, so crystallinity is less likely to proceed inside the glass calcined body, and the degree of crystallinity of the surface of the resulting first glass seal portion 135 is relatively higher. Alternatively, the degree of crystallinity of the first glass seal portion 135 can be adjusted by adjusting the temperature profile during heat treatment. For example, the temperature profile near the crystallinity temperature of glass may be adjusted so that crystallinity proceeds rapidly. This makes it possible to make the degree of crystallinity of the surface, which is relatively more likely to crystallize, higher than the degree of crystallinity of the interior. Alternatively, seed crystal particles of glass may be attached to the surface of the glass calcined body before heat treatment. The seed crystal particles may be, for example, particles containing at least one element from Ba, Ca, Mg, Al, La, Ti, Cr, Zr, Ce, and B, or an oxide of at least one of these elements. This promotes the progression of crystallization on the surface, resulting in a relatively higher degree of crystallinity on the surface. The same applies to the second glass seal portion 125.

[0081] Before heat treatment, the orientation angle of the rod-shaped particles 136 in orientation adjustment regions Ao1 and Ao2 can be adjusted by attaching rod-shaped seed crystal particles to the surface of the glass calcined body. For example, a seed crystal paste containing rod-shaped seed crystal particles may be applied to the outer and inner surfaces of the glass calcined body by screen printing. In this case, by reducing the size of the opening of the screen used for printing to the limit that the seed crystal particles can pass through, the orientation angle of the seed crystal particles with respect to the coated surface can be brought closer to 90°. During heat treatment, the seed crystal particles grow while maintaining the orientation angle at the time of application, becoming rod-shaped particles 136. Therefore, when applying the paste containing seed crystal particles, the average orientation angle of the rod-shaped particles 136 in orientation adjustment regions Ao1 and Ao2 can be adjusted by adjusting the orientation angle of the seed crystal particles with respect to the coated surface as described above. Also, the longer the heat treatment time, the larger the aspect ratio of the rod-shaped particles 136 becomes. Similarly, by attaching rod-shaped seed crystal particles to the surface of the glass paste before heat treatment, the orientation angle and aspect ratio of the rod-shaped particles 126 in the third orientation adjustment region Ao3 can be adjusted.

[0082] When glass is joined to a component, the glass becomes fluid due to heat treatment and deforms to conform to the surface shape of the component to be joined. This causes the glass to adhere closely to the surface of the component to be joined, ensuring gas sealing. However, if the glass becomes too fluid, there is a concern that unintended gaps may form between the glass and the component to be joined, resulting in a faulty joint. In this embodiment, the heat treatment is performed so that the crystallinity of the surface regions As1 and As2 in the first glass seal portion 135 becomes relatively high, making it difficult for the surface regions As1 and As2 to fluidize during heat treatment. As a result, the outer shape of the first glass seal portion 135 is more easily maintained. On the other hand, the first non-surface region Ai1, which has a relatively low crystallinity, becomes more fluid and adheres more easily to the single-cell separator 120 and the IC separator 180. As a result, gas sealing is ensured. The same applies to the second glass seal portion 125.

[0083] (Operation of fuel cell stack 10) As shown in Figures 2 and 4, the oxidizer gas OG is supplied from the oxidizer gas supply manifold 311 to the air chamber 313 via the gas passage member 280. Also, as shown in Figures 3 and 5, the fuel gas FG is supplied from the fuel gas supply manifold 321 to the fuel chamber 323 via the gas passage member 280.

[0084] When oxidant gas OG is supplied to the air chamber 313 of each reaction unit 100U and fuel gas FG is supplied to the fuel chamber 323, electricity is generated in the single cell 110 by an electrochemical reaction between the oxidant gas OG and fuel gas FG. This power generation reaction is an exothermic reaction. As described above, the interconnector 190 is shared by two adjacent reaction units 100U, and the interconnector 190 ensures conductivity between the two adjacent reaction units 100U. In other words, the multiple reaction units 100U included in the fuel cell stack 10 are electrically connected in series. Furthermore, the second terminal plate 250 is electrically connected to the reaction unit 100U located at one end (the lower end of Figure 2), and the first terminal plate 240 is electrically connected to the reaction unit 100U located at the other end (the upper end of Figure 2). As a result, the electrical energy generated in each reaction unit 100U is extracted from the terminal plates 240 and 250, which function as output terminals of the fuel cell stack 10. Since SOFCs generate electricity at relatively high temperatures (for example, 700°C to 1000°C), the fuel cell stack 10 may be heated by a heater (not shown) after startup until the high temperature can be maintained by the heat generated by power generation.

[0085] As shown in Figures 2 and 4, the oxidizer off-gas OOG discharged from the air chamber 313 of each reaction unit 100U to the oxidizer gas discharge manifold 312 is discharged to the outside of the fuel cell stack 10 through the inside of the main body 281. Also, as shown in Figures 3 and 5, the fuel off-gas FOG discharged from the fuel chamber 323 of each reaction unit 100U to the fuel gas discharge manifold 322 is discharged to the outside of the fuel cell stack 10 through the inside of the main body 281.

[0086] The glass material of the first glass seal portion 135 contains volatile elements such as boron and silicon. There is a concern that if these elements volatilize during the operation of the fuel cell stack 10 and reach the single cell 110, the deterioration of the single cell 110 will accelerate. In this embodiment, the relatively high crystallinity of the surface regions As1 and As2 reduces the volatilization of elements contained in the first glass seal portion 135 from the non-bonding surfaces 135S3 and 135S4, thereby reducing the deterioration of the single cell 110 caused by the volatilized elements. Since elemental volatilization occurs in a very shallow region near the surface of the glass, it is sufficient for the crystallinity to be relatively high in the region from the first non-bonding surface 135S3 to a depth of 10 μm. The same applies to the second glass seal portion 125.

[0087] The fuel cell stack 10 becomes hot during operation and returns to room temperature when operation is stopped. As a result, stress is generated in the first glass seal portion 135 due to the difference in thermal expansion coefficients between it and the single-cell separator 120 and IC separator 180 that are to be joined. This stress can cause cracks to form in the first glass seal portion 135. Cracks tend to spread from the corners between the non-jointed surfaces 135S3 and 135S4 and the joined surfaces 135S1 and 135S2, along the non-jointed surfaces 135S3 and 135S4. The closer the average orientation angle of the rod-shaped particles 136 contained in the orientation adjustment regions Ao1 and Ao2 is to 90°, the more the rod-shaped particles 136 are likely to hinder the propagation of cracks along the non-jointed surfaces 135S3 and 135S4. Also, the larger the aspect ratio of the rod-shaped particles 136, the more likely the rod-shaped particles 136 are to hinder the propagation of cracks. Since crack propagation is likely to occur in the region from the non-bonding surfaces 135S3 and 135S4 to a depth of 80 μm, it is sufficient if the average orientation angle of the rod-shaped particles 136 contained in this region is close to 90°. The same applies to the second glass seal portion 125.

[0088] (Effects and Benefits) As described above, the fuel cell stack 10 of this embodiment includes seal structures 410 and 420.

[0089] The seal structure 410 comprises an IC separator 180, a single-cell separator 120, and a first glass seal portion 135 interposed between the IC separator 180 and the single-cell separator 120. The first glass seal portion 135 contains crystallized glass. The first glass seal portion 135 has a first non-bonding surface 135S3 and a second non-bonding surface 135S4 that do not contact either the IC separator 180 or the single-cell separator 120, a first surface region As1 extending from the first non-bonding surface 135S3 to a depth of 10 μm, a second surface region As2 extending from the second non-bonding surface 135S4 to a depth of 10 μm, and a first non-surface region Ai1 which is the remaining region excluding the surface regions As1 and As2. The crystallinity of the first surface region As1 and the crystallinity of the second surface region As2 are higher than that of the first non-surface region Ai1.

[0090] The seal structure 420 comprises a single cell 110, a single cell separator 120, and a second glass seal portion 125 interposed between the single cell 110 and the single cell separator 120. The second glass seal portion 125 contains crystallized glass. The second glass seal portion 125 has a third surface region As3 extending to a depth of 10 μm from a third non-bonding surface 125S2 that does not contact either the single cell 110 or the single cell separator 120, and a second non-surface region Ai2 which is the remaining region excluding the third surface region As3. The degree of crystallinity of the third surface region As3 is higher than that of the second non-surface region Ai2.

[0091] According to the above configuration, it is possible to maintain gas sealing performance by the glass seal portions 125 and 135 and suppress the volatilization of elements from the surface of the glass seal portions 125 and 135.

[0092] The value obtained by dividing the crystallinity of the first surface region As1 by the crystallinity of the first non-surface region Ai1 is 1.1 or greater. The value obtained by dividing the crystallinity of the second surface region As2 by the crystallinity of the first non-surface region Ai1 is 1.1 or greater. The value obtained by dividing the crystallinity of the third surface region As3 by the crystallinity of the second non-surface region Ai2 is 1.1 or greater. With this configuration, it is possible to maintain gas sealing properties by the glass seal portions 125 and 135 and suppress the volatilization of elements from the surface of the glass seal portions 125 and 135.

[0093] The crystallinity of surface regions As1, As2, and As3 is 45% or higher. With this configuration, the volatilization of elements contained in the glass seal portions 125 and 135 from the non-bonding surfaces 125S2, 135S3, and 135S4 is further reduced.

[0094] The first glass seal portion 135 contains rod-shaped particles 136 in a first orientation adjustment region Ao1, which is the region from the first non-bonding surface 135S3 to a depth of 80 μm. The average orientation angle of the rod-shaped particles 136 with respect to the first non-bonding surface 135S3 is 45° or more and 90° or less. The first glass seal portion 135 contains rod-shaped particles 136 in a second orientation adjustment region Ao2, which is the region from the second non-bonding surface 135S4 to a depth of 80 μm. The average orientation angle of the rod-shaped particles 136 with respect to the second non-bonding surface 135S4 is 45° or more and 90° or less. The second glass seal portion 125 contains rod-shaped particles 126 in a third orientation adjustment region Ao3, which is the region from the third non-bonding surface 125S2 to a depth of 80 μm. The average orientation angle of the rod-shaped particles 126 with respect to the third non-bonding surface 125S2 is 45° or more and 90° or less. With this configuration, the propagation of cracks that occur in the glass seal portions 125 and 135 is reduced.

[0095] B. Examples Multiple fuel cell stack samples were prepared and tested, each having the same configuration as the above embodiment but with different crystallinity levels in the glass seal portion and orientation angles of the rod-shaped particles.

[0096] (Samples S1, S2, S9) Glass raw material powder was press-molded, and the resulting cylindrical molded body was calcined at a temperature below the crystallization temperature of glass to obtain a calcined glass body.

[0097] A paste was prepared by mixing seed crystal glass particles with a solvent and a binder. This paste was then applied to the outer surface of a calcined glass body.

[0098] An air electrode frame was placed on a ferritic stainless steel single-cell separator, and the obtained glass calcined body was placed inside each of the two sealing holes. An IC separator made of ferritic stainless steel was placed on top of the air electrode frame. Other components constituting the fuel cell stack were then sequentially stacked on the resulting laminate to assemble the fuel cell stack. The assembled fuel cell stack was placed in a firing furnace and heat-treated at 850°C to obtain three types of fuel cell stack samples S1, S2, and S9.

[0099] (Samples S3, S4, S13, S14) Glass raw material powder was press-molded to obtain a cylindrical molded body, which was then calcined at a temperature below the crystallization temperature of glass to obtain a calcined glass body. Using this calcined glass body, a fuel cell stack was assembled in the same manner as in sample S1. The assembled fuel cell stack was placed in a firing furnace and heat-treated at 850°C. During this heat treatment, the temperature program of the firing furnace and the arrangement of the stacks in the firing furnace were adjusted so that the degree of crystallinity of the glass seal portion was as shown in Table 1, thereby obtaining four types of fuel cell stack samples S3, S4, S13, and S14.

[0100] (Sample S5-8) A glass calcined body was prepared in the same manner as for sample S1, and a paste containing seed crystal particles was applied to the outer surface of this glass calcined body. A fuel cell stack was assembled using this glass calcined body in the same manner as for sample S1. The assembled fuel cell stack was placed in a firing furnace and heat-treated at 850°C. During this heat treatment, the temperature program of the firing furnace and the arrangement of the stacks in the firing furnace were adjusted so that the degree of crystallinity of the glass seal portion was as shown in Table 1, thereby obtaining four types of fuel cell stacks: samples S5, S6, S7, and S8.

[0101] (Sample S10-12) A glass calcined body was prepared in the same manner as sample S1. A paste containing seed crystal particles was applied to the outer surface of the glass calcined body by screen printing. At this time, the orientation angle of the seed crystal particles relative to the outer surface was adjusted by adjusting the dimensions of the opening of the screen used. Using this glass calcined body, a fuel cell stack was assembled in the same manner as sample S1. The assembled fuel cell stack was placed in a firing furnace and heat-treated at 850°C. During this heat treatment, the holding time at 850°C was adjusted to be as shown in Table 2, and three types of fuel cell stacks, samples S10, S11, and S12, were obtained.

[0102] (Sample S15) A glass calcined body was prepared in the same manner as for sample S1. Using this glass calcined body, a fuel cell stack was assembled in the same manner as for sample S1. The assembled fuel cell stack was placed in a firing furnace and heat-treated at 850°C. During this heat treatment, the holding time at 850°C was adjusted to match the conditions shown in Table 2, thereby obtaining sample S15.

[0103] (Measurement of crystallinity) Three arbitrary points were cut from the surface region of the glass seal portion provided in sample S1. Each of the cut-out portions was embedded in resin and mirror-polished to obtain three test pieces. For each test piece, an SEM image was acquired as described in the above embodiment, and the degree of crystallinity Rc was determined by image analysis. The average value of the degree of crystallinity was calculated from the Rc data of the three test pieces and defined as the crystallinity of the surface region Rcs. Three arbitrary points were cut from the non-surface region of the same glass seal portion, and the crystallinity of the non-surface region Rci was determined in the same manner. In addition, the value Rcs / Rci was calculated by dividing the crystallinity of the surface region Rcs by the crystallinity of the non-surface region Rci. Similarly, for the other sample S2-15, the crystallinity of the surface region Rcs, the crystallinity of the non-surface region Rci, and the value Rcs / Rci obtained by dividing the crystallinity of the surface region Rcs by the crystallinity of the non-surface region Rci were determined.

[0104] (Measurement of average orientation angle) The glass seal portion of sample S10 was cut perpendicular to the single-cell separator 120, and its cross-section was imaged using a SEM at an observation magnification of 200x, including the outer surface (first non-bonding surface). Using the obtained SEM image, the average orientation angle of the rod-shaped particles contained in the orientation adjustment region was determined in the manner described in the above embodiment. Similarly, the average orientation angle of the rod-shaped particles contained in the orientation adjustment region was determined for samples S11, S12, and S15.

[0105] (Gas sealing test) Gas was introduced from the fuel gas supply manifold 321 of sample S1, and the gas flow rate was measured at the outlet of the fuel gas discharge manifold. The amount of gas leakage was determined by comparing the amount of gas flowing into the fuel gas supply manifold with the gas flow rate at the outlet of the fuel gas discharge manifold. Similarly, the amount of gas leakage was determined for each of samples S2-9, S13, and S14. No gas leakage was rated as A, a small amount of gas leakage that did not affect the initial performance was rated as B, and a large amount of gas leakage that affected the initial performance was rated as C. The results are shown in Table 1.

[0106] Table 1 shows that samples S13 and S14, with Rcs / Rci ratios of 1.0 or less, exhibited significant gas leakage. In contrast, samples S1-9, with Rcs / Rci ratios of 1.1 or higher, either had no gas leakage or, if present, it was negligible and did not affect the initial performance. In particular, samples S1, S3, S5, and S7, with Rcs / Rci ratios of 1.2 or higher, showed no gas leakage at all.

[0107] (Durability test) Samples S1-9, S13, and S14 were each operated at 850°C for 1000 hours. The degradation rate was calculated using the following formula.

[0108] Degradation rate (%) = {(Cell stack voltage at start of operation - Cell stack voltage after 1000 hours of operation) / Cell stack voltage at start of operation} × 100 We evaluated the products as follows: A1 if the degradation rate was 5% or less, A2 if the degradation rate was between 5% and 8%, and B if the degradation rate was greater than 8%. The results are shown in Table 1.

[0109] Table 1 shows that samples S9, S13, and S14, which had a surface crystallinity Rcs of less than 45%, had a degradation rate exceeding 8%. Samples S1-8, which had a surface crystallinity Rcs of 45% or more, all had a degradation rate of 8% or less. In particular, samples S5-8, which had a surface crystallinity Rcs of 50% or more, all had a degradation rate of 5% or less.

[0110] [Table 1]

[0111] (Thermal cycle test) Samples S10-12 and S15 were placed in electric furnaces, respectively. The temperature was raised from 100°C to 700°C, and then lowered back down to 100°C. This cycle was repeated 100 and 200 times. The presence or absence of crack propagation in the glass seal area was observed after 100 and 200 cycles. If no crack propagation was observed after 200 cycles, it was rated A1. If no crack propagation was observed after 100 cycles but crack propagation was observed after 200 cycles, it was rated A2. If crack propagation was observed after 100 cycles, it was rated C. The results are shown in Table 2.

[0112] In sample S15, where the average orientation angle of the rod-shaped particles in the orientation adjustment region was 30°, crack propagation was observed after 100 cycles. In samples S10-12, where the average orientation angle was 45° or higher, no crack propagation was observed after 100 cycles. In particular, in samples S11 and S12, where the average orientation angle was 70° or higher, no crack propagation was observed even after 100 cycles.

[0113] [Table 2]

[0114] C. Variations The technologies disclosed herein are not limited to the embodiments described above and can be modified in various forms without departing from their essence, for example, the following modifications are possible. (1) The first member to be joined may be a different member from the IC separator 180 and the single cell 110. The second member to be joined may be a different member from the single cell separator 120, and may be any member that constitutes the electrochemical reaction cell stack and is different from the first member to be joined. (2) In the first embodiment, the non-joint surfaces 135S3 and 135S4 were perpendicular to the first joint surface 135S1 and the second joint surface 135S2, but the non-joint surfaces do not have to be perpendicular to the joint surfaces. (3) In the above embodiment, the fuel cell stack 10 was equipped with a plurality of flat-plate type single cells 110, but the electrochemical reaction cell stack may be equipped with other types of single cells (for example, cylindrical, flat cylindrical). (4) The above configuration can also be applied to cell stacks used in other types of fuel cells such as polymer electrolyte fuel cells (PEFCs), phosphoric acid fuel cells (PAFCs), and molten carbonate fuel cells (MCFCs), or to electrolytic cell stacks that have electrolytic cell units, which are constituent units of solid oxide electrolytic cells (SOECs), as single cells. [Explanation of symbols]

[0115] 10: Fuel cell stack (electrochemical reaction cell stack) 100: Power generation block 100U: Electrochemical reaction unit 110: Single cell (first joint target component) 112: Electrolyte layer 114: Air electrode 116: Fuel electrode 118: Reaction prevention layer 120: Single cell separator (second joint target component) 121: Through hole 124: Joint part 125: Second glass seal part 125S1: Third joint surface 125S2: Third non-joint surface (non-joint surface) 126: Rod-shaped particles 130: Air electrode frame 131: Through hole 132: Seal hole 135: First glass seal part (glass seal part) 135C: Edge 135S1: First joint surface 135S2: Second joint surface 135S3: First non-joint surface (non-joint surface) 135S4: Second non-bonding surface (non-bonding surface) 136: Rod-shaped particles 140: Fuel electrode frame 141: Through hole 144: Fuel electrode current collector 145: Electrode opposing part 146: Interconnector opposing part 147: Connecting part 149: Spacer 180: IC separator (first bonding target member) 181: Through hole 190: Interconnector 191: Flat plate part 192: Air electrode current collector part 193: Coating layer 196: Conductive bonding material 200: Magnification 210: First end plate 211: Flat part 212: Through hole 213: Outer protrusion 214: Inner protrusion 220: Insulating part 230: End separator 231: Through hole 232: First plate 240: First terminal plate 241: Through hole 250: Second terminal plate 260: Second plate 270: Second end plate 271: Flat section 272: Through hole 273: Outer protrusion 274: Inner protrusion 280: Gas passage member 281: Main body section 282: Flange section 284: Bolt hole 311: Oxidizer gas supply manifold 312: Oxidizer gas discharge manifold 313: Air chamber 321: Fuel gas supply manifold 322: Fuel gas discharge manifold 323: Fuel chamber 410, 420: Seal structure Ai1: First non-surface area (non-surface area) Ai2: Second non-surface area (non-surface area) Ao11, Ao12, Ao13: Divided area Ao1: First orientation adjustment area (orientation adjustment area) Ao2: Second orientation adjustment area (orientation adjustment area) Ao3: Third orientation adjustment area (orientation adjustment area) As1: 1st surface area (surface area) As2: 2nd surface area (surface area) As3: 3rd surface area (surface area) B: BoltBH: Bolt hole Dmax: Maximum ferret diameter Dmin: Minimum ferret diameter FG: Fuel gas FOG: Fuel off-gas Lc: Straight line Lt: Tangent N: Nut OG: Oxidizer gas OOG: Oxidizer off-gas P: Intersection

Claims

1. The first member to be joined, The second member to be joined, A glass seal portion interposed between the first member to be joined and the second member to be joined, Equipped with, The aforementioned glass seal portion Contains crystallized glass, It has a surface region which is the area from the non-joining surface that does not come into contact with the first and second joining target members to a depth of 10 μm, and a non-surface region which is the remaining area excluding the surface region, The crystallinity of the surface region is higher than that of the non-surface region. The value obtained by dividing the crystallinity of the surface region by the crystallinity of the non-surface region is 1.1 or greater. Seal structure.

2. A seal structure according to claim 1, The crystallinity of the surface region is 45% or more. Seal structure.

3. A seal structure according to claim 1 or claim 2, The orientation adjustment region, which is the area from the non-bonding surface to a depth of 80 μm, contains rod-shaped particles. The average orientation angle of the rod-shaped particles with respect to the non-joining surface is 45° or more and 90° or less. Seal structure.

4. An electrochemical reaction cell stack comprising the seal structure described in claim 1 or claim 2.

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