JP2011108620A - Bonding agent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bonding agent for bonding an air electrode of a cell of a solid oxide fuel cell with an inter-connector, in which an electric resistance is sufficiently small and bonding strength is sufficiently large even if a sintering temperature is set at a comparatively low temperature. <P>SOLUTION: Powder of each metal elements (Mn, Co) which can compose a transition metal oxide (MnCo<SB>2</SB>O<SB>4</SB>) having a spinel type crystal structure is a starting raw material. The paste containing the above powder mixture is sintered in a state of the same being interposed between the air electrode and the inter-connector to obtain the bonding agent. The bonding agent is of a spherical particles exposing a plurality of crystal faces on its surface and contains particles having a side of 1 μm or longer out of a plurality of sides composing an outline of the crystal faces. Diameters of the particles are 5-80 μm. As compared with a bonding agent formed of powder of a spinel system material (MnCo<SB>2</SB>O<SB>4</SB>) as a starting raw material, this has a small electric resistance and moreover a larger bonding strength. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a bonding agent for bonding two conductive connecting members.

A solid oxide fuel cell (SOFC) cell (single cell) includes a solid electrolyte, a fuel electrode arranged integrally with the solid electrolyte, and an air electrode arranged integrally with the solid electrolyte. And. By supplying fuel gas (hydrogen gas, etc.) to the fuel electrode and supplying oxygen-containing gas (air, etc.) to the air electrode, the following formulas (1) and (2) are shown. A chemical reaction occurs. Thereby, a potential difference is generated between the fuel electrode and the air electrode. This potential difference is based on the oxygen conductivity of the solid electrolyte.
(1/2) · O ₂ +2 ^e− → O ²⁻ (where: air electrode) (1)
H ₂ + O ²⁻ → H ₂ O + 2 ^e− (in the fuel electrode) (2)

  In the SOFC, normally, a conductive connecting member for collecting current (hereinafter referred to as an interconnector) is bonded and fixed to each of a fuel electrode and an air electrode by a bonding agent, and based on the potential difference via each interconnector. Electric power is extracted outside. In the following, attention is paid particularly to the joining of the air electrode and the interconnector.

  Conventionally, an expensive Pt material has been used as a bonding agent that joins the air electrode and the interconnector to electrically connect the air electrode and the interconnector. In order to reduce the cost, a silver-based material can be considered as a substitute material for the Pt material, and a conductive ceramic material can be considered as a ceramic-based material. For example, in Patent Document 1, a La—Sr—Co—Fe-based perovskite complex oxide is cited as a conductive ceramic material that firmly bonds an air electrode and an interconnector.

JP 2005-339904 A

Incidentally, the present inventor has proposed a transition metal oxide having a spinel crystal structure (for example, MnCo ₂ ) as a conductive ceramic material that joins an air electrode and an interconnector to electrically connect the air electrode and the interconnector. Attention is focused on O ₄ , CuMn ₂ O ₄ ). The conductive spinel type oxide has a characteristic that it is excellent in sinterability although it is slightly inferior to the above-described perovskite type oxide.

When such a spinel material is used as a bonding agent, the paste is baked in a state in which the paste as a precursor of the bonding agent is interposed between the bonding portion of the air electrode and the bonding portion of the interconnector. Thus, the air electrode and the interconnector are joined and electrically connected by the bonding agent that is a sintered body. Here, as the material for the interconnector on the air electrode side, a ferrite SUS material or the like is usually used. Ferrite-based SUS materials are generally used in a state where a uniform chromia (Cr ₂ O ₃ ) film is formed on the surface by pre-oxidation treatment.

Chromia (Cr ₂ O ₃ ) is more easily formed as the temperature is higher. Therefore, when an excessively high temperature heat treatment (heat treatment given to a bonding agent made of glass or the like) is performed in the subsequent assembly process, excessive chromia (Cr ₂ O ₃ ) is formed at the interface with the bonding agent in the interconnector. Can be done. The electrical resistance of chromia (Cr ₂ O ₃ ) is relatively large. Therefore, if chromia (Cr ₂ O ₃ ) is excessively formed at the interface, the electrical resistance of the SOFC as a whole increases and the output of the SOFC as a whole tends to decrease. From the above, in order to suppress the excessive formation of chromia (Cr ₂ O ₃ ) at the interface with the bonding agent in the interconnector during the baking of the paste that is the precursor of the bonding agent, the baking of this paste is performed. It needs to be done at a relatively low temperature.

In the case where the paste, which is a precursor of the bonding agent, is thus fired at a relatively low temperature, the following two are required as the bonding agent that is a sintered body.
1. It must be sufficiently densified to obtain high conductivity (low electrical resistance).
2. High bonding strength should be obtained.

  The present inventor has found that a bonding agent having a spinel material can sufficiently achieve the above two requirements even when the precursor paste is fired at a relatively low temperature.

That is, the bonding agent according to the present invention joins the first conductive connecting member and the second conductive connecting member which is separate from the first conductive connecting member, and the first and second conductive members. This is a bonding agent for electrically connecting the conductive connecting member, and includes a transition metal oxide having a spinel crystal structure. As the first conductive connecting member, “a solid electrolyte, a fuel electrode that is integrally disposed with the solid electrolyte and that reacts with the fuel gas to react with the fuel gas, and a solid electrolyte that is integrally disposed with the solid electrolyte. And a fuel cell fixed to the fuel electrode of the cell and the fuel electrode of the solid oxide fuel cell having an air electrode that contacts the gas containing oxygen and reacts with the gas containing oxygen. electrode and electrically connected to the chemical formula _{La 1-x a x Cr 1} -y + z B y O 3 ( provided that, a: Ca, at least one element Sr, is selected from Ba, B: Co, Ni, Al At least one element selected from x, lanthanum represented by x range: 0.05 to 0.2, y range: 0.02 to 0.22, z range: 0.02 to 0.05) From chromanite Rushirubeden portion, secured to said fuel electrode and the fuel electrode and electrically connected to the chemical formula of the cell _{(A 1-x, B x} ) 1-z (Ti 1-y, D y) O 3 ( provided that A: at least one element selected from alkaline earth elements, B: at least one element selected from Sc, Y, and lanthanoid elements, D: fourth period, fifth period, sixth period Transition metal and at least one element selected from Al, Si, Zn, Ga, Ge, Sn, Sb, Pb, Bi, x range: 0 to 0.5, y range: 0 to 0.5 , Z range: -0.05 to 0.05), and a conductive portion made of a titanium oxide.

  A feature of the bonding agent according to the present invention is a spherical particle having a plurality of crystal faces exposed on the surface, and has a side having a length of 1 μm or more among a plurality of sides constituting the outline of the crystal face (1 One or more particles). Here, when a plurality of the particles are included in the adhesive, it is preferable that each particle has a side having a length of 1 μm or more among a plurality of sides constituting the outline of the crystal plane.

The diameter of the particles is preferably 5 to 80 μm. The transition metal oxide preferably includes one of MnCo ₂ O ₄ and CuMn ₂ O ₄ .

  In the bonding agent made of such a spinel material and containing the particles, a paste containing a mixture of powders of the respective metal elements constituting the transition metal oxide is interposed between the first and second conductive connecting members. It can be formed by firing in a heated state. As described above, when a bonding agent made of a spinel material is formed by oxidizing the powder of each metal element as a starting material during firing, the firing temperature is set to a relatively low temperature (for example, 700 to 900 ° C.). Even so, it is possible to obtain a bonding agent that is sufficiently densified, has a sufficiently high conductivity (low electrical resistance), and has a sufficiently high bonding strength.

  In the bonding agent according to the present invention, a noble metal may be contained in addition to the transition metal oxide. Examples of the noble metal include Pt and Ag. By including a noble metal in the bonding agent, the electric resistance of the bonding agent itself can be reduced.

It is the schematic diagram which showed the structure by which the air electrode and interconnector of the cell of SOFC were joined by the bonding agent which concerns on embodiment of this invention. It is the figure which showed a mode that the bonding agent which concerns on embodiment of this invention was expanded and observed 2000 times with the scanning electron microscope. It is the figure which showed a mode that the bonding agent which concerns on embodiment of this invention was expanded and observed 5000 times with the scanning electron microscope. It is the figure which showed a mode that the bonding agent which concerns on embodiment of this invention was expanded by 10000 time and observed with the scanning electron microscope. It is the figure which showed a mode that the bonding agent which concerns on a comparative example was expanded and observed 5000 times with the scanning electron microscope. It is the figure which showed a mode that the bonding agent which concerns on a comparative example was expanded and observed 10,000 times with the scanning electron microscope. It is the schematic diagram which showed the structure of the sample for joining strength evaluation. It is the schematic diagram which showed the structure at the time of using for the sample shown in FIG. 7 for a tension test. It is the schematic diagram which showed a mode that the electroconductive part comprised including LC fixed to the fuel electrode, and the interconnector were joined by the joining agent. Is a schematic diagram in which the conductive portion and the interconnector consists showing how are bonded by a bonding agent include SrTiO ₃ which is fixed to the fuel electrode.

(Constitution)
FIG. 1 shows an example of a configuration (joint) in which an air electrode of an SOFC cell and an interconnector are joined by a joining agent according to an embodiment of the present invention. In the joined body shown in FIG. 1, the SOFC cell 100 includes a fuel electrode 110, an electrolyte 120 stacked on the fuel electrode 110, a reaction preventing layer 130 stacked on the electrolyte 120, and a reaction preventing layer 130. It is the laminated body which consists of the air electrode 140 laminated | stacked on. The shape of the cell 100 viewed from above is, for example, a square with one side of 1 to 30 cm, a long side with 5 to 30 cm and a short side with 3 to 15 cm, or a circle with a diameter of 1 to 30 cm. The thickness of the cell 100 is 0.1 to 3 mm.

  The fuel electrode 110 (anode electrode) is, for example, a porous thin plate-like fired body made of nickel oxide NiO and yttria-stabilized zirconia YSZ. The thickness T1 of the fuel electrode 110 is 0.1 to 3 mm. The thickness of the fuel electrode 110 is the largest among the thicknesses of the constituent members of the cell 100, and the fuel electrode 110 functions as a support substrate for the cell 100.

  The electrolyte 120 is a dense thin plate-like fired body made of YSZ. The thickness T2 of the electrolyte 120 is 3 to 30 μm.

  The reaction preventing layer 130 is a dense thin plate-like fired body made of ceria. Specific examples of ceria include GDC (gadolinium doped ceria) and SDC (samarium doped ceria). The thickness T3 of the reaction preventing layer 130 is 3 to 20 μm. The reaction preventing layer 130 is formed between the electrolyte 120 and the air electrode 140 by reacting YSZ in the electrolyte 120 with strontium in the air electrode 140 in the cell 100 during cell fabrication or in the operation of the SOFC. In order to suppress the occurrence of a phenomenon in which the electrical resistance increases, it is interposed between the electrolyte 120 and the air electrode 140.

The air electrode 140 (cathode electrode) includes two layers of a base layer 141 and an outermost layer 142. The base layer 141 is a porous thin plate fired body made of lanthanum strontium cobalt ferrite LSCF (La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ ). The outermost layer 142 is a porous thin plate-like fired body having a perovskite structure containing manganese. The outermost layer 142 is made of, for example, lanthanum strontium manganite LSM (La _0.8 Sr _0.2 MnO ₃ ), lanthanum manganite LM (LaMnO ₃ ), or the like. In the air electrode 140, the thickness T41 of the base layer 141 is 5 to 50 μm, and the thickness T42 of the outermost layer 142 is 5 to 50 μm.

  The air electrode 140 has two layers because the LSCF has a higher activity than the LSM and the reaction rate of the chemical reaction shown in the above formula (1) is higher, and the LSM has a higher reaction rate than the LSCF. This is based on the fact that the bonding strength with the bonding agent having the spinel material is higher. That is, in order to increase the reaction rate of the chemical reaction shown in the above formula (1) in the air electrode 140 and to increase the bonding strength between the air electrode and the bonding agent, the air electrode 140 is divided into two layers. Yes.

In the above example, the base layer 141 is composed of one LSCF layer, but the base layer 141 may be composed of a plurality of layers. For example, the base layer 141 is stacked between the LSCF layer (air electrode) stacked on the reaction preventing layer 130 and the LSCF layer (that is, between the LSCF layer and the outermost layer (LSM layer) 142). The lanthanum strontium cobalt LSC (La _0.8 Sr _0.2 CoO ₃ ) layer (current collection layer) interposed between the two layers may be used. Further, an LSCF layer (thermal stress buffer layer) may be interposed between the LSC layer and the outermost layer (LSM layer) 142 (that is, the base layer 141 may be composed of three layers). As the material of the air electrode, instead of LSCF, LSC, lanthanum strontium ferrite LSF (La _0.8 Sr _0.2 FeO ₃ ), lanthanum nickel ferrite LNF (LaNi _0.6 Fe _0.4 O ₃ ), etc. May be used.

  The interconnector 200 is a conductive connection member made of a ferrite SUS material. Each joint portion of the plurality of identical interconnectors 200 and the joint portion of the outermost layer 142 (ie, LSM layer) of the air electrode 140 of the cell 100 are joined and electrically connected by the joining agent 300. .

The bonding agent 300 is a fired body composed of a transition metal oxide having a spinel crystal structure, and is composed of, for example, MnCo ₂ O ₄ , CuMn ₂ O ₄ or the like. The thickness TA of the bonding agent 300 is 20 to 500 μm. The bonding agent 300 may contain a noble metal such as Pt or Ag. By including a noble metal in the bonding agent 300, the electric resistance of the bonding agent itself can be reduced.

(Production method)
Next, an example of the manufacturing method of the joined body shown in FIG. 1 will be described. First, an example of the manufacturing method of the cell 100 will be described.

  The fuel electrode layer 110 was manufactured as follows. That is, 60 parts by weight of NiO powder and 40 parts by weight of YSZ powder were mixed, and polyvinyl alcohol (PVA) was added as a binder to this mixture to prepare a slurry. This slurry was dried and granulated with a spray dryer to obtain a fuel electrode powder. This powder was molded by a die press molding method, and then fired in air in an electric furnace at 1400 ° C. for 3 hours to produce a fuel electrode 110.

  The electrolyte 120 was formed on the fuel electrode 110 as follows. That is, water and a binder were added to the YSZ powder, and this mixture was mixed with a ball mill for 24 hours to prepare a slurry. This slurry was applied and dried on the fuel electrode 110 and co-sintered in air at 1400 ° C. for 2 hours in an electric furnace to form the electrolyte 120 on the fuel electrode 110. When forming a film that will later become the electrolyte 120 on the fuel electrode 110, a tape lamination method, a printing method, or the like may be used.

  The reaction preventing layer 130 was formed on the electrolyte 120 as follows. That is, water and a binder were added to the GDC powder, and this mixture was mixed with a ball mill for 24 hours to prepare a slurry. This slurry was applied and dried on the electrolyte 120 and baked in air at 1350 ° C. for 1 hour in an electric furnace to form the reaction preventing layer 130 on the electrolyte 120. In forming a film that will later become the reaction preventing layer 130 on the electrolyte 120, a tape lamination method, a printing method, or the like may be used. Further, the reaction preventing layer 130 may be formed by co-sintering.

  The base layer 141 of the air electrode 140 was formed on the reaction preventing layer 130 as follows. That is, water and a binder were added to the LSCF powder, and this mixture was mixed with a ball mill for 24 hours to prepare a slurry. This slurry was applied and dried on the reaction preventing layer 130 and baked in an electric furnace at 1000 ° C. for 1 hour in the air to form an air electrode 140 on the reaction preventing layer 130.

  The outermost layer 142 was formed on the base layer 141 as follows. That is, water and a binder were added to the LSM powder, and this mixture was mixed with a ball mill for 24 hours to prepare a slurry. This slurry was applied and dried on the base layer 141 and sintered in the air at 1000 ° C. for 1 hour in an electric furnace, so that the outermost layer 142 was formed on the base layer 141. The example of the method for manufacturing the cell 100 has been described above.

  The interconnector 200 was produced by processing a ferrite SUS material into a predetermined shape by machining or the like. A plurality of interconnectors 200 having the same shape were prepared.

The joining of the outermost layer 142 and the interconnector 200 with the joining agent 300 was achieved as follows. A case where the spinel material is MnCo ₂ O ₄ will be described as an example. First, manganese Mn metal powder and cobalt Co metal powder as starting materials were weighed and mixed at a molar ratio of 1: 2. The metal powder had a particle size of 0.5 to 5 μm and an average particle size of 2 μm. Powders of noble metals such as Pt and Ag may be added. If necessary, ethyl cellulose as a binder and terpineol as a solvent were added to this mixture, and this mixture was mixed in a mortar to prepare a bonding paste. The bonding paste was applied to the surface of the outermost layer 142 (that is, the LSM layer) of the air electrode 140 of the cell 100 and the joint portion of the interconnector 200, and the outermost layer 142 and the interconnector 200 were bonded together. Thereafter, the paste was dried at 100 ° C. for 1 hour and then fired in air at a relatively low temperature of 850 ° C. for 1 hour, whereby the bonding agent 300 as a sintered body was formed.

  That is, a powder of each metal element constituting the spinel material was used as a starting material, and this powder was oxidized during firing, whereby the bonding agent 300 having the spinel material was formed. Even if the firing temperature of the paste is relatively low, the paste is sufficiently baked because the temperature of the powder surface rises locally due to the heat generated due to the oxidation reaction (= exothermic reaction) of each metal element powder. This is considered to be based on the synthesis and growth of spinel crystals (complex oxide crystals). By this bonding agent 300, the outermost layer 142 and the interconnector 200 were bonded and electrically connected. The example of the manufacturing method of the joined body of the air electrode and the interconnector of the SOFC cell shown in FIG. 1 has been described above.

  JP 2009-16351 describes that an air electrode made of a manganese spinel compound is joined to a metal interconnector with an adhesive made of a manganese spinel compound (see particularly paragraph 0029). However, no specific examples are described. In general, a manganese spinel compound is produced by mixing manganese oxide powder and cobalt oxide powder at a spinel ratio and sintering the mixture. That is, the manufacturing method of the bonding agent 300 according to the present embodiment is completely different from the normal manufacturing method of a manganese spinel compound.

(Features of bonding agent)
Next, regarding the bonding agent 300 according to the above-described embodiment, that is, the bonding agent formed by oxidizing each metal element powder (starting material) constituting the spinel-based material (MnCo ₂ O ₄ ) during firing. This will be described with reference to FIGS. FIGS. 2 to 4 each show a state (SEM image) of the surface of the bonding agent 300 observed with a scanning electron microscope (SEM) at a magnification of 2000 times, 5000 times, and 10,000 times.

  As can be understood from FIGS. 2 to 4, the bonding agent 300 includes a plurality of spherical particles in which a plurality of crystal faces are exposed on the surface. The diameter of the plurality of particles is 5 to 80 μm. Here, as the “particle diameter”, in this example, the longest of the linear distances (length corresponding to the diameter) in the particle passing through the center of the spherical particle that can be confirmed from the SEM image is adopted. It was. In addition, among the plurality of particles, at least one particle having a side with a length of 1 μm or more among the plurality of sides constituting the outline of the crystal plane is included (see FIG. 4). The formation of the “particles” is considered to be related to the above-mentioned “growth action of spinel crystals by heat caused by oxidation reaction during paste firing”.

As described above, in the above embodiment, the bonding agent having the above characteristics is synthesized by using the metal as the starting material and utilizing the reaction heat during the heat treatment. Alternatively, an organic metal may be used as a starting material. For example, di-i-propoxy manganese (II) (chemical formula: Mn (Oi-C ₃ H ₇ ) ₂ ) is used as an organic metal containing manganese, and di-i-propoxy is used as an organic metal containing cobalt. Cobalt (II) (chemical formula: Co (O-i-C ₃ H ₇ ) ₂ ) is an organic metal containing copper, and bis (dibivaloylmethanato) copper (chemical formula: Cu (C ₁₁ H ₁₈ O ₂ )) ₂ ) can be used.

(Action / Effect)
Next, functions and effects of the bonding agent 300 according to the above embodiment will be described. In order to explain the action and effect of the bonding agent 300, as a comparative example, a bonding agent formed using a powder of a spinel material synthesized in advance as a starting material is introduced. The bonding agent according to the comparative example was formed as follows.

First, a spinel material (MnCo ₂ O ₄ ) synthesized by a predetermined procedure was pulverized by a pot mill to obtain a spinel material (composite oxide) powder. The particle size of this powder was 0.2-2 μm, and the average particle size was 0.5 μm. If necessary, ethyl cellulose as a binder and terpineol as a solvent are added to the powder to produce a bonding paste. And the outermost layer 142 and the interconnector 200 are bonded together using this paste, and this paste is dried at 100 degreeC for 1 hour. Then, the bonding agent which concerns on the comparative example which is a sintered compact was formed by baking at 1000 degreeC of high temperature in air for 1 hour.

  In the case of the comparative example, if the baking temperature of the paste is lowered as in the above embodiment, the paste is not sufficiently baked. This is because, in the case of the comparative example, an oxide paste that has already been oxidized is used, and unlike the above embodiment, the growth effect of the spinel crystal due to the heat caused by the oxidation reaction can be expected during the baking of the paste. Based on not.

  FIG. 5 and FIG. 6 each show a state where the surface of the bonding agent according to the comparative example is observed with a scanning electron microscope (SEM) at a magnification of 5000 times and 10,000 times. As can be understood from FIGS. 5 and 6, in the bonding agent according to this comparative example, the above-mentioned “particles” are not seen, but instead, a structure in which the powder of the starting material is simply assembled and sintered is seen. It was.

<Evaluation of bonding strength>
The inventor has found that the bonded body according to the present embodiment has a higher bonding strength between the outermost layer 142 and the bonding agent than the bonded body according to the comparative example. Hereinafter, test A in which this has been confirmed will be described.

(Test A)
In Test A, for each of the bonded body according to the present embodiment and the bonded body according to the comparative example, the material of the bonding agent, the average particle diameter of the powder as the starting material of the bonding agent, and the firing temperature at the time of forming the bonding agent A plurality of samples having different combinations of (heat treatment temperature) were produced. Specifically, as shown in Table 1, 18 kinds of levels (combinations) were prepared. And five samples were produced for each level. In Table 1, the starting materials are powders (metal powders) of the respective metal elements constituting the spinel material (levels 1 to 8, 12 to 15) corresponding to this embodiment, and the starting materials were synthesized in advance. Spinel-based material powders (ceramic powders) (levels 9 to 11 and 16 to 18) correspond to the comparative examples.

  As shown in FIG. 7, in these samples, the interconnector 200 and the bonding agent both have the same plate shape as viewed from above, as viewed from above. That is, the air electrode 140 (specifically, the outermost layer 142) and the interconnector 200 having the same shape as viewed from above are joined to each other by the joining agent over the entire joining surface.

  In these samples, the thickness T1 of the fuel electrode 110 (NiO-YSZ) is 500 μm, the thickness T2 of the electrolyte 120 (3YSZ) is 5 μm, the thickness T3 of the reaction preventing layer 130 (GDC) is 5 μm, and the air electrode 140 The thickness T41 of the base layer 141 (LSCF) is 30 μm, the thickness T42 of the outermost layer 142 (LSM) is 20 μm, the thickness TA of the bonding agent 300 is 200 μm, and the thickness TB of the interconnector 200 is 450 μm. . The shape of these samples viewed from above was a circle with a diameter of 30 cm.

  As shown in FIG. 8, jigs for tensile tests were attached to the upper and lower surfaces of each sample with an epoxy resin. As the epoxy resin, a thermosetting epoxy adhesive (trade name: TB2222P) manufactured by ThreeBond Co., Ltd., which has a large adhesive force, was used. The reason why the epoxy resin having a large adhesive force is used is to obtain a bonding strength higher than the bonding strength of the bonding portion by the bonding agent 300. The conditions for curing the epoxy resin (adhesion conditions) were set at 100 ° C. for 60 minutes.

  A tensile force was applied to each sample in the vertical direction by applying a force to separate the upper and lower jigs in the vertical direction. And the magnitude | size (henceforth "tensile strength") at the time of the joining site | part by a joining agent destroying was measured. Here, in each sample, the joint part (weakest part) to be destroyed is the joint part (interface) between the outermost layer 142 and the bonding agent in the present embodiment (levels 1 to 8, 12 to 15). Yes, in the comparative examples (levels 9 to 11 and 16 to 18), it was inside the bonding agent. The results are shown in Table 2.

  As can be understood from Table 2, the bonding agent 300 according to the present embodiment tends to have a higher tensile strength than the bonding agent according to the comparative example. In other words, it can be said that the bonding agent 300 according to the present embodiment has higher bonding strength between the outermost layer 142 and the bonding agent than the bonding agent according to the comparative example.

<Evaluation of electrical resistance>
The present inventor has found that the joined body according to the present embodiment has a lower electrical resistance (higher conductivity) than the joined body according to the comparative example. Hereinafter, test B in which this has been confirmed will be described.

(Test B)
Also in the test B, a plurality of samples corresponding to FIG. 1 having the same combination as the test A were produced for each of the joined body according to the present embodiment and the joined body according to the comparative example. Specifically, as in Test A, 18 types (combinations) shown in Table 1 above were prepared. And three samples were produced for each level. As in Test A, the starting materials are powders (metal powders) of each metal element constituting the spinel material (levels 1 to 8, 12 to 15) correspond to this embodiment, and the starting materials are synthesized in advance. Further, powders (levels 9 to 11 and 16 to 18) that are spinel-based material powders (ceramic powders) correspond to the comparative examples. In these samples, the shape and dimensions of the portion excluding the interconnector and the bonding agent are the same as those in the sample in Test A.

  Further, in this test B, for each sample, the fuel electrode-side interconnector (made of Ni) was joined to the surface of the fuel electrode 110. This joining was achieved by firing a joining paste made of Ni.

  While supplying nitrogen gas to the fuel electrode 110 side and air to the air electrode 140 side for each sample, the temperature was raised to 800 ° C., and when the temperature reached 800 ° C., hydrogen gas was supplied to the fuel electrode 110 and reduced. Processing was carried out for 3 hours. After this reduction treatment, the output (output density) taken out through the interconnector 200 on the air electrode 140 side and the interconnector on the fuel electrode 110 side was measured. As the output density, a value at a temperature of 800 ° C. and a rated voltage of 0.8 V was used. High power density means low electrical resistance. The results are shown in Table 3.

  As can be understood from Table 3, the joined body according to the present embodiment tends to have a higher output density than the joined body according to the comparative example. That is, it can be said that the electrical resistance of the bonding agent 300 according to the embodiment is smaller than that of the bonding agent according to the comparative example.

As described above, in the bonding agent according to the present embodiment the powders of the respective metal elements (Mn, Co) constituting the spinel type material (MnCo ₂ O ₄₎ is formed as a starting material, pre-synthesized spinel type material (MnCo ₂ Compared with the bonding agent according to the comparative example formed using O ₄ ) powder as a starting material, the electric conductivity is large (the electric resistance is small) and the bonding strength is large. That is, according to the bonding agent 300 according to the present embodiment, even if the firing temperature is set to a relatively low temperature (for example, 700 to 900 ° C.), the paste is sufficiently baked, whereby the electrical resistance is sufficiently small. In addition, a bonding agent having sufficiently high bonding strength can be obtained.

As described above, the air electrode 140 (corresponding to the “first conductive connecting member”) and the interconnector 200 (corresponding to the “second conductive connecting member”) are “transition metal oxides (MnCo having a spinel crystal structure)”. ₂ O ₄ , CuMn ₂ O _4, etc.) ”, the bonding agent starts with powder of each metal element (Mn, Co) constituting the spinel material (MnCo ₂ O ₄ ) In this embodiment formed as a raw material, the electrical conductivity is larger (electric resistance is lower than that in a comparative example formed using a powder of a spinel material (MnCo ₂ O ₄ ) in which a bonding agent is synthesized in advance as a starting material. It was explained that the joint strength was small.

Similarly, as shown in FIG. 9, a conductive portion 150 including the lanthanum romanite LC fixed to the fuel electrode 110 and electrically connected to the fuel electrode 110 (the “first conductive connecting member”). And the interconnector 200 (corresponding to the “second conductive connecting member”) include a “transition metal oxide having a spinel crystal structure (MnCo ₂ O ₄ , CuMn ₂ O _4, etc.)”. Also in the case of bonding with a bonding agent, when the bonding agent is formed using a powder of each metal element (Mn, Co) constituting the spinel material (MnCo ₂ O ₄ ) as a starting material, the bonding agent was synthesized in advance. the powder of spinel type material (MnCo 2 _{O 4)} as compared with when formed as a starting material, the conductivity is high (low electric resistance), and, this results in that the bonding strength is large is obtained There has been found.

  The chemical formula of lanthanum romanite LC is represented by the following formula (3). In the following formula (3), A is at least one element selected from Ca, Sr, and Ba. B is at least one element selected from Co, Ni, V, Mg, and Al. The range of x is 0 to 0.4, and more preferably 0.05 to 0.2. The range of y is 0 to 0.3, and more preferably 0.02 to 0.22. The range of z is 0 to 0.1, and more preferably 0.02 to 0.05. δ is a minute value including zero.

La _1-x A _x Cr _{1-y + z} B _y O _3-δ (3)

  Here, in FIG. 9, the conductive portion 150 has two layers of a base layer 151 made of LC and an outermost layer 152 made of LSM. Thus, the fact that the outermost layer (LSM layer) is provided is the fact that the bonding strength between the conductive portion 150 and the bonding agent 300 is greater than when the outermost layer (LSM layer) is not provided. based on.

  As shown in FIG. 10, in the conductive portion 150, a base layer 151 made of titanium oxide may be adopted instead of the base layer 151 made of LC.

The chemical formula of titanium oxide is represented by the following formula (4). In the following formula (4), A is at least one element selected from alkaline earth elements. B is at least one element selected from Sc, Y, and lanthanoid elements. D is a transition metal of the fourth period, the fifth period, the sixth period, and at least one element selected from Al, Si, Zn, Ga, Ge, Sn, Sb, Pb, Bi, The range is 0 to 0.5, the range of y is 0 to 0.5, and the range of z is -0.05 to 0.05. δ is a minute value including zero. As the titanium oxide, for example, “strontium titanate SrTiO ₃ ” in which strontium Sr is used as A may be employed.

(A _1-x , B _x ) _1-z (Ti _1-y , D _y ) O _3-δ (4)

As shown in FIGS. 9 and 10, LC and titanium oxide (particularly, strontium titanate SrTiO ₃ ) are used as the terminal electrode on the fuel electrode side because one end (inside) of the terminal electrode is exposed to a reducing atmosphere. And the other end (outside) is exposed to an oxidizing atmosphere. Currently, LC and SrTiO ₃ are the best conductive ceramics that are stable in both oxidizing and reducing atmospheres.

As described above, generally, the first conductive connecting member and the second conductive connecting member are made of a bonding agent containing “transition metal oxide having a spinel crystal structure (MnCo ₂ O ₄ , CuMn ₂ O _4, etc.)”. In the case of bonding, when the bonding agent is formed using powder of each metal element (Mn, Co) constituting the spinel material (MnCo ₂ O ₄ ) as a starting material, the bonding agent is synthesized in advance. It can be said that the electric conductivity is large (the electric resistance is small) and the bonding strength is large as compared with the case where the powder of the material (MnCo ₂ O ₄ ) is formed as a starting material.

  DESCRIPTION OF SYMBOLS 100 ... Cell, 110 ... Fuel electrode, 120 ... Electrolyte, 130 ... Reaction prevention layer, 140 ... Air electrode, 141 ... Base layer, 142 ... Outermost layer, 150 ... Conductive part, 151 ... Base layer, 152 ... Outermost layer, 200 ... interconnector, 300 ... bonding agent

Claims (8)

Joining the first conductive connecting member and the second conductive connecting member separate from the first conductive connecting member and electrically connecting the first and second conductive connecting members An agent,
It is composed of a transition metal oxide having a spinel crystal structure, and is a spherical particle having a plurality of crystal faces exposed on the surface, and has a length among a plurality of sides constituting the outline of the crystal face. An adhesive comprising particles having sides of 1 μm or more. The bonding agent according to claim 1,
A bonding agent having a particle diameter of 5 to 80 μm. In the bonding agent according to claim 1 or 2,
The transition metal oxide is a bonding agent including one of MnCo ₂ O ₄ and CuMn ₂ O ₄ . In the bonding agent according to any one of claims 1 to 3,
A bonding agent formed by firing a paste containing a mixture of powders of respective metal elements constituting the transition metal oxide in a state of being interposed between the first and second conductive connecting members. In the bonding agent according to any one of claims 1 to 4,
A bonding agent containing a noble metal in addition to the transition metal oxide. In the bonding agent according to any one of claims 1 to 5,
The first conductive connecting member is
A solid electrolyte, a fuel electrode disposed integrally with the solid electrolyte and contacting the fuel gas to react with the fuel gas; and a solid electrode disposed integrally with the solid electrolyte and in contact with a gas containing oxygen A bonding agent, which is the air electrode in a cell of a solid oxide fuel cell having an air electrode for reacting a gas containing oxygen. In the bonding agent according to any one of claims 1 to 5,
The first conductive connecting member is
A solid electrolyte, a fuel electrode disposed integrally with the solid electrolyte and contacting the fuel gas to react with the fuel gas; and a solid electrode disposed integrally with the solid electrolyte and in contact with a gas containing oxygen solid oxide is fixed to the fuel electrode in the fuel cell of the cell and the fuel electrode and electrically connected to the chemical formula La _{1-x a} having a cathode reacting a gas containing oxygen _x Cr _1-y + _z B _y O ₃ (However, A: at least one element selected from Ca, Sr, Ba, B: at least one element selected from Co, Ni, Al, x range: 0.05-0. 2, a range of y: 0.02 to 0.22, a range of z: 0.02 to 0.05), a bonding agent, which is a conductive part configured to include lanthanum romanite. In the bonding agent according to any one of claims 1 to 5,
The first conductive connecting member is
A solid electrolyte, a fuel electrode disposed integrally with the solid electrolyte and contacting the fuel gas to react with the fuel gas; and a solid electrode disposed integrally with the solid electrolyte and in contact with a gas containing oxygen A chemical formula (A _1-x , B _x ) ₁₋ fixed to the fuel electrode and electrically connected to the fuel electrode in a cell of a solid oxide fuel cell having an air electrode for reacting a gas containing oxygen. _z (Ti _1-y , D _y ) O ₃ (where A: at least one element selected from alkaline earth elements, B: at least one element selected from Sc, Y, and lanthanoid elements, D: transition metal of the 4th period, 5th period, 6th period, and at least one element selected from Al, Si, Zn, Ga, Ge, Sn, Sb, Pb, Bi, range of x: 0 ~ 0.5 y ranges: 0 to 0.5, range of z: -0.05~0.05) a conductive portion configured to include a titanium oxide represented by the bonding agent.