JP2012012289A - Molded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molded body before being fired, which is a precursor of a joining material (fired body) for joining two conductive connection members so as to be electrically connected, and which hardly generates exfoliation on a joining interface after being fired.SOLUTION: Powder of each metal element (Mn, Co) constituting transition metal compound oxide (MnCoO) having a spinel type crystal structure is used as a starting raw material. A molded body comprising paste containing the powder and an organic component is fired in the interposed state between the two conductive connection members, and thereby the two conductive connection members are joined so as to be electrically connected by the transition metal compound oxide (joining material) which is the fired body. The molded body is expanded by being fired. Hereby, the molded body has a tendency to be expanded in the thickness (film thickness) direction when being fired. Resultantly, a compressive stress is applied onto a joining interface between the conductive connection members and the joining material, and therefor exfoliation is hardly generated on the joining interface.

Description

  The present invention relates to a molded body before firing, which is a precursor of a bonding material (fired body) for joining two conductive connecting members so as to be electrically connected.

A solid oxide fuel cell (SOFC) (cell) includes a solid electrolyte, a fuel electrode integrated with the solid electrolyte, and an air electrode integrated with the solid electrolyte. I have. By supplying fuel gas (hydrogen gas, etc.) to the fuel electrode and supplying oxygen-containing gas (air, etc.) to the air electrode, the chemical reaction shown in the following formulas (1) and (2) Will occur. 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)

  A large voltage can be obtained by electrically connecting a plurality of SOFCs (cells) in series. In this configuration, for example, an air electrode of one SOFC of two adjacent SOFCs and a conductive portion (interconnector) fixed to the fuel electrode of the other SOFC are electrically connected via a current collecting member. It is obtained by connecting in series. In this case, the air electrode and the current collecting member of one SOFC, and the interconnector and the current collecting member of the other SOFC are joined and fixed so as to be electrically connected by the joining material. Hereinafter, the air electrode, the interconnector, the current collecting member, and the like may be collectively referred to as “conductive connection member”.

  Conventionally, an expensive noble metal material such as Pt has been used as a material for a joining material for joining two conductive connecting members so as to be electrically connected. In order to reduce the cost, a conductive ceramic material can be considered as an alternative material for the noble metal 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 a current collecting member.

JP 2005-339904 A

  By the way, in general, when a conductive ceramic material is used as a material for a bonding material, the green body is fired in a state where a green body before firing which is a precursor of the bonding material is interposed between two conductive connecting members. The Thereby, two electroconductive connection members are joined and electrically connected by the electroconductive ceramic material (joining material) which is a sintered compact.

  In this case, a molded body containing a conductive ceramic material powder and an organic substance (binder, plasticizer, etc.) is usually used as the molded body before firing. As described above, when a molded body (before firing) in which a powder of “already oxidized oxide material” is used as a starting material is subjected to firing, the powders are neck-grown (sintered). Due to so-called firing shrinkage, a phenomenon occurs in which the molded body shrinks.

  Therefore, for example, when the conductive connecting member cannot move following the shrinkage in the thickness (film thickness) direction of the molded body due to firing shrinkage, and the molding that occurs due to warping of the conductive connecting member (before firing) If there is a difference in the amount of firing shrinkage in the thickness direction of the molded body due to variation in the thickness of the body, there may be a problem that peeling occurs at the interface (bonding interface) between the conductive connecting member and the bonding material. .

  The present invention has been made in order to cope with such a problem, and the purpose thereof is a firing of a bonding material (fired body) that joins two conductive connection members so as to be electrically connected. An object of the present invention is to provide a former molded body that is less likely to be peeled off at the interface (bonding interface) between the conductive connecting member and the bonding material after firing.

The inventor has paid attention to transition metal composite oxides having a spinel crystal structure (for example, MnCo ₂ O ₄ , CuMn ₂ O ₄ ) as the conductive ceramic material. 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.

  The molded body before firing according to the present invention is a transition metal composite oxide having a spinel crystal structure, which is a joining material for joining the first conductive connecting member and the second conductive connecting member so as to be electrically connected This is a precursor of a bonding material that is a fired body including an object (conductive ceramic material). The feature of the molded body before firing according to the present invention is that it contains a powder of a metal element constituting the transition metal composite oxide and an organic substance.

  The present inventor uses, as a starting material, a powder of the metal element constituting the transition metal composite oxide instead of the powder of the transition metal composite oxide (already oxidized conductive ceramic material). It has been found that the molded body does not shrink (or expands). This is considered to be based on the expansion of the molded body due to the oxidation reaction and synthesis reaction of each metal material as a starting material during firing. That is, it is considered that the amount of expansion of the molded body due to the oxidation reaction and the synthesis reaction of each metal material is equal to or larger than the amount of shrinkage due to the volatilization of organic components and the amount of shrinkage of the molded body due to firing shrinkage. It is done.

  Therefore, according to the molded body according to the present invention, the phenomenon that the molded body shrinks in the thickness (film thickness) direction does not occur during firing. As a result, the stress in the peeling direction does not act on the interface (bonding interface) between the conductive connecting member and the bonding material, and the above-described peeling does not easily occur at the bonding interface.

Here, the compact may include powders of two kinds of metal elements constituting the transition metal composite oxide, or an oxide of one of the two kinds of metal elements. And a powder of the other metal element of the two kinds of metal elements. A combination of Mn and Co can be used as the two kinds of metal elements. In this case, the bonding material (transition metal composite oxide having a spinel crystal structure) formed by firing is made of MnCo ₂ O ₄ or Mn _1.5 Co _1.5 O ₄ . Similarly, Cu powder and Mn powder may be used as the two kinds of metal elements. In this case, the bonding material (transition metal composite oxide having a spinel crystal structure) formed by firing is made of CuMn ₂ O ₄ .

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. In the solid oxide fuel cell having an air electrode that contacts the gas containing oxygen and reacts with the gas containing oxygen, and is fixed to the fuel electrode in the solid oxide fuel cell and the fuel electrode and electrically connected to the chemical formula _{La 1-x a x Cr 1} -y-z B y O 3-δ ( However, a: Ca, Sr, at least one element selected from Ba, B : At least one element selected from Co, Ni, Mg, Al, x range: 0.05 to 0.2, y range: 0.02 to 0.22, z range: 0 to 0. 05, δ is a minute value including 0) Conductive portion configured to include a lanthanum chromite to be I, as well, the solid oxide is fixed to the fuel electrode in the fuel cell and the fuel electrode is electrically connected to the chemical formula (A _1-x, B _x ) _1-z (Ti _1-y , D _y ) O _3-δ (where A: at least one element selected from alkaline earth elements, B: at least selected from Sc, Y, and lanthanoid elements) One element, D: 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, x range: 0 to 0.5, y range: 0 to 0.5, z range: -0.05 to 0.05, and δ is a minute value including 0). Examples thereof include a conductive portion.

  The second conductive connecting member is a current collecting member that is interposed between two adjacent solid oxide fuel cells and electrically connects the two solid oxide fuel cells. Is mentioned.

  When the molded body according to the present invention is a precursor of the bonding material in the form of a thin film interposed between the first and second conductive connecting members, the representative length in the thickness direction of the film in the molded body The rate of increase after firing of the molded body with respect to before firing is 0 to 33%, and the rate of increase after firing of the molded body with respect to the representative length in the plane direction of the film in the molded body before firing is − It is suitable that it is 1-2%. These numerical values are the state in which the thin film-like molded body is placed and bonded on the table, that is, unconstrained in the thickness direction, and only the lower surface (bonding surface with the table) in the planar direction. Is a value obtained in a state of being restrained to some extent.

  This increase rate can be adjusted by adjusting the content of organic matter (binder, plasticizer, etc.) in the molded body (before firing). Specifically, the larger the organic content, the smaller the increase rate. This is based on the fact that the higher the content of the organic substance, the smaller the content of the metal element powder that oxidizes and expands.

  Further, in the case where the transition metal composite oxide powder is contained in the compact (before firing), this increase rate adjusts the content of the transition metal composite oxide powder in the compact (before firing). Can be adjusted. Specifically, the larger the content of the transition metal composite oxide powder, the smaller the increase rate. This is based on the fact that the higher the content of the transition metal composite oxide powder, the smaller the content of the metal element powder that undergoes oxidative expansion.

  Moreover, in the molded body (before firing) according to the present invention, a noble metal powder may be included. Examples of the noble metal include Pt and Ag. By including the noble metal, the electrical resistance of the bonding material itself (after firing) can be reduced.

It is the schematic diagram which showed the structure of SOFC used as the object for which the joining material formed by baking the molded object before baking which concerns on embodiment of this invention is used. It is the schematic diagram which showed a mode that two SOFC shown in FIG. 1 were electrically connected in series via the current collection member and the joining material.

  FIG. 1 shows an example of the configuration of a SOFC (cell) to which a bonding material formed by firing a green body before firing according to an embodiment of the present invention is used. The SOFC 10 shown in FIG. 1 includes a cylindrical fuel electrode 110, a cylindrical solid electrolyte 120 stacked on the outer periphery of the fuel electrode 110, a cylindrical air electrode 130 stacked on the outer periphery of the solid electrolyte 120, a fuel And a plate-like interconnector (terminal electrode) 140 fixed to a part of the outer periphery of the electrode 110. That is, the SOFC 10 has a cylindrical shape, the outer diameter of the SOFC 10 is 3 to 50 mm, and the length of the SOFC 10 in the axial direction (y-axis direction) is 50 to 2000 mm. The thickness of the SOFC 10 (the total thickness in the radial direction of the fuel electrode 110, the solid electrolyte 120, and the air electrode 130) is 0.5 to 3 mm.

  The fuel electrode 110 (anode electrode) is a porous fired body composed of, for example, nickel oxide NiO and yttria stabilized zirconia YSZ. The thickness (in the radial direction) of the fuel electrode 110 is 0.1 to 3 mm. Of the thicknesses of the fuel electrode 110, the solid electrolyte 120, and the air electrode 130 (in the radial direction), the fuel electrode 110 has the largest thickness, and the fuel electrode 110 functions as a support substrate for the SOFC 10.

The fuel electrode 110 may be composed of nickel oxide NiO and / or nickel Ni and yttria Y ₂ O ₃ . Further, the fuel electrode 110 may be composed of two layers of a fuel electrode current collecting layer (radially inner side) and a fuel electrode active layer (radial outer side). In this case, the content rate of YSZ is larger in the anode active layer than in the anode current collecting layer.

  The solid electrolyte 120 is a dense fired body made of YSZ. The thickness (in the radial direction) of the solid electrolyte 120 is 3 to 30 μm.

The air electrode 130 (cathode electrode) is a porous fired body made of lanthanum strontium cobalt ferrite LSCF (La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ ). The thickness (in the radial direction) of the air electrode 130 is 5 to 50 μm. The air electrode 130 is composed of two layers, a first layer made of LSCF (inner side in the radial direction) and a second layer (outer side in the radial direction) made of lanthanum strontium manganite LSM (La _0.8 Sr _0.2 MnO ₃ ). May be.

  It should be noted that the occurrence of a phenomenon in which the electrical resistance between the solid electrolyte 120 and the air electrode 130 is increased due to the reaction between YSZ in the solid electrolyte 120 and strontium in the air electrode 130 in the SOFC 10 during production or operation of the SOFC. In order to suppress, a reaction preventing layer may be interposed between the solid electrolyte 120 and the air electrode 130. The reaction preventing layer is preferably a dense cylindrical fired body made of ceria. Specific examples of ceria include GDC (gadolinium doped ceria) and SDC (samarium doped ceria).

  The interconnector 140 is insulated from the air electrode 130, and is electrically connected to the fuel electrode 110. The interconnector 140 is a conductive connecting member made of lanthanum chromite LC. The chemical formula of lanthanum chromite 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 to 0.05. δ is a minute value including zero.

La _1-x A _x Cr _1-yz B _y O _3-δ (3)

The interconnector 140 may be made of titanium oxide. 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)

Note that LC and titanium oxide (particularly, strontium titanate SrTiO ₃ ) are used as the fuel electrode interconnector (terminal electrode) because one end (radially inner side) of the interconnector is exposed to a reducing atmosphere and the other end ( This is based on exposure of the outer (radially outer) to an oxidizing atmosphere. At present, LC and SrTiO ₃ are excellent as conductive ceramics that are stable in both oxidizing and reducing atmospheres.

  By supplying a fuel gas (hydrogen gas or the like) to the fuel electrode 110 and a gas (air or the like) containing oxygen to the air electrode 130 to the SOFC 10, the above formulas (1) and (2) are shown. A chemical reaction occurs. As a result, a potential difference is generated between the fuel electrode 110 and the air electrode 130. This potential difference is based on the oxygen potential difference between the two surfaces of the solid electrolyte 120.

  Next, an example of a method for manufacturing the SOFC 10 shown in FIG. 1 will be described.

  The molded body to be the fuel electrode 110 was manufactured as follows. That is, NiO powder and YSZ powder were mixed, and polyvinyl alcohol (PVA) was added to the mixture as a binder. By molding this mixture by an extrusion molding method, a molded body to be a cylindrical fuel electrode 110 was obtained.

  The film to be the solid electrolyte 120 was formed on the outer peripheral surface of the molded body to be 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 outer peripheral surface of the molded body to be the fuel electrode 110. Thereby, the film | membrane used as the solid electrolyte 120 was formed in the outer peripheral surface of the molded object used as the fuel electrode 110. FIG. In this case, in order to secure a space for providing the interconnector 140, a film that becomes the solid electrolyte 120 is formed so that a part of the outer peripheral surface of the molded body that becomes the fuel electrode 110 is exposed. When forming a film that will be the solid electrolyte 120 on the outer peripheral surface of the molded body that will be the fuel electrode 110, a tape lamination method, a printing method, or the like may be used.

  The film to be the interconnector 140 was formed on the outer peripheral surface of the molded body to be the fuel electrode 110 as follows. That is, water and a binder were added to lanthanum chromite LC 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 exposed portion of the outer peripheral surface of the molded body to be the fuel electrode 110. As a result, a laminated molded body was obtained in which a film to be the solid electrolyte 120 and a film to be the interconnector 140 were laminated on the outer peripheral surface of the molded body to be the fuel electrode 110.

  The laminated molded body was simultaneously sintered at 1400 ° C. for 2 hours in air in an electric furnace (in an oxygen-containing atmosphere). Thereby, the solid electrolyte 120 and the interconnector 140 were formed on the outer peripheral surface of the fuel electrode 110. In forming the film to be the interconnector 140 on the outer peripheral surface of the molded body to be the fuel electrode 110, a tape lamination method, a printing method, or the like may be used.

  The air electrode 130 was formed on the outer peripheral surface of the solid electrolyte 120 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 is applied and dried on the outer peripheral surface of the solid electrolyte 120, and is baked in air at 1000 ° C. for 1 hour in an electric furnace (in an oxygen-containing atmosphere) to form the air electrode 130 on the outer peripheral surface of the solid electrolyte 120. It was done.

  Thus, the stacking of the members constituting the SOFC 10 is completed. Here, the fuel electrode 110 needs to have conductivity. Therefore, heat treatment (reduction treatment) for supplying a reducing gas at a high temperature of 800 ° C. is performed on the fired fuel electrode 110 (fired body). By this reduction treatment, NiO is reduced to Ni, and the fuel electrode 110 acquires electrical conductivity. In the above, an example of the manufacturing method of SOFC10 shown in FIG. 1 was demonstrated.

  Next, an example of a configuration in which the two SOFCs 10 illustrated in FIG. 1 are electrically connected in series via a current collecting member and a bonding material will be described with reference to FIG. In the example shown in FIG. 2, the current collecting member 200 is interposed between the air electrode 130 of the upper SOFC 10 in the figure and the interconnector 140 of the lower SOFC 10 in the figure, of the two adjacent SOFCs 10. Yes. The current collecting member 200 is, for example, a metal mesh made of a SUS material or the like.

  An upper side surface of the current collecting member 200 in the drawing is joined by a bonding material 300 so as to be electrically connected to the air electrode 130 of the SOFC 10 on the upper side in the drawing. The lower side surface of the current collecting member 200 in the drawing is joined by a bonding material 300 so as to be electrically connected to the interconnector 140 of the lower SOFC 10 in the drawing.

The bonding material 300 is a thin-film fired body made of a transition metal composite oxide having a spinel crystal structure, and is made of, for example, MnCo ₂ O ₄ , CuMn ₂ O _4, or the like. The thickness of the layer of the bonding material 300 is 1 to 500 μm. The bonding material 300 may contain a noble metal such as Pt or Ag. By including a noble metal in the bonding material 300, the electric resistance of the bonding material itself can be reduced.

The joining of the air electrode 130 and the current collecting member 200 and the joining of the interconnector 140 and the current collecting member 200 by the joining material 300 were 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 joining paste is applied to the joint portion of the air electrode 130 of the upper SOFC 10 in the drawing and the upper joint portion of the current collecting member 200 in the drawing, and the joint portion of the interconnector 140 of the lower SOFC 10 in the drawing. The bonding paste was applied to the lower joint portion of the current collecting member 200 in the figure. That is, a “molded body before firing” that is a precursor of the bonding material 300 is formed. Then, the air electrode 130 of the upper SOFC 10 in the figure and the interconnector 140 of the lower SOFC 10 in the figure were bonded together via the current collecting member 200. 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 material 300 as a sintered body was formed.

  That is, the powder of each of the two types of metal elements constituting the spinel material was used as a starting material, and this powder was oxidized during firing, whereby the bonding material 300 having the spinel material was formed. Note that, as a starting material, a powder of an oxide of one of the two metal elements constituting the spinel material and a powder of the other metal element of the two metal elements are used. May be. In addition, as a starting material, an oxide powder of the one metal element, a powder of the one metal element, and a powder of the other metal element may be used. Further, as the starting material, the one metal element oxide powder, the one metal element powder, the other metal element oxide powder, and the other metal element powder are used. May be. In each of these combinations, a powder of a spinel material (transition metal composite oxide) may be included as a starting material. As described above, the starting material only needs to contain powder of at least one of the two metal elements constituting the spinel material.

  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).

  With the bonding material 300, the air electrode 130 and the current collecting member 200, and the interconnector 140 and the current collecting member 200 are joined and electrically connected, respectively. Heretofore, an example of a method of electrically connecting the two SOFCs 10 illustrated in FIG. 1 in series via the current collecting member 200 and the bonding material 300 has been described.

  JP 2009-16351 describes that an air electrode made of a manganese spinel compound is joined to a metal interconnector by 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 material 300 according to the present embodiment is completely different from the normal manufacturing method of the manganese spinel compound.

(Action / Effect)
Next, the operation and effect of the “molded body before firing that is a precursor of the bonding material 300” according to the embodiment will be described. In order to explain this action and effect, as a comparative example, a molded body (joining material) formed using only a powder of a spinel-based material (transition metal composite oxide) synthesized in advance as a starting material is introduced. The bonding material 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. Then, in the same manner as described above, the “molded body before firing” according to the comparative example, which is a precursor of the bonding material, is formed at each of the bonding portions using the paste. Then, the air electrode 130 of the upper SOFC 10 in the figure and the interconnector 140 of the lower SOFC 10 in the figure were bonded together via the current collecting member 200. This paste is dried at 100 ° C. for 1 hour. Then, the joining material which concerns on the comparative example which is a sintered compact was formed by baking at high temperature 850-1000 degreeC in the 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.

<Evaluation of dimensional increase rate>
The inventor has found that the molded body according to the comparative example contracts by firing, and the molded body according to the present embodiment expands by firing. Hereinafter, test A in which this has been confirmed will be described.

(Test A)
In Test A, the material of the bonding material, the starting material of the bonding material, and the inclusion of organic components in the molded body for each of the molded body (bonding material) according to the present embodiment and the molded body (bonding material) according to the comparative example. A plurality of samples having different combinations of the rate and the firing temperature (heat treatment temperature) at the time of forming the bonding material were produced.

  Specifically, as shown in Table 1, 13 types (combinations) of levels were prepared. And five samples were produced for each level. In Table 1, those containing at least one metal element powder (metal powder) of two kinds of metal elements constituting a spinel material (transition metal composite oxide) as a starting material (levels 3 to 13), Specifically, the starting material is “each powder of the two types of metal elements” (levels 3 to 9), and the starting material is “of one of the two types of metal elements. An oxide powder and a powder of the other metal element of the two kinds of metal elements (levels 10 to 13) correspond to the present embodiment, and a spinel material in which starting materials are synthesized in advance ( A transition metal composite oxide) powder (levels 1 and 2) corresponds to the comparative example.

  In Test A, each sample (molded body before firing) was molded into the same shape (thin film shape) on the upper surface (plane) of a predetermined table. Each sample was placed and joined on the table in this way, that is, unconstrained in the thickness direction, and only the lower surface (joint surface with the table) was restrained to some extent in the planar direction. In the state, it was fired for a predetermined time at a corresponding heat treatment temperature. And about each sample, the increase rate after baking with respect to the length (film thickness) in the thickness direction of the film in the molded body, and the length in the planar direction of the film in the molded body (film width) In particular, the increase rate after firing with respect to before firing was measured for the width of the upper surface of the film. This measurement was performed by measuring a shape change (plane direction, film thickness direction) before and after firing of the molded body with a non-contact type three-dimensional shape measuring machine including a laser displacement sensor. The results are shown in Table 2. In addition, the volume increase rate shown in Table 2 was calculated based on the increase rate in the plane direction and the film thickness direction.

As can be understood from Table 2, the molded body according to the comparative example shrinks by firing (particularly, the dimensional increase rate in the thickness direction is negative), and the molded body according to the present embodiment does not shrink or expands by firing (in particular, The dimensional increase rate in the thickness direction is zero or positive). The shrinkage of the molded body according to the comparative example (especially in the thickness direction) is considered to be based on so-called firing shrinkage. The reason why the level 1 shrinkage is smaller than the level 2 shrinkage is that the compact does not shrink at a heat treatment temperature of 850 ° C. On the other hand, the molded body according to the present embodiment does not shrink (or expands in particular in the thickness direction) due to the oxidation reaction and synthesis reaction of each metal material as a starting material during firing. Is considered to be based on the expansion. That is, it is considered that the expansion amount of the molded body due to the oxidation reaction and the synthesis reaction of each metal material is equal to or larger than the shrinkage amount of the molded body due to firing shrinkage. Such a tendency was confirmed even when the bonding material was made of CuMn ₂ O _{4 as} can be understood from Level 9 in Table 2.

  As can be understood from Table 2, the molded body according to the present embodiment was able to expand only in the thickness direction (film thickness direction) by firing and hardly expand in the planar direction. That is, the bonding area (bonding area) to the table hardly expanded. The reason why the molded body hardly expands in the planar direction in this way is that the molded body is placed on and joined to the table during firing (that is, the lower surface is constrained to some extent in the planar direction). Based on

  Further, as can be understood from levels 3 to 6 in Table 2, the dimensional increase rate can be adjusted by adjusting the content of organic components (binder, plasticizer, etc.) in the molded body (before firing). Specifically, the larger the organic component content, the smaller the dimensional increase rate. This is based on the fact that the larger the content of the organic component, the smaller the content of the metal element powder that oxidizes and expands.

  Similarly, as can be understood from the levels 5, 7, and 8 in Table 2, the dimensional increase rate is to adjust the content of the spinel-based material (transition metal composite oxide) powder in the molded body (before firing). Can be adjusted. Specifically, the larger the content of the spinel-based material powder, the smaller the dimensional increase rate. This is based on the fact that the higher the content ratio of the spinel-based material powder, the smaller the content ratio of the metal element powder that undergoes oxidative expansion.

  Although not shown in Table 2, levels 10 to 13 in Table 2 (that is, the starting material is an oxide powder of one of the two types of metal elements and the two types of metal elements). In the case of including the powder of the spinel material as a starting material in the metal element powder of the other metal element), the larger the content of the spinel material powder, the smaller the dimensional increase rate. It has been confirmed that Similarly to the above, this is also based on the fact that the higher the content of the spinel-based material powder, the smaller the content of the metal element powder that undergoes oxidative expansion.

  Further, although not shown in Table 2, in the levels 3 to 9 in Table 2 (that is, the starting material is a powder of each of the two types of metal elements), When the metal element oxide powder for one or both of the metal elements is included, the larger the content of the metal element oxide powder, the smaller the dimensional increase rate (especially in the thickness direction). It has been confirmed. This is based on the fact that the larger the content of the metal element oxide powder, the smaller the content of the metal element powder that undergoes oxidative expansion. As can be understood from levels 10 to 13 in Table 2, as a starting material, all of the metal element powders of the two kinds of metal elements are replaced with oxide powders of the one metal element. In this case, the dimensional increase rate (especially in the thickness direction) becomes substantially zero.

<Evaluation of electrical resistance>
The inventor of the present invention uses a comparative example in “a structure in which two SOFCs are electrically connected in series via a current collector and a bonding material” (hereinafter referred to as “structure”) shown in FIG. It has been found that the structure using the molded body (bonding material) according to the present embodiment has a low electrical resistance (high electrical conductivity) relative to the structure using the molded body (bonding material). Hereinafter, test B in which this has been confirmed will be described. In this test B, the relative position between the two SOFCs is unchanged. Therefore, the relative distance between the air electrode 130 of the upper SOFC 10 in the figure and the interconnector 140 of the lower SOFC 10 in the figure is also unchanged.

(Test B)
In Test B, six levels (levels 2, 3, 4, 6, 8, and 10 shown in Table 1) among the 13 types (combinations) shown in Table 1 were prepared. And three samples were produced for each level. As in Test A, those containing at least one metal element powder (metal powder) of the two types of metal elements constituting the spinel-based material as a starting material (levels 3, 4, 6, 8, 10) Corresponding to this embodiment, the starting material is only a powder of a spinel material (transition metal composite oxide) synthesized beforehand (level 2) corresponds to the comparative example.

  In test B, as shown in FIG. 2, each sample (molded body before firing) is separated between the air electrode 130 of the upper SOFC 10 and the current collecting member 200 in the figure, and between the lower SOFC 10 in the figure. Each was formed between the connector 140 and the current collecting member 200. 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 air electrode 130 of the upper SOFC 10 in the figure and the interconnector 140 of the lower SOFC 10 in the figure was measured. As the output density, a value at a temperature of 800 ° C. and a rated voltage of 0.8 V was used. Small output density means high electrical resistance. High electrical resistance means that peeling or the like has occurred at the bonding interface of the bonding material (see surfaces a, b, c, and d in FIG. 2). The results are shown in Table 3.

  As can be understood from Table 3, the structure according to the present embodiment tends to have a higher output density than the structure according to the comparative example. That is, it can be said that the structure according to the present embodiment has a smaller electrical resistance than the structure according to the comparative example. This means that in the structure according to the comparative example (the dimension increase rate in the thickness direction of the molded body is negative), peeling or the like is likely to occur at the bonding interface of the bonding material. If the dimensional increase rate in the thickness direction is zero or positive), it means that peeling or the like hardly occurs at the bonding interface of the bonding material.

  In the structure according to the comparative example, peeling or the like is likely to occur at the bonding interface of the bonding material because the relative distance between the air electrode 130 of the upper SOFC 10 in the figure and the interconnector 140 of the lower SOFC 10 in the figure is reduced by firing shrinkage. This is considered to be based on the fact that it cannot be reduced following the contraction in the thickness (film thickness) direction (z-axis direction in the figure) of the molded body. On the other hand, in the structure according to the present embodiment, separation or the like hardly occurs at the bonding interface of the bonding material because the molded body does not shrink in the thickness (film thickness) direction (z-axis direction in the drawing). This is considered to be based on the fact that the stress in the peeling direction does not act on the interface.

  In addition, as understood from Table 3, in the structure according to this embodiment (the volume increase rate of the molded body is zero or positive), the dimensional increase rate in the thickness direction of the molded body (unconstrained in the thickness direction). If the value is greater than 33%, the power density tends to decrease (and thus the electric resistance tends to increase). This is because when the dimensional increase rate in the thickness direction of the molded body (value in the unconstrained thickness direction) is greater than 33%, the above-described expansion in the thickness (film thickness) direction (z-axis direction in the figure). It is considered that (compressive stress) becomes excessive and cracks and the like are generated at the joints. As mentioned above, it can be said that it is especially preferable that the dimensional increase rate in the thickness direction of the thin-film-shaped molded body (value in the thickness direction without constraint) is 0 to 33%.

As described above, the molded body according to the present embodiment formed using a powder of at least one metal element (Mn, Co, etc.) of two kinds of metal elements constituting the spinel material (MnCo ₂ O ₄ etc.) as a starting material. (Bonding material) is different from a molded body (bonding material) according to a comparative example formed using only a powder of a spinel-based material (MnCo ₂ O ₄ or the like) synthesized in advance as a starting material. It does not shrink (or tries to expand) in the thickness (film thickness) direction (z-axis direction in FIG. 2). As a result, the stress in the peeling direction does not act on the interface (bonding interface, surfaces a, b, c, and d shown in FIG. 2) between the conductive connecting member and the bonding material, and the above-described peeling is less likely to occur at the bonding interface. .

  In addition, this invention is not limited to this embodiment, A various modification can be employ | adopted within the scope of the present invention. For example, in the present embodiment, the molded body (joining material) according to the present embodiment is used to electrically connect two cylindrical SOFCs in series, but the two flat SOFCs are electrically connected. In order to connect in series, the molded object (joining material) which concerns on this embodiment may be used.

  DESCRIPTION OF SYMBOLS 10 ... SOFC, 110 ... Fuel electrode, 120 ... Solid electrolyte, 130 ... Air electrode, 140 ... Interconnector, 200 ... Current collecting member, 300 ... Joining material

Claims (11)

A bonding material for bonding a first conductive connection member and a second conductive connection member so as to be electrically connected, and a fired body including a transition metal composite oxide having a spinel crystal structure It is a molded body before firing, which is a precursor of the bonding material,
The molded object containing the powder of the metal element which comprises the said transition metal complex oxide, and organic substance. In the molded product according to claim 1,
The molded body is a precursor of the thin-film bonding material interposed between the first and second conductive connecting members,
The increase rate after firing with respect to the representative length in the thickness direction of the film in the molded body after firing is 0 to 33%, and the representative length in the planar direction of the film in the molded body is The molded body having an increase rate after firing of -1 to 2% with respect to that before firing of the molded body. In the molded product according to claim 1 or 2,
The molded object containing the powder of the said transition metal complex oxide. In the molded product according to any one of claims 1 to 3,
The molded object containing each powder of two types of metal elements which comprise the said transition metal complex oxide. In the molded product according to any one of claims 1 to 3,
A compact comprising an oxide powder of one metal element of two kinds of metal elements constituting the transition metal composite oxide and a powder of the other metal element of the two kinds of metal elements. In the molded product according to claim 4 or 5,
The molded body in which the two kinds of metal elements are Mn and Co. In the molded product according to claim 4 or 5,
The formed body in which the two kinds of metal elements are Cu and Mn. In the molded product according to any one of claims 1 to 7,
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 molded body that is the air electrode in a solid oxide fuel cell including an air electrode that reacts with a gas containing oxygen. In the molded product according to any one of claims 1 to 7,
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 oxygen is fixed to the fuel electrode in solid oxide fuel cell comprising an air electrode of reacting a gas containing and the fuel electrode and electrically connected to the chemical formula _{La 1-x a x Cr 1} -y-z B _y O ₃ (A: at least one element selected from Ca, Sr, Ba, B: at least one element selected from Co, Ni, Mg, Al, range of x: 0.05 to 0.2, y range: 0.02 to 0.22, z range: 0 to 0.05), and a molded body that is a conductive part configured to include lanthanum chromite. In the molded product according to any one of claims 1 to 7,
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-z (fixed to the fuel electrode and electrically connected to the fuel electrode in a solid oxide fuel cell having an air electrode for reacting a gas containing oxygen. 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: 4th period, 5th period, 6th 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, range of z: -0.05~0.05) a conductive portion configured to include a titanium oxide represented by the molded body. In the molded product according to any one of claims 8 to 10,
The second conductive connecting member is
A molded body that is interposed between two adjacent solid oxide fuel cells and is a current collecting member for electrically connecting the two solid oxide fuel cells.

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