JP5615771B2 - Solid oxide fuel cell system and conductive bonding material - Google Patents

Description

  The present invention relates to a solid oxide fuel cell (single cell and fuel cell system), and more particularly to a conductive bonding material used for construction of the fuel cell.

  A solid oxide fuel cell (hereinafter sometimes referred to simply as “SOFC”) is also called a third generation fuel cell, and has the following advantages over other fuel cells. There is. For example, in SOFC, since the operating temperature can be increased, a reaction accelerator (catalyst) is unnecessary, and running cost is reduced. Further, by reusing the high-temperature exhaust gas (exhaust heat), the overall efficiency (total efficiency) can be increased. Furthermore, since the SOFC has a high output density, it can be miniaturized. From these facts, it is expected as a distributed power generation apparatus that replaces an internal combustion engine such as a steam turbine or a gas turbine.

A SOFC has a basic structure (hereinafter, a minimum unit constituting the SOFC is referred to as a “single cell”) and is a dense solid electrolyte made of an oxide ion conductor (typically an oxide ion conductive ceramic body). (For example, a dense membrane layer) is formed by forming an air electrode (cathode) having a porous structure on one surface and forming (for example, laminating) a fuel electrode (anode) having a porous structure on the other surface. Yes. A fuel gas (for example, H ₂ (hydrogen) -containing gas) is supplied to the surface of the solid electrolyte on the side where the anode is formed, and an O ₂ (oxygen) -containing gas (on the surface of the solid electrolyte on the side where the cathode is formed). Typically air).
In addition, in order to supply such gas to both electrodes of the SOFC (single cell), a gas pipe that connects the gas source and the SOFC and distributes each gas is connected to the SOFC, so that the SOFC is formed. A power generation system is established.

  The SOFC is typically operated as a stack in which a plurality of single cells are stacked to obtain a high voltage. In an SOFC having such a stack structure, an interconnector is used to connect single cells. The interconnector serves as a separator that separates the oxidizing gas (oxygen-containing gas such as air) and reducing gas (fuel gas such as hydrogen) at the same time as connecting the single cells physically and electrically. Also bears. The interconnector and the solid electrolyte surface facing the interconnector need to be joined (sealed) so as to ensure high airtightness.

As a solid electrolyte material for SOFC, a zirconia-based material (for example, yttria-stabilized zirconia: YSZ) is widely used because of its high ion conductivity, chemical stability, and mechanical strength. As the solid electrolyte (layer) becomes thinner, the ion permeation rate increases and the battery performance such as charge / discharge characteristics is improved. As a result, in recent years, an anode in which a solid electrolyte is formed in the form of a thin film on the surface of a porous substrate functioning as an anode for the purpose of thinning the solid electrolyte in order to improve the battery performance of SOFC (single cell) Support SOFC is being developed. In this type of SOFC, for example, a mixture (cermet) of NiO and YSZ is used as the anode. Since this mixture is reduced to Ni and YSZ during use, the difference in thermal expansion can be approximated to that of a solid electrolyte (YSZ) while taking advantage of the conductivity of Ni. On the other hand, an oxide having a perovskite structure such as LaCoO ₃ or LaMnO ₃ is used as the cathode.

As SOFC (SOFC system) is put to practical use, in order to improve durability and reliability, bonding strength is ensured between single cells and single cells or between single cells and interconnectors. There is an increasing demand to increase In response to this requirement, for example, Patent Document 1 discloses a glass in which cristobalite crystals (SiO ₂ ) and / or leucite crystals (KAlSi ₂ O ₆ ) are precipitated in a glass matrix, and at least one conductive material. A conductive bonding material is formed. Moreover, as this type of prior art, for example, Patent Document 2 can be cited.

JP 2010-159175 A JP 2010-184826 A

  By the way, from the viewpoint of reducing energy consumption and SOFC operating costs in recent years, the operating temperature of SOFC has been lowered (typically 800 ° C. or lower, for example, 600 to 800 ° C.). In order to realize this requirement, high electrical conductivity and mechanical strength (bonding force) between single cells constituting SOFC or between single cells and other connecting members such as interconnectors in a low temperature range of 800 ° C. or lower. There has been a demand for a conductive bonding material that can form a bonding structure having the following. In addition, there is a need for an SOFC (SOFC system) in which a bonding structure is formed using such a bonding material while maintaining suitable electrical conductivity and mechanical strength.

  Therefore, the present invention was created to solve the above-mentioned problems related to the construction of SOFC (SOFC system), and its purpose is typically less than 800 ° C. (for example, 600 to 800 ° C.). An object of the present invention is to provide a conductive bonding material capable of stably bonding a single cell constituting an SOFC or a single cell and another connecting member (for example, an interconnector) in a low temperature range. Another object is to provide a SOFC (SOFC system) having preferable conductivity and mechanical strength formed by using such a bonding material.

In order to achieve the above object, according to the present invention, a solid oxide fuel cell including an anode (fuel electrode), a cathode (air electrode), and a solid electrolyte, and at least one joined to the solid oxide fuel cell. There is provided a solid oxide fuel cell system comprising two conductive connecting members. Specifically, in the SOFC system disclosed herein, the joint between the solid oxide fuel cell and the conductive connecting member has the following two components:
(A). Ag; and
(B). It is characterized in that at least one crystal selected from cristobalite (SiO ₂ ) crystal, leucite (KAlSi ₂ O ₆ ) crystal and forsterite (Mg ₂ SiO ₄ ) crystal is precipitated in the glass matrix. Glass to do;
Are formed together.
In the context of the present invention, the “solid oxide fuel cell system (SOFC system)” refers to a structure (system) that generates power mainly from SOFC, and is not limited to a special form. For example, a stack comprising a plurality of single cells (that is, a fuel cell structure having a solid electrolyte, an anode, and a cathode) that are the smallest units constituting the SOFC (that is, a set in which a plurality of single cells are connected to each other through an interconnector) Body), a structure (module) in which a gas pipe or the like for supplying fuel gas or oxygen-containing gas to the stack is connected, and the like are typical examples included in the SOFC system. Therefore, a typical example of the conductive connection member constituting the SOFC system is an interconnector that can be connected to a single cell constituting the SOFC.
In the present invention, Ag is pure silver or a silver-based alloy (typically an Ag-based alloy containing other noble metal components in a smaller ratio to silver, such as an Ag—Au alloy, Ag— Pd alloy etc.).

The junction part comprised from this component shows favorable electroconductivity by containing Ag (silver) as an electroconductive substance.
Further, the bonding portion is a glass in which any one of the above crystals is precipitated in a glass matrix (hereinafter referred to as “crystal-deposited glass”), and typically any one of the above fine crystals is dispersed in the glass matrix. It is difficult to flow in a temperature range such as 600 to 800 ° C. because it is formed by precipitated glass. For this reason, it can prevent that glass elutes from a joined part, and can realize a conductive joined part with high mechanical strength.

  A particularly suitable conductive connection member is an interconnector that is conductively connected to a cell constituting the solid oxide fuel cell. According to the present invention, a joint having high conductivity and excellent mechanical strength can be formed between a solid oxide fuel cell (for example, a cathode or an anode, or a solid electrolyte) and an interconnector.

In a preferable aspect of the SOFC system disclosed herein, the glass mixed in the joint portion has the following composition in mass ratio in terms of oxide:
SiO ₂ 60 to 75 wt%;
Al ₂ O ₃ 5 to 15 wt%;
Na ₂ O 3-15% by mass;
K ₂ O 5-15% by mass;
MgO 0 to 3% by mass;
CaO 0 to 3% by mass;
Is substantially composed of.
More preferably, the glass mixed in the joint portion has the following composition in mass ratio in terms of oxide:
SiO ₂ 60 to 75 wt%;
Al ₂ O ₃ 5 to 15 wt%;
Na ₂ O and K ₂ O 10-25% by weight;
MgO and / or CaO 1-5% by mass;
Is substantially composed of.
By including the glass having such a composition, the physical stability of the bonded portion in the temperature range can be improved.

Further, another preferable aspect of the SOFC system disclosed herein is characterized in that the entire joint portion is 100 mass%, and the Ag content in the joint portion is 50 to 80 mass%.
By containing Ag (silver) at such a high content, high conductivity can be realized at the joint. Preferably, the electrical conductivity of the joint in the SOFC system disclosed herein under a temperature condition of 700 ° C. may be at least 500 S / cm or more (for example, 500 to 1500 S / cm).

Further, in another preferred aspect of the SOFC system disclosed herein, the thermal expansion coefficient of the bonding portion is ^{10 × 10 -6 / K~16 × 10} -6 / K ( particularly preferably 11 × ^{10 -6} / K to 16 × 10 ⁻⁶ / K). In addition, a thermal expansion coefficient means the average value between room temperature (25 degreeC) based on a general differential expansion system (TMA)-the temperature below the softening point of glass (500 degreeC or 450 degreeC) here.
The thermal expansion coefficient in such a range is close to the thermal expansion coefficient of the SOFC single cell that is the member to be joined, or the conductive connection member (for example, a metal interconnector) to be joined to the SOFC single cell. Can do. As a result, in an SOFC having a joint that exhibits such a coefficient of thermal expansion, temperature rise and fall between an operating temperature range (for example, 600 to 800 ° C.) and a temperature when not in use (typically normal temperature). Even when the treatment is repeated or exposed to a temperature higher than the above use temperature range, the airtightness and mechanical strength of the joint can be maintained over a long period of time.

In order to achieve the above object, the present invention provides a conductive bonding material for bonding a SOFC and a conductive connection member connected to the SOFC.
The conductive bonding material for SOFC (SOFC system) construction application disclosed here has the following two components:
(A). Ag; and
(B). A glass characterized in that at least one crystal selected from a cristobalite crystal, a leucite crystal and a forsterite crystal is precipitated in a glass matrix, and has the following composition in terms of an oxide-converted mass ratio: :
SiO ₂ 60 to 75 wt%;
Al ₂ O ₃ 5 to 15 wt%;
Na ₂ O 3-15% by mass;
K ₂ O 5-15% by mass;
MgO 0 to 3% by mass;
CaO 0 to 3% by mass;
Glass substantially consisting of;
including.
Preferably, the glass has the following composition with a mass ratio in terms of oxide:
SiO ₂ 60 to 75 wt%;
Al ₂ O ₃ 5 to 15 wt%;
Na ₂ O and K ₂ O 10-25% by weight;
MgO and / or CaO 1-5% by mass;
It is characterized by substantially comprising.
By using the conductive bonding material having such a configuration, it is possible to form a bonding portion having good conductivity and mechanical strength as described above.
Preferably, it further includes a binder and a liquid medium (typically a high boiling point organic solvent) so as to be easily supplied (applied) to the surfaces of the members to be joined, and includes a paste form (slurry form or ink form). The same shall apply hereinafter) provided and used.

Moreover, in one preferable aspect as the conductive bonding material disclosed here, the total content of Ag and glass is 100% by mass, and the content of Ag is 50 to 80% by mass.
By using the bonding material having such a configuration, it is possible to form a bonding portion exhibiting desired high conductivity.

Further, in another preferable aspect as a conductive bonding material described herein, the thermal expansion coefficient of ^{10 × 10 -6 / K~16 × 10} -6 / K ( particularly preferably 11 × ¹⁰ -6 / K~ 16 × 10 ⁻⁶ / K), characterized in that it was prepared to form a joint.
The joint formed using the joining material having such a configuration repeatedly increases and decreases in temperature between the operating temperature range (for example, 600 to 800 ° C.) and the temperature when not in use (typically normal temperature). Or even when it is a case where the process exposed to the high temperature beyond the said use temperature range is performed, high airtightness and mechanical strength can be maintained over a long period of time.

Further, in another preferred embodiment as the conductive bonding material disclosed herein, the Ag-coated glass particles characterized in that a plurality of Ag fine particles are fixed on the surface of the glass particles are the main components. And
The conductive bonding material having such a configuration is not a simple mixing of the powder made of glass and the powder made of Ag, but Ag in which a plurality of fine Ag particles smaller than the glass particles are fixed to the surface of the particles made of glass. Mainly coated glass particles. According to such a configuration, it is possible to suppress the ubiquitous presence of the Ag component when forming the bonded portion, and in the formed bonded portion, the Ag component (typically, the above Ag fine particles) is in a good dispersed state throughout. Can be maintained. For this reason, higher electrical conductivity and mechanical strength can be realized at the joint.

It is sectional drawing which shows typically flat SOFC (single cell) and the interconnector (electroconductive connection member) joined to this single cell as an example. It is a disassembled perspective view which shows typically the structure of a flat SOFC system (stack) as an example.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification (for example, the structure of the conductive bonding material) and matters necessary for the implementation of the present invention (for example, a method for constructing the SOFC itself) are the conventional ones in this field. It can be grasped as a design matter of those skilled in the art based on the technology. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  As described above, the conductive bonding material disclosed herein is a conductive bonding material for bonding the SOFC and a conductive connection member (typically an interconnector) connected to the SOFC to each other. (A) Ag and (b) the said crystal precipitation glass are included.

First, the crystal precipitated glass will be described.
When the SOFC (SOFC system) is used in a predetermined temperature range (typically 600 ° C. or higher, for example, 600 to 800 ° C.), a glass having a composition that hardly melts in the use temperature range is preferable as such a constituent component. In this case, the desired melting point (softening point) can be realized by adding or increasing or decreasing the component capable of adjusting the melting point (softening point) of the glass.
The conductive bonding material disclosed here is preferably an oxide glass containing SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O as essential constituent components. In addition to these essential components, various components (typically various oxide components) can be additionally contained depending on the purpose.

Is not particularly limited, the mass ratio of the oxide basis the total glass components (including the crystalline _portion), SiO 2: 60 to 75 _{wt%, Al} 2 O 3: _{5~15 wt%,} Na 2 O: _{3~15 wt%,} K 2 O: 5 to 15 wt%, MgO: 0-3% by weight, and CaO: it is preferable 0 to 3% by weight (preferably 0.1 to 3% by weight).
Further, the mass ratio of the oxide basis the total glass components (including the crystalline _portion), SiO 2: 60 to 75 _{wt%, Al} 2 O 3: _5~15 wt%, the total of Na ₂ O and _{K 2} O: What is 10-25 mass% and at least any one or both of MgO and CaO: 1-5 mass% is especially preferable. By adopting such a glass composition, it is possible to form a joint having a buffering effect and excellent sealing performance.
Further, a glass having such a composition has a glass softening point in a range of 600 to 800 ° C., for example, and an SOFC and a conductive connecting member (for example, a metal interface such as SUS) having the temperature range as a use temperature range. It is suitable as a material for joining (sealing) a connector or other connecting member. By having a glass softening point in the operating temperature range of SOFC, it is possible to achieve both high sealing performance (adhesion) and buffer performance (preventing cell breakage due to stress relaxation) at the joint.

The main constituent of the glass matrix of the conductive bonding material disclosed herein is silicon oxide (SiO ₂ ). That is, SiO ₂ is a main component constituting the skeleton of the glass layer (glass matrix) at the joint. It is also a component constituting the three types of crystals (cristobalite, leucite, and forsterite).
It is suitable that about 60 to 75% by mass of the total glass forming the joint is composed of SiO ₂ in terms of oxide, and about 60 to 70% by mass is composed of SiO _2. Particularly preferred. Also, undesirable SiO ₂ content is too too high melting point (softening point) is higher than the above range. On the other hand, if the SiO ₂ content is too lower than the above range, the water resistance and chemical resistance may be lowered, and the amount of crystal precipitation is reduced, which is not preferable.

Aluminum oxide (Al ₂ O ₃ ) constituting the glass matrix is a component involved in adhesion stability by controlling the fluidity of the glass. Al ₂ O ₃ is also a component constituting the leucite crystal.
Preferably, about 5 to 15% by mass is suitable as the oxide-converted mass ratio of the entire glass forming the joint, and about 10 to 15% by mass is preferred. If the Al ₂ O ₃ content is too lower than the above range, the adhesion stability may be lowered, and the amount of leucite crystals precipitated is reduced, which is not preferable. On the other hand, if the Al ₂ O ₃ content is too higher than the above range, the chemical resistance may be lowered.

Sodium oxide (Na ₂ O) and potassium oxide (K ₂ O) as alkali components constituting the glass matrix of the conductive bonding material disclosed herein are components that increase the thermal expansion coefficient (thermal expansion coefficient) of the glass matrix. It is. K ₂ O is a component constituting a leucite crystal.
The content of Na ₂ O and / or K ₂ O in the mass ratio in terms of oxide in the entire glass matrix forming the joint is suitably about 10 to 25% by mass (more preferably 15 to 25% by mass). If the content of these alkali components is too lower than the above range, the thermal expansion coefficient may be too low. Further, if the K ₂ O content is too low, the amount of leucite crystals precipitated is also not preferred. On the other hand, if the content of these alkali components is too high, the thermal expansion coefficient becomes excessively high. For the purpose of improving the stability (for example, chemical resistance) of the glass matrix, it is preferable to include both a sodium component and a potassium component. For example, the K ₂ O content is 5 to 15% by mass, and the Na ₂ O content is Is preferably 3 to 15% by mass (however, the total is 10 to 25% by mass of the entire glass matrix).

In the conductive bonding material disclosed here, MgO and CaO, which are alkaline earth metal oxides, are optional additives that can adjust the thermal expansion coefficient. CaO is a component that can increase the hardness of the glass and improve the wear resistance, and MgO is also a component that can adjust the viscosity during glass melting. MgO is a component constituting a forsterite crystal.
It contains MgO and / or CaO, which are alkaline earth metal oxides, in a mass ratio in terms of oxide of the entire glass matrix that forms the joint, approximately 6% by mass or less (typically 1 to 5% by mass). Is preferred. By containing these components, a glass matrix having a suitable thermal expansion coefficient in the operating temperature range (use temperature range) of SOFC can be formed. MgO is a component constituting a forsterite crystal.
For example, when SOFC is one joining target and a metal connecting member such as a metal interconnector is the other joining target, CaO is contained in a content of 3% by mass or less, and MgO is contained in a content of 3%. % Or less is preferable.

Moreover, the glass component of the conductive bonding material disclosed here is only the above-mentioned SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O, or those obtained by further adding CaO and / or MgO. However, as long as the object of the present invention can be realized, secondary components other than these main oxide components may be added according to various purposes. Examples of such secondary components include ZnO, Li ₂ O, Bi ₂ O ₃ , SrO, SnO, SnO ₂ , CuO, Cu ₂ O, TiO ₂ , ZrO ₂ , La ₂ O ₃ , B ₂ O _{3 and the} like. Can be mentioned. When these components are contained, the glass matrix itself is composed of a multi-component system, so that the stability (for example, chemical resistance) of the glass can be improved. For example, these secondary glass components may be contained in a content ratio of 10% by mass or less (typically 5% by mass or less, for example, 3% by mass or less) in terms of oxide in the entire glass matrix. That is, “substantially composed” with respect to the glass disclosed herein means that only the main oxide component is composed of a secondary component other than the main oxide component in terms of a mass ratio in terms of oxide. Including at a content of 10% by mass or less (preferably 5% by mass or less, particularly preferably 3% by mass or less) of the entire glass.
Moreover, it is preferable that the electroconductive joining material disclosed here does not contain boron (oxide form is B ₂ O ₃ ) as a glass constituent component. By not containing boron, it is possible to obviate the possibility that boron scattered at the interface between the solid electrolyte and the electrode will be deposited and cause the performance of the SOFC to deteriorate.
In addition, the precipitation amount of 1 type, 2 types, or 3 types of crystals of cristobalite crystal, leucite crystal, and forsterite crystal contained in the glass of the bonding material (crystal precipitation glass) is a constituent in the glass composition. It can adjust suitably with the content rate (composition) of (structural element).

On the other hand, Ag (silver or an alloy mainly composed of silver) is typically contained as a particulate material. As long as the object of the present invention can be realized, various shapes and sizes of Ag can be used. When granular Ag is used, the particle size of the Ag particles can be satisfactorily dispersed in the glass matrix. For example, the average particle diameter based on the light scattering method (typically laser diffraction / scattering method) (or the average particle diameter based on electron microscope observation; the same shall apply hereinafter) is 5 μm or less (for example, 1 μm to 5 μm). A degree of Ag particles is suitable.
Alternatively, Ag fine particles (Ag nanoparticles) composed of nano-order fine particles (that is, nanoparticles) having an average particle diameter of 1 μm or less (typically 1 nm to 1000 nm, for example, 5 nm to 200 nm) can be preferably used. .
Further, the content of Ag is not particularly limited as long as the object of the present invention is achieved, but the Ag content is 20% by mass or more and 90% by mass with the total amount of the crystal-deposited glass and the Ag component being 100% by mass. Less than is suitable, 20-80 mass% is preferable, and 50-80 mass% is especially preferable.
For example, according to the bonding material containing the Ag component at such a content, suitably, the electrical conductivity can be at least 400 S / cm or more, preferably at least 500 S / cm or more (for example, 500 ˜1500 S / cm, in particular 700-1500 S / cm).

There is no restriction | limiting in particular regarding the manufacturing method of the electroconductive joining material of the above compositions, The same method as manufacturing the conventional crystal precipitation glass is used. Typically, a compound as a starting material for obtaining various oxide components constituting the glass composition (for example, industrial products, reagents, oxides, carbonates, nitrates, composite oxides, etc. containing each component, Alternatively, various mineral raw materials) and other additives as required are charged into a mixer such as a dry or wet ball mill at a predetermined blending ratio and mixed for several to several tens of hours. The obtained admixture (powder) is dried, placed in a refractory crucible, and heated and melted under suitable high temperature (typically 1000 ° C. to 1500 ° C.) conditions.
Next, the obtained glass is crushed and subjected to crystallization heat treatment. For example, cristobalite is heated in the glass matrix by heating the glass powder from room temperature to about 100 ° C. at a heating rate of about 1 to 5 ° C./min and holding it in the temperature range of 800 to 1000 ° C. for about 30 to 60 minutes. One, two, or three kinds of crystals among crystals, leucite crystals and forsterite crystals can be precipitated.
The crystal-deposited glass thus obtained can be formed into a desired form by various methods. For example, a glass powder having an average particle diameter of about 0.1 μm to 10 μm based on, for example, a laser diffraction / scattering method can be obtained by pulverizing with a ball mill or classifying by appropriate sieving.

  An Ag component is added to the glass powder thus obtained. For example, the Ag component is added to the glass powder at a blending ratio determined so that the desired electrical conductivity can be achieved, and then to an appropriate amount of water or the like. An appropriate amount of medium is added and mixed using a ball mill similar to the above. Then, the powdery conductive joining material which concerns on this invention containing granular glass and granular Ag can be obtained by implementing the drying process for predetermined time.

Alternatively, various organic metal solutions containing Ag as a constituent metal element are added to the glass powder instead of mixing the previously produced Ag powder, and then Ag fine particles are deposited (coated) on the surface of the glass particles. Also good. For example, an organometallic compound (resinate) of Ag as a precursor of Ag, such as Ag alkoxide, acetylacetone complex, fatty acid salt, alkylsulfonate, alkylphosphonate, etc., is used as a reducing organic solvent (eg, propanol, butanol, pentanol). , Monohydric alcohols such as hexanol, heptanol, octanol, etc.) prepared by dissolving or dispersing in Ag can be used.
Specifically, by mixing an appropriate amount of such an Ag organometallic solution and glass powder, and then performing a heat treatment (typically 200 ° C. or higher, such as 500 ° C. or higher, eg 500 to 800 ° C.), The Ag precursor can be reduced, and Ag fine particles having an average particle size of typically 100 nm or less can be deposited on the surface of the mixed glass particles. By using such an Ag organometallic solution, it is possible to obtain a conductive bonding material in a state where a plurality of Ag fine particles having a particle size of nano order are fixed on the surface of glass particles. In the conductive bonding material having such a configuration, the precipitated Ag fine particles are prevented from being ubiquitous in the bonded portion, and the Ag component can be maintained in a substantially uniformly dispersed state throughout. For this reason, high electroconductivity and mechanical strength are realizable in this junction part.

As in the case of conventional bonding materials, the conductive bonding material in the powder state prepared as described above is typically prepared in the form of a paste and applied to the connecting portion between the member constituting the SOFC and the connecting member. can do. For example, a paste can be prepared by mixing an appropriate binder or solvent with the obtained conductive bonding material. Note that the binder, solvent, and other optional components (for example, a dispersant) that can be added to the paste are not particularly limited, and can be appropriately selected from conventionally known ones in paste production.
For example, a suitable example of the binder includes cellulose or a derivative thereof. Specific examples include hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, carboxyethyl cellulose, carboxyethyl methyl cellulose, cellulose, ethyl cellulose, methyl cellulose, ethyl hydroxyethyl cellulose, and salts thereof. It is preferable that a binder is contained in 2-20 mass% of the whole paste.

  Examples of the solvent that can be contained in the paste include ether solvents, ester solvents, ketone solvents, and other organic solvents. Preferable examples include ethylene glycol and diethylene glycol derivatives, high-boiling organic solvents such as toluene, xylene and terpineol, or combinations of two or more thereof. Although the content rate of the solvent in a paste is not specifically limited, About 5-35 mass% of the whole paste is preferable.

  The conductive bonding material disclosed here can be used in the same manner as the conventional bonding material of this type. Specifically, when joining the SOFC to be joined and at least one conductive connecting member (for example, a metal interconnector), a joining material is applied (applied) to at least one of the parts to be joined. To do. Then, both members are connected to each other via an applied (applied) material of the conductive material so that the two members do not directly contact each other. Then, the coated material is dried at an appropriate temperature (typically 60 to 100 ° C., for example, 80 ° C. ± 10 ° C.). Next, a temperature range (typically 600 to 1000 ° C., preferably 600 to 900 ° C., for example, 600 to 800) that is preferably equal to or higher than the use temperature range of the electrochemical cell and does not flow out of the glass. Calcination at about 0 ° C.). Thus, the electrochemical cell provided with the conductive material and the conductive connection member can be bonded via the conductive bonding material without directly contacting each other. In addition, it is possible to form a joint portion (seal portion) that blocks gas flow (that is, there is no gas leak) at the joint portion. Further, a joint portion made of such a conductive bonding material is interposed between the SOFC and the conductive connection member, thereby buffering a difference in thermal expansion between the SOFC and the conductive connection member. It is possible to prevent the SOFC and / or the conductive connecting member from being damaged or the SOFC (single cell) from being peeled off from the connecting member due to the generated stress.

  For example, the SOFC (single cell) and the interconnector can be joined by applying the above-mentioned bonding material so as to close the gap that may occur between the SOFC (single cell) and the metal interconnector. A predetermined gas (for example, fuel gas) can be supplied to the SOFC (single cell) without leaking at the joined portion. In addition, the joint made of such a conductive bonding material exhibits flexibility in the operating temperature range of the SOFC (single cell), thereby buffering the difference in thermal expansion between the SOFC (single cell) and the interconnector. It is possible to maintain airtightness at the joint while preventing damage and peeling.

The conductive bonding material disclosed herein is an SOFC having various structures, for example, a conventionally known flat plate shape, a tubular shape, a tubular shape, or a flat tube shape (Flat) in which a peripheral side surface of a cylinder is vertically crushed. It can be preferably applied to SOFC such as (tubular), and is not particularly limited in shape or size.
For example, as schematically shown in FIG. 1 as a basic configuration, one of the plate-like solid electrolytes (typically an oxide ion conductor made of a zirconia-based ceramic material such as yttria-stabilized zirconia (YSZ)) 112 An anode (fuel electrode) 116 is formed on the other surface, and an anode (fuel electrode) 116 is formed on the other surface. The solid electrolyte 112, the cathode 114, and the anode 116 are joined to each other via a joint (joining material) 120. An SOFC (SOFC system) 110 including connectors (conductive connection members) 118A and 118B can be provided. An oxygen supply gas flow path (typically an air flow path) 102 is formed between the cathode 114 and the cathode side interconnector 118A, and a fuel gas (which is between the anode 116 and the anode side interconnector 118B). A hydrogen supply gas) channel 104 is formed.

As a specific example of the SOFC system to which the present invention can be preferably applied, the SOFC stack 100 shown in FIG. 2 will be described with reference to the drawings.
As shown in FIG. 2, this flat SOFC stack 100 is composed of a single-cell 20A, 20B including a layered solid electrolyte 22, a cathode (air electrode) 24, and an anode (fuel electrode) 26. 10 is configured as a stack in which a plurality of layers are stacked. The unit cells 20A and 20B have a sandwich structure in which the solid electrolyte 22 is sandwiched between a layered cathode 24 and an anode 26, respectively.

The interconnector 10 provided in the SOFC stack 100 is typically made of metal, and the structure thereof will be described below using the interconnector 10A disposed in the center of the drawing as an example.
The interconnector 10A is sandwiched between two single cells 20A and 20B, one cell facing surface 12 faces (adjacent) the anode 26 of the cell 20A, and the other cell facing surface 14 faces the cell 20B. Opposite (adjacent) the cathode 24. The cell facing surfaces 12 and 14 of the interconnector 10A and the corresponding surfaces of the anode 26 or the cathode 24 on the corresponding single cells 20A and 20B are bonded by the conductive bonding material disclosed herein (described above). (See the joint 120 in FIG. 1).
The cell facing surface 12 is formed with a plurality of grooves, and constitutes a fuel gas passage 13 through which the supplied fuel gas (for example, H ₂ gas) flows. Similarly, a plurality of grooves are also formed in the opposite cell facing surface 14 to constitute an air flow path 15 through which supplied air (Air) flows. In the interconnectors 10 and 10A of this form, as shown in FIG. 2, typically, the fuel gas passage 13 and the air passage 15 are formed so that the directions of the passages are orthogonal to each other.

Next, materials preferable for constituting the SOFC (single cell) and the interconnector as described above will be described.
The material for forming the anode is not particularly limited as long as it is a material that is conventionally suitable for constituting this kind of SOFC anode. Preferred materials include nickel (Ni) and copper (Cu). , Gold (Au), platinum (Pt), palladium (Pd), ruthenium (Ru) and other platinum group elements, cobalt (Co), La (lanthanum), Sr (strontium), Ti (titanium) and the like And / or a metal oxide composed of one or more of these metal elements and capable of functioning as a catalyst. Specific examples include metals or metal oxides made of Ni, Co, Ru or other platinum group elements. Of these, Ni is a particularly suitable metal species because it is cheaper than other metals and has a sufficiently high reactivity with fuel gas such as hydrogen.

  Alternatively, a composite in which these metals or metal oxide elements or oxides are mixed can also be used. For example, the anode can be formed using a composite material of a metal or metal oxide to be an anode forming material as described above and a solid electrolyte forming material described later. For example, a suitable example is cermet of Ni or Ru and stabilized zirconia described later. Although not particularly limited, for example, the mixing ratio of the anode forming material and the solid electrolyte forming material described later (anode forming material: solid electrolyte forming material) is suitably about 90:10 to 40:60 by mass ratio. is there. By setting the mixing ratio in such a range, sufficient electrode (anode) activity and matching of the thermal expansion coefficients of the anode and the fixed electrolyte layer can be achieved at a high level. The range of the mixing ratio (mass ratio) is more preferably about 80:20 to 45:55.

As a material for forming the solid electrolyte, a compound having high oxide ion conductivity is preferably used. For example, zirconium (Zr), cerium (Ce), magnesium (Mg), scandium (Sc), titanium (Ti), aluminum (Al), yttrium (Y), calcium (Ca), gadolinium (Gd), samarium (Sm), barium (Ba), lanthanum (La), strontium (Sr), gallium (Ga), bismuth An oxide containing two or more elements selected from (Bi), niobium (Nb), and tungsten (W) is preferable. For example, substances (stabilizers) such as yttria (Y ₂ O ₃ ), calcia (CaO), scandia (Sc ₂ O ₃ ), magnesia (MgO), ytterbia (Yb ₂ O ₃ ), and erbia (Er ₂ O ₃ ) ) Stabilized zirconia (ZrO ₂ ), or ceria (CeO ₂ ) doped with yttria (Y ₂ O ₃ ), gadolinia (Gd ₂ O ₃ ), samaria (Sm ₂ O ₃ ), etc. Can be mentioned. The stabilized zirconia is preferably stabilized by one or more stabilizers.
For example, yttria-stabilized zirconia (YSZ) in which yttria is added at a rate of 5 to 10 mol%, or gadolinia-doped ceria (GDC) to which gadolinia is added at a rate of 5 to 10 mol% is given as a preferable example. It is done. When the content ratio of the stabilizer or the dopant is too lower than 5 mol%, it is not preferable because the oxide ion conductivity of the anode is lowered. Conversely, when the content ratio is too higher than 10 mol%, the oxide ion conductivity (ion conductivity) of the adjacent anode is lowered, which is not preferable.

The material for forming the cathode is preferably a material that is highly active in ionizing oxygen, and in particular, silver (Ag), lanthanum (La), samarium (Sm) or other lanthanoid elements, strontium (Sr), manganese ( Mn), cobalt (Co), iron (Fe), calcium (Ca), barium (Ba), nickel (Ni), magnesium (Mg) elements and materials composed of one or more of these oxides are suitable. It is. For example, a transition metal perovskite oxide, or a composite of a transition metal perovskite oxide and a solid electrolyte forming material can be preferably used. Examples thereof include lanthanum strontium manganite (LSM) and lanthanum strontium cobaltite (LSC) perovskite oxides. More specifically, transition metal perovskite oxides include LaSrMnO _3-δ , LaCaMnO _3-δ , LaMgMnO _3-δ , LaSrCoO _3-δ , LaCaCoO _3-δ , LaSrFeO _3-δ , LaSrCoFeO _3-δ , LaSrNiO _3-δ , SmSrCoO _{3-δ and the} like. In the above chemical formula, δ is a value determined to satisfy the charge neutrality condition. That is, the number of oxygen atoms in each chemical formula listed above varies depending on the type of atom that substitutes a part of the perovskite structure, the substitution ratio, and other conditions, so that it is difficult to display accurately. For this reason, it is appropriate to adopt a positive number δ (0 <δ <1) not exceeding 1 as a value that is determined so as to satisfy the charge neutrality condition, and to display the number of oxygen atoms as 3-δ. However, in the following, 3 may be displayed for convenience. However, even if the number of oxygen atoms in the chemical formula showing this type of compound is represented as 3 for convenience, it does not represent a different compound.

  A suitable example is a composite (composite material) of these transition metal perovskite oxides and the above solid electrolyte forming material such as zirconia. In the case of adopting the composite, the oxide ion conductivity is improved among the electron conductivity and oxide ion conductivity, which are necessary characteristics for the cathode, so that the oxide ions generated at the cathode are transferred to the solid electrolyte. This is preferable because it easily migrates and improves the electrode activity of the cathode. Although not particularly limited, for example, the mixing ratio of the transition metal perovskite oxide to the solid electrolyte forming material (perovskite oxide: solid electrolyte forming material) is about 90:10 to 60:40 in mass ratio. Is appropriate. By setting the mixing ratio in such a range, sufficient electrode (cathode) activity and matching of the thermal expansion coefficient between the cathode and the fixed electrolyte layer can be achieved at a high level. The range of the mixing ratio (mass ratio) is more preferably about 90:10 to 70:30.

  The interconnector only needs to have sufficient conductivity under the temperature conditions for operating the SOFC, and may be various metal materials or ceramic materials. In consideration of the effect of forming the joint portion using the conductive joint material disclosed herein, an interconnector made of various metal materials can be suitably used. For example, an interconnector made of a steel material such as silver, nickel, iron, stainless steel (various SUS) or an alloy containing these metals can be suitably used.

In addition, about the method of manufacturing SOFC (single cell) and SOFC system (stack etc.) using the various materials mentioned above, what is necessary is just to employ | adopt a conventionally well-known manufacturing method, and does not characterize this invention. . For example, when the flat SOFC stack 100 as shown in FIG. 2 is manufactured, the solid electrolyte 22 is prepared by a predetermined forming method (or film forming method) using an appropriate solid electrolyte material. Next, an appropriate cathode forming material as described above is applied to one side surface of the solid electrolyte 22, and an appropriate anode forming material as described above is applied to the other side surface of the solid electrolyte 22. Then, the cathode 24 and the anode 26 are formed on both sides of the solid electrolyte 22 by firing the solid electrolyte 22 provided with the cathode forming material and the anode forming material on both sides at an appropriate temperature. SOFC (single cell) 20A, 20B can be obtained.
The predetermined interconnectors 10 and 10A are prepared, and the cell facing surfaces 12 and 14 and the corresponding facing surfaces of the anode 26 or the cathode 24 on the side of the single cells 20A and 20B, respectively, are electrically conductively disclosed. A SOFC system (here, a stack) in which a plurality of single cells 20A and 20B are stacked via the interconnectors 10 and 10A is constructed by joining the materials by firing preferably in the above-described temperature range. .

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the following examples.

<Production of anode supported SOFC (single cell)>
8 mol% yttria-stabilized zirconia (YSZ) powder (average particle size: about 1 μm) and NiO powder (average particle size: about 3 μm), a common binder (here, polyvinyl alcohol (PVA) was used), a dispersant. (Ammonium polyacrylate was used here) and a solvent (water here) were added and kneaded. Subsequently, sheet formation was performed using this kneaded material (slurry or paste-form anode forming material) to obtain a disk-shaped anode molded body having a diameter of about 20 mm and a thickness of about 1 mm.
Next, the same binder, dispersant and solvent as above were added to 8 mol% YSZ powder (average particle size: about 1 μm) and kneaded. Subsequently, this kneaded material (form material for forming a paste-like solid electrolyte membrane) was printed and formed on the anode molded body into a disk shape having a diameter of 16 mm and a thickness of 10 μm to 30 μm. The unfired laminate comprising the anode molded body and the solid electrolyte membrane supported on the molded body was dried and then fired in the air at a firing temperature of 1200 ° C to 1400 ° C.
Next, a binder common to La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ powder (average particle size: about 1 μm) (here, ethyl cellulose was used), and a solvent (here Turpineol was used) and kneaded. Next, this kneaded product (pasted cathode forming material) was printed on the solid electrolyte membrane in a disk shape having a diameter of 13 mm and a thickness of 10 μm to 30 μm. Subsequently, it baked in air | atmosphere at the calcination temperature of 1000 to 1200 degreeC. In this way, an anode-supported SOFC (single cell) composed of an anode, a solid electrolyte membrane, and a cathode was produced.

<Preparation of paste-like conductive bonding material>
The ratios of SiO ₂ powder, Al ₂ O ₃ powder, Na ₂ CO ₃ powder, K ₂ CO ₃ powder, MgCO ₃ powder and CaCO ₃ powder having an average particle diameter of about 1 to 10 μm in terms of oxides are shown below ( (Mass%) to prepare a glass raw material powder.
SiO ₂ 62% by weight;
Al ₂ O ₃ 13% by mass;
Na ₂ O 11% by mass;
12% by mass of K ₂ O;
MgO 1% by mass;
CaO 1% by mass;
Subsequently, the glass raw material powder prepared above was melted in a temperature range of 1000 to 1500 ° C. (for example, 1400 ° C.) and rapidly cooled to form glass. Thereafter, the glass was crushed and heat-treated at 800 to 1000 ° C. for 30 to 60 minutes. By this heat treatment, at least one kind of crystal of cristobalite crystal, leucite crystal and forsterite crystal was precipitated in the glass matrix. Thereafter, the obtained crystal-deposited glass was pulverized and further classified to obtain a crystal-deposited glass powder having an average particle diameter of about 2 μm based on the light scattering method.

Next, as a conductive component,
(1) An Ag powder having an average particle diameter of about 2 μm based on the light scattering method, and (2) an organometallic solution (specifically, a silver resinate solution) containing Ag as a constituent metal element were prepared.
Then, the crystallized glass powder prepared above was mixed with the above (1) Ag powder or (2) Ag organometallic solution. Specifically, as shown in Table 1 below, a total of seven types of samples were prepared. That is, with respect to a predetermined amount of crystal-deposited glass, (1) Ag powder or (2) in which the Ag mass ratio (the total of glass and Ag is 100% by mass) is the value shown in Table 1. ) Ag organometallic solution was added and mixed. Furthermore, the said binder and solvent were mixed and the paste-form electroconductive joining material was produced. Specifically, by adding and mixing the above-mentioned binder in an amount of 3% by mass of the entire paste and terpineol in an amount of 30% by mass of the entire paste, it corresponds to Samples 1 to 7 shown in Table 1. In total, seven types of paste-like conductive bonding materials were produced. Further, as sample 8, the Ag powder of (1) above was added to a predetermined amount of commercially available Pyrex (registered trademark) glass powder (average particle size: about 2 μm) so that the mass ratio of Ag was 50% by mass. And the process similar to another sample was performed and the paste-form electroconductive joining material was produced.

<Joint treatment>
Using the total of 8 types of conductive bonding materials corresponding to Samples 1 to 8 shown in Table 1, the anode-supported SOFC single cell produced above and the interconnector were bonded.
Specifically, a thin plate-like interconnector (thickness: about 1 mm) made of SUS430 is used, and any one of the above samples 1 to 8 is provided on the surface of the interconnector and / or the surface of the anode-supported SOFC single cell. The pasty conductive bonding material was applied. Then, the interconnector and the single-cell cathode were bonded together by interposing the bonding portion made of the bonding material by firing in the atmosphere at 600 to 800 ° C. for 1 hour.
Here, the thermal expansion coefficient (however, an average value between 25 ° C. and 500 ° C. based on differential expansion type thermomechanical analysis (TMA)) of the joint obtained by using the paste-like bonding materials of Samples 1 to 8 It was measured. The results are shown in the corresponding column of Table 1. As shown in Table 1, the samples 1 to 5 was in the range of either ^{10 × 10 -6 / K~16 × 10} -6 / K. In addition, the thermal expansion coefficient of the single cell used here was approximately 10 to 11 × 10 ⁻⁶ / K. Moreover, the thermal expansion coefficient on the same conditions of the SUS interconnector used here was about 12 * 10 < ^-6 > / K.
Moreover, the softening point (degreeC) of the electroconductive joining part obtained from each joining material measured based on the said TMA is shown in the applicable column in Table 1. As shown in Table 1, the softening points of Samples 1 to 5 were all in the range of 600 to 800 ° C (particularly 650 to 750 ° C).

<Measurement of conductivity>
Next, the powdered samples 1 to 8 before being made into a paste are press-molded into columns each having a diameter of 3 mm and a height of 20 mm, and these are fired at 700 ° C. on the SUS430 interconnector. The fired body corresponding to 1-8 was produced.
And after apply | coating the platinum paste used as an electrode on the surface of each baking body, the platinum wire for connecting an electric current terminal and a voltage terminal was attached to this electrode part, and it baked at 850-1100 degreeC for 10 to 60 minutes, arbitrary Conductivity [S / cm] was determined by a DC four-terminal method in an apparatus adjustable to temperature. The measurement results of conductivity under a certain temperature condition (here, 700 ° C.) are shown in the corresponding column of Table 1.
As shown in Table 1, good electrical conductivity was shown except for the fired body of Sample 6. In particular, Samples 2 to 5 had a conductivity of 400 S / cm or more. Among them, the conductivity of Samples 3 to 5 was 500 S / cm or more (specifically 700 to 1500 S / cm). In particular, as is clear from the comparison between Sample 2 and Sample 4 and the comparison between Sample 3 and Sample 5, when the Ag content is the same, the sample using the Ag organometallic solution of (2) above as the Ag supply source It was recognized that this contributed to the improvement of electrical conductivity.
Samples 7 and 8 also showed high electrical conductivity, but cracks were observed at the joint during electrical conductivity measurement at 700 ° C., confirming that they were unsuitable as a joint material. Moreover, scattering of boron was observed in the fired body of Sample 8 containing commercially available Pyrex (registered trademark) glass powder.

<Measurement of mechanical strength (peel strength)>
The mechanical strength (peel strength) of the joint obtained from each sample was measured as follows. That is, with the universal testing machine, the interconnector (that is, the cell) was fixed as a specimen, and a tensile stress was applied to measure the stress when the specimen was broken.
The measurement results are shown in the corresponding column of Table 1. It was confirmed that the joints obtained using the joining materials of Samples 1 to 5 had sufficient strength of 100 MPa (specifically, about 100 to 200 MPa). In particular, as is clear from the comparison between Sample 2 and Sample 4 and the comparison between Sample 3 and Sample 5, when the Ag content is the same, the sample using the Ag organometallic solution of (2) above as the Ag supply source It was confirmed that this contributed to the improvement of mechanical strength.

  As is clear from the above test, according to the present invention, using the conductive bonding material disclosed herein, the SOFC and the conductive connecting member (for example, a metal interconnector) are bonded well, An electrically good conductive joint can be formed.

10, 10A, 118A, 118B Interconnector 12, 14 Cell facing surface 13, 104 Fuel gas flow path 15, 102 Air flow path 20A, 20B Single cell 22, 112 Solid electrolyte 24, 114 Cathode (air electrode)
26, 116 Anode (fuel electrode)
100, 110 SOFC system 120 joint

Claims (11)

A solid oxide fuel cell comprising an anode, a cathode, and a solid electrolyte;
At least one conductive connecting member joined to the solid oxide fuel cell;
A solid oxide fuel cell system comprising:
The joint between the solid oxide fuel cell and the conductive connecting member is formed by depositing Ag fine particles having an average particle size of 100 nm or less on the surface of the glass particles, and the deposited Ag on the surfaces of the glass particles. By firing Ag-coated glass particles characterized in that a plurality of fine particles are fixed in a temperature range in which the glass does not flow out, the following two components:
(A) Ag; and
(B) Glass characterized in that at least one crystal selected from cristobalite crystal, leucite crystal and forsterite crystal is precipitated in the glass matrix;
Are formed together,
Here, the glass mixed in the joint portion has the following composition in mass ratio in terms of oxide:
SiO ₂ 60 to 75 wt%;
Al ₂ O ₃ 5 to 15 wt%;
Na ₂ O 3-15% by mass;
K ₂ O 5-15% by mass;
MgO 0 to 3% by mass;
CaO 0 to 3% by mass;
Pressurized et al. Have been configured,
A solid oxide fuel cell system in which the Ag component composed of the precipitated Ag fine particles is dispersed throughout the joint. The glass mixed in the joint is
The following composition in mass ratio in terms of oxide:
SiO ₂ 60 to 75 wt%;
Al ₂ O ₃ 5 to 15 wt%;
Na ₂ O and K ₂ O 10-25% by weight;
MgO and / or CaO 1-5% by mass;
Pressurized et al and consists, solid oxide fuel cell system according to claim 1.   3. The solid oxide fuel cell system according to claim 1, wherein the entire joint is 100 mass%, and the Ag content in the joint is 50 to 80 mass%.   The solid oxide fuel cell system according to claim 3, wherein the electrical conductivity of the joint at 700 ° C is at least 500 S / cm or more. Thermal expansion coefficient of the bonding portion is in the range of ^{10 × 10 -6 / K~16 × 10} -6 / K, a solid oxide fuel cell system according to any one of claims 1-4.   The solid oxide fuel cell system according to any one of claims 1 to 5, wherein the conductive connecting member is an interconnector that is conductively connected to a cell constituting the solid electrolyte fuel cell. A conductive joining material for joining a solid oxide fuel cell and a conductive connecting member connected to the solid oxide fuel cell, the following two components:
(A) Ag; and
(B) A glass characterized in that at least one crystal selected from cristobalite crystal, leucite crystal and forsterite crystal is precipitated in a glass matrix, and having a mass ratio in terms of oxide The following composition:
SiO ₂ 60 to 75 wt%;
Al ₂ O ₃ 5 to 15 wt%;
Na ₂ O 3-15% by mass;
K ₂ O 5-15% by mass;
MgO 0 to 3% by mass;
CaO 0 to 3% by mass;
Pressurized et al. Structure made is to have a glass;
Including
An Ag-coated glass formed by depositing Ag fine particles having an average particle diameter of 100 nm or less on the surface of glass particles made of the glass, wherein a plurality of the precipitated Ag fine particles are fixed to the surface of the glass particles. A conductive bonding material mainly composed of particles. The glass is
The following composition in mass ratio in terms of oxide:
SiO ₂ 60 to 75 wt%;
Al ₂ O ₃ 5 to 15 wt%;
Na ₂ O and K ₂ O 10-25% by weight;
MgO and / or CaO 1-5% by mass;
Pressurized et al and consists, conductive bonding material according to claim 7.   The conductive bonding material according to claim 7 or 8, wherein the total content of Ag and glass is 100% by mass, and the content of Ag is 50 to 80% by mass. Coefficient of thermal expansion were prepared in order to form the joint in the range of ^{10 × 10 -6 / K~16 × 10} -6 / K, conductive bonding according to any one of claims 7 to 9 Wood. The conductive bonding material according to any one of claims 7 to 10, further comprising a binder and a liquid medium and prepared in a paste form.

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