JP2008200724A - Joining material, joint member, joining method, and solid electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive joining material for forming a joint member which is free from any degradation of the joining strength or less degraded in the joining strength even when the joint member is used under a reducing atmosphere during the operation of an SOFC. <P>SOLUTION: A joining material is formed of a material containing a base material containing nickel oxide, metal nickel and a thermal expansion adjusting material having the coefficient of thermal expansion of ≤10×10<SP>-6</SP>/°C, but substantially not containing iron oxide. As a result, the metal nickel is turned into nickel oxide during the atmospheric heat treatment, resulting in the volumetric expansion. Thus, the joining member obtained after the atmospheric heat treatment becomes dense, and the joining strength after the atmospheric heat treatment is enhanced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a bonding material used when an electrode such as a solid oxide fuel cell (hereinafter referred to as “SOFC”) or a steam electrolysis cell and other structural members are electrically bonded, and bonding using the same. The present invention relates to a member, a joining method, and an SOFC having the joining member.

  As a general configuration of the main part of the SOFC, the one shown in FIG. 1 is known. The power generation membrane 2 includes a solid electrolyte membrane 4 of yttria-stabilized zirconia, a fuel side electrode 3 and an air side electrode 5 formed on both sides thereof, and has a dimple shape. An interconnector 7 electrically connected to the fuel side electrode 3 is provided on the fuel side electrode 3 side of the power generation membrane 2, and the air side electrode 5 and the electrical side are connected to the air side electrode 5 side of the power generation membrane 2. Connected interconnector 7 is provided. In the SOFC having such a configuration, conductive joining members 11 and 12 are generally used between the interconnector 7 and the fuel-side electrode 3 and between the interconnector 7 and the air-side electrode 5.

  In the SOFC having the configuration shown in FIG. 1, the conductive joining members 11 and 12 are generally formed by sintering a paste-like joining material disposed between an electrode and another constituent member. Since SOFC generally generates power at an operating temperature of about 1000 ° C., the conductive joining members 11 and 12 are also required to have heat resistance that can withstand this temperature.

  By the way, generally, when electrically joining members at low temperatures, silver paste or platinum paste is known as the joining material. Here, the silver paste has a low electric resistance of silver and is generally used as a conductive adhesive. However, the melting point of silver is about 960 ° C., and it cannot be used for the power generation at 1000 ° C. like the SOFC. In the case of platinum paste, it can be used even at 1000 ° C., but there is a problem that the cost is increased.

Therefore, a bonding material including nickel oxide, iron oxide, and titanium oxide as a base material has been proposed as a material for forming a bonding member having good conductivity and bondability (see, for example, Patent Document 1).
JP-A-8-287930

  However, as described above, in the joining material containing nickel oxide, iron oxide, and titanium oxide as the base material, nickel oxide is added, and the nickel oxide is reduced to metallic nickel during operation to ensure the conductivity of the joining member. However, since the volumetric shrinkage is accompanied when nickel oxide is reduced, the joining member becomes slightly porous, and there is a problem that the joining strength after reduction is reduced as compared with the case where it is manufactured in an oxidizing atmosphere. .

This invention is made | formed in view of such a situation, Comprising: It aims at providing the bonding | jointing material which forms the joining member which does not reduce a joint strength after reduction | restoration or there is little decline in a joint strength.
It is another object of the present invention to provide a joining member which is formed from the joining material and whose joining strength is not easily lowered even when used in a reducing atmosphere in SOFC operation or the like.
Further, the present invention uses the above-mentioned bonding material to provide a bonding portion in which the bonding strength is not easily lowered even when used in a reducing atmosphere during operation or the like between the fuel-side electrode in SOFC and another member such as an interconnector. An object is to provide a bonding method to be formed.
In addition, the present invention provides a SOFC having improved reliability, including a joint portion between the fuel side electrode and another member such as an interconnector, in which the joint strength is not easily lowered even when used in a reducing atmosphere in operation or the like. The purpose is to provide.

In order to solve the above problems, the present invention employs the following means.
The bonding material according to the present invention includes a base material containing nickel oxide, metallic nickel, and a thermal expansion adjusting material having a thermal expansion coefficient of 10 × 10 ⁻⁶ / ° C. or less, and substantially does not contain iron oxide. It is.
Since the bonding material of the present invention uses metallic nickel and the volume expansion occurs when the metallic nickel becomes nickel oxide during the atmospheric heat treatment, the bonding member obtained after the atmospheric heat treatment becomes dense, and the bonding strength after the atmospheric heat treatment. Will improve. Further, when the joining member is reduced, only the volume expansion during the sintering by the atmospheric heat treatment contracts, so the reduction in joining strength is small. In addition, the thermal expansion adjusting material suppresses the thermal expansion difference with the electrolyte and the interconnector by reducing the thermal expansion coefficient of the entire conductive bonding material, and the thermal expansion difference during the thermal cycle due to the shutdown of the SOFC cell. This contributes to suppression of peeling due to.
Therefore, the joining member formed from the joining material of the present invention has high joining strength both in the initial use after sintering by atmospheric heat treatment and after use in a reducing atmosphere.

The joining member according to the present invention is obtained by sintering the joining material of the present invention disposed between a plurality of members.
Therefore, the joint member of the present invention has high joint strength both in the initial use and after use in a reducing atmosphere when used in a joint portion between a fuel-side electrode and an interconnector in SOFC.

The bonding method according to the present invention is a method in which the bonding material of the present invention is disposed between a plurality of members and the bonding material is sintered.
Therefore, according to the bonding method of the present invention, it is possible to form a bonded portion having excellent bonding strength between the fuel-side electrode and the interconnector and the like in the SOFC.

The SOFC according to the present invention includes a plurality of members and the joining member of the present invention that joins between the plurality of members.
Therefore, the SOFC of the present invention is excellent in reliability because it can increase the bonding strength of the bonding portion between the fuel side electrode and the interconnector.

According to the present invention, it is possible to provide a bonding material that forms a bonding member that has no decrease in bonding strength or a small decrease in bonding strength even after reduction.
Further, according to the present invention, it is possible to provide a joining member in which the joining strength is not easily lowered even when used in a reducing atmosphere in SOFC operation or the like.
Further, according to the present invention, there is provided a joining method for forming a joint portion in which the joining strength is not easily lowered even when used in a reducing atmosphere in operation or the like between the fuel side electrode in SOFC and another member such as an interconnector. Can be provided.
In addition, according to the present invention, there is a joint between the fuel side electrode and another member such as an interconnector, etc., and the joint strength is not easily lowered even when used in a reducing atmosphere in operation, etc., and reliability is improved. SOFC can be provided

Hereinafter, embodiments of the present invention will be described.
The first embodiment of the present invention includes a base material containing nickel oxide (NiO), metallic nickel (Ni), and a thermal expansion adjusting material having a thermal expansion coefficient of 10 × 10 ⁻⁶ / ° C. or less, In particular, the bonding material does not contain iron oxide (Fe ₂ O ₃ ).
When the thermal expansion coefficient of the thermal expansion adjusting material exceeds 10 × 10 ⁻⁶ / ° C., the thermal expansion coefficient of the entire conductive bonding material is lowered, and peeling due to a thermal expansion difference during a thermal cycle due to the operation stop of the SOFC cell or the like. This is not preferable because the effect of suppressing the above cannot be sufficiently obtained.
Since iron oxide decreases the bonding strength and increases the bonding resistance after reduction of the bonding member, it is preferable that the bonding material does not substantially contain iron oxide.

The bonding material preferably contains 30 parts by weight or more and 70 parts by weight or less of the metal nickel out of 100 parts by weight of the total amount of the nickel oxide and the metal nickel.
If the content of the metallic nickel is less than 30 parts by weight, the effect of improving the joining strength of the joining member obtained after the atmospheric heat treatment and the effect of suppressing the reduction of the joining strength after reduction are not sufficient, which is not preferable. Moreover, when the content of the metallic nickel exceeds 70 parts by weight, the thermal expansion coefficient of the joining member becomes larger than other members (for example, a power generation film or an interconnector in SOFC), which is not preferable.

The bonding material preferably contains 10 parts by weight or more and 20 parts by weight or less of the thermal expansion adjusting material in 100 parts by weight of the base material.
When the content of the thermal expansion adjusting material is less than 10 parts by weight, the effect of preventing reduction shrinkage may be small and insufficient, which is not preferable. In addition, if the content of the thermal expansion adjusting material exceeds 20 parts by weight, the conductivity may be lowered, which is not preferable.

The thermal expansion adjusting material preferably contains at least one material selected from the group consisting of alumina, silicon nitride, silicon carbide, and fused silica.
The thermal expansion coefficients of these materials are about 8 × 10 ⁻⁶ / ° C. for alumina, about 4 × 10 ^{−6 for} silicon nitride, about 5 × 10 ^{−6 for} silicon carbide, and about 1 × 10 ⁻⁶ / for fused silica. Each material functions as a thermal expansion adjusting material having a good reduction shrinkage preventing effect in the bonding material of the present invention.

The nickel oxide is preferably particulate nickel oxide having an average particle size of 0.5 μm to 5 μm. The metallic nickel is preferably particulate metallic nickel having an average particle size of 0.3 μm to 5 μm.
When the average particle diameter of metallic nickel is smaller than 0.3 μm and the average particle diameter of nickel oxide is smaller than 0.5 μm, the shrinkage rate of the joining member increases, so that cracking occurs during the atmospheric heat treatment, and the bonding strength decreases. This is not preferable. On the other hand, if the average particle diameter of metallic nickel and the average particle diameter of nickel oxide are larger than 5 μm, the sinterability of the joining member is lowered, so that the joining strength may be lowered.

The thermal expansion adjusting material is preferably a particulate thermal expansion adjusting material having an average particle diameter of 5 μm to 15 μm.
If the average particle diameter of the thermal expansion adjusting material is smaller than 5 μm, the shrinkage rate of the joining member increases, so that cracking occurs during the atmospheric heat treatment, the bonding strength decreases, and the thermal expansion adjusting material enters between the nickel particles. Since it becomes a resistor and reduces the conductivity of the joining member, it is not preferable. Moreover, when the average particle diameter of the thermal expansion adjusting material is larger than 15 μm, the sinterability of the joining member is lowered, and the joining strength of the joining member is lowered, which is not preferable.

The bonding material preferably includes a vehicle in addition to the base material.
The vehicle is a raw material that evaporates when the bonding material is sintered and does not remain in the sintered bonding member. By using the vehicle, the base material of the bonding material is made into a paste to facilitate handling. be able to.
The vehicle is not particularly limited as long as it can disperse the powder, but preferably includes butyl carbitol, turpentine oil, butanol and the like, and particularly preferably butyl carbitol. The addition amount of the vehicle varies depending on the type of the vehicle, but when the base material is 100 parts by weight, it is preferable to add 30 parts by weight or more and 50 parts by weight or less.

  In the second embodiment of the present invention, the bonding material according to the first embodiment is disposed between a plurality of members, and the bonding material is sintered from the bonding material, and the bonding material is obtained from the bonding material by the bonding method. It is a joining member.

  Examples of the plurality of members to be joined include SOFC constituent members, and the fuel-side member that is in a reducing atmosphere during operation of the SOFC can suppress a reduction in joining strength during reduction. Since the effect can be exhibited, it is preferable. Therefore, the joining method of the present embodiment can be suitably applied to joining of the SOFC fuel-side electrode and another fuel-side member (for example, an interconnector).

In the bonding method of the present embodiment, a known coating method is employed, for example, a screen printing method can be employed. For example, when joining an interconnector and a fuel-side electrode formed on a dimple-like solid electrolyte by a screen printing method, first a screen printing method of printing a paste-like joining material from a hole in the screen Then, uniformly apply to a thickness of 100 to 200 μm on the flat plate of the interconnector, place the corrugated plate for connection, and perform heat treatment in the air. In the heat treatment, the vehicle is evaporated up to 200 ° C., and is further processed and sintered at 1000 ° C. or higher, preferably 1000 to 1250 ° C. in consideration of the working temperature of SOFC. This heat treatment is particularly preferably a treatment at 1250 ° C. for 4 hours. By this heat treatment, the bonding material is sintered and becomes the bonding member of this embodiment. Since this heat treatment is treatment in air, a part of the nickel metal in the bonding material is oxidized to become nickel oxide, and the volume expands. As a result, the shrinkage of the nickel oxide in the joining member that is reduced to become nickel in the SOFC can be mitigated thereafter, and the decrease in conductivity caused by the disconnection of the electron flow due to the shrinkage can be mitigated. Further, the nickel oxide surface newly generated by oxidation of nickel in the bonding material has an advantage of high bakeability by sintering and high adhesion after sintering.

The third embodiment of the present invention is an SOFC having a plurality of members and the joining member according to the second embodiment that joins the plurality of members.
As the plurality of members, the fuel-side member that is in a reducing atmosphere during the operation of the SOFC is preferable because the effect of the bonding material of the present invention that can suppress a decrease in bonding strength during reduction can be achieved. Therefore, the SOFC of this embodiment includes an SOFC in which a fuel-side electrode of the SOFC and another fuel-side member (for example, an interconnector) are joined by the joining member according to the second embodiment.

  The SOFC of this embodiment can have the same configuration as that of a conventional SOFC except that the joining member used on the fuel side is replaced with the joining member according to the second embodiment. Therefore, a configuration example of the SOFC of this embodiment will be described below with reference to FIG. Components having functions similar to those of the above-described components will be described using the same reference numerals. The SOFC of the present invention is not limited to the following configuration example.

  As shown in FIG. 1, the power generation membrane 2 is composed of a yttria-stabilized zirconia solid electrolyte membrane 4, a fuel side electrode 3 and an air side electrode 5 formed on both sides thereof, and has a dimple shape. Yes. An interconnector 7 electrically connected to the fuel side electrode 3 is provided on the fuel side electrode 3 side of the power generation membrane 2, and the air side electrode 5 and the electrical side are connected to the air side electrode 5 side of the power generation membrane 2. Connected interconnector 7 is provided. Between the interconnector 7 and the air side electrode 5, the conductive joining member 12 suitable for the usage environment of this part is used. Further, the joining member 11 according to the second embodiment is used between the interconnector 7 and the fuel side electrode 3.

  Next, the present invention will be described based on experimental examples, but the present invention is not limited to these experimental examples.

Experimental example 1
The total amount of metallic nickel powder (average particle size 1 μm) and nickel oxide powder (average particle size 1 μm) shown in Table 1 is 85 parts by weight, and 15 parts by weight of alumina (average particle size 10 μm) is adjusted for thermal expansion. In addition, it was used as a base material. Butyl carbitol was added to this base material as a vehicle (mixed solvent) and kneaded using a three-roll mill made of alumina to obtain each sample of the bonding material paste as a paste.
A joining sample of the power generation film and the interconnector as shown in FIG. 2 was prepared using this joining material paste, and the joining strength of the joining portion was measured by the method described below.

  First, the bonding material paste was uniformly applied to one side of a 30 mm square interconnector 22 to a thickness of 100 to 200 μm, and the fuel side electrode side of the 30 mm square power generation film 23 was adhered to this applied portion. Next, the bonding material paste was baked at 1250 ° C. for 1 hour and then cooled in the furnace to form the conductive bonding member 21. After baking, in order to measure the bonding strength between the interconnector 22 and the fuel electrode 13 side of the power generation film 23 formed by forming the fuel electrode 13 and the air electrode 15 on both surfaces of the solid electrolyte membrane 4, the interconnector is measured. 22 was bonded to the acrylic plate 25 with an adhesive, and a container 27 was attached on the air electrode 15 side of the power generation film 23 so that a weight could be placed. A weight was put into this container, and the weight by which the interconnector 22 and the fuel-side electrode side of the power generation membrane 23 were peeled off was evaluated. The measurement results are shown in Table 1.

Since the sample to which metallic nickel is added expands in volume when the metallic nickel becomes nickel oxide during atmospheric firing, the joining member 21 becomes dense, and the joint strength after atmospheric firing is improved. Further, after the reduction, when nickel oxide is reduced to metallic nickel, volume contraction occurs. Therefore, in sample 1 containing only nickel oxide, many pores are formed in the joining member 21 and the joining strength is reduced. In the sample to which nickel is added, the amount of volume expansion during sintering only shrinks, so the decrease in bonding strength is small.
In sample 5 made of 100% metallic nickel, the thermal expansion coefficient of the joining member 21 is larger than that of the power generation film 23 and the interconnector 22, so that the joining strength is lowered.
In the sample 6 using the bonding material to which iron oxide (Fe ₂ O ₃ ) is added, the bonding strength of the bonding member 21 after air firing is excellent, but the bonding strength after reduction is reduced.

Experimental example 2
The power generation membrane is the same as Experimental Example 1 except that the mixing weight ratio of metallic nickel and nickel oxide in the base material is constant at 50:50 and the average particle diameter of metallic nickel and nickel oxide is as shown in Table 2. An interconnector joining sample was prepared and the joining strength of the joined portion was measured. The measurement results are shown in Table 2.

In the sample 7 in which the average particle diameter of the metallic nickel is smaller than 0.3 μm and the average particle diameter of the nickel oxide is smaller than 0.5 μm, since the shrinkage rate of the bonding material 21 is increased, the bonding member 21 is cracked during the atmospheric heat treatment. Has occurred and the bonding strength is reduced.
Moreover, in the sample 12 whose average particle diameter is larger than 5 μm for both metallic nickel and nickel oxide, since the sinterability of the bonding material is reduced, the bonding strength of the bonding member 21 is reduced.

Experimental example 3
Power generation in the same manner as in Experimental Example 1 except that the mixing weight ratio of metallic nickel and nickel oxide in the base material is constant at 50:50 and the average particle diameter of the thermal expansion adjusting material (alumina) is as shown in Table 3. A joining sample of the membrane and the interconnector was prepared, and the joining strength of the joined portion was measured. Table 3 shows the measurement results.

In the sample 13 in which the alumina is smaller than 5 μm, the shrinkage rate of the bonding member 21 is increased, cracks are generated during the atmospheric heat treatment, and the bonding strength is reduced.
Moreover, in the sample 17 whose alumina is larger than 15 μm, the sinterability of the joining material is lowered, and the joining strength of the joining member 21 is lowered.

Experimental Example 4
Experimental Example 1 except that the mixing weight ratio of metallic nickel and nickel oxide in the base material is constant at 50:50, and the thermal expansion adjusting material is silicon nitride, silicon carbide or fused silica (all having a particle size of 10 μm). Similarly, a joining sample of the power generation film and the interconnector was produced, and the joining strength of the joined portion was measured. Table 4 shows the measurement results.
With respect to these thermal expansion adjusting materials, the effect of improving the bonding strength of the bonding member 21 was obtained as in the case where the thermal expansion adjusting material was alumina.

Experimental Example 5
Regarding the bonding agent pastes of Sample 3 and Sample 6 in Experimental Example 1, a fuel-side electrode / interconnector bonding sample as shown in FIG. 3 was prepared, and the bonding resistance of the bonding portion was measured by the method described below.
First, the bonding material paste was uniformly applied to one side of each 30 mm square interconnector 37 to a thickness of 100 to 200 μm. Next, the dimple-shaped power generation membrane 32 (fuel side electrode 33 / yttria stabilized zirconia solid electrolyte membrane 34 / air side electrode 35) is coated with a bonding material for the fuel side electrode 33 and the interconnector 37 facing the fuel side electrode 33. The parts were glued. This bonding material was baked at 1250 ° C. for 1 hour to obtain a bonding member 31. After baking, in order to measure the resistance of the joint between the power generation film and the interconnector, platinum is interposed via the platinum paste 41 at positions on the diagonal lines on the side where the joining material of the power generation film 32 and the interconnector 37 is not applied. Two terminals 43 made of wires were attached. This was heated to 1000 ° C. in an air atmosphere, and terminals 43 were baked.

When a constant current generator and a voltmeter are connected to the terminal 43 on the joined sample, the temperature is raised to 1000 ° C. in air, and 100% by volume of H ₂ is introduced for reduction treatment, and 4% by volume. In the case where the temperature was raised to 1000 ° C. in H ₂ / N ₂ and the reduction treatment was performed by introducing 100% by volume of H ₂ , the junction resistance was measured by the direct current four-terminal method. Table 5 shows the measurement results of each bonded sample.
It can be seen that in the sample 3a in which iron oxide is not added to the base material of the bonding agent, there is almost no change in the bonding resistance compared to the sample 6a in which iron oxide is added.

It is the schematic which shows an example of SOFC. It is the schematic which shows the joining sample in Experimental example 1 thru | or Experimental example 4. FIG. It is the schematic which shows the joining sample in Experimental example 5. FIG.

Explanation of symbols

11, 12, 21, 31 Conductive joining members 2, 23, 32 Power generation membranes 3, 13, 33 Fuel side electrodes 4, 14, 34 Solid electrolyte membranes 5, 15, 35 Air side electrodes 7, 22, 37 Interconnector

Claims (15)

Nickel oxide,
Metallic nickel,
A joining material including a base material containing a thermal expansion adjusting material having a thermal expansion coefficient of 10 × 10 ⁻⁶ / ° C. or less and substantially free of iron oxide.   2. The bonding material according to claim 1, wherein the metal nickel is contained in an amount of 30 parts by weight or more and 70 parts by weight or less in a total amount of 100 parts by weight of the nickel oxide and the metal nickel.   The bonding material according to claim 1 or 2, wherein the thermal expansion adjusting material is contained in an amount of 10 parts by weight or more and 20 parts by weight or less of 100 parts by weight of the base material.   The bonding material according to any one of claims 1 to 3, wherein the thermal expansion adjusting material includes at least one material selected from the group consisting of alumina, silicon nitride, silicon carbide, and fused silica.   The bonding material according to any one of claims 1 to 4, wherein the nickel oxide is particulate nickel oxide having an average particle size of 0.5 µm or more and 5 µm or less.   The joining material according to any one of claims 1 to 5, wherein the metallic nickel is particulate metallic nickel having an average particle size of 0.3 µm to 5 µm.   The bonding material according to any one of claims 1 to 6, wherein the thermal expansion adjusting material is a particulate thermal expansion adjusting material having an average particle diameter of 5 µm to 15 µm.   The joining material according to any one of claims 1 to 7, comprising the base material and a vehicle.   The joining member obtained by sintering the joining material as described in any one of Claims 1-8 arrange | positioned between several members. The bonding material according to any one of claims 1 to 8 is disposed between a plurality of members,
A joining method for sintering the joining material.   The joining method according to claim 10, wherein the plurality of members include a fuel-side member in a solid oxide fuel cell.   The joining method according to claim 10, wherein the plurality of members include a fuel-side electrode and another fuel-side member in a solid oxide fuel cell. A plurality of members;
A solid oxide fuel cell comprising: the joining member according to claim 9 that joins the plurality of members.   The solid oxide fuel cell according to claim 13, wherein the plurality of members include fuel-side members.   The solid oxide fuel cell according to claim 13, wherein the plurality of members include a fuel side electrode and another fuel side member in the solid oxide fuel cell.

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