JP2016192291A - Spray coating slurry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spray coating slurry for forming a coating layer of an inter-connector for SOFC, the spray coating slurry being capable of reducing surface roughness of a dry film.SOLUTION: The present invention relates to the spray coating slurry for forming a coating layer of an inter-connector for a solid oxide electrolyte type fuel cell. The slurry is obtained by mixing: a ceramic powder; a binder in 0.5 mass% or more and 10 mass% or less with respect to the powder; and an organic solvent in 200 mass% or more and 1000 mass% or less with respect to the powder. The organic solvent is ethanol containing diethylene glycol monobutyl ether acetate (BCA) in 5 mass% or more and 20 mass% or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a slurry for spray coating for forming a sintered coating layer of an interconnector for a solid oxide electrolyte fuel cell.

The solid oxide electrolyte fuel cell (SOFC) uses ceramics such as stabilized zirconia as an electrolyte, and recently, an application for operating at a medium high temperature of 700 to 800 ° C. has been developed. This SOFC interconnector is a conductive plate that is electrically connected in series to form a cell stack, and is a separator plate that separates fuel gas and oxidant gas, and consists of three layers: electrolyte, fuel electrode, and air electrode. It has a role of supporting, forming the gas flow path and flowing current.
Accordingly, the interconnector is required to have excellent electrical conductivity at medium and high temperatures, oxidation resistance, a small difference in thermal expansion from the electrolyte, low cost, ease of processing, and the like. For these reasons, as a material for the interconnector, a metal base material made of ferritic stainless steel, for example, an Fe—Cr alloy is preferably used.

However, when an Fe-Cr alloy is used for an interconnector, oxidation proceeds on the cathode (air electrode) side surface of the metal substrate by being placed in a high-temperature oxidizing atmosphere with the operation of the fuel cell. There is a problem that an oxide film of Cr ₂ O ₃ (hereinafter referred to as Cr oxide film) grows, which deteriorates the current collection characteristics and deteriorates the power generation performance of the cell stack. There is also a problem of so-called chromium poisoning, in which Cr vapor is generated from the Cr oxide film and the performance of the cathode is gradually lowered.
In order to solve this problem, an interconnector in which a coating layer having both oxidation resistance and conductivity is provided on the surface of a metal substrate is used.

For example, Patent Document 1 discloses a metal substrate made of an Fe—Cr-based alloy and a chemical formula AB ₂ O ₄ (however, selected from at least one metal element selected from A: Mn, Cu, B: Co, Mn. An interconnector comprising a coating layer comprising a transition metal oxide having a spinel crystal structure represented by at least one metal element, wherein the surface of the metal substrate is covered with the coating layer is disclosed. .

JP 2011-99159 A

  As shown in FIGS. 6 and 7, the interconnector has a plurality of grooves formed on the surface as flow paths for oxygen gas and fuel gas. Therefore, the coating layer needs to be formed so as to cover the inner surface of the groove. As an application method for this purpose, the present inventor has adopted spray application.

  In order to perform spray coating, the slurry to be used includes ceramic powder, a binder for fixing the ceramic powder to the surface of the metal substrate, and an organic solvent for enhancing the fluidity of the slurry during coating. A coating film formed by spray coating (hereinafter referred to as a coating film) is a coating film (hereinafter referred to as a dry coating film) mainly formed from ceramic powder and a binder, with the organic solvent volatilized by drying. By sintering this dried coating film after the binder removal treatment, a coating layer made of, for example, a spinel compound of Mn and Co is formed.

However, when the coating layer is formed by spray coating, if the dispersion state of the ceramic powder in the slurry is poor, the ceramic powder aggregates in the coating film and the surface roughness of the dried coating film increases. Even if the dispersibility of the powder in the slurry is good, if the fluidity is poor, flattening (leveling) during drying does not occur, and as a result, the ceramic powder in the coating film aggregates and the surface roughness of the dry coating film Becomes bigger. When the surface roughness of the dried coating film is large, the surface roughness of the coating layer after sintering is also increased.
When the surface roughness of the coating layer is large, there is a problem that the electrical contact resistance between the interconnector and the air electrode or fuel electrode adjacent to the interconnector increases, and the current collection characteristics of the interconnector deteriorate.

  Accordingly, an object of the present invention is to provide a slurry for spray coating for forming a coating layer of an SOFC interconnector that can reduce the surface roughness of a dry coating film.

The present invention is a slurry for spray coating for forming a coating layer of an interconnector for a solid oxide electrolyte fuel cell, the slurry comprising ceramic powder and 0.5 mass% or more and 10 mass relative to the powder. % Or less binder and an organic solvent of 200 mass% or more and 1000 mass% or less with respect to the powder, and the organic solvent contains 5 mass% or more and 20 mass% or less of diethylene glycol monobutyl ether (BCA). It is characterized by being ethanol.
As this binder, ethyl cellulose (EC) can be used.

ADVANTAGE OF THE INVENTION According to this invention, what can reduce the surface roughness of a dry coating film as a slurry for spray application for forming the coating layer of the interconnector for SOFC could be provided.
By subjecting this dry coating film to binder removal and sintering, the surface roughness of the coating layer is also reduced, and the electrical contact resistance between the interconnector and the air and fuel electrodes adjacent to it can be reduced. . Therefore, the current collection characteristics can be improved, and an SOFC with good power generation efficiency can be provided.

It is the figure which showed the relationship between the repetition frequency of spray application, and the film thickness of a dry coating film for every addition ratio of BCA. It is the figure which showed the relationship between the film thickness of a dry coating film, and surface roughness Ra for every addition ratio of BCA. It is the surface observation photograph of the dry coating film which changed the addition ratio of BCA. It is the surface observation photograph of the dry coating film which changed the amount of organic solvents. It is a figure which shows the relationship between binder (ethylcellulose) addition amount and surface roughness Ra of a dry coating film. It is a cross-sectional schematic diagram of the interconnector for SOFC. It is a perspective view which shows an example of a cell stack.

The present invention is a slurry for spray coating for forming a coating layer of an SOFC interconnector, wherein the slurry is a ceramic powder, a binder of 0.5 to 10 mass% with respect to the powder, and 200 to 1000 mass% organic solvent is mixed, and the organic solvent is ethanol containing 5 mass% or more and 20 mass% or less of diethylene glycol monobutyl ether acetate: molecular formula C ₁₀ H ₂₀ O ₄ (hereinafter referred to as BCA). Features.
Since the organic solvent used in the slurry is ethanol containing 5 mass% or more and 20 mass% or less of BCA, the surface roughness of the dried coating film can be reduced. Therefore, the surface roughness of the coating layer after sintering can be reduced. .

First, general SOFC technology will be described.
FIG. 6 is a schematic cross-sectional view of an SOFC interconnector (hereinafter referred to as an interconnector) 1 and shows the relationship between the metal substrate 1a and the coating layer 1b. FIG. 7 is a perspective view showing an example of the cell stack 10.
The cell stack 10 is mainly composed of an interconnector 1, an air electrode 3, a solid electrolyte layer 4, and a fuel electrode 5 each having a plate shape.
The interconnector 1 is disposed between the air electrode 3 and the fuel electrode 5 and electrically joins both. The interconnector 1 has grooves formed on both surfaces thereof, the groove on the air electrode 3 side is used as a flow path for air 6, and the groove on the fuel electrode 5 side is used as a flow path for fuel gas 7. For example, hydrogen H ₂ is used as the fuel gas.
Oxygen ions (O ²⁻ ) can be transmitted between the air electrode 3 and the fuel electrode 5 via the solid electrolyte layer 4. The fuel electrode 5 and the air electrode 3 are electrically joined via an external conductor (not shown).
Thus, a unit cell is formed by stacking the interconnector 1, the air electrode 3, the solid electrolyte layer 4, and the fuel electrode 5, and the unit cell is stacked in the thickness direction to form a cell stack 10.

The principle of SOFC power generation using this cell stack will be described.
When the cell stack operates, the following reactions occur simultaneously on the air electrode 3 side and the fuel electrode 5 side.
On the fuel electrode 5 side, hydrogen is deprived of electrons by touching the fuel electrode 5, and the fuel electrode 5 emits the electrons. Hydrogen turns into hydrogen ions. That is, the reaction of (H ₂ → 2H ⁺ + 2e ⁻ ) occurs on the fuel electrode 5 side. Since electrons emitted from the fuel electrode 5 cannot pass through the solid electrolyte layer 4 disposed between the fuel electrode 5 and the air electrode 3, they flow to the air electrode 3 through an external conductor.
On the other hand, on the air electrode 3 side, hydrogen ions that have been deprived of electrons on the fuel electrode 5 side move to the air electrode 3 side that can receive electrons via the solid electrolyte layer 4 in order to be electrically stable. The hydrogen ions receive electrons and combine with oxygen to become water. That is, the reaction of (2H + 2e ⁻ + 1 / 2O ₂ → H ₂ O) occurs on the air electrode 3 side.
As described above, SOFC can generate electricity from the process of producing water by the chemical reaction between hydrogen and oxygen.

As shown in FIG. 6, the interconnector 1 includes a metal substrate 1a and a coating layer 1b covering the surface thereof.
By forming the coating layer so as to cover the metal substrate, it is possible to suppress Cr in the metal substrate from volatilizing on the cathode (air electrode) side to become Cr vapor. The problem of so-called chromium poisoning, which gradually reduces the performance of
As the material of the metal substrate 1a, for example, an Fe—Cr-based alloy can be adopted because of its small electrical expansion difference from electrical conductivity, oxidation resistance, and electrolyte, low cost, and ease of processing.

  In the present invention, it is assumed that a slurry containing ceramic powder is spray-coated on the surface of the metal substrate 1a, dried, debindered, and then sintered to form a coating layer. Went.

The slurry of this invention mixes 0.5 mass% or more and 10 mass% or less of binder with respect to ceramic powder, and 200 mass% or more and 1000 mass% or less of organic solvent similarly with respect to ceramic powder.
If the binder is 0.5 mass% or more, the ceramic powder can be held on the surface of the metal substrate 1a. However, if the binder is less than 0.5 mass%, the ceramic powder is not sufficiently held to be fired before firing. The coating film may be peeled off. Therefore, in this invention, the binder was 0.5 mass% or more with respect to the ceramic powder. However, if the binder exceeds 10 mass%, the yield stress of the coating film is easily exceeded when the organic solvent is dried, and cracks are likely to occur, and the surface roughness of the formed coating film exceeds 1 μm. Therefore, in the present invention, the upper limit of the binder is set to 10 mass%. A more preferable amount of the binder is 1 mass% or more and 7.5 mass% or less.

  As the binder, ethyl cellulose (hereinafter referred to as EC) can be used. EC is preferable as a binder for the slurry used in the present invention because it is excellent in the smoothness and shape retention of the coating film and has good solubility in BCA.

  Next, when the organic solvent is 200 mass% or more with respect to the ceramic powder, the ceramic powder can be uniformly applied by spray coating. If it is less than 200 mass%, the viscosity of the slurry becomes high, so that the surface roughness of the formed coating film becomes large and the surface roughness of the coating layer exceeds 1 μm. Therefore, in the present invention, the lower limit of the organic solvent is set to 200 mass%. However, when the organic solvent exceeds 1000 mass%, the time for drying the organic solvent becomes long, which is not suitable for mass production. Further, since the proportion of the ceramic powder in the slurry is reduced, in order to ensure the thickness of the coating layer, the number of spray coatings must be increased, and the spray coating time is increased. Therefore, in the present invention, the upper limit of the organic solvent is set to 1000 mass%. A more preferable amount of the organic solvent is 300 mass% or more and 600 mass% or less.

As the organic solvent, ethanol containing BCA of 5 mass% or more and 20 mass% or less is used.
Ethanol has a relatively high drying rate and has a smaller adverse effect on the human body than other solvents (toluene, xylene, etc.). Therefore, it was adopted as an organic solvent for the slurry used in the present invention. BCA can control the drying rate of a coating film by using with ethanol. Further, since the ceramic powder in the coating film is dried while being uniformly dispersed, a dry coating film having a small surface roughness can be obtained.
The reason why the dispersibility is improved by mixing two organic solvents, ethanol and BCA, is that when the evaporation rate of relative evaporation rate R (butyl acetate: C ₆ H ₁₂ O ₂ is set to 100, such as ethanol). By mixing a material having a relative evaporation rate of less than 0.01 and a material having a relative evaporation rate R of 1 or more, such as BCA, a leveling phenomenon occurs before the coating film is completely dried. This is probably because of this.

  If the BCA in the organic solvent is 5 mass% or more, the surface roughness Ra of the resulting coating layer can be 1 μm or less, but if it is less than 5 mass%, the surface roughness Ra tends to exceed 1 μm. Therefore, in the present invention, the BCA in the organic solvent is set to 5 mass% or more. However, if the BCA exceeds 20 mass%, the dispersion of the ceramic powder occurs and the distribution of film pressure varies. In addition, the problem that the dry coating film becomes thin and the ceramic powder in the coating film flows out from the metal substrate even if spray coating is repeated multiple times, and the dry coating film cannot be thickened. To do. Therefore, in the present invention, the upper limit value of BCA is set to 20 mass%. A more preferable range is 7.5 mass% or more and 15 mass% or less.

As raw materials for the ceramic powder, it is preferable to use two or more of Mn ₃ O ₄ , Co ₃ O ₄ , and CuO. By sintering these raw materials, it is possible to form a coating layer made of, for example, a Mn (Co · Cu) spinel system. For example, by changing the ratio of Mn and (Co · Cu), a spinel-based coating layer such as Mn (Co · Cu) ₂ O ₄ , Mn _1.5 (Co · Cu) _1.5 O ₄ is used. Can do.
The coating layer having this composition has a high composition decomposition temperature, and can maintain the spinel structure even inside the SOFC operated at a high temperature, so that the function as the coating layer can be maintained. Moreover, it is excellent also in the function which suppresses that the Cr contained in a metal base material volatilizes outside the coating layer.

The ceramic powder preferably has an average particle size of 0.1 μm or more and 2 μm or less. A powder having a particle size of less than 0.1 μm tends to aggregate. On the other hand, if the thickness exceeds 2 μm, leveling during coating hardly occurs. Dispersibility in the coating film can be improved by using the ceramic powder in the above range. When the ceramic powder is a spinel-based coating layer such as Mn (Co · Cu) ₂ O ₄ or Mn _1.5 (Co · Cu) _1.5 O ₄ , for example, Mn ₃ O ₄ and Co ₃ O _{4 are used.} , CuO and other raw material powders are mixed so as to be uniform by a technique such as a ball mill, and then heat-treated under conditions that allow solid solution (for example, 700 ° C. or more and 2 hours or more). There is also a method of obtaining a compound having a predetermined composition by a coprecipitation method using a chloride solution of Mn, Co, etc., adding a sodium hydroxide solution, stirring and washing to obtain a powder.

Although it changes with the specific surface areas of the powder to be used for the slurry described above, it is preferable to use a dispersant of 0.1 mass% or more and 10 mass% or less with respect to the ceramic powder. By adding 0.1 mass% or more, the dispersibility of the ceramic powder can be improved, and the viscosity of the slurry can be reduced. However, even if it exceeds 10 mass%, the further effect as a dispersing agent is not acquired, conversely, a thickening phenomenon occurs and the spray application is hindered. In addition, organic substances tend to remain in the coating film.
As the dispersant, for example, a polymer-type polycarboxylic acid-based material for non-aqueous use or a surfactant-type polyhydric alcohol ester-based material can be used.

The slurry preferably uses a plasticizer of 10 mass% or more and 100 mass% or less with respect to the added binder. By adding 10 mass% or more, when drying a coating film, the softness | flexibility of a binder can be improved and generation | occurrence | production of a crack can be suppressed. It also promotes leveling during drying of the coating. However, if it exceeds 100 mass%, bleeding may occur at the time of drying and coating spots may occur.
Examples of the plasticizer include phthalic acid esters such as dioctyl phthalate (DOP) and diisononyl phthalate (DINP), and adipic acid esters such as dioctyl adipate.

  The coating layer formed using the slurry of the present invention preferably has a thickness of 5 μm or more and 50 μm or less. If it is 5 micrometers or more, it can suppress that Cr volatilizes outside the interconnector. However, in order to form so that thickness may exceed 50 micrometers, the man-hour which repeats spray application increases too much, and a manufacturing process becomes long. In addition, the surface roughness of the coating layer tends to increase. Therefore, the thickness is preferably 50 μm or less.

Spray coating can be performed by a coating method using a hand gun or a spray coater using air spray, a method using ultrasonic spraying or electrostatic spraying. Among these, the spray coater application by the air spray method is preferable from the viewpoint that the film thickness can be easily made uniform and the mass productivity is excellent.
Moreover, it is preferable to apply | coat on the conditions by which a spray nozzle is scanned on the conditions of 100-300 mm / s as application | coating conditions, and the film thickness of 5 micrometers-50 micrometers is obtained about several times (2-5 times). When the number of coatings is large, there is a problem in mass productivity, and the smoothness of the dried coating film is deteriorated.

A dry coating film is obtained by removing the organic solvent from the coating film.
The coating film is preferably dried at a temperature at which the organic solvent is sufficiently volatilized. Heating methods include direct heating by a hot plate, drying by hot air blowing, induction heating, and the like. For example, when the above-mentioned organic solvent is used, it can be dried at 70 ° C. to 250 ° C. It is preferable to appropriately change the drying time depending on the amount of the organic solvent used.

  Organic substances such as a binder contained in the dried coating film are removed by a binder removal treatment before sintering. If carbon contained in the organic matter remains in the dry coating film, it becomes a factor that inhibits sintering, and a dense film cannot be obtained. Since the decomposition temperature differs depending on the binder to be used, the debinding process is performed at a temperature that matches the binder. When it is necessary to prevent the powder from being oxidized, it is necessary to perform the treatment in an inert gas stream such as nitrogen. When using EC, since the thermal decomposition temperature is around 450 ° C., it is preferably held at 450 ° C. or higher and 650 ° C. or lower for 1 hour or longer.

A dried coating film that has been subjected to binder removal processing is sintered to form a coating layer.
Sintering is preferably performed in an atmosphere and temperature at which the ceramic powder does not decompose. For example, when a spinel-based coating layer such as Mn (Co · Cu) ₂ O ₄ or Mn _1.5 (Co · Cu) _1.5 O ₄ is used, the sintering temperature is 800 ° C. or higher and 1000 ° C. in an air atmosphere. The following is preferable. Although sintering in the atmosphere can be performed, in order to improve the density, a two-stage heat treatment in which heat treatment is performed in an atmosphere containing oxygen that can be reoxidized after sintering in a reducing atmosphere may be used. Thereby, it can suppress that Cr in a metal base material volatilizes the exterior of a coating layer because the density of a coating layer improves.

Next, the metal substrate will be described.
A conventional Fe—Cr alloy can be used for the metal substrate.
This Fe—Cr alloy is in mass%, Cr: 16.0 to 28.0%, Mn: 0.05% or more and 0.4% or less (not including additive), Ni: 1.5% or less (Including no addition), REM (rare earth element including Y) or Zr: one or more types: 1.0% or less in total (excluding no addition), W: 1.0% or more and 3.0% Hereinafter, it is possible to use a ferrite-based metal material composed of Cu: 4.0% or less (including no addition) and the balance of Fe and inevitable impurities.
The Fe-Cr alloy of this composition adds W for the purpose of suppressing the outward diffusion of Cr, and further adds Cu, thereby dramatically improving the oxidation resistance and reducing the performance of the fuel cell. Can be suppressed.

[Surface roughness Ra]
In the present invention, the surface roughness Ra of the dried coating film is a center line average roughness (a value obtained by folding the roughness curve from the center line and dividing the area obtained by the roughness curve and the center line by the length L: Unit μm). A contact-type surface roughness meter was used as a measuring instrument.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited by these Examples.

Example 1
The addition ratio of BCA in the organic solvent was examined.
An Fe—Cr alloy having a surface roughness Ra of 0.1 μm or less was used as the metal substrate of the interconnector.
The slurry was prepared as follows.
Mn ₃ O ₄ , Co ₃ O ₄ , and CuO were used as raw materials for the ceramic powder, and the amounts of Mn, Co, and Cu were adjusted so that the composition ratio was Mn _1.5 Co _1.1 Cu _9,4 O ₄ .
The mixed raw materials were mixed with a ball mill using ethanol as a solvent for 20 hours to obtain a slurry. Thereafter, the slurry was dried with a hot plate, pulverized, and calcined at 850 ° C. for 4 hours in an air atmosphere.
100 mass% of ethanol as an organic solvent was added to the raw material after calcination and mixed for 20 hours with a ball mill. Thereafter, it was dried on a hot plate, pulverized, and calcined at 850 ° C. for 4 hours in an air atmosphere to obtain ceramic powder.
Moreover, it added so that the quantity of the organic solvent might be 300 mass% with respect to ceramic powder. The organic solvent is obtained by adding BCA to ethanol, and the content ratio of BCA in ethanol is 5%, 7.5%, 10%, 12.5%, 15%, 20%, 25% Was used.
In addition, 5 mass% of EC was added to the ceramic powder as a binder, and 5 mass% of ammonium polycarboxylate was added as a dispersant to the ceramic powder. As a plasticizer, 50 mass% of dioctyl phthalate (DOP) was added to the binder.

Using the obtained slurry, the slurry was applied to the surface of the metal base material on the surface of the metal base material by a spray coater with a scanning speed of 300 mm / s, a coating width of 7 to 8 mm, and a coating pitch of 1 mm. Applied. This spray application was repeated 1 to 5 times.
The metal substrate coated with the coating film was dried at 100 ° C. for 2 hours in the atmosphere.

FIG. 1 is a diagram for showing the basis of the upper limit of the BCA addition ratio, and is a diagram showing the relationship between the number of spray coating repetitions and the thickness of the dried coating film for each BCA addition ratio. Larger film thickness is obtained, so that the addition ratio of BCA in an organic solvent is small. On the other hand, as the BCA increases, the film thickness tends to be thinner. In particular, in the case of using a slurry having a BCA of 25 mass% in an organic solvent, the film thickness did not increase even after the third application, and a thick coating film of 20 μm or more could not be formed.
As the Cr diffusion preventing layer, the coating layer is preferably provided with a thickness of 10 μm or more, and the thickness of the dried coating film should be 20 μm or more in consideration of the shrinkage ratio in firing. From this point, a slurry having a BCA of 25 mass% in an organic solvent cannot form a coating layer having a desired thickness unless a plurality of drying steps such as spray coating, drying, spray coating, drying, and the like are performed.

FIG. 2 is a diagram showing the relationship between the film thickness of the dried coating film and the surface roughness Ra for each BCA addition ratio.
It was confirmed that the surface roughness Ra of the slurry using the BCA in the organic solvent of 5 mass% or more can be suppressed to 1 μm or less.
Furthermore, when the BCA in the organic solvent was 7.5 mass% or more, the surface roughness Ra was suppressed to 0.6 μm or less.

  FIG. 3 is a surface observation photograph (magnification 2000 times) of the dried coating film when the addition ratio of BCA is changed to 5%, 10%, 15%, and 25%. It was found that the dry coating films with the addition ratio of BCA of 10% and 15% were the most homogeneous surfaces. When the addition ratio of BCA was 5%, it was found that the ceramic powder was slightly agglomerated (in the center of the photograph), but the surface was homogeneous. On the other hand, when the addition ratio of BCA was 25%, the ceramic powder was dried and solidified without being uniformly dispersed.

The interconnector on which these dry coating films were formed was subjected to binder removal treatment at 500 ° C. × 2 h. After that, sintering was performed at 965 ° C. × 15 h to produce an interconnector on which a coating layer made of each composition of spinel type Mn _1.5 Co _1.1 Cu _0.4 O ₄ was formed.
A plate-shaped air electrode was laminated on the obtained interconnector. It was confirmed that the interconnector obtained in this way maintained good electrical conductivity at the boundary between the two.

(Comparative Example 1)
For comparison, a similar experiment was performed using a slurry in which the content ratio of BCA in ethanol was 0 mass%. The dried coating film obtained by repeating spray application twice had a thickness of 33.4 μm, a surface roughness Ra of 5.5 μm (not shown in FIG. 1), and a large surface roughness Ra. .
Furthermore, the dry coating film obtained by repeating spray coating three times has a thickness of 66.4 μm and the surface roughness Ra is 14.9 μm, and the dry coating film obtained by repeating four times has a thickness of 79. The dried coating film obtained by repeating 5 times with a thickness of 101.9 μm and a surface roughness Ra of 23.7 μm was obtained. The length greatly exceeded 1 μm.
The interconnector obtained by similarly sintering these dried coating films had deteriorated electrical conductivity with the air electrode as compared with the interconnector obtained in the examples.

In addition to the above experiment, a similar experiment was performed using polyvinyl butyral (PVB) instead of EC as a binder.
The surface roughness Ra was about 10% larger than that using EC, but showed the same tendency with respect to the amount of BCA added.

(Example 2)
The amount of organic solvent was examined.
In the same manner as in Example 1, a metal substrate and ceramic powder were obtained.
To this ceramic powder, 5 mass% of ethyl cellulose (EC) was added as a binder.
Moreover, what added 200 mass%, 300 mass%, and 400 mass% of organic solvents with respect to the ceramic powder was produced. What made the organic solvent 200 mass% made BCA in the organic solvent 15 mass%. In the case where the organic solvent was 300 mass% and 400 mass%, the BCA in the organic solvent was 10 mass%.
In addition, 5 mass% ammonium polycarboxylate was added to the ceramic powder as a dispersant. As a plasticizer, 50 mass% of dioctyl phthalate (DOP) was added to the binder.

Using the obtained slurry, the slurry was applied to the surface of the metal base material on the surface of the metal base material by a spray coater with a scanning speed of 300 mm / s, a coating width of 7 to 8 mm, and a coating pitch of 1 mm. Applied. This spray application was repeated three times.
The metal substrate coated with the coating film was dried at 100 ° C. for 2 hours in the atmosphere.

FIG. 4 is a surface observation photograph of the obtained dried coating film.
It was found that the dried coating film obtained with the amount of organic solvent of 300 mass% and 400 mass% with respect to the ceramic powder had a homogeneous surface. The dry coating film obtained as 200 mass% was able to withstand practical use although the surface roughness was slightly rough.

Table 1 shows the surface roughness Ra of the obtained dried coating film.
All the dried coating films had a surface roughness Ra of 1 μm or less.

The metal substrate coated with the above-mentioned dried coating film was subjected to binder removal treatment at 600 ° C. × 2 h in the atmosphere, and then sintered at 965 ° C. × 15 h in the atmosphere to obtain a spinel type Mn _1.5 Co _1.1 Cu. An interconnector on which a coating layer having a composition of _0.4 O ₄ was formed was produced.
As in Example 1, when a plate-like air electrode was laminated on the interconnector and the conductivity was measured at the boundary between the two, it was confirmed that good conductivity was maintained.

  In addition, when experiment was conducted by further reducing the amount of organic solvent, the surface roughness of the dried coating film exceeded 1 μm, and cracks were observed.

Example 3
The amount of binder was examined.
In the same manner as in Example 1, a metal substrate and ceramic powder were obtained.
To this ceramic powder, 1 mass%, 2 mass%, 5 mass%, and 10 mass% of EC were added as a binder.
Moreover, what added 300 mass% of organic solvents with respect to the ceramic powder was produced. As the organic solvent, ethanol and BCA were used, and the content ratio of BCA in ethanol was 10 mass%.
In addition, 5 mass% ammonium polycarboxylate was added to the ceramic powder as a dispersant.
Moreover, 50 mass% (0.5 mass%, 1 mass%, 2.5 mass%, 5 mass%) of ceramic dioctyl phthalate (DOP) was added as a plasticizer.

Using the obtained slurry, the slurry was applied to the surface of the metal base material on the surface of the metal base material by a spray coater with a scanning speed of 300 mm / s, a coating width of 7 to 8 mm, and a coating pitch of 1 mm. Applied. This spray coating produced what was repeated 2 times and what was repeated 5 times.
The metal substrate coated with the coating film was dried at 100 ° C. for 2 hours in the atmosphere.
The metal substrate coated with the dried coating film was subjected to binder removal treatment at 600 ° C. × 2 h, and then sintered at 965 ° C. × 15 h in the atmosphere to form a spinel type Mn _1.5 Co _1.1 Cu _0.4 An interconnector having a coating layer formed of each composition of O ₄ was produced.

FIG. 5 is a diagram showing the relationship between the addition amount of EC and the surface roughness Ra of the dried coating film.
It was confirmed that the surface roughness Ra of the dried coating film was 1 μm or less under the condition where the amount of EC was 10 mass% or less. When the amount of EC increases, the surface roughness Ra tends to increase, and when it exceeds 10 mass%, the surface roughness Ra tends to exceed 1 μm and cracking of the coating film tends to occur.

DESCRIPTION OF SYMBOLS 1: Interconnector, 1a: Metal substrate, 1b: Coating layer, 3: Fuel electrode, 4: Solid electrolyte layer, 5: Fuel electrode, 6: Gas flow path containing oxygen 6, 7: Fuel gas flow path 10: Cell stack

Claims (2)

A slurry for spray coating for forming a coating layer of an interconnector for a solid oxide electrolyte fuel cell,
The slurry is a mixture of ceramic powder, a binder of 0.5 mass% to 10 mass% with respect to the powder, and an organic solvent of 200 mass% to 1000 mass% with respect to the powder.
The organic solvent is ethanol containing diethylene glycol monobutyl ether (BCA) in an amount of 5 mass% to 20 mass%. The slurry for spray coating according to claim 1, wherein ethyl cellulose (EC) is used as the binder.

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