JP2001297781A - Film forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film forming method which is economical, suitable for mass production, and easily applicable to big surface area, to form a fine solid state electrolyte film/interconnector film, and a porous air electrode film/fuel electrode film. SOLUTION: The film forming method of slurry coat is a method to form a homogeneous film on a fine or porous cylindrical base board. By forming the film under atmospheric or reduced pressure, arranging the cylindrical base board in horizontal direction, and making the base board rotate on its own axis, such a films as a fine solid state electrolyte film.an interconnector film, a porous air electrode film.a fuel electrode film, which are provided especially to such elements as SOFC with high efficiency at a low cost, oxygen sensor, oxygen pump, are enabled to form so as to have homogeneous thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid electrolyte thin film, an air electrode, an interconnector (separator), and a fuel electrode on a cylindrical base of a solid oxide fuel cell (hereinafter also referred to as SOFC). To a film forming method for forming a uniform film by a slurry coating method which is an inexpensive manufacturing method.

[0002]

2. Description of the Related Art The prior art of a method for forming a dense electrolyte membrane will be described by taking a solid electrolyte thin film for SOFC as an example. SOFC
Has oxygen ion (O ²⁻ ) permeability, and
A solid electrolyte thin film having no gas permeability is required. This solid electrolyte thin film (ZrO ₂ , CeO _2, etc.) is required to be thin and dense in order to satisfy both these characteristics. Furthermore, it is also required that a large-area thin film can be formed economically. In the power generation cell of this SOFC, a solid electrolyte membrane having a thickness of 30 to 2000 μm is generally formed on a porous substrate having a thickness of 0.3 to 5.0 mm. Further, a fuel electrode (Ni-based cermet or the like) is formed thereon.

The following has been proposed with the aim of obtaining a thin, dense, low-cost, and highly mass-producible solid electrolyte thin film for an SOFC cell. Production method by CVD / EVD (Chemical Electrodeposition) (JP-A-61-91880): In this production method, a first electrode is adhered to a porous support, and a conductive and oxygen-permeable intermediate substance is first produced. The first electrode is protected from high-temperature metal halide vapor by being deposited on the electrode, and the intermediate layer material is brought into contact with the high-temperature metal halide vapor to form a solid metal oxide on the entire surface of the intermediate layer. Form electrolyte.

Production method by plasma spraying (Japanese Patent Application Laid-Open No. 61-198570): In this production method, a solid electrolyte raw material comprising zirconium oxide and a metal oxide such as a rare earth element is dissolved, and then the solidified raw material is pulverized. Then, after adjusting the particle size of the powder obtained by the pulverization, the powder is attached to the substrate of the fuel cell as an electrolyte thin film by plasma spraying. According to the example in the publication,
Using a spray powder having a particle size of 2 μm or less, a thickness of 200 μm,
It is alleged that a solid electrolyte thin film having a terminal voltage of 790 mV was obtained.

[0005] Manufacturing method by slurry application (Japanese Patent Application Laid-Open No. 1-93065): In this manufacturing method, one of an air electrode layer and a fuel electrode layer is formed in a cylindrical shape, and an electrolyte and another electrode layer are formed. The method is characterized in that a powder slurry of each material to be applied is sequentially applied to the surface of the cylindrical material, dried, and then fired. According to the embodiment of the publication, a thickness of 150 μm
It is said that m YSZ films were obtained.

[0006] Manufacturing method by thermal spraying + slurry filler (Japanese Patent Laid-Open No. 220361/1990): This manufacturing method uses a method in which a solid electrolyte layer formed on a base tube by thermal spraying is formed in a gap portion.
It is characterized in that after applying a filler containing yttria-stabilized zirconia at a solid concentration of 40% by weight or more, drying and firing are performed. According to the example of the publication, a particle diameter of 0.05 to 100 μm is applied to an air plasma sprayed film having a thickness of 100 μm.
It is said that a 2.5 μm YSZ powder-containing slurry was applied (hand-painted with a brush), dried and fired to obtain a solid electrolyte thin film having an extremely low air permeability.

[0007]

The above-mentioned prior arts have the following technical problems. CVD method / EVD method: This method is suitable for forming a dense thin film. However, it is necessary to perform the film formation under a special atmosphere and physical conditions shielded from the atmosphere, so that an expensive apparatus is required. For a large member, a large device capable of accommodating the member is required. Therefore, it is difficult to apply a film to a large member, the productivity is low, and the cost is high. Further, since a corrosive raw material gas is used, there is a high risk that the substrate is corroded.

[0008] Plasma spraying: A film formed by this method is basically porous. Therefore, in order to eliminate air permeability, it is necessary to form a thick film to some extent. Therefore, a high-performance cell cannot be obtained. In addition, mass productivity is low.

Slurry coating method: This is an economical method because the film forming operation can be performed in the atmosphere and no expensive equipment is required. However, it was said that there was a problem in the denseness and thinning of the film. In fact, the solid electrolyte thin film disclosed in the embodiment of JP-A-2-220361 has a thickness of 200 μm, which is considerably larger than the development target of such a film of 10 to 50 μm. In addition, since the firing of the film was apt to occur, a plurality of firings were required to achieve densification while filling the cracks. In order to solve such problems, raising the sintering temperature and pulverizing the slurry powder have been studied to increase the sinterability of the film material, but in the former case, the reaction between the substrate and the solid electrolyte is problematic. As for the latter, it was difficult to produce a large amount of fine powder having a particle size of 0.1 μm or less.

[0010] Thermal spraying + slurry filling method: The film thickness tends to become thicker as the number of steps increases.

[0011] The present invention provides a solid electrolyte membrane, air, which has a uniform thickness, is economical, mass-producible, can be easily applied to a large area, and has a dense and porous structure of the tissue. very,
It is intended to provide the formation of interconnectors and anodes.

[0012]

According to a first aspect of the present invention, there is provided a first step of preparing a cylindrical base, and a second step of setting the cylindrical base in a horizontal direction, and applying a slurry while rotating the cylindrical base. And a third step of drying and firing the cylindrical substrate coated with the slurry.

In the present invention, the cylindrical base is set in the horizontal direction to make the film thickness uniform in the axial direction, and the slurry is applied while rotating, so that the film thickness in the circumferential direction is made uniform. In order to This is also because if the film is installed in the vertical direction and the film is formed, the lower side becomes thicker in the axial direction and the upper side becomes thinner, and a difference in film thickness occurs in the axial direction.

According to a second aspect of the present invention, there is provided the film forming method according to the first aspect, wherein the slurry is applied in the second step by dipping in which a cylindrical base is immersed in the slurry. .

The reason why the film is formed by dipping in the present invention is that dipping is suitable for a uniform film because it is easy to uniformly immerse the entire substrate in a slurry.

According to a third aspect of the present invention, there is provided the film forming method according to the first aspect, wherein the slurry is applied in the second step by flow coating in which the slurry flows from above the cylindrical base. .

In the present invention, film formation by flow coating is suitable for a uniform film of the same degree as dipping when forming a film while rotating the substrate, and is performed with a smaller amount of slurry than dipping. This is because a film can be formed.

According to a fourth aspect of the present invention, there is provided the film forming method according to the first aspect, wherein the slurry is applied to the cylindrical substrate by spraying the slurry in the second step.

In the present invention, film formation by spraying a slurry is suitable for a uniform film of the same degree as dipping when forming a film while rotating the substrate, and is inexpensive as a film forming apparatus. Because there is.

According to a fifth aspect of the present invention, the cylindrical base is porous and one side in the longitudinal direction is sealed, and the inside of the cylindrical base is depressurized in the second step. A film forming method according to any one of the first to fourth inventions is provided.

In the present invention, the reason why the film is formed while the inside of the substrate is being depressurized is to obtain a fine structure in the film formation of the solid electrolyte and the interconnector.

According to a sixth aspect of the present invention, in the film forming method according to any one of the first to fifth aspects, in the third step, the cylindrical substrate is dried while rotating. provide.

The reason why the cylindrical substrate is dried while rotating in the present invention is to prevent the substrate from rotating when it is not dried, thereby preventing the slurry from dripping and forming an uneven film.

In the seventh invention, the viscosity of the slurry is 1
A film forming method according to any one of the first to sixth inventions, wherein the method is adjusted to 500 cps.

The slurry viscosity in the present invention is from 1 to 500.
adjusting to cps, preferably 5-100 cps,
The reason why the lower limit is limited to 1 cps is that when the film is formed on a dense substrate and the viscosity is low, the film is repelled, causing unevenness in the film, or the film itself due to the viscosity (stickiness) of the slurry itself is insufficient. This is because it is not performed. In addition, in film formation on the porous substrate, it is to prevent the slurry from entering the substrate. The reason why the upper limit is limited to 500 cps is to prevent cracks during drying after film formation.

According to an eighth aspect, there is provided the film forming method according to any one of the first to seventh aspects, wherein a solid electrolyte powder is mixed into the slurry.

The reason why the solid electrolyte powder is mixed into the slurry of the present invention is that the present film forming method is suitable for uniformly forming a dense thin film required for a solid electrolyte or the like.

According to a ninth aspect, there is provided the film forming method according to the eighth aspect, wherein a zirconia-based solid electrolyte is used as the solid electrolyte powder.

In the present invention, zirconia is used as the solid electrolyte powder because zirconia is the most promising material for the solid electrolyte.

According to a tenth aspect, there is provided the film forming method according to the ninth aspect, wherein a powder (YSZ) doped with yttria is used as the zirconia-based solid electrolyte.

The reason for using YSZ in which zirconia-based solid electrolyte is doped with yttria in the present invention is that yttria-doped zirconia-based solid electrolyte is most easily available.

According to an eleventh aspect, there is provided the film forming method according to the tenth aspect, wherein the yttria doping amount of the YSZ powder is 8 to 12 mol%.

In the present invention, the doping amount of yttria in the YSZ powder is set to 8 to 12 mol% because this range is very excellent in terms of ionic conductivity.

In the twelfth aspect, (La, Sr) MnO ₃ and / or (L
a, Ca) A film forming method according to any one of the first to seventh inventions, wherein a MnO ₃ -based perovskite oxide powder is mixed.

In the slurry of the present invention, (L
The reason for mixing the (a, Sr) MnO ₃ and / or (La, Ca) MnO ₃ -based perovskite-type oxide powder is that the present film formation method controls the porosity required for an air electrode or the like and forms a uniform film. This is because it is possible.

In the thirteenth invention, any of the first to seventh inventions is characterized in that (La, Ca) CrO ₃ -based perovskite oxide powder is mixed as the interconnector powder in the slurry. And a film forming method described in

The interconnector in the slurry of the present invention
(La, Ca) CrO as powder _ThreeSystem perovskite
This type of film formation method is used for interconnecting
To form the dense thin film required for
Because it is suitable.

According to a fourteenth aspect of the present invention, any one of the first to seventh aspects of the present invention is characterized in that Ni and / or a composite powder of NiO and YSZ is mixed as the fuel electrode powder in the slurry. Is provided.

As the fuel electrode powder in the slurry of the present invention,
The reason why the composite powder of Ni and / or NiO and YSZ is mixed is that the film forming method can control the porosity required for the fuel electrode and the like, and can form a uniform film.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION

The specific surface area of the solid electrolyte powder and the interconnector powder is desirably 50 m ² / g or less. This is because if the powder is larger than 50 m ² / g, the sinterability is too high and cracks occur in the solid electrolyte membrane and the interconnector membrane during firing on the substrate.

The particle diameters of the air electrode powder and the fuel electrode powder are as follows:
It is desirable to set the range to about 1 to 200 μm. This is because the air electrode and the fuel electrode require high conductivity and gas permeability. These have contradictory characteristics, and it is desirable to use a powder having a small particle size in order to obtain high conductivity, but to obtain a high gas permeability, it is preferable to use a powder having a large particle size. It is desirable to use a powder of
Therefore, the particle size should be determined in the range of about 1 to 200 μm depending on the electric conductivity of the material to be the air electrode and the fuel electrode.

It is desirable that the thickness of the solid electrolyte membrane and the interconnector membrane be 5 to 150 μm.
If it is less than 5 μm, a sufficiently dense film cannot be obtained;
If the thickness is 150 μm or more, the internal resistance is too large. Preferably, it is 100 μm or less, more preferably 50 μm or less.

The thickness of the air electrode and fuel electrode films is 50
It is desirable to set it to 500 μm. This is because the air electrode and the fuel electrode require high conductivity and gas permeability. These have contradictory characteristics, and it is desirable to increase the film thickness in order to obtain high conductivity, but to reduce the film thickness in order to obtain high gas permeability. desirable. Therefore, the film thickness should be determined in the range of about 50 to 500 μm depending on the conductivity of the material to be the air electrode and the fuel electrode.

In the zirconia-based solid electrolyte material, Y
It is preferable to dope ₃ to 20 mol% of ₂ O ₃ ,
More preferably, it is good to dope 8 to 12 mol%. This is because this range is very excellent in terms of ionic conductivity.

In the present invention, the content of the solid electrolyte powder in the slurry is from 10 parts to 100 parts of the slurry solution.
50 parts are preferred. The composition of the slurry solution of the slurry in the present invention is not particularly limited. The slurry may include solvents, binders, dispersants, defoamers, and the like. However, it is desirable that a non-volatile solvent be contained as a solvent in an amount of 10 to 80% by weight of the slurry solvent. The effect of the hardly volatile solvent is to suppress a change in viscosity of the slurry during preparation and storage of the slurry, and to suppress the occurrence of cracks due to drying after film formation (for example, dipping) using the slurry. It is. Here, the degree of low volatility is, for example, 1 when the volatility of butyl acetate is 100.
The following is desirable. For example, α-terpineol and the like can be mentioned.

The slurry solution may contain a general volatile solvent in addition to the hardly volatile solvent. The action of the solvent contained in the solution is to improve the dispersibility of the powder and the defoaming property. As an example of such a solvent, ethyl alcohol is suitable. Its desirable content is 20-90 wt% of the slurry solution.

The function of the binder contained in the slurry solution is to improve the coating property (degree of adhesion) of the powder on the substrate. The amount of the binder is preferably 0.1 to 10 parts based on 100 parts of the solvent. The reason is that if the concentration is low (less than 0.1 wt%), the coating property is low, and if the concentration is high (exceeding 10 wt%), the dispersibility of the powder becomes poor. As a specific example of the binder, ethyl cellulose is suitable.

The action of the dispersant contained in the slurry solution is as follows:
This is an improvement in the dispersibility of the powder. The amount of dispersant is 100
0.1 to 4 parts per part is preferred. The reason is that when the concentration is low (less than 0.1 wt%), the dispersibility is low, and when the concentration is high (4 wt%).
This is because, if it exceeds 0.1% by weight, the slurry tends to be denatured. Specific examples of the dispersant include polyoxyethylene alkyl phosphate.

The antifoaming agent contained in the slurry solution has the function of eliminating air bubbles in the slurry. The amount of the defoamer is 10
0.1 to 4 parts is preferable to 0 part. The reason is that if the concentration is low (less than 0.1 wt%), the effect is not so expected, and if the concentration is high (more than 4 wt%), the slurry is likely to be denatured. Specific examples of the antifoaming agent include sorbitan sesquioleate. A method such as a ball mill can be adopted as a mixing method of each agent / powder.

As the slurry coating method of the present invention, dipping, flow coating and spraying methods can be selected under atmospheric pressure or reduced pressure.

[0052]

EXAMPLES Examples of the present invention will be described below with reference to 10 mol% Y ₂ O _3.
Film formation by dipping with slurry using added ZrO ₂ (10YSZ) powder will be described.

Preparation of slurry solution: The solution for the slurry contains a solvent, a binder, a dispersant, and an antifoaming agent. As a solvent, 40 wt% of α-terpineol is mixed with 60 wt% of ethyl alcohol. Ethyl cellulose is used as a binder, polyoxyethylene alkyl phosphate is used as a dispersant, and sorbitan sesquioleate is used as a defoaming agent. Each mixing ratio in the solution is
Solvent: binder: dispersant: defoamer = 93: 6.8:
0.1: 0.1 was set. Mixing was performed for 24 hours with a stirrer.

Preparation of Slurry Using 10 YSZ powder having a specific surface area of 10 m ² / g, 30 parts of the powder was added to 70 parts of the above solution, and 2 parts were added by a ball mill.
Mixing was performed for 4 hours to prepare a slurry. The viscosity of the slurry was 35 cps.

(3) Film formation: The above-mentioned slurry was used to form an air electrode material and YSZ on a porous air electrode having a total length of 1100 mm, an outer diameter of 22 mm, and an average pore diameter of 11 μm and sealed on one side.
The substrate on which the composite powder was formed was placed in a horizontal direction (horizontal film formation), and the central axis of the cylindrical substrate was rotated at a speed of 0.5 rotation / sec while reducing the pressure inside the substrate to about 1 × 10 ² Pa. The YSZ film was formed by a dipping method. After the substrate was immersed in the dipping tank for 1 minute, it was taken out of the slurry while being held horizontally and rotated under reduced pressure, and dried at 100 ° C. Also, the substrate is installed in the vertical direction (vertical film formation), and the inside of the substrate is similarly set to 1 × 10 ²
YSZ by dipping while reducing the pressure to about Pa
A film was formed. After the substrate was immersed in the dipping tank for 1 minute, it was taken out of the slurry at a speed of 50 mm / sec under reduced pressure and dried at 100 ° C. In both film forming methods, dipping and drying were repeated so that the YSZ film thickness on the sample was about 50 μm on average.

(4) Firing: A film forming sample was heated at 1500 ° C.
The firing was performed for 5 hours.

(5) Evaluation of film sample: The film thickness and the density of the fired sample were measured at intervals of 100 mm in the longitudinal direction of the sample. As a method of measuring the film thickness, a cross section of the sample was actually measured using an electron microscope. The denseness was measured by measuring a gas leak amount when a differential pressure of 9.8 × 10 ⁴ Pa was applied to the sample with nitrogen gas. FIG. 1 shows the film thickness of the YSZ cross section at each portion in the longitudinal direction of the sample. In FIG.
4 shows the gas permeation flux at each part in the longitudinal direction of the sample.
In FIGS. 1 and 2, the position at 0 mm in the cell longitudinal direction is the sealed side of the sample, and the position at 1000 mm is the open side of the sample. From the results shown in FIG. 1, the film thickness was 50 μm ± 6 μm in the vertical film formation, but it was possible to form the film uniformly in the range of 50 μm ± 2 μm in the horizontal film formation. Understand. Also, from the results shown in FIG.
In the vertical film formation, the density of the sample sealing part is very poor,
The density also tends to decrease on the sample opening side, but when the film is formed horizontally, there is almost no difference in the density depending on the sample position, and the absolute value of the gas permeation flux is also smaller than that in the vertical film formation. It can be seen that the density is small and the density is good.

[Brief description of the drawings]

FIG. 1 is a diagram of one embodiment illustrating a film thickness distribution according to a film forming direction in the present invention.

FIG. 2 is a view of one embodiment for explaining a gas permeation flux distribution according to a film forming direction in the present invention.

Claims (14)

[Claims] 1. A first step of preparing a cylindrical base, a second step of installing the cylindrical base in a horizontal direction, and applying a slurry while rotating the cylindrical base, and a cylindrical base to which the slurry is applied 3rd to dry and bake
And a film forming method comprising: 2. The film forming method according to claim 1, wherein the slurry is applied in the second step by dipping in which a cylindrical substrate is immersed in the slurry. 3. The film forming method according to claim 1, wherein the slurry is applied in the second step by flow coating in which the slurry flows from above a cylindrical base. 4. The film forming method according to claim 1, wherein the slurry is applied to the cylindrical substrate by spraying the slurry in the second step. 5. The cylindrical base is porous, and one side in a longitudinal direction is sealed, and the inside of the cylindrical base is depressurized in the second step. 4. The film forming method according to any one of the above items 4. 6. The method according to claim 1, wherein in the third step, the cylindrical substrate is dried while rotating.
6. The film forming method according to any one of claims 1 to 5. 7. The slurry has a viscosity of 1 to 500 cps.
7. The method according to claim 1, wherein the adjustment is made to:
The film forming method according to the above section. 8. The film forming method according to claim 1, wherein a solid electrolyte powder is mixed into the slurry. 9. The method according to claim 8, wherein a zirconia-based solid electrolyte is used as the solid electrolyte powder. 10. The film forming method according to claim 9, wherein a powder (YSZ) doped with yttria is used as the zirconia-based solid electrolyte. 11. The method according to claim 1, wherein the doping amount of yttria in the YSZ powder is 8 to 12 mol%.
0. The film forming method according to item 0. 12. An air electrode powder in the slurry,
(La, Sr) MnO _ThreeAnd / or (La, Ca) Mn
O_ThreeIt is especially important to mix a perovskite oxide powder.
The film forming method according to any one of claims 1 to 7, wherein
Law. 13. The film forming method according to claim 1, wherein (La, Ca) CrO ₃ -based perovskite oxide powder is mixed as the interconnector powder in the slurry. . 14. A fuel electrode powder in the slurry,
The film forming method according to any one of claims 1 to 7, wherein a composite powder of Ni and / or NiO and YSZ is mixed.