JP2000024579A - Film forming method by dipping - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently form a film in uniform film thickness, when a slurry is formed into a film on a film forming substrate by dipping, by separating the film forming substrate and the slurry at a specific speed to form the film. SOLUTION: When a slurry is formed into a film on a film forming substrate by dipping in forming a solid electrolyte membrane in a solid electrolyte type fuel cell, the slurry and the film forming substrate are separated at a speed of 5,000 mm/sec or less. This dipping is pref. performed a plurality of times and, in this case, treatment is performed so that the number of times bringing the upper part of the film forming substrate to an upper side and that bringing the lower part thereof to the upper side become equal and the upper and lower parts of the film forming substrate are alternately turned over. The viscosity of the slurry is adjusted to 1-500 cPs, pref., 5-100 cPs. Further pref., a solid electrolyte powder, that is, a zirconia type solid electrolyte is used in the slurry and, as the zirconia type solid electrolyte, a powder doped with yttria (YSZ) is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a solid electrolyte type fuel cell (hereinafter also referred to as SOFC) having a cylindrical shape or a flat shape, or a solid electrolyte thin film on a base having various shapes.
The present invention relates to a film forming method for uniformly forming films of an air electrode, an interconnector (separator), and a fuel electrode by dipping, 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 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. Plasma spraying: A film formed by the same 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. And the latter is 0.1μ
It was difficult to produce a large amount of fine powder having a particle size of m or less. Thermal spraying + slurry filling method: The film thickness tends to become thicker as the number of steps increases.

The present invention provides a solid electrolyte membrane, an air electrode, an interconnector, and a fuel electrode in which the density and porosity of a tissue are controlled with a uniform film thickness, which is economical, mass-producible, and easy to apply to a large area. The purpose is to provide the formation.

[0009]

In order to achieve the above object, in a method of forming a slurry on a film forming substrate by dipping, the film forming substrate and the slurry are formed at a speed of 5000 mm / sec or less. The film is formed by being separated.

A feature of the present invention is that a solid electrolyte membrane, an air electrode membrane, an interconnector membrane, and a fuel electrode membrane are uniformly formed by a dipping method. The feature is that the slurry and the film-forming substrate are separated at a speed of 5000 mm / sec or less, and the amount of slurry adsorbed or adhered to the substrate is kept constant, thereby forming a film with a uniform film thickness. It is.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The separation of the slurry and the film-forming substrate at a speed of 5000 mm / sec or less in the present invention is performed when the slurry is separated at a speed higher than 5000 mm / sec. This is because a difference in film thickness of twice or more occurs between the upper part and the lower part of the film formation substrate.

Preferably, the slurry or the film-forming substrate is
Separating at a speed of 00mm / sec or less is 5
When separated at a speed slower than 00 mm / sec,
This is because the thickness difference between the upper and lower portions of the film forming substrate having a length of about 1000 mm in the vertical direction can be suppressed to within 1.5 times.

More preferably, separating the slurry or the film-forming substrate at a speed of 50 mm / sec or less
If you pull off at a speed slower than 50mm / sec,
This is because the thickness difference between the upper and lower portions of the film forming substrate having a length of about 1000 mm in the vertical direction can be suppressed to within 1.25 times.

It is preferable that the dipping of the present invention is performed a plurality of times. In this case, it is preferable that the number of times that the upper and lower portions of the film forming substrate come to the upper side is equal. The reason is that, regardless of the length of the substrate, the amount of dripping of the slurry due to the adhered slurry can be kept constant in the vertical direction, making it possible to form a film with almost no difference in film thickness in the vertical direction. This is because

The dipping of the present invention is preferably performed a plurality of times, and in this case, it is better to alternately turn the upper and lower portions of the film-forming substrate upside down. The reason is that, regardless of the length of the base, the amount of dripping of the slurry by the attached slurry can be made constant in the vertical direction, and the amount of slurry adsorbed on the formed film can be made constant, This is because it is possible to form a film with almost no difference in film thickness in the vertical direction.

The slurry viscosity in the present invention is from 1 to 500.
adjusting to cps, preferably 5-100 cps,
The reason that the lower limit is limited to 1 cps is that, when the viscosity is low, when the film is formed on the dense substrate, the film is repelled and spots are generated on the film. 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.

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.

The thickness of the solid electrolyte membrane and the interconnector membrane is preferably 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 film thickness of the air electrode and the fuel electrode film 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 properties, 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 electric 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 non-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 dipping method of the present invention, besides the usual dipping method in which the substrate is immersed in a slurry in the air, a dipping method in a pressurized gas or vacuum can be adopted. In that case, the number of times of dipping can be selected according to the required film thickness and the slurry composition to be used.

[0028]

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. (1) 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 the binder, polyoxyethylene alkyl phosphate is used as the dispersant, and sorbitan sesquioleate is used as the defoaming agent. The respective mixing ratio in the solution is as follows: solvent: binder: dispersant: defoamer = 93: 6.8: 0.
1: 0.1. Mixing was performed for 24 hours with a stirrer.

(2) Preparation of Slurry Using 10 YSZ powder having a specific surface area of 20 m 2 / g, 30 parts of the powder was added to 70 parts of the above solution, and 2 parts were prepared by a ball mill.
Mixing was performed for 4 hours to prepare a slurry. The viscosity of the slurry was 74 cps.

(3) Film formation: Using the above slurry, a YSZ film is formed by dipping on a substrate having a film of an air electrode material and YSZ composite powder formed on an air electrode having a total length of 1100 mm, an outer diameter of 22 mm and an average pore diameter of 11 μm. The membrane was made. As a dipping method, the substrate was inserted into the container filled with the slurry at a speed of 50 mm / sec in the longitudinal direction, and then the substrate was taken out at a lifting speed of 10 mm / sec to 10000 mm / sec. After drying the substrate after dipping at 100 ° C., the YSZ film thickness is about 5 on average.
Dipping and drying were repeated until the thickness became 0 μm.

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

(5) Evaluation of film thickness: The thickness of the fired sample was measured at intervals of 100 mm in the longitudinal direction of the sample. As a measuring method, a cross section of the sample was actually measured using an electron microscope. FIG. 1 shows YSZ in the longitudinal direction of the sample at each pulling speed.
The thickness of the cross section is shown. Note that, in FIG.
The position of mm is the lower side of the sample, and the position of 1000 mm is the upper side of the sample.

From the results of this example, it can be seen that as the sample is pulled up more slowly from the slurry, the difference in the thickness of the sample in the vertical direction can be reduced. In the pulling of the sample at 10 mm / sec performed in this example, the difference in film thickness between the upper part and the lower part having a length of 1000 mm in the vertical direction could be suppressed to about 1.1 times.

By slowly pulling up the sample from the slurry, the difference in film thickness in the vertical direction can be reduced because the slurry attached to the substrate is prevented from flowing from the upper part to the lower part. Because you can.

[0035]

As is apparent from the above description, the present invention has the following effects. By controlling the speed at which the film-forming substrate is separated from the slurry, it is possible to reduce the difference in film thickness between the upper and lower portions of the film-forming substrate. Films can be formed on the entire surface of a substrate of various shapes (the inner and outer surfaces of a pipe, a flat plate, or the like) or any part thereof. Compared with the CVD / EVD method, the plasma spraying method or the like, an expensive manufacturing apparatus is not required, and application to a large-sized product is easy. Therefore, a high-performance and low-cost SOFC cell, an oxygen sensor, an oxygen pump, and other elements can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

Claims (13)

[Claims] 1. A method for forming a film on a film forming substrate by dipping a slurry, wherein the film forming substrate and the slurry are
A film forming method by dipping, wherein the film is formed by separating the film at a speed of 0 mm / sec or less. 2. A method for forming a film on a film forming substrate by dipping the slurry, wherein the film forming substrate and the slurry are
A film forming method by dipping, wherein the film is formed by separating the film at a speed of not more than mm / sec. 3. The film forming method according to claim 1, wherein the film forming speed is to pull up a film forming substrate installed in the slurry. 4. The film forming method according to claim 1, wherein the film forming speed is to discharge the slurry in the film forming container filled with the slurry. 5. The dipping method according to claim 1, wherein the film formation by dipping is performed a plurality of times, and the upper and lower portions of the film formation base are equal to each other on the upper side. Film formation method. 6. The film formation method by dipping according to claim 1, wherein the film formation by dipping is performed a plurality of times, and the upper and lower portions of the film formation base are alternately turned upside down. 7. The slurry has a viscosity of 1 to 500 cps.
7. The film forming method by dipping according to any one of claims 1 to 6, wherein the adjustment is performed. 8. The film forming method by dipping 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 to be mixed into the slurry. 10. A powder (YSZ) doped with yttria as a zirconia-based solid electrolyte mixed in a slurry.
10. The film forming method by dipping according to claim 9, wherein: 11. An air electrode powder is mixed in a slurry, and (La, Sr) MnO ₃ and / or (La, Ca) MnO ₃ based perovskite oxide powder is mixed as the air electrode powder. The film forming method by dipping according to claim 1. 12. An interconnector powder is mixed into a slurry to obtain an interconnector powder (La, C
8. The film forming method by dipping according to claim 1, wherein a) a CrO ₃ -based perovskite oxide powder is mixed. 13. The dipping method according to claim 1, wherein a fuel electrode powder is mixed in the slurry, and a composite powder of Ni and / or NiO and YSZ is mixed as the fuel electrode powder. Film formation method.