JP3525601B2 - Method for forming dense ceramic thin film - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for forming a dense ceramic thin film such as a dense solid electrolyte thin film used in a solid electrolyte fuel cell (hereinafter referred to as SOFC), an oxygen sensor, an oxygen pump and the like. In particular, the present invention relates to a method for forming a ceramic thin film capable of obtaining a dense thin film while preventing cracks (burning out) during firing.

[0002]

2. Description of the Related Art The prior art will be described by taking a solid electrolyte thin film for SOFC as an example. In SOFC, a solid electrolyte thin film having oxygen ion (O ²⁻ ) permeability and no gas permeability is required. This solid electrolyte thin film (ZrO
₂ , CeO ₂ etc.) are required to be thin and dense in order to satisfy both of these characteristics. Furthermore, it is required to economically form a thin film having a large area. This SOFC power generation cell generally has a thickness of 0.3 to
30 ~ 2000μ thickness on 5.0mm porous substrate
An m air electrode (LaMnO ₃ or the like) is formed, and a solid electrolyte thin film having a thickness of 30 to 1000 μm is formed thereon. Furthermore, a fuel electrode (Ni-based cermet or the like) is formed thereon.

The following have been proposed for the purpose of obtaining a thin and dense solid electrolyte thin film for SOFC cells which is low in cost and excellent in mass productivity. Manufacturing method by CVD / EVD (Chemical Electro Vapor Deposition) (Japanese Patent Laid-Open No. 61-91880): In this manufacturing method, a first electrode is attached to a porous support, and an electrically conductive, oxygen-permeable intermediate layer material is applied. Protecting the first electrode from the vapor of the high temperature metal halide by depositing it on the first electrode and contacting the intermediate layer material with the vapor of the high temperature metal halide to remove metal oxide from the metal oxide over the entire surface of the intermediate layer. To form a solid electrolyte.

Manufacturing method by plasma spraying (Japanese Patent Laid-Open No. 61-198570): In this manufacturing method, a solid electrolyte raw material composed of zirconium oxide and a metal oxide such as a rare earth element is solid-solubilized, and then the solid-solubilized raw material is ground. Then, after adjusting the particle size of the powder obtained by the pulverization, the powder is adhered as an electrolyte thin film to the substrate of the fuel cell by plasma spraying. According to the example of the specification of the publication,
Using a thermal spray powder with a particle size of 2 μm or less, a thickness of 200 μm,
It is said that a solid electrolyte thin film having a terminal voltage of 790 mV was obtained.

Manufacturing method by slurry coating (Japanese Patent Laid-Open No. 1-93065): In this manufacturing method, either one of an air electrode layer and a fuel electrode layer is formed into a tubular shape to form an electrolyte and another electrode layer. The powder slurry of each material is applied to the surface of the cylindrical object in order, dried, and then fired. According to the embodiment of the specification of the publication, the thickness is 150 μm.
It is said that a thin film of YSZ of m was obtained.

Manufacturing method by thermal spraying + slurry coating (JP-A-2-220361): In this manufacturing method, a solid electrolyte layer formed by thermal spraying on a base tube has a gap between the solid electrolyte layers.
The present invention is characterized in that after applying a sealing agent containing yttria-stabilized zirconia in a solid matter concentration of 40% by weight or more, it is dried and baked. According to the example of the specification of the publication, a particle size of 0.05 to 2.
Apply slurry containing YSZ powder of 5 μm (hand painted by brush)
After that, it is said that the solid electrolyte thin film having an extremely low air permeability was obtained by drying and firing.

[0007]

The above-mentioned conventionally proposed techniques have the following problems. CVD method / EVD method: This method is suitable for forming a dense thin film. However, since it is necessary to form the film under a special atmosphere and physical conditions that are shielded from the atmosphere, an expensive apparatus is required. For a large member, a large device capable of accommodating the member is naturally required. Therefore, it is difficult to attach a film to a large member, the productivity is low, and the cost is high. Moreover, since the corrosive source gas is used, the risk of corroding the substrate is high. Plasma spraying method: The film formed by this method is basically porous. Therefore, in order to eliminate air permeability, the film must be thick to some extent. for that reason,
It is not possible to obtain a high-performance cell. Also, mass productivity is low.

Slurry coating method: A film forming operation can be performed in the atmosphere, and an expensive device is not required, and thus is an economical method. However, it has been said that there are problems in the denseness and thinning of the film. In fact, the solid electrolyte thin film disclosed as an example of JP-A-2-220361 is considerably thicker than the thickness of 200 μm, which is a development target of this type of membrane of 10 to 50 μm. Further, since the film was likely to be burnt out, it was necessary to burn the film multiple times in order to densify the film while filling the cracks. In order to increase the sinterability of the membrane material in order to solve such problems, raising the firing temperature and making the slurry powder finer were also studied, but in the former case, the reaction between the substrate and the solid electrolyte was a problem. In the latter case, it was difficult to produce a large amount of fine powder having a particle size of 0.1 μm or less. Thermal spraying + slurry filling method: The film thickness tends to become thicker with the double process.

An object of the present invention is to provide a method for forming a dense solid electrolyte thin film in the range of 10 to several hundreds μm, which has mass productivity, easiness of application in a large area, and economy. Another object of the present invention is to provide a method for forming a dense thin film in the field of ceramic thin films that have similar needs.

[0010]

In order to solve the above problems, the method for forming a ceramic dense thin film of the present invention is a method for forming a dense ceramic thin film on a substrate by a slurry coating method; Slurry adjusting step of adjusting slurry containing particles, and the ceramic
Coarse sol preparation step for preparing a crude sol containing coarse particles of the material
And preparing a sol containing fine particles of the ceramic material
Sol adjustment step, and the above slurry, coarse sol and
By applying the sol individually and drying,
, A coarse sol and a laminated sol in which a plurality of sol coat layers are laminated.
Coating step and baking to co-fire this laminated coat layer.
And a forming step.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The constituent material of the ceramic thin film in the present invention is not limited to a specific substance,
The preferred field of application is Y ₂ O ₃ stabilized ZrO ₂ (YSZ)
And solid electrolytes such as CeO ₂ type and TiO ₂ type. These materials are preferably pure, especially Si
Impurities such as O ₂ and MnO are preferably 0.5% or less. The content of Y ₂ O ₃ in YSZ is preferably _{3 to} 20 mol%, more preferably 8 to 1
It is 2 mol%. The reason is that this range is excellent in terms of ionic conductivity.

Among the above CeO ₂ -based materials, typical ones are (CeO ₂ ) _1-x (M ₂ O ₃ ) _x , and M is S.
It is a rare earth element such as m, Gd, Yb, and Nb. The role of rare earth oxides is to add these oxides,
Ionic conductivity occurs in the CeO _{2 element} material. x is preferably 0.02 to 0.12. The reason is that outside this range,
This is because the ionic conductivity due to oxygen ions decreases.
The same applies to the TiO ₂ and ZrO ₂ systems.

The term "slurry" as used in the present invention means a suspension in which solid particles are relatively large and the particles easily precipitate by standing. The particle diameter is generally 0.1-10.
μm. The sol referred to in the present invention means a suspension in which solid particles are relatively small and do not easily settle even when standing. The particle size is generally between 10 and 5000 Angstroms. In the present invention, the sol particles serve as a sintering aid.

In one aspect of the method for forming a ceramic dense thin film of the present invention, the ceramic thin film is a solid electrolyte thin film made of yttria-stabilized zirconia (YSZ), and the particle diameter of the slurry is mainly 0.1 to 3. .0
μm, and the particle diameter of the sol is mainly 10
It is 1,000Å (angstrom). Alternatively,
The ceramic thin film is a solid electrolyte thin film made of YSZ, the BET (specific surface area value) of the slurry particles is 0.5 to 15 m ² / gr, and the BET of the sol particles is
Is 15 to 500 m ² / gr. The reason why this range is preferable in such a solid electrolyte thin film is the sinterability of the sol,
This is because the YSZ has a good balance of the sinterability, both particle diameters, and the total film thickness.

The method for producing the slurry particles of the present invention is not limited to a particular method. It can be performed by a spray dry method, an evaporation dryness method, or the like. Further, the method of adjusting the particle size can be carried out by classification after crushing. Further, the content of the ceramic particles in the slurry is 1
It is preferably 10 to 50 parts with respect to 00 parts.

The composition of the slurry solution of the slurry of the present invention is not particularly limited. The slurry solution is a solvent,
It may contain a binder, a dispersant, an antifoaming agent and the like. However, a non-volatile solvent is used as the solvent in the slurry solution 10
80 wt% is preferable. More preferably, the content is 15-40 wt%. The action of this hardly volatile solvent suppresses the change in the viscosity of the slurry during slurry preparation and storage, and also suppresses the occurrence of cracks due to drying after film formation (for example, dipping) using this slurry. Is. Here, the degree of volatility is, for example,
When the degree of butyl acetate is 100, 1 or less is desirable.

As an example of the hardly volatile solvent, α-terpineol can be mentioned. The content of refractory solvent is 1
The reason why 0 to 80 wt% is preferable is that a low concentration (less than 10 wt%) easily causes dry cracks after film formation (dipping), and a high concentration (more than 80 wt%) results in poor powder dispersibility. Because it will be. The content of the hardly volatile solvent is more preferably 15 to 40 wt%. This is because, within this range, the dispersibility of the powder in the slurry and the drying condition after dipping are most balanced.

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. Ethyl alcohol is suitable as an example of such a solvent. The preferable content is 10 to 40 wt% of the slurry solution.

The function of the binder contained in the slurry solution is to improve the coating property (adhesion) of the powder on the substrate. The amount of the binder is preferably 0.1 to 10 parts with respect to 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 (exceeds 10 wt%), the dispersibility of the powder is deteriorated. Ethyl cellulose is suitable as a specific example of the binder.

The action of the dispersant contained in the slurry solution is
This is to improve the dispersibility of the powder. The amount of dispersant is 100
The amount is preferably 0.1 to 4 parts. The reason is that low concentration (less than 0.1 wt%) has low dispersibility and high concentration (4 wt%).
This is because if it exceeds (%), the metamorphism of the slurry is likely to occur. Specific examples of the dispersant include polyoxyethylene alkyl phosphate ester.

The defoaming agent contained in the slurry solution acts to eliminate bubbles in the slurry. The amount of defoamer is 100
The amount is preferably 0.1 to 4 parts. The reason is that if it is less than that, the effect cannot be expected so much, and if it exceeds that, the binder in the slurry is likely to be transformed. A specific example of the defoaming agent is sorbitan sesquioleate. As a method for mixing each agent / powder, a general method such as a ball mill can be adopted.

The method of applying the slurry to the substrate in the manufacturing method of the present invention is not particularly limited. It may be a dipping method, a spray method, a brush coating method or the like. Of these, the dipping method is preferable. This is because it is simple, rich in mass productivity, and low in cost. As the dipping method, a usual dipping method of immersing the substrate in the slurry in the atmosphere, or a method of dipping in a pressurized gas or in a 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 used.

The method for producing the sol of the present invention is not particularly limited. A hydrothermal synthesis method, a coprecipitation method, an alkoxide method, etc. can be used. Of these, the hydrothermal synthesis method is preferable. The reason is that it is easier to control the particle size and crystallite size by pressure than other manufacturing methods.

[0024]

[0025]

In the present invention, the slurry has a viscosity of 1 to
It is preferably 100 cps and the viscosity of the sol is 50 cps or less. Furthermore, the viscosity of the slurry is 5-50 cps
And the viscosity of the sol is more preferably 20 cps or less. The reason why the above range is preferable is to control the thickness of the coat layer in an appropriate range.

The method of forming the ceramic dense film of the present invention is a method of forming on a substrate a dense ceramic thin film by a slurry coat method; a slurry adjusting step of adjusting a slurry containing particles of the ceramic material, A coarse sol adjusting step of adjusting a coarse sol containing coarse particles of the ceramic material; a sol adjusting step of adjusting a sol containing fine particles of the ceramic material;
By applying the crude sol and the sol separately and drying,
A laminate coating step of laminating a plurality of coat layers of the slurry, the precursor sol and the sol, and a firing step of co-firing the laminated coat layers are included .

That is, a suspension containing ceramic particles, which should be called a crude sol having an intermediate property between the slurry and the sol, is further used. The coating layer of this crude sol is
Since it has an intermediate sinterability between the slurry coat layer and the sol coat layer, it can be interposed between both layers to give the sinterability a gradient characteristic, which is effective for preventing burnout. The method for producing this crude sol is not particularly limited, but hydrothermal synthesis, alkoxide method and the like can be used.

In the method for forming a ceramic dense thin film of the present invention, the ceramic thin film is a solid electrolyte thin film made of YSZ, the particle diameter of the slurry is mainly 0.1 to 3.0 μm, and the coarse sol of The particle diameter may be mainly 500 to 5,000 Å, and the particle diameter of the sol may be mainly 10 to 1,000 Å (angstrom). In addition, it goes without saying that the average particle diameter in the actual combination has the relationship of slurry> coarse sol> sol. Alternatively, the BET of the particles of the slurry is 0.5 to 15 m ² / gr, the BET of the particles of the crude sol is 3 to 100 m ² / gr, and the BET of the particles of the sol is 15 to 500 m ² / gr. May be In such a thin film, the reason why this range is preferable is to control the sinterability of the sol for YSZ.

[0030]

EXAMPLES Examples of the present invention will be described below. (1) Slurry preparation: (1.1) Slurry powder preparation: ZrO ₂ +8 mol% Y ₂
The O ₃ powder was crushed using a ball mill, and then the particle size was adjusted with an air classifier. The particle size range was 0.1 to 3 μm, and the average particle size was 0.8 μm. (1.2) Slurry solution: After mixing 33 parts of α-terpineol and 100 parts of ethyl alcohol, 1.2 parts of ethyl cellulose as a binder, 1 part of polyoxyethylene alkyl phosphate ester as a dispersant, and a defoaming agent. 1 part of sorbitan sesquioleate as
Mixed to obtain a slurry solution. (1.3) Mixing: 40 parts of the slurry powder and 200 parts of the slurry solution were mixed and sufficiently stirred to obtain a slurry. The viscosity of this slurry was 5 cps.

(2) Sol preparation: A sol containing YSZ powder having the same composition as the slurry powder was prepared by a hydrothermal synthesis method. The diameter of the particles in this sol was 100 to 1,000 (average 300) Å when measured using a laser diffraction method. The components of the solution of this sol were 95% ultrapure water and 5% binder. Also, its viscosity is 3.5 cp
It was s.

(3) Preparation of crude sol: A crude sol was prepared in the same manner as the above sol. The diameter of the particles in the sol is 0.1 to
It was 3 (average 0.3) μm. The components of the solution of this sol were 95% ultrapure water and 5% binder. The viscosity was 5 cps.

(4) Dipping: Substrate (material: La _0.9 Sr _0.1 MnO ₃ , size: outer shape 12 × inner diameter 10 × length 100 mm, porosity: 35%)
The surface of the above was coated with the above slurry and sol by dipping. The combinations of coat layers (from the substrate side to the top) are as follows. Comparative Example: Slurry layer only, 3 coats, thickness 25 μm Reference Example : Slurry layer 25 μm, sol layer 1.2 μm, slurry layer 16 μm Example 2: Coarse sol layer 2 μm, sol layer 1.2 μm, slurry layer 16 μm Example 3: 25 μm slurry layer, 1.7 μm coarse sol layer,
Sol layer 1.1 μm, slurry layer 14 μm Example 4: Slurry layer 25 μm, coarse sol layer 1.7 μm,
Sol layer 1.1 μm, coarse sol layer 1.4 μm, slurry layer 1
1 μm

(5) Drying: 1 hour at room temperature, then 100
Hold at 1 ° C for 1 hr. It should be noted that each time it was dipped, it was dried under these conditions. (6) Baking: It was baked at 1450 ° C. for 5 hours.

(7) Performance test: The gas permeability of each of the above samples was measured. The measuring method was a differential pressure gas flow rate measuring method. The result is shown in FIG. If you look at this,
It can be seen that the one-time firing (6 dips) of the comparative example has an insufficient gas permeation coefficient of 2 × 10 ⁻⁸ (m ³ sec / kg, the same applies hereinafter). Even in this example, the gas permeation coefficient decreased to a sufficient level of 10 ^{−11 by} firing twice (total of four dips). On the other hand, in each of the examples, the gas permeation coefficient was 10 ^-11 or less even after the single firing, which was a sufficient level.

[0036]

As is apparent from the above description, the present invention exhibits the following effects. A thin and dense ceramic thin film can be obtained even with a small number of firings. Therefore, the performance of the element such as the fuel cell can be improved and the manufacturing cost can be reduced. Since burnout can be suppressed, the yield of film formation can be improved. The solid electrolyte thin film can be formed on the entire surface of a substrate (flat plate, inner and outer surfaces of a pipe, etc.) of various shapes or an arbitrary part. Compared with the CVD / EVD method, plasma spraying, etc., an expensive manufacturing device is not required and it can be easily applied to a large size product. Because of, a high-performance and low-cost SOFC cell, an element such as an oxygen sensor, an oxygen pump, or the like can be provided.

[Brief description of drawings]

FIG. 1 is a graph showing the gas permeability test results of solid oxide fuel cell cell samples according to a comparative example and an example of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Haruo Nishiyama Inventor Haruo Nishiyama 2-1-1 Nakajima, Kokurakita-ku, Kitakyushu, Fukuoka Totoki Kiki Co., Ltd. (56) Reference JP-A-6-283179 (JP, A) JP-A-5-251094 (JP, A) JP-A-6-260182 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 8/02 B28B 1/30 G01N 27/409 H01M 8/12

Claims (6)

(57) [Claims] 1. A method of forming a dense ceramic thin film on a substrate by a slurry coating method; a slurry adjusting step of adjusting a slurry containing particles of the ceramic material, and a coarse sol containing coarse particles of the ceramic material. And a sol adjusting step for adjusting a sol containing fine particles of the ceramic material, and the slurry, the coarse sol and the sol are separately applied onto a substrate and dried to obtain the slurry, the coarse sol. A method of forming a ceramic dense thin film, comprising: a lamination coating step of laminating a plurality of sol and sol coating layers; and a firing step of co-firing the laminated coating layers. 2. The ceramic thin film is a solid electrolyte thin film made of YSZ, and the particle diameter of the slurry is mainly 0.1 to 3.0 μm.
The average diameter of the particles of the crude sol is smaller than that of the particles of the slurry, and the diameter of the particles of the crude sol is mainly 500 to
5,000Å, the average diameter of the particles of the sol is smaller than that of the coarse sol, and the diameter of the particles of the sol is mainly 10 to 1,000.
0 Å (Angstrom) a method of forming a ceramic dense film of claim 1, wherein. 3. The ceramic thin film is a solid electrolyte thin film made of YSZ, BET of particles of the slurry is 0.5 to 15 m ² / gr, and BET of particles of the crude sol is 3 to 100 m ² / gr. , and the method of forming a ceramic dense film of claim 1, wherein the BET is 15~500m ² / gr of the sol particles. 4. A said substrate, from bottom to top, the coating layer of coarse sol coating layer of the sol, a method of forming the ceramic dense film of claim 1, wherein forming the coating layer of the slurry . 5. A said substrate, from bottom to top, the coating layer of the slurry, coating layer of coarse sol coating layer of sol claim 1, 2 or 3 to form a coating layer of the slurry
A method for forming a ceramic dense thin film as described above. 6. A slurry coating layer, a coarse sol coating layer, a sol coating layer, a crude sol coating layer, and a slurry coating layer are formed on the substrate from the bottom to the top . 2. The method for forming a ceramic dense thin film according to 2 or 3 .