JP2000044369A - Production of lanthanum chromite compact film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a lanthanum chromite compact film, capable of forming the lanthanum chromite compact film, which can be easily attached to a large member and is useful for the interconnector of a solid electrolyte type fuel battery, in high productivity and at a low cost by subjecting the surface of a ceramic substrate compact in some extent to a roughening treatment and subsequently forming the lanthanum chromite compact film on the ceramic substrate by a wet method. SOLUTION: This method for producing a lanthanum chromite compact film comprises subjecting the surface of a ceramic substrate compact in some extent to a roughening treatment, subsequently repeatedly subjecting the treated ceramic substrate to processes each comprising dipping the treated ceramic substrate in a lanthanum chromite slurry and then drying the dipped ceramic substrate to form a coating film, and subsequently baking the formed coating film. The ceramic substrate compact in some extent preferably has a film thickness of <=200 μm, and the roughening treatment is preferably carried out by a method comprising blast-grinding the ceramic substrate so as to give the relation of the inequality: 0.01<=(t1-t2)/t1<=0.2 (t1 μm is a film thickness before the roughening treatment; t2 μm is a film thickness after the roughening treatment). The gas penetration flux Q of the ceramic substrate after the roughening treatment is preferably <=50 (m3/m2.hr.atm).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a lanthanum chromite dense membrane suitable for an interconnector of a solid oxide fuel cell. In particular, the present invention relates to a method for forming a lanthanum chromite dense film capable of obtaining a dense thin film having a porosity of 1% or less by a wet method.

[0002]

2. Description of the Related Art Conventionally, as disclosed in JP-A-61-153280, CVD / E is used as a method for producing an interconnector film of a cylindrical cell type solid oxide fuel cell.
The details of what is carried out by the VD method and which is found in the publication are as follows. In this method, a first reactant containing an oxygen source permeates through pores in a base material, reacts with a metal halide gas on the other side of the base material, and forms a metal oxide on the base material. Form a film. As the reaction product metal oxide grows on the substrate, chemical vapor deposition (CV
According to D), the reaction product tightly closes the plurality of small holes in the substrate. The coating is deposited by electrochemical deposition (EVD) as the transfer of oxygen from the oxygen source through the growing oxide layer occurs.
Grow by.

[0003]

SUMMARY OF THE INVENTION Conventional CVD / EVD
The method is suitable for forming a dense film having good adhesion. 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-sized member, the productivity is low, and the cost is high. Also, C
In VD / EVD, the composition of the material of the film to be formed is limited.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems that it is difficult to form a film on a large-sized member by the CVD / EVD method, the productivity is low, and the cost is high. An object of the present invention is to provide formation of a dense lanthanum chromite film that can easily obtain a dense lanthanum chromite film even by a low-cost wet method, in which the film can be easily applied to a large-sized member and the productivity is high.

[0005]

Means for Solving the Problems The present invention has been made to solve the above-mentioned problems. According to the present invention, there is provided a method for producing a dense film of lanthanum chromite by a wet method on a ceramic substrate which is somewhat dense. And a lanthanum chromite film is formed thereon.

[0006] The ceramic substrate having a certain degree of density means that the gas permeation flux is Q (m ³ / m ² · hr · atm) and Q ≦ 50 (m ³ / m ² · hr · atm). Point to.

In a method of forming a lanthanum chromite dense film on a somewhat dense ceramic substrate by a wet method, the surface of the somewhat dense ceramic substrate is roughened, and a lanthanum chromite film is formed thereon. As a result, a dense film having good adhesion can be produced even by a wet method.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, it is stated that a film is formed on a ceramic substrate which is dense to some extent. This is because when (mate) is in a liquid phase at the time of firing, if a film is formed directly on the porous substrate, the film diffuses into the porous substrate, so that a dense film cannot be obtained.

In the present invention, a lanthanum chromite film is formed after performing a roughening treatment on a ceramic substrate which is dense to some extent. However, when a lanthanum chromite film is formed on a smooth ceramic substrate, the film has poor adhesion. This is to cause peeling of the film after firing.

In the present invention, when the film thickness of the ceramic substrate to some extent before the surface roughening treatment is t1 (μm) and the film thickness after the surface roughening treatment is t2 (μm), 0.01
≦ (t1−t2) /t1≦0.2,
If (t1−t2) / t1 <0.01, the unevenness of the surface is too small, so that the adhesion of the film is poor and the lanthanum chromite is peeled off. On the other hand, (t1-
If t2) / t1> 0.2, as shown in Table 1, there is a possibility that the function of the ceramic substrate that is somewhat dense may be impaired.

[0011]

[Table 1]

In the present invention, the gas permeation flux of the ceramic substrate after the surface roughening treatment is defined as Q (m ³ / m ² · hr · atm).
Then, it is assumed that Q ≦ 50 (m ³ / m ² · hr · atm). However, as shown in Table 1, Q> 50 (m ³
/ M ² · hr · atm), the gas permeation flux of lanthanum chromite is 0.01 (m ³ / m ² · hr · atm).
This is because the larger the gas permeation flux of the ceramic substrate subjected to the surface roughening treatment, the larger the gas permeation flux of lanthanum chromite tends to be. From this viewpoint, the denser the ceramic base, the better.

In the present invention, the substance to be doped into lanthanum chromite is not particularly limited.
Ca, Sr, Mg, Co, Cu, Zn, Ti, Li and the like can be adopted. Among them, Ca dope is preferable because it can be sintered at a low temperature.

In a typical application of the present invention, the porous ceramic substrate is an air electrode of a solid oxide fuel cell, and a somewhat dense ceramic substrate is an intermediate layer (precoat layer) between the air electrode and the interconnector. Yes,
The lanthanum chromite dense thin film is the interconnector. The interconnector of the solid oxide fuel cell is required to have the following characteristics. The method for forming a dense lanthanum chromite thin film of the present invention is suitable as a method for forming such an interconnector.

(1) High electrical conductivity. Since the role of the interconnector is to establish electrical continuity between the unit cells of the solid oxide fuel cell, it is the most basic requirement. If the electric conductivity is low, the self-consumption of electric power in the interconnector increases, and the power generation efficiency of the cell decreases. Electrical conductivity, 10S · cm at a film formation condition ^{- 1} or more (more preferably 40S · cm ^{- 1} or more) is required. (2) Low air permeability. Fuel gas (H ₂ , CO, etc.) and oxidant (air, etc.) flow on the front and back surfaces of the interconnector, but if these mix through the interconnector, the power generation performance of the cell will be reduced. The air permeability is 0.
01 (m ³ / m ² · hr · atm) or less (more preferably 0.0001 (m ³ / m ² · hr · atm) or less). (3) Both oxidation and reduction have durability. (4) The coefficient of thermal expansion is close to that of other cells such as YSZ (yttria stabilized zirconia). (5) Low reactivity with air electrode materials such as LaSrMnO ₃ and LaCaMnO ₃ and YSZ. (6) Being able to form a thin film. Since a current flows through the interconnector in the thickness direction, the thinner the resistance, the lower the resistance. A film thickness of 200 μm or less is required.

In the present invention, the method for synthesizing the lanthanum chromite powder is not particularly limited. Coprecipitation method,
A powder mixing method, a spray pyrolysis method, a sol-gel method, an evaporation to dryness method and the like can be employed. Among them, the spray pyrolysis method is preferred from the viewpoints of high uniformity of composition, low contamination of impurities such as silica and iron, and short working process (low cost).

The method of the surface roughening treatment in the present invention is not particularly limited. There are a method of treating with a paper file, a method of spraying an abrasive on the surface with a spray (blast polishing), and a method of dipping using a chemical such as acid or alkali. Among these, the blast polishing method is preferable because the working process can be completed in a short time.

The abrasive used for the surface roughening treatment in the present invention is not particularly limited. Silicon carbide, boron carbide, alumina, diamond, zirconia, or the like can be used. When it is used for manufacturing an interconnector membrane of a solid oxide fuel cell, it is desirable to use alumina and zirconia.

In the present invention, the aqueous solution for obtaining the lanthanum chromite powder slurry may include the following. (1) Binder: PVA, EC (ethyl cellulose)
etc. The content is 0.1 to 1 with respect to 10 parts by weight of the solvent.
0 parts by weight is preferred. (2) Non-volatile solvents: α-terpineol and the like. The content is preferably from 10 to 80 parts by weight based on 100 parts by weight of the solvent. (3) Solvent: ethanol, 2-propanol, methanol and the like. Its content is from 20 to 100 parts by weight of the solvent.
90 parts by weight are preferred. (4) Dispersant: polyoxyethylene alkyl phosphate, CTAB and the like. The content is preferably 0.1 to 4 parts by weight based on 100 parts by weight of the solvent. (5) Antifoaming agent: sorbitan sesquioleate and the like. The content is preferably 0.1 to 4 parts by weight based on 100 parts by weight of the solvent.

[0020]

Embodiments of the present invention will be described below. La _0.8
Sr _0.2 MnO ₃ (gas permeation flux: 2000 (m ³ / m ² ·
hr.atm)) on a porous substrate of La _0.8 Ca _0.2 Mn.
O ₃ film is formed and fired, and La _0.8 Ca _0.2 M
An nO ₃ film (film thickness 100 μm) was produced. On this membrane surface,
Alumina powder was sprayed with a spray to perform a roughening treatment. After the membrane was washed with distilled water and dried, the roughened membrane surface was dipped (dipped) into a slurry containing La _0.8 Ca _0.2 CrO ₃ powder. After repeating the step of immersing in this slurry and drying, firing at 1400 ° C. for 10 hours was performed.

[0021] The conditions for the roughening process, the thickness of the surface-roughening treatment before the La _0.8 Ca _0. film t1, and the thickness of the La _0.8 Ca _0.2 MnO ₃ films after roughening t2 It controlled so that it might become.

(1) Preparation method of lanthanum chromite powder La, Ca, Cr is selected so that La _0.8 Ca _0.2 CrO ₃ is obtained.
Was prepared and a powder was prepared by a spray pyrolysis method. The produced powder was further calcined and subjected to a particle size control step to obtain a slurry powder.

(2) Slurry aqueous solution After mixing 33 parts of terpineol and 100 parts of ethanol, 1.2 parts of ethyl cellulose as a binder,
A slurry aqueous solution was prepared by adding and mixing 1 part of polyoxyethylene alkyl phosphate as a dispersant and 1 part of sorbitan sesquioleate as a defoaming agent.

(3) Preparation of Slurry An average diameter of 1 to 2 μm was added to 100 parts by weight of the slurry solution.
A slurry was prepared by mixing 40 parts of La _0.8 Ca _0.2 CrO ₃ powder controlled to m and 10 parts of La _0.8 Ca _0.2 CrO ₃ powder controlled to an average diameter of 0.5 μm.

(4) Film Formation The step of immersing the surface subjected to the surface roughening treatment in the slurry for 30 seconds and drying was repeated seven times.

(5) Drying The slurry coat film was dried at 80 ° C. for 1 hour.

(6) Film Thickness The thickness of the lanthanum chromite obtained after firing is from 40 to
It was 60 μm.

(7) Peeling Test Table 1 shows the relationship between the roughening conditions and the peeling of the film. When the La _0.8 Ca _0.2 CrO ₃ film was formed without performing the surface roughening treatment, not only peeling of the film but also gas permeability tended to be large. Further, even if the surface is roughened (t
In the treatment of about 1-t2) / t1 <0.01, the adhesion of the film was poor and the film was easily peeled. (T1-t2) / t1 ≧
At 0.01, no peeling of the film was observed.

(8) Gas Permeation Flux Table 1 and FIG. 1 show the results of the gas permeation flux of the La _0.8 Ca _0.2 CrO ₃ film. (T1-t2) / t1 is 0.05
In the following, the gas permeation flux tended to decrease, and it was recognized that the gas permeation flux tended to increase from 0.05 to 0.1, and to increase at 0.1 or more. If it exceeds 0.2, the gas permeation flux becomes 0.01 (m ³ /
m ² · hr · atm), the film was not a dense film, and when (t 1 -t 2) / t 1> 0.2, the value of the gas permeation flux tended to be significantly increased. In this embodiment, when (t1−t2) / t1> 0.2,
La _0. Although ₈ Ca _0.2 denseness of CrO ₃ film is severely degraded, which sintering aid La _0.8 Ca _0.2 CrO ₃ at the time of firing for La _0.8 Ca _0.2 MnO ₃ films underlying becomes porous base It was speculated that a dense La _0.8 Ca _0.2 CrO ₃ film could not be obtained. From this perspective, 0.0
It is preferable that the range of 1 ≦ (t1−t2) /t1≦0.2 is satisfied.

(9) La_0.8Ca_0.2MnO_ThreeFilm roughening
Gas permeation flux after treatment Table 1 shows La_0.8Ca_0.2MnO_ThreeGas after film roughening
Permeate flux and La_0.8Ca _0.2CrO_ThreeOf the gas permeation flux of the membrane
Show the relationship. From this result, La_0.8Ca_0.2MnO_Threefilm
Gas permeation flux Q> 50 (m^Three/ M^Two・ H
r ・ atm) is La_0.8Ca_0.2CrO_ThreeGas permeation of membrane
Flux> 0.01 (m^Three/ M^Two・ Hr ・ atm)
To produce a dense lanthanum chromite film, a roughening treatment
After processing, the ceramic substrate has Q ≦ 50 (m^Three/ M^Two・ Hr ・ a
tm).

[0031]

According to the present invention as described above,
A dense lanthanum chromite film having good adhesion can be produced by a relatively simple and inexpensive wet method. SOF
When a roughening treatment is performed on the intermediate layer (precoat layer) of the air electrode C and the interconnector to form lanthanum chromite, a dense interconnector film having good adhesion can be produced.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between surface roughening treatment conditions and gas permeation flux according to an embodiment of the present invention.

Claims (3)

[Claims] 1. A method for producing a dense lanthanum chromite film on a ceramic substrate that is somewhat dense by a wet method, comprising subjecting a surface of the substrate to a roughening treatment and forming a lanthanum chromite film on the surface. Characteristic method for producing a dense lanthanum chromite film. 2. When the thickness of the ceramic substrate to some extent before the surface roughening treatment is t1 (μm) and the film thickness after the surface roughening treatment is t2 (μm), 0.01 ≦ ( t1-
2. The method for producing a lanthanum chromite dense film according to claim 1, wherein t2) /t1≦0.2. 3. The ceramic substrate after the surface roughening treatment.
The permeation flux is Q (m ^Three/ M^Two・ Hr ・ atm)
Q ≦ 50 (m^Three/ M^Two.Hr.atm).
Method for producing a dense lanthanum chromite film described above.