JP2000290065A - Dense sintered film, its manufacture and inner connector for solid electrolyte type fuel cell using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a film suitable for use as the electrically conductive layer of a ceramic heater, the inner connector film of a solid electrolyte type fuel cell or the like by disposing a somewhat dense ceramic layer on a porous substrate and a dense ceramic film on the ceramic layer. SOLUTION: A ceramic middle layer having <=50 m3/m2.hr.atm gas permeation flux is disposed between a porous substrate and a dense ceramic film. The composition of the middle layer is preferably (La1-XMX)YMnO3, wherein 0<X<=0.4, 0.9<=Y<=1 and M is Ca or Sr. After the formation of the middle layer, surface roughening treatment is preferably carried out so as to enhance the adhesion of the film and to prevent the peeling of the film after firing. A blasting method is preferably used for the surface roughening treatment. Methods for forming the middle layer and the dense ceramic film are not particularly limited but wet processes are cost-wise advantageous.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sintered film requiring gas tightness, such as a conductive layer of a ceramic heater and an interconnector for a solid oxide fuel cell (hereinafter referred to as SOFC), and a method for producing the same. In particular, it relates to a dense sintered film from which a dense thin film can be obtained even by a low-cost wet method.

[0002]

2. Description of the Related Art Conventionally, in Japanese Patent Application Laid-Open No. 4-248272,
La _1-X Ca _X Cr _1-Y O ₃ composition (0 <X ≦ 0.4, 0 <Y
≦ 0.05), a dense film of the interconnector is formed by applying a slurry on the air electrode and firing it.

[0003]

The above-mentioned conventional methods have the following problems. (1) Although it is described that it is applied on the air electrode, calcium doptolan chromite is directly formed on the porous air electrode and calcined. Since calcium chromate, which is a sintering aid, is in a liquid phase at the time of calcination, air It is difficult to obtain a dense lanthanum chromite film that diffuses into the poles.

(2) It is described that a dense film of an interconnector is formed by slurry-coating a powder having the above composition. However, even if diffusion of calcium chromate does not occur, it is not enough to simply apply the slurry on the air electrode. In addition, it is difficult to obtain a dense film because of low powder filling property.

An object of the present invention is to provide a method for producing a ceramic dense film suitable for producing a sintered film requiring high density, such as a conductive layer of a ceramic heater or an interconnector film for SOFC.

[0006]

In order to achieve the above object, the present invention provides a method of forming a lanthanum chromite such as a lanthanum chromite by providing a somewhat dense ceramic layer on a porous substrate and providing a dense ceramic film thereon. It has become possible to produce a dense film of a hardly sinterable material.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a gas permeation flux Q ≦ 50 (m) between a porous substrate and a dense ceramic film is used.
It is stated that it is preferable to provide a ceramic intermediate layer of ³ / m ² · hr · atm). The reason is that Q> 50 (m
³ / m ² · hr · atm), because the gas tightness of the dense ceramic film formed thereon becomes poor.
This is because, in the case of liquid phase sintering such as lanthanum chromite doped with an alkaline earth metal, if the underlayer is porous, liquid phase components are diffused and it is difficult to be dense. From this viewpoint, the lower the gas permeability of the ceramic intermediate layer, the better.

[0008] The dense sintered film shown here refers to a ceramic film composed of two layers, a ceramic intermediate layer and a dense ceramic film.

The gas permeation flux Q of the dense sintered membrane shown here
′ Is a gas permeation flux Q ′ ≦ 0.01 (m ³ / m ² · hr · a) measured between the porous substrate and the dense ceramic film.
tm). The reason for this is that when the dense sintered film is used as an interconnector film for an SOFC, if the gas permeation flux Q ′> 0.01, the output of the SOFC may be reduced.

In the present invention, the composition of the ceramic intermediate layer is _{(La 1-X M X)} Y MnO 3 (0 <X ≦ 0.4,0.
9 ≦ Y ≦ 1, M = Ca or Sr). The reason for this is that when X = 0, the sinterability of the material itself is low, so that it is difficult to produce a somewhat dense film with Q ≦ 50 (m ³ / m ² · hr · atm). X
If> 0.4, the sinterability is too high, and the film is burned out,
This is because peeling or the like may be caused.

On the other hand, when Y <0.9, the manganese component is easily released and diffused, and there is a problem in durability of the material. When Y> 1, the sinterability is remarkably reduced, so that it is difficult to produce a dense film. This is because

In the present invention, it is preferable that a surface roughening treatment is performed after the production of the ceramic intermediate layer. The reason for this is that when a film is formed on a smooth ceramic substrate, the adhesion of the film is poor, and the film may be peeled off after firing.

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 erosion 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, or the like can be used.

The method for producing the ceramic intermediate layer and the dense ceramic film in the present invention is not particularly limited. Wet method, thermal spray method, CVD method and E
The VD method or the like can be considered. Of these, the wet method is preferred from the viewpoint of cost.

In a typical application of the present invention, the porous substrate is an air electrode support of an SOFC comprising Sr-doped or Ca-doplantan manganite, and the ceramic intermediate layer is formed of Sr-doped or Ca-doplantan manganite. It is an intermediate layer between the air electrode of the solid oxide fuel cell and the interconnector, and the dense sintered film is a lanthanum chromite interconnector. Although the following characteristics are required for the interconnector of the SOFC, 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 electric conductivity. This is the most basic requirement because the role of the interconnector is to establish electrical continuity between the unit cells of the SOFC. 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 (H2, 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 cell components 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.

[0018]

EXAMPLE: La _0.8 Ca _0.2 CrO ₃ Preparation of dense membranes La _0.8 Sr _0.2 MnO ₃ (gas permeation flux: 2000 (m ^{3
/ M 2 · hr · atm)} ) La 0.8 on a porous substrate Ca
_A ceramic intermediate layer (gas permeation flux: 0.01 to 100 (m ³ / m ² · hr · atm)) composed of a _0.2 MnO ₃ film was formed and fired. La _0.8 Ca _0.2 after the MnO ₃ films were subjected to a roughening treatment with alumina powder, La _0.8 Ca in the film
_A dense ceramic film made of a _0.2 CrO ₃ film was formed and fired. Hereinafter, a detailed manufacturing method will be described.

[0019] _{(1) La 0.8 Ca 0.2 MnO} 3 Preparation of ceramic intermediate layers _{(1-1) La 0.8 Ca 0.2 MnO} 3 powder synthesized _{La (NO 3) 3 aq,} Ca (NO 3) 2 · 4H 2 O, Mn
(NO ₃ ) ₂ aq was mixed so as to have a predetermined composition ratio to prepare a nitrate aqueous solution containing La, Ca, and Mn.
The oxide content at this time was set to 20 wt%.

A separately prepared oxalic acid aqueous solution (the amount of oxalic acid was 1.05 times the stoichiometric ratio with respect to La, Ca and Mn) was added to the above aqueous nitrate solution and stirred for about 5 hours. After stirring, the mixture was dried at 120 ° C. in order to remove moisture, and further thermally decomposed at 500 ° C. for 5 hours to remove nitric acid components and residual oxalic acid. Further, after the pyrolyzed powder was calcined, it was pulverized and classified so as to have a predetermined particle size to obtain a slurry powder.

(1-2) Slurry aqueous solution After mixing 33 parts of α-terpineol and 100 parts of ethanol, ethyl cellulose as a binder was mixed with 1.
2 parts, 1 part of polyoxyethylene alkyl phosphate as a dispersant, and 1 part of sorbitan sesquioleate as an antifoaming agent were added and mixed to obtain a slurry solution.

(1-3) Preparation of Coarse Powder Slurry 100 parts of the above slurry solution was calcined at 1300
40 parts of coarse powder of La _0.8 Ca _0.2 MnO ₃ composition controlled to an average diameter of 2 μm at 400 ° C. and an average diameter of _0.5 μm at a calcination temperature of 1100 ° C.
10 parts of fine powder of La _0.8 Ca _0.2 MnO ₃ composition controlled to m was mixed to prepare a coarse powder slurry.

(1-4) Preparation of Fine Powder Slurry 100 parts of the above slurry solution was calcined at 1100 ° C.
Then, 20 parts of fine powder of La _0.8 Ca _0.2 MnO ₃ composition controlled to have an average diameter of 0.5 μm was mixed to prepare a fine powder slurry.

(1-5) Preparation of La _0.8 Ca _0.2 MnO ₃ Ceramics Intermediate Layer Using the above coarse powder slurry and fine powder slurry, a gas permeation flux of 0.01 to 100 (m ³ / m ² · hr · atm)
La _0.8 Ca _0.2 MnO ₃ film was produced.

(2) Roughening treatment The degree of the roughening treatment is as follows, where the thickness of the La _0.8 Ca _0.2 MnO ₃ film is t1 and the thickness after the roughening treatment is t2.
(T1−t2) / t1 = about 0.05

(3) Preparation of La _0.8 Ca _0.2 CrO ₃ dense ceramic film (3-1) Method of preparing La _0.8 Ca _0.2 CrO ₃ powder La, Ca, Cr to obtain La _0.8 Ca _0.2 CrO ₃
Was prepared and spray pyrolyzed at 700 ° C. to produce a powder. The produced powder was further calcined and subjected to a particle size control step to obtain a slurry powder.

(3-2) Method for Producing Powder with Low Sinterability The precursor obtained by spray pyrolysis was calcined at 1200 ° C.
The calcined powder is further crushed by a ball mill, and the average particle size is 1 μm.
m. (Hereinafter referred to as A powder)

(3-3) Method for Producing Powder with High Sinterability The precursor obtained by spray pyrolysis was calcined at 900 ° C. The calcined powder was further crushed by a ball mill to obtain an average particle size of 0.5.
μm. (Hereinafter referred to as B powder)

(3-4) Preparation of Slurry Solution After mixing 33 parts of α-terpineol and 100 parts of ethanol, ethyl cellulose as a binder was mixed with 1.
2 parts, 1 part of polyoxyethylene alkyl phosphate as a dispersant, and 1 part of sorbitan sesquioleate as an antifoaming agent were added and mixed to obtain a slurry solution.

(3-5) Preparation of A powder slurry A slurry was prepared by mixing 100 parts by weight of the above slurry solution with 60 parts by weight of A powder having a calcining temperature of 1200 ° C.

(3-6) Preparation of B Powder Slurry 100 parts by weight of the above slurry solution was mixed with B powder at a calcination temperature of 900 ° C.
A slurry was prepared by mixing 60 parts by weight of the powder.

[0032] (3-7) a La _0.8 Ca _0.2 CrO ₃ film forming method La _0.8 Ca _0.2 CrO ₃ film was formed by a film forming method shown in Table 1.

[0033]

[Table 1]

(3-8) Outline of Film Forming Apparatus La _0.8 Ca _0.2 CrO ₃ film was formed using the film forming apparatus shown in FIG. The outline of the film formation will be described with reference to FIG. The dipping apparatus 1 of FIG. 1 includes a dipping tank 2, a decompression device 3 and a pressure device 4. The dip tank 2 has an oblong tank 5 having a relatively shallow depth. A lid is detachably mounted on the tank 5. Between the tank 5 and the lid 6, means (such as packing) for ensuring airtightness in the dip tank 2 is provided. In the dip tank 2,
The slurry 7 is filled to a certain level.

A base 10 is placed on the bottom 8 of the dip tank 2 via two tables 9 on the left and right sides. The base 10 has a cylindrical shape with a bottom, and the left end is a bottom 11.
The right end is the opening end 12. The open end 13 is covered with a stopper 14. An exhaust tube 15 is inserted into the center of the stopper 14. The exhaust tube 15 is connected to an exhaust pump 17 via an exhaust line 16.
(Vacuum pump). When the exhaust pump 17 is operated, the air in the substrate 10 is exhausted from the exhaust port 18 on the exit side of the pump 17 through the exhaust tube 15 and the exhaust pipe 16, and the inside of the substrate 10 is depressurized.

The pressurizing device 19 comprises a pressurizing tube 20, a valve 21, and a gas cylinder 22. When the valve 21 is opened, nitrogen gas is sent from the gas cylinder 22 through the pressurizing tube 20 into the dip tank 2 to pressurize the dip tank. The space between the lid 6, the pressurizing tube 20 and the exhaust pipe 16 is also sealed by an appropriate means.

Using such a dipping apparatus 1,
The slurry coat can be applied to the substrate 10 under various pressure conditions. The substrate 10 shown in this figure is a cell of a cylindrical solid electrolyte fuel cell. Slurry coating cannot be performed on the portions that come into contact with the mounting tables 9 and 9 ′, but there is no problem if the position is set as the non-film forming section. Further, the differential pressure device may be a vertical type, and the base tube is held by the main body. In this case, when the base tube is placed in the container, the placing tables 9 and 9 'become unnecessary, and a film can be formed on the entire surface.

(3-9) Film Forming Step As shown in FIG. 1, a slurry was placed in a container, and a sample was dipped therein for 30 seconds. After the sample was taken out, it was kept at room temperature for 30 minutes, and further dried at 100 ° C. for 1 hour. A film was obtained from the dipping and drying steps. The film formation without differential pressure shown in Table 1 is a film forming method in which the sample is immersed in the slurry as it is. In the differential pressure film forming (5 atm), the sample is immersed in the slurry while the inside of the tube is evacuated, and the sample is further immersed in the slurry. From 4
This is a method of forming a film while applying a pressure difference of atm and applying a total pressure difference of 5 atm to the sample.

(3-10) Firing: Firing was performed at 1400 ° C. for 10 hours.

(4) Evaluation of gas permeation flux of La _0.8 Ca _0.2 CrO ₃ dense ceramic membrane La _0.8 Sr _0.2 M under conditions of N ₂ gas and pressure difference 1 atm
The gas permeation flux between nO ₃ film and La _0.8 Ca _{0 .2} CrO ₃ film was measured to evaluate the compactness of the La _0.8 Ca _0.2 CrO ₃ film.

(5) Results of gas permeation flux of La _0.8 Ca _0.2 CrO ₃ dense ceramic membrane FIG. 2 shows gas permeation flux (Q1) and La _0.8 Ca _0.2 CrO ₃ of La _0.8 Ca _0.2 MnO ₃ ceramic intermediate layer. The relation of gas permeation flux (Q2) of a dense ceramic film is shown. L
a _0.8 gas permeability of the Ca _0.2 CrO ₃ film La _0.8 Ca _0.2
The lower the gas permeability of the MnO ₃ film, the lower the tendency. Further, the gas permeation flux Q of the La _0.8 Ca _0.2 MnO ₃ film
If 1 is 50 (m ³ / m ² · hr · atm) or less, La
The gas permeation flux Q2 of the _0.8 Ca _0.2 CrO ₃ film is 0.01
(M ³ / m ² · hr · atm)
It was found that preferable gas permeability as an interconnector film for SOFC can be secured.

[0042]

As described above, according to the present invention, a ceramic intermediate layer having a gas permeation flux Q ≦ 50 (m ³ / m ² · hr · atm) in forming a dense sintered film on a porous substrate. Because of this, a dense ceramic film made of a hardly sinterable material such as lanthanum chromite can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a film forming method according to an embodiment of the present invention.

FIG. 2 shows the gas permeation flux (Q1) and La _0.8 Ca _0.2 of the La _0.8 Ca _0.2 MnO ₃ ceramic intermediate layer of the embodiment of the present invention.
Gas permeation flux (Q2) of CrO ₃ dense ceramic membrane
Diagram explaining the relationship

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 dipping device 2 dipping tank 3 depressurizing device 4 pressurizing device 5 tank 6 lid 7 slurry 8 tank bottom 9 units 10 substrate 11 bottom 12 open end 14 stopper 15 exhaust tube 16 exhaust line 17 exhaust pump 18 exhaust port 20 pressurizing tube 21 Valve 22 Gas cylinder

Continued on front page F-term (reference) 4G031 AA02 AA04 AA09 AA16 BA02 BA03 CA08 5H026 AA06 EE13 HH00

Claims (5)

[Claims] 1. A dense sintered film comprising a ceramic layer which is provided to a certain degree on a porous substrate, and a dense ceramic film is provided thereon. 2. The gas permeation flux Q of said somewhat dense ceramic layer (hereinafter referred to as a ceramic intermediate layer) is Q
^2. The dense sintered film according to claim 1, wherein ≤50 (m ³ / m ² · hr · atm). 3. The composition of the ceramic intermediate layer is (La)
_{1-X M X) Y MnO} 3 (0 <X ≦ 0.4,0.9 ≦ Y ≦ 1,
3. The dense sintered film according to claim 1, wherein M = Ca or Sr). 4. A method for producing a dense sintered film on a porous substrate, comprising the steps of: preparing a ceramic intermediate layer on the porous substrate; roughening the ceramic intermediate layer; A method for producing a dense sintered film, comprising a step of producing a dense ceramic film on a treated surface. 5. The method according to claim 1, wherein the porous substrate is Sr-doped or Ca-doped.
An air electrode support for a solid oxide fuel cell made of doppanthan manganite, wherein the ceramic interlayer is Sr
The intermediate layer between an air electrode and an interconnector of a solid oxide fuel cell made of doped or Ca-doplantan manganite, and the dense ceramic film is an interconnector of lanthanum chromite doped with an alkaline earth metal or the like. The interconnector for a solid oxide fuel cell according to any one of the above.