JPH05287539A - Coating method for conductive oxide and metal-ceramic composite separator of solid electrolyte type fuel battery produced by this method - Google Patents

Abstract

PURPOSE:To rapidly obtain a coating film which is dense and has an excellent electrical conductivity by acting ultrasonic waves on a raw material soln. prepd. by dissolving metal soap into a solvent to generate aerosol and spraying this aerosol to a heated substrate. CONSTITUTION:The raw material soln. is prepd. by dissolving the metal soap of the metal elements constituting a conductive oxide, such as lanthanum cobaltite (LaCoO3), in the solvent such as acetyl acetone. The raw material soln. is put into an aerosol generator under atm. pressure and the ultrasonic waves are acted on the raw material soln. to generate the aerosol. Air is fed as a carrier gas into the aerosol generator. The aerosol is entrained in the air and is sent into a reaction tube. The aerosol is thermally cracked in instant of collision against the substrate when the aerosol is sprayed to the high-temp. substrate heated by IR rays. The film formation is thus executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating a conductive oxide such as lanthanum cobaltite or lanthanum oxide by an ultrasonic spray pyrolysis method and a separator for a solid oxide fuel cell manufactured by this method. is there.

[0002]

2. Description of the Related Art Recently, a fuel cell, which uses oxygen and hydrogen as an oxidant and a fuel, directly converts the chemical energy originally possessed by the fuel into electric energy, has been attracting attention from the viewpoint of resource saving and environmental protection. .. In particular, a solid oxide fuel cell in which an electrolyte membrane is formed on an electrode plate has a high operating temperature of 800 to 1000 ° C, and therefore, in principle, it generates electricity as compared with a phosphoric acid type or molten carbonate type fuel cell. Since the efficiency is high and the exhaust heat at high temperature is obtained, the total efficiency can be further increased by utilizing this exhaust heat, so that research and development is progressing.

A solid oxide fuel cell is constructed as a multi-layered laminated cell by alternately laminating flat plate-shaped cells each having a fuel electrode and an air electrode sandwiching a solid electrolyte layer and separators. .. The separator has the function of separating the fuel gas and the oxidant gas used in the fuel electrode and air electrode of the unit cells to prevent their mixing, and the function of electrically connecting the unit cells in series. is there.

[0004]

However, since the solid oxide fuel cell operates at a high temperature, there are considerable restrictions on usable materials, and in particular, it is chemically stable in a high temperature oxidizing atmosphere or a reducing atmosphere. It is hard to say that a practical level material has been found for a separator material that has a dense structure and is required to have high conductivity and great mechanical strength.

Conventionally, La (M) CrO ₃ (M: which is a perovskite type conductive oxide has been used as a separator material.
Although Sr, Ca, Mg) is used, it is difficult to sinter densely and to increase the strength, and the film forming technique is difficult. Also, in the presence of H ₂ O, the contact resistance with the fuel electrode is large,
Moreover, since it is an oxide, it has drawbacks such as brittleness.

Conductive oxides such as lanthanum cobaltite (LaCoO ₃ ) are promising as heat resistant coatings for alloy separators of solid oxide fuel cells, but at low cost, low temperature, densely and uniformly. There is no coating technology.

The coating method using CVD, vapor deposition, sputtering, ion plating, etc., has the drawback of being expensive because a vacuum device is used. Further, it is difficult to obtain a dense coating by the thermal spraying method, and it is difficult to perform coating at a low temperature by the slurry coating method.

The present invention has been made in view of the above points, and it is dense and excellent in electrical conductivity, has a large mechanical strength, and is chemically stable by working at a low temperature by using an ultrasonic spray pyrolysis method. An object of the present invention is to provide a method for rapidly producing a low-cost coating film of lanthanum cobaltite or lanthanum oxide and a metal-ceramic composite separator for a solid oxide fuel cell produced by this method.

[0009]

In order to solve the above-mentioned problems, the present invention is to dissolve a metallic soap of La and a metallic soap of Co and a solvent such as acetylacetone to prepare a raw material solution, and apply ultrasonic waves to the raw material solution. An aerosol is generated as a result, and the aerosol is sprayed on a substrate heated by infrared rays to be thermally decomposed to form a film.

[0010]

[Function] By applying ultrasonic waves to the raw material solution and atomizing it, a good quality aerosol is generated, and only the refractory metal of the substrate is heated to a high temperature by infrared rays, and the aerosol is thermally decomposed at the moment when it collides with this substrate. Form a film.

[0011]

EXAMPLE A lanthanum cobaltite was coated on a refractory metal by the following process according to the coating method of the present invention. (1) A raw material solution is prepared by using La octylate and Co octylate as raw materials and acetylacetone and toluene as solvents. (2) Put the above raw material solution into the aerosol generator under atmospheric pressure. (3) When ultrasonic waves of 1.7 MHz are applied to the raw material solution, aerosol is generated at 1.0 × 10 ³ g / s. Send in. (5) The aerosol rides on the air and is fed into the quartz glass reaction tube. (6) Only the heat-resistant metal substrate mounted in the reaction tube is heated by infrared rays to about 770 ° C. (7) When the aerosol is sprayed on a high-temperature substrate, it is thermally decomposed at the moment of collision to form a film. Deposition rate is 5
μm / hour.

As a result, a coating film of lanthanum cobalt as shown in FIGS. 1 and 2 was obtained.

FIGS. 1 and 2 are photomicrographs showing the structure of a dense thin film particle obtained by forming a lanthanum cobaltite film on a substrate using the coating method of the present invention.

According to these photographs, the particles are dense,
It turns out to be dense with no pores.

[0015]

As described above, in the method for coating a conductive oxide by the ultrasonic spray pyrolysis method of the present invention, a solution containing metal soap is atomized using ultrasonic waves to generate an aerosol. Since the infrared rays are used to raise the temperature of only the substrate inside the transparent quartz tube to a high temperature so that the aerosol can be rapidly pyrolyzed, the following excellent effects can be obtained. (1) All film forming operations are performed under atmospheric pressure.
The temperature of only the substrate rises to about 770 ° C., but the other parts are configured to operate at room temperature, so the apparatus is simple, inexpensive, easy to work with, and the film formation rate is fast. (2) With this apparatus, dense and homogeneous lanthanum cobaltite or the like can be rapidly coated.

[Brief description of drawings]

FIG. 1 is a micrograph showing a plane structure of lanthanum cobaltite obtained by an ultrasonic spray pyrolysis method of the present invention.

FIG. 2 is a micrograph showing a cross-sectional structure of lanthanum cobaltite obtained by the ultrasonic spray pyrolysis method of the present invention.

Claims (5)

[Claims] 1. A raw material solution is prepared by dissolving metal soap of a metal element constituting a conductive oxide in a solvent such as acetylacetone, and ultrasonic waves are applied to the raw material solution to generate an aerosol, which is heated by infrared rays. A method for coating a conductive oxide by ultrasonic spray pyrolysis, which is characterized in that a film is formed by spraying and thermally decomposing on a substrate. 2. The coating method according to claim 1, wherein the conductive oxide is lanthanum cobaltite (LaCoO ₃ ). 3. The conductive oxide is lanthanum oxide (La ₂ O).
₃ ) The coating method according to claim 1, which is 4. The coating method according to claim 1, wherein the metallic soap is a metal octylate. 5. A metal-ceramic composite separator for a solid oxide fuel cell manufactured by the method of coating a conductive oxide by the ultrasonic spray pyrolysis method according to claim 1.