JPH0718451A - Method and device for forming oxide film on porous substrate - Google Patents

Abstract

PURPOSE:To efficiently form an oxide film on a porous substrate by permeating the oxygen generated from the thermally decomposed oxidizing agent oxide through the substrate from its one side to the other and allowing the oxygen to react with a raw gas on the other side. CONSTITUTION:An NiO powder is filled in a closed vessel 3 made of alumina, the vessel is set in the reaction tube 2 of a CVD film forming device, the vessel 3 is evacuated and heated, and a hydrogen-contg. gaseous Ar is supplied. Consequently, the NiO powder is decomposed to generate oxygen, and the generated oxygen diffuses through the pore of a porous anode substrate 4 and then diffuses into the reaction tube 2 from the vessel 4 surface. Heated zirconium tetrachloride and yttrium trichloride are entrained onto the substrate 4 surface by gaseous Ar and allowed to react with the diffused oxygen to form an yttria- stabilized zirconium film 5 on the substrate 4. Consequently, the oxide film forming equipment is simplified, production efficiency is improved, and the production cost is reduced.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method and apparatus for forming an oxide film on a porous substrate.

[0002]

2. Description of the Related Art Recently, a fuel cell that directly converts chemical energy originally possessed by fuel into electric energy by using oxygen and hydrogen as an oxidant and a fuel, respectively, is a resource saving,
It is drawing attention from the perspective of environmental protection. In particular, a flat plate solid electrolyte fuel cell using zirconia doped with yttria or the like (referred to as YSZ) as an electrolyte layer and using lanthanum chromite oxide or the like as a separator is low cost, compact, has a high operating temperature, and generates electricity. R & D is progressing because of its high efficiency and high overall efficiency due to the use of high-temperature waste heat, which is advantageous for cogeneration.

The cell performance of this fuel cell is governed by the internal resistance of the cell, especially the ohmic resistance of the constituent materials therein. This ohmic resistance loss can be reduced by thinning the YSZ solid electrolyte having the highest resistivity. Also, YS
By forming a battery of the electrolyte supporting membrane system, the Z solid electrolyte can be made significantly thinner than the electrolyte self-supporting system. Therefore, in order to construct a supporting membrane type solid electrolyte fuel cell with good performance, a fuel electrode plate which is a Ni-YSZ cermet is used as a porous substrate, or an air electrode plate made of LaMnO 2 is used as a porous substrate and It is necessary to deposit a YSZ electrolyte membrane which is a very thin (typically 1 to 200 microns) oxide coating.

As a method for forming an oxide film on a porous substrate, a so-called ceramics method such as a slurry coating method, a dip coating method or a slip casting method, and a CVD (Ch
emical Vaper Deposition) -EVD (Electrochemica
l Vaper Deposition) method has been used. CVD-E
The VD method is disclosed in, for example, JP-A-61-153280.

In a conventional method and apparatus for forming an oxide film on a porous substrate, a source gas made of a metal halide is supplied to one side of the porous substrate, and an oxidizing gas is fed from the other side through a cylinder and a pipe. It is supplied at a pressure higher than that of the gas, and the differential pressure is adjusted so that it spouts to the raw material gas side. The oxidant gas (oxygen or water vapor) that has passed through the porous body and reached the raw material gas side reacts directly with the metal halide that is the raw material, and C
The oxide is formed while blocking the pores of the porous substrate by the VD reaction. When the pores of the porous substrate are closed by the oxide formed by the CVD reaction, the oxide divides the atmosphere into a high oxygen partial pressure atmosphere of water vapor or oxygen and a low oxygen partial pressure atmosphere of metal halide. Become. At this time, oxygen is reduced on the side of the oxidizing gas to form oxide ions, which diffuse to the side of the halide having a low oxygen partial pressure. The film grows by an EVD reaction in which the oxide ions diffused on the halide side react with the halide to form an oxide.

[0006]

However, as described above, in forming the oxide film on the porous substrate by the conventional CVD method, oxidizing gas is supplied from the cylinder to the back surface of the porous substrate through a pipe. Was there. Therefore, there is a limit to the number of porous substrates that can supply the oxidizing gas per pipe. Further, a cylinder or a pipe for supplying an oxidizing gas has to be installed and a means for controlling the differential pressure of the reaction gas on both sides of the porous substrate has to be provided.

The present invention has been made in view of the above points, and is characterized in that the manufacturing equipment can be simplified, the manufacturing efficiency can be improved, and the manufacturing cost can be reduced, thereby forming an oxide film on a porous substrate. It is an object of the present invention to provide a method and apparatus for producing

[0008]

In order to solve the above problems, the present invention provides a method for forming an oxide film on a porous substrate by chemical vapor deposition, wherein the porous substrate is heated at a temperature rise or film formation temperature. Oxygen generated by the decomposition of an oxide having a decomposition oxygen pressure that oxidizes or decomposes and does not impair its properties is permeated and blown out from one side of the porous substrate as an oxidizing gas, and is present on the opposite side. It is characterized by reacting with a raw material gas. Hereinafter, the oxide that generates oxygen that oxidizes the metal halide raw material will be referred to as an oxidant oxide.

Further, according to the present invention, in an apparatus for forming an oxide film on a porous substrate by chemical vapor deposition, a part of the wall is formed of the porous substrate, and the porous substrate is heated at a temperature rise or film formation temperature. A closed container containing a powder of an oxidizer oxide having a decomposition oxygen pressure that does not impair its properties by oxidizing or decomposing, a means for supplying a raw material gas to the outer surface side of the porous substrate, Means for heating the closed container to the film formation temperature of the porous substrate.

[0010]

[Function] Oxygen generated by the decomposition of oxides such as NiO placed in a closed container becomes a reactive oxidizing gas, permeates through the small holes of the porous substrate, and reacts with the metal halide gas on the other side of the porous substrate. To form a metal oxide film on the porous substrate, the metal oxide film seals the small pores by the CVD method as it grows, and the film continues to grow by the EVD method to form a thin film on the porous substrate. A YSZ film of oxide layer is deposited.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

[0012] Briefly, the present invention uses an oxide powder having a decomposing oxygen pressure that does not impair the properties of a porous substrate by oxidizing or decomposing the porous substrate at a film-forming temperature. The porous substrate is placed in a closed container and the oxygen generated by decomposition of the oxide by heating the porous substrate to a film-forming temperature is used as an oxidizing gas from the inside of the closed container to form a large number of small holes in the porous substrate. And the oxidizing gas is reacted with the source gas supplied to the outer surface of the porous substrate to form an oxide film on the porous substrate by the CVD-EVD method.

FIG. 1 shows a schematic structure of an apparatus for forming an oxide film on a porous substrate of the present invention, FIG. 2 shows temperature characteristics of equilibrium oxygen partial pressure of an oxide, and FIG. 3 is a method of the present invention. 2 is a cross-sectional electron micrograph of a YSZ film formed on a porous substrate by using the apparatus.

The solid electrolyte membrane producing apparatus of the present invention shown in FIG. 1 has a reaction tube 2, an electric furnace 1, a gas supply tube 9, and a vacuum pump 10.
Etc. The reaction tube 2 is made of quartz glass and is installed horizontally. The electric furnace 1 consists of three units, and their temperatures are controlled independently. These electric furnaces 1 are composed of an electric furnace for sublimating zirconium tetrachloride as a raw material, an electric furnace for sublimating yttrium trichloride, and an electric furnace for heating a substrate to grow a film. In the reaction tube, an alumina boat 8 for filling each metal chloride, a stand 9 on which the boat 8 is placed, a mixing plate 7 for uniformly mixing the sublimed metal chloride, a substrate 4 and an oxidant oxide 6 are placed. A shelf 11 on which a large number of alumina closed containers 3 are placed is appropriately arranged. During the film growth, the reaction tube 2 is depressurized by the vacuum pump 10 connected thereto in order to accelerate the vapor phase diffusion rate of the raw material. In addition, a cylinder 13 for introducing an argon gas for transporting the raw material and a mass flow controller 12 for adjusting the flow rate are connected to the gas supply pipe 9.

Example 1 Using the apparatus shown in FIG. 1, the anode (Ni-YSZ cermet) was used as the substrate 4, and chemical vapor deposition of the zirconia film 5 was performed. As can be seen from the temperature characteristic diagram of the equilibrium oxygen partial pressure in FIG. 2, the oxidizer oxide 6 placed in the alumina closed container 3 is an equilibrium oxygen in which metallic nickel in the anode is not oxidized at the time of temperature rise or film formation temperature (1000 ° C.). NiO, Fe which becomes partial pressure
_It is necessary to select from ₃ O ₄ . Here, NiO was selected as the oxidant oxide. NiO with an average particle size of 7 microns
Container 3 was filled with 30 grams of powder. On the other hand, the substrate 4 on which the film is formed uses a porous anode having a diameter of 20 mm, a thickness of 2 mm, a porosity of 30%, and an average pore diameter of 0.6 μm.
It was fixed to the position shown in.

A plurality of alumina containers 3 were installed inside the CVD film forming apparatus reaction tube 2, and the pressure was reduced by the vacuum pump 10 to raise the temperature. The alumina container 3 has a closed structure,
Ventilation of its interior and exterior is taken from the pores of the porous anode. In the vapor phase atmosphere at the time of temperature rise, 4% H ₂ + Ar gas was supplied so that the metallic nickel was not oxidized, and the pressure inside the reaction tube 2 was set to about 2 Torr. 4% H ₂ + N
_Since the oxygen partial pressure in the _two- gas atmosphere is lower than the equilibrium oxygen partial pressure of metallic nickel and nickel oxide, nickel oxide is unilaterally decomposed to generate oxygen. The generated oxygen diffuses in the pores of the porous anode substrate 4 and diffuses from the surface of the substrate 4 into the reaction tube 2.

When the temperature is raised to 1030 ° C. at 4 ° C./min and reaches a predetermined temperature, zirconium tetrachloride heated to 230 ° C. and yttrium trichloride heated to 510 ° C. are applied to the substrate with a predetermined flow rate of an argon carrier gas. 4 surface. At this time, the oxygen gas diffused from the inside of the substrate 4 reacts with the zirconium and yttrium chloride vapors which are the raw materials, and immediately the yttria-stabilized zirconia (YSZ) film 5 is formed on the surface of the porous anode substrate 4. The holes of the substrate 4 were gradually closed. This is CV
It is a D reaction.

When the CVD reaction ends, the raw material metal chloride and oxygen do not directly react with each other. As a result, there is a difference in oxygen partial pressure through the YSZ that closes the pores, and the oxidant oxide side is 10 ¹⁰ atm at 1030 ° C. and the metal chloride side of the raw material is about 10 ¹⁸ atm. Oxygen generated by the oxidant oxide is reduced on the YSZ plane that closes the pores, diffuses in the YSZ film as oxide ions, and advances to the EVD reaction process in which it reacts with the source metal chloride to grow the film 5. Thus 5
FIG. 3 shows a cross-sectional electron micrograph of the grain structure of the YSZ film that has been reacted for a time. A dense and uniform YSZ film having a thickness of about 10 μm is adhered on the porous anode so as to fill the surface pores of the anode. The average film formation rate per hour is about 1.
It was 5 microns.

Example 2 When the cathode material (LaMnO ₃ ) is used as the substrate 4, it is necessary to select an oxide having an equilibrium oxygen partial pressure that does not decompose the cathode material. From the temperature characteristic diagram of equilibrium oxygen partial pressure in FIG. 2, it can be seen that NiO and Mn ₂ O ₃ are suitable as oxides for oxidants. Using NiO as an oxidant, 20 g was filled in an alumina container. A porous cathode having a diameter of 20 mm and a thickness of 2 mm was fixed as a substrate 4 at a predetermined position and placed in the reaction tube 2.

The temperature was raised to 1030 ° C. in an air atmosphere at a rate of 4 ° C./min. After reaching the film formation temperature, the reaction tube 2
The atmosphere inside was replaced with 4% H ₂ + Ar, zirconium tetrachloride and yttrium trichloride that had been heated to a predetermined temperature were transported by argon gas, and the porous cathode was diffused in the substrate 4. NiO was decomposed to generate a CVD reaction with oxygen generated, the holes of the substrate 4 were gradually closed, and the YSZ film 5 was grown by the subsequent EVD reaction.

[0021]

As described above, according to the present invention, an oxidant oxide having a decomposed oxygen pressure which does not impair the properties of the porous substrate by oxidizing or decomposing at the time of temperature rise or film formation temperature. Oxygen generated by decomposition is used as an oxidizing gas to permeate and blow out from the one side of the porous substrate, and to react with the raw material gas on the opposite side, so an oxide film is formed on the porous substrate. It is possible to simplify the manufacturing equipment for improving the manufacturing efficiency and to reduce the manufacturing cost.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an apparatus for forming an oxide film on a porous substrate of the present invention.

FIG. 2 is a diagram showing temperature characteristics of equilibrium oxygen partial pressure of oxide.

FIG. 3 is a sectional electron micrograph of the particle structure of a YSZ film formed on a porous substrate by the method and apparatus of the present invention.

[Explanation of symbols]

 1 Electric Furnace 2 Reaction Tube 3 Alumina Sealed Container 4 Porous Substrate 5 Zirconia Film 6 Oxidant Oxide 7 Mixing Plate 8 Alumina Boat 9 Gas Supply Pipe 10 Vacuum Pump 11 Shelf 12 Mass Flow Controller 13 Argon Cylinder

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[Procedure amendment]

[Submission date] August 9, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0005

[Correction method] Change

[Correction content]

In a conventional method and apparatus for forming an oxide film on a porous substrate, a source gas made of a metal halide is supplied to one side of the porous substrate, and an oxidizing gas is fed from the other side through a cylinder and a pipe. It is supplied at a pressure higher than that of the gas, and the differential pressure is adjusted so that it spouts to the raw material gas side. The oxidant gas (oxygen or water vapor) that has passed through the porous body and reached the raw material gas side reacts directly with the metal halide that is the raw material, and C
The oxide is formed while blocking the pores of the porous substrate by the VD reaction. When the pores of the porous substrate are closed by the oxide formed by the CVD reaction, the oxide divides the atmosphere into a high oxygen partial pressure atmosphere due to water vapor or oxygen and a low oxygen partial pressure atmosphere due to the metal halide. Become. At this time, oxygen is reduced on the side of the oxidizing gas to form oxide ions, which diffuse to the side of the halide having a low oxygen partial pressure. The film grows by an EVD reaction in which the oxide ions diffused on the halide side react with the halide to form an oxide.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

The solid electrolyte membrane producing apparatus of the present invention shown in FIG. 1 has a reaction tube 2, an electric furnace 1, a gas supply tube 9, and a vacuum pump 10.
Etc. The reaction tube 2 is made of quartz glass and is installed horizontally. The electric furnace 1 consists of three units, and their temperatures are controlled independently. These electric furnaces 1 are composed of an electric furnace for sublimating zirconium tetrachloride as a raw material, an electric furnace for sublimating yttrium trichloride, and an electric furnace for heating a substrate to grow a film. In the reaction tube, an alumina boat 8 for filling each metal chloride, a stand 9 on which the boat 8 is placed, a mixing plate 7 for uniformly mixing the sublimed metal chloride, a substrate 4 and an oxidant oxide 6 are placed. A shelf 11 on which a large number of alumina closed containers 3 are placed is appropriately arranged. During the film growth, the reaction tube 2 is depressurized by the vacuum pump 10 connected thereto in order to accelerate the evaporation rate of the raw material. In addition, a cylinder 13 for introducing an argon gas for transporting the raw material and a mass flow controller 12 for adjusting the flow rate are connected to the gas supply pipe 9.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

When the CVD reaction ends, the raw material metal chloride and oxygen do not directly react with each other. As a result, there is a difference in oxygen partial pressure through the YSZ that has closed the pores, and the oxidant oxide side is 10 ⁻¹⁰ atm at 1030 ° C., and the metal chloride side of the raw material is about 10 ⁻¹⁸ atm. Oxygen generated by the oxidant oxide is reduced on the YSZ surface that closes the pores,
The film 5 progresses to the EVD reaction process in which it diffuses as oxide ions in the film and reacts with the material metal chloride, and the film 5 grows. A cross-sectional electron micrograph of the grain structure of the YSZ film thus reacted for 5 hours is shown in FIG. Thickness of about 10 on porous anode
A dense and uniform YSZ film of micron is adhered so as to fill the surface pores of the anode. The average film formation rate for one hour was about 1.5 microns.

Claims (2)

[Claims] 1. A method of forming an oxide film on a porous substrate by chemical vapor deposition, wherein decomposed oxygen which does not impair the properties of the porous substrate by oxidizing or decomposing at the time of temperature rise or film formation temperature. Oxygen generated by decomposition of an oxidant oxide having a pressure is used as an oxidizing gas to permeate and blow out the porous substrate from one side thereof, and the porous substrate is characterized by reacting with a raw material gas on the opposite side. A method of forming an oxide film on a substrate. 2. An apparatus for forming an oxide film on a porous substrate by chemical vapor deposition, wherein a part of the wall is formed of the porous substrate and the porous substrate is oxidized or heated at a temperature rise or film formation temperature. A closed container containing a powder of an oxidant oxide having a decomposition oxygen pressure that does not degrade the properties of the porous substrate, a means for supplying a source gas to the outer surface side of the porous substrate, and the closed container. An apparatus for forming an oxide film on a porous substrate, comprising: a means for heating the porous substrate to a film forming temperature.