JPH10231188A - Production of ceramic member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a coated film excellent in bonded state and high in airtightness in forming a coated film for covering at least a part of a laminate of a porous ceramic body and a dense ceramic body by a flame coating method. SOLUTION: The boundary 5 between a porous ceramic body 3 and a dense ceramic body 1 appears on the surface of a laminate 4 at a part 6. A ceramic member 9 provided with a coated film 13 covering at least a part of the porous ceramic body 3, the boundary part 6 and at least a part of the dense ceramic body 1 is produced. The surface of the porous ceramic body 3 adjoining the boundary 6 and the surface of the dense ceramic body 1 are processed by an abrasive grain polishing process to form processed faces 11 and 12. A coated film 7 is formed by a flame coating method so as to cover the processed faces 11 and 12 and the boundary 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic member, such as a solid oxide fuel cell or a steam electrolytic cell, which comprises a porous ceramic body and a dense ceramic body and needs to maintain airtightness. And a method for producing the same.

[0002]

2. Description of the Related Art Solid oxide fuel cells are roughly classified into a so-called flat type and a cylindrical type. In a plate-type solid oxide fuel cell, a so-called separator and a power generation layer are alternately stacked to form a power generation stack.
There are several forms of the flat solid electrolyte fuel cell. The present inventors have tried to join a self-supporting air electrode and a separator or an interconnector, and then sequentially form a solid electrolyte membrane and a fuel electrode membrane on the surface of the joined body.

As a method for forming a solid electrolyte membrane, a chemical vapor deposition method (CVD method) and an electrochemical vapor deposition method (EVD method) are generally used. The processing speed is too low, and the running cost increases. If a solid electrolyte film is formed by a plasma spraying method, the film forming rate can be increased, the handling of the apparatus and the like can be simplified, and the film can be formed relatively densely (Sunshine 1981, Vo1.2, No.1: Integrated Energy Engineering 13-
2, 1990). However, it is difficult to obtain an airtight solid electrolyte membrane by the plasma spraying method. On the other hand, in particular, in a solid electrolyte membrane of a solid oxide fuel cell, airtightness is required to prevent a decrease in output due to fuel leakage.

As a method for solving such a problem, Japanese Patent Application Laid-Open Nos. 4-115469 and 3-624 are known.
No. 59 discloses a method of forming a solid electrolyte film by plasma spraying and heat-treating the plasma sprayed film.

[0005] However, when a self-supporting air electrode and an interconnector are joined together and a solid electrolyte film is formed on the surface of the joined body by a thermal spraying method, adhesion between the interconnector and the sprayed film is low. Peeling of both occurred.

[0006] For this reason, the present inventor sandblasted the surface of the interconnector and formed a sprayed film thereon, but the sprayed film also peeled off. In addition, because the adhesion between the interconnector and the sprayed film is low, even after the sprayed film is heat-treated into an airtight solid electrolyte film, a high degree of airtightness is maintained between the solid electrolyte film and the interconnector. It was difficult.

In order to solve such a problem, the present inventor disclosed in Japanese Patent Application Laid-Open No. Hei 8-3714 that when forming a sprayed film on an interconnector, a porous film was formed on the interconnector. It has been disclosed that an open pore having a small opening and a widened interior is provided on the surface side of the porous membrane. This method is an extremely useful technique for improving the adhesion at the interface between the interconnector and the sprayed solid electrolyte membrane and preventing leakage of oxidizing gas.

[0008]

However, as the present inventors proceeded with further studies, a new problem requiring improvement has emerged. That is, in order to form a porous film on the interconnector and the air electrode, it is necessary to apply a predetermined paste so as to cover at least the interconnector and bake it at a high temperature. However, during the baking process, it has been found that the laminated body of the interconnector and the air electrode has a problem that the entire body is warped, the dimensions are out of order, and the production yield is reduced.

An object of the present invention is to form a coating covering at least a part of a laminate of a dense ceramic body such as an interconnector and a porous ceramic body such as an air electrode by a thermal spraying method. The purpose of the present invention is to make it possible to form a highly airtight film having a good bonding state.

[0010]

According to the present invention, a ceramic member includes a laminate of a porous ceramic body and a dense ceramic body, and a boundary between the porous ceramic body and the dense ceramic body is a laminate. When producing a ceramic member having a coating covering at least a part of the porous ceramic body, the boundary and at least a part of the dense ceramic body, the porous ceramic body being adjacent to the boundary The surface of the body and the surface of the dense ceramic body are processed by an abrasive polishing method to form each processed surface, and then the coating is formed on the processed surface of the porous ceramic body, the processed surface and the boundary of the dense ceramic body. It is characterized by being formed by a thermal spraying method so as to cover.

Further, the present invention provides a method of manufacturing a ceramic member, comprising: forming a processed surface by processing a surface of a porous ceramic body and a surface of a dense ceramic body adjacent to a boundary; The center line average surface roughness Ra of the processed surface of the body and the processed surface of the dense ceramic body is set to 1.0 μm or more and 10 μm or less, and then the coating is formed on the processed surface of the porous ceramic body, the processed surface of the dense ceramic body and It is characterized by being formed by a thermal spraying method so as to cover the boundary.

The inventor of the present invention processes each surface of each ceramic body adjacent to the boundary between the porous ceramic body and the dense ceramic body by an abrasive polishing method to form a processed surface. It has been discovered that when formed by a thermal spraying method so as to cover each processing surface and the boundary, the thermal sprayed film adheres to all the processing surfaces with extremely good adhesion, and high airtightness can be obtained.

In particular, in the step of further heat-treating the sprayed film to improve the airtightness, thermal stress is applied between the sprayed film and each processed surface of each ceramic body, and peeling is likely to occur. However, according to the present invention, peeling does not occur even after heat treatment between the processed surface of the porous ceramic body and the sprayed film, and between the dense ceramic body and the sprayed film, and extremely high airtightness is obtained. It was found that it was retained, and reached the present invention.

The reason why such remarkable effects are obtained is not clear. However, the present inventor provided the surface of the porous ceramic body and the surface of the dense ceramic body to various processing methods such as sandblasting, grinding stone polishing, and water-resistant paper processing at positions including these boundaries. Surprisingly, it was found that sufficient airtightness and adhesion could not be obtained by any of the processing methods.

Further, the present inventor evaluated various characteristics of the processed surface of the porous ceramic body and the processed surface of the dense ceramic body after performing various processes such as an abrasive polishing process, respectively. As a result, it was found that when Ra on each of the processed surfaces was in the range of 1 to 10 μm, the adhesion between the sprayed film and the heat-treated film was highest, and peeling or the like was hardly caused.

The abrasive polishing method used in the present invention will be described. At the time of abrasive grain polishing, silica sand or corundum (Al ₂ O ₃ ) And a suspension obtained by mixing abrasive grains with water. The flat plate is rotated about a vertical axis to continuously pour the abrasive grains and water. The fired body to be polished moves irregularly around on a flat plate for polishing. As a result, the abrasive grains roll around between the fired body and the flat plate that are relatively moving, and at this time, the protruding portion of the surface of the fired body to be polished is scraped off.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION As abrasive grains for use in the abrasive grain polishing method, abrasive grains having high hardness such as silicon carbide, boron carbide and alumina are preferable. Also, apply abrasive grains on the rotating table,
It is preferable to polish while adding water.

The present invention can be applied to various ceramic members requiring airtightness, but is particularly preferably applied to an electrochemical cell.

The electrochemical cell can be used as an oxygen pump or a high-temperature steam electrolysis cell. The high-temperature steam electrolysis cell can be used for an apparatus for producing hydrogen and for an apparatus for removing steam. In this case, the following reaction occurs at each electrode.

[0020]

Embedded image Cathode: H ₂ O + 2e ⁻ → H ₂ + O ^{2 −} Anode: O ^{2 −} → 2e ⁻ + 1 / 2O ₂

Further, the electrochemical cell can be used as a NOx decomposition cell. This decomposition cell can be used as a purification device for exhaust gas from automobiles and power generation devices. At present, NOx generated from a gasoline engine is handled by a three-way catalyst. However, when the number of fuel-efficient engines such as lean burn engines and diesel engines increases, the amount of oxygen in the exhaust gas of these engines is large, so that the three-way catalyst does not function.

Here, the electrochemical cell is referred to as a NOx decomposition cell.
When used, oxygen in exhaust gas passes through the solid electrolyte membrane
While removing NOx by electrolyzing NOx._TwoAnd O ^2-When
Decomposes and removes oxygen generated by this decomposition.
You. In addition to this process, the water vapor in the exhaust gas is
Cracked to form hydrogen and oxygen, which convert NOx into N_Two
Reduce to

The interconnector of the electrochemical cell is required to have conductivity and airtightness. That is, the interconnector needs to separate the oxidizing gas from the fuel gas, and needs to have high density. In the case of ceramics, the index of the relative density of a sintered body that is impermeable to gas is 9
4% or more, and it is necessary to sinter the interconnector densely to this extent.

On the other hand, in the case of the electrode, it is necessary to increase the porosity to some extent in order to allow gas to permeate. Specifically, the porosity is preferably 15 to 40%, and more preferably 25 to 3%.
More preferably, it is set to 5%. As a result, even if the same processing is performed on the electrode and the interconnector, the surface condition of the processed surface is generally completely different, which makes it difficult to adhere the sprayed film over both the interconnector and the electrode. It is thought that it became.

In the present invention, it is preferable to apply an abrasive grain polishing method to the laminate, form a coating on each of the processed surfaces by a thermal spraying method, and then heat-treat the coating to make the coating airtight. . Thus, the airtightness of the entire ceramic member can be maintained by the coating and the dense ceramic body.

The main raw material of the anode of the electrochemical cell is preferably a perovskite-type composite oxide containing lanthanum, more preferably lanthanum manganite or lanthanum cobaltite, and more preferably lanthanum manganite. Lanthanum manganite may be doped with strontium, calcium, chromium, cobalt, iron, nickel, aluminum and the like.

The main raw materials of the cathode of the electrochemical cell are nickel, nickel oxide, nickel-zirconia mixed powder, nickel oxide-zirconia mixed powder, palladium, platinum,
Palladium-zirconia mixed powder, platinum-zirconia mixed powder, nickel-ceria, nickel oxide-ceria, palladium-ceria, platinum-ceria mixed powder and the like are preferable.

As the solid electrolyte, yttria-stabilized zirconia, yttria partially stabilized zirconia, cerium oxide-based ceramics, and the like are particularly preferable.

The main raw material of the interconnector is preferably a perovskite-type composite oxide containing lanthanum, and more preferably lanthanum chromite. Lanthanum chromite can also be doped with the above metals.

FIG. 1A is a plan view showing an interconnector 1 according to an embodiment of the present invention, and FIG.
FIG. 2 is a front view showing a laminate 4 of the interconnector 1 and the air electrode 3. The interconnector 1 is, for example, rectangular in a plan view, provided with quadrangular prism-shaped partitions 1a and 1b, between the partitions 1a and 1b, and between the partitions 1b and 1b.
b, groove-shaped oxidizing gas flow paths 2 are provided.

The lower surface 3c of the air electrode 3 and the upper surfaces 1e, 1f of the partition walls 1a, 1b are joined, and the side surface 3b of the air electrode 3 and the side surface 1c of the interconnector 1 are continuous without any step. An end portion 2a of the square-column-shaped oxidizing gas flow path 2,
2b is open to the end face 1d side of the separator 1.
Reference numeral 5 denotes a boundary between the interconnector 1 and the air electrode 3, and reference numeral 6 denotes a portion where the boundary 5 is exposed on the surface.

Next, the side surface 1c of the interconnector 1
And the side surface 3b of the air electrode 3 is processed by an abrasive polishing method. As a result, as shown in FIG. 2A, the processing surface 12 is formed on the interconnector 1, and the processing surface 11 is also formed on the air electrode 3. The processing surfaces 11 and 12 are adjacent to each other across the boundary 6.

Next, the coating 7 is formed by a thermal spraying method. At this time, the horizontal portion 7a of the coating 7 is
a, and the vertical portion 7b of the coating 7
Was coated. Next, the laminated body was subjected to a heat treatment to form the coating 7 into an airtight solid electrolyte membrane 13 as shown in FIG. Next, the fuel electrode membrane 10 is formed on the solid electrolyte membrane 13 to obtain the electrochemical cell 9.

[0034]

EXAMPLES Hereinafter, more specific experimental results will be described. (Example) A laminate 4 was manufactured according to the method described with reference to FIGS. Interconnector 1
Is made of lanthanum chromite having a porosity of 0.1%, and the air electrode 3 is made of lanthanum manganite having a porosity of 30%. The surface 3b of the air electrode 3 and the surface 1c of the interconnector 1 are processed by an abrasive polishing method.
Nos. 1 and 12 were formed. As the abrasive grains, # 180 abrasive grains made of silicon carbide were used.

The center line average surface roughness Ra of the processed surface 11 of the air electrode 3 was 3.3 μm, Rmax was 17.6 μm, and Rz was 12.2 μm. Ra of the processing surface 12 of the interconnector 1 is 2.5 μm, and Rmax
Was 14.8 μm and Rz was 8.9 μm.

An 8 mol% yttria-stabilized zirconia was plasma sprayed on the upper surface 3a and the processing surfaces 11 and 12 to form a coating 7 having a thickness of 100 μm. The coating film 7 was heat-treated in air at 1400 ° C. for 3 hours to form an airtight solid electrolyte membrane 13, thereby obtaining a sample 9. This sample 9 was embedded in the resin. Next, the sample 9 was cut so that the bonding interface 8A between the air electrode 3 and the solid electrolyte membrane 13 and the bonding interface 8B between the interconnector 1 and the solid electrolyte membrane 13 were exposed, and the cut surface was polished. The polished surface was photographed by a scanning electron micrograph.

In this case, the air electrode 3 or the interconnector 1 and the solid electrolyte membrane 13 are located near the joining interfaces 8A and 8B.
Can be clearly distinguished into a part where the boundary line is visible and a part where such a boundary line is not visible. The total length of the joint interface was measured from a scanning micrograph, and the length of the portion where the boundary line was not visible was measured, and this ratio was calculated. The ratio of the length of the part where the boundary line is not visible is the "ratio without peeling"
And

As a result, the ratio of no separation at the junction interface 8A between the air electrode 3 and the film 13 is 98%, and the ratio of no separation at the junction interface 8B between the interconnector 1 and the film 13 is 95%. there were.

Comparative Example 1 Sample 9 was manufactured in the same manner as in the example. However, the surface 3b of the air electrode 3 and the surface 1c of the interconnector 1 were sandblasted to form the processed surfaces 11 and 12.

Ra of the processing surface 11 of the air electrode 3 is 2.0 μm
, Rmax is 16.9 μm, and Rz is 9.2.
μm. R of processing surface 12 of interconnector 1
a was 0.02 μm, Rmax was 0.11 μm, and Rz was 0.02 μm. Thus, it was found that the surface state between the air electrode 3 and the interconnector 1 was significantly different.

When the above-mentioned test was performed on the obtained sample 9, the ratio of no peeling at the bonding interface 8A between the air electrode 3 and the film 13 was 84%, and the bonding between the interconnector 1 and the film 13 was performed. The ratio of no separation at the interface 8B was 11%.

Comparative Example 2 Sample 9 was manufactured in the same manner as in the example. However, the surface 3b of the air electrode 3 and the surface 1c of the interconnector 1 were polished with a grindstone.

Ra of the processing surface 11 of the air electrode 3 is 0.3 μm
And Rmax is 2.8 μm and Rz is 1.9 μm.
m. 12 R of processing surface of interconnector 1
a is 0.2 μm, Rmax is 2.3 μm,
Rz was 1.7 μm. Thus, it has been found that both the air electrode 3 and the interconnector 1 have very smooth surface conditions.

However, when the above-described test was performed on the obtained sample 9, the bonding interface 8 between the air electrode 3 and the film 13 was determined.
The ratio of no peeling at A was 40%, and the ratio of no peeling at the bonding interface 8B between the interconnector 1 and the film 13 was 22%.

Comparative Example 3 A sample 9 was manufactured in the same manner as in the example. However, the surface 3b of the air electrode 3 and the surface 1c of the interconnector 1 were polished with water-resistant paper.

Ra of the processing surface 11 of the air electrode 3 is 1.2 μm
, Rmax is 10.2 μm, and Rz is 6.0.
μm. The Ra of the processed surface 12 of the interconnector 1 was 0.7 μm, the Rmax was 5.8 μm, and the Rz was 3.8 μm. Thus, the cathode 3
It was found that both the interconnector 1 and the interconnector 1 had smooth surface conditions.

However, when the above-mentioned test was performed on the obtained sample 9, the bonding interface 8 between the air electrode 3 and the film 13 was determined.
The ratio of no peeling at A was 72%, and the ratio of no peeling at the bonding interface 8B between the interconnector 1 and the film 13 was 30%.

[0048]

As described above, according to the present invention, when a coating for covering at least a part of a laminate of a porous ceramic body and a dense ceramic body is formed by a thermal spraying method, the bonding state is reduced. And a highly airtight film having good airtightness can be formed.

[Brief description of the drawings]

FIG. 1A is a plan view showing a self-supporting interconnector 1 used in an embodiment of the present invention,
(B) is a front view showing the laminated body 4 of the interconnector 1 and the air electrode 3.

FIG. 2A is a front view showing a state in which processed surfaces 11 and 12 are formed on a laminated body 4 by an abrasive polishing method,
(B) is a front view showing the electrochemical cell 9.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Interconnector 2 Oxidizing gas flow path 3
Air electrode 3b Side surface of air electrode 3 4 Laminated body of air electrode 3 and interconnector 1 5 Boundary between interconnector 1 and air electrode 3 6
Exposed portion of boundary 5 on surface of laminate 4 7 Coating formed by thermal spraying method 8A Bonding interface between air electrode 3 and solid electrolyte film 13 8B Bonding interface between interconnector 1 and solid electrolyte film 13 9 Electrochemical cell ( Sample) 10 Fuel electrode membrane 11 Processed surface of air electrode 3
12 Processed surface of interconnector 1

Claims (6)

[Claims] 1. A ceramic member comprising a laminate of a porous ceramic body and a dense ceramic body, wherein a boundary between the porous ceramic body and the dense ceramic body appears on the surface of the laminate. And producing a ceramic member having a coating covering at least a part of the porous ceramic body, the boundary and at least a part of the dense ceramic body. The surface of the ceramic body and the surface of the dense ceramic body are processed by an abrasive polishing method to form each processed surface, and then the coating is formed on the processed surface of the porous ceramic body, A method for manufacturing a ceramic member, wherein the ceramic member is formed by a thermal spraying method so as to cover a processing surface and the boundary. . 2. A process according to claim 1, wherein a center line average surface roughness Ra of said processed surface of said porous ceramic body and said processed surface of said dense ceramic body is 1.0 μm or more and 10 μm or less. 2. The method for producing a ceramic member according to 1. 3. The method for manufacturing a ceramic member according to claim 1, wherein after forming the coating, the coating is heat-treated to make the coating airtight. 4. The method according to claim 1, wherein the porous ceramic body is one electrode of an electrochemical cell, the dense ceramic body is an interconnector of the electrochemical cell, and the coating is a sprayed film made of a solid electrolyte. The method for producing a ceramic member according to any one of claims 1 to 3, wherein the method is characterized in that: 5. The laminate according to claim 1, wherein said one electrode is an anode, and said laminate is a laminate comprising said anode and said interconnector having a self-supporting ability, wherein said laminate comprises said anode and said interconnector. 5. The method for producing a ceramic member according to claim 4, wherein an oxidizing gas flow path facing the surface is formed. 6. A ceramic member comprising a laminate of a porous ceramic body and a dense ceramic body, wherein a boundary between the porous ceramic body and the dense ceramic body appears on the surface of the laminate. And producing a ceramic member having a coating covering at least a part of the porous ceramic body, the boundary and at least a part of the dense ceramic body. Each processed surface is formed by processing the surface of the ceramic body and the surface of the dense ceramic body, and the center line average surface roughness of the processed surface of the porous ceramic body and the processed surface of the dense ceramic body Ra is 1.0 μm or more and 10 μm
m, and then forming the coating by a thermal spraying method so as to cover the processed surface of the porous ceramic body, the processed surface of the dense ceramic body, and the boundary.