JP5832405B2 - Method for forming protective film, method for manufacturing cell connecting member, and method for manufacturing cell for solid oxide fuel cell - Google Patents

Description

The present invention may be referred to as an alloy or oxide (hereinafter referred to as “alloy etc.”) containing Cr (chromium) used in a cell for a solid oxide fuel cell (hereinafter referred to as “SOFC” where appropriate). A protective film forming method for forming a protective film on the surface of the substrate comprising:
The present invention relates to a cell connection member in which a metal oxide film is formed as a protective film on the surface of a base material made of an alloy or oxide containing Cr, and an SOFC in which an air electrode is joined to the cell connection member.

Such a SOFC cell has a single cell in which an air electrode is joined to one surface side of an electrolyte membrane and a fuel electrode is joined to the other surface side of the electrolyte membrane, and electrons are transferred to the air electrode or the fuel electrode. The structure is sandwiched between a pair of electronically conductive base materials that perform the above.
Such a SOFC cell operates at an operating temperature of, for example, about 700 to 900 ° C., and the oxide ions move from the air electrode side to the fuel electrode side through the electrolyte membrane. An electromotive force is generated in the meantime, and the electromotive force can be taken out and used. The cell connecting member corresponds to an interconnector or a member that electrically connects cells via the interconnector.

  The cell connection member is a member that serves as a partition wall between fuel and air. With the progress of development in recent years, the operating temperature of SOFC is decreasing. The conventional operating temperature is about 1000 ° C, and metal oxides typified by lanthanum chromite have been used from the viewpoint of heat resistance, but recently the operating temperature has dropped to 700 ° C to 800 ° C, and alloys are used. It has become possible. The use of alloys can be expected to reduce costs and improve robustness.

As the alloy, ferritic stainless steel is often used because of its consistency with the thermal expansion coefficient of the metal oxide to be joined, but an Fe-Cr-Ni alloy which is an austenitic stainless steel superior in heat resistance. Alternatively, a Ni _- Cr alloy that is a nickel-based alloy may be used. In addition, instead of an alloy, a metal oxide typified by (La, Ca) CrO ₃ (calcium dopeplank chromite) may be used.

These alloys and the like almost always contain Cr, and an oxide film of Cr ₂ O ₃ or MnCr ₂ O ₄ is formed on the surface in a high-temperature air atmosphere that is an operating environment. This oxide film is known to increase in thickness over time, evaporate as a hexavalent chromium compound in a high-temperature atmospheric atmosphere as an operating environment, and poison the air electrode to cause deterioration. Even when (La, Ca) CrO ₃ (calcium dope lanthanum chromite) is used, there is a case where Cr poisoning occurs although it is less than when an alloy is used. Therefore, attempts have been made to suppress deterioration by coating a surface of an alloy or the like with a metal oxide material having excellent heat resistance to form a protective film.

As a material for forming the protective film, a part of La in LaMO ₃ (for example, M = Mn, Fe, Co) is replaced with an alkaline earth metal AE (AE = Sr, Ca) (La, AE) MO. ₃ perovskite oxide, spinel oxide represented by AB ₂ O ₄ , specifically, NiCo ₂ O ₄ , (Zn _x Co _1-x ) Co ₂ O ₄ (0.45 ≦ x ≦ 1. 00), FeMn ₂ O ₄ , NiMn ₂ O ₄ , CoMn ₂ O ₄ , MnFe ₂ O ₄ , MnNi ₂ O ₄ , MnCo ₂ O ₄ , Mn (Mn _0.25 Co _0.75 ) ₂ O ₄ , (Mn _0.5 Co _.5 ) Co ₂ O ₄ , TiCo ₂ O ₄ , ZnFe ₂ O ₄ , FeCo ₂ O ₄ , CoFe ₂ O ₄ , MgCo ₂ O ₄ , Co ₃ O ₄ , Zn _x (Co _y Mn _(1-y) ) _{(3 -x)} O ₄ (0 <x <1, 0 <y × (3-x) ≦ 2).

Such a protective film is often formed by coating as disclosed in Patent Document 1, for example.
In general, the base material used as a cell connection member has a complicated shape, and it is necessary to form a deterioration preventing film in order to suppress deterioration such as increase in oxide film and occurrence of Cr poisoning. is there. It is desirable that the deterioration preventing film is dense and has a uniform film thickness. When the film thickness becomes non-uniform, or when there is a part where the film thickness is too large, thermal stress (often due to mismatch of thermal expansion coefficients of the members to be joined) occurs at the start and stop, Cracks and exfoliation are likely to occur, and the part where the film thickness is too small cannot sufficiently exert the function of preventing deterioration (suppressing the increase in the oxide film of the alloy, suppressing Cr poisoning), and the deterioration of the part cannot be sufficiently suppressed. The problem is likely to occur.

  Therefore, a film forming method capable of realizing uniform film formation on a cell connecting member having a complicated shape has been studied. The present inventors were not bound by the conventional fixed idea that electrodeposition coating is a technique for obtaining a resin film, and increased the proportion of the metal oxide component in the coating film, and tried to form a metal oxide film. Surprisingly, it has already been found that a metal oxide film having a dense and uniform film thickness that functions as a protective film can be formed.

  Specifically, in the anion electrodeposition coating, in the anion resin mixed liquid containing the anion resin as a main component, the anion resin is moved to the anode by applying a voltage between the pair of electrodes with the base material as the anode, An electrodeposition coating film can be formed by depositing on the surface of the substrate. At this time, if the metal oxide fine particles are contained in the anionic resin mixed solution, the electrodeposition coating film is obtained as an electrodeposition coating film deposited as a mixture of the anion resin and metal oxide fine particles. When this electrodeposition coating film is heat-treated, depending on the heating conditions, the anion resin may be polymerized to obtain a resin coating film, or the resin component itself functions as a binder, and the metal oxide fine particles are integrated as a coating film. It can be burned off to form a protective film of metal oxide fine particles.

International Publication WO2009 / 131180 Pamphlet

  By the way, when anion electrodeposition coating is performed, a voltage is applied between a pair of electrodes using a base material as an anode. However, there is a phenomenon that an anionic resin mixture is deposited on an anode to form an electrodeposition coating film. At the same time, electrolysis of water occurs at the anode and oxygen bubbles are generated around the anode. When the bubbles generated at the anode interface move to the surface side of the coating film and pass through, the passage of the bubbles becomes a pinhole, and the obtained electrodeposition coating film may be defective.

  When an electrodeposition coating film is formed on a substrate as described above, even if a defect derived from water electrolysis gas such as pinholes occurs, a general electrodeposition coating film is almost made of a resin component. When the heat curing process is performed, the pinhole is closed while the resin component flows, so there is almost no pinhole remaining in the electrodeposition coating, but electrodeposition for forming a protective film. In the case of coating, the anion-type resin mixed solution contains 30% by mass or more of metal oxide fine particles in the solid content, and therefore does not flow so much in the heat curing treatment step. Therefore, the anionic resin mixture in the heat curing treatment process cures without blocking the pinhole generated in the process of forming the electrodeposition coating film, so that the pinhole remains in the obtained protective film. End up.

  In addition, when the electrodeposition coating is heat-cured, it may be possible to promote the flow of the electrodeposition coating by maintaining the heating conditions at a relatively low temperature for a long time. For the connection member, the edge part tends to be thinned by surface tension when the electrodeposition coating flows, and the uniformity of the film thickness is likely to be impaired, and a protective film is formed without generating pinholes Therefore, a protective film forming method is desired.

  That is, an object of the present invention is to provide a technology for forming a more uniform and dense protective film having no pinholes on the surface of a Cr-containing substrate used for SOFC, and a SOFC cell using the protective film. There is to do.

Pin hole formed in the upper Symbol electrodeposition coating film, electrodeposition coating film can not be closed removed can not be fluidized be heated electrodeposition coating film from being mainly composed of metal oxide particles. On the other hand, as a result of studying various methods, the inventors easily washed the electrodeposition coating film with water even if a pinhole was formed on the electrodeposition coating film, and then applied the pinhole easily. It has been found that a protective film that can be closed and that has metal oxide fine particles as a main component can be formed to a sufficient thickness.
In other words, electrodeposition coating is a coating method that has been industrialized by undercoating the body of automobiles and coating exterior parts of mobile phones, and is a technique that in principle provides a coating film with a uniform film thickness. However, it is basically a technique for obtaining a film composed mainly of a resin with a uniform film thickness, and in order to obtain a metal oxide film as required this time, the components of the coating film and the range of film thickness differ greatly. Therefore, it is difficult to close the pinhole by heating flow, and the pinhole tends to remain. However, while overcoming the cause of pinhole residue, it is possible to make a thick coat by overcoating, and furthermore, by performing firing and sintering processes, it can be used for solid oxide fuel cell cells It has been clarified that the present invention is also suitable for forming a protective film on the surface of a base material made of an alloy or oxide containing Cr.

That is, the characteristic configuration of the protective film forming method for forming the protective film on the surface of the base material made of an alloy or oxide containing Cr used in the SOFC cell of the present invention is as follows:
A first electrodeposition step of forming a first electrodeposition coating film on the surface of the base material by an anion electrodeposition coating method using an anionic resin mixed solution containing metal oxide fine particles in a solid content of 30% by mass or more. ,
A water washing step of washing the first electrodeposition coating film formed by the first electrodeposition step,
A second electrodeposition coating film is formed on the surface of the first electrodeposition coating film after washing with water using an anionic resin coating solution containing 30% by mass or more of metal oxide fine particles in the solid content by an anion electrodeposition coating method. A second electrodeposition step to form,
Are performed sequentially in this order,
A firing step of firing the first and second electrodeposition coating films to form a fired coating in which the resin components in the first and second electrodeposition coatings are burned off;
Furthermore, the sintered film is sintered to form a protective film made of a metal oxide.

In addition, the water-washing process as used in the present invention refers to removing water from the water-washed object after bringing the water into contact with the water-washed object. Typically, shower water-washing is performed. It may be immersion water washing that is taken out after being immersed in a water bath, or ultrasonic water washing that irradiates ultrasonic waves when immersed in a water bath.
In addition, the steps such as the firing step and the sintering step referred to in the present invention are typically performed by heat treatment for a predetermined time in a predetermined temperature range. For example, in a continuous heating step, Even if the resin component therein is burned off, the fired film can be formed by the firing process, and even if the fired film is sintered in the continuous heating process, the fired film is fired by the sintering process. It can be concluded. The same applies to other heating steps.

When a protective film is formed on the surface of a base material made of an alloy or oxide containing Cr used in the SOFC cell of the present invention, a highly durable member for SOFC can be provided.

When a first electrodeposition coating film is formed on the surface of the base material by an anion electrodeposition coating method using a mixed solution of metal oxide fine particles and an anionic resin by an electrodeposition step (first electrodeposition step) Even when the anionic resin component in the electrodeposition coating film is removed, a layer of metal oxide fine particles that can function as a protective film can be formed. At this time, the anionic resin is dissolved or dispersed in a solvent in the mixed solution in a state of being included in the metal oxide fine particles, polymerized by electrodeposition, and deposited on the surface of the substrate. By forming the anionic resin into a polymerized polymer, an electrodeposition coating film in which a dense and strong layer is formed is obtained.
At this time, since the anionic resin mixed solution contains 30% by mass or more of metal oxide fine particles in the solid content, the metal oxide fine particles are sufficiently taken into the anionic resin and formed after the disappearance of the anionic resin. It is not too brittle and has sufficient strength, and can be converted into a dense and strong protective film by sintering. The formed electrodeposition coating film is a coating film in which the metal oxide fine particles are gathered in a sufficiently dense amount. Therefore, when formed into a thick film, the effect of preventing scattering of Cr is easily exhibited.

  Next, when the first electrodeposition coating film formed by the first electrodeposition step is washed with water (water washing step), pinholes are generated in the first electrodeposition coating film formed by the first electrodeposition step. Even so, based on the above new knowledge, the second electrodeposition process can supply an anionic resin mixture into the pinhole to form an electrodeposition coating film, and the pinhole remains inside the coating film. Can be suppressed.

That is, if pinholes are generated in the first electrodeposition coating film immediately after the first electrodeposition step, bubbles remain in the pinholes. The bubbles remain inside the pinhole by being caught inside the pinhole or being covered with the liquid film of the anionic resin mixed solution. This bubble is thought to inhibit the penetration of the anionic resin mixture into the pinhole in the electrodeposition process. Therefore, by performing a water washing step, the liquid film covering the bubbles is destroyed by washing with water, and if the bubbles are destroyed and removed, the gas in the pinhole can be removed, and the first electrodeposition coating in the state where the washing has been completed is completed. Even if there is a pinhole on the film surface, the inside of the pinhole can be made into a condition where an electrodeposition coating film is easily formed by the subsequent second electrodeposition process. Moreover, the liquid mixture is maintained in an uncured state. When a second electrodeposition coating film is formed by an anionic electrodeposition coating method using an anionic resin mixed solution containing 30% by mass or more of metal oxide fine particles in the solid content (second electrodeposition step), uncured A second electrodeposition coating film is formed on the surface of the first electrodeposition coating film. Then, a 2nd electrodeposition coating film is formed, filling the pinhole produced | generated in the 1st electrodeposition coating film with the anionic resin liquid mixture. Moreover, since the 1st electrodeposition coating film is an uncured state, it is easy to integrate with the 1st electrodeposition coating film. Therefore, even if a pinhole has occurred in the first electrodeposition process, it can be integrated with the pinhole closed, and the electrodeposition coating can be performed without leaving the pinhole in the electrodeposition coating film. The film thickness can be increased.
In addition, after forming a 2nd electrodeposition coating film in this way, the water washing process, the 3rd electrodeposition process which forms a 3rd electrodeposition coating film, a water washing process, the 4th which forms the 4th electrodeposition coating film By repeating the same operation as in the electrodeposition step, a thick electrodeposition coating film with no pinhole remaining can be obtained.

  After the first electrodeposition step, the water washing step, and the second electrodeposition step were sequentially performed in this order, the electrodeposition coating film was baked to burn out the resin components in the first and second electrodeposition coating films. When the baking process which forms a baking film is performed, the said electrodeposition coating film can be made into the baking film which consists of metal oxide fine particles. In this fired film, the anion-type resin that has connected the metal oxides burns away, so that substantially only the metal oxide fine particles in the electrodeposition film remain as components of the fired film. It will be.

Conventionally, the reason why electrodeposition coating has not been used to form a protective film made of a metal oxide is that when the resin component is burned out, the proportion of metal oxide particles in the electrodeposition coating film is too small. The fired film becomes brittle, and the fired film cannot maintain the form as a film. On the other hand, if the ratio of the metal oxide particles is too large, the anionic resin mixed solution cannot exist stably and the two layers are separated. Therefore, it is due to two problems that it is not used as an anionic resin mixed solution for electrodeposition coating. However, according to the knowledge of the present inventors, surprisingly, the anionic resin mixed liquid prepared for electrodeposition coating is in a stable mixed state and has a sufficient strength as a fired film after the firing process. It was found that it can be prepared as an anionic resin mixed liquid in which metal oxide fine particles capable of forming a cation and an anionic resin are mixed. Therefore, a strong fired film can be created by a simple process using an electrodeposition coating method.

  When the sintering step is further performed, the fired coating is sintered, whereby the bonds between the metal oxide fine particles are strengthened, and the fired coating is converted into a dense protective film.

  Then, since the obtained electrodeposition coating film is firmly integrated without including pinholes, a dense protective film can be formed.

Also, features a method for manufacturing a cell connecting member of the present invention produces cell connecting member is formed a protective film on the surface of a base material made of an alloy or oxide containing Cr, the cell connection member A manufacturing method comprising :
There the protective film to the point that to form a protective film forming method described above.

This interconnector cell connecting member, since is formed by the protective film forming process has been granted dense and highly preventing deterioration effect protective film, chemically stable, reliable over time less deterioration It is possible to provide a cell connection member that can be used highly.
Furthermore, according to the protective film forming method, since a protective film with few pinholes is formed, scattering of Cr from the base material is suppressed with high accuracy, and a highly durable cell connection member for SOFC is manufactured . Can do.

In the above SL manufacturing method, it is possible to the metal oxide fine particles and made of an oxide containing Co.

Oxide containing C o of the upper Symbol metal oxide, the thermal expansion coefficient, mainly ferritic stainless steel used as the base material (thermal expansion coefficient: 11 × 10 ^-6 K ^-1) and, joining (La, Sr) (Co, Fe) O ₃ (thermal expansion coefficient: 15 to 21 × 10 ⁻⁶ K ⁻¹ ), (La, Sr) MnO ₃ (thermal expansion coefficient) : 11 × 10 ⁻⁶ K ⁻¹ ). For example, the thermal expansion coefficient of ZnCo ₂ O ₄ is 9.3 × 10 ⁻⁶ K ⁻¹ , and the thermal expansion coefficient of (Zn _0.45 Co _0.55 ) Co ₂ O ₄ is 10.7 × 10 ⁻⁶ K ⁻¹ , MnCo _2. The thermal expansion coefficient of O ₄ is 11.8 × 10 ⁻⁶ K ⁻¹ . Therefore, it can be said that the film by this production method is a film excellent in durability without being easily peeled off from the substrate even when the substrate is thermally expanded.

In the above SL manufacturing method, it is possible to the metal oxide fine particles and made of an oxide containing Zn and Co.

Also, those of Zn-Co system, when performing film formation by sintering at relatively low temperatures as compared with other materials, so obtained a dense oxygen barrier highly membranes, preferred industrially. In addition, Zn—Co-based materials have an advantage that electrical resistance at a relatively low temperature (for example, 650 ° C.) is small, and high performance is easily maintained even when the operating conditions of SOFC are shifted to low temperatures.

Also, it is possible to contain at least one or more kinds anionic resin mixture containing a metal oxide fine particles at least 30 wt% in solids is selected from polyacrylic acid and polymethacrylic acid.

Before SL polyacrylic acid and polymethacrylic acid as the anionic resin together with the anionic resin mixture containing the metal oxide fine particles in a highly dispersed can be easily formed, in the electrodeposition step, the metal oxide Fine particles can be formed into a film-like electrodeposition coating film. In addition, since the bonding between the metal oxide fine particles can be promoted at this time, even if the anionic resin is burned out in the baking step, a dense fired film in which the metal oxide fine particles are firmly bonded is formed. It is preferable because it helps.

Also, the substrate can be a ferritic stainless steel.

If before Kimotozai is ferritic stainless steel, the the higher affinity for coating the metal oxide fine particles obtained by sintering hardly even cause thermal stress in the film in terms of thermal expansion coefficient, It is suitable for producing a more durable protective film because it has a coefficient of thermal expansion close to that of the constituent material of the SOFC cell.

Also, it features a method for manufacturing a solid oxide fuel cell of this invention is that you produce a solid oxide fuel cell with the cell connection member joined to the air electrode.

SOFC cell manufactured by the manufacturing method of this, since having the above cell connecting member, it is possible to provide a high solid oxide fuel cell in performance stability.

  Therefore, it is possible to provide a cell connection member and a SOFC cell that have high durability and can be used stably over a long period of time.

Schematic diagram of solid oxide fuel cell The figure which shows the usage condition of the cell connection member of a solid oxide fuel cell Sectional view of cell connection member test piece with protective film formed Enlarged view of the protective film formed on the substrate surface

  The protective film forming method, SOFC cell connecting member, and SOFC cell for forming the protective film 12 on the surface of the base material 11 made of an alloy or oxide containing Cr used in the SOFC of the present invention will be described below. . Preferred examples are described below, but these examples are described in order to more specifically illustrate the present invention, and various modifications can be made without departing from the spirit of the present invention. The present invention is not limited to the following description.

<Solid oxide fuel cell>
Embodiments of a cell connection member for SOFC and a method for manufacturing the same according to the present invention will be described with reference to the drawings.
The SOFC cell C shown in FIG. 1 and FIG. 2 has an air electrode made of an oxide ion and an electron conductive porous body on one side of an electrolyte membrane 30 made of a dense oxide oxide conductive solid oxide. 31 and a single cell 3 formed by joining a fuel electrode 32 made of an electron conductive porous body to the other surface side of the electrolyte membrane 30.

  Further, the SOFC cell C exchanges electrons with the single cell 3 with respect to the air electrode 31 or the fuel electrode 32, and at the same time, a pair of electronically conductive elements in which grooves 2 for supplying air and hydrogen are formed. The cell connecting member 1 in which the protective film 12 is formed on the base material 11 made of an alloy or oxide (a schematic diagram in the case where the shape is a simple shape having a rectangular cross section is shown in FIG. 3) is appropriately gas at the outer peripheral edge. It has a structure in which the sealing body is sandwiched. And the said groove | channel 2 by the side of the air electrode 31 functions as the air flow path 2a for supplying air to the air electrode 31, because the air electrode 31 and the cell connection member 1 are closely_contact | adhered, on the other hand, fuel The groove 2 on the electrode 32 side functions as a fuel flow path 2 b for supplying hydrogen to the fuel electrode 32 by arranging the fuel electrode 32 and the cell connecting member 1 in close contact with each other.

In addition, when a general material used in each element constituting the SOFC cell C is described, for example, the material of the air electrode 31 is LaMO ₃ (for example, M = Mn, Fe, Co). A perovskite oxide of (La, AE) MO ₃ in which a part of La of Al is substituted with an alkaline earth metal AE (AE = Sr, Ca) can be used. And yttria-stabilized zirconia (YSZ) can be used, and yttria-stabilized zirconia (YSZ) can be used as the material of the electrolyte membrane 30.

Furthermore, in the SOFC cell C described so far, the material of the cell connection member 1 is a perovskite oxide such as LaCrO ₃ which is excellent in electronic conductivity and heat resistance, or ferritic stainless steel. Alloys or oxides containing Cr are used, such as certain Fe—Cr alloys, Fe—Cr—Ni alloys that are austenitic stainless steels, and Ni—Cr alloys that are nickel-based alloys.

In a state where a plurality of SOFC cells C are arranged in a stacked manner, a pressing force is applied in the stacking direction by a plurality of bolts and nuts to form a cell stack.
In this cell stack, the cell connecting members 1 disposed at both ends in the stacking direction may be any one as long as only one of the fuel flow path 2b or the air flow path 2a is formed, and the cells disposed in the other middle. The connecting member 1 may be one in which the fuel flow path 2b is formed on one surface and the air flow path 2a is formed on the other surface. In the cell stack having such a laminated structure, the cell connecting member 1 may be called a separator.
An SOFC having such a cell stack structure is generally called a flat-plate SOFC. In the present embodiment, a flat plate type SOFC will be described as an example, but the present invention can be applied to SOFCs having other structures.

When the SOFC having such a SOFC cell C is operated, air is supplied through the air flow path 2a formed in the cell connection member 1 adjacent to the air electrode 31, as shown in FIG. In addition, hydrogen is supplied through the fuel flow path 2b formed in the cell connection member 1 adjacent to the fuel electrode 32, and the fuel electrode 32 operates at an operating temperature of, for example, about 800 ° C. Then, the air electrode 31 O ₂ electrons e ^- are reacting with O ^2- is generated, the O ^2- passes through the electrolyte membrane 30 to move to the fuel electrode 32, H ₂ supplied in the fuel electrode 32 Reacts with the O ²⁻ to generate H ₂ O and e ⁻ , so that an electromotive force E is generated between the pair of cell connecting members 1, and the electromotive force E is taken out and used. Can do.

<Cell connection member>
As shown in FIGS. 1 and 3, the cell connection member 1 is configured by providing a protective film 12 on the surface of a substrate 11 for a cell connection member. And it forms in the shape of a groove plate which can be connected, forming the air flow path 2a and the fuel flow path 2b between each said single cell 3. As shown in FIG.

  The protective film 12 is formed as a thick film by electrodeposition coating a base material 11 with a coating film-forming material containing a conductive ceramic material.

<Protective film>
The protective film 12 is made of, for example, metal oxide fine particles such as ZnCo ₂ O ₄ and polyacrylic on the surface of the base material 11 made of ferritic stainless steel containing 22% Cr and about 0.5% Mn. An anionic resin mixed solution containing an anionic resin such as an acid in a mass ratio of (metal oxide fine particles: anionic resin) = (0.5: 1) to (1.7: 1) And performing an electrodeposition step of forming an electrodeposition coating film by an anionic electrodeposition coating method, and firing the electrodeposition coating film to form a fired coating film in which the resin component in the electrodeposition coating film is burned off. It is formed by performing a step and further performing a sintering step in which the fired coating is sintered to form a protective film 12 made of a metal oxide.

  The film thickness of the electrodeposition coating film forms a dense and strong protective film 12 after firing and sintering, but if it is too thin at the stage of the electrodeposition coating film, it has a sufficient deterioration preventing function during long-time power generation. It is preferable that the thickness is 1 μm or more because it is difficult to exhibit, care is required in the firing and sintering processes in terms of strength, and the operability is lowered. On the contrary, if the electrodeposition coating is too thick, the sufficient deterioration prevention function during power generation for a long time becomes high, but the electrical resistance when used for battery cells is increased, and the film thickness becomes thicker. The thickness is preferably 30 μm or less because it tends to be weak against thermal stress, increases the material necessary for forming the electrodeposition coating film, and is uneconomical. The protective film 12 formed in this manner allows diffusion of gas phase Cr (VI) oxide (or oxyhydroxide) from the substrate side to the air electrode side or the interface between the air electrode 31 and the electrolyte. It can be surely suppressed. As a result, the occurrence of Cr poisoning of the air electrode 31 can be reliably suppressed. Moreover, since the scattering of Cr from the base material 11 side is suppressed, the progress of oxidative deterioration of the base material 11 due to Cr withering can be suppressed.

  The fired film forms a dense metal oxide layer by sintering and functions as the protective film 12. At this time, if the porosity of the fired film is too large, the protective film 12 becomes brittle, it is difficult to maintain sufficient strength, and the function as an oxygen barrier layer, which is the original role of the protective film 12, is sufficiently fulfilled. I can't. Therefore, it is preferable that the porosity of the fired coating is 40% or less in order to form the protective film 12 having high strength.

  In the electrodeposition step, if the particle size of the metal oxide fine particles is too large, the metal oxide fine particles are converted into the anionic resin mixed solution when an anion type resin mixed solution is formed during the electrodeposition step. It is difficult to uniformly disperse the resin in the inside, and it is difficult to adjust to an appropriate viscosity. On the other hand, if the electrodeposition film is too small, the volume shrinkage due to the sintering tends to proceed excessively when the electrodeposition coating film is sintered, so that cracks and peeling tend to occur.

  That is, since the protective film 12 can easily form a uniform film thickness on the base material 11, a high-quality SOFC cell with high productivity and uniform physical properties can be manufactured. It is desirable that the protective film 12 has a uniform thickness and an appropriate thickness. As shown in FIG. 3, the thickness of the protective film 12 crosses the test piece of the base material 11 on which the protective film 12 is formed, and the average thickness of the protective film 12 in FIGS. x) was evaluated as the rolled film thickness, and the average (z) of the c, d, e, and f protective films 12 corresponding to the corners was used as the edge film thickness. When the film thickness ratio (x / z) between the rolled surface and the edge portion was obtained as the evaluation value of uniformity, it was 1.5. By providing the thickness ratio (x / z) between the rolled surface and the edge portion of the protective film 12 to 2 or less, a high-quality fuel cell connection member that can be said to be practically sufficiently homogeneous is provided at low cost. Can now.

  Although the specific manufacturing method of the said protective film 12 is explained in full detail below, this invention is not limited to a following example.

<Example 1>
(1) Synthesis of anionic resin 50 parts of 1,4 dioxane was heated to about 82 ° C. in a four-necked flask equipped with a reflux condenser, a thermometer, a stirrer, and a dropping funnel, and the dropping funnel was stirred. To the mixture shown in Table 1 below and 50 parts of 1,4 dioxane are continuously added dropwise over 3 hours.
After completion of the dropwise addition, the reaction is continued for 3 hours at the same temperature to synthesize an anionic acrylic resin (solid content 50%). The obtained anion type resin had a Tg of −27 ° C. (calculated estimate) and a molecular weight MW of 120,000 to 150,000.

AIBN in Table 1 is a polymerization initiator. L-SH is a chain transfer agent.

The chemical properties of the anionic resin are preferably Tg: −50 ° C. to + 25 ° C. and molecular weight (MW mass average molecular weight): 50,000 to 200,000. In general, the Tg of an anionic resin is around + 20 ° C., and the MW is about 30,000 to 70,000. In order to improve the eutectoid rate by electrophoretically coagulating a large amount of inorganic fine particles and generating an electrolytic gas locally, it is preferable to use an anionic resin having a low Tg and a high molecular weight. When Tg is -50 ° C or less, the viscosity of the deposited coating is too strong, and the flow is large after baking and hardening. When the temperature is + 25 ° C or more, the fluidity decreases and the gas traces generated during eutectoidation of ZnCo ₂ O ₄ particles can be erased. It cannot be pinhole-shaped. When the MW is 50,000 or less, the dispersibility of the ZnCo ₂ O ₄ fine particles decreases. On the other hand, when it is 200,000 or more, the fluidity is lowered, the uniform dispersion of the ZnCo ₂ O ₄ fine particles in the coating film is deteriorated, and the appearance is not uniform.

In addition, when an anionic resin and metal oxide fine particles are subjected to a coupling reaction using a silane coupling agent described later, the deposition efficiency of metal oxide fine particles represented by ZnCo ₂ O ₄ fine particles is dramatically improved. be able to.

(2) As the anionic resin mixture prepared silane coupling agent, with isocyanate-functional silane _{(OCN-C 3 H 6 -Si} (OC 2 H 5) 3), the solvent nMP (n-methyl pyrrolidone) 3 After mixing 120 parts by mass of the anionic resin prepared in (1) and 60 parts of the solvent nMP (n-methylpyrrolidone), add a tin-based catalyst (DBTDL 0.2 part) and react at 60 ° C. for 1 hour. Thus, the isocyanate group of the silane coupling agent and the OH group of the anionic resin react to add the silane coupling agent to the anionic resin. (Table 2, first component)

100 parts by weight of ZnCo ₂ O ₄ fine particles (average particle size 0.5 μm), 200 parts of solvent nMP (n-methylpyrrolidone) and 750 parts by weight of 3 mm diameter zirconia beads are mixed, and wet dispersed with a stirrer to form a slurry. ZnCo ₂ O ₄ fine particles are obtained. (Table 3, second component)

The first component is added to the second component and mixed uniformly.
Further, 1.4 parts by mass of triethylamine, 10 parts by mass of a solvent nMP (n-methylpyrrolidone) and 10 parts by mass of an antifoaming agent (Surfinol 104) are added and stirred.
After uniformly mixing, 500 parts by mass of ion-exchanged water is added little by little to prepare a mixed solution of ZnCo ₂ O ₄ fine particles and an anionic resin. After stirring for 24 hours to promote hydrolysis reaction of the silane coupling agent, impurities are removed by ion exchange treatment, and an anionic resin mixture having a pH of 9.0 ± 0.2 bath conductivity of 200 ± 50 μS / cm is obtained. can get. The obtained dispersion is used as an anionic resin mixture of ZnCo ₂ O ₄ fine particles: resin = 1: 1 (mass ratio).

Note that in ZnCo ₂ O ₄ particulates changing the mixing ratio of the first component and the second component blend of the following: The resin can create various modified anionic resin mixture. In addition, although acrylic acid-based and methacrylic acid-based resins are used as anionic resins, various known anionic resins can be used and are not limited to those described above. Furthermore, although Zn—Co-based fine particles are used as the metal oxide fine particles, as another material for forming the protective film, a part of La in LaMO ₃ (for example, M = Mn, Fe, Co) is alkalinized. Perovskite oxide of (La, AE) MO ₃ substituted with earth metal AE (AE = Sr, Ca), spinel oxide represented by AB ₂ O ₄ , specifically NiCo ₂ O ₄ , FeMn ₂ O ₄ , NiMn ₂ O ₄ , CoMn ₂ O ₄ , MnFe ₂ O ₄ , MnNi ₂ O ₄ , MnCo ₂ O ₄ , Mn (Mn _0.25 Co _0.75 ) ₂ O ₄ , (Mn _0.5 Co _0.5 ) Co ₂ O ₄ TiCo ₂ O ₄ , ZnFe ₂ O ₄ , FeCo ₂ O ₄ , CoFe ₂ O ₄ , MgCo ₂ O ₄ , Co ₃ O ₄ , and the like.

(3) Electrodeposition coating The anionic dispersant composition prepared in (2) above is dispersed so that the dispersant particles in the electrodeposition solution are 100 g per liter of electrodeposition solution, and a direct current voltage is applied in a solution at 25 ° C. Electrodeposition coating was performed at 40 V for 30 seconds under stirring with a stirrer (20 rpm).
Electrodeposition coating was performed as follows.

After subjecting the test piece of the base material 11 having a simple rectangular shape (bar shape) to a degreasing treatment, pickling treatment, etc., if necessary, the base material 11 is immersed in the anionic resin mixture, By applying electricity, an uncured electrodeposition coating film is formed on the surface of the substrate 11. As the base material, ferritic stainless steel is often used because of its consistency with the thermal expansion coefficient of the metal oxide to be joined, but Fe-Cr-Ni which is an austenitic stainless steel superior in heat resistance. An alloy or a Ni-Cr alloy that is a nickel-based alloy may be used.
In addition, instead of an alloy, a metal oxide typified by (La, Ca) CrO ₃ (calcium dopeplank chromite) may be used. In any case, when Cr is contained and used as a cell connection member 1 for SOFC, Cr is scattered during high-temperature operation of SOFC, and poisoning of other components of SOFC (for example, air electrode material) This may cause a decrease in SOFC durability. Therefore, for such a base material, it is desired to suppress the scattering of Cr by forming the protective film 12 and to improve the durability of the SOFC.
The substrate 11 may have a simple bar shape, but generally has a complicated shape such as a lattice shape (shown in FIG. 2) or a comb shape.
In the following description, the test piece of the base material 11 is previously subjected to surface polishing by # 800 wet polishing.

(3-1) Pretreatment In addition, the pretreatment which performs the following 1-7 in order on each electrode was performed.
1. Cathodic electrolysis with electrolytic cleaner (Activator S (manufactured by Shimizu) 100 g / L, 40 ° C., 10 A / dm 2, 30 seconds)
2. 2. Washing with water Anode electrolysis with electrolytic cleaner (Activator S (manufactured by Shimizu) 100 g / L, 40 ° C., 10 A / dm 2, 30 seconds)
4). 5. Washing with water Acid neutralization (Nitric acid 200mL / L)
6). 6. Washing with water Pure water washing

Moreover, you may perform a degreasing process, a pickling process, etc. separately to the test piece of the base material 11 used as an anode.
A degreasing process is performed by supplying alkaline aqueous solution to the surface of the base material 11, for example. The supply of the alkaline aqueous solution is performed, for example, by spraying the alkaline aqueous solution onto the base material 11 or immersing the base material 11 in the alkaline aqueous solution. As the alkali, those commonly used for metal degreasing can be used, and examples include alkali metal phosphates such as sodium phosphate and potassium phosphate. The alkali concentration in the aqueous alkali solution is appropriately determined according to, for example, the type of metal to be treated, the degree of contamination of the substrate 11, and the like. Furthermore, the alkaline aqueous solution may contain an appropriate amount of a surfactant such as an anionic surfactant and a nonionic surfactant. Degreasing is performed at a temperature of about 20 to 50 ° C. (liquid temperature of the alkaline aqueous solution) and is completed in about 1 to 5 minutes.

  After degreasing, the substrate 11 is washed with water and subjected to the next pickling treatment. In addition, degreasing to be immersed in an acidic bath, bubbling immersion degreasing, electrolytic degreasing, and the like can be appropriately combined. The pickling treatment is performed, for example, by supplying an acid aqueous solution to the surface of the substrate 11. The supply of the acid aqueous solution is performed by spraying the acid aqueous solution on the base material 11 or immersing the base material 11 in the acid aqueous solution, as in the case of supplying the alkaline aqueous solution in the degreasing treatment. As the acid, those commonly used for metal pickling can be used, and examples thereof include sulfuric acid, nitric acid, and phosphoric acid. The acid concentration in the acid aqueous solution is appropriately determined according to, for example, the type of the substrate 11. The pickling treatment is performed at a temperature of about 20 to 30 ° C. (liquid temperature of the acid aqueous solution) and is completed in about 15 to 60 seconds. In addition to the degreasing treatment and pickling treatment, scale removal treatment, ground treatment, rust prevention treatment, and the like may be performed. In addition, after these treatments, if the substrate or the base treatment film or the rust preventive film is not contaminated with an organic material such as an oil film, an inorganic material, etc., the substrate 11 is dried at a temperature of about 70 to 120 ° C. It may be used for electrodeposition coating.

(3-2) Electrodeposition process Electrodeposition is performed according to a known method, for example, by immersing the base material 11 completely or partially in an energization tank filled with the anionic resin mixed solution to form an anode. It is carried out by doing.
(3-2-1) First Electrodeposition Process In this way, in the test piece of the base material 11 that was pretreated, in the solution at 25 ° C., the base material 11 was positive, and the SUS304 electrode plate was negative. The uncured first electrodeposition coating film is formed on the surface of the substrate 11 by energizing with a stirrer stirring (20 rpm) for 40 seconds at a DC voltage of 40 V.

Electrodeposition coating conditions are not particularly limited, depending on various conditions such as the type of metal that is the substrate 11, the type of the anionic resin mixture, the size and shape of the current-carrying tank, and the intended use of the cell connection member 1 obtained. In general, the bath temperature (temperature of the anionic resin mixture) is about 10 to 50 ° C., the applied voltage is about 10 to 450 V, the voltage application time is about 1 to 10 minutes, and the anionic resin mixing. The liquid temperature of the liquid may be 10 to 45 ° C.
In addition, the film thickness of a 1st electrodeposition coating film can be controlled by changing an electrodeposition voltage and electrodeposition time. By appropriately controlling the electrodeposition voltage and the electrodeposition time, bubble formation due to water electrolysis can be suppressed, but even if properly controlled, it should be avoided to generate a certain amount of pinholes on the electrode surface. I can't.

(3-2-2) Washing step Next, the first electrodeposition coating film formed on the substrate 11 was washed with pure water.
For cleaning, various known cleaning methods such as shower cleaning, immersion cleaning, and ultrasonic cleaning can be applied. Here, shower cleaning is applied. In the immersion cleaning, there may be a case where the force for breaking the liquid film forming the bubbles is not sufficient. On the other hand, the shower cleaning is considered to have a sufficient force. In addition, it is expected that bubbles remaining in the pinholes can be more efficiently destroyed by performing ultrasonic cleaning. However, since ultrasonic cleaning devices are expensive, it is possible to perform inexpensive and simple water washing by performing shower cleaning. It becomes possible. In addition, shower water washing was performed until the color of the anionic resin mixed solution was not visually observed in the water after the water washing. Thereby, the bubbles in the pinhole formed in the first electrodeposition coating film can be broken together with the water flow to form a state in which the anionic resin mixed solution easily enters the pinhole.

(3-2-3) Second electrodeposition step and water washing step Further, the second electrodeposition step is performed on the washed first electrodeposition coating film in the same manner as the first electrodeposition step. Moreover, the 2nd electrodeposition coating film obtained at the 2nd electrodeposition process performed the water washing process similarly to the said water washing process.
In this way, a second electrodeposition coating film can be obtained using the anionic resin mixture. Since this second electrodeposition coating film is formed on the uncured first electrodeposition coating film while filling and closing the pinhole with an anionic resin mixture, it is integrated with the first electrodeposition coating film. It is easy to form an electrodeposition coating film with few pinholes.

(3-3) Heat treatment The base material 11 after the electrodeposition step is taken out of the energization tank and subjected to heat treatment after washing with water. By heating the base material 11 on which the uncured electrodeposition coating film is formed, the cell connection member 1 on which the cured electrodeposition coating film is formed on the surface of the base material 11 is obtained.

(3-3-1) Heat curing treatment The heat curing treatment includes preliminary drying for drying the electrodeposition coating film and curing heating for curing the electrodeposition coating film, and curing heating is performed after the preliminary drying. The preliminary drying is performed under heating at about 60 to 140 ° C. and is completed in about 3 to 30 minutes. Curing heating is performed under heating at about 150 to 220 ° C. and is completed in about 10 to 60 minutes. Specifically, using an electric furnace, preliminary drying at 110 ° C. for 10 minutes was performed, and curing heating at 180 ° C. for 30 minutes was performed.

(3-3-2) Firing Step and Sintering Step An electrodeposition coating film formed using ZnCo ₂ O ₄ fine particles: resin = 1: 1 (mass ratio) as the anionic resin mixed solution is 500 ° C. After holding the baking step of burning off the acrylic resin by holding for 2 hours, the temperature is raised to 1000 ° C. and held for 2 hours to sinter ZnCo ₂ O ₄ particles and react with the surface of the test piece of the substrate 11. The sintering process to raise was performed and the dense protective film 12 which has adhesiveness with respect to the base material 11 was formed.

  After completion of the sintering process, the formation state of the protective film 12 was visually confirmed.

<Comparative Example 1>
In the electrodeposition process in Example 1, in the energization tank filled with the anionic resin mixed liquid maintained at 25 ° C., the base material 11 is positive, the counter electrode (electrode plate made of SUS304) is negative polarity, and direct current The first electrodeposition step of forming an electrodeposition coating film on the surface of the object to be coated is carried out by applying a voltage of 40 V for 80 seconds. The protective film 12 was formed in the same manner as in Example 1 except that the electrodeposition coating film was obtained by performing the water washing step of washing by the above method.

  That is, the electrodeposition process in Example 1 was performed once, and the electrodeposition process was performed by changing the conditions so that the total electrodeposition time was the same.

  After completion of the sintering process, the formation state of the protective film 12 was visually confirmed.

<Comparative Example 2>
The protective film 12 was formed in the same manner as in Example 1 except that the electrodeposition process in Example 1 was left without the water washing process between the first electrodeposition process and the second electrodeposition process.
After completion of the sintering process, the formation state of the protective film 12 was visually confirmed.

<Comparative Example 3>
The protective film 12 is formed in the same manner as in Example 1 except that the electrodeposition process in Example 1 is performed by air-blow cleaning by air blow instead of water washing in the water-washing process between the first electrodeposition process and the second electrodeposition process. Went.
After completion of the sintering process, the formation state of the protective film 12 was visually confirmed.

<Summary 1>
The results of Example 1 and Comparative Examples 1 to 3 are shown in FIG.

In the table, ○ indicates that no pinhole was observed in the protective film,
△ indicates that pinholes were observed but the number was small.
X means that many pinholes were generated. (In addition, in FIG. 4, the black dots shown by arrows are pinholes.)
In either case, a uniform protective film 12 having a film thickness of about 6 μm is obtained.

  From the comparison of the state of the protective film obtained from FIG. 4, when the water washing process was performed between the first and second electrodeposition processes, no pinholes were observed on the protective film, but the water washing process was performed. If not, a large number of pinholes were generated, and it was found that the physical properties of the protective film were expected to deteriorate in practice.

  Therefore, it was found that the protective film 12 having high practicality with few pinholes could be formed by the protective film forming method of the present invention.

<Example 2>
The composition of the anionic resin mixed solution in Example 1 is (ZnCo ₂ O ₄ fine particles: resin) = (1.7: 1) (mass ratio, content of metal oxide fine particles in solid content 63 mass%) A protective film 12 was prepared in the same manner as in Example 1 except that the adjustment was performed.
After completion of the sintering process, the formation state of the protective film 12 was visually confirmed.

<Example 3>
The composition of the anionic resin mixed solution in Example 1 is (ZnCo ₂ O ₄ fine particles: resin) = (0.75: 1) (mass ratio, content of metal oxide fine particles in solid content is 43 mass%) A protective film 12 was prepared in the same manner as in Example 1 except that the adjustment was performed.
After completion of the sintering process, the formation state of the protective film 12 was visually confirmed.

<Example 4>
The composition of the anionic resin mixed solution in Example 1 is (ZnCo ₂ O ₄ fine particles: resin) = (0.5: 1) (mass ratio, content of metal oxide fine particles in solid content is 33% by mass). A protective film 12 was prepared in the same manner as in Example 1 except that the adjustment was performed.
After completion of the sintering process, the formation state of the protective film 12 was visually confirmed.

<Comparative Example 4>
The composition of the anionic resin mixed solution in Example 1 is (ZnCo ₂ O ₄ fine particles: resin) = (0.25: 1) (mass ratio, content of metal oxide fine particles in solid content is 20% by mass). A protective film 12 was prepared in the same manner as in Example 1 except that the adjustment was performed.
After completion of the sintering process, the formation state of the protective film 12 was visually confirmed.

<Summary 2>
The results of Examples 2 to 4 and Comparative Example 4 are shown in Table 5.

As shown in Table 5, (ZnCo ₂ O ₄ fine particles: resin) = (1.7: 1) to (0.5: 1) (mass ratio, 30 to 30 as the content of metal oxide fine particles in the solid content) 70% by mass) of the anionic resin mixed solution is formed by the method for forming a protective film of the present invention so as to form a high-performance protective film with few pinholes and to exhibit a high Cr scattering suppression effect. I was able to do it.

  According to the protective film forming method of the present invention, it is possible to provide a cell connection member and a cell for SOFC that have high durability and can be used stably over a long period of time.

1: Cell connecting member 2: Groove 2a: Air flow path 2b: Fuel flow path 3: Single cell 11: Base material 12: Protective film 30: Electrolyte film 31: Air electrode 32: Fuel electrode C: Cell for SOFC

Claims (7)

A protective film forming method for forming a protective film on the surface of a base material made of an alloy or oxide containing Cr used in a solid oxide fuel cell,
A first electrodeposition step of forming a first electrodeposition coating film on the surface of the base material by an anion electrodeposition coating method using an anionic resin mixed solution containing metal oxide fine particles in a solid content of 30% by mass or more. ,
A water washing step of washing the first electrodeposition coating film formed by the first electrodeposition step,
A second electrodeposition coating film is formed on the surface of the first electrodeposition coating film after washing with water using an anionic resin coating solution containing 30% by mass or more of metal oxide fine particles in the solid content by an anion electrodeposition coating method. A second electrodeposition step to form,
Are performed sequentially in this order,
A firing step of firing the first and second electrodeposition coating films to form a fired coating in which the resin components in the first and second electrodeposition coatings are burned off;
Furthermore, the protective film formation method which performs the sintering process which sinters the said baking film and forms the protective film which consists of metal oxides. A method for producing a cell connection member, which produces a cell connection member having a protective film formed on the surface of a base material made of an alloy or oxide containing Cr,
The manufacturing method of the cell connection member which forms the said protective film with the protective film formation method of Claim 1. The method for manufacturing a cell connection member according to claim 2, wherein the metal oxide fine particles are made of an oxide containing Co. The method for producing a cell connection member according to claim 2 or 3, wherein the metal oxide fine particles are made of an oxide containing Zn and Co. The cell according to any one of claims 2 to 4, wherein the anionic resin mixed solution containing 30% by mass or more of metal oxide fine particles in the solid content contains at least one selected from polyacrylic acid and polymethacrylic acid. A method for manufacturing a connecting member. The method for producing a cell connecting member according to any one of claims 2 to 5, wherein the base material is made of ferritic stainless steel. A cell for a solid oxide fuel cell, wherein a cell for a solid oxide fuel cell is manufactured by joining the cell connecting member obtained by the production method according to any one of claims 2 to 6 to an air electrode. Manufacturing method .