JP2015011958A - Protective film formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique which allows for formation of a protective film that is less likely to cause cracking or peeling on the surface of an alloy containing Cr and used in a SOFC.SOLUTION: In a protective film formation method for forming a protective film on the surface of a base material, i.e., an alloy or an oxide containing Cr and used in a SOFC, by electrodeposition coating, an electrolytic polishing step is performed, and followed by a coating formation step, a calcination step of calcining the coating by charging a base material, having the coating on the surface, into a furnace held at a weight stable temperature (endothermic peak) or more where the endothermic amount incident to weight reduction when the resin heats the coating is maximized, and a sintering step of forming a protective film composed of a metal oxide by sintering the coating obtained by the calcination step.

Description

  The present invention relates to 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 for a solid oxide fuel cell (hereinafter referred to as SOFC) cell.

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 indirect 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 operating temperature of the conventional SOFC is about 1000 ° C., and metal oxides typified by lanthanum chromite have been used for the cell connection member from the viewpoint of heat resistance, but recently the operating temperature has increased from 700 ° C. to 800 ° C. It has been lowered and alloys can be used. 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. In addition, 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 almost always contain Cr, and form an oxide film of Cr ₂ O ₃ or MnCr ₂ O _{4 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 candidate for a coating material, a perovskite of (La, AE) MO ₃ in which a part of La in LaMO ₃ (for example, M = Mn, Fe, Co) is replaced with an alkaline earth metal AE (AE = Sr, Ca). Type oxide, spinel type 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 Examples thereof include O ₄ , TiCo ₂ O ₄ , ZnFe ₂ O ₄ , FeCo ₂ O ₄ , CoFe ₂ O ₄ , MgCo ₂ O ₄ , and Co ₃ O ₄ .

  In general, the cell connecting member often has a complicated shape, and in order to suppress deterioration such as an increase in the oxide film and the occurrence of Cr poisoning, it is necessary to form a deterioration preventing film. It is desirable that the deterioration preventing film is dense and has a uniform film thickness. When the film thickness is non-uniform, the part where the film thickness is too large is subject to thermal stress (often due to a mismatch in the thermal expansion coefficient of the members to be joined), and cracking or peeling is likely to occur. Therefore, the part where the film thickness is too small cannot sufficiently exert the function of preventing deterioration (suppression of the increase in the oxide film of the alloy, suppression of Cr poisoning), and the problem that the deterioration of the part is difficult to be suppressed is likely to occur.

Therefore, it is necessary to study a film forming method capable of realizing uniform film formation on a cell connecting member having a complicated shape.
Examples of general film forming methods include the following.
For example, it can be formed by a wet coating method or a dry coating method.
Examples of the wet coating method include a screen printing method, a doctor blade method, a spray coating method, an ink jet method, a spin coating method, a dip coating, an electroplating method, an electroless plating method, and an electrodeposition coating method. Examples of dry coating methods include vapor deposition, sputtering, ion plating, chemical vapor deposition (CVD), electrochemical vapor deposition (EVD), ion beam, laser ablation, and atmospheric pressure plasma. Examples thereof include a film forming method, a low pressure plasma film forming method, and a thermal spraying method. Examples thereof include a pressure plasma film forming method and a thermal spraying method.

However, as a dry coating method, the CVD / EVD method, the thermal spraying method, and the like have drawbacks such as a complicated process for forming the protective film, and the composition of the protective film is not stable. It is also considered to form a protective film by a laser ablation method. (Patent Document 1)
In addition, if laser ablation is used, the manufacturing cost is higher than that of CVD / EVD or thermal spraying, so in reality, when wet coating is used as a technology that can manufacture a protective film at low cost. There are many.

  As described above, various materials are used as protective films in order to suppress Cr poisoning and oxidative deterioration of the substrate. The base material used for the SOFC cell connection member is often formed in a complicated shape by a molding method such as press working, and the point is whether a dense protective film can be formed on the entire surface with a uniform film thickness. If a dry coating method (sputtering, PLD, laser ablation) is employed, a relatively uniform film thickness can be realized. However, the film formation cost is relatively high. From the viewpoint of an inexpensive film formation process considering mass productivity, wet coating is preferable.

  Examples of the wet coating method include a screen printing method, a doctor blade method, a spray coating method, an ink jet method, a spin coating method, a dip coating, an electroplating method, an electroless plating method, and an electrodeposition coating method.

  When a metal oxide film is formed by a wet coating method, the metal oxide itself has almost no binding property, so a mixed solution of metal oxide fine particles and a resin composition is used to form metal oxide fine particles and a resin. A method in which a metal oxide is used as a main component is employed by performing a film forming step for forming a film made of and removing a resin component from the film.

  However, in such a method, first, a coating film in which metal oxide fine particles are dispersed in a resin-flowable manner from the mixed solution is generated. Therefore, it is preferable to remove the resin component by baking while maintaining the state of the coating. That is, it is considered that a uniform protective film is formed by forming a uniform film from the mixed solution, maintaining it as it is, and performing firing and sintering.

However, in practice, even if a uniform film is formed in this way and fired / sintered, the obtained protective film usually has a non-uniform film thickness distribution than the first film. is there. In particular, when the coating film is formed on the surface of a substrate having a complicated shape, for example, there is a fact that the ratio of the film thickness between the rolled surface of the base material with the thickest film thickness and the thinnest corner is increased, There is a need for a protective film manufacturing method in which the film thickness ratio is less likely to increase before and after sintering.
Therefore, the present inventors have proposed a technique for suppressing an increase in the film thickness ratio by controlling the rate of temperature rise when firing the protective film, as described in Patent Document 2.

Japanese Patent Laid-Open No. 05-174853 JP 2012-204008 A

  As described above, a non-uniform protective film having a large film thickness ratio has a problem that it easily causes cracking and peeling. To solve this problem, the technique described in Patent Document 2 is actually applied to various substrates. The present inventors have found that the problem cannot be solved even if applied.

  Therefore, when the above-mentioned problem cannot be solved, the conditions under which the protective film cracks and peels are examined in detail. After performing the electropolishing step of electropolishing the surface of the substrate, the metal oxide is oxidized. It is found that cracks and delamination are likely to occur in the protective film, especially when performing a film formation process that forms a film composed of metal oxide fine particles and a resin using a mixed liquid of material fine particles and a resin composition. Even when the polishing step is performed, a technique for making the protective film difficult to crack or peel off is desired.

  In view of the above situation, an object of the present invention is to provide a technique capable of easily forming a protective film that is unlikely to be cracked or peeled on the surface of an alloy or the like containing Cr used in SOFC.

[Configuration 1]
The characteristic configuration of the protective film forming method of the present invention for achieving the above object is as follows:
A protective film forming method for forming a protective film on a surface of a base material of an alloy or oxide containing Cr used for a solid oxide fuel cell by an electrodeposition coating method,
After performing an electropolishing step of electropolishing the surface of the substrate,
Using a mixed liquid of the metal oxide fine particles and the resin composition, a film forming step of forming a film made of the metal oxide fine particles and the resin is performed,
The base material having the coating film formed on the surface thereof is put into a furnace maintained at a temperature higher than a weight stable temperature (endothermic peak) at which the endotherm accompanying the weight reduction when the resin heats the coating film is maximized. And performing a firing step of firing the coating film,
Furthermore, it is in the point which performs the sintering process which forms the protective film which consists of a metal oxide by sintering the film obtained at the said baking process.

[Operation effect 1]
By performing the film forming step, a film in which a mixed liquid of metal oxide fine particles and a resin composition is adhered is formed on the surface of the base material. This coating film is formed by the metal oxide fine particles and the resin composition as main components, and the metal oxide fine particles are aggregated and integrated as the resin component is polymerized. By removing the resin component from the coating, a protective film in which the metal oxide fine particles aggregate to form a coating can be formed.

  In addition, by performing the electrolytic polishing step, it is possible to maintain the smoothness of the rolled surface of the base material, or to remove burrs that occur in the portion where the shear force worked when molding the base material shape, Uneven coating of the coating can be suppressed. If burrs or uneven coating occurs, it will cause deterioration, so that an improvement in durability can be expected by the electrolytic polishing process.

  According to the present inventors, in firing this film, in the process of raising the temperature of the film to a temperature range where the resin component is burned and removed, the thinnest rolling surface of the substrate having the largest film thickness is the thinnest. It was found that the phenomenon of increasing the film thickness ratio with the corners was observed. This phenomenon occurs when the resin component in the coating passes through the temperature range where the resin component softens and fluidizes in the process of being heated to the temperature range where the combustion is removed. It can be considered that this is due to the movement of the resin component so as to gather in the portion where the resin component tends to adhere on the base due to tension. That is, the resin moves from a portion having a large surface area relative to the amount of resin such as a corner portion of the base material to a portion having a small amount of resin relative to the surface area such as a rolled surface of the base material. It is thought to change to a large, rounded shape.

  However, as described above, after performing the electropolishing step of electropolishing the surface of the base material, a coating composed of the metal oxide fine particles and the resin is formed using a mixed liquid of the metal oxide fine particles and the resin composition. It has been found that when the film forming process to be formed is performed, cracks and peeling are likely to occur particularly in the protective film in the subsequent baking process. Therefore, as a result of intensive studies by the present inventors, when a pinhole is generated in the protective film in the firing process, a phenomenon has been found in which cracking or peeling occurs starting from the pinhole. This is because during the firing, when the coating is bonded to the surface of the substrate surface after electropolishing, the adhesion between the coating and the substrate is uneven due to a slight difference in the degree of firing during the firing process. Therefore, it is considered that cracks and peeling occur starting from the bubbles due to the difference in thermal expansion and shrinkage between the coating and the substrate.

  Therefore, various investigations were made on the temperature raising conditions in the firing step, and the film was heated to a temperature higher than the weight stable temperature at which the endothermic amount associated with the weight loss when the resin heated the film was maximized, The coating film is rapidly heated to shift to an environment in which the resin component is immediately burned and removed, and a protective film can be formed under the condition that the degree of adhesion between the coating film and the substrate is less likely to cause unevenness and less likely to generate bubbles. As a result, it has become possible to form a protective film having a uniform thickness under conditions where cracks and peeling are unlikely to occur.

  In addition, the weight stable temperature (endothermic peak) at which the endothermic amount accompanying the weight reduction when the resin as the weight stable temperature heats the coating is maximized is higher than the upper limit temperature at which the resin softens and fluidizes, The temperature is in a temperature range slightly higher than the resin burnout temperature at which the resin can be burned and removed from the coating, and the coating can be quickly baked without causing uneven heating and causing the resin to disappear quickly.

[Configuration 2]
In addition, the characteristic configuration of the protective film forming method of the present invention for achieving the above object is as follows:
A protective film forming method for forming a protective film on a surface of a base material of an alloy or oxide containing Cr used for a solid oxide fuel cell by an electrodeposition coating method,
After performing an electropolishing step of electropolishing the surface of the substrate,
Using a mixed liquid of the metal oxide fine particles and the resin composition, a film forming step of forming a film made of the metal oxide fine particles and the resin is performed,
The base material formed by forming the coating film on the surface thereof is put into a furnace maintained at a temperature higher than a weight stable temperature at which the weight loss when the resin is burned and removed from the coating film is stabilized, and the coating film is fired. Perform the firing process,
Furthermore, it is in the point which performs the sintering process which forms the protective film which consists of a metal oxide by sintering the film obtained at the said baking process.

[Operation effect 2]
In addition, the weight stabilization temperature at which the weight reduction when the resin is burned and removed from the coating as the weight stabilization temperature is the maximum endothermic amount due to the weight reduction when the resin heats the coating. The temperature range is higher than the weight stable temperature, and the resin is quickly lost, and the coating temperature can be quickly baked without causing uneven heating.

  Therefore, the coating film is heated more rapidly to shift to an environment where the resin component is immediately burned and removed, and a protective film is formed under the condition that the degree of adhesion between the coating film and the substrate is less likely to cause unevenness and less likely to generate bubbles. As a result, a protective film having a uniform thickness can be formed under conditions where cracks and peeling do not easily occur.

[Configuration 3]
The resin can be an acrylic resin.

[Operation effect 3]
As the resin, it is considered that the same phenomenon occurs in the thermoplastic resin in general, and it can be applied to any resin that softens and fluidizes as a resin contained in a mixed solution for electrodeposition coating. However, acrylic resins that are widely used in electrodeposition coating applications are preferably used.

  It is known that the acrylic resin exists stably without causing a problem of physical properties until it is burned and removed in the baking step, and is softened and fluidized to a degree that can be molded at about 260 ° C. In addition, the resin is burned out at an appropriate temperature of about 350 ° C. to 500 ° C., and the resin reaches 400 ° C. or more. It can be said that it is preferable in terms of handling since the weight loss when being burned and removed from the coating is stable at a temperature of 0 ° C. or higher.

  Explaining the above configuration as an example, the film obtained by anionic electrodeposition coating containing an acrylic resin becomes a rapidly sintered film by rapidly raising the temperature to 500 ° C. or more, and is strong on the substrate. Since it adheres closely to the film, it becomes a film that does not easily crack or peel off. The weight stable temperature to be raised here is almost the same temperature range with some variations in ordinary resins, but the temperature of the coating should be raised sufficiently quickly and sintered even if the temperature exceeds 500 ° C. Can do. However, in consideration of heat shock to the member provided with the anion electrodeposition coating by being rapidly brought to a high temperature from room temperature, damage to the firing furnace, etc., it is considered that 750 ° C. or lower is desirable.

[Configuration 4]
The metal oxide fine particles include Zn—Co-based spinel oxides made of (Zn _x Co _1-x ) Co ₂ O ₄ (0.45 ≦ x ≦ 1.00), or CoMn ₂ O _4. Co-Mn spinel oxide fine particles selected from MnCo ₂ O ₄ , Mn (Mn _0.25 Co _0.75 ) ₂ O ₄ , and (Mn _0.5 Co _.5 ) Co ₂ O ₄ can be used.

[Operation effect 4]
As the metal oxide fine particles, (Zn _0.15 Co _0.85 ) ₃ O ₄ was used, but a part of La in LaMO ₃ (for example, M = Mn, Fe, Co) was replaced with alkaline earth metal AE (AE = Sr, (La, AE) MO ₃ perovskite oxide substituted with Ca), 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 , etc. Can
In particular, a Zn—Co-based spinel oxide made of (Zn _x Co _1-x ) Co ₂ O ₄ (0.45 ≦ x ≦ 1.00), or CoMn ₂ O ₄ , MnCo ₂ O ₄ , Mn (Mn Co—Mn spinel oxide fine particles selected from _0.25 Co _0.75 ) ₂ O ₄ and (Mn _0.5 Co _.5 ) Co ₂ O ₄ are preferable.
In this case, there is an advantage that the protective film to be formed is dense and has high strength, high adhesion to the base material, and high effect of preventing scattering of Cr contained in the base material.

  Therefore, even if electrolytic polishing is performed on the surface of a Cr-containing alloy or oxide base material used for SOFC cells, a dense, uniform and durable protective film with little peeling can be easily obtained. Now available to form.

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 The graph which shows the temperature rising process of each Example and a comparative example TG / DTA analysis results of coating weight fluctuation and heat flow due to firing External plan view of protective film in each comparative example and example

  Hereinafter, a protective film forming method, a SOFC cell connecting member, and a SOFC cell for forming a protective film on the surface of a base material made of an alloy or oxide containing Cr used in the SOFC of the present invention will be described. 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 SOFC will be described as an example. However, the present invention is applicable 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 base material of the cell connection member 1 is formed in a groove plate shape that allows connection while forming the air flow path 2a and the fuel flow path 2b between the single cells 3. Use what you have. As a method of processing such a substrate surface, various known processes such as rolling or etching a rod-like or plate-like substrate can be employed.

  The shaped substrate is electropolished in an electropolishing liquid bath by using the base as an anode and the counter electrode as an insoluble metal plate and performing electrolysis for a certain period of time.

  Then, a protective film is provided on the surface of the electropolished base material to form the cell connection member 1.

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

<Protective film>
The protective film 12 is, for example, an etching process for forming an uneven surface on the surface of the base material 11 made of ferritic stainless steel containing 22% Cr, and an electropolishing process for performing electropolishing on the surface of the base material. For example, a film containing metal oxide fine particles such as ZnCo ₂ O ₄ , (Zn _0.15 Co _0.85 ) ₃ O _4, and Co—Mn spinel and a resin is formed, and the film is baked. Performing a firing process for forming a fired film in which the resin component in the electrodeposition coating film is burned off, and further performing a sintering process for sintering the fired film to form a protective film 12 made of a metal oxide. It is formed by. An electrodeposition process for forming an electrodeposition coating film by an anion electrodeposition coating method can be employed to form the film. An anionic resin such as polyacrylic acid is mixed with metal oxide fine particles as the resin. A mixed liquid containing (metal oxide fine particles: anionic resin) = (0.5: 1) to (3: 1) in a ratio (mass ratio) can be used.

  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.

<Comparative Example 1>
First, as a comparative example, an uneven surface is formed on the base material by etching, and without electropolishing.

(Electrodeposition coating)
Metal oxide fine particles such as (Zn _0.15 Co _0.85 ) ₃ O ₄ [particle diameter 0.5 μm] are dispersed so as to be 100 g per liter of electrodeposition liquid, and contain an anionic resin such as polyacrylic acid. Electrodeposition coating was performed using the mixed solution. Here, (metal oxide fine particles: anionic resin) = (1: 1) (mass ratio).

  An uncured electrodeposition coating film is formed on the surface of the base material 11 by energizing the electrode plate of the SUS304 with a negative polarity using the mixed solution as a positive electrode and the base material 11 as a counter electrode.

The electrodeposition coating is carried out according to a known method, for example, by immersing the base material 11 completely or partially in an energization tank filled with the mixed solution as an anode and energizing.
Electrodeposition coating conditions are not particularly limited, and a wide range is available depending on various conditions such as the type of metal that is the substrate 11, the type of the mixed solution, the size and shape of the current-carrying tank, and the use of the resulting cell connection member 1. Usually, the bath temperature (mixed solution temperature) is about 10 to 40 ° C., the applied voltage is about 10 to 450 V, the voltage application time is about 1 to 10 minutes, and the liquid temperature of the mixed solution is 10 to 40 ° C. do it.
In addition, the film thickness of the electrodeposition coating film can be controlled by changing the electrodeposition voltage and the electrodeposition time. Various pretreatments can also be performed on the substrate.

  By heating the substrate 11 on which the uncured electrodeposition coating film is formed, a cured electrodeposition coating film is formed on the surface of the substrate 11.

  The heat 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.

(Heat treatment, firing process and sintering process)
An electrodeposition coating film formed using (Zn _0.15 Co _0.85 ) ₃ O ₄ fine particles: resin = 1: 1 (mass ratio) as the mixed solution was put into an electric furnace at 350 ° C. and held for 1 hr. The electrodeposition coating film was dried and cured. Next, the temperature was raised to 500 ° C. for 1 hour and held for 2 hours to burn off the resin component in the electrodeposition coating film (firing step). Furthermore, the temperature was raised to 1000 ° C. for 2 hours, and the temperature was maintained at that temperature for 2 hours to sinter the metal oxide fine particles in the electrodeposition coating film, and then the electric furnace power was turned off and gradually cooled. That is, a heat treatment, a firing process, and a sintering process were performed through a temperature raising process indicated by a thick solid line in FIG. Thereby, the cell connection member test piece which had the adhesive force with respect to the base material 11 and formed the dense protective film 12 was obtained. In this case, the base material is burned and removed from the coating film from the cured state maintaining temperature lower than the lower limit temperature at which the resin softens and fluidizes, and higher than the upper temperature limit at which the resin softens and fluidizes. The temperature raising process is completed in a very short time (within 1 minute) until the temperature is reached, and the resin component starts to burn out.

  Further, it can be seen that both the rolled surface and the etched surface of the base material in Comparative Example 1 are less peeled, and when electropolishing is not performed, it is possible to provide a protective film that is free from cracks and peeling. (See FIG. 6 (c)). However, if there are sharp burrs that occur during etching, it is difficult to form a uniform film, even with electrodeposition coating with high uniform film formation, and it is difficult to ensure sufficient durability for practical use. There is.

(Comparative Example 2)
The substrate used in Comparative Example 1 was subjected to an electrolytic polishing treatment and similarly tested.
By the electrolytic treatment, the rolled surface and the etched surface are smoothed from the state having the sharp burr without the electrolytic treatment shown in FIG. 3A, and there is no sharp portion in the edge portion as shown in FIG. 3B. A smooth surface is formed.

  In the electrolytic polishing treatment, 20 μm of the surface was dissolved according to a conventional method using the base material as an anode.

(Electrodeposition coating)
Metal oxide fine particles such as (Zn _0.15 Co _0.85 ) ₃ O ₄ [particle diameter 0.5 μm] are dispersed so as to be 100 g per liter of electrodeposition liquid, and contain an anionic resin such as polyacrylic acid. Electrodeposition coating was performed using the mixed solution. Here, (metal oxide fine particles: anionic resin) = (1: 1) (mass ratio).
An uncured electrodeposition coating film is formed on the surface of the base material 11 by energizing the electrode plate of the SUS304 with a negative polarity using the mixed solution as a positive electrode and the base material 11 as a counter electrode.
The electrodeposition coating is carried out according to a known method, for example, by immersing the base material 11 completely or partially in an energization tank filled with the mixed solution as an anode and energizing.
Electrodeposition coating conditions are not particularly limited, and a wide range is available depending on various conditions such as the type of metal that is the substrate 11, the type of the mixed solution, the size and shape of the current-carrying tank, and the use of the resulting cell connection member 1. Usually, the bath temperature (mixed solution temperature) is about 10 to 40 ° C., the applied voltage is about 10 to 450 V, the voltage application time is about 1 to 10 minutes, and the liquid temperature of the mixed solution is 10 to 40 ° C. do it.
In addition, the film thickness of the electrodeposition coating film can be controlled by changing the electrodeposition voltage and the electrodeposition time. Various pretreatments can also be performed on the substrate.
By heating the substrate 11 on which the uncured electrodeposition coating film is formed, a cured electrodeposition coating film is formed on the surface of the substrate 11.
The heat 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.

(Heat treatment, firing process and sintering process)
An electrodeposition coating film formed using (Zn _0.15 Co _0.85 ) ₃ O ₄ fine particles: resin = 1: 1 (mass ratio) as the mixed solution was put into an electric furnace at 350 ° C. and held for 1 hr. The electrodeposition coating film was dried and cured. Next, the temperature was raised to 500 ° C. for 1 hour and held for 2 hours to burn off the resin component in the electrodeposition coating film (firing step). Furthermore, the temperature was raised to 1000 ° C. for 2 hours, and the temperature was maintained at that temperature for 2 hours to sinter the metal oxide fine particles in the electrodeposition coating film, and then the electric furnace power was turned off and gradually cooled. That is, a heat treatment, a firing process, and a sintering process were performed through a temperature raising process indicated by a thick solid line in FIG. Thereby, the cell connection member test piece which had the adhesive force with respect to the base material 11 and formed the dense protective film 12 was obtained. In this case, the base material is burned and removed from the coating film from the cured state maintaining temperature lower than the lower limit temperature at which the resin softens and fluidizes, and higher than the upper temperature limit at which the resin softens and fluidizes. The temperature raising process is completed in a very short time (within 1 minute) until the temperature is reached, and the resin component starts to burn out.

  As a result, although a film having a thickness of about 10 μm could be formed on both the rolled surface and the etched surface, many sites where the protective film was peeled were observed in the sintering process. (See Fig. 6 (b) and (d)) If the peeling state of the protective film is further enlarged and observed, cracks and peeling will enter the sintered protective film starting from the pinholes generated in the coating during firing. It was possible to observe the situation where the film layer was cracked and peeled. (See Fig. 6 (d) and (e))

  Comparing Comparative Example 1 and Comparative Example 2, the result of sintering the coating is greatly different depending on the presence or absence of the electropolishing treatment. By performing the electropolishing treatment, the adhesion of the protective film to the substrate is greatly reduced, It has been found that it is difficult to obtain a protective film having a sufficient strength.

(Example)
The base material used in Comparative Example 2 was subjected to a heating process, a firing process, and a sintering process through a temperature raising process shown in FIG. That is, the base material on which the electrodeposition coating film is formed is put into an electric furnace at 500 ° C. and held for 2 hours, the electrodeposition coating film is dried and cured, and the resin component in the electrodeposition coating film is burned out. (Firing process). Furthermore, the temperature was raised to 1000 ° C. for 2 hours, and the temperature was maintained at that temperature for 2 hours to sinter the metal oxide fine particles in the electrodeposition coating film, and then the electric furnace power was turned off and gradually cooled. Thereby, the cell connection member in which the protective film 12 was formed was obtained.

  As a result, it was confirmed that both the rolled surface and the etched portion had no adhesion, no cracks, no peeling, no float, etc., and had a close contact with the substrate 11 and a dense protective film was formed (FIG. 6). (See (b) and (f)). Moreover, the formation state of the protective film 12 at this time is as shown in Table 2, and it was found that a strong protective film was obtained with a uniform film thickness as in Comparative Example 1.

(Confirmation experiment)
An experiment was conducted to verify the factors that greatly change the properties of the protective film due to the difference in the heat treatment temperature in the above examples.
FIG. 5 shows the results of TG / DTA analysis of weight fluctuation and heat flow when forming a film on the substrate surface in the same manner as in the example. The experiment was performed in air, and the rate of temperature increase was 10 ° C./min.

  From the figure, as the drying of the coating proceeds with heating, the resin component in the coating flows from about 250 ° C., begins to thermally decompose, begins to absorb a large amount of heat, and is higher than the upper limit temperature at which the resin softens and fluidizes, It is considered that the resin reaches the resin burning temperature at which the resin can be burned and removed from the coating (region indicated by A in FIG. 4). When the temperature is further raised to 350 ° C. to 400 ° C., it reaches a weight stable temperature at which the endothermic amount accompanying the weight reduction when the coating is heated is maximized, and it is considered that pyrolysis and gasification are progressing (FIG. 4). Region shown in middle B). After that, although the weight of the coating continues to decrease, it can be seen that the resin component disappears completely at 500 ° C. and reaches a weight stable temperature at which the weight reduction when being burned and removed from the coating reaches a stable temperature (region indicated by C in FIG. 4). ).

Considering this situation and experimental data, it can be seen that cracking and peeling tend not to occur as the time required to eliminate the resin component is shorter. The electrodeposition coating film is mostly composed of a resin component in a volume ratio, and it is assumed that a large stress is generated when it disappears.
In addition, cracks and peeling are thought to occur starting from the bubble component contained in the coating, but when the time to disappear the resin is short, it is sufficiently shorter than the time required for cracks and peeling to progress. It is estimated that a good film can be obtained.

  That is, as the weight stabilization temperature, 350 ° C. to 400 ° C. “the weight stabilization temperature at which the endothermic amount accompanying the weight reduction when the coating is heated is the maximum” or 500 ° C. It can be seen that the protective film forming method of the present application can be satisfactorily realized at “weight stable temperature at which weight reduction is stable”.

In the above embodiment, (Zn _0.15 Co _0.85 ) ₃ O ₄ is used as the metal oxide fine particles, but a part of La in LaMO ₃ (for example, M = Mn, Fe, Co) is replaced with alkaline earth. Perovskite oxide of (La, AE) MO ₃ substituted with metal AE (AE = Sr, Ca), 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 , etc. can be used.

  According to the method for forming a protective film of the present invention, it is possible to provide a fuel cell equipped with a cell connection member and a SOFC cell that are highly durable 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 (4)

A protective film forming method for forming a protective film on a surface of a base material of an alloy or oxide containing Cr used for a solid oxide fuel cell by an electrodeposition coating method,
After performing an electropolishing step of electropolishing the surface of the substrate,
Using a mixed liquid of the metal oxide fine particles and the resin composition, a film forming step of forming a film made of the metal oxide fine particles and the resin is performed,
The base material having the coating film formed on the surface thereof is put into a furnace maintained at a temperature higher than a weight stable temperature (endothermic peak) at which the endotherm accompanying the weight reduction when the resin heats the coating film is maximized. And performing a firing step of firing the coating film,
Furthermore, the protective film formation method which performs the sintering process which sinters the film obtained at the said baking process and forms the protective film which consists of metal oxides. A protective film forming method for forming a protective film on a surface of a base material of an alloy or oxide containing Cr used for a solid oxide fuel cell by an electrodeposition coating method,
After performing an electropolishing step of electropolishing the surface of the substrate,
Using a mixed liquid of the metal oxide fine particles and the resin composition, a film forming step of forming a film made of the metal oxide fine particles and the resin is performed,
The base material formed by forming the coating film on the surface thereof is put into a furnace maintained at a temperature higher than a weight stable temperature at which the weight loss when the resin is burned and removed from the coating film is stabilized, and the coating film is fired. Perform the firing process,
Furthermore, the protective film formation method which performs the sintering process which sinters the film obtained at the said baking process and forms the protective film which consists of metal oxides.   The protective film forming method according to claim 1, wherein the resin is an acrylic resin. The metal oxide fine particles are Zn—Co based spinel oxides composed of (Zn _x Co _1-x ) Co ₂ O ₄ (0.45 ≦ x ≦ 1.00), or CoMn ₂ O ₄ , MnCo _{2. 4.} The fine particle of a Co—Mn spinel oxide selected from O ₄ , Mn (Mn _0.25 Co _0.75 ) ₂ O ₄ , (Mn _0.5 Co _.5 ) Co ₂ O ₄ . The method for forming a protective film according to Item.