JPH07118328B2 - Method for producing molten carbonate fuel cell constituent material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a molten carbonate fuel cell constituent material having excellent corrosion resistance, marketability, processability, and economic efficiency.

[Prior Art] A molten carbonate fuel cell has high energy conversion efficiency,
It is promising as a next-generation power source because it has advantages such as no pollution and no need for expensive catalysts. Currently, small-scale batteries are assembled to study durability and stacking technology. , Development for large scale, and development of battery electrode materials and other constituent materials.

[Problems to be Solved by the Invention] As a current problem, it is mentioned that battery constituent materials such as electrodes and separators of molten carbonate fuel cells are generally susceptible to corrosion and do not have long-term durability. .

Means for applying a complex oxide such as perovskite in order to solve the above-mentioned problems relating to corrosion resistance have been studied, and further, it has been proposed to form an oxide layer mainly composed of alumina on the surface of the Fe-Fr-Al alloy. (Japanese Patent Laid-Open No. 58-217677
However, none of them is preferable from the viewpoints of marketability, processability and economic efficiency.

In view of the above-mentioned problems, it is an object of the present invention to provide a method for producing a molten carbonate fuel cell constituent material which is excellent in corrosion resistance and has good marketability, processability and economical efficiency.

[Means for Solving the Problems] A method for producing a molten carbonate fuel cell constituent material of the present invention that has been able to solve the above problems is to include Al and Co and / or Ni as a simple metal or an alloy. By coating the surface of the iron-based material as an oxide or a combination of these, and then heat treating it, spinel-type oxides are generated on the surface of the iron-based material and become amorphous, and the adhesion with the surface of the iron-based material is enhanced. This is the basic gist, and by using Cr in combination with the above Al, a more excellent effect can be obtained. When the iron-based material serving as the base material is Cr-Ni-containing steel, it is not necessary to coat the above Cr or Ni, and such an implementation is also included in the technical scope of the present invention.

[Operation] The molten carbonate fuel cell constituent material obtained by the method of the present invention is an iron-based material or a Cr-based material excellent in marketability, processability, and economy.
Ni-containing steel is adopted as the base material, and by coating and heat treatment respectively, (1) Al and Co and / or Ni on the surface of the iron-based material (in the case of the first invention) (2) Surface of the iron-based material And Al and Cr and Co and / or Ni (in the case of the second invention) (3) Al on the surface of the Cr-Ni containing steel (in the case of the third invention) (4) Al on the surface of the Cr-Ni steel Co (in the case of the fourth invention) is diffused as a simple metal, an alloy, an oxide, or a combination thereof. When such a molten carbonate fuel cell constituent material is immersed in a molten carbonate bath containing Li ₂ CO ₃ , Al forms a lithium aluminate film and Cr forms a lithium chromate film on the material surface, respectively. In particular, the former exhibits excellent corrosion resistance by itself, and the latter exhibits excellent corrosion resistance in collaboration with the former. On the other hand, Co and Ni are oxides having a spinel type crystal structure (FeO
・ Al ₂ O ₃ and FeO · Cr ₂ O ₃ etc.) have the effect of making them amorphous. If the surface of the base material is spinel-type oxide, even if a corrosion resistant coating such as lithium aluminate or lithium chromate is formed after immersion in a molten carbonate bath as described above, the adhesion to the base material is insufficient and sufficient. It cannot exhibit corrosion resistance. However, since Co and Ni amorphize the spinel type oxide, the adhesion between the base material and the lithium aluminate or lithium chromate coating becomes strong, so that the corrosion resistance derived from the above corrosion resistant coating can be sufficiently exerted. Become.

Next, (a) the action of the components diffused in the surface layer in the molten carbonate bath, (b) the coating method, and (c) the heat treatment method will be described in detail.

(A) Action of each component diffused in the surface layer in the bath Al: Al forms a very stable lithium aluminate film in the molten carbonate bath, which significantly improves the corrosion resistance, but the melting point is low, so It is necessary to form an alloy layer by heat treatment, which is an essential condition.

Cr: Cr is an element that forms a stable lithium chromate coating in a molten carbonate bath, but this coating alone is not sufficient for the anticorrosion effect of the base metal, and it does not coexist with Al or Al alloys or Al oxides. Form a corrosion resistant coating. 1% or more Cr-based low alloy steel, preferably 3% or more Cr-based low alloy steel
Since Cr is supplied, a film with excellent corrosion resistance can be formed without coating. Here, the role of Cr is considered to have a catalytic action to promote the formation of honey film,
Cr-based low alloy steel provides sufficiently good corrosion resistance.

Co: An element effective in improving the adhesion between the iron-based base material and lithium chromate or lithium aluminate, and has the effect of improving the adhesion by amorphizing the spinel oxide formed on the surface of the iron-based material.

It has the same effect as Ni: Co, and also has the effect of improving the anticorrosion performance of the coating by coexisting in an oxide of Cr or Al.

(B) Coating method Any method such as plating (including dispersion plating), thermal spraying, vapor deposition (CVD, PVD), and rolling may be used. The processing thickness is preferably 0.1 to 200 μm. If it is too thin, the corrosion resistant coating is not sufficiently formed, and if it is too thick, the effect reaches saturation and, conversely, problems such as peeling tend to occur. As a basic coating process, it is better to treat Fe, Ni, Co, and Cr (oxide-containing), which easily forms spinel-type oxides, and then Al (oxide-containing) on top of them. (Cr forms a lithium chromate film with excellent corrosion resistance similar to Al, and easily forms spinel oxide with Fe like Ni and Co). It goes without saying that it is best to carry out thin and repeated treatments, as long as it is economically possible to facilitate diffusion.

(C) Heat treatment method: After performing surface treatment on the base material at 300 to 1200 ° C, heat treatment in the above temperature range to diffuse the coating metal (hereinafter referred to as heat treatment diffusion) and amorphize the spinel oxide. Improves mutual adhesion and enhances anticorrosion effect. The heat treatment atmosphere is not particularly limited. If the temperature is lower than 300 ° C, it takes a long time to process. At 1200 ° C or higher, performance deterioration of the base material occurs.

[Example] A 25 x 35 x 5 mm test piece was cut out from the commercial grade ordinary steel, low alloy steel, ferritic stainless steel, martensitic stainless steel, and austenitic stainless steel sheet shown in Table 1, and further Table 1 After coating under the conditions shown in (coating order: left to right), heat treatment diffusion (650 to 700 ° C., 0.5 to 2 hours) was performed. At this time, the metal form was in a diffused state as it was at the time of coating. Then molten carbonate (62mol% Li ₂
CO ₃ + 38mol% K ₂ CO ₃ ) It was exposed to the environment for 100 hours, and the corrosion rate was calculated from the weight change before and after the exposure. The result is first
Shown in the table.

Nos. 1 to 8 are according to the present invention, and No. 1 is the one in which Co plating and Cr plating in an aqueous solution on the surface of ordinary steel, then Al vapor deposition plating, and heat treatment diffusion, No. 2 and 3 Is a standard steel that has been plated with Ni with an oxide of aluminum and chromium dispersed on the surface, and has been subjected to heat treatment diffusion. Nos. 4 and 5 are low alloy steels as the base material, and Nos. 6 to 8 are The base material is stainless steel. All have excellent corrosion resistance as compared with Comparative Examples SUS316 and nickel. That is, even if the base material is ordinary steel or low alloy steel, it has corrosion resistance higher than SUS316. Also,
Even when the base material was SUS316, the corrosion resistance was improved several times or more by the coating process and heat treatment diffusion.

The present embodiment is applied to a steel plate, but it goes without saying that the present invention is also applied to a porous electrode material.

[Advantages of the Invention] As described above, the molten carbonate fuel cell constituent material obtained by the method of the present invention uses the iron-based material and the Cr-Ni-containing steel as the base material, and therefore is excellent in marketability, workability, and economic efficiency. However, it is excellent in corrosion resistance because a lithium aluminate or a lithium aluminate and lithium chromate film having good adhesion is easily formed on the surface of the material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Fujiwara 3-4-6 Matsugaeda-cho, Kita-ku, Kobe-shi, Hyogo (72) Inventor Koji Torii Hiraizu 580, Yoneda-cho, Kakogawa-shi, Hyogo (72) Inventor Takenori Nakayama Hyogo 1-3-1 -604 Uozaki Naka-cho, Higashinada-ku, Kobe-shi, Japan Judge's panel Judge Yoshiyuki Nishi Judge Hideyuki Ono Judge Asahi Aizawa (56) Reference JP 59-201371 (JP, A) JP 59 -75575 (JP, A) JP-A-59-141174 (JP, A)

Claims (4)

[Claims] 1. A spinel-type oxide is formed on the surface of an iron-based material by coating Al and Co and / or Ni on the surface of the iron-based material as a simple metal, an alloy, an oxide, or a combination thereof, and then performing heat treatment. A method for producing a molten carbonate type battery constituent material, which comprises producing a substance and amorphizing it to improve the adhesion to the surface of the iron-based material. 2. Al and Cr, and Co and / or Ni,
By coating the surface of the iron-based material as a simple metal, an alloy, an oxide, or a combination thereof, and then performing heat treatment, a spinel-type oxide is generated on the surface of the iron-based material, and the spinel-type oxide is amorphized. A method for producing a molten carbonate type battery constituent material, which is characterized by enhancing adhesion. 3. A Cr-Ni-containing steel surface is coated with Al or an oxide of Al and then heat-treated to form Cr.
A method for producing a molten carbonate type battery constituent material, which comprises forming a spinel type oxide on the surface of a Ni-containing steel and amorphizing the oxide to improve adhesion with the surface of the Cr-Ni containing steel. 4. A spinel oxide is produced on the surface of Cr-Ni-containing steel by coating Al and Co on the surface of Cr-Ni-containing steel as a simple metal, an alloy, an oxide or a combination thereof and then heat-treating. A method for producing a molten carbonate type battery constituent material, characterized by increasing the adhesion to the surface of a Cr-Ni containing steel by making it amorphous.