KR100660212B1 - Metal interconnection material for solid oxide fuel cell having cobalt/lanthanum coating layers and method for preparing the cobalt/lanthanum coating layers - Google Patents

Abstract

Provided are a metallic connecting material for a solid oxide fuel cell which is excellent in oxidation resistance and high temperature conductivity, and a method for coating the metallic connecting material. The metallic connecting material is a ferrite-based stainless steel sheet whose surface is coated on a cobalt coating layer having a thickness of 1-10 micrometers and a lanthanum coating layer having a thickness of 50-1,000 Angstrom. The method comprises the steps of forming a cobalt coating layer on the surface of a ferrite-based stainless steel sheet by an electron beam vapor deposition; and forming a lanthanum coating layer on the cobalt coating layer by an electron beam vapor deposition.

Description

Metal interconnection material for solid oxide fuel cell having cobalt / lanthanum coating layers and method for preparing the cobalt / lanthanum coating layers}

The present invention relates to a metal connection material for a solid oxide fuel cell having a cobalt / lanthanum coating layer and a coating method thereof, and more particularly, to high temperature oxidative resistance and high temperature conductivity by performing cobalt / lanthanum coating on a commercially available ferritic stainless steel sheet. A metal connection material for a solid oxide fuel cell and a coating method thereof.

In general, the solid oxide fuel cell connection material is basically a material that electrically connects the anode of one cell and the cathode of a neighboring cell and physically blocks air gas and fuel gas. Metal connectors have superior properties in terms of processability, economy, electrical conductivity, and thermal conductivity compared to ceramic connectors.

The various alloys that have been used as solid oxide fuel cell metal interconnects so far include Cr-based alloys based largely on Cr, ferritic Fe-Cr alloys based on Fe, and Ni-based superalloys based on Ni. There is this.

Among these alloys, ferritic Fe—Cr alloys are more advantageous in terms of economy and processability in flat solid oxide fuel cells having an operating temperature of 800 ° C. or lower than Cr-based alloys or Ni-based alloys.

Such representative ferritic Fe-Cr alloys include "ZMG232" and "Crofer22APU", which have the same Cr concentration of 22 wt%, 0.5 wt% of Mn, and trace amounts of La.

However, since the metal connecting material forms an oxide on the surface in the solid oxide fuel cell operating environment, the resistance is increased to decrease the electrical conductivity. That is, the electrical conductivity of the metal connecting material is dependent on the electrical conductivity of the oxide formed on the surface rather than the electrical conductivity of the metal itself. Therefore, it is important to form an oxide having excellent conductivity on the surface. This is why most metal connectors for solid oxide fuel cells are designed based on Cr ₂ O ₃ -formers.

However, Cr ₂ O ₃ -former type metal interconnects form volatile Cr (VI) in the solid oxide fuel cell operating environment. These Cr (VI) interferes with the normal electrochemical reaction of the cell and decreases the cell's performance. Act as a factor.

As a result, the metal connecting material for the fuel cell has difficulty in developing due to these two contradictions.

Recently, attempts have been made to develop alloys for metal interconnects and surface treatment techniques for controlling surface characteristics.

In particular, the coating material for surface treatment is sprayed with a perovskite structure oxide such as LSM, LSC, LSCF to increase oxidation resistance and electrical conductivity of existing products and to prevent Cr evaporation. pyrosis), PVD, thermal spraying, slurry coating, etc. in various ways.

However, in the case of such a perovskite ceramic coating, the coating layer should have excellent electron conductivity, similar thermal expansion coefficient to neighboring components, and excellent adhesion, so that peeling should not occur.

In addition, MnCr ₂ O ₄ , CoCr ₂ O ₃ , CoFe ₂ O ₄ of spinel structure at the interface between the coating layer and the substrate after prolonged exposure at high temperature It is advantageous for the same oxide to be formed. Because these oxides are non-insulating, they do not significantly increase the contact resistance at the interface. On the other hand, if an oxide such as SrCrO ₄ or La ₂ O ₃ is formed as a reactant, it should not be overlooked that the electrical conductivity of the coating layer is greatly reduced.

Furthermore, the texture of the coating layer should be dense. This is because it is possible to prevent the movement of oxygen diffused inward through the coating layer from the outside, and to prevent the external diffusion of the Cr component from the substrate. Therefore, even if the coating layer has the same perovskite phase, it may have different properties depending on the components of the coating layer, the structure and composition of the coating layer.

Therefore, since the control of the coating layer has a close relationship with the coating process, an appropriate coating method having an economical coating layer having excellent properties is required.

The present invention has been made in view of the limitations of the prior art as described above, and has been developed to solve this problem, by coating a suitable metal on the surface of a conventional ferritic stainless steel sheet used for a solid oxide fuel cell, the high temperature during operation of the solid oxide fuel cell The main object of the present invention is to provide a solid oxide fuel cell metal interconnect material that maximizes the utilization of the existing ferrite metal interconnect material by forming an oxide having excellent high temperature oxidation resistance and electrical conductivity in an oxidation atmosphere of.

In another aspect, the present invention is to provide a coating method of the metal connection material for a solid oxide fuel cell excellent in oxidation resistance and high temperature conductivity.

In order to achieve the above technical problem, there is provided a metal connection material for a solid oxide fuel cell in which a cobalt coating layer having a thickness of 1-10 μm and a lanthanum coating layer having a thickness of 50-1000 μs are formed on a ferritic stainless steel surface.

In addition, according to the present invention, the oxidation resistance and high temperature conductivity comprising the step of forming a cobalt coating layer on the surface of the ferritic stainless steel sheet using an electron beam deposition method, and forming a lanthanum coating layer on the cobalt coating layer using an electron beam deposition method Provided is a coating method of the metal interconnect material for an excellent solid oxide fuel cell.

Hereinafter, the present invention will be described in detail.

When the ferritic stainless steel sheet such as "SUS444", which is conventionally commercialized, is used without being coated, spinel structured MnCr ₂ O ₄ and corundum structured Cr ₂ O ₃ oxide are formed.

Comparing only the phases of these oxides, it is the same as the "Crofer22APU" alloy or "ZMG232" developed as the solid oxide fuel cell metal coupling material.

However, ferritic stainless steel plates such as "SUS444" have a lower electrical conductivity than "Crofer22APU" alloy or "ZMG232" developed as a solid oxide fuel cell metal coupling material because the concentration of Cr and Mn is small and does not contain rare earth metal components such as La. Falls.

In other words, when ASR (Area Specific Resistance) is measured after oxidizing under the same conditions in a high temperature oxidizing atmosphere with materials "SUS444" and "Crofer22APU", the ASR value of the "Crofer22APU" alloy is small.

This means that the rho (Resistivity) value of the oxide formed on the surface of the "Crofe22APU" material is much smaller than that formed on "SUS444". This is because the "Crofer22APU" alloy is designed to form an oxide layer having excellent electrical conductivity on the surface layer by appropriately adding Mn and Cr with a small amount of La.

The present invention is to improve the properties of the oxide formed on the surface in a high temperature oxidizing atmosphere to reduce the ASR value of the material and to increase the high temperature oxidation resistance, by coating the Co and La in two layers, excellent spinel structure Of CoCr ₂ O ₃ , CoFe ₂ O ₄ The same oxide can be formed. In addition, a small amount of La serves to increase the adhesion of the oxide.

That is, in the present invention, the phase of the oxide formed on the surface of the spinel structure of CoCr ₂ O ₃ , CoFe ₂ O ₄ having excellent high temperature conductivity In order to make, etc., Co metal was selected and coated on the lower layer of the coating layer, and the quality characteristics were determined by changing the thickness of La so as to secure the adhesion of the oxide and at the same time increase the high temperature oxidation resistance of the test piece.

The composition of the coating layer according to the present invention is a lower layer is cobalt, the upper layer is a two-layer coating layer consisting of lanthanum. At this time, it is very important because it greatly affects the adhesion, high temperature oxidation resistance and high temperature conductivity after coating depending on the thickness of lanthanum.

The cobalt coating layer and lanthanum coating layer may be formed on the surface of the ferritic stainless steel sheet by a method commonly known in the art. For example, electron beam deposition may be used to form the cobalt coating layer and the lanthanum coating layer, and deposition conditions may be readily determined by those skilled in the art.

In the present invention, the cobalt layer has a thickness of 1 μm to 10 μm under the coating layer. If the cobalt thickness is 10 μm or more, cobalt oxides such as Co ₃ O ₄ may be formed on the surface of the substrate during operation of the solid oxide fuel cell. Since the conductivity does not increase and the thickness of the cobalt is less than or equal to 1 μm, the function of the coating layer may not be long.

On the other hand, in order to increase the high temperature oxidation resistance of the specimen La should be coated with a thickness of 50Å to 1000Å. The function of La not only increases the adhesion of oxides formed on the surface of the Fe-Cr alloy in the high temperature oxidizing atmosphere, but also reduces the growth rate of the scale, thereby increasing the high temperature oxidation resistance and reducing the ASR value of the material. Play a role. This is because as the growth rate of the scale decreases and the thickness of the scale formed on the surface decreases, the ASR value decreases and thus the conductivity increases. However, if the coating layer of La on the Fe-Cr alloy surface is too small, less than 50 kPa, this effect is lost. And when La is coated with 1000Å or more, insulating La ₂ O ₃ is formed on the surface, the conductivity is lowered. Therefore, the coating layer thickness of lanthanum should be coated with a thickness of 50 kPa to 1000 kPa.

As a result, the present invention is characterized in that a two-layer coating layer made of cobalt having a thickness of 1 μm to 10 μm and lanthanum having a thickness of 50 μm to 1000 μm is formed on the surface of a ferritic stainless steel sheet which is a substrate for a solid oxide fuel cell connection material.

Hereinafter, the present invention will be described in more detail with reference to the following examples.

EXAMPLE

After depositing a deposition object in the alumina crucible to have the composition and thickness of the coating layer according to the present invention, the temperature of the substrate was fixed at 350 ° C. under the coating conditions during vacuum deposition, and the degree of vacuum was kept below 5 × 10 ⁻⁵ torr. , Cobalt and lanthanum were coated one after the other.

Thereafter, the coating was made to test pieces, and the oxidation resistance and high temperature conductivity of the test pieces were evaluated.

At this time, the oxidation resistance was exposed for 1000 hours in an air atmosphere at 700 ℃, and the weight increase of the test piece was measured, the evaluation criteria are ◎, if the weight increase (mg / cm ² ) is less than 0.2, ◎, if 0.5 to 0.5, ○, 0.5 It was set as x as it was above.

In addition, the conductivity of the coating layer was evaluated by measuring the ASR value after exposure for 1000 hours in an air atmosphere at 700 ° C., for example, the evaluation criterion was: ◎ when the ASR value was 0.01 m 2 or less; If it is 0.01-0.015 mm <2>, it is ○; It was set as x if it was 0.015 cm <2> or more.

First, within the range of the composition of the present invention, the thickness of the Co coating layer was fixed at 5 μm, and then the deposition targets of which the thickness of the lanthanum coating layer was changed to 50, 189, 387, and 1017 Å were Inventive Examples 1, 2, 3, and 4, respectively. As a result of depositing by the electron beam evaporation method to form a coating layer. The thickness of the Co coating layer was changed to 1 and 10 μm, and the deposition targets made of the lanthanum coating layer was 189 Å, respectively, as Inventive Examples 5 and 6, respectively, and were deposited by electron beam deposition to form a coating layer.

And, after evaluating each oxidation resistance and high temperature conductivity by the above-mentioned evaluation method through a specimen having such a coating layer is shown in Table 1 below.

On the other hand, for comparison with the present invention, a substrate without Co and La added at all, Comparative Example 1, the thickness of Co is 5㎛, the deposition object consisting of La, the thickness of 20, 1540Å Comparative Example 2, 3, the thickness of La was fixed to 189Å, and the specimens were fabricated through the same process as the above Inventive Examples 1 to 6 using Comparative Examples 4 and 5 as the deposition targets having a thickness of Co of 0.5 and 20 µm. After the evaluation in the same manner each oxidation resistance and high temperature conductivity of each specimen are shown in Table 1 below.

TABLE 1

Coating layer thickness Oxidation resistance conductivity Co (μm) La (Å) Inventive Example 1  5 50 ◎ ◎ Inventive Example 2 189 ◎ ◎ Inventive Example 3 387 ○ ◎ Inventive Example 4 1017 ○ ○ Inventive Example 5 One 189 ◎ ○ Inventive Example 6 10 189 ◎ ◎ Comparative Example 1 0 0 × × Comparative Example 2 5 20 ◎ × Comparative Example 3 5 1540 × × Comparative Example 4 0.5 189 ◎ × Comparative Example 5 20 189 ◎ ×

As shown in Table 1, in the manufacture of the Co / La two-layer coating layer, the thickness of the Co coating layer 1 to 10㎛ thickness, La coating layer 50 to 1000Å thickness of the conventional commercialized ferritic stainless steel sheet It was confirmed that the oxidation resistance and conductivity can be increased. That is, the present invention confirmed that by coating two layers of Co / La on an existing ferritic stainless steel sheet without appropriately producing a new alloy, an oxide having excellent conductivity on the surface in a high temperature oxidation atmosphere can be formed.

As described in detail above, according to the present invention, a solid oxide having excellent high temperature oxidation resistance and high temperature conductivity by forming a two-layer coating layer by coating cobalt on a lower layer and lanthanum on an upper layer on a surface of an already manufactured ferritic stainless steel sheet. Fuel cell interconnects can be manufactured.

Claims (4)

A metal connection material for a solid oxide fuel cell in which a cobalt coating layer having a thickness of 1-10 μm and a lanthanum coating layer having a thickness of 50-1000 μm are formed on a ferritic stainless steel surface. Forming a cobalt coating layer on the surface of the ferritic stainless steel sheet using an electron beam deposition method, and Forming a lanthanum coating layer on the cobalt coating layer using an electron beam deposition method Coating method of the metal connection material for a solid oxide fuel cell excellent oxidation resistance and high temperature conductivity comprising a. The method of claim 2, wherein the cobalt coating layer is formed to a thickness of 1-10 μm. 3. The method of claim 2, wherein said lanthanum coating layer is formed 50-1000 mm thick.