KR20090129665A - Dense spinel conducting film, preparation method therof and metal interconnect using the same - Google Patents

Abstract

PURPOSE: A dense spinel conductive film is provided to maintain electric conductivity of 20 mΩ/cm^2 or less during thermal process at a high temperature for a long time and to prepare a conductive substrate with excellent stability. CONSTITUTION: A dense spinel conductive film has MnxCo3-xO4(1<=x<=2). The thin film is 1-50 micron. A method for preparing the spinel conductive film comprises the steps of: milling, mixing, and calcining raw material powder to prepare conductive oxides; re-milling the conductive oxide to prepare conductive oxide powder; and depositing the conductive oxide powder on the metal substrate to form a thin film.

Description

Dense spinel conducting film, preparation method therof and metal interconnect using the same}

The present invention relates to a spinel-based conductive thin film having a dense structure, a manufacturing method thereof and a metal connector using the same.

The solid oxide fuel cell, called the third generation fuel cell, was first operated by Bauer and Preis in 1937 as a fuel cell that uses a solid oxide with oxygen or hydrogen ion conductivity as an electrolyte. Solid oxide fuel cells operate at the highest temperatures (700 ° C to 1000 ° C) of existing fuel cells, and are simpler in structure than other fuel cells because all components are solid, resulting in electrolyte loss, replenishment and corrosion. There is no problem, no noble metal catalyst and easy fuel supply through direct internal reforming. In addition, it has the advantage that thermal combined cycle power generation using waste heat is possible because the high-temperature gas is discharged. Because of these advantages, research on solid oxide fuel cells has been actively conducted in developed countries such as the United States and Japan with the aim of commercializing in the early 21st century.

A typical solid oxide fuel cell is composed of an oxygen ion conductive electrolyte and a three-layer cell of a cathode and an anode positioned on both sides thereof. The principle of operation is to produce water by oxygen ions produced by the reduction reaction of oxygen in the cathode move to the anode through the electrolyte and react with hydrogen supplied to the anode again. At this time, electrons are generated in the anode and electrons in the cathode Since the two electrodes are connected to each other, electricity will flow. An interconnect is required to electrically connect these cells and to separate gases from the fuel electrode and the air electrode.

The connector should be chemically stable at both the cathode of the high temperature and oxidation atmosphere and the anode of the reducing atmosphere, and should have excellent electrical conductivity, heat resistance, oxidation resistance, mechanical strength, coefficient of thermal expansion, and the like. Although a conductive oxide such as LaSrCrO ₃ was first proposed as such a connector material, the conductive oxide has a problem of poor processability and high cost.

On the other hand, solid oxide fuel cells have recently been developed in the form of a cylindrical type with high energy density in a cylindrical shape, and high battery density performance is possible even at low and low temperatures below 800 ° C due to the decrease of electrolyte thickness and the improvement of component properties. As a result, it is possible to use a metal material connector excellent in workability and economical efficiency, and stainless steel is typically used as a metal material having suitable electrical conductivity and thermal expansion coefficient as the connector.

However, since the stainless steel is oxidized at a high temperature such as an operating environment of a solid oxide fuel cell to form an oxide having low conductivity on the surface, there is a problem in that contact resistance is increased and electrical conductivity is decreased. In addition, Cr is volatilized from Cr ₂ O ₃ -based oxides formed on the surface of stainless steel and then deposited on the anode, thereby reducing electrode characteristics.

Therefore, the conductive oxide layer is coated on the surface of stainless steel to prevent oxidation, and conventional coating methods include slurry coating, plasma coating, sol-gel coating, and the like. have. However, the oxide film formed by these methods is less dense than required, and thus there is a problem that the function of oxidation prevention is reduced.

In Korean Patent No. 284892, in the manufacture of a dense membrane using a pressure reduction / pressure type slurry coating apparatus, pressure is applied from the outside to cause a pressure difference across both ends of the porous support to remove the solvent from the slurry in which the ceramic solid particles are dispersed. Disclosed is a method for producing a dense membrane using a slurry coating method, which is formed for a support.

European Patent No. 0974564 discloses a method of coating a (La, Sr) MnO ₃ (LSM) or (La, Sr) (Co, Fe) O ₃ (LSCF) coating having a perovskite structure with a high speed flame spray. Doing. However, in the case of the high speed flame spray coating, the temperature of the flame may be low so that the conductive oxide may not be sufficiently melted. In addition, the density of the oxide film formed when the conductive oxide layer is coated on the stainless steel by these methods is still lower than required, there is a problem of low oxidation prevention. In addition, LSM or LSCF-based coatings require a relatively thick coating of 10 μm or more, which increases electrical resistance and consumes relatively many raw materials.

Accordingly, the present inventors deposited a conductive oxide layer having a spinel structure by an aerosol deposition method, and then heat-treated to form a conductive oxide layer having improved compactness, and coating it on a metal substrate to produce a chemically and electrically stable metal connector at high temperature. The present invention was completed by confirming that it had a low electrical resistance of mΩ / cm 2 or less.

An object of the present invention is to provide a spinel-based conductive thin film having a dense structure.

Another object of the present invention is to provide a method for manufacturing a spinel-based conductive thin film having a dense structure.

Still another object of the present invention is to provide a metal connector using a spinel-based conductive thin film having a dense structure.

In order to solve the above object, the present invention provides a spinel-based conductive thin film having a compact structure.

In addition, the present invention provides a method for producing a spinel-based conductive thin film having a dense structure.

Furthermore, the present invention provides a metal connector using a spinel-based conductive thin film having a dense structure.

The thin film according to the present invention is a thin film having a dense structure of a spinel-based conductive oxide, which reduces the formation of a metal oxide layer formed by high temperature, thereby maintaining stability by maintaining electrical conductivity of 20 mΩ / cm 2 or less even at high temperature and long time heat treatment. Not only can the excellent conductive substrate be manufactured, but also it can be used for a long time under high temperature, and can be usefully used to increase the long-term stability of the metal material interconnector of the low temperature solid oxide fuel cell (SOFC) used at 800 ° C or lower. .

Hereinafter, the present invention will be described in detail.

The present invention Mn _x Co _{3 - x} O ₄ Provided is a spinel-based conductive thin film having improved density with (1 ≦ x ≦ 2).

The thin film is Mn _x Co _{3 - x} O ₄ It is composed of a spinel structure having (1 ≦ x ≦ 2), which is chemically stable at a high temperature and an oxidizing atmosphere, and has an improved electrical density due to improved compactness.

At this time, the thin film is preferably 1 to 50 ㎛. If the thickness of the thin film is less than 1 μm, there is a problem in that electrical conductivity is lowered because oxidation of the metal substrate is not prevented. there is a problem.

In addition, the present invention comprises the steps of mixing the raw powder by milling and calcining to produce a conductive oxide (step 1); Remilling the conductive oxide of step 1 to produce a conductive oxide powder (step 2); And forming a thin film by depositing the conductive oxide powder prepared in step 2 on a metal substrate (step 3).

Step 1 according to the present invention is a step of preparing a conductive oxide by calcining after mixing the raw material powder,

The raw material powder of step 1 is Mn _x Co _{3 - x} O ₄ Manganese oxide and cobalt oxide may be mixed and used to form a composition of (1 ≦ x ≦ 2).

As the manganese oxide, Mn (NO ₃ ) ₂ , MnO ₂ , MnCO ₃ , and the like may be used, and the cobalt oxide may be Co ₃ O ₄ , CoCO ₃ , Co (NO ₃ ) _2, or the like.

At this time, the milling of the step 1 is preferably performed for 6 to 24 hours at 100-300 rpm.

Furthermore, the calcination of step 1 is preferably carried out at 900-1400 ℃. If the temperature is less than 900 ℃, there is a problem that the unreacted raw material remains because the reaction is not completed, if the temperature exceeds 1400 ℃ raw material powder is volatilized to change the composition ratio of manganese and cobalt Mn _x Co _{3 - x} O ₄ There is a problem that an oxide deviating from the structure of (1 ≦ x ≦ 2) is produced. In addition, the calcination is preferably performed for 1-8 hours.

Step 2 according to the present invention is a step of re-milling the conductive oxide of step 1 to produce a conductive oxide powder of a size suitable for aerosol injection of a subsequent step.

At this time, the powder of step 2 preferably has an average particle size of 0.5-5 ㎛ size. If the average particle diameter of the powder is less than 0.5 ㎛ difficult to obtain a dense film, if it exceeds 5 ㎛ there is a problem that the film formation rate is slow and the film uniformity is lowered

Re-milling in step 2 is preferably performed for 10-48 hours at 100-300 rpm.

Step 3 according to the present invention is a step of depositing the conductive oxide powder of step 2 on a metal substrate.

Titanium, stainless steel, copper, nickel or a nickel alloy may be used as the metal substrate, but the metal substrate is not limited as long as it is a conventional metal connector or a metal substrate having excellent conductivity.

Preferably, the deposition of step 3 uses an aerosol spraying method, and a rigid molded film may be deposited by accelerating the conductive oxide powder of step 2 onto the substrate at a speed of 100-500 m / s.

Equipment for deposition using the aerosol injection method comprises an aerosol chamber (aerosol chamber) and a deposition chamber (deposition chamber), lowering the vacuum degree of the deposition chamber through the pump powder and transport gas mixture formed in the aerosol chamber Moves to the deposition chamber and collides with the substrate to form a film.

In addition, the thin film manufactured as described above may improve conductivity by increasing crystallinity through heat treatment.

Furthermore, the present invention provides Mn _x Co _{3 - x} O ₄ on a metal substrate. Provided is a metal connector using a spinel-based conductive thin film having improved density with (1 ≦ x ≦ 2).

As a result of treating the metal connector using the spinel-based conductive thin film prepared according to the present invention as an anti-oxidation layer at 800 ° C. for 1000 hours, even when the spinel-based conductive thin film of the present invention was deposited to a thickness of 5 μm or less, 5-20 mΩ. Sufficient electrical conductivity can be maintained by having a cm 2 resistance value (see FIG. 8). This prevents the formation of an oxide on the metal substrate, it can be seen that it can be used as a stable metal connector while maintaining a low resistance value even if used for a long time while maintaining sufficient electrical conductivity at high temperatures.

In particular, the metal connector using a stainless steel, which is used as a conventional metal connector as a metal substrate and the spinel-based conductive thin film according to the present invention, is a volatile volatilization of chromium contained in the stainless steel even under high temperature and long time use. It is suppressed and is chemically and electrically stable, but also has excellent electrical conductivity.

Hereinafter, the present invention will be described in detail by Examples and Experimental Examples. However, the following Examples and Experimental Examples are merely illustrative of the present invention, and the content of the present invention is not limited by the following Examples and Experimental Examples.

< Example  1> Spinel  Preparation of Conductive Thin Film

Step 1: Prepare Conductive Oxide

58.27 g and 41.72 g of MnCO ₃ and Co ₃ O ₄ , respectively, were mixed with a ball mill for 24 hours, and then calcined at 900 ° C. for 2 hours to prepare a conductive oxide.

Step 2: Prepare Conductive Oxide Powder

Ball milling the conductive oxide prepared in step 1 was remilled to prepare an MnCo ₂ O ₄ powder having an average particle diameter of 1.49 μm.

Step 3: Spinel  Conductive thin film manufacturing

MnCo ₂ O ₄ powder prepared in step 2 was accelerated to 300 m / s using an aerosol deposition method and deposited on a stainless steel (STS 444) to a thickness of 3-5 ㎛.

The apparatus for aerosol deposition includes an aerosol chamber and a deposition chamber, and the powder and transport gas mixture formed in the aerosol chamber is moved to the deposition chamber by lowering the vacuum degree of the deposition chamber through a pump. It was made to form a film while colliding.

Comparative Example 1 Fabrication of Conventional Metal Substrate

A commercially available stainless steel substrate was prepared by heat treatment at 800 ° C. for 1000 hours.

Spinel  conductivity Powder Phase analysis , Particle size analysis  And microstructure analysis

In order to determine the physical and chemical properties of the spinel-based conductive thin film according to the present invention, the microstructure, phase analysis, and particle size analysis were performed.

(1) Phase analysis of conductive oxides according to calcination temperature

The conductive oxides prepared in Step 1 of Example 1 were calcined at 800-1000 ° C., respectively, and then subjected to X-ray diffraction analysis. The results are shown in FIG. 1.

As shown in Figure 1, it was confirmed through the X-ray diffraction analysis graph that MnCo ₂ O ₄ of the spinel structure is synthesized at 900 ℃.

(2) microstructure observation and particle size analysis

The microstructure of the conductive oxide prepared according to Example 1 was observed using a scanning electron microscope, and the results are shown in FIG. 2 (a).

As shown in Figure 2 (a), it was confirmed that the conductive oxide has a structure of MnCo ₂ O ₄ of the spinel structure in the same manner as the X-ray diffraction analysis graph.

The particle size of the powder was measured using a dry particle size analyzer for particle size analysis of the conductive oxide powder prepared in Example 1, and the results are shown in FIG.

As shown in Figure 2 (b), the conductive oxide powder prepared according to the present invention was confirmed that the average diameter is 1.49 ㎛.

< Experimental Example  1> Antioxidation Test

In order to determine the oxidation effect of the thin film according to the present invention, the following experiment was performed.

(One) Phase analysis

Example 1 was subjected to phase analysis of the specimens after heat treatment at 800 ° C. for 1000 hours through X-ray diffraction analysis, and the results are shown in FIG. 3.

MnCo ₂ O ₄ as shown in FIG. 3 It was found that a thin film having a phase was formed and a secondary phase was not produced by oxidation of the stainless steel even after the heat treatment, and it can be confirmed that the conductive oxide coating of the present invention is effective in preventing oxidation of the stainless steel.

(2) microstructure observation

In Example 1 and Example 1, the microstructure of the surface of the thin film after heat treatment at 800 ° C. for 1000 hours was observed using a scanning electron microscope, which is shown in FIGS. 4 (a) to (d), respectively. In addition, Table 1 shows the results of the EDS composition analysis on the thin film surface.

atomic% Comparative Example 1 Before Heat Treatment Comparative Example 1 Example 1 Before Heat Treatment Example 1 Cr 19.9 97.1 1.16 1.96 Fe 80.1 2.93 1.49 2.48

As shown in Fig. 4 (a) to (b), the stainless steel specimen without coating shows a smooth surface before the heat treatment (a), but it can be seen that the oxide is formed after the heat treatment (b), As shown in FIG. 1, it may be confirmed that the formed oxide is an oxide mainly containing Cr (eg, Cr ₂ O ₃ ).

As shown in Figure 4 (c) and 4 (d), the thin film according to the present invention does not have a large difference in the microstructure before (c) and after the heat treatment (d), as shown in Table 1, Cr composition ratio also did not increase significantly. When the compound containing Cr is formed on the surface, the characteristics of the solid oxide fuel cell (SOFC) electrode may be prevented from being lowered by volatilization of Cr, which may be useful as a SOFC separator material.

In order to determine the thickness of the oxide layer of the metal connection coated with the thin film according to the present invention, Example 1 and Comparative Example 1 was polished to observe the microstructure using a scanning electron microscope, which is shown in FIG. Their cross-sectional composition analysis was performed through EDS line scans, and are shown in FIGS. 6 (a) and 6 (b).

As shown in FIG. 5, in Comparative Example 1 (a) before heat treatment, an oxide layer was hardly observed on the surface, but it can be seen that thick oxide is formed in Comparative Example 1 ((b)).

Furthermore, the oxide formed through the EDS line scan of the cross section of FIG. 6 (a) is Cr ₂ O _3. It can be confirmed that, the thickness is confirmed to reach 10 ㎛.

As shown in FIGS. 5C and 5D, in Example 1 and Example 1, in which the heat treatment was not performed, the microstructure difference of the cross section was not large, and the EDS line scan composition analysis result of FIG. 6 (b). It can be confirmed that through the coating layer and the stainless steel interface formed a reaction layer containing Cr. However, it can be confirmed that the thickness thereof is about 1 μm, compared to 10 μm of the oxide layer produced in Comparative Example 1.

The microstructure of Example 1 was observed with a transmission electron microscope, and composition analysis was performed through EDS mapping, which is shown in FIG. 7.

As shown in FIG. 7, the interfacial reaction layer of Example 1 was confirmed that Cr is the main component, and the thickness was 0.5-1 μm. Through this, it can be seen that the thickness of the interface reaction layer after the heat treatment is significantly reduced compared with the case where it is not coated.

< Experimental Example  2> electric resistance change measurement

In order to measure the electrical conductivity of the metal connector of the present invention according to the heat treatment temperature, the electrical resistance change was measured by the 4-probe method during the heat treatment of Example 1 for 1000 hours, and the results are shown in FIG. 8. .

As shown in FIG. 8, Comparative Example 1 had an area specific resistance (ASR) of 100 mΩ / cm 2, which is a limit of use after 100 hours, which is caused by the formation of an oxide layer. On the other hand, Example 1 was confirmed to maintain a low resistance value of 16.1 mPa / ㎠ even after the heat treatment for 1000 hours or more.

1 is a graph showing the crystal structure change with the temperature of the conductive oxide used in the present invention through an X-ray diffractometer;

2 is a scanning electron micrograph (a) and a particle size analysis graph (b) of a conductive oxide used in the present invention;

3 is an X-ray diffraction graph of an embodiment according to the present invention ((a) Example 1, (b) Example 1 after heat treatment);

4 is a scanning electron micrograph of an embodiment according to the present invention ((a): Comparative Example 1 before heat treatment, (b) Comparative Example 1, (c) Example 1 before heat treatment, (d) Example 1) ;

5 is a photograph of a cross section of an embodiment according to the present invention with a scanning electron microscope ((a): Comparative Example 1 before heat treatment, (b) Comparative Example 1, (c) Example 1, before heat treatment (d) Example 1);

6 is a cross-sectional composition analysis through an EDS line scan of the cross section of an embodiment according to the present invention ((a) Comparative Example 1, (b) Example 1);

7 is a microstructure and composition analysis of the cross-section of an embodiment according to the present invention through transmission electron microscope and EDS mapping ((a) transmission electron microscope picture, (b) Fe mapping picture, (c) Cr mapping picture, (d) Mn mapping photo, (f) Co mapping photo); And

8 is a graph of measuring the electrical resistance change according to the heat treatment according to one embodiment of the present invention by a 4-probe method.

Claims (14)

Mn _x Co _{3 - x} O ₄ A spinel-based conductive thin film having improved density with (1 ≦ x ≦ 2). The method according to claim 1, wherein the thin film is a spinel-based conductive thin film having improved density, characterized in that 1 to 50 ㎛. Milling the raw powder to mix and calcining to prepare a conductive oxide (step 1); Remilling the conductive oxide of step 1 to produce a conductive oxide powder (step 2); And Method of manufacturing a spinel-based conductive thin film of claim 1 comprising the step (step 3) of depositing the conductive oxide powder prepared in step 2 on a metal substrate to form a thin film. The method according to claim 3, wherein the raw material powder of step 1 is manganese oxide and cobalt oxide. The method of claim 4, wherein the manganese oxide is Mn (NO ₃ ) ₂ , MnO ₂ Or MnCO _{3 The} method of manufacturing a spinel-based conductive thin film of claim 1, wherein the compactness is improved. The method of claim 4, wherein the cobalt oxide is Co ₃ O ₄ , CoCO ₃ Or Co (NO ₃ ) ₂ The method of manufacturing the spinel-based conductive thin film of claim 1, wherein the compactness is improved. The method according to claim 3, wherein the milling of step 1 is performed for 6 to 24 hours at 100 to 300 rpm. The method according to claim 3, wherein the calcination of step 1 is performed at 900-1400 ° C for 1-8 hours. The method according to claim 3, wherein the remilling of step 2 is performed for 10 to 24 hours at 100 to 300 rpm. The method according to claim 3, wherein the average particle diameter of the powder of step 2 is 0.5-5 [mu] m. The method according to claim 3, wherein the metal substrate of step 3 is any one selected from the group consisting of titanium, stainless steel, copper, nickel and nickel alloys. . 4. The method of claim 3, wherein the deposition of step 3 is aerosol deposition. A metal connector using the spinel conductive thin film of claim 1 on a metal substrate. The metal connector using the spinel-based conductive thin film of claim 1, wherein the metal connector maintains sufficient electrical conductivity by having a resistance of 5-20 mΩ · cm 2.

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