KR20100062456A - Dense complex oxides films comprising conductive oxides and non-conductive oxides, method for preparing the same, and metallic interconnector using the same - Google Patents

Abstract

PURPOSE: A thin film having conductive powder and non-conductive powder complex oxides is provided to lower price of raw powder and to manufacture a conductive substrate with high stability. CONSTITUTION: A dense complex oxides film contains conductive oxides(La_xSr_(1-x))MnO_3(LSM, here, 0<=x<=1) and non-conductive oxides(Y_xZr_(1-x)O_(3-0.5x)(YSZ, here 0<=x<=20)). A method for manufacturing the thin film comprises: a step of mixing conductive LSM powder and non-conductive YSZ powder with a ball mill to obtain a complex oxide powder; and a step of depositing the complex oxide powder on a metal substrate to form thin film.

Description

Dense complex oxides films comprising conductive oxides and non-conductive oxides, method for preparing the same, and metallic interconnector using the same}

The present invention relates to a thin film of a composite oxide having a dense structure including a conductive oxide and a nonconductive oxide, a method for manufacturing the same, 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 using a solid oxide with oxygen or hydrogen ion conductivity as an electrolyte. Solid oxide fuel cells operate at the highest temperatures (700 ° C-1000 ° C) of existing fuel cells, and because they are all solid, they are simpler in structure than other fuel cells, and lose and replenish electrolytes and corrode. 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 advanced countries such as the United States and Japan with the aim of commercializing in the early 21st century.

A typical solid oxide fuel cell consists of an oxygen ion conductive electrolyte and a three layer cell of cathode and anode located on both sides thereof. The working principle is that the oxygen ion generated by the reduction reaction of oxygen in the cathode moves to the anode through the electrolyte and reacts with hydrogen supplied to the anode to produce water, where electrons are generated at the anode and electrons at the cathode. Since the two electrodes are connected to each other, electricity will flow. An interconnector is required to electrically connect between these cells and to separate gases from the anode and the cathode.

The connector should be chemically stable at both the cathode of the high temperature and the oxidizing atmosphere and the anode in 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 it is possible to perform high power density cell performance even at low and low temperatures below 800 ° C due to the reduction of electrolyte thickness and the improvement of component properties. As a result, it has become possible to use a metal material connector excellent in workability and economical efficiency, and stainless steel is typically used as a metal material having electrical conductivity and thermal expansion coefficient suitable as such a 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 electrical conductivity on the surface, there is a problem that the electrical resistance is decreased due to an increase in contact resistance. In addition, since Cr is volatilized from Cr ₂ O ₃ based oxides formed on the surface of stainless steel, it is deposited on the anode to reduce 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, and sol-gel coating. Law, etc. 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, a pressure difference is applied to both ends of a porous support to remove a solvent from a slurry in which ceramic solid particles are dispersed by applying pressure from the outside. Disclosed is a method for producing a dense membrane using a slurry coating method, which is formed for a support.

EP 0974564 discloses a (La, Sr) MnO ₃ (LSM) coating of perovskite structure, or a (La, Sr) (Co, Fe) O ₃ (LSCF) coating with high-velocity. Oxygen Fuel Spraying (HVOF) coating method is disclosed. However, in the case of the high-speed flame spray coating, the temperature of the flame is low, the conductive oxide may not be sufficiently melted. In addition, when the conductive oxide layer is coated on the stainless steel by these methods, the density of the formed oxide film is still lower than the required degree, and thus there is a problem of low oxidation prevention.

In addition, since LSM-based or LSCF-based coatings contain rare earth elements La and relatively expensive elements such as Sr and Mn, the coating powder is expensive and the sintering temperature of the powder is relatively low at 1100 ° C to 1200 ° C. There is a drawback that a change in characteristics may be caused by causing a change in the microstructure near the operating temperature of 800 ° C.

Aerosol deposition is a process of making ceramic thin films with high density by spraying ceramic powder at room temperature.It is possible to make dense film at room temperature regardless of powder sintering temperature. Deposition is possible.

The present inventors add a non-conductive powder having a relatively low cost and high sintering temperature to a conventional conductive powder and coating the metal substrate by an aerosol deposition method, thereby reducing the cost of raw material powder and lowering the process cost. By suppressing the microstructure change at high temperature, a chemically and electrically stable metal splicer was produced for a long time even at high temperature, and it was confirmed that the area specific resistance (ASR) value has a low electrical resistance of 10 mΩ / ㎠ or less. The invention has been completed.

In order to solve the above object, the present invention provides a thin film of a composite oxide having a dense structure containing a conductive oxide and a non-conductive oxide.

The present invention also provides a method for producing a thin film of a composite oxide having a dense structure including a conductive oxide and a nonconductive oxide.

Furthermore, the present invention provides a metal connector using a thin film of a complex oxide having a dense structure including a conductive oxide and a nonconductive oxide.

The thin film according to the present invention is a thin film of a composite oxide having a dense structure composed of a complex oxide of a conductive oxide and a non-conductive oxide, and can reduce the process cost by reducing the cost of raw material powder compared to the conventional conductive thin film, and have a microstructure at high temperature. By suppressing the change to reduce the formation of the metal oxide layer generated by the high temperature to maintain the electrical conductivity of 10 mΩ / ㎠ or less even at high temperature and long time heat treatment can be produced a conductive substrate with excellent stability. Moreover, since it can be used for a long time at high temperature, it can be usefully used to improve long-term stability of the metal material connector of a low temperature type solid oxide fuel cell (SOFC) used at 800 degrees C or less.

Hereinafter, the present invention will be described in detail.

The present invention mixes a powder of non-conductive Y ₂ O ₃ -ZrO ₂ (Yttria-Stablized Zirconia, YSZ) to a powder of conductive (La, Sr) MnO ₃ (Lanthanum-Strontium-Manganese Oxide, hereinafter, LSM). In addition, a thin film of a complex oxide having a dense structure is provided.

The thin film has a lower raw material price than the conventional conductive powder, is chemically stable in a high temperature and an oxidizing atmosphere, and has an improved density, thereby having excellent electrical conductivity.

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 due to preventing oxidation of the metal substrate. If the thickness is larger than 50 μm, the adhesion between the thin film and the metal substrate is reduced and the thin film is easily separated from the substrate. There is a problem.

In addition, the present invention,

Mixing the nonconductive YSZ powder with the conductive LSM powder by a ball mill and then post-heating to prepare a composite oxide powder (step 1); And

Depositing a complex oxide powder prepared in step 1 on a metal substrate to form a thin film (step 2)

It provides a method for producing a thin film of the composite oxide of the conductive powder and non-conductive powder having improved density.

Step 1 according to the present invention is a step of preparing a composite oxide powder of a conductive oxide and a non-conductive oxide by mixing the raw material powder in a ball mill, followed by post-heat treatment,

The mixed powder used in the present invention has the advantage of reducing the process cost by significantly lowering the raw material price by using a non-conductive YSZ powder in which the raw material price is about 1/10 lower than that of the conventional conductive LSM powder.

The raw material powder of step 1 is a conductive oxide powder having a composition of (La _x Sr _1-x ) MnO ₃ (LSM, 0 ≦ x ≦ 1) and Y _× Zr _1-x O _3-0.5x (YSZ, 0 ≦ x Non-conductive oxide powder having a composition of ≦ 20).

In this case, 5-50 vol% of the non-conductive YSZ powder ratio after film-forming is preferable. When the ratio of the non-conductive YSZ powder after film formation is less than 5%, the effect of adding the non-conductive YSZ powder is not sufficient, and when the ratio is more than 50%, there is a problem in that the conductivity of the thin film of the composite oxide is rapidly decreased.

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

Furthermore, the post heat treatment of Step 1 is preferably performed at 300-900 ° C. If the temperature is less than 300 ℃, there is a problem that the density of the deposited film is not enough due to the small particle size of the powder, and if the temperature is greater than 900 ℃, the size of the raw material powder is large, there is a problem that the thickness of the deposited film is thin or not deposited. . In addition, the post heat treatment is preferably performed for 1 to 4 hours.

At this time, the powder of step 1 preferably has an average particle size of 0.5-5 ㎛ size. If the average particle diameter of the powder is less than 0.5 ㎛, it is difficult to obtain a dense film, if it is more than 5 ㎛, there is a problem that the film formation rate is slow and the film uniformity is lowered

Step 2 according to the present invention is a step of depositing the complex oxide powder of step 1 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 2 uses an aerosol deposition method, and a hard molded film may be deposited by accelerating the composite oxide powder of step 1 onto the substrate at a speed of 100-500 m / s.

Equipment for deposition using the aerosol deposition method comprises an aerosol chamber (aerosol chamber) and a deposition chamber (deposition chamber), by lowering the vacuum of the deposition chamber through a pump to deposit the powder and transport gas mixture formed in the aerosol chamber It is characterized by colliding with the substrate while moving to the chamber to form a film.

In addition, the thin film prepared as described above may improve conductivity by increasing crystallinity and average particle size through heat treatment.

Furthermore, the present invention provides a metal connector in which a thin film of the conductive composite oxide having improved density, which is composed of a conductive powder and a non-conductive powder composite, is deposited on a metal substrate.

As a result of treating a metal connector using a conductive oxide with a conductive LSM prepared in accordance with the present invention and a non-conductive YSZ as an oxidation prevention layer at 800 ° C. for 250 hours, an area specific resistance (ASR) value of 9.1 mΩ / cm 2 was obtained. Sufficient electrical conductivity can be maintained, and it can be seen that the resistance value is improved by 30% or more compared to 13.3 mΩ / cm 2, which is the ASR value of the conductive LSM deposition alone (see FIG.).

Due to its compact structure, it effectively prevents the formation of oxide on the metal substrate, and by adding YSZ oxide having a high sintering temperature, suppresses the microstructure change at high temperature, improves long-term stability, and maintains sufficient electrical conductivity at high temperature. It can be seen that it can be used as a stable metal connector while maintaining a low resistance even when used for a long time.

In addition, the metal interconnector using a thin film of a composite oxide of a conductive oxide and a non-conductive oxide according to the present invention is a stainless steel in which a thin film using only a conductive powder is deposited on the volatilization of chromium contained in the stainless steel even under high temperature and long time use environment. Since it is small compared to the above, it has an advantage of more effectively suppressing the deterioration of characteristics of the SOFC anode caused by chromium volatilization.

Hereinafter, the present invention will be described in detail with 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 Preparation of Thin Film of Composite Oxide of Conductive Oxide and Non-Conductive Oxide

Step 1: Preparation of Powder of Complex Oxide of Conductive Oxide and Non-Conductive Oxide

Commercially conductive LSM (LSM2-P, fuel cell materials) powder and commercially nonconductive YSZ (FYT13.0-010H, unitec ceramics) powder were weighed with LSM 67.82 g: YSZ 32.18 g (volume ratio 70:30), respectively. After mixing for 6 hours in a ball mill (ball-mill), a post-heat treatment for 2 hours at 600 ℃ to prepare a powder of the composite oxide.

Step 2: Preparation of Thin Film of Composite Oxide of Dense Structure Conductive Powder and Non-Conductive Powder

The LSM-YSZ composite powder prepared in Step 1 was accelerated to 300 m / s by aerosol deposition and deposited on a stainless steel (STS 444) to a thickness of up to 5 μm.

The aerosol deposition apparatus includes an aerosol chamber and a deposition chamber, and lowers the vacuum degree of the deposition chamber through a pump so that a mixture of powder and transport gas formed in the aerosol chamber moves to the deposition chamber and collides with the substrate. To form a film.

Example 2 Preparation of Thin Film of Composite Oxide of Conductive Oxide and Non-Conductive Oxide

Step 1: Preparation of Powder of Complex Oxide of Conductive Oxide and Non-Conductive Oxide

Commercially conductive LSM (LSM2-P, fuel cell materials) powder and commercially nonconductive YSZ (FYT13.0-010H, unitec ceramics) powder were weighed with LSM 47.46 g: YSZ 52.54 g (volume ratio 50:50), respectively. After mixing for 6 hours in a ball mill (ball-mill), a post-heat treatment for 2 hours at 600 ℃ to prepare a powder of the composite oxide.

Step 2: Preparation of Thin Film of Composite Oxide of Dense Structure Conductive Powder and Non-Conductive Powder

A thin film of a composite oxide was prepared in the same manner as in Step 2 of Example 1.

Example 3 Preparation of Thin Film of Composite Oxide of Conductive Oxide and Non-Conductive Oxide

Step 1: Preparation of Powder of Complex Oxide of Conductive Oxide and Non-Conductive Oxide

Commercially conductive LSM (LSM2-P, fuel cell materials) powder and commercially nonconductive YSZ (FYT13.0-010H, unitec ceramics) powder were weighed with LSM 27.91 g: 72.09 g (volume ratio 30:70), respectively, After mixing for 6 hours in a ball mill (ball-mill), a post-heat treatment for 2 hours at 600 ℃ to prepare a powder of the composite oxide.

Step 2: Preparation of Thin Film of Composite Oxide of Dense Structure Conductive Powder and Non-Conductive Powder

A thin film of a composite oxide was prepared in the same manner as in Step 2 of Example 1.

Comparative Example 1: Preparation of a Conductive Oxide Thin Film

A conductive LSIM thin film was prepared in the same manner as in Example 1, except that the conductive LSM powder was used instead of the composite oxide powder of Example 1.

Comparative Example 2: Preparation of Non-Conductive Oxide Thin Film

A nonconductive YSZ thin film was prepared in the same manner as in Example 1 except that a nonconductive YSZ powder was used instead of the composite oxide powder of Example 1.

Phase and Microstructure Analysis of Powders and Thin Films of Composite Oxides of Conducting and Non-Conductive Oxides

In order to determine the physical and chemical properties of the powder and the thin film of the composite oxide of the conductive oxide and the non-conductive oxide according to the present invention, phase analysis and microstructure analysis were performed as follows.

(1) Phase analysis of powders and deposited films of complex oxides of conductive and nonconductive oxides

X-ray diffraction analysis of the LSM-YSZ composite powder, LSM powder and YSZ powder prepared in Step 1 of Example 1 was performed, and the results are shown in FIG.

As shown in FIG. 1, it can be seen from the X-ray diffraction graph that the LSM-YSZ composite powder is maintained alone without phase change and reaction even after the post heat treatment.

X-ray diffraction analysis results of the thin film of the LSM-YSZ composite oxide, the LSM thin film and the YSZ thin film deposited on the stainless steel (STS 444) prepared in step 2 of the examples are shown in FIG. 2.

As shown in FIG. 2, it can be seen that the LSM and YSZ phases are also present in the film deposited using the mixed powder, and other phases are not found, so that each phase exists in the deposited film without reaction and generation of the secondary phase. Can be. In addition, since the intensity of the XRD peak became smaller and wider, it can be estimated that the grain size of the crystal phase in the deposited film was significantly smaller than that of the starting powder.

(2) microstructure observation and composition analysis

The microstructures of the surfaces and cross-sections of the LSM-YSZ composite oxide thin film, the LSM thin film and the YSZ thin film were observed using a scanning electron microscope, and the results are shown in FIGS. 3 and 4, respectively.

3 and 4, the oxide thin film has a dense structure and is well bonded to stainless steel.

An EDS analysis was performed to compare the composition of the conductive oxide thin film with that of the raw powder, and the results are shown in the graph of FIG. 5.

According to the analysis results, when the LSM: YSZ volume ratio of the raw material powder is 3: 7, the LSM: YSZ volume ratio of the deposited film was found to be about 5: 5. It was confirmed that the prepared conductive oxide powder had an average diameter of 1.49 μm.

Experimental Example 1: Antioxidation Experiment

In order to investigate the anti-oxidation effect of the thin film of the composite oxide prepared according to the present invention at high temperature, the following experiment was performed.

(1) microstructure observation

The surface microstructure of the LSM-YSZ composite oxide, LSM and YSZ-deposited stainless steel prepared by Example 1 after heat treatment at 800 ° C. for 250 hours was observed using a scanning electron microscope, and the results are shown in FIG. 6. Indicated.

As shown in FIG. 6, even after the heat treatment, a large microstructure change was not observed due to the oxidation of stainless steel on the surface, and it was confirmed that the composite oxide coating of the present invention was stably maintained even after the heat treatment at high temperature.

(2) composition analysis

EDS mapping and composition quantitative analysis of the surface after heat treatment of the composite oxide of LSM-YSZ prepared in Example 1, LSM and YSZ deposited stainless steel at 800 ° C. for 250 hours were performed. 7 is shown.

As shown in FIG. 7, it can be seen that the thin film of the composite oxide is maintained in the LSM and YSZ composition even after the heat treatment. According to the surface composition analysis, when the Cr content ratio is performed for the composite oxide coating of LSM-YSZ, the LSM alone It was confirmed that the reduction from 4.45 mol% to 2.02 mol% compared to the case of coating. This shows that when a compound containing Cr is formed on the surface, the characteristics of the solid oxide fuel cell (SOFC) electrode are prevented from being deteriorated by the volatilization of Cr, which can be used as an SOFC separator material.

Experimental Example 2: Measurement of Change in Electrical Resistance

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 during the heat treatment of the composite oxide, LSM and YSZ-coated stainless steel of LSM-YSZ of Example 1 for 250 hours was 4- Measured by the probe (probe) method is shown in Figure 8 the results.

As shown in FIG. 8, the YSZ coating of Comparative Example 1 has very low conductivity, and the composite oxide coating of LSM-YSZ has an ASR of 9.1 mΩ / cm 2 after 250 hours, compared to 13.3 mΩ / cm 2, which is the ASR value of LSM alone deposition. It can be seen that the resistance value is improved by more than 30%.

1 is a graph showing the results of X-ray diffraction analysis of the LSM-YSZ composite powder, LSM powder and YSZ powder prepared according to an embodiment of the present invention.

Figure 2 is a graph showing the results of X-ray diffraction analysis of the thin film, LSM thin film and YSZ thin film of the LSM-YSZ composite oxide according to an embodiment of the present invention.

Figure 3 shows the results of observing the microstructure of the surface and the cross-section of the thin film of the composite oxide of the LSM-YSZ, LSM thin film and YSZ thin film according to an embodiment of the present invention using a scanning electron microscope.

Figure 4 shows the results of observing the microstructure of the surface and the cross-section of the thin film of the composite oxide of the LSM-YSZ, LSM thin film, and YSZ thin film according to an embodiment of the present invention using a scanning electron microscope.

5 is a graph showing the results of EDS analysis of a thin film of a composite oxide according to the present invention.

Figure 6 shows the observation results of the surface after the heat treatment of the composite oxide, LSM and YSZ of LSM-YSZ prepared in accordance with an embodiment of the present invention.

Figure 7 shows the results of EDS mapping and composition quantitative analysis of the surface of the LSM-YSZ composite oxide thin film, LSM thin film and YSZ thin film prepared after the heat treatment according to the embodiment of the present invention.

8 shows measurement results of electrical resistance change during heat treatment of a composite oxide of LSM-YSZ, stainless steel coated with LSM and YSZ according to an exemplary embodiment of the present invention.

Claims (14)

_Compact structure including conductive (La _x Sr _1-x ) MnO ₃ (LSM, 0 ≤ x ≤ 1) and non-conductive Y _x Zr _1-x O _3-0.5x (YSZ, 0 ≤ x ≤ 20) Thin film of oxide. The thin film of the composite oxide of dense structure according to claim 1, wherein the ratio of nonconductive YSZ in the thin film is 5-50 vol%. The thin film of the complex oxide of claim 1, wherein the thin film has a thickness of 1 to 50 μm. Mixing the nonconductive YSZ powder with the conductive LSM powder by a ball mill and then post-heating to prepare a composite oxide powder (step 1); And Depositing a complex oxide powder prepared in step 1 on a metal substrate to form a thin film (step 2) A method for producing a thin film of a composite oxide of a conductive powder and a non-conductive powder according to claim 1 comprising a. The method of claim 4, wherein the average particle diameter of each powder is 0.5-5 μm. 5. The method of claim 4, wherein milling is performed at 100-300 rpm for 6-24 hours in step 1. The method of claim 4, wherein the post-heat treatment of step 1 is performed at 300-900 ° C. for 1-4 hours. The method of claim 4, wherein the metal substrate of step 2 is titanium, stainless steel, copper, nickel, or a nickel alloy. The method of claim 8, wherein the metal substrate of step 2 is made of stainless steel. 10. The method of claim 9, wherein the stainless steel is SUS 444. 5. The method of claim 4, wherein the deposition of step 2 is performed by aerosol deposition. 6. The method of claim 9, wherein the deposition rate by the aerosol deposition method is 100-500 m / s. The method of manufacturing a thin film of a composite oxide of conductive powder and non-conductive powder according to claim 4, wherein the heat treatment is further performed after step 2. The metal connector by which the thin film of the composite oxide of the conductive powder and the non-conductive powder manufactured by the method of Claim 4 was deposited.

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