KR20130118093A - Ceramic interconnect and synthetic method thereof - Google Patents

Abstract

PURPOSE: A synthesizing method for a ceramic interconnect provides a ceramic interconnect with high electric conductivity in both an oxidation atmosphere and a reduction atmosphere. CONSTITUTION: A synthesizing method for a ceramic interconnect comprises a step of mixing and crushing a first solvent and a starting material of an interconnect powder; a step of drying the liquefied starting material, heat-treating and powderizing the dried starting material; a step of crushing the powder by a milling method and adding additives; and a step of particularizing the powder into a predetermined particle size by a spray drying method. The interconnect powder has a basic composition of La_(1-x)Ca_xCr_(1-y)Co_yO_3 and satisfies 0.1<=x<=0.3 and 0.1<=y<=0.2.

Description

CERAMIC INTERCONNECT AND SYNTHETIC METHOD THEREOF

The present invention relates to a ceramic connecting material of a solid oxide fuel cell and a method of synthesizing it.

Fuel cells are devices that generate electricity by chemical reactions. Various fuel cells have been developed depending on the type of electrolyte. Among them, solid oxide fuel cells (SOFCs) are the first generation of phosphate acid fuel cells and the second generation of molten carbonates. Compared with other fuel cells such as molten carbonate fuel cells, the fuel cell is more efficient and has less pollution, does not require a fuel reformer, and can combine power generation with a fuel cell-gas turbine-steam turbine.

SOFCs utilize hard ceramic compounds of metal (eg calcium or zirconium) oxides as electrolytes. Typically, in SOFC, oxygen gas such as 0 ₂ is reduced to oxygen ions (O ^{2 −} ) at the cathode (air electrode), and fuel gas such as H ₂ gas is oxidized with oxygen ions at the anode (fuel electrode) to form water. do. In general, a fuel cell is designed as a stack, in which subassemblies each comprising a cathode, an anode, and a solid electrolyte between the cathode and the anode are continuously assembled, whereby an electrical interconnect is connected between the cathode of one subassembly and the anode of the other subassembly. ) Is placed.

In developing SOFCs with this advantage, a key material needs to be addressed in the connection material, which provides a conductive path for current to flow between the electrodes and into the external circuit. The linker also acts as a separating plate to physically separate the fuel in the anode cavity from the air or oxygen in the cathode cavity. Therefore, the connecting material must have good electrical conductivity to minimize resistive losses and must be stable under both oxidation and reduction conditions. Since SOFCs operate at high temperatures, the thermal expansion coefficient (CTE) of the interconnect must be close to that of the rest of the battery components to minimize thermal stress. Other requirements of the connecting material include adequate mechanical strength, relatively low permeability to oxygen and hydrogen, and moderate thermal conductivity.

There are two general methods for developing connectors for SOFCs: metallic connectors and ceramic connectors, each of which offers different advantages and solutions. Metallic connectors have good electrical conductivity, but are generally not stable when exposed to oxidizing conditions at the cathode of the SOFC, so it is generally necessary to coat the surface with a conductive oxide (eg, spinel). Since ceramic interconnects are oxides, they are stable under an oxidizing atmosphere, but usually have lower conductivity compared to metals. High raw material costs and high manufacturing costs in the case of high density ceramic connecting materials impede the application of ceramic connecting materials in SOFCs.

Accordingly, the present invention has been made to solve the problems of the prior art as described above, the general purpose of the present invention is a ceramic connecting material and its that can substantially compensate for the various problems caused by the limitations and disadvantages in the prior art It is to provide a synthesis method.

Another specific object of the present invention is to provide a ceramic connecting material having a high electrical conductivity in both the oxidizing atmosphere and the reducing atmosphere, and a method for synthesizing the same.

Another specific object of the present invention is to provide a ceramic connecting material suitable for mass synthesis, and a method for synthesizing the same, in which properties such as compactness, sinterability, and electrical conductivity do not change significantly even after mass synthesis.

To this end, the ceramic connecting material according to an embodiment of the present invention includes a plurality of cells each consisting of an anode layer, an electrolyte layer, and a cathode layer, each of which is sequentially stacked, wherein the plurality of cells are electrically connected. As a material of the connecting material to be connected, it is represented by the composition formula La _{1 - x} Ca _x Cr _{1 - y} Co _y O ₃ (where each of x and y represents a molar ratio and satisfies 0.1 ≦ x ≦ 0.3 and 0.1 ≦ y ≦ 0.2). It comprises a ceramic composition as a main component.

In the connecting member of an embodiment of the present invention, x may be 0.3 and y may be 0.1.

In the connection material of an embodiment of the present invention, 0.7 mol La ₂ O ₃ , 0.1 mol CaCo ₃ , 0.2 mol CaF ₂ , 0.9 mol Cr ₂ O ₃ , 0.1 mol as starting materials satisfying the molar ratio x, y of Co ₃ O ₄ may be included.

In the connection material of an embodiment of the present invention, 0.7 mol La ₂ O ₃ , 0.2 mol CaCo ₃ , 0.1 mol CaF ₂ , 0.9 mol Cr ₂ O ₃ , 0.1 mol as starting materials satisfying the molar ratio x, y It may include a Co ₃ O ₄ .

In addition, the method of synthesizing the linker powder according to an embodiment of the present invention has a basic composition of La _{1- x} Ca _x Cr _1-y Co _y O ₃ , 0.1 _{≤ x ≤} 0.3, 0.1 _{≤ y ≤} 0.2 A method of synthesizing a powder, the method comprising: pulverizing and mixing a starting material and a first solvent of the linker powder; Drying the starting material in a liquid state and then heat-processing to powder; Grinding the powder by a milling method after the heat treatment and adding an additive; And granulating the powder to which the grinding and additives are added to a predetermined particle size by spray drying.

In the method of an embodiment of the present invention, the process of powdering by heat treatment is the process of calcining the starting material in the liquid state at a temperature increase rate of 0.5 ℃ / min to 10 ℃ / min at 850 ℃ to 1200 ℃, Pulverizing and mixing the calcined powder and the second solvent, and drying the starting material in a liquid state, and then sintering at a temperature increase rate of 0.5 ° C./min to 10 ° C./min at 1100 ° C. to 1400 ° C. It may include.

In the method of an embodiment of the present invention, the milling of the powder in a milling method may further comprise at least one of a jet mill, a bead mill or an attrition mill process after a ball mill operation. The method may further include miniaturizing the particle size.

In the method of an embodiment of the present invention, the additive may include at least one of a binder, a release agent, a dispersant, an antifoaming agent.

In an embodiment of the present invention, the method may further include a heat treatment process for burning the additive contained in the spray-dried raw material, and the heat treatment process may be performed at a temperature increase rate of 0.5 ° C./min at a temperature of 450 ° C. to 800 ° C. It may be made by heat treatment at 5 ℃ / min for 3 to 10 hours.

According to the ceramic connecting material and the synthesis method according to the present invention, it is possible to provide a ceramic connecting material having a high electrical conductivity in both the oxidizing atmosphere and the reducing atmosphere and the synthesis method thereof.

In addition, according to the present invention, it is possible to stably supply mass-produced products by deriving a highly reproducible composition of linking materials having little change in properties even after mass synthesis and establishing the synthesis method.

1 is a view showing the electrical conductivity with time in the oxidation atmosphere (Oxidizing).
2 is a view showing the electrical conductivity with time in the reducing atmosphere (Reducing).
3 is a diagram showing a coefficient of thermal expansion of Sample 3 after synthesizing a connecting material powder.
4 is a diagram showing an XRD spectrum after synthesizing a linking powder.
5 is a SEM (scanning electron microscope) photograph showing a sintered shape after synthesis and a shape after grinding.
6 is a view showing the results of electrical conductivity measurement in the oxidizing atmosphere for a mass synthesis sample.
7 is a view showing a result of measuring the density of the heating temperature during calcination or sintering.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. In addition, the terms described below are defined in consideration of the functions of the present invention, and these may vary depending on the intention of the user, the operator, or the precedent. Therefore, the definition should be based on the contents throughout this specification.

In the solid oxide fuel cell, the present inventors are disposed between a plurality of cells each consisting of an anode layer, a solid electrolyte layer, and a cathode layer stacked in order, and interconnecting the plurality of cells electrically in series. In order to obtain a connecting material that can be chemically stable in any of the atmospheres of oxidation and reduction, high electrical conductivity (low conductivity), low ion conductivity, and low sintering temperature can be considered. In addition, the commercial materials for mass production of solid oxide fuel cells and their synthesis methods were discussed.

On the basis of this study the present inventors have ceramic compositions of particular La ₁ represented by LCCCO _- has reviewed the use of a _y Co _y O ₃ ceramic composition as a solid oxide fuel cell consolidated _{material, La 1 - - x Ca x} Cr 1 x Ceramic compositions represented by Ca _x Cr _{1 - y} Co _y O ₃ were produced at various composition ratios and their properties were tested.

As a result, when it satisfies 0.1≤x≤0.3 and satisfies 0.1≤y≤0.2, it was confirmed that both the oxidation and reduction atmospheres of about 800 ° C were chemically stable and the electrical conductivity (conductivity) was high.

In addition, even after a relatively large amount of synthesis of several to several tens of kilograms at a time, the characteristics were not significantly changed, it was confirmed that the performance is reproduced.

When explaining the embodiment of the present invention in detail as follows.

Sample powder synthesis

Step 1: Raw Material Weighing

A process for accurately mixing each powder to the calculated mole ratio, taking into account the purity of each starting material by applying the molar ratio using a composition designed to form the ABO ₃ Perovskite structure. Calculate

When _{x of the} composition formula La _{1 - x} Ca _x Cr _{1 - y} Co _y O ₃ is 0.3 and y is 0.1, that is, La _0.7 Ca _0.3 Cr _0.9 Co _0.1 O ₃ , the samples 1, 2, 3, 4 Weigh the molar ratio of starting material as shown in Table 1 below.

Subsidies / Departures La ₂ O ₃ CaCo ₃ CaF ₂ Cr ₂ O ₃ Co ₃ O ₄ Sample 1 0.7 0.3 _ 0.9 0.1 Sample 2 0.7 0.2 0.1 0.9 0.1 Sample 3 0.7 0.1 0.2 0.9 0.1 Sample 4 0.7 0.15 0.15 0.9 0.1

For example, in case of Sample 3, if the purity of starting material is 99.9%, La ₂ O ₃ 546.04 g, CaCo ₃ 47.92 g, CaF ₂ 74.76 g, Cr ₂ O ₃ 327.50 g, Co ₃ O ₄ 38.51g (measured to two decimal places) is put in the bottle, ethyl alcohol is used as the solvent, and 1L is added per 1kg basis.

Step 2: Ball mill ( Ball milling ( Mix ))

As a process for physically mixing the powder mixed with the solvent, it is mixed at 150rpm to 300rpm for 5 hours to 10 hours. At this time, 5mm, 10mm, 15mm zirconia ball is used.

Step 3: Dry ( Drying )

A process for completely drying the powder which becomes a liquid state with a solvent to make it solid state, it is dried for 2 to 3 days. At this time, the temperature of the dry oven (Dry oven) to 60 ℃ to 80 ℃ ethanol is evaporated, the temperature of the oven is raised to 90 ℃ to 110 ℃ completely dried. This is because the powder may overflow due to the low boiling point of ethyl alcohol upon drying at 90 ° C. to 110 ° C. from the beginning.

Step 4: Calculate Calcination )

The mixed powder is formed into an ABO ₃ perovskite structure and is a heat treatment process for burning organic materials. The temperature is lowered from 0.5 ° C./min to 10 ° C./min at 850 ° C. to 1200 ° C. for 2 to 10 hours. Keep and calcinate.

Step 5: Ball Mill Ball milling )

After the calcined powder is completely cooled, the mixture is sufficiently mixed with ethyl alcohol and Z-ball for about 12 to 36 hours.

Step 6: Sinter Sintering )

The ball-like liquid powder is placed in a drier and completely dried, then placed in a crucible and sintered at 1100 ° C. to 1400 ° C. for 2 to 10 hours at a temperature of 0.5 ° C./min to 10 ° C./min.

Step 7: Grind and Additive Mixing ( Grinding  & Binder Mixing )

After heat treatment, the particles are agglomerated like ceramic ceramics, and a process for mixing various additives by pretreatment of pulverization and spray drying. As an additive, a DI water binder, a mold release agent, a dispersant, an antifoaming agent, etc. may be added. .

More specifically, the heat treated powder is ground using a ball mill and the additives are mixed. At this time, deionized water is used as a solvent and the ratio is 1: 1 to the raw material volume. As an additive, 0.01% to 0.1% of a binder and 0.001% to 0.009% of a dispersant are added. Next, the release agent and the antifoaming agent are added at 0.001% to 0.009% and 0.005% to 0.01% before spray drying 2 hours to 8 hours, respectively. In addition, the zirconia ball is put about 2 times by volume relative to the raw material and mixed thoroughly pulverized 12 hours to 36 hours at 100rpm to 400rpm.

On the other hand, after the ball mill operation, a jet mill, bead mill, or attrition mill process may be further performed to make the particle size finer. For example, a jet mill is a method of pulverizing powder by rotating a disk under the pressure of compressed air. As a result, the particle size is 0.8-1.0 μm, which is not significantly different from the particle size during ball milling. It was confirmed that it appeared. In addition, the bead mill is a method in which a bead (bead) in the chamber and pulverized by the rotational force and centrifugal force, it is possible to obtain particles much smaller than the ball mill or jet mill with a particle size of 0.4 ~ 0.6㎛. At this time, by adjusting the speed of the bead mill chamber or the pump injection speed it is possible to obtain particles of a smaller size.

Step 8: Spray Drying Spray Drying )

Process to make the heat-treated powder particles into the size of plasma coating, which is spherical according to the conditions of spray drying, for example, additive, inlet and outlet temperature, dosage, temperature, spray rate (rpm), etc. It is very important to set the process conditions because it is determined whether granules are formed and it has a great influence on the feeding of powder during plasma coating.

In the present embodiment, the inlet temperature of the spray dryer is set at 100 ° C to 250 ° C, the outlet temperature is 50 ° C to 200 ° C, and the spray rate is warmed up to 1000rpm to 5000rpm and then 5000rpm To 12000 rpm.

Step 9: Burnout Burn Out )

In the heat treatment process for burning the additive contained in the spray-dried raw material, it is maintained for 3 to 10 hours at a temperature of 450 ℃ to 800 ℃. At this time, the temperature increase rate is 0.5 ℃ / min to 5 ℃ / min to allow the additive to gradually escape and to combine with a high density as a spherical shape.

Step 10: Quarter ( Sieving )

A process for separating the finished powder to the desired particle size (sieving the powder using a sieve of the desired particle size).

Characterization of Sample Powder

(1) electrical conductivity

The synthesized powder is made of pellets for conductivity measurement, and the oxidizing atmosphere is maintained at 800 ° C and the oxidizing gas (80% nitrogen, 20% oxygen) is injected into the furnace (Pot type furnace) at the beginning. Check the resistance value for each gap and the temperature of gas injection.

Reducing atmosphere is also maintained at 800 ℃ and after the temperature rises to a certain amount of reducing gas (hydrogen 100%) is injected.

Conductivity measurement uses a 4-probe measurable digital multimeter to measure the resistance and then calculate the conductivity taking into account the pellet size and the distance between the electrodes.

In this embodiment, as a result of the measurement, the electrical conductivity as shown in Figs. 1 and 2 was measured. Figure 1 shows the electrical conductivity with time in the oxidation atmosphere (Oxidizing) of 800 ℃, Figure 2 shows the electrical conductivity with time in the reducing atmosphere (Reducing) of 800 ℃, the average value of the electrical conductivity is shown in Table 2 below Same as

Composition / gas atmosphere Oxidation atmosphere (S / cm) Reducing atmosphere (S / cm) Sample 1 (LCCC-1) 31.2 1.52 Sample 2 (LCCC-2) 26.5 1.62 Sample 3 (LCCC-3) 33.7 3.73 Sample 4 (LCCC-4) 29.2 1.34

Through Table 2, the electrical conductivity of Sample 3 was 33.7 S / cm in the oxidation atmosphere, 3.73 S / cm in the reducing atmosphere, and Samples 1 (LCCC-1), 2 (LCCC-2), and 4 (LCCC-4). It can be seen that the electrical conductivity is greater than that of. For reference, see N. Q. Minh et al, Proc. According to the 25th Intersociety Energy Conversion Engineering Conference, AICE, New York, Vol. 13, 256 (1990), etc., it must be at least 1 S / cm for use as SOFC interconnects.

(2) Coefficient of thermal expansion

3 shows the coefficient of thermal expansion of Sample 3 after synthesizing the powder of the connecting material, and it can be seen that the coefficient of thermal expansion is appropriate as about 108.4 × 10 ⁻⁷ / ° C. FIG. In general, the thermal expansion coefficient of the connecting member is known to have a range of 100 ~ 120x10 ^-7 / ℃.

(3) XRD measurement

Figure 4 shows the XRD spectrum after the synthesis of the linker powder, XRD was measured to determine whether the synthesized powder has a perovskite structure. As a result of the measurement, it can be inferred that it has a single-phase perovskite structure and thus the process is stabilized during calcination and sintering operations.

(4) Scanning Electron Microscope (SEM) Photo

5 is a SEM (scanning electron microscope) photograph showing the sintered shape and the shape after crushing after synthesis, and it can be seen that the fine particles are formed after pulverization and have a particle size of about 0.4 to 0.6 μm.

As described above, according to the present embodiment, a mass production product can be stably supplied by deriving a highly reproducible composition of linking material having little change in properties even after mass synthesis and establishing the synthesis method.

On the other hand, in the process of synthesizing the powder of the connecting material, the electrical conductivity and the density density change according to the temperature and holding time during calcination or sintering were also considered.

Figure 6 shows the results of the electrical conductivity measurement in the oxidation atmosphere for the mass synthesis sample. FIG. 6 (a) shows the electrical conductivity of the sample sintered at a temperature of 1.5 ° C./min, and FIG. 6 (b) shows the electrical conductivity of the sample sintered at a temperature of 5 ° C./min. The linker powder was synthesized with the composition of (LCCC-3), and the remaining process conditions were the same.

As shown in Figure 6, the electrical conductivity of the sample sintered at 1.5 ℃ / min temperature average 31S / cm, the electrical conductivity of the sample sintered at 5 ℃ / min temperature average 2.3S / cm, through the experiment As the temperature rises, the electrical conductivity was greatly changed.

Figure 7 shows the results of the measurement of the density according to the elevated temperature at the time of calcination or sintering, it is enlarged to 1000 times, 5000 times, 10000 times.

Referring to FIG. 7, the samples ① and ② are calcined at 800 ° C., and then set to 5 ° C./min and 1.5 ° C./min, respectively. In the case of primary sintering, both samples were sintered but it can be seen that a large number of pores were seen. Samples ③ and ④ were calcined at 1000 ° C., and then set to 5 ° C./min and 1.5 ° C./min, respectively, followed by sintering. Similarly, pores appear a lot. In the case of sample ④, compared to other samples, the structure is almost densified, the sintering is completed, and the pores are almost invisible.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and similarities. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be construed as including not only the claims below but also equivalents thereof.

Claims (10)

In a solid oxide fuel cell comprising a plurality of cells each consisting of an anode layer, an electrolyte layer and a cathode layer stacked in order,
As a material of a connecting material for electrically connecting the plurality of cells, a composition formula La _{1- x} Ca _x Cr _1-y Co _y O ₃ (wherein x and y each represents a molar ratio, and 0.1 ≦ x ≦ 0.3 and 0.1 ≦ y ≦). Ceramic connection material comprising a ceramic composition represented by the main component).
The ceramic connecting material of claim 1, wherein x is 0.3 and y is 0.1.
The method of claim 2, wherein as a starting material satisfying the molar ratio x, y
0.7 mol La ₂ O ₃ , 0.1 mol CaCo ₃ , 0.2 mol CaF ₂ , 0.9 mol Cr ₂ O ₃ , 0.1 mol Ceramic connecting material comprising Co ₃ O ₄ .
The method of claim 2, wherein as a starting material satisfying the molar ratio x, y
A ceramic connecting material comprising 0.7 mol La ₂ O ₃ , 0.2 mol CaCo ₃ , 0.1 mol CaF ₂ , 0.9 mol Cr ₂ O ₃ , 0.1 mol Co ₃ O ₄ .
In the method for synthesizing a linker powder having a basic composition of La _{1 - x} Ca _x Cr _{1 - y} Co _y O ₃ and satisfying 0.1 ≦ _x ≦ 0.3 and 0.1 ≦ y ≦ 0.2,
Grinding and mixing the starting material and the first solvent of the linker powder;
Drying the starting material in a liquid state and then heat-processing to powder;
Grinding the powder by a milling method after the heat treatment and adding an additive; And
A method for synthesizing a ceramic connecting material, comprising granulating the powder to which the grinding and additives are added to a predetermined particle size by spray drying.
The process of claim 5, wherein the process of powdering by heat treatment
The starting material in the liquid state is calcined at a temperature increase rate of 0.5 ℃ / min to 10 ℃ / min at 850 ℃ to 1200 ℃,
Grinding and mixing the calcined powder and the second solvent,
And drying the starting material in a liquid state, followed by sintering at a temperature rising rate of 0.5 ° C / min to 10 ° C / min at 1100 ° C to 1400 ° C.
The process of claim 5, wherein the grinding of the powder by milling
After the ball mill operation further comprising the step of further performing at least one of a jet mill, bead mill or attrition mill process to refine the particle size of the ceramic connecting member Synthesis method.
The method of claim 5, wherein the additive
A method of synthesizing a ceramic connecting material comprising at least one of a binder, a release agent, a dispersant, and an antifoaming agent.
9. The method according to any one of claims 5 to 8,
A method of synthesizing a ceramic connecting material, further comprising a heat treatment process for burning the additive contained in the spray-dried raw material.
The method of claim 9, wherein the heat treatment process
A method of synthesizing a ceramic connecting material, characterized in that the heat treatment for 3 to 10 hours at a temperature increase rate of 0.5 ℃ / min to 5 ℃ / min at a temperature of 450 ℃ to 800 ℃.

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