JPH06240435A - Production of airtight film - Google Patents

Abstract

PURPOSE:To enhance the yield of powdery starting material at the time of a thermal spraying, to enhance the yield of substrates by suppressing the cracking of them, to improve productivity by increasing the rate of film formation and to form a film having high airtightness. CONSTITUTION:Powdery starting material for the thermal spraying is thermally sprayed on a substrate to form a thermally sprayed film and this film is heat- treated to form an airtight film. The average particle diameter (d50) of the powdery starting material is regulated to 20-40mum, preferably 25-35mum. Value [(d90-d10)/d50] given by dividing the difference between 90% diameter (d90) and 10% diameter (d10) of the volume cumulative particle size distribution of the powdery starting material by the average particle diameter (d50) is regulated to >=0.9, preferably 1.1-1.6. This invention is preferably applied at the time of producing the solid electrolyte membrane of a solid electrolyte type fuel cell or an interconnector.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a solid electrolyte membrane of a solid oxide fuel cell (SOFC), an airtight membrane such as an interconnector.

[0002]

2. Description of the Related Art A method of forming a solid electrolyte membrane of SOFC is divided into a dry method and a wet method. EVD as a dry method
A typical method is a thermal spraying method, and a wet method includes a tape casting method, a slip casting method, and an extrusion molding method (Energy Engineering 13-2, 1990).
Chemical vapor deposition (CVD) and electrochemical vapor deposition (EVD)
According to a so-called vapor phase method such as a method), the apparatus becomes large and the processing area and processing speed are too small. Further, since zirconium chloride or the like is used or steam is mixed with oxygen to be used, running cost is increased.

If the solid electrolyte membrane is formed by plasma spraying, the film formation rate can be increased, the handling of the apparatus and the like is simple, and the thin film can be formed relatively densely. For this reason, the plasma spraying method has been used conventionally (Sunshine 1981, Vol.2, No. 1: Integrated Energy Engineering 13-
2, 1990).

However, since the porosity of the solid electrolyte membrane formed by plasma spraying generally exceeds 5% and reaches 10%, the solid electrolyte membrane for SOFC is not sufficiently dense, and the solid phase of plasma spraying is insufficient. As a result, cracks and layered defects are generated in this film.

In the SOFC, generally, the fuel electrode and the air electrode of the adjacent unit cells are connected in series via the interconnector and the connection terminal. Therefore, it is particularly desired to thin the interconnector to reduce its electrical resistance. On the other hand, since the interconnector separates the oxidant and the fuel, airtightness is required.

At present, as a method for improving the above-mentioned drawbacks of the sprayed coating, a method of heat treating the sprayed coating to densify it, a method of impregnating the sprayed coating with a slurry, a spraying method and an EV.
A method of combining the D method is known.

[0007]

However, the method of impregnating the sprayed film with the slurry and the method of combining the spraying method with the EVD method require a long manufacturing time and a high equipment cost. Therefore, the method of densifying the sprayed film by heat treatment is excellent in terms of manufacturing technology. However, when spraying the material of the solid electrolyte membrane or interconnector on the SOFC substrate,
The yield of the raw material powder was low, and the substrate was often cracked, resulting in a low yield of the substrate.

An object of the present invention is to improve the yield of raw material powder during thermal spraying, to reduce the cracking of the substrate to improve the yield of the substrate, to increase the film forming rate to improve the productivity, and to improve the airtightness. It is to be able to form a film having high properties.

[0009]

According to the present invention, a raw material powder for thermal spraying is sprayed on a substrate to form a sprayed film, and the sprayed film is heat treated to form an airtight film. A value obtained by dividing the difference between the 90% diameter (d ₉₀ ) and the 10% diameter (d ₁₀ ) of the volume cumulative particle size distribution of the raw material powder by the average particle diameter, which has an average particle diameter (d ₅₀ ) of 20 μm to 40 μm. (D ₉₀ −
d ₁₀ ) / d ₅₀ is 0.9 or more, and relates to a method for producing an airtight film.

[0010]

The present inventors have found that the raw material particle size of the raw material powder for thermal spraying is
The inventors have found that it is extremely important for the airtightness of the sprayed film after heat treatment and the productivity of the sprayed film, and arrived at the present invention. That is, selection of the thermal spraying raw material powder was fatally important.

That is, with respect to the yield of the substrate after thermal spraying, it was found that the yield increased as the particles of the raw material powder were made larger. Especially, the average particle size (d ₅₀ ) of the raw material powder is 20 μm
As described above, more preferably 25 μm or more markedly improves the yield of the substrate after thermal spraying. Further, if the average particle size of the raw material powder is 20 μm or more, the film formation rate during thermal spraying also increases.

Further, regarding the yield of the sprayed raw material, it was important to specify the particle size of the raw material powder. Here, the yield of the sprayed raw material means the inking weight (%) of the sprayed coating when the supply amount of the raw material powder is 100%. That is, when the average particle size of the raw material powder was within the range of 20 to 40 μm, the yield of the thermal spray raw material was greatly improved.

When the average particle size of the raw material powder is smaller than 20 μm, it is considered that the yield of the thermal spraying raw material is low because the fine powder does not enter the plasma flame well. Further, when the average particle size of the raw material powder is larger than 40 μm, large particles are in an unmelted or semi-molten state, and it becomes difficult to adhere to the substrate.

Furthermore, the present inventor has found that the particle size distribution of the raw material powder has a great influence on the airtightness and microstructure of the film and the yield of the substrate. That is, it was found that the raw material powder having a broad particle size distribution had a higher film airtightness and a denser quality than the raw material powder having a sharp particle size distribution, and the yield of the substrate was also high.

Specifically, the difference between the 90% diameter (d ₉₀ ) and the 10% diameter (d ₁₀ ) of the volume cumulative particle size distribution of the raw material powder is defined as the average particle diameter.
If the value (d ₉₀ −d ₁₀ ) / d ₅₀ divided by (d ₅₀ ) is set to 0.9 or more, the nitrogen gas permeation coefficient of the membrane after the heat treatment becomes further smaller, and the number of coarse atmosphere pores with a diameter of 1 μm or more decreases and the pores Rate and average pore diameter decreased. Also, the number of cracks in the substrate during the thermal spraying process was reduced. It is considered that this is because when the powder is melted and adheres to the substrate, the packed state of the molten powder is improved by appropriately mixing the relatively large particles and the small particles.

It is particularly preferable to apply the manufacturing method of the present invention to an electrically conductive film of SOFC. Here, the electrically conductive film includes an electron conductive film such as an interconnector and an ion conductive film such as a solid electrolyte film. Especially, in SOFC, since the voltage per one is small, a large number of unit cells are connected to produce a plant. For this reason, it is possible to manufacture solid electrolyte membranes and interconnectors for single cells with high productivity,
In addition, there has been a strong demand for many years to improve the airtightness.

In the present invention, spraying the raw material powder onto the substrate includes spraying the raw material powder onto the surface of the substrate and spraying the raw material powder onto the surface of another layer on the substrate. Further, when the substrate is a porous substrate for SOFC, this includes the case where an air electrode film or a fuel electrode film is formed on the surface of this porous substrate and the raw material powder is sprayed on the surface of these electrode films.

[0018]

EXAMPLES In the case of forming an interconnector according to the present invention, a material for interconnector is sprayed on a substrate and then this sprayed film is heat-treated. The interconnector is preferably formed of a lanthanum-based perovskite complex oxide, for example, lanthanum chromite. If the interconnector is made of lanthanum chromite, the material for the interconnector is lanthanum chromite or a mixture of lanthanum oxide and chromium oxide. In such interconnector materials, copper,
Doping with zinc, calcium, strontium, etc. has the effect of promoting densification of the interconnector during the subsequent heat treatment step.

When the solid electrolyte membrane is formed according to the present invention, a raw material that produces a solid electrolyte at least after heat treatment is used. As the material of the solid electrolyte membrane, for example, zirconia stabilized by an alkaline earth metal or a rare earth element and ceria containing an alkaline earth metal or a rare earth element are currently promising. To produce a solid electrolyte membrane made of these materials, as raw material powder,
A mixed powder of a powder of an alkaline earth metal compound or a compound powder of a rare earth element and a zirconia powder or a ceria powder is used. Alternatively, powder of a solid solution of an alkaline earth metal compound or a compound of a rare earth element and a zirconia compound or a ceria compound can be used.

When a self-supporting air electrode substrate is used as the substrate, the manufacturing process can be simplified as compared with the case where the air electrode film is formed on the surface of the zirconia porous substrate. The present invention can also be applied when a self-supporting fuel electrode substrate is adopted as the substrate.

The present invention relates to a flat plate type SOFC and a cylindrical type SOF.
It can be applied to any type of SOFC such as C that can adopt the thermal spraying method. However, it is particularly suitable for a cylindrical SOFC.

When the present invention is applied to a cylindrical SOFC, the substrate should have a cylindrical shape with both ends open, or
Alternatively, it may have a cylindrical shape with one end open and the other end closed. 1 and 2 are perspective cutaway views of such a cylindrical SOFC.

In FIG. 1, a solid electrolyte membrane 2 and a fuel electrode membrane 3 are arranged on the outer surface of a single-layer cylindrical air electrode substrate 1 made of an air electrode material, and an upper right region in FIG. In the above, the interconnector 4 is provided on the surface of the air electrode substrate 1, and the connection terminal is attached thereon. Then, in order to connect the cylindrical SOFCs in series, the air electrode substrate 1 of the SOFC and the fuel electrode film 3 of the adjacent SOFC are connected via the interconnector 4 and the connection terminal, and the cylindrical SOFCs are connected in parallel. The fuel electrode films 3 of the adjacent SOFC elements are connected by Ni felt or the like. The solid electrolyte membrane 2 and the interconnector 4 are provided according to the present invention.

In the SOFC of FIG. 2, the air electrode film 11 is provided on the outer surface of the cylindrical porous ceramic substrate 5, and the solid electrolyte film 2 and the interconnector 4 are provided on the outer surface of the air electrode film 11. ing.

Next, taking the SOFC shown in FIG. 1 as an example,
A procedure for forming the solid electrolyte membrane 2 and the interconnector 4 will be illustrated. First, the air electrode substrate 1 is surface-treated, a mask for interconnector is placed on the substrate 1, the substrate is preheated, and the material for interconnector is sprayed on the substrate to form a first sprayed film. The mask for use is removed from the substrate, and the first sprayed film is heat-treated to form the interconnector 4. Interconnector 4 of base 1
Other than the above, the surface treatment is performed, a mask for a solid electrolyte membrane is installed on the base body 1, the base body 1 is preheated, and a solid electrolyte material is sprayed on the base body 1 to form a second sprayed film. The electrolyte membrane mask is removed from the substrate, and the second sprayed membrane is heat treated to form a solid electrolyte membrane.

In another method, first, the air electrode substrate 1 is surface-treated, an interconnector mask is placed on the substrate 1, the substrate 1 is preheated, and the interconnector material is sprayed on the substrate 1. The first sprayed film is formed, and the interconnector mask is removed from the substrate 1.
A solid electrolyte membrane mask is placed on the base 1, the base body 1 is preheated, a solid electrolyte material is sprayed on the base body 1 to form a second sprayed film, and the solid electrolyte membrane mask is removed from the base body 1. . And by heat-treating the entire structure,
The solid electrolyte membrane 2 and the interconnector 4 are formed.

According to such a method, the first sprayed film and the second sprayed film can be simultaneously densified by a single heat treatment, and an airtight interconnector and a solid electrolyte film can be manufactured. Therefore, the time and labor are greatly reduced. The thermal spraying method also includes low pressure plasma spraying, atmospheric pressure plasma spraying, and explosion spraying.

[Experiment 1] Hereinafter, more specific experimental results will be described. Raw material powders of 8 mol% yttria-stabilized zirconia having average particle diameter, 90% diameter and 10% diameter shown in Table 1 were prepared. La _0.9 Sr _0.1 M _n O ₃ composed of outer diameter 20
A porous air electrode substrate 1 having a diameter of 16 mm, an inner diameter of 16 mm and a length of 300 mm was prepared. Each of the above raw material powders was plasma sprayed onto the air electrode substrate 1 using a plasma sprayer. A mixed gas of argon and hydrogen was used as the plasma gas, the output was 40 kw, the powder supply amount was 15 g / min, and the spraying distance was 120 mm.

While rotating the cylindrical air electrode substrate 1 with the central axis in the longitudinal direction as the axis of rotation, the spray gun
It was moved parallel to the axis of rotation. At this time, the moving speed of the spray gun is 100 mm / sec, and the rotation speed of the air electrode substrate 1 is 800 rpm.
Then, a sprayed film having a thickness of 100 μm was formed.

The average particle diameter (d ₅₀ ), 10% diameter (d ₁₀ ) and 90% diameter (d ₉₀ ) of each raw material powder were measured by the laser diffraction scattering method. Then, for each example, the yield of the air electrode substrate 1 during thermal spraying and the yield of the raw material during thermal spraying were measured.
The yield of the air electrode substrate 1 is the ratio (%) at which the air electrode substrate 1 was not cracked when plasma sprayed under the above-mentioned spraying conditions.

The yield of the raw material during thermal spraying was determined as follows. That is, it was determined by the time during which the raw material powder was sprayed on the air electrode substrate, the supply amount of the raw material powder, and the weight change of the air electrode substrate 1 before and after the thermal spraying.

Raw material yield during thermal spraying = (weight of air electrode substrate 1 after thermal spraying (g) -weight of substrate 1 before thermal spraying (g)) × 100
% / Feeding amount of raw material powder (g / min) × spraying time (min). The results are shown in Table 1 below.

As can be seen from Table 1, by setting the average particle size of the raw material powder to 20 to 40 μm, the yield of the substrate during thermal spraying is remarkably improved. Also, the average particle size of the raw material powder is 20 to
Within the range of 40 μm, the raw material yield was high.

Further, the sprayed coating was heat-treated to evaluate the denseness of the obtained coating. After forming the sprayed film on the air electrode substrate 1, it was heat-treated at 1500 ° C. for 3 hours to provide a solid electrolyte film.

The cross section of the solid electrolyte membrane after the heat treatment was exposed, the cross section was mirror-polished, the cross section was observed with a scanning electron microscope (SEM), and a microstructure photograph was taken. This photograph was processed by an image processor to determine the average pore diameter, the number of pores having a diameter of 1 μm or more, and the porosity. When taking a microstructure photograph by SEM, the magnification was 2000 times, several photographs were taken, and the total area of 0.005 mm ² was measured. Further, the N ₂ gas permeation coefficient of the solid electrolyte membrane was measured.

[0036]

[Table 1]

As can be seen from Table 1, (d ₉₀ −d ₁₀ ) / d
_It was found that the average particle diameter of the solid electrolyte membrane, the number of pores having a diameter of 1 μm or more, and the porosity of the raw material powder having a value of ₅₀ larger than 0.9, that is, the raw material powder having a broad particle size distribution, became smaller after the heat treatment. . It was also confirmed that a film having a higher density can be obtained when the average particle size is 35 μm or less.

[Experiment 2] An SOFC unit cell was prepared and
Confirmed the performance of. La₂O₃ 106.1 g and MnO₂6
8.4g and SrCO₃10.8 g was weighed. 800 g of cobblestone
, 200 g of water and 2 liters of the above-mentioned weighed three compounds
Place in a tor ball mill and mix for 3 hours to form a slurry.
It was After drying this slurry at 110 ° C for 20 hours,
Crushed to 149 μm or less and calcined in air at 1200 ° C for 10 hours
And La _0.9Sr_0.1MnO₃Was synthesized.

Thereafter, this was crushed and crushed by a ball mill to obtain a powder having an average particle size of 1 μm, 20 wt% of cellulose was added and mixed, and this was pressed by a rubber press to give an inner diameter of 16 m.
It was molded into a cylindrical shape with m and an outer diameter of 20 mm. This is 1500 ℃ × 10
The porous air electrode substrate 1 was fired for a period of time.

Average particle size 28.9 μm, 90% diameter 50 μm, 10%
An 8 mol% yttria-stabilized zirconia powder having a diameter of 12 μm and (d ₉₀ −d ₁₀ ) / d ₅₀ = 1.31 was prepared. Further, the powder obtained by crushing the lanthanum chromite compound is slurried, and the slurry is dried and granulated, and the slurry is dried in air at 1500 ° C. for 1 hour.
Calcination for an hour, then classification, average particle size 34.5 μm, (d ₉₀ −
A lanthanum chromite thermal spraying powder having d ₁₀ ) / d ₅₀ = 1.51 was obtained.

Masking was performed on the surface of the cylindrical substrate 1 in the form of a strip in the axial direction, leaving a spraying area having a width of 5 mm, and the above-mentioned lanthanum chromite spraying raw material was sprayed on the surface of the substrate 1 to give a thickness of 150 μm. A belt-shaped sprayed film was formed. Then
Only the sprayed film portion of the lanthanum chromite was masked, and the other portion was sprayed with the above 8 mol% yttria-stabilized zirconia powder to obtain a sprayed film having a thickness of 100 μm. Then, this structure was heat treated together with the substrate at 1500 ° C. for 5 hours to obtain a substrate 1 having an airtight interconnector and a solid electrolyte membrane. After that, a slurry of Ni / 8 mol% yttria-stabilized zirconia = 4/6 (weight ratio) is applied to the surface of the solid electrolyte membrane and fired at 1300 ° C for 5 hours to form a fuel electrode to form an SOFC unit cell. It was made.

The unit cell thus produced is cut out and length
A member of 50 mm was obtained, air was introduced into this inner space as an oxidizing gas, and hydrogen humidified at room temperature was introduced as a fuel gas,
This cell is operated at 1000 ℃, electromotive force (open end voltage)
Was measured. The electromotive force was 1.07V.

Further, in order to evaluate the airtightness of the above solid electrolyte membrane, under the above conditions, the entire surface of the air electrode substrate 1 was
The above 8 mol% yttria-stabilized zirconia powder was sprayed without masking and heat-treated at 1500 ° C. for 5 hours, and the nitrogen gas permeability coefficient of the zirconia film thus obtained was measured. As a result, a measured value of 2 × 10 ⁻⁸ cm ⁴ / g · sec was obtained. Thus, it was confirmed that a solid electrolyte membrane having an extremely high airtightness was obtained.

Further, in order to evaluate the airtightness of the interconnector, the lanthanum chromite thermal spraying powder was sprayed on the entire surface of the air electrode substrate 1 under the above conditions without masking, and at 1500 ° C. After heat treatment for 5 hours, the nitrogen gas permeability coefficient of the interconnector thus obtained was measured. As a result, a measured value of 8 × 10 ⁻⁸ cm ⁴ / g · sec was obtained. Thus, it was confirmed that an interconnector having an extremely high airtightness was obtained.

The raw material powder used for thermal spraying in the present invention is
It may be granulated by a spray dryer, crushed sinter, or crushed after solidifying a high temperature melt. However, it is necessary to have the average particle size and the particle size distribution defined in the present invention.

[0046]

As described above, according to the present invention, the cracking of the substrate after thermal spraying is reduced and the yield of the substrate is improved.
The film formation rate during thermal spraying is increased, and the yield of thermal spraying raw material is also improved. Due to these synergistic effects, the production amount of the airtight film is significantly improved, and the production cost is significantly reduced. Moreover, after the heat treatment, the denseness of the airtight film is further improved and the nitrogen gas permeability coefficient is lowered.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing an example of a cylindrical SOFC.

FIG. 2 is a partially cutaway perspective view showing an example of a cylindrical SOFC.

[Explanation of symbols]

 1 Air Electrode Substrate 2 Solid Electrolyte Membrane 3 Fuel Electrode Membrane 4 Interconnector 5 Porous Substrate 11 Air Electrode Membrane

Claims (3)

[Claims] 1. A raw material powder for thermal spraying is sprayed on a substrate to form a sprayed film, and when this sprayed film is heat-treated to form an airtight film, the average particle diameter (d ₅₀ ) of the raw material powder is 20 μm
˜40 μm, which is 90 of the volume cumulative particle size distribution of the raw material powder.
The value (d ₉₀ −d ₁₀ ) / d _{50 obtained} by dividing the difference between the% diameter (d ₉₀ ) and the 10% diameter (d ₁₀ ) by the average particle diameter is 0.9 or more, and Production method. 2. The raw material powder has an average particle diameter of 25 to 35 μm, and a value obtained by dividing the difference between the 90% diameter and the 10% diameter by the average particle diameter (d ₉₀ −d ₁₀ ) / d _50. Is 1.1 to 1.6, The method for producing an airtight film according to claim 1. 3. The method for producing an airtight film according to claim 1, wherein the airtight film is an electrically conductive film of a solid oxide fuel cell.