JPH06144940A - Material for thermally spraying lanthanum chromite, solid electrolyte fuel cell, and production of thermally spraying powdery material - Google Patents

Abstract

PURPOSE:To stably produce the lanthanum chromite small in permeation constant of gaseous nitrogen without deposition of lanthanum oxide. CONSTITUTION:The granulated particles of lanthanum chromite in which chromium oxide particles are dispersed is used as the thermally spraying material. A thermally sprayed film is formed by thermally spraying the granulated particles on a substrate, and the thermally sprayed film is heat treated, and a airtight lanthanum chromite film is obtained. The specific surface area of the granulated particle is preferably <=0.9m<2>/g. More than 80vol.% of the granulated particles has 20-110mum grain size preferably. And, the granulated particles are thermally sprayed on the electrode of the solid electrolyte type fuel cell and the thermally sprayed film is heat treated, and an interconnector is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lanthanum chromite thermal spray material and a solid oxide fuel cell produced by using the same.

[0002]

2. Description of the Related Art A solid oxide fuel cell (SOFC) has 1000
Since it operates at a high temperature of ℃, the electrode reaction is extremely active, no expensive noble metal catalyst such as platinum is required, the polarization is small, and the output voltage is relatively high, so the energy conversion efficiency is remarkably higher than other fuel cells. high. Furthermore, since the structural material is composed entirely of solid, it is stable and has a long life.

In such SOFCs, in general, adjacent SOFCs
The fuel electrode and the air electrode of the element (single cell) are connected in series via the interconnector and the connection terminal. Therefore, in particular, it is desired to reduce the electrical resistance by thinning the interconnector.

Chemical vapor deposition (CVD), electrochemical vapor deposition (EVD), and the like are conceivable as techniques for thinning the interconnector, but this increases the size of the film forming apparatus and
Processing area and processing speed are too small.

The method of using plasma spraying for manufacturing a solid oxide fuel cell is excellent in that the film formation rate is fast, simple, and thin and relatively dense can be formed. (Sunshine 1981, vo12, No.1).
For example, it is known to form a solid electrolyte membrane by plasma spraying a spraying raw material in which cerium oxide or zirconium oxide and a metal oxide such as an alkaline earth metal or a rare earth element are solid-solved after particle size adjustment (JP 61-198569 and 61-198570).

However, a film produced by plasma spraying has cracks and layered defects. For this reason, when the SOFC interconnector is formed by plasma spraying, fuel leakage occurs when hydrogen, carbon monoxide, etc. permeate the interconnector during operation of the SOFC.
The electromotive force per SOFC single cell became smaller than, for example, the usual 1 V, the output decreased, and the conversion rate of fuel to electric power deteriorated.

At this time, it is conceivable to increase the film thickness of the interconnector to cope with fuel leakage, but in this case, the battery resistance increases and the battery output decreases.
Therefore, at the same time as making the interconnector airtight,
There is a demand for a method of increasing the output of the battery by thinning the film as long as fuel leakage does not occur.

It was announced that lanthanum calcium chromite was sprayed on the surface of a lanthanum manganite substrate and then heat-treated to form a dense lanthanum chromite film, which was used as an interconnector of SOFC (September 1991).
March, 32nd Battery Symposium Abstracts, p. 205). Prior to this announcement, the applicant also developed a technology for heating and densifying the lanthanum chromite sprayed film, and has applied for a patent (filed on January 28, 1991, Japanese Patent Application No. 3-25245). (Specification).

[0009]

However, when the present inventor further studied this technique, it was found that there was a new problem. That is, when the lanthanum chromite film is formed by plasma spraying, the chromium component is partially evaporated during the spraying, and the chromium component is lost from the raw material composition. Therefore, lanthanum oxide is deposited in the sprayed film,
It was found that the electric resistance increased. Furthermore, since lanthanum oxide has a remarkably high hygroscopicity, it absorbs moisture in the sprayed film and chemically changes to lanthanum hydroxide. Along with this chemical change, the volume changes and the lanthanum chromite film is destroyed. Therefore, the lanthanum chromite film in which lanthanum oxide is deposited is not practical.

To solve this problem, the present inventor has developed a technique for preventing the precipitation of lanthanum oxide by adding an excessive chromium component in advance to the thermal spraying raw material and compensating for the evaporation of the chromium component during thermal spraying. (See Japanese Patent Application No. 03-320584, unpublished at the time of this application). However, it was discovered that this method still had some problems. That is,
Pore, which is a trace of diffusion of chromium component, was generated in the thermal sprayed film after the heat treatment, which sometimes increased the nitrogen gas permeation coefficient of the film.

An object of the present invention is to make it possible to stably produce a lanthanum chromite film having no nitrogen gas permeation coefficient and no precipitation of lanthanum oxide. Also,
An object of the present invention is to apply this lanthanum chromite film to SOFC and increase the output of SOFC.

[0012]

The present invention is a lanthanum chromite thermal spray comprising a lanthanum chromite granulated particle for thermal spraying, characterized in that chromium oxide particles are dispersed in the granulated particle. It relates to raw materials.

In the above, "lanthanum chromite"
Is a complex oxide having a perovskite structure having lanthanum at the A site and chromium at the B site, including those in which the A site and the B site are doped with a metal element other than the above. In this case, calcium and strontium can be exemplified as the substitution metal element of the A site, and the substitution rate is
It is preferably 10 to 30 mol%. Examples of the substitutional metal element at the B site include iron, titanium, cobalt, zinc, copper, aluminum and nickel, and the substitution ratio is 10 to 50.
It is preferably set to mol%.

[0014]

In the present invention, it was found that the dispersion state of chromium in the sprayed film is improved by spraying the lanthanum chromite spraying raw material in which the chromium oxide particles are dispersed in the granulated particles onto the substrate. It was Then, a lanthanum chromite film free of lanthanum oxide and having a small nitrogen gas permeation coefficient was obtained by heat-treating this sprayed film.
As a result, the lanthanum chromite film, which has low electric resistance and is stable for a long time, can be produced from the viewpoint of the characteristics of the film.

Here, the absence of lanthanum oxide in the lanthanum chromite film means that the presence of lanthanum oxide cannot be confirmed by the backscattered electron image of a scanning electron microscope and EDS (energy dispersive X-ray microanalyzer). .

The above-mentioned "spraying" refers to currently known plasma spraying, flame spraying, and explosion spraying, and plasma spraying is particularly preferable. This plasma spraying includes low pressure plasma spraying and atmospheric pressure plasma spraying.

Further, by applying the present invention to SOFC, it becomes possible to form an interconnector that is airtight, has low electric resistance, and is stable for a long period of time. As a result, fuel leakage at the interconnector is reduced and electromotive force per SOFC single cell is increased. Further, the resistance of the interconnector portion is lowered, and the output of the battery can be improved accordingly. Furthermore, SOFC can be operated stably for a long period of time.

The specific surface area of the raw material for lanthanum chromite spraying is preferably set to less ^{0.9m 2 / g, 0.2 ~0.9m 2} /
More preferably, it is within the range of g. This specific surface area is 0.2m
^{If the} powder is less than ² / g or more than 0.9 m ² / g, the meltability of the powder when fed into the plasma arc is poor, and the sprayed film is difficult to be dense.

Further, 80 vol% or more of all the granulated particles are
It is preferable to have a particle size of 20 μm to 110 μm,
More preferably, 90 vol% or more has a particle size of 20 μm to 110 μm. That is, if there are many granulated particles having a particle size of less than 20 μm, the fluidity of the granulated particles as a whole deteriorates, and the film thickness of the sprayed film tends to become non-uniform. Also, if there are many granulated particles having a particle size of more than 110 μm, the particles are not completely melted and taken into the sprayed film as unmelted particles, so that the denseness and uniformity of the sprayed film deteriorate.

The heat treatment temperature is preferably 1250 ° C to 1500 ° C. If this is less than 1250 ° C, the nitrogen gas permeability coefficient (described later) of the lanthanum chromite membrane becomes too large, and the airtightness is insufficient. If it exceeds 1500 ° C, the substrate is easily deformed. For example, an air electrode substrate made of lanthanum manganite shrank when the temperature exceeded 1500 ° C., and a large warpage occurred due to the difference in shrinkage with the lanthanum chromite film (interconnector) on the air electrode substrate.

The lanthanum chromite film of the present invention is characterized in that it is airtight and can be made into a thin film.
In addition to FC interconnectors, it is also possible to spray high temperature corrosion resistant conductors on metal surfaces.

[0022]

EXAMPLES Next, the SO to which one of the present invention is applied
The FC will be exemplified. FIG. 1 is a cutaway perspective view showing an example of a cylindrical SOFC. In FIG. 1, the air electrode film 3 is provided on the outer periphery of the cylindrical porous ceramic substrate 4.
The solid electrolyte membrane 2 and the fuel electrode membrane 1 are arranged along the outer periphery of the air electrode membrane 3, and the interconnector 6 is provided on the air electrode membrane 3 in the upper region in FIG. 7 is attached. And cylindrical SOF
In order to connect C in series, the SOFC air electrode film 3 and the adjacent SOFC fuel electrode film 1 are connected via the interconnector 6 and the connection terminal 7, and in order to connect the cylindrical SOFCs in parallel, they are adjacent to each other. Between the fuel electrode membranes 1 of the SOFC element
Connect with Ni felt or the like. Then, at the time of forming the interconnector 6, according to the present invention, a sprayed film is formed on the surface of the air electrode film 3 (on the porous substrate 4) and heat treatment is performed.

In FIG. 1, the arrangement of the fuel electrode membrane 1 and the air electrode membrane 3 may be reversed. Further, instead of providing the air electrode film 3 on the surface of the porous substrate 4, as shown in FIG. 2, a single layer cylindrical air electrode substrate 13 made of a porous air electrode material may be used. In this case, the interconnector 6 is provided directly on the surface of the cylindrical air electrode substrate 13.

Both ends of the cylindrical SOFC may be opened, or one end may be opened and the other end may be sealed to form a tubular tubular SOFC.

The air electrode is made of doped or undoped LaMnO ₃ , CaMnO ₃ , LaNiO ₃ , LaCo.
LaMnO ₃ which can be produced from O ₃ , LaCrO ₃ or the like and is doped with strontium or calcium is preferable. Generally, the fuel electrode is preferably a nickel-zirconia cermet or a cobalt-zirconia cermet. The solid electrolyte is preferably formed of zirconium oxide stabilized or partially stabilized with a rare earth metal element such as yttria or cerium oxide containing a rare earth element.

Hereinafter, more specific experimental results will be described. (Experiment 1) As starting materials, La ₂ O ₃ , CaCO ₃ , Cr ₂ O ₃ and SrC
O ₃ and CuO powders were used. Each powder of this was weighed and mixed so as to have the composition shown in Table 1. This mixed powder 10
200 parts by weight of water and 200 zirconia boulders for 0 parts by weight
Parts by weight, and pulverized and mixed by a ball mill for 15 hours to obtain a slurry. The slurry is dried at 120 ° C, then the dried product is crushed to a particle size of 149 µm or less, and the particles are dried at 1300 ° C in air
The mixture was calcined for 5 hours to obtain a lanthanum chromite compound having a desired composition. This lanthanum chromite compound was crushed, and 200 parts by weight of water and 200 parts by weight of zirconia boulder were added to 100 parts by weight of this crushed product, and the mixture was crushed for 15 hours in a ball mill and mixed to obtain a slurry. Next, this slurry was supplied to a spray dryer for granulation to obtain a lanthanum chromite thermal spraying raw material in which chromium oxide was dispersed in the granulated particles of the present invention.

For comparison, B used in the preparation of Sample 1-1
5.3 parts by weight of chromium oxide powder was mixed with 100 parts by weight of the site-defective thermal spraying raw material powder to prepare powder (A) for preparing sample 1-2. As shown in Table 1, the composition ratio of this powder as a whole is the same as that of the powder (B) used in the preparation of Sample 1-3.

In Table 1, "state of chromium oxide particles"
When described as “none” in the above item, there is only lanthanum chromite granulated particles, and there is no chromium oxide powder. Further, in the case where the granulated particles of lanthanum chromite and the chromium oxide particles are mixed, “A” is described in the section “State of chromium oxide particles”. Further, in the case where the chromium oxide particles are dispersed in the lanthanum chromite granulated particles, "B" is added in the "state of chromium oxide particles" section.
Was written. The item "Lantan chromite thermal spray raw material composition" in Table 1 shows a chemical analysis value containing chromium oxide particles when the chromium oxide particles are contained in the raw material.

Regarding the difference between the above "A" and "B",
Further description. "A" is a state in which lanthanum chromite granulated particles and chromium oxide particles are present separately and two kinds of particles are mixed. “B” is a state in which chromium oxide particles are dispersed in the lanthanum chromite granulated particles, and the lanthanum chromite particles and the chromium oxide particles cannot be separated.

The surface of the cylindrical air electrode substrate 13 shown in FIG. 2 was plasma sprayed using a plasma sprayer so that each of the above-mentioned spraying raw materials had a thickness of 200 μm. Next, each sprayed air electrode substrate was placed in an electric furnace and heat-treated at 1500 ° C. for 5 hours. The nitrogen gas permeation coefficient of the lanthanum chromite membrane thus obtained was measured. Moreover, the presence or absence of lanthanum oxide was confirmed by the backscattered electron image of a scanning electron microscope and EDS. The results are shown in Table 1.

The N ₂ gas permeation coefficient was measured using an apparatus schematically shown in FIG. That is, a cylindrical sample
25 was set on the jig 24, and the sample 25 and the jig 24 were sealed with an adhesive. The inner surface of the sample 25 is exposed to a pressurized nitrogen atmosphere at 2 atm, and the outer surface of the sample is exposed to an atmospheric air atmosphere (measured at room temperature). At this time, the flow rate flowing from 2 atm side to 1 atm side was measured by the mass flow controller 23, and the N ₂ gas permeation coefficient K (cm ⁴ g ^-1 se
c ^-1 ). However, in FIG. 3, 22 indicates an N ₂ cylinder, 26 indicates a pressure gauge, and 27 indicates a valve.

K = t · Q / (ΔP · A). t: sample thickness (cm). Q: N ₂ gas permeation flow rate (cm ³ / s). ΔP: differential pressure (g / cm ² ). A: Surface area of sample 25 (cm ² ).

[0033] At this time, with the sample 25 by setting the air electrode substrate alone and measuring the N ₂ gas permeation coefficient K _1, Part N ₂ gas permeability set the laminate of the air electrode substrate and the interconnector The coefficient K ₃ was measured. Then, the N ₂ gas permeation coefficient K ₂ of the interconnector alone was calculated from the following formula.

K ₂ = t ₂ · K ₁ · K ₃ / (K ₁ · t ₃ +
t ₁ · K ₃ ). t ₂ : Thickness of interconnector t ₃ : Thickness of laminated body t ₁ : Thickness of air electrode substrate

[0035]

[Table 1]

In sample 1-1, chromium oxide particles were not present in the thermal spraying raw material, and the B site of lanthanum chromite was missing. In this case, lanthanum oxide was present in the lanthanum chromite film after the heat treatment.

In sample 1-2, lanthanum chromite granulated particles and chromium oxide particles are mixed. In this case, lanthanum oxide does not exist in the film after the heat treatment,
The N ₂ gas permeation coefficient increases, reaching a value of the order of 10 ⁻⁷ cm ⁴ / g · sec. As described above, when the N ₂ gas permeation coefficient of the membrane is 10 ⁻⁷ or more, the SOFC causes leakage of the fuel gas, which is not practical.

In Samples 1-3, 1-4 and 1-5, chrome oxide particles are dispersed in the lanthanum chromite granulated particles. In these cases, lanthanum oxide was not present in the film after the heat treatment, and the nitrogen gas permeability coefficient of the film was in the order of 10 ^-8 .

(Experiment 2) In the same manner as in Experiment 1, raw materials for lanthanum chromite spraying having the compositions shown in Table 2 were obtained. Then, the thermal spraying raw material was subjected to heat treatment, and at this time, the heat treatment time was changed to change various specific surface areas of the thermal spraying raw material as shown in Table 2. Then, a lanthanum chromite film was prepared in the same manner as in Experiment 1, and the nitrogen gas permeation coefficient and the presence or absence of lanthanum oxide were measured. The results are shown in Table 2. However, in this example, chromium oxide particles are dispersed in the lanthanum chromite granulated particles. The thermal spraying raw material composition shown in Table 2 is a chemical analysis value containing the chromium oxide particles.

[0040]

[Table 2]

As can be seen from Table 2, no lanthanum oxide was present in the film after the heat treatment in any of the examples. When a thermal spraying raw material having a specific surface area of 0.9 m ² / g or less is used, the N ₂ gas permeation coefficient of the obtained lanthanum chromite film is 10 ⁻⁸ or less. However, the specific surface area is 0.9 m ² / g
When a larger raw material powder is used, the N ₂ gas permeation coefficient becomes 10 ⁻⁷ or more.

(Experiment 3) In the same manner as in Experiment 1, raw materials for lanthanum chromite spraying having the compositions and specific surface areas shown in Table 3 were obtained. Then, this thermal spraying raw material was classified using a sieve to obtain each thermal spraying raw material having a particle size distribution shown in Table 3. Then, a lanthanum chromite film was prepared in the same manner as in Experiment 1, and the nitrogen gas permeation coefficient and the presence or absence of lanthanum oxide were measured. The results are shown in Table 3. However, in this example, chromium oxide particles are dispersed in the lanthanum chromite granulated particles. The thermal spraying raw material composition shown in Table 3 is a chemical analysis value containing chromium oxide particles.

[0043]

[Table 3]

As can be seen from Table 3, no lanthanum oxide was deposited in the film after the heat treatment in any of the examples. In addition, the proportion of particles with a particle size of 20 to 110 μm is 80 vol%.
When the above raw materials are used, the N ₂ gas permeation coefficient of the obtained lanthanum chromite membrane is 10 ⁻⁸ or less. But 20 ~
When a raw material in which the proportion of particles of 110 μm is less than 80 vol% is used, the N ₂ gas permeation coefficient is 10 ⁻⁷ or more. Particle size 20
Since the powder for thermal spraying containing 10 vol% or more of granulated particles of less than μm had poor fluidity, the granulated particles were clogged in the raw material powder supply device and could not be sprayed.

(Experiment 4) La ₂ O ₃ 106.1 g and MnO ₂ 68.4 g
And 10.8 g of SrCO ₃ were weighed. 800g boulders and 200g water
Then, the weighed three kinds of compounds were put into a 2 liter ball mill and mixed for 3 hours to form a slurry. After drying this slurry at 110 ℃ for 20 hours, the dried material was crushed to 149 μm or less, and calcined in air at 1200 ℃ for 10 hours to obtain La _0.9 Sr.
_0.1 MnO ₃ was 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 have an inner diameter of 16 m.
It was molded into a cylindrical shape with m and an outer diameter of φ20 mm. This is 1500 ℃ × 10
The porous air electrode substrate was fired for a period of time.

This substrate was masked so as to have a width of 5 mm in the lengthwise direction in the axial direction of the cylindrical substrate, and each of the lanthanum chromite thermal spraying raw materials of Experiments 1 to 3 had a thickness of 150 on the surface of the substrate.
Sprayed at μm. Thereafter, only the sprayed film portion of the lanthanum chromite was masked, and 8 mol% yttria-stabilized zirconia (8YSZ), which is a solid electrolyte material, was sprayed on the other portion at a thickness of 100 μm. Then, this structure was heat-treated together with the substrate at 1500 ° C. for 5 hours to obtain a structure having an airtight lanthanum chromite film and a YSZ film. After that, a slurry of Ni / YSZ = 4/6 (weight ratio) was applied to the surface of the solid electrolyte membrane and fired at 1300 ° C. for 5 hours to prepare a fuel electrode to prepare a fuel cell unit cell.

Air was made to flow to the air electrode side of the SOFC thus manufactured, and hydrogen that had been humidified at room temperature was made to flow to the fuel electrode side,
An endurance test of holding at 00 ° C. for 1000 hours was performed. When the appearance of the fuel cell after this durability test was examined, a lanthanum chromite film containing no lanthanum oxide, which was produced using the thermal spraying raw materials of Experiments 1 to 3, was used as an interconnector.
SOFC showed no difference from the pre-test. However, in SOFC using the lanthanum chromite film of Sample 1-1, in which lanthanum oxide was deposited, as an interconnector, the lanthanum chromite film was peeled from the cylindrical substrate after the above test.

[0049]

As described above, lanthanum oxide free from lanthanum and having a small nitrogen gas permeation coefficient is obtained by subjecting the substrate to thermal spraying using the thermal spraying raw material of the present invention and subjecting this thermal sprayed film to heat treatment. A chromite film can be manufactured stably. As a result, in view of the characteristics of the film, the electric resistance is low,
It became possible to fabricate a lanthanum chromite film that was stable for a long period of time.

Further, by forming an SOFC interconnector with such a dense lanthanum chromite film having a low electric resistance, the resistance of the interconnector can be reduced and the airtightness can be increased to reduce the resistance of the battery. . Therefore, the output of the battery can be improved.

[Brief description of drawings]

FIG. 1 is a cutaway perspective view of a cylindrical SOFC seen from one end side.

FIG. 2 is a cutaway perspective view of a cylindrical SOFC seen from one end side.

FIG. 3 is a schematic view showing a measuring device of a nitrogen gas permeation coefficient.

[Explanation of symbols]

 1 Fuel Electrode Membrane 2 Solid Electrolyte 3 Air Electrode Membrane 4 Porous Substrate 6 Interconnector 7 Connection Terminal 13 Air Electrode Substrate

Claims (7)

[Claims] 1. A lanthanum chromite thermal spraying raw material comprising lanthanum chromite granulated particles, wherein chromium oxide particles are dispersed in the granulated particles. 2. The raw material for lanthanum chromite thermal spraying according to claim 1, which has a specific surface area of 0.9 m ² / g or less. 3. 80% by volume or more of the granulated particles are 20
The raw material for lanthanum chromite spraying according to claim 1, which is a granulated particle having a particle diameter of µm to 110 µm. 4. A solid oxide fuel cell comprising a lanthanum chromite film formed by heating a thermal sprayed film obtained from the lanthanum chromite thermal spraying raw material according to claim 1 as an interconnector. 5. The solid oxide fuel cell according to claim 4, wherein lanthanum oxide is not present in the lanthanum chromite film. 6. A method for producing a raw material powder for thermal spraying, which comprises dispersing powders of lanthanum chromite in the lanthanum chromite granulated particles by granulating a powder in which lanthanum chromite particles and chromium oxide particles are mixed. 7. The method for producing a raw material powder for thermal spraying according to claim 6, wherein the granulation is performed with a spray dryer.