JPH07277848A - Porous sintered compact, heat resistant electrode and solid electrolyte type fuel cell - Google Patents

Abstract

PURPOSE:To prevent the occurrence of cracks between a heat resistant electrode and other constituent material because of very low dimensional shrinkage due to a heat cycle by using a porous sintered compact made of a multiple oxide having a perovskite structure (ABO3) and contg. an Mn atom in the B site and regulating the average valence of Mn atoms in the oxide to a prescribed value or above at a prescribed temp. CONSTITUTION:This porous sintered compact is made of a multiple oxide contg. an Mn atom in the B site and the average valence of Mn atoms in the oxide is regulated to >=3.25 at 1,000 deg.C so as to reduce the dimensional shrinkage of this porous sintered compact due to a heat cycle between room temp. and 1,000 deg.C to <=0.01% per one heat cycle. It is preferable that the multiple oxide contains atoms of one or more kinds of metals selected from among rare earth metals other than Ce, alkaline earth metals and Y in the A site and further, contains about 10-70% atoms of Ca and/or Sr as secondary metals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous sintered body, a heat resistant electrode using the same, and a solid oxide fuel cell.

[0002]

2. Description of the Related Art In solid oxide fuel cell development projects, it is important to search for stable materials at high temperatures. Therefore, the power generation temperature of the solid oxide fuel cell has conventionally been 10
In the vicinity of 00 ° C., an experiment has been conducted in which the air electrode is held for a long time and its durability is measured. As an air electrode material for a solid oxide fuel cell, a lanthanum manganite sintered body is currently considered to be promising (Energy Engineering, 13, 2, 52-68, 1990). The above-mentioned porous sintered body made of lanthanum manganite is excellent in terms of stability and heat resistance at the operating temperature of the power generator, and is therefore being paid attention to. As such lanthanum manganite sintered bodies, those having a substantially stoichiometric composition and those having a partial loss of A site (lanthanum site) (manganese-rich composition) are known. In particular, a porous sintered body made of lanthanum manganite having A site doped with Ca or Sr is regarded as a promising material for an air electrode including a self-supporting air cathode tube.

[0003]

However, the present inventor first discovered that the lanthanum manganite porous sintered body has the following problems. That is, the present inventor of the conventional lanthanum manganite porous sintered body has a power generation temperature of the solid oxide fuel cell of 900 to 1
A heating-cooling cycle was applied between a temperature of 100 ° C. and a temperature of room temperature to 600 ° C. to test its stability.
In this lanthanum manganite, the B site is not particularly replaced, and 10% to 20% of the A site is replaced by calcium, or 10% of the A site is replaced.
% To 15% were replaced by strontium.

As a result, a temperature of 900 to 1100 ° C.
It was found that when a heating-cooling cycle was applied between room temperature and 600 ° C., the dimensions of the above porous sintered body shrank by 0.01 to 0.04% per thermal cycle. Moreover, it was found that the shrinkage due to this thermal cycle did not converge even after 100 thermal cycles, and reached several percent after 100 thermal cycles. When the air electrode made of a porous sintered body contracts in this way, cracks may occur between the air electrode made of a porous sintered body and other constituent materials of the unit cell, resulting in destruction of the unit cell. There was found. Moreover,
Even when this unit cell was operated at 1000 ° C. for a long time, such a crack did not occur at all. Therefore, this phenomenon was considered not to be due to the firing shrinkage of the porous sintered body, but to the dimensional change due to the thermal cycle.

An object of the present invention is to provide a heat-resistant porous sintered body which is stable against the above heat cycle. Further, the object of the present invention, particularly in the heat-resistant electrode used in the solid oxide fuel cell, etc., due to the dimensional shrinkage of the heat-resistant electrode due to the thermal cycle, between the heat-resistant electrode and other constituent materials. The purpose is to prevent the occurrence of cracks.

[0006]

The present invention is a porous sintered body composed of a complex oxide having a perovskite structure, in which the B site of the complex oxide contains a manganese atom,
The average valence of manganese atoms in this composite oxide is 10
3.25 or higher at 00 ° C, room temperature and 1000 ° C
The dimensional shrinkage of the porous sintered body caused by the heat cycle between and is 0.01% or less per heat cycle.

Further, the present invention is a porous sintered body composed of a complex oxide having a perovskite structure, wherein the B site of the complex oxide contains a manganese atom. After heat treatment at 1000 ℃ for 2 hours, 1
After being exposed to the outside air at 20 ° C. within seconds and rapidly cooled to the outside temperature, the average valence of manganese atoms in the composite oxide is 3.25 or more, and the thermal cycle between room temperature and 1000 ° C. The present invention relates to a porous sintered body characterized in that the dimensional shrinkage that occurs is 0.01% or less per thermal cycle.

The present invention also relates to a heat-resistant electrode comprising the above-mentioned porous sintered body. The present invention also relates to a solid oxide fuel cell, characterized by comprising an air electrode made of the above-mentioned porous sintered body.

[0009]

First of all, the present inventor has studied the mechanism by which dimensional shrinkage of the porous sintered body occurs with the above thermal cycle.
I proceeded with my research. As a result, it was found that when the temperature was raised from room temperature to about 1000 ° C., the weight of the porous sintered body slightly decreased, and when the temperature was lowered to room temperature again, this weight was restored.

As a result of further studying this phenomenon, the present inventor has confirmed that oxygen flows in and out of the crystal lattice between a low temperature region of 600 ° C. or lower and a high temperature region of 900 ° C. or higher. Further pursuit of this point has revealed that the valence of manganese atoms present at the B site of the crystal lattice of the perovskite structure is related to the stability of such a crystal lattice.

More specifically, when the valence of manganese atoms in the composite oxide at 1000 ° C. is 3.25 or more, the crystal lattice of the composite oxide becomes stable against the thermal cycle, and It has been found that oxygen is prevented from entering and leaving the crystal lattice when a cycle is applied, and the shrinkage of the porous sintered body due to the thermal cycle can be prevented.

As a result, particularly in a solid oxide fuel cell, such as a solid oxide fuel cell, in a power generation article in which an electrode made of a porous sintered body and other constituent materials are joined, a temperature of 900 to 1100 ° C. and a room temperature to 600 ° C. It was confirmed that no cracks were generated between the electrode made of the porous sintered body and the other constituent materials even when the heating-cooling cycle was performed at the temperature of.

Since it is difficult to directly measure the average valence of manganese in the composite oxide at 1000 ° C.,
The porous sintered body was heat-treated in the air at 1000 ° C. for 2 hours, then exposed to the outside air of 20 ° C. within 1 second, rapidly cooled to the outside air temperature, and then the porous sintered body was pulverized to obtain this powder. The average valence of manganese is measured.

The porous sintered body was heated in the atmosphere at 1000 ° C. for 2 hours.
The heat treatment for a period of time is for stabilizing the state of manganese, and the rapid cooling from 1000 ° C. to 20 ° C. is for gradually cooling the porous sintered body. This is because the average valence may change.

Further, the average valence of manganese is 3.27.
As a result of the above, the dimensional shrinkage ratio is 1
Remarkably decreased to 0.005% or less per time. Further, in the range where the average valence is 3.30 or more, the dimensional shrinkage due to the heat cycle is almost not observed. Also,
In practice, the average valence is preferably 3.75 or less.

[0016]

EXAMPLES First, the composition of the composite oxide constituting the porous sintered body according to the present invention will be illustrated. First, manganese is contained in the B site of the composite oxide, but preferably, one or more metals selected from the group consisting of rare earths other than cerium, alkaline earths and yttrium are contained in the A site of the composite oxide. Contains atoms.

In a preferred embodiment, the composite oxide A
The site contains one kind of first metal atom selected from the group consisting of rare earths and yttrium other than cerium, and one or more second metal atom selected from the group consisting of calcium and strontium. , The content ratio of this second metal atom in the A site is 10% or more, 70%
It is the following. This composite oxide preferably has a composition represented by the following general formula (I).

[0018]

Embedded image R _1-X A _X MnO ₃ (I)

Here, R and A occupy the A site of the composite oxide, and Mn occupies the B site of the composite oxide. R is 1
It is the first metal atom of the seed. A is one or more second metal atoms. x is the content ratio of the second metal atom A and is 10% or more and 70% or less (x = 0.10 to
0.70).

The term "group consisting of rare earths other than cerium and yttrium" means a group consisting of yttrium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. is there. R is a lantern,
Those selected from the group consisting of praseodymium, neodymium, samarium, dysprosium, gadolinium and yttrium are preferred.

As x increases, the electrical conductivity improves.
However, when x exceeds 0.70, a sharp decrease in electrical conductivity was observed. Therefore, x is preferably 0.70 or less.

When the porous sintered body of the present invention is used as a heat-resistant electrode of a power-generating article, the average line of the heat-resistant electrode is set in order to reduce the difference in thermal expansion with other constituent materials. It is necessary to keep the coefficient of thermal expansion as low as possible.
From this viewpoint, when the average linear thermal expansion coefficient of the heat-resistant electrode was measured, as x increased, the average linear thermal expansion coefficient of the porous sintered body also increased. Especially when the first metal atom R is lanthanum, a remarkable increase was observed when x exceeded 0.50. Therefore, x is preferably 0.5 or less.

In particular, when the porous sintered body of the present invention is used as an air electrode material for a solid oxide fuel cell,
The coefficient of thermal expansion of the porous sintered body must be close to that of the solid electrolyte membrane, the fuel electrode membrane and the like.

When the solid electrolyte membrane is yttria-stabilized zirconia, it is known that the average linear thermal expansion coefficient between 25 ° C. and 1000 ° C. is 10.5 × 10 ^-6 K ^-1. ing. In this case, if the average coefficient of linear thermal expansion of the porous sintered body is suppressed to 11.8 × 10 ^-6 K ^-1 or less, the difference in thermal expansion between the porous sintered body and the solid electrolyte membrane will occur. The generation of cracks due to this could be prevented.

When the first metal atom R is lanthanum, the average linear thermal expansion coefficient of the porous sintered body is 11.8 × 10 ⁻⁶ K ⁻ if x is suppressed to 0.40 or less. ^Since it can be suppressed to ¹ or less, x is preferably suppressed to 0.40 or less from this viewpoint.

Further, a complex oxide having a composition represented by the following general formula (II) is also preferable.

Embedded image R _1-X A _X Mn _1-Z E _z O ₃ (II)

Here, R and A occupy the A site of the composite oxide, and Mn and E occupy the B site of the composite oxide. R
Is one first metal atom. A is one or more second metal atoms. E is aluminum, cobalt,
It is one or more third metal atoms selected from the group consisting of copper, magnesium, chromium, nickel, iron, titanium and zinc.

X is the content ratio of the second metal atom A, and is 10% or more and 70% or less (x = 0.10 to 10).
0.70). As x increases, electrical conductivity improves.
However, when x exceeds 0.70, a sharp decrease in electrical conductivity was observed. Therefore, x needs to be 0.70 or less.

When the first metal atom R is lanthanum, when x exceeds 0.50, a remarkable increase in average linear thermal expansion coefficient was observed. Therefore, x needs to be 0.50 or less. When x was suppressed to 0.40 or less, the average coefficient of linear thermal expansion of the porous sintered body could be suppressed to 11.8 × 10 ⁻⁶ K ⁻¹ or less. It is preferably suppressed to 40 or less.

When z exceeds 0.35, the electric conductivity of the porous sintered body lowers and falls below the electric conductivity limit value that can be used as an electrode element. Therefore, z must be 0.35 or less. is there. Furthermore, when z is 0.20 or less, the electric conductivity of the porous sintered body is significantly improved. Also, z is 0.0
It is more preferable to set it to 2 or more from the viewpoint of reducing the dimensional shrinkage rate of the porous sintered body due to the heat cycle.

In another preferred composition, at the A site of the composite oxide, two or more kinds of first metal atoms selected from the group consisting of rare earths other than cerium and yttrium, and the group consisting of calcium and strontium. Contains one or more second metal atoms selected from
The content ratio of the second metal atom in the A site is 10% or more and 70% or less, and the content ratio of the first metal atom in the A site is 30% or more and 90% or less.

The composition of this composite oxide is preferably represented by the following general formula (III).

[0033]

Embedded image R _1-X A _X MnO ₃ (III)

R is two or more kinds of first metal atoms.
A is one or more second metal atoms.

The substitution ratio x by the second metal atom A is A
10 to 70% of the sites (x = 0.10 to 0.70)
And As x increases, electrical conductivity improves. However, when x exceeds 0.70, a sharp decrease in electrical conductivity was observed. Therefore, x needs to be 0.70 or less.

When the first metal atom R is lanthanum, a remarkable increase in the average linear thermal expansion coefficient was observed when x exceeded 0.50. Therefore, x needs to be 0.50 or less. When x was suppressed to 0.40 or less, the average coefficient of linear thermal expansion of the porous sintered body could be suppressed to 11.8 × 10 ⁻⁶ K ⁻¹ or less. It is preferably suppressed to 40 or less.

The content ratio (1-x) of the first metal atom R in the A site is 30% or more and 90% or less. When one kind of the first metal atom R is lanthanum, the content ratio of lanthanum in the A site is 1 to 76%.
It is preferable that The content ratio of the other first metal atom is preferably 1 to 76% of the A site,
It is more preferably 20 to 50%.

The composition of the composite oxide is preferably represented by the following general formula (IV).

[0039]

Embedded image R _1-X A _X Mn _1-z E _z O ₃ (IV)

R is two or more kinds of first metal atoms.
A and E are the metal atoms described above. The substitution rate x by the first metal atom A is 10 to 70% of the A site.
(X = 0.10 to 0.70). As x increases,
The electric conductivity is improved. However, when x exceeds 0.70, a sharp decrease in electrical conductivity was observed. Therefore, x
Must be 0.70 or less.

When the first metal atom R is lanthanum, a remarkable increase in the average linear thermal expansion coefficient was observed when x exceeded 0.50. Therefore, in this case, x is 0.5
It must be 0 or less. When x is suppressed to 0.40 or less, the average coefficient of linear thermal expansion of the porous sintered body is 11.8 × 10 ^−6.
Since it could be suppressed to K ^-1 or less, from this viewpoint,
It is preferable to suppress x to 0.40 or less.

When z exceeds 0.35, the electric conductivity of the porous sintered body lowers and falls below the electric conductivity limit value that can be used as an electrode element. Therefore, z must be 0.35 or less. is there. Furthermore, when z is 0.20 or less, the electric conductivity of the porous sintered body is significantly improved. Also, z is 0.0
It is more preferable to set it to 2 or more from the viewpoint of reducing the dimensional shrinkage rate of the porous sintered body due to the heat cycle.

The content ratio of the first metal atom R in the A site is 30% or more and 90% or less. When one kind of the first metal atom R is lanthanum, the content ratio of lanthanum in the A site is preferably 1 to 76%. The content ratio of the other first metal atom is preferably 1 to 76% of the A site, and 20 to 5%.
It is more preferably 0%.

In each of the above-mentioned compositions, the composition variation of the composite oxide derived from some impurities inevitably mixed in the manufacturing process of the porous sintered body is allowed. Further, since the complex oxide having a perovskite structure can have a non-stoichiometric composition, in the general formulas showing the respective compositions described above,
Although the ratio of A site to B site is expressed as 1: 1 for convenience, this composition ratio may vary.

In order to manufacture the porous sintered body according to the present invention, the raw material powders of the composite oxide are mixed to prepare a mixed powder, the mixed powder is molded, and the molded body is fired to obtain a synthetic product. Is preferably prepared and the compound is crushed. At this time, the ratio of each metal atom in the composite oxide is controlled by changing the mixing ratio of the raw material powder of the composite oxide.

The firing temperature of the molded body is 1300 ° C to 160 ° C.
The temperature is preferably 0 ° C. If the firing temperature is less than 1300 ° C, the sintering will not be completed completely. If the temperature is higher than 1600 ° C, the structure of the sintered body will be too dense.

As in the present invention, the following method is used for producing a porous sintered body made of a composite oxide having an average valence of manganese atoms at 1000 ° C. of 3.25 or more. That is, the amount of oxygen per crystal lattice of the composite oxide forming the porous sintered body is about 3.0. In the above firing step, the partial pressure of oxygen contained in the firing atmosphere is about 20% when the firing atmosphere is the atmosphere.
Met. A conventional lanthanum manganite porous sintered body is usually fired in the air.

However, according to the study by the present inventor, when the amount of oxygen in the firing atmosphere was increased, the amount of oxygen in the porous sintered body after firing was slightly increased, and the average valence of manganese atoms was increased. Come on. Therefore, in order to produce a porous sintered body made of a composite oxide in which the average valence of manganese atoms at 1000 ° C. is 3.25 or more, each composition described above is selected and the firing atmosphere at the time of this firing is selected. The oxygen partial pressure contained therein may be increased.

However, since the average valence of manganese varies depending on the composition described above, how much the oxygen partial pressure in the firing atmosphere needs to be increased depends on the composition of the composite oxide, and therefore is unique. Cannot be specified.

The porous sintered body produced according to the present invention is
In particular, it can be preferably used as a material for a heat resistant electrode which is stable against heat cycles. Materials for such heat-resistant electrodes include electrode materials for power generation products such as fusion reactors and MHD power generation.

The porous sintered body of the present invention can be particularly preferably used as an air electrode material for a solid oxide fuel cell. Further, it is preferably used as a material for a self-supporting air electrode substrate. Such an air electrode base is used as a base material of a single cell, and each component such as a solid electrolyte membrane, a fuel electrode membrane, an interconnector and a separator is laminated on the air electrode base. At this time, the shape of the air electrode substrate may be a cylindrical shape with both ends open, a bottomed cylindrical shape with one end open and the other end closed, or a flat plate shape. Of these, one of the above cylindrical shapes
It is particularly preferable because it is less likely to be subjected to thermal stress and gas sealing is easy.

The porosity of the porous sintered body is preferably 5-40%. When it is used as an air electrode material for a solid oxide fuel cell, the porosity is further increased to 1
It is preferably 5 to 40%, and more preferably 25 to 35%. In this case, the porosity of the air electrode should be 15%.
With the above, the gas diffusion resistance is reduced, and the porosity is set to 40% or less, so that a certain level of strength can be secured.

Hereinafter, more specific experimental results will be described. [Experiment A: Experiment on Porous Sintered Body Composed of Complex Oxide Having La _0.80 Ca _0.20 MnOx System Composition] (Method for Manufacturing Porous Sintered Body) As a starting material, La ₂ O was used.
Powders of ₃ , CaCO ₃ , and Mn ₃ O ₄ were used. La
For each sample, a predetermined amount of starting materials were weighed and mixed so that the composition ratio was _0.80 Ca _0.20 MnOx. This mixed powder was molded by a cold isostatic press method at a pressure of 1 tf / cm ² to prepare a molded body. This compact was heat-treated in the air at 1500 ° C. for 15 hours to synthesize a composite oxide having a composition of La _0.80 Ca _0.20 MnOx.

This synthetic material was ground with a trommel for 8 to 12 hours to prepare a synthetic powder having an average particle diameter of 2 to 6 μm. Next, water and an acrylic binder as an organic binder were added to and mixed with this synthetic powder to prepare a slurry having a water content of 40%, and granulated with a spray dryer. Then, this granulated powder and an acrylic powder as a pore-forming agent are dry-mixed and molded by a cold isostatic press method at a pressure of 1 tf / cm ² to give an outer diameter of 20 m.
A ring-shaped molded body having a diameter of m and an inner diameter of 15 mm was manufactured. The annular shaped body was fired at 1300 ° C to 1500 ° C for 5 hours to obtain a porous sintered body.

The atmosphere during firing was adjusted by mixing pure oxygen and pure nitrogen. However, the oxygen concentration in this mixed atmosphere was changed as shown in Table 1. In Table 1, the oxygen concentration during firing is 20.6%, which almost corresponds to the atmosphere. The porosity of each of these annular porous sintered bodies was measured by the water replacement method,
All were 30% ± 1%.

(Measurement of Dimensional Shrinkage Rate by Thermal Cycle) From each of these porous sintered bodies, a flat sample having a width of 5 mm, a thickness of 1 mm and a length of 50 mm was cut out and used for measuring the dimensional shrinkage rate by a thermal cycle. It was used as a sample. First, the length of the measurement sample at 40 ° C. was accurately measured. Further, the displacement of the tip of the measurement sample at 40 ° C. was precisely measured by a thermal expansion meter. Next, this measurement sample is heated to 1000 ° C. at a rate of 200 ° C./hour in the atmosphere, and then 10
The temperature was maintained at 00 ° C for 30 minutes, then the temperature was lowered to 600 ° C at a temperature lowering rate of 200 ° C / hour, and the temperature was allowed to cool from 600 ° C to 40 ° C. Even after this thermal cycle, the displacement of the tip of the measurement sample at 40 ° C. was accurately measured by a thermal expansion meter.

As the thermal dilatometer, a high precision thermal dilatometer “TMA” manufactured by Rigaku Denki was used. The dimensional shrinkage rate (%) due to the heat cycle was calculated by the following formula. Table 1 shows the result of measuring the dimensional shrinkage ratio by the thermal cycle for each measurement sample.

[Equation 1] Dimensional shrinkage rate (%) due to thermal cycle = (displacement of measuring sample at 40 ° C before thermal cycle-displacement of measuring sample at 40 ° C after thermal cycle) / for measuring before thermal cycle Sample length)

(Measurement of Oxygen Content (x) per Crystal Lattice and Valence of Manganese) After cutting out a sample for measuring the dimensional shrinkage ratio by heat cycle from the above-mentioned annular porous sintered body. , The remaining part was used as a sample. First,
This sample was processed using the apparatus schematically shown in FIG. That is, the sample 3 was hung on the furnace ceiling 1 by the platinum wire 2. The guide 6 was installed in the heat treatment space 5 in the electric furnace 4 so that the sample 3 was positioned in the space 6 a in the guide 6. The lower end of the guide 6 extends to the lower side of the electric furnace 4 through the furnace bottom 4a of the electric furnace 4, and the lower opening 6b of the guide 6 is formed.
The saucer 7 is installed under. The area around the saucer 7
It is outside air at 20 ° C.

In this state, the electric furnace is operated to 1000 ° C.
Sample 3 was heat treated for 2 hours. Next, the platinum wire 2 was cut, the sample 3 was dropped in the guide 6, dropped in the pan 7, and rapidly cooled to 20 ° C. The sample after the heat treatment and the rapid cooling was pulverized in an alumina mortar until it passed through a 45 μm opening sieve to obtain a sample for manganese valence measurement.

The valence of manganese was analyzed based on "Basic research on solid oxide fuel cell" (Report of Central Research Institute of Electric Power: Research report: W90002). The analysis procedure is
It is as follows.

(1) Reaction of Na ₂ C ₂ O ₄ with manganese valence measurement sample Na ₂ C ₂ O ₄ 30.00 m dried at 110 ° C.
g, and about 40.00 mg of the above-mentioned sample for manganese valence measurement (perovskite complex oxide powder), 200 m
Place in a 1 L Erlenmeyer flask. 100 ml of sulfuric acid diluted to 10% by volume is placed in an Erlenmeyer flask and heated on a thermomagnetic stirrer for about 30 minutes to dissolve the powder in sulfuric acid. The reaction at this time is as shown in the following formula (V).

[0062]

(V) Formula Mn ^{4 +} + Na ₂ C ₂ O ₄ → Mn ^{2 +} + 2CO + 2Na
+ O ₂ Mn ^{3 +} + 1 / 2Na ₂ C ₂ O ₄ → Mn ^{2 +} + CO + N
a + 1 / 2O ₂

(2) KMnO_FourPreparation of titration solution KMnO_FourPowder (nakarai tesque, guaranteed reagen
t) is dissolved in distilled water to obtain a solution of about 0.01 mol / l.
Prepare. This solution should be boiled sufficiently to remove gas such as carbon dioxide.
Degas the air. KMnO_FourAnd carbon dioxide in distilled water
This is because they are easily reacted and reduced. Then this melt
The liquid is allowed to cool to room temperature in a cool dark place, and MnO₂Impurities such as
Removed over time. KMnO_FourThe concentration after titration is
Na₂C ₂O_FourIt was determined from the titration amount required for the oxidation of.

(3) Titration As described above, Na ₂ C ₂ O ₄ was reacted with manganese in the manganese valence measurement sample, and Na ₂ C ₂ O ₄ remaining after this reaction was dissolved in a KMnO ₄ solution. Titrated by The end point of titration with KMnO ₄ solution was the point where the pink KMnO ₄ solution is titrated solution began to appear.
The redox reaction that occurs during titration is as shown in the following formula (VI).

[0065]

(VI) Formula 5Na ₂ C ₂ O ₄ + 2KMnO ₄ + 16H ⁺ → 2Mn
^{2 +} + 10CO ₂ + 8H ₂ O + 10Na ⁺ + 2K ⁺

(4) Calculation Known KMnO_FourThe concentration of the solution is C (mol / l),
For manganese valence measurement when all valences of Mn are trivalent
The molecular weight of the sample is d₁And the weight of the manganese valence measurement sample
The amount is 1 (g), and Na₂C₂O_FourThe weight of f (g)
And KMnO_FourThe titer of the solution is g (ml). (V
Na required for the titration reaction of the formula I)₂C₂O _FourMol number of
Is h (mol). h (mol) is Na₂C₂
O_FourAnd the total mol number of KMnO_FourReacted with Na₂
C₂O_FourIs the difference with the mol number.

The molecular weight of Na ₂ C ₂ O ₄ is 134,
The purity is 0.995. Therefore, the total number of moles of Na ₂ C ₂ O ₄ is f × 0.995 / 134. The number of moles of Na ₂ C ₂ O ₄ reacted with KMnO ₄ is (C × g × 5/2) / 1000. Therefore, the following equation is established.

[0068]

(2) h = f × 0.995 / 134− (C × g × 5 /
2) / 1000

From the lower part of the equation (V), the electron number i when Mn ^{3 +} is reduced in 1 mol of the manganese valence measurement sample consisting of a perovskite type complex oxide is Na ₂ C ₂ O.
_{4 Since} it is 2 mol per 1 mol, the following formula is established.

[0070]

[Equation 3] i = 2 × h / (e / d ₁ )

The average valence of Mn in the perovskite type complex oxide is (i + 2), assuming that the atoms other than Mn do not change in valence. In this way, the average valence (i + 2) of manganese can be calculated when all the valences of Mn are assumed to be 3. Of course, since (i + 2) is larger than 3, the initial assumption that the average valence of manganese is 3 is incorrect. When the average valence of manganese increases, the oxygen amount x per crystal lattice also increases, so the molecular weight (d ₁ ) of the above-mentioned perovskite complex oxide is also incorrect.

Therefore, the molecular weight (d ₂ ) of the whole perovskite type complex oxide containing oxygen is calculated from the calculated value of the average valence (i + 2) of manganese. This calculated value (i +
2) is closer to the actual value than 3 and d ₂ is closer to the actual value than d ₁ . Again using this molecular weight (d ₂ ),
Repeat the above calculation. This operation was repeated 5 times to obtain the final average valence of Mn.

In this way, the average valence of manganese and the amount of oxygen (x) per one crystal lattice of the porous sintered body of each example were calculated and shown in Table 1. Further, the relationship between the average valence of manganese and the dimensional shrinkage rate due to the heat cycle is shown in the graph of FIG.

[0074]

[Table 1]

As shown in Table 1, increasing the oxygen concentration in the firing atmosphere tended to increase the average valence of manganese. Further, as can be seen from Table 1 and FIG. 1, when the average valence of manganese is set to 3.25 or more, the dimensional shrinkage ratio is 0.01% per thermal cycle.
It turned out that it is suppressed below. Furthermore, by setting the average valence to 3.27 or more, the dimensional shrinkage rate was significantly reduced to 0.005% or less per thermal cycle. Further, in the range where the average valence is 3.30 or more, the dimensional shrinkage due to the heat cycle is almost not observed.

Further, in Table 1, for the porous sintered body having an average valence of manganese of 3.2464, the temperature was raised and lowered from room temperature to 1000 ° C., and the size of the porous sintered body was measured by a thermal expansion meter. The change was measured. As a result, it was found that the dimensional shrinkage phenomenon occurred in the temperature range of 900 ° C. to 800 ° C. when the temperature decreased. Therefore, it is assumed that oxygen atoms are absorbed and metal atoms are moved in this temperature range. Moreover, the result of the thermal cycle between 600 ° C. and 1000 ° C. is the same as the result of the thermal cycle between room temperature and 1000 ° C.

Further, in Table 1, with respect to the porous sintered body having an average valence of manganese of 3.2464, when the above-mentioned thermal cycle was applied 10 times, the porous sintered body was subjected to 10 thermal cycles. The dimensional shrinkage rate of 0.34% was reached.
Further, the dimensional shrinkage due to this heat cycle did not converge even if the number of heat cycles was increased.

On the other hand, this porous sintered body was treated in air at 100
After maintaining at 0 ° C for 10 hours and cooling to room temperature, the dimensional change rate before and after heating was measured and found to be 0.031%.
Showed shrinkage of. Shrinkage of 0.031% by holding at 1000 ° C. for 10 hours is almost equivalent to the amount of dimensional shrinkage for one heat cycle. 1000 per thermal cycle
The holding time at 0 ° C is only 30 minutes.

From this result, the above-mentioned 0.34% dimensional shrinkage did not occur during the holding at 1000 ° C., but during the temperature decreasing process from 1000 ° C. to room temperature. is there. In other words, the shrinkage phenomenon of the porous sintered body due to the above-mentioned thermal cycle is caused by a mechanism completely different from the progress of sintering due to the holding of the porous sintered body at a high temperature.

[Experiment B: La _0.80 Ca _0.20 Mn _0.98 Ni
Experiment on Porous Sintered Body Composed of Complex Oxide with _0.02 Ox Composition] As starting materials, La ₂ O ₃ , C
Powders of aCO ₃ , Mn ₃ O ₄ and NiO were used.
Others were the same as that of experiment A, and the porous sintered body of each example was manufactured. However, the oxygen concentration during firing was changed as shown in Table 2.

For each of these porous sintered bodies, the porosity, the dimensional shrinkage due to the heat cycle, the valence of manganese, and the oxygen amount x per crystal lattice were determined in the same manner as in Experiment A in which the dimensional shrinkage was performed. It was measured. The measurement results are shown in Table 2.
Further, the relationship between the average valence of manganese and the dimensional shrinkage rate due to the heat cycle is shown in the graph of FIG.

[0082]

[Table 2]

The porosity of each porous sintered body was 30% ± 1%. As shown in Table 2, increasing the oxygen concentration in the firing atmosphere tended to increase the average valence of manganese. Also, as can be seen from Table 2 and FIG.
By setting the average valence of manganese to 3.25 or more,
It was found that the dimensional shrinkage ratio was suppressed to 0.01% or less per thermal cycle. Furthermore, by setting the average valence to 3.27 or more, the dimensional shrinkage rate was significantly reduced to 0.005% or less per thermal cycle. Further, in the range where the average valence is 3.30 or more, the dimensional shrinkage due to the heat cycle is almost not observed.

[0084]

As described above, the porous sintered body of the present invention has the following characteristics when subjected to a heating-cooling cycle between a temperature of 900 to 1100 ° C and a temperature of room temperature to 600 ° C. It is stable against heat cycles. Therefore, the heat-resistant electrode formed by this porous sintered body, because the dimensional shrinkage due to the above-mentioned thermal cycle is extremely small, cracks occur between the heat-resistant electrode and other constituent materials, It can be prevented.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the average valence of manganese and the dimensional shrinkage rate due to the heat cycle in a porous sintered body made of a composite oxide having a La _0.80 Ca _0.20 MnOx system composition.

FIG. 2 shows a porous sintered body composed of a composite oxide having a La _0.80 Ca _0.20 Mn _0.98 Ni _0.02 Ox composition.
It is a graph which shows the relationship between the average valence of manganese and the dimensional shrinkage rate by the said thermal cycle.

FIG. 3 is a cross-sectional view schematically showing an apparatus for applying heat treatment and quenching treatment to a porous sintered body to obtain a sample for measuring the average valence of manganese.

[Explanation of symbols]

2 platinum wire, 3 sample, 4 electric furnace, 5 heat treatment space, 6 guide, 7 saucer

Claims (6)

[Claims] 1. A porous sintered body composed of a complex oxide having a perovskite structure, wherein the B site of the complex oxide contains manganese atoms, and the average valence of manganese atoms in the complex oxide is 3.25 at 1000 ° C
The above is the dimensional shrinkage of the porous sintered body caused by the thermal cycle between room temperature and 1000 ° C.
A porous sintered body characterized by being 0.01% or less per time. 2. A porous sintered body composed of a complex oxide having a perovskite structure, wherein the B site of the complex oxide contains a manganese atom, and the porous sintered body is heated to 1000 ° C. in air. 20 seconds within 1 second after heat treatment for 2 hours
After being exposed to the outside air at a temperature of ℃ and rapidly cooled to the outside temperature, the average valence of manganese atoms in the composite oxide is 3.25 or more, and the porosity caused by a thermal cycle between room temperature and 1000 ° C. A porous sintered body characterized by having a dimensional shrinkage of 0.01% or less per thermal cycle. 3. The porous sintered body according to claim 2, wherein the A site of the composite oxide contains a lanthanum atom. 4. A heat-resistant electrode comprising the porous sintered body according to claim 2 or 3. 5. A solid oxide fuel cell, comprising an air electrode made of the porous sintered body according to claim 2 or 3. 6. The solid oxide fuel cell according to claim 5, wherein the air electrode is a self-supporting air electrode.