JP2553296B2 - Method for manufacturing porous sintered body - Google Patents

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 porous sintered body.

[0002]

2. Description of the Related Art In the development of a solid oxide fuel cell (SOFC), it is important to search for a stable material at a high temperature. As a SOFC air electrode material, a lanthanum manganite sintered body having a perovskite structure is currently considered to be promising (Energy Engineering, 13, 2, 52-68).
Page, 1990). Among such lanthanum manganite sintered bodies, those having a substantially stoichiometric composition and those having a composition in which part of the A site (lanthanum site) is deficient (manga rich composition) are also known. In particular, a porous sintered body made of lanthanum manganite with A site doped with Ca and Sr is
It is regarded as a promising material for cathodes including self-supporting cathodes. To make such a porous cathode,
At present, for example, a thickening material, a pore-forming material, and a binder are mixed with a raw material powder made of La (Ca) MnO ₃ , and the mixture is molded and fired. Increasing the firing temperature of the porous air electrode lowers its porosity. For example, in order to obtain an air electrode having a porosity of about 30%, in the case of lanthanum manganite having a perovskite structure having a stoichiometric composition, 1580 to 1600 ° C.
It must be fired at a very high temperature.

[0003]

However, at such a high temperature, the life of the firing furnace is shortened, the cost of the equipment is very high, and it takes time to raise and lower the temperature and consumes a large amount of energy. Therefore, it is necessary to lower the firing temperature.

In the case of a lanthanum manganite sintered body having a composition in which A site, that is, lanthanum is partially lost and A / B <1, porosity is 30 even at a firing temperature of about 1500 ° C.
The present inventor has confirmed that about 10% of the air electrode can be obtained. However, it was found that this air electrode had extremely poor heat resistance. In particular, it was found that when reheated to a high temperature of about 1400 ° C., the dimensional shrinkage rate reaches about 2%. In this case, the solid electrolyte membrane or interconnector formed on the air electrode may be separated from the air electrode and the air electrode itself may be destroyed at the same time. Further, it has been reported that the weight of the lanthanum manganite sintered body having a composition in which the A site is partially lost decreases as the temperature rises from room temperature to 1000 ° C (J. Electrochem. Soc. 138, 5). ， 1519〜1523
Page, 1991). Therefore, it is considered that there is a problem in long-term durability during use at high temperatures and during operation.

An object of the present invention is to produce a porous sintered body made of lanthanum manganite having a perovskite structure, which has a porosity equal to or lower than the conventional one at a firing temperature lower than the conventional one. As well as
It is intended to obtain a porous sintered body having high heat resistance and less shrinkage during reheating.

[0006]

The present invention is a method for producing a porous sintered body composed of lanthanum manganite having a perovskite structure, wherein the number of A-site atoms in the perovskite structure is the number of B-site atoms. Value divided by (A
/ B) is larger than 1 and is composed of lanthanum manganite, and the number of A-site atoms of the perovskite structure is B
At least a binder and a pore-forming material are added to a mixed powder with particles of lanthanum manganite whose value divided by the number of site atoms is smaller than 1, and the mixture is molded, and the molded body is fired to form the porous sintered body. The present invention relates to a method for producing a porous sintered body, which is characterized by being obtained.

[0007]

The present inventor conducted a study to produce a SOFC air electrode material by adding a binder, a pore former, a thickener, etc. to a raw material powder of lanthanum manganite and mixing, granulating, molding and firing. Was there. In this process, the value (A / B) obtained by dividing the number of A-site atoms by the number of B-site atoms is less than 1, and is composed of lanthanum manganite having a composition in which some of the A sites are deficient. It was conceived to mix the particles with refractory particles having an (A / B) greater than 1.

Then, when actually conducting the firing experiment,
It was found that it is possible to manufacture a porous sintered body having a porosity equivalent to that of a conventional one, even at a firing temperature much lower than that of the conventional one. Moreover, the heat resistance of this porous sintered body is unexpectedly large, and exceeds the heat resistance of the conventional porous sintered body made of lanthanum manganite having a stoichiometric composition.

The reason why such an effect is obtained is not clear. However, at the firing stage, the relatively easily sinterable particles made of lanthanum manganite having a composition in which part of the A site is deficient react preferentially to act as a kind of binder, which makes the particles difficult to sinter. It seems that they bind each other and, as a result, sintering proceeds.

Further, at the same time with the progress of sintering, manganese diffuses from the manganese-rich particles in which the A site is partially deficient to the particles having a composition that is difficult to sinter and has an excess of A site. It is assumed that the overall composition gradually becomes uniform and approaches the stoichiometric composition as a whole. As a result,
It will be possible to obtain a porous sintered body having heat resistance equal to or higher than conventional ones.

As described above, when the lanthanum manganite powder having a manganese-rich composition having a deficient A site is simply fired, lowering the firing temperature from the prior art causes no problem in porosity, but the heat resistance is low. to degrade. The present invention
It is possible to overcome these difficulties.

[0012]

EXAMPLES The chemical composition of lanthanum manganite which constitutes the porous sintered body of the present invention is changed to increase the conductivity.
It is preferable that the A site contains a rare earth or alkaline earth metal atom other than lanthanum in a form that substitutes lanthanum, and it is more preferable that the A site contains calcium or strontium.

The chemical composition of the lanthanum manganite in the present invention may or may not include a substitution atom other than manganese at the B site. When the B site contains a substitution atom other than manganese, the substitution atom can be selected from the group consisting of iron, chromium, titanium, cobalt, magnesium, zinc, copper, aluminum and nickel. Also, this substitution amount is 1 for the B site.
It is preferably 0% or less. The presence of inevitable impurities is also allowed.

The porous sintered body of the present invention can be preferably used as a high temperature electrode material. As such high temperature electrode materials, there are electrode materials for fusion reactors, MHD power generation, and the like.
Further, the porous sintered body of the present invention can be particularly preferably used as an air electrode material for SOFC. 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.

The porosity of the porous sintered body is preferably 5 to 40%. When this is used as an air electrode material for SOFC, the porosity is preferably 15 to 40%, and more preferably 25 to 35%. In this case, the gas diffusion resistance is reduced by setting the porosity of the air electrode to 15% or more, and the porosity of 35% or less can ensure practically sufficient strength.

In one embodiment of the present invention, particles comprising lanthanum manganite having (A / B) greater than 1,
The average particle size of the particles made of lanthanum manganites having (A / B) smaller than 1 is made almost the same. In this case, the average particle size is preferably 5 to 7 μm.

In this embodiment, in the case of particles in which (A / B) is larger than 1, (A / B) is preferably 1.02 or more, and more preferably 1.05 to 1.10. (A / B) is 1
In the case of smaller particles, (A / B) is preferably 0.98 or less, and more preferably (A / B) is 0.95 to 0.90.

In this embodiment, the powder having a composition of (A / B) larger than 1 and the powder having a composition of (A / B) smaller than 1 can be mixed in equal amounts or mixed in different amounts. be able to. It is considered that the composition of the sintered body becomes substantially uniform when the diffusion of manganese described above progresses sufficiently.

In still another embodiment of the present invention, (A /
B) is larger than 1 and the particle size of the powder is made relatively large,
The particle size of the powder having (A / B) smaller than 1 is made relatively small. In this case, in the present invention, the sintering proceeds particularly at a low temperature, and the heat resistance of the porous sintered body is maximized.

The reason for this is not clear, but probably
It is considered that by making the particle diameter of the easily sinterable particles having (A / B) smaller than 1 smaller, the sintering is more likely to proceed. From a microstructural point of view, it is considered that such easily sinterable particles are aggregated and fused between particles of larger sinterability that are difficult to sinter to form a neck. When the particle size of such easily sinterable particles is reduced, the above-mentioned neck portion becomes thicker, and the more difficult to sinter particles having a larger particle size come close to each other to form a microstructure that is difficult to shrink as a whole. Presumed to be.

In this embodiment, the particle size of the powder having (A / B) larger than 1 is preferably 6.0 to 10.0 μm, and the particle size of the powder having (A / B) smaller than 1 is 0.5 to 6.0.
μm is preferred. The difference in particle size is 7.0 μ
It is preferably m or more, and more preferably 8.0 μm or more.

In this embodiment, in the case of particles having (A / B) greater than 1, (A / B) is preferably 1.02 or more, and more preferably 1.05 to 1.10. (A / B) is 1
In the case of smaller particles, (A / B) is preferably 0.98 or less, and more preferably (A / B) is 0.95 to 0.80.

Also in this embodiment, the powder having a composition of (A / B) larger than 1 and the powder having a composition of (A / B) smaller than 1 can be mixed in equal amounts or mixed in different amounts. can do.

Hereinafter, more specific experimental results will be described. (Experiment 1). For each of Samples 1-1 to 1-5,
Raw material powder was prepared. However, in the samples 1-1 to 1-4, and amol% of _{(La 0.8 Sr 0.2) x MnO} 3, (La 0.8 S
The r _{0. 2) y} MnO ₃ was mixed with bmol%. x, y, a,
The value of b is shown in Table 1. In Sample 1-5, (La _0.8 S
r _0.2 ) _1.00 MnO ₃ was used as the raw material powder.

Although the number of oxygen is expressed as "O ₃ " as a custom of ABO ₃ type perovskite structure, the number of oxygen can actually be increased or decreased.

[0027]

[Table 1]

In producing the raw material powder, Mn ₃ O ₄ powder,
La ₂ O ₃ powder and SrCO ₃ powder were mixed with an attritor so that the above-mentioned predetermined composition was obtained, and the mixture was heated in air at 1580 ° C. for 10 minutes.
Hold for a period of time to obtain a synthetic product. The composition was then milled in trommel with zirconia cobblestone and dried. In this experiment, the average particle size of all powders was adjusted to 6.0 μm.

Next, in Samples 1-1 to 1-4,
The above-mentioned two kinds of raw material powders were dry-mixed at a ratio shown in Table 1 so as to be sufficiently uniform in a rocking mixer.
In this case, for all samples, the overall composition after mixing was A: B =
It becomes 1: 1. To this mixed powder, cellulose was added as a pore-forming material, and a 20 wt% solution of polyvinyl alcohol was added as a binder. This mixing ratio is
Cellulose: Polyvinyl alcohol solution: Mixed powder =
It was set to 5: 10: 100 (weight ratio).

The mixture thus obtained is kneaded with a kneader,
The kneaded material is degassed in vacuum, put into a plunger and extruded, and the extruded material is cut to a length of 200 mm, a width of 100 mm, and a length of 10 mm.
To obtain a flat plate-shaped molded product. It was dried in air and placed in an electric furnace. The temperature was raised at 100 ° C./hour, and firing was performed at the firing temperature shown in Table 2 for 4 hours.

A flat plate-shaped sintered body was obtained in the same manner as in Samples 1-5. However, of course, there is no dry mixing step for mixing the raw material powders.

The porosity of the thus obtained sintered body of each example was measured by the underwater Archimedes method. Then the dimensions
A 150 mm × 30 mm × 5 mm flat plate was cut out, measured for dimensions, dried, and placed in an electric furnace. The temperature is raised at a heating rate of 200 ° C / hour and kept at 1380 ° C for 2 hours.
After cooling to room temperature for 1 hour, the size was measured after the temperature reached room temperature.

Reheat shrinkage was measured from the dimensions before and after heating by the following formula: Reheat shrinkage (%) = (L ₀ −L) ×
100 / L ₀ . However, L ₀ is the dimension of the sample at room temperature before heating at 1400 ° C., and L is the dimension of the sample after heating. Table 2 shows the results.

[0034]

[Table 2]

With respect to Samples 1-1 to 1-5, the relationship between the firing temperature and the porosity is shown in FIG. 1, and the relationship between the firing temperature and the reheat shrinkage is shown in FIG. As can be seen from these results, according to the samples 1-1 to 1-4 of the present invention, as compared with the conventional sample 1-5, those having a porosity or a reheat shrinkage ratio equal to or lower than the conventional sample 1-5 can be obtained. Has been obtained.

For example, in order to obtain a porous sintered body having a porosity of about 30%, the conventional sample 1-5 requires a firing temperature of 1600 ° C. On the other hand, sample 1-1, 1530 ℃, sample 1
-2, 1560 ° C, Sample 1-3, 1580 ° C, Sample 1-4, 1590 ° C.

In particular, the porosity of the SOFC air electrode is O ₂
It affects the permeation efficiency of molecules. Therefore, if the porosity is not constant, the performance of the unit cell is not constant. Therefore, when manufacturing an air electrode, it is important to control the porosity of the air electrode.

In the sample of the present invention, the value of x is increased,
As the value of y becomes smaller, a sintered body having a predetermined porosity can be obtained at a lower firing temperature. However, the value of x is 1.2
In sample 1-1 in which the values of 0 and y were 0.80, x was 1.10 and y
The reheat shrinkage ratio is larger than that of Sample 1-2 in which 0.90 is 0.90. Therefore, in order to reduce the reheat shrinkage ratio, 0.90 ≦ y ≦ 0.95 and 1.05 ≦ x ≦ 1. It can be seen below that it is the most preferable.

(Experiment 2). Samples 2-1, 2-2, 2-3
For each of the above, two types of powders were prepared. That is,
The powder having a composition of (La _0.8 Sr _0.2 ) _x MnO ₃ was added as amol% and (La
_0.8 Sr _0.2 ) _y MnO ₃ powder with bmol% was prepared,
Mix as in Experiment 1. The average particle size of each powder is 6.0
μm. Table 3 shows the values of x, y, a, and b.

[0040]

[Table 3]

That is, in Samples 2-1 to 2-3, x
The value of was fixed to 1.10 and the value of y was changed. At this time, the mixing ratio of each powder was adjusted so that the A site and the B site were 1: 1 on average in the entire mixed powder.

Then, for each sample, a flat plate-shaped porous sintered body was prepared in the same manner as in Experiment 1, and the porosity and reheat shrinkage rate thereof were measured. Table 4 shows the results. In addition, Table 4 also shows the data of Sample 1-5 in Experiment 1.

[0043]

[Table 4]

For each of the samples shown in Table 4, the relationship between the firing temperature and the porosity is shown in FIG. 3, and the relationship between the firing temperature and the reheat shrinkage ratio is shown in FIG. As can be seen from these results, according to the samples 2-1 to 2-3 of the present invention, as compared with the conventional sample 1-5, the porosity and the reheat shrinkage ratio which are equal to or lower than those of the conventional sample 1-5 are low. A sintered body is obtained.

Further, among the samples 2-1 to 2-3, the sample 2-1 has the greatest effect of the present invention, and the sample 2-2 is the second best. As described above, the effect of the present invention is further enhanced by using particles having a composition in which the A site is more defective (particles having a smaller y value), even if the amount thereof is relatively small.

(Experiment 3). For Samples 3-1 to 3-7
Then, two kinds of powders were prepared respectively. That is, (La_{0 .8}Sr
_0.2)_xMnO₃Amol% of powder (average particle size c μm) having the composition
And (La_0.8Sr_0.2) _yMnO₃(Average particle size dμm) is bmol
% Were prepared and mixed in the same manner as in Experiment 1. x, y,
Table 5 shows the values of a, b, c and d.

[0047]

[Table 5]

That is, in samples 3-1 to 3-5, x
The value of was fixed at 1.10 and the value of y was fixed at 0.80. Also,
The values of a and b were fixed at 66.6 mol% and 33.4 mol%, respectively. However, the average particle size c (μm) and the average particle size d (μm) of the non-sinterable powder having a value of x of 1.10.

In samples 3-6 and 3-7, the value of x is
It was fixed at 1.05 and the value of y was fixed at 0.80. Then, only the average particle diameter d (μm) was changed and the influence thereof was investigated.

Then, for each sample, a flat plate-like porous sintered body was prepared in the same manner as in Experiment 1, and the porosity and reheat shrinkage rate thereof were measured. The results are shown in Table 6. In addition, Table 6 also shows data for Samples 1-5 in Experiment 1.

[0051]

[Table 6]

The relationship between the firing temperature and the porosity of Samples 3-1 to 3-5 and 1-5 is shown in FIG. 5, and the relationship between the firing temperature and the reheat shrinkage ratio is shown in FIG. Sample 3-
The relationship between the firing temperature and the porosity for Nos. 4, 3-5, 3-6, 3-7, and 1-5 is shown in FIG. 7, and the relationship between the firing temperature and the reheat shrinkage ratio is shown in FIG.

Comparing Samples 3-1 to 3-5 and 1-5, according to the present invention, a porous sintered body having a porosity and a reheat shrinkage ratio equal to or lower than those of the conventional one at a firing temperature lower than the conventional one was obtained. It is clear that For example, the firing temperature for obtaining a porous sintered body having a porosity of about 30% is
Sample 3-1, 1550 ℃, Sample 3-2, 1530 ℃, Sample 3
-3, 3-4 is 1500 ° C, sample 3-5 is 1470 ° C, and sample 1-5 is 1600 ° C.

Particularly, in the samples 3-1 to 3-5, the y value was 0.
The average particle size of the easily sinterable particles of 80 is 6.0 to 0.5 μm, and the average particle size of the hardly sinterable particles of which the value of x is 1.10 is 6.
It is set to 0 to 10.0. As can be seen from this, the smaller d is, the more the firing can be performed at a lower temperature. Moreover, in Samples 3-2 to 3-5, the reheat shrinkage rate is further smaller, even if the porosity is the same as the conventional one. This tendency shows that the porosity is about 30-
It is particularly noticeable in the 33% area.

The reason for this is not necessarily clear, but by increasing the particle diameter of the relatively hard-to-sinter particles to 9.0 or 10 μm, a microstructure in which hot shrinkage of a certain degree or more is unlikely to occur is formed. It is considered to be something.

Also in the samples 3-6 and 3-7, the value of y is
A very remarkable effect is obtained by decreasing the average particle diameter d of 0.8 and increasing the average particle diameter c.

Samples 3-4, 3-5 and 3-6, 3-
7 is compared with Samples 3-4 and 3-5 using the powder having the composition of x = 1.10, rather than Samples 3-6 and 3-7 using the powder of x = 1.05. The effect of the invention is excellent. In particular, it is noted that Samples 3-4 and 3-5 have extremely small reheat shrinkage rates.

(Experiment 4). With respect to the conventional sample 4-1 and the sample 4-2 of the present invention, a porous sintered body was manufactured in the same manner as in Experiment 1, and the porosity and reheat shrinkage rate thereof were measured.
However, in Sample 4-1, a powder of (La _0.9 Sr _0.1 ) MnO _{3 having} an average particle size of 6.0 μm was used as the raw material powder.

On the other hand, in Sample 4-2, (La
_0.9 Sr _0.1 ) _1.1 MnO ₃ powder with an average particle size of 6.0 μm
Average particle size of 50mol% and (La _0.9 Sr _0.1 ) _0.9 MnO ₃ .
0 μm powder was mixed with 50 mol%. The results are shown in Table 7.
Shown in

[0060]

[Table 7]

As described above, according to the sample 4-2 of the present invention, even when the substitution amount at the A site was changed to 0.1, the porosity and the re-percentage were the same as or lower than those in the conventional case at the firing temperature lower than the conventional one. A porous sintered body having a heat shrinkage rate can be obtained.

Even when the substitution metal at the A site was calcium and the substitution amounts were 10% and 20%, the same experimental results as above were obtained.

[0063]

As described above, according to the present invention, when a porous sintered body made of lanthanum manganite having a perovskite structure is produced, the firing temperature is lower than the conventional one and the same or lower than the conventional one. A porous sintered body having porosity and high heat resistance can be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the firing temperature and the porosity of each sample in Experiment 1.

FIG. 2 is a graph showing the relationship between the firing temperature and the reheat shrinkage rate of each sample in Experiment 1.

FIG. 3 is a graph showing the relationship between firing temperature and porosity of each sample in Experiment 2.

FIG. 4 is a graph showing the relationship between the firing temperature and the reheat shrinkage rate of each sample in Experiment 2.

FIG. 5 is a graph showing the relationship between the firing temperature and the porosity of each sample in Experiment 3.

FIG. 6 is a graph showing the relationship between the firing temperature and the reheat shrinkage rate of each sample in Experiment 3.

FIG. 7 is a graph showing the relationship between the firing temperature and the porosity of each sample in Experiment 3.

FIG. 8 is a graph showing the relationship between the firing temperature and the reheat shrinkage rate of each sample in Experiment 3.

Claims (1)

(57) [Claims] 1. A method for producing a porous sintered body made of lanthanum manganite having a perovskite structure, comprising a value (A / B) obtained by dividing the number of A-site atoms of the perovskite structure by the number of B-site atoms. ) Is greater than 1 and particles of lanthanum manganite and particles of lanthanum manganite having a value smaller than 1 obtained by dividing the number of A-site atoms of the perovskite structure by the number of B-site atoms are at least a binder. And a pore-forming material, which is then molded, and the molded body is fired to obtain the porous sintered body.