JPH0737348B2 - Method for manufacturing conductive porous ceramic tube - 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 conductive porous ceramic tube.

[0002]

2. Description of the Related Art Solid oxide fuel cells (SOFC) are
It has recently attracted attention as an extremely promising power generation device having features such as high power generation efficiency, diversification of fuels (naphtha, natural gas, methanol, coal reformed gas, etc.) and low pollution.

In this solid oxide fuel cell, the thin film electrodes and electrolytes, which are the main constituents, are not strong enough to support themselves. Therefore, conventionally, the electrode film and the solid electrolyte film have been formed on the porous support by plasma spraying or slurry coating.

However, when the electrode film and the electrolyte film are formed on the porous support as described above, there is a problem that the output decreases due to the gas diffusion resistance of the support, and the overall structure is complicated. Met. Therefore, instead of providing the electrode on the porous support, if the porous electrode itself can be used as the support, the entire structure can be simplified, the manufacturing process can be simplified, and the cost can be reduced. The output can be improved by eliminating the loss due to the gas diffusion resistance. However, the conventional porous electrode itself cannot obtain sufficient strength and is not suitable as a structural support material.

In order to solve this problem, the present applicant has disclosed in Japanese Patent Laid-Open No. 2-293384 a method for producing a porous ceramic tube that can also be used as an air electrode. By this manufacturing method, it has become possible to stably manufacture a tube having a much higher strength than ever before.

[0006]

[Problems to be Solved by the Invention] However, further research has revealed that a problem still remains. That is, La ₂ O ₃ , MnO ₂ , Ca, Mg, B as starting materials
Wet mixing was performed in a pot mill using either a or Sr carbonate powder, but it was found that the mixing time at this raw material stage affects the strength of the final product. That is, this wet mixing time is usually required to be 2 hours or more, which causes a decrease in productivity. When this mixing time was stopped to about 1 hour, the strength of the air electrode tube which was the final product did not reach the standard value and the dispersion became large.

Further, La ₂ O ₃ powder has an extremely high hygroscopic property, and in the above mixing process, La ₂ O ₃ rapidly absorbs water to become lanthanum hydroxide, and at this time, a large amount of heat is generated. Therefore, the temperature of the mixture rises rapidly in the ball mill,
The pressure inside the ball mill increased, which could cause an explosion. Therefore, it was necessary to take some measures.

An object of the present invention is to increase the strength of a ceramic porous tube made of lanthanum manganate in which a part of the lanthanum moiety is replaced with strontium, and to increase the strength of the ceramic tube and to mix the starting materials. It is to shorten the time required for increasing the productivity and to eliminate the risk of explosion due to temperature rise during mixing.

[0009]

Means for Solving the Problems The present invention comprises mixing manganese oxide powder, a carbonate powder of any of Ca, Mg, Ba, and Sr and lanthanum oxide powder, and molding and firing the mixture thus obtained. , A lanthanum manganate in which a part of the lanthanum moiety was substituted with any of Ca, Mg, Ba, and Sr was added, and an organic binder, water, and a pore-forming agent were added to the powder obtained by crushing this compound. A method for producing a conductive porous ceramics tube by drying and firing the thus obtained molded body, kneading and kneading the kneaded product in a medium stirring mill equipped with zirconia cobblestones and an agitator. Manganese oxide powder and C
Carbonate powder of a, Mg, Ba, or Sr, lanthanum oxide powder, and water are supplied, and the agitator is rotated at 100 to 250 rpm and mixed for 20 to 40 minutes, so that the radial crushing strength is 25 MPa or more. It is characterized in that a certain conductive porous ceramics tube is obtained.

[0010]

In the present invention, manganese oxide powder and Ca, M
When mixing the carbonate powder of any one of g, Ba, and Sr and the lanthanum oxide powder, a medium stirring mill equipped with zirconia cobblestone and an agitator is used.

That is, the conventionally used pot mill is a so-called rolling type mill, in which the cobblestone and the mixture are put in a cylindrical container, which is hermetically sealed, and the cylindrical container is rotated. Met. On the other hand, in the present invention, the mixture is agitated by the agitator and at the same time, the powder is pulverized, and the mixture is not sealed. Therefore, even if the temperature of the mixture rises due to the water absorption reaction of lanthanum oxide, there is no danger of explosion.

If such a medium agitating mill is used, even if mixing is performed only for a short time of 40 minutes,
It does not affect the strength of the final product, and the radial crushing strength is 25.
It was found that a conductive porous ceramics tube having a pressure of at least MPa can be obtained. As a result, the time required for mixing could be reduced to about 1/3 of the conventional time. After that, the final product can be obtained only through the steps of molding, firing, crushing, kneading, molding, and firing, so that the strength of the final product is not reduced by any factor at the first powder mixing stage. It is not clear if the mixing time could be shortened. However, it is considered by the present inventors that the particle size distribution of the powder after being ground in the mill and the shape of the powder are related.

As described above, the time required for the first mixing step can be shortened, and as a result, the overall productivity is remarkably improved. However, it has been found that when the mixing time exceeds 40 minutes, the strength of the final product is rather lowered. . This may be due to the powder being over-ground. Also,
It was also found that when the above mixing time was less than 20 minutes, the strength of the final product also decreased. This is probably because the powder shape and particle size distribution did not reach an appropriate shape and distribution.

It was also found that the boulders had to be zirconia boulders. This is also surprising, but if you use ordinary alumina boulders, the strength of the final product,
It was found that the electrical resistance, porosity, etc. are affected and the characteristics of the final product vary. This is probably because the impurities mixed in from the cobblestone promote the sintering of the product in the later process.

The rotation speed of the agitator is 100 to 250.
Must be rpm. If this is less than 100 rpm, the raw material powder is difficult to be crushed and the particles remain coarse, so that the strength of the final product is reduced. On the other hand, this rotation speed
After 250 rpm, the strength of the final product still decreased. It is considered that this is because the raw material powder exceeds the appropriate particle size distribution and shape and is excessively ground.

During the above mixing, the temperature of the mixture is set to 90
It is preferable to keep the temperature below ° C. That is, the temperature of the mixture inevitably rises due to the absorption of lanthanum oxide, and the mixture boils when left to stand. However, if this temperature exceeds 90 ° C., the water content will evaporate significantly, which will increase the viscosity of the mixture, making the mixing itself difficult. As described above, in order to maintain the temperature of the mixture at 90 ° C. or lower, it is preferable to install a cooling pipe on the outer periphery of the medium agitation type mill and to flow cooling water through the cooling pipe.

When the above mixing is started, the weight ratio of water in the mixture is preferably 40 to 65% by weight. If it is less than 40% by weight, the viscosity of the mixture is increased, and it becomes difficult to mix and grind it. 65% by weight of water
If it exceeds, the productivity will decrease as the next drying process takes time.

In the method of the present invention, the mixture is molded,
By firing, lanthanum manganate in which a part of the lanthanum moiety is substituted is synthesized. This can be expressed by the following formula.

La _−x A _x MnO ₃ −α Here, it is preferable that 0 <× ≦ 0.5. A is Ca,
Either Mg, Ba, or Sr. -Α represents that the perovskite structure always contains a defect. The firing temperature is 10
The temperature is preferably 00 to 1400 ° C.

Next, an organic binder, water, and a pore-forming agent are added to the powder obtained by crushing this composite, and the mixture is kneaded. The amount of the pore-forming agent added is 1 to 100 parts by weight of the above compound.
It is preferably 8 parts by weight. Examples of the pore-forming agent include acrylic powder and carbon powder.

The kneaded material is molded, and the molded body thus obtained is dried and fired to produce a conductive porous ceramic tube. The firing temperature is preferably 1300 to 1600 ° C. The conductive porous ceramics tube thus obtained is
It is particularly useful as an FC air electrode tube.

[0022]

Example Next, an example of manufacturing an air electrode tube for SOFC
I will describe. This composition is La _0.9Sr_0.1MnO₃And (Experiment 1) First, 45.3% by weight of La₂O₃And 8.0% by weight
SrCO₃And 46.8 wt% MnO₂And prepared. Each of these powders
The average particle size at the end was 1 to 5 μm. Of these, La₂O₃powder
Since the powder has high hygroscopicity, open the bag containing the raw materials.
After sealing, the weighing was done as quickly as possible.

Then, according to the present invention, the above raw material powders were mixed by an attritor which was a medium stirring type mill. At this time, the weight ratio of water was 50% by weight, and the inner dimensions of the attritor were 600 mm in diameter and 600 mm in height. Further, zirconia boulders were used as the boulders, and the total weight thereof was 3 kg. The temperature of the mixture was maintained at 60 to 90 ° C, and the rotation speed of the agitator was set to 200 rpm. The mixing time was three kinds of 20, 30, and 40 minutes. After this mixing is completed, the mixture is dried in an electric furnace until the water content becomes 0% by weight, and the dried product is cooled to 1400
It was fired at ℃ for 5 hours to synthesize La _0.9 Sr _0.1 MnO ₃ . This synthetic material was crushed, and 3 parts by weight of cellulose (a pore-forming agent) and polyvinyl alcohol (organic binder) were added to 100 parts by weight of the pulverized powder, and 18 parts by weight of water was further added. These were kneaded in a clay kneader for 2 hours. This kneaded product was extrusion-molded to obtain a cylindrical molded body having an outer diameter of 35 mm, a length of 1700 mm and a wall thickness of 4.35 mm. This cylindrical molded body was subjected to humidity control drying with an electric dryer, and the water content of the cylindrical molded body was adjusted to 10%.

The dried cylindrical molded body was fired at 1400-1500 ° C. to obtain a conductive porous ceramic tube having a porosity of 25%. The dimensions of this pipe are 30 mm outer diameter, 1500 mm length, and 3.75 wall thickness.
It was mm.

A conductive porous ceramics tube was manufactured in the same manner as above. However, a ball mill was used when mixing the raw material powders. This mixing and stirring time is 20, 3
The time was 0, 40 minutes, zirconia boulders were used as the boulders, and the rotation speed of the ball mill was 100 rpm.

The radial crushing strength of each of the conductive porous ceramic tubes thus obtained was measured. Here, the radial crushing strength is calculated from the following formula. Radial crushing strength = P (D−d) / Ld ² Here, P is the maximum load at break, D is the outer diameter of the test piece, d
Is the wall thickness of the test piece, and L is the length of the test piece. Further, since each conductive ceramic tube manufactured here is for an SOFC air electrode tube, it must be capable of efficiently permeating oxygen. Therefore, its porosity must be 25% or more.

Table 1 Examples of the present invention Mixing stirring time (min) Radial crushing strength (MPa) 20 30 30 38 40 27 Comparative example 20 5 30 10 40 12

As can be seen from the above results, according to the present invention, a high radial crushing strength can be obtained with a short mixing and stirring time.

(Experiment 2) A conductive porous ceramics tube was prepared in the same manner as above, and the radial crushing strength was measured. However, when mixing the raw material powders, the rotation speed of the agitator in the attritor was set to 80, 100, 250, and 270 rpm, and the mixing time was changed between 10 and 60 minutes. The relationship between the rotation speed of the agitator, the mixing time and the radial crushing strength of the final product is shown in the graph of FIG.

As can be seen from FIG. 1, when the rotating speed of the agitator deviates from 100 rpm to 250 rpm, the radial crushing strength of the final product, the ceramic tube, remarkably decreases. When the number of revolutions of the agitator is 100 rpm and 250 rpm, there is a peak of radial crushing strength at a mixing time of 25 to 30 minutes. Then, when the mixing time is out of the range of 20 to 40 minutes, the strength of the final product suddenly decreases. In particular, since this conductive porous ceramics tube functions as a support for the structure of the entire SOFC, the radial crushing strength must exceed the target strength of 25 MPa. Therefore, the mixing time must be 20-40 minutes.

When calcium carbonate, magnesium carbonate or barium carbonate is used instead of strontium carbonate,
The same result as above was obtained.

[0032]

As described above, according to the present invention, a conductive porous ceramic tube made of lanthanum manganate in which a part of the lanthanum moiety is substituted with any of Ca, Mg, Ba, and Sr is used. In the case of manufacturing by any method, the time required for the first mixing step of the raw material powders can be shortened and the productivity of the product can be remarkably improved. Moreover, by using zirconia cobblestone, it is possible to suppress the influence of impurities mixed in the mixture at the time of mixing and prevent variations in the strength and porosity of the final product. In addition, the radial crushing strength of the final product can be maintained at 25 MPa or higher. Furthermore, there is no risk of explosion due to temperature rise during mixing.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between agitator rotation speed, mixing time, and radial crushing strength of a final product.

Claims (3)

[Claims] 1. A mixture of manganese oxide powder, a carbonate powder of any of Ca, Mg, Ba, and Sr and lanthanum oxide powder, and the mixture thus obtained is molded and fired so that a part of the lanthanum moiety is Ca. , Mg, Ba, or Sr-substituted lanthanum manganate was synthesized, and the powder obtained by crushing this compound was kneaded by adding an organic binder, water, and a pore-forming agent, and kneading the kneaded product. Molding, a method for manufacturing a conductive porous ceramics tube by drying and firing the molded body thus obtained, in a medium stirring mill equipped with zirconia cobblestone and agitator, manganese oxide powder and Ca, By supplying carbonate powder of any one of Mg, Ba, and Sr, lanthanum oxide powder, and water, and rotating the agitator at 100 to 250 rpm and mixing for 20 to 40 minutes, the radial crushing strength is 25 MPa or more. Characterized by obtaining a conductive porous ceramics tube To method for manufacturing a conductive porous ceramic tube. 2. The method for producing a conductive porous ceramic tube according to claim 1, wherein the temperature of the mixture is maintained at 90 ° C. or lower in the mixing step. 3. When the mixing is started, the weight ratio of the water content in the mixture is set to 40 to 65% by weight.
A method for producing a conductive porous ceramics tube described in the above.