JPH0664975A - Production of ceramic composite material - Google Patents

Abstract

PURPOSE:To obtain a ceramic composite material by monolithic sintering without causing any crack. CONSTITUTION:The objective composite material is obtained by mutual laminating of two kinds of ceramic materials 1, 2 followed by sintering. In this case, the respective thermally shrinking behaviors of the above materials are made as equal as possible. A material 3 as stress-relaxing layer is put in between the ceramic materials 1 and 2 so as to relax the stress developed between the materials 1 and 2 during the sintering. The material 3 is extremely different in thermally shrinking behavior from the above materials 1, 2 so as to be liable to be cracked during the sintering. Owing to the material 3's cracking in the sintering process, no cracks will be developed in the ceramic materials 1, 2.

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 ceramic composite material by joining ceramic materials having different heat shrinkage behaviors during sintering.

[0002]

2. Description of the Related Art When firing a ceramic material to make it dense, there is generally about 20% (50% by volume) shrinkage (heat shrinkage). FIG. 7 shows a heterogeneous ceramic material 1.
It shows the state of heat shrinkage of the ceramic materials 1 and 2 before firing (green state) (b) to during firing (b) and after firing (c). To do. The behavior of this shrinkage (heat shrinkage) depends on the chemical properties of the material, the particle size distribution, and the like. Therefore, when the different types of ceramic materials 1 and 2 are bonded to each other in a state before firing shown in FIG. 8A and then fired, as shown in FIG.
In many cases, one ceramic material 1 produces a compressive stress as indicated by an arrow and the other ceramic material 2 produces a tensile stress as indicated by an arrow. There is a problem that the ceramic materials 1 and 2 are cracked or damaged.

In order to alleviate the stress generated when such different kinds of ceramic materials are bonded and fired in a green state, conventionally, thermal contraction is gradually or absent at the joint interface between different kinds of ceramic materials. Different materials (gradient materials) are layered in layers so that they change in stages,
Relief of stress generated between different kinds of ceramic materials has been performed.

[0004]

However, in the above-described conventional method, since different materials are interposed between different kinds of ceramic materials, stress does not act suddenly, but different layers of different materials are used. In addition, since the heat shrinkage is changed stepwise by interposing them in layers, many materials intervene and are complicated.

Therefore, the present invention is intended to provide a method for producing a ceramic composite material capable of relaxing the stress caused by the difference in heat shrinkage without using different materials in multiple layers.

[0006]

In order to solve the above-mentioned problems, the present invention is extremely different from the heat-shrinking behavior of the ceramic material between different ceramic materials whose heat-shrinking behavior during firing is as close as possible. A thin plate of a material exhibiting heat shrinkage is sandwiched as a stress relaxation layer, and then these are fired and integrally sintered to obtain a composite material.

[0007]

[Function] Since the material as the stress relaxation layer between the ceramic materials having similar thermal contraction behavior is extremely thin and easily cracked,
The stress is relieved by the generation of minute cracks during firing, and the ceramic materials to be bonded do not crack.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which the heat shrinkage behavior is made as close as possible by adjusting the particle size and the like.
When two different ceramic materials 1 and 2 are bonded to each other to manufacture a composite material having an integrated structure, the (a) of FIG.
As described above, the material 3 exhibiting a heat shrinkage behavior extremely different from the heat shrinkage behaviors of the above-mentioned ceramic materials 1 and 2 is sandwiched in the form of a thin plate as a stress relaxation layer, and then the material is placed at 1300 ° C.
〜1400 ℃ fired, the different ceramic materials 1,
2 is sintered together to make a composite material consisting of ceramic materials 1 and 2.

In the above, the material 3 as the stress relaxation layer
Of the ceramic materials 1 and 2 to be joined are extremely different from each other in thermal shrinkage behavior, and therefore, the ceramic materials 1 and 2 are different from each other in the middle stage of the baking shown in FIG. 1B. When the material 3 in the heat shrinking behavior is stretched or contracted, the material 3 is broken or has small cracks, so that it is generated between the ceramic materials 1 and 2 to be joined. Thus, the ceramic composite materials I and 2 which have been calcined as shown in (c) of FIG. Is obtained.

As the material 3 used as the stress relaxation layer, one having the same chemical composition as the ceramic materials 1 and 2 which have similar thermal contraction behaviors but having different thermal contraction behaviors by adjusting the grain size or the like may be used. , Or ceramic material 1,
A chemical composition different from that of 2 should be used.

Explaining it concretely, FIG. 2 shows the relationship between temperature and the amount of heat shrinkage. In the figure, a curve a shows the heat shrinkage behavior of the ceramic material 1, a curve b shows the heat shrinkage behavior of the ceramic material 2, and a curve c shows the heat shrinkage behavior of the material 3. As shown in FIG. 2, the ceramic materials 1 and 2 to be bonded and sintered together have a heat shrinking behavior as close as possible, but the difference in heat shrinkage is within 3%, preferably within 1%. And Next, the ceramic materials 1 and 2 and the material 3 used as the stress relaxation layer sandwiched between the ceramic materials 1 and 2 are those having a thermal contraction of 5 to 20%. Below 5%, ceramic materials 1 and 2
This is because the effect of relieving stress due to cracking is small, and at 20% or more, the shrinkage amount of the ceramic material is generally about 20%, and there is no further shrinkage.

It has been confirmed by experiments that the ceramic materials 1 and 2 are not damaged after firing and the ceramic materials 1 and 2 are sufficiently bonded to each other if the above conditions are satisfied.

As an example, an experiment in which the difference in heat shrinkage between the ceramic materials 1 and 2 is within 1% and the difference in heat shrinkage between the ceramic materials 1 and 2 is 15% The result was good.

The method of the present invention can be applied to other fields, for example, the production of solid oxide fuel cells.

Among the solid oxide fuel cells, the flat type, in particular, the single cell type, as shown in FIG. 3, has both sides of the solid electrolyte plate 4 to which yttria-stabilized zirconia (YSZ) is applied. , The air electrode 5 and the fuel electrode 6 are arranged in an overlapping manner, and a separator (interconnector) 8 is arranged on the air electrode 5 side via an air flow path column 7 for forming an air flow path,
Further, a separator (interconnector) 8 is arranged on the fuel electrode 6 side through a fuel flow channel pillar 9 for forming a fuel gas flow channel, and air is provided on the air electrode 5 side. By flowing the fuel gas to the fuel electrode 6 side, oxygen ions generated by the reaction on the air electrode 5 side are made to reach the fuel electrode 6 side through the electrolyte plate 4, while the fuel gas H ₂ is generated on the fuel electrode 6 side. And the oxygen ions react with each other to be released as water H ₂ O.

The method of the present invention is applied to the integral sintering of the air electrode 5, the electrolyte plate 4, the fuel electrode 6 and the fuel flow channel pillar 9 in the flat plate type solid oxide fuel cell having the above-mentioned structure, and the following method is applied. I did some experiments.

That is, on the green sheet of the electrolyte plate 4 formed by the doctor blade method, the air electrode 5 and the fuel electrode 6 whose thermal contraction behavior is made as close as possible by adjusting the particle size are printed by the screen printing method, and the fuel electrode After the fuel electrode material 10 whose heat shrinkage behavior has been extremely changed by adjusting the particle size or the like is printed on the No. 6 as a stress relaxation layer by the screen printing method in the same manner, the fuel electrode 6 is formed on the fuel electrode material 10. The fuel flow channel pillars 9 formed of the same material are arranged in an overlapping manner,
Firing was performed at 00 ° C to 1400 ° C. Further, in the experiment, the stress relaxation layer was also prepared without the fuel electrode material 10.

As a result of the experiment, when the fuel electrode material 10 was put in as a stress relaxation layer, no cracks were found in the electrolyte plate 4 and the fuel flow path column 9 after firing, but the fuel electrode material 10 was stress relaxation layer. If not included, the fuel flow channel pillar 9
It has been confirmed that the particles fall off and the electrolyte plate 4 is broken. The electrolyte plate 4, the air electrode 5 and the fuel electrode 6 are
Although the thermal shrinkage behavior is as close as possible, cracks may occur in the electrode due to the difference in thermal shrinkage behavior during firing. However, even if cracks occur, there is no problem because the electrode is porous.

The joint state was confirmed by power generation of the cell, but the fuel electrode material 1 was used as the stress relaxation layer.
Even if 0 was entered, the joining was sufficiently performed. This is proved from the result of the power generation test, as shown in FIG. 5, in which no increase in the polarization A on the fuel electrode side was observed and the electrical connection was sufficiently secured.

The above power generation test was conducted under the following conditions: fuel: 3% humidified hydrogen utilization rate: 0.6% or less, oxidizer: oxygen current: 0.3 A / cm ² temperature: (1000 ± 3) ° C. This was carried out with and without the relaxation layer. In the case without the stress relaxation layer, an increase in the polarization A on the fuel electrode side was observed as shown in FIG. 5 and 6, B is the electromotive force, C is the polarization on the air electrode side, and D is the generated voltage.

[0022]

As described above, according to the method for producing a ceramic composite material of the present invention, a material having extremely different heat shrinkage behavior from those materials is thinned between the ceramic materials to be joined to reduce stress. Since it is put in as a relaxation layer, fired and integrally sintered, only a thin stress relaxation layer is interposed between the ceramic materials, so that it can be simplified and sufficient bonding can be obtained without cracking. Further, by the wet method, the composite material can be obtained at a low cost, and other excellent effects can be obtained.

[Brief description of drawings]

FIG. 1 shows an embodiment of the method of the present invention, (a) is a state diagram before firing, (b) is a state during firing, and (c) is a state diagram after firing.

FIG. 2 is a diagram showing a difference in heat shrinkage behavior of materials used in the method of the present invention.

FIG. 3 is a cross-sectional view showing a configuration example of a unit cell of a solid oxide fuel cell.

FIG. 4 is a cross-sectional view showing a state when the solid oxide fuel cell shown in FIG. 3 is integrally sintered by the method of the present invention.

5 is a diagram showing power generation performance when integrally sintered in FIG.

FIG. 6 is a diagram showing power generation performance when integrally sintered without a stress relaxation layer in FIG.

FIG. 7 shows general heat shrinkage that occurs when firing a ceramic material, (a) before firing, (b) during firing, and (c) after firing.

FIG. 8 shows a state in which different kinds of ceramic materials are stuck together and fired, where (a) is before firing and (b) is during firing.

[Explanation of symbols]

 I Ceramic composite material 1, 2 Ceramic material 3 Material 4 Electrolyte plate 5 Air electrode 6 Fuel electrode 10 Fuel electrode material

Claims (1)

[Claims] 1. A material having a heat shrinkage behavior extremely different from the heat shrinkage behavior of the ceramic material is sandwiched between separate ceramic materials whose heat shrinkage behaviors are as close as possible, as a stress relaxation layer, and then thinned. A method for manufacturing a ceramic composite material, which comprises firing and integrally sintering the composite material into a composite material.