JPH07196367A - Electrically conductive sintered ceramic and production thereof - Google Patents

Abstract

PURPOSE:To obtain an electrically conductive sintered ceramic having uniform gas permeation, lowered overvoltage and high strength by constituting the sintered product with particles having a specific composition and particles sizes in a certain range. CONSTITUTION:Ceramic powder mainly composed of La1-xSrxMnO3 (0.05<=x <=0.5) and of 10 to 30mum average particle size is formed in a usual manner and fired to give the electrically conductive sintered ceramic of 10 to 50mum average particle size. It is also preferred that the main constitution is changed to (La1-x-Srx)a Mn1-y-zAlyNizO3 (0.8<=1<=1.0; 0.05<=x<=0.50; 0.01<=y<=0.03; 0.03<=z<=0.15) instead of La1-xSrxMnO3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic sintered body having conductivity and a method for manufacturing the same. In particular, the present invention relates to a conductive ceramic sintered body (including a membrane), which is suitable for use as an electrode of a solid oxide fuel cell (hereinafter referred to as SOFC) and has excellent perovskite electrocatalytic performance and high strength, and a method for producing the same.

[0002]

2. Description of the Related Art The prior art will be described by taking an air electrode of a cylindrical cell type SOFC or a porous support tube as an example. A cylindrical cell type SOFC (hereinafter referred to as T-SOFC) is known from Japanese Patent Publication No. 1-59705. T-SOF
C has a cylindrical cell composed of a porous support tube-air electrode-solid electrolyte-fuel electrode-interconnector. When oxygen (air) is made to flow to the air electrode side and gas fuel (H ₂ , CO, etc.) is made to flow to the fuel electrode side, O ₂ ⁻ ions move in this cell to cause chemical combustion and An electric potential is generated between the fuel electrodes to generate electricity.

As a material for the air electrode of T-SOFC, Japanese Patent Publication No. 1-59705 discloses CaO-stabilized ZrO ₂ , La.
Oxide ceramics such as MnO ₃ and LaNiO ₃ have been proposed. Then, according to JP-A-2-293384, La _1-x Sr _x MnO ₃ was converted into JP-A-2-28815.
According to 9, La _1-x Sr _x Mn _1-y A _y O ₃ (A is C
u, Zn, Ni, Fe, Co, Cr, Al, Ti, Mg
More than one) was proposed.

The characteristics required for the material for the air electrode of T-SOFC are the following characteristics. 1000 ° C (SOFC operating temperature), chemically stable in an oxidizing atmosphere. Be breathable. Must be conductive (electronically conductive). High ion dissociation catalytic action. Good compatibility with ZrO ₂ , which is regarded as a favorite material for solid electrolytes (similar thermal expansion coefficient, no reactivity). Being able to form thin (eg 0.3-3.0 mm) pipes. High strength to some extent. It is economical.

It is quite difficult to industrially obtain a material which fully satisfies all of these characteristics, and research and development for obtaining such an ideal material and its manufacturing process have been conducted in various countries around the world. Is the current situation. Among them, the La-Sr-Mn-based perovskite structure composite oxide described above is regarded as promising.

On the other hand, as a method for producing a La-Sr-Mn-based composite oxide (hereinafter referred to as LSM) sintered body, Japanese Patent Application Laid-Open No. HEI-2 is proposed.
There is a method proposed in −293384. This method
It consists of the following steps. La or La compound, Mn or Mn compound, S
Step of mixing r or Sr compound These mixtures are fired at a temperature of 1000 to 1400 ° C. to obtain La _1-x Sr _x MnO ₃ (where 0 <x ≦
0.5) Step of synthesizing this La _{1 -x} Sr _x MnO ₃ is crushed to obtain an average particle size of 2
Step of making powder of 10 to 10 μm, kneading by adding 100 parts by weight of this powder, an organic binder, water, and 1 to 8 parts by weight of a pore-forming agent Step of making this kneaded product This molded product Dried, then 1300 to 16
Step of firing at a temperature of 00 ° C.

[0007]

The ceramic sintered body obtained by this method has the following problems. Gas permeability is insufficient or non-uniform. The reason is that when firing is performed using a raw material powder having a particle size of 10 μm or less, the pore diameter becomes small (3 μm or less), and sufficient gas permeability cannot be obtained. In addition, when pores are formed by adding a pore-forming agent, the pore distribution is non-uniform due to the non-uniform distribution of the pore-forming agent, and thus the gas permeability becomes non-uniform.

The overvoltage, which is an index representing the perovskite electrocatalyst performance, is high. The lower the overvoltage, the higher the perovskite electrocatalyst performance. The reason is,
This is because the gas permeability becomes insufficient or non-uniform, resulting in an increase in electrical resistance. Insufficient strength. The reason is that stress concentration is likely to occur because the structure becomes non-uniform due to the addition of the pore increasing agent.

An object of the present invention is to provide a conductive ceramic sintered body having a uniform gas permeability, a low overvoltage, and a high strength, which is suitable for an SOFC air electrode constituent material, and a method for producing the same. And

[0010]

Means and Actions for Solving the Problems The present inventors have
Based on the idea that the problems of the above-mentioned conventional technology may be solved by manipulating the constituent particle size of the sintered body,
The present invention has been completed by repeating various experiments and analyses.

That is, the conductive ceramic sintered body of the present invention is La _1-x Sr _x MnO ₃ (0.05 ≦ x ≦ 0.
It is characterized in that it is composed of a sintered body containing 5) as a main component, and the average constitutional grain size of this sintered body is 10 to 50 μm.

The reason for using La _1-x Sr _x MnO ₃ as a main component is that this substance basically satisfies the above-mentioned required characteristics. Note that 0.05 ≦ x ≦ 0.5
The reason why x is limited to is that the conductivity is good and the matching of the thermal expansion coefficient with ZrO ₂ is good as compared with the case where Sr is not added. Particularly good conductivity is that x is 0.25 to 0.40 (electrical resistance 120 to 135).
S / cm) range. Matching of the coefficient of thermal expansion is particularly good when x is 0.05 to 0.25 (coefficient of thermal expansion 1
The range is 0.0 to 10.8 × 10 ⁻⁶ / ° C.). Considering the balance of both characteristics, the particularly preferable range of x is 0.
It is 20 to 0.30.

It is preferable that the impurities other than La _1-x Sr _x MnO ₃ are small. Particularly, SiO ₂ is preferably 0.01% or less. The total amount of impurities is preferably 0.1% or less.

The average constituent particle size is measured by observing the particle size by SEM observation as shown in FIG. The average constituent particle size is particularly preferably in the range of 15 to 30 μm. This is because the properties such as conductivity, strength and gas permeability have the best balance in this range. The particle size distribution is in the range of 5 μm with respect to the average constituent particle size, and the number of particles outside this range is preferably 4% or less of the whole.

In the conductive ceramic sintered body of the present invention, (La _1-x Sr _x ) _a Mn _1-yz Al _y Ni _z O ₃ (0.8 is used instead of La _1-x Sr _x MnO ₃ ). ≦ a ≦ 1.0, 0.05 ≦ x ≦ 0.50, 0.
It is preferable that the main component is 01 ≦ y ≦ 0.03, 0.03 ≦ z ≦ 0.15). The reason is that the electrocatalytic property is good in this composition range. In particular, the reason for setting 0.8 ≦ a ≦ 1.0 is to improve the electrocatalytic property by reducing the contents of La and Sr, which are slightly reactive with the solid electrolyte (YSZ, etc.). .

In the above chemical formula, 0.01 ≦ y ≦ 0.
The reason why it should be 03 is that the electrocatalytic property is particularly good in this range, and if added excessively, a mismatch occurs in the perovskite structure and the electrode characteristics deteriorate. In that sense, the added amount is kept small.

The reason why 0.03 ≦ z ≦ 0.15 should be satisfied is that the electrocatalytic property is particularly good in this range.
This is because if added excessively, the perovskite structure will be mismatched and the electrode characteristics will be deteriorated. In that sense, the added amount is kept small.

The method for producing a conductive ceramic sintered body according to the present invention is the method for producing a conductive ceramic sintered body according to claim 1, 2 or 3 of the present specification, wherein the average particle size is 10 to 30 μm.
The method is characterized by including a step of molding and firing m 2 of the above ceramic powder. Further, the average particle size is 15 to 25.
It is preferably μm.

Regarding the relationship between the average particle size of the raw material ceramic powder and the average constituent particle size of the sintered body, the latter is 5 more than the former.
It is preferably about 30% large (slightly thickened during sintering). By doing so, the air permeability, conductivity, and strength of the sintered body can be set to desirable values.

Other production conditions are not particularly limited, but in order to achieve the above-mentioned sintering conditions,
It is preferable to select raw material adjustment, molding, sintering temperature and the like. The method for molding the sintered body of the present invention is not particularly limited, and may be a slurry method, an extrusion method, or the like.

[0021]

[Examples and Comparative Examples] L having an average particle size of 2.5 to 40 μm
a _0.75 Sr _0.25 MnO ₃ powder is used as a raw material, well mixed and kneaded with an organic binder and water, and an extrusion molding method is used to prepare a pellet of diameter 20 × thickness 2 m / m and a solid rod of diameter 6 × length 40 m / m. Molded. The pellet was fired at 1300 to 1600 ° C to prepare an air electrode as a sample for measuring overvoltage. A YSZ (yttria-stabilized zirconia) thin film was applied onto the obtained air electrode by a slurry coating method, baked, and then Y
Pt was baked on the SZ as an electrode to obtain a sample for measuring overvoltage. FIG. 1 is a side view showing this overvoltage measurement sample, in which 1 is an air electrode, 3 is a YSZ thin film, and 5 is a Pt electrode.

Using this sample, O ₂ gas (concentration: 21% to 100%) was passed on the air electrode side, and H ₂ gas was passed on the Pt electrode side, and the overvoltage between the air electrode and YSZ was measured. The current density at this time is 1 A / cm ² . The area for which the current density is to be calculated is the area of the Pt electrode 5. The measurement results are shown in FIG. From FIG. 2, when the average particle size of the La _1-x Sr _x MnO ₃ powder is less than 10 μm or exceeds 30 μm, the overvoltage increases and the oxygen concentration increases from 100% to 50%.
→ When it is reduced to 30%, it can be seen that the overvoltage further increases. In particular, when the average particle size is 10 μm or less, the degree of increase in overvoltage when the oxygen concentration decreases is remarkable.

A solid rod having a diameter of 6 and a length of 40 m / m was fired at the same temperature as the pellets, and the three-point bending strength at room temperature was measured (FIG. 3). Considering the reliability of the SOFC cell, the strength of the air electrode material is preferably 1.5 kg / mm ² or more, and for this purpose, the average particle size is preferably 30 μm or less. From the above, the average particle size of LaSrMnO ₃ powder is 10 to 30 μm, preferably 15 to 25 μm.
Is good.

[0024]

As is apparent from the above description, the conductive ceramic sintered body and the manufacturing method of the present invention have the following effects. It has uniform and sufficient gas permeability. Good conductivity. Due to its relatively high strength, it is possible to form a cylindrical battery cell without being assisted by other supporting materials. Therefore, a highly efficient cell with low gas flow resistance can be economically formed. As a result of the use of particularly high concentration oxygen gas (especially 30
% Or more) as a high efficiency SOFC air electrode material.

[Brief description of drawings]

FIG. 1 is a side view showing a sample for measuring overvoltage in which a conductive ceramic sintered body of the present invention is used as an air electrode.

FIG. 2 is a graph showing a relationship between an average particle diameter of raw material powders of conductive ceramic sintered bodies of Examples and Comparative Examples and overvoltage.

FIG. 3 is a graph showing the relationship between the average particle size of raw material powders of the conductive ceramic sintered bodies of Examples and Comparative Examples and room temperature strength.

FIG. 4 is a diagram showing a state in which an average constituent grain size of a sintered body is measured by SEM observation.

[Explanation of symbols]

 1 Air electrode 3 YSZ thin film 5 Pt electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01M 4/86 T 8/02 E 9444-4K 8/12 9444-4K

Claims (5)

[Claims] 1. La _1-x Sr _x MnO ₃ (0.05 ≦ x
A conductive ceramic sintered body comprising a sintered body containing ≦ 0.5) as a main component, and the average constituent grain size of the sintered body is 10 to 50 μm. 2. The conductive ceramic sintered body according to claim 1, wherein the average constituent particle size is 15 to 30 μm. 3. (La _1-x Sr _x ) _a Mn _1-yz Al _y Ni _z O ₃ (0.8 ≦ a ≦ 1.0, 0.05 instead of La _1-x Sr _x MnO ₃ ) ≦ x ≦ 0.50, 0.
01 ≦ y ≦ 0.03, 0.03 ≦ z ≦ 0.15) as a main component, The conductive ceramic sintered body according to claim 1 or 2. 4. The method for producing a conductive ceramic sintered body according to claim 1, including the step of molding and firing the ceramic powder having an average particle diameter of 10 to 30 μm. 5. The method according to claim 1, 2 or 3 including a step of molding and firing the ceramic powder having an average particle size of 15 to 25 μm.
A method for producing the conductive ceramic sintered body described.