Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2000-10-20
2004-02-17
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000, C429S006000
Reexamination Certificate
active
06692855
ABSTRACT:
This application claims the benefit of International Application No. PCT/JP99/02048, which has the international filing date of Apr. 19, 1999, and which was not published under PCT Article 21(2) in English.
1. Technical Field
The present invention relates to a solid electrolyte type fuel cell (hereinafter sometimes referred to as SOFC) having high power generating performance and durability.
2. Background Art
A solid electrolyte type fuel cell comprises an air electrode, a solid electrolyte film, a fuel electrode and an interconnector. In the following, the respective prior art techniques are explained.
First, with regard to an air electrode, prior art is explained by referring to an air electrode or an air electrode supporting tube of a solid electrolyte type fuel cell of a cylindrical cell type as an example. Solid electrolyte type fuel cells are disclosed in Japanese Patent publication number Kokoku Hei:1-59705, etc. The solid electrolyte type fuel cell has a cylindrical cell constituted by a porous supporting tube-an air electrode-a solid electrolyte-a fuel cell-an interconnector. When oxygen (air) is flown to the air electrode side and a fuel gas (H
2
, CO, etc.) is flown to the fuel electrode side, O
2−
is moved in the cell to cause a chemical burning whereby potential difference between the air electrode and the fuel electrode occurs to cause power generation. There is a system in which the air electrode also has a function of a supporting tube (an air electrode supporting tube).
As a material for an air electrode of a solid electrolyte type fuel cell, a perovskite type oxide ceramics has been proposed such as LaMnO
3
in Japanese Patent publication number Kokoku Hei:1-59705, and La
1−x
Sr
x
MnO
3
in Japanese Patent publication number Kokai Hei:2-288159. Also, in Proc. of the 3rd Int. Symp. on SOFC, 1993, La
0.09
Sr
0.10
MnO
3
has been introduced as an air electrode.
A size of an air electrode supporting tube is generally an outer diameter of 10 to 20 mm, a thickness of 1 to 2 mm and a length of 1 to 2 m. For producing such a long ceramics formed product, an extrusion forming method has generally been used.
For producing such a long ceramics sintered body, a bend to the lateral direction becomes a problem. As a method of decreasing a bend of a long sintered body, a hanging sintering is carried out. The hanging sintering is to carry out the sintering in the state that a material to be sintered is hanged to the longitudinal direction. A tensile stress by weight of the material to be sintered itself is affected to the sintered material so that a correcting force is applied to the sintered body whereby a sintered body with a little bend can be obtained.
In Japanese Patent publication number Kokoku Hei: 6-10113, with regard to a production process of a long sintered body, there is disclosed a technique in which a ceramics long body is subjected to lateral sintering at a temperature not less than a shrinkage starting temperature of said ceramics material, and then, subjecting to hanging sintering at a temperature not less than the lateral sintering temperature. According to said publication, it is described that a rod of ZrO
2
with a length of 1.1 m and a diameter of 20 mm is sintere data lateral sintering temperature between 1300 to 1450° C. and a hanging sintering temperature of 1450° C. so that a good result can be obtained.
In La
0.09
Sr
0.10
MnO
3
which is representative as an air electrode composition, there are cases where gas permeability is insufficient so that high power generating performance cannot be obtained. On the contrary, when gas permeability is heightened to improve power generating performance, strength is lowered so that a cell is broken during power generation or a cell is broken during preparation thereof
As a preparation method of a perovskite type oxide, a method of repeating pulverization—pressurizing—heat treatment is disclosed in Japanese Patent publication number Kokai Hei:7-6769. As a pulverizing method of ceramics powder, an impact type pulverizer, a stream type pulverizer, aba mill, etc. has been used, and the impact type pulverizer has been used in many cases in the point of easiness in operation.
In the case of the present method, a metal material containing Fe as a main component has been used as a material for a pulverization blade or a pulverization room. Thus, when the above-mentioned pulverization is repeated by using, for example, stainless as a material of the pulverization blade or the pulverization room, 0.5 to 1.0 w % or so of Fe component is migrated in the synthesized lanthanum manganite powder. Experiments were carried out with regard to a Fe content in the lanthanum manganite and power generating performance of a cell, and as a result, it was found that the Fe component in the lanthanum manganite markedly affects to the power generating performance of the cell and the Fe component with 0.5 wt % or more markedly lowers the power generating performance of the cell.
In a material other than the long sintered body comprising a material or having a size specifically mentioned as an object in the above-mentioned Japanese Patent publication number Kokoku Hei:6-10113, if a temperature of a lateral sintering before a hanging sintering is lowered, sintering at the lateral sintering does not proceed sufficiently so that high temperature strength is insufficient whereby there is a fear of dropping the sintered body by breaking the sintered body due to itself weight in many cases in a subsequent hanging sintering. For example, a shrinkage starting temperature of the lanthanum manganite is 1000° C. When a sintered body subjected to lateral sintering within the range of 1000 to 1350° C. is to be subjected to hanging sintering at a temperature exceeding 1350° C., there is an extremely high risk of dropping the material. In a solid electrolyte type fuel cell, it is preferred that a roundness of an air electrode supporting tube is 97% or more to decrease contact resistance when the cell is stacked. When the lateral sintering temperature is raised, the roundness is lowered so that it is difficult to use as an air electrode supporting tube for a solid electrolyte type fuel cell.
Prior art of a solid electrolytic film is explained. In SOFC, solid electrolyte thin films having permeability of oxygen ions (O
2−
) and impermeability of gas are required. These solid electrolyte thin films (ZrO
2
base, CeO
2
base, and such) are required to be thin and tight to achieve these characteristics.
In addition, they are required to be economically formed into large sized thin films. For the cell of SOFC for power generation, in general, a solid electrolytic film having a thickness of 30 to 2000 &mgr;m is formed on a porous substrate having a thickness of 0.3 to 5.0 mm. Further, over the solid electrolyte thin film, a fuel electrode (made of Ni base cermets, and such materials) is formed.
For SOFC cell, in order to obtain solid electrolyte thin films which are thin and tight, and at the same time, low in production cost and excellent in mass productivity as a goal, the following have been proposed in the past.
Production Method by CVD.EVD (Chemical Electrical vapor deposition) (Japanese Patent Publication Number Kokai Sho: 61-91880):
This production method is characterized in that the first electrode is adhered onto a porous support member, an intermediate layer substance with electrical conductivity and oxygen permeability is adhered onto the first electrode to protect the first electrode from a high temperature vapor of metal halides, and the intermediate layer substance is contacted with a high temperature vapor of metal halide to form a solid electrolyte composed of metal oxides on the whole surface of the intermediate layer.
Production Method by Plasma Spray Coatings (Japanese Patent Publication Number Kokai Sho: 61-198570):
This production method is characterized in that solid electrolyte starting materials comprising zirconium oxides and metal oxides of rare earth elements and the like are formed into a solid solution. Then, the
Aizawa Masanobu
Hiwatashi Ken-ichi
Nishiyama Haruo
Omoshiki Koji
Ueno Akira
Chaney Carol
Day Jones
Toto Ltd.
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