Metal working – Method of mechanical manufacture – Electrical device making
Patent
1996-02-20
1998-09-08
Bell, Bruce F.
Metal working
Method of mechanical manufacture
Electrical device making
296231, H01M 600
Patent
active
058039341
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This is a 371 of PCT/DK94/00304 filed on Aug. 08, 1994.
The present invention relates to a method of producing an electrode layer on, for instance, a solid electrolyte of a solid state fuel cell, where the electrode material is of the type La.sub.x Ca.sub.y CrO.sub.3, and X+Y.gtoreq.1 and Y>0, the electrode material being subjected to a sintering.
2. Description of the Related Art
The sintering must be as efficient as possible. In addition, it must be possible to carry out cosintering with other materials, such as YSZ. The sinterings were originally carried out at relatively high temperatures. It was discovered that it was possible to lower the temperature by adding La and Ca in excess to the composition, whereby the fluid and spreading characteristics of an intrinsic wet phase and consequently the densification are improved. However, the resulting stability may be deteriorated, and the excess ingredients may react with the adjacent materials which presents a drawback for instance in connection with SOFC (Solid oxide fuel cell) cells.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method of producing all electrode material with improved sintering properties, the risk of reactions with the adjacent materials simultaneously being reduced or eliminated.
The method according to the invention is characterised by adding a few mol %, preferably 1 10 mol %, of vanadium to the electrode material, whereby the resulting densities turned out to be considerably improved. A cosintering with YSZ indicates that it is possible to cosiniter with YSZ without involving reactions with YSZ.
According to the invention it is particularly advantageous to add 1 to 2 mol % of vanadium, whereby the density can be increased to 96%.
The method according to the invention may for instance be used for producing a heat resistance.
As an alternative, the method according to the invention can be used for producing a sensor electrode, such as an oxygen sensor electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a photograph of an unpolished surface of a material according to the present invention;
FIG. 2 is a photograph of a magnified view of the material in FIG. 1;
FIG. 3a is a photograph of a magnified view of LCC65 particles;
FIG. 3b is a photograph of a magnified view of the material of FIG. 3a after coating and calcination;
FIG. 4 is a photograph of an unpolished surface of a material according to the present invention;
FIG. 5 is a graph of an x-ray diffraction pattern of a material according to the present invention;
FIG. 6 is a series of graphs of a high temperature x-ray diffraction pattern of the material of the invention; and
FIG. 7 is a series of graphs of a high temperature x-ray diffraction study for another material according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A ceramic La.sub.x Ca.sub.y CrO.sub.3 can be used as an electric conductor at high temperatures. The electrical conductivity thereof at 1,000.degree. C. is 5 to 50 S/cm at an oxygen partial pressure P.sub.02 of 10.sup.-18 to 1 atm. This material can be used as a heating unit in an oven, as connectors and anodes in SOFC, and as electrodes for zirconia-based O.sub.2 sensors.
One of the greatest challenges of using La.sub.x Ca.sub.y CrO.sub.3 is to sinter in air at moderate temperatures of less than 1,500.degree. C. Chromium oxides (CrO.sub..delta., where .delta.=2 to 3) volatilize from La.sub.x Ca.sub.y CrO.sub.3 and result in concentrating particle coarsening mechanisms. Alkaline earth doped LaCrO.sub.3 was originally sintered at 1,700.degree. C. in a reducing atmosphere (P.sub.02 =10.sup.-11 atm) to lower the vapour pressure of CrO.sub..delta.. This method provided densities of more than 95% of the theoretically possible densities.
Later it was found that such densities could be achieved in air at 1,300.degree. to 1,500.degree. C. by synthesizing La.sub.x Ca.sub.y CrO.sub.3 with y.gtoreq.0.25 and x+y>1 or by creating an excess of A sites, reference
Bell Bruce F.
Forskningscenter RIS.O slashed.
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