Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1986-01-31
1987-12-29
Niebling, John F.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
G01N 2758
Patent
active
047159448
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a gas sensor. More particularly, the present invention relates to a structure of a novel solid electrolyte type gas sensor for measuring the concentrations of various gas components such as CO.sub.2, Cl.sub.2, SO.sub.x, and NO.sub.x.
BACKGROUND ART
A solid electrolyte is a substance in which an electric current is caused to flow by migration of ions in the solid. If a solid electrolyte cell, in which a gas component to be detected, contained in the gas to be tested, is used as a reactant, is fabricated by using such a solid electrolyte, the concentration of the intended gas component can be known from the amplitude of the electromotive force of the cell or an electric current that can be taken out from the cell. This gas sensor is called "a solid electrolyte type gas sensor".
Various solid electrolyte type gas sensors differing in the structure have been proposed (see Mizusaki, Yamauchi and, Fueki, "Ideas of Solid Electrolyte Sensors", Electrical Chemistry and Industrial Physical Chemistry, Vol. 50, No. 1, pages 7-12, 1982, Yamauchi and Fueki, "Solid Electrolyte Gas Sensors", ibid, pages 46-53, and literature cited therein). In most conventional solid electrolyte type gas sensors, a reference electrode to be contacted with a standard gas should be disposed, and therefore, the structure is complicated and the size is inevitably large. On the other hand, solid electrolyte type gas sensors having a structure in which a standard gas is not necessary are defective in that a satisfactory stability cannot be obtained. Accordingly, only a stabilized zirconia O.sub.2 sensor is practically used at the present.
DISCLOSURE OF THE INVENTION
Under this background we made research and, as a result, found that if a part of the surface of a solid electrolyte is covered with a layer of a metal salt capable of forming a dissociative equilibrium with a gas component to be measured and the remaining part of the surface of the solid electrolyte is substantially completely sealed and covered with a gas-intercepting layer so as to prevent contact with the ambient atmosphere as much as possible, there can be obtained a solid electrolyte type gas sensor in which the structure is simplified, the size is drastically reduced, and the operation characteristics are sufficiently stable. We have completed the present invention based on this finding.
More specifically, in accordance with the present invention, there is provided a gas sensor comprising a solid electrolyte, a measurement electrode attached to a part of the surface of the solid electrolyte, a layer of a metal salt capable of forming a dissociative equilibrium with a gas component to be measured, which covers the surface of the measurement electrode and the measurement electrode-surrounding region of the surface of the solid electrolyte, a reference electrode attached to a part of the surface, not covered with the metal salt layer, of the solid electrolyte, a gas-intercepting layer covering the surface of the reference electrode and substantially all of the remaining surface, not covered with the metal salt layer, of the solid electrolyte, and lead lines for taking out potentials from the measurement electrode and the reference electrode.
This gas sensor is prominently characterized in that a standard gas is not necessary and the gas sensor has a sealed structure in which only the metal salt layer falls in contact with the measurement atmosphere such as the gas to be measured, apart from the gas-intercepting layer, and the solid electrolyte is completely isolated from the ambient atmosphere. The gas sensor of the present invention is decisively distinguishable over the conventional techniques in the above-mentioned characteristic feature.
The operation mechanism of the gas sensor of the present invention having the above-mentioned structure has not been completely elucidated, but in view of the fact that, as illustrated in the examples given hereinafter, the gas sensor of the present invention has a sufficient operation s
REFERENCES:
patent: 4207159 (1980-06-01), Kimura et al.
patent: 4296148 (1981-10-01), Friese
patent: 4462890 (1984-06-01), Torida et al.
patent: 4622105 (1986-11-01), Liu et al.
M. Gauthier and A. Chamberland, "J. Electrochem. Soc." 124 (1977) 1579.
Ogata Tadashi
Yanagida Hiroaki
Hsing Ben C.
Kabushiki Kaisha Advance Kaihatsu Kenkyujo
Niebling John F.
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