Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1996-02-12
1998-05-26
Tung, T.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204421, 204426, 204427, 205784, G01N 27407
Patent
active
057559406
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a lithium ionic conducting glass thin film and a carbon dioxide sensor comprising the lithium ionic conducting glass thin film. This carbon dioxide sensor is compact, of the power saving type and inexpensive and can measure the concentration of carbon dioxide in the air.
BACKGROUND ART
The conventional carbon dioxide sensor of the solid electrolyte type comprises a sort of battery in which a noble metal electrode and a metal carbonate capable of creating a dissociation equilibrium with carbon dioxide are arranged on one side of a bulky solid electrolyte composed of a sintered ceramic body capable of conducting alkali ions such as Na+ and Li+ while a noble metal electrode is disposed on the opposite side of the bulky solid electrolyte and in which, when carbon dioxide contacts the metal carbonate, an electromotive force depending on the concentration of carbon dioxide is generated between the two electrodes. This electromotive force satisfies the following Nernst formula: temperature, n is the number of kinetic electrons, F is the Faraday constant and P.sub.CO2 is a partial pressure of carbon dioxide. That is, the above carbon dioxide sensor enables determining the concentration of carbon dioxide by measuring the electromotive force.
It has been reported that, when the reference electrode of the conventional carbon dioxide sensor of the solid electrolyte type is composed of an oxygen ionic. conductor and a noble metal electrode, the whole body of the carbon dioxide sensor can be inserted in a subject gas in the measurement of carbon dioxide concentration (Nobuhito IMANAKA et al, Denki Kagaku, 61, 909 (1993)).
The carbon dioxide sensor of the solid electrolyte type detects the concentration of carbon dioxide by an electrode reaction effected between the metal carbonate disposed on one side of the solid electrolyte layer and carbon dioxide, so that the metal carbonate side is left open to the subject atmosphere while the opposite side is left open to the reference concentration atmosphere (generally, the air) in the measurement of carbon dioxide concentration. Therefore, the solid electrolyte for use therein is required to have a dense structure which completely shuts off both the atmospheres.
However, the conventionally proposed carbon dioxide sensor of the solid electrolyte type is in the form of a pellet having a thickness ranging from several millimeters to several centimeters and a size ranging from several millimeters square to several centimeters square and prepared by the process such as the melt solidification process or the sintering process. The sintered ceramic body having been employed as the solid electrolyte has a porous structure, so that it occurs that carbon dioxide permeates the sintered ceramic body to thereby cause sensor output variation, i.e., noise. This is the cause of error found in carbon dioxide concentration measurements.
The internal resistance of the carbon dioxide sensor is in direct proportion to the thickness of the employed solid electrolyte. In the use of the bulky solid electrolyte, the large thickness thereof leads to an extremely large internal resistance, so that the electromotive force of the carbon dioxide sensor is lowered to thereby disenable accurate measurement of the carbon dioxide concentration. Thus, for lowering the internal resistance, the carbon dioxide sensor must be used at high temperatures such that the ion conductivity is high and the internal resistance is reduced, so that the operating temperature of the carbon dioxide sensor is generally as very high as about 350.degree. to 600.degree. C. The carbon dioxide sensor must be provided with a heater in the vicinity thereof for achieving the practical use of the carbon dioxide sensor. The heater for use therein must have a large capacity, so that the problem is encountered that the whole body of the carbon dioxide sensor inevitably has a large volume.
Although a thin film of solid electrolyte is especially desired for miniaturizing the whole body of the
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Mitsui Petrochemical Industries Ltd.
Tung T.
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