Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1997-12-19
2001-07-03
Tung, T. (Department: 1743)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S425000, C204S426000, C204S427000, C205S784500
Reexamination Certificate
active
06254749
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a CO gas sensor for measuring a concentration of carbon monoxide (CO) gas contained in air or an exhaust gas from a combustion engine or the like and a CO gas concentration measuring apparatus using said CO gas sensor, and more particularly to a CO gas sensor that is operatable at a high temperature of 600 to 900° C. with reducing an adverse affect of coexistence oxygen (O
2
) to a CO gas measurement value, and a CO gas concentration measuring apparatus using said CO gas sensor.
2. Related Art Statement
There are many poisoning and fatal accidents caused by CO gas generated by an incomplete combustion in an apparatus for burning fossil fuel, i.e., heater equipment such as a petroleum stove, a petroleum or oil fan heater, a gas heater or a hot water supplying equipment for heating water. This is because the human being can not notice the generation of the CO gas since CO gas has no color and no smell. Also, in a room or the like in which the above-described equipment is installed, since CO gas is a gas having substantially the same molecular weight as that of air, CO gas is diffused uniformly in the air. As a result, the human being unconsciously inspires CO gas, so that the inspired CO gas is combined directly with hemoglobin in the blood. In this case, he or she can not continue the inspiration of oxygen to cause a suffocation.
On the other hand, as described above, CO gas is a harmful gas to the human body but is useful in the industrial field. For example, methanol is synthesized from hydrogen (H
2
) gas and CO gas and used as material for various chemical products.
It is desired to reduce the concentration of CO gas discharged from an internal combustion engine or a combustion furnace for reasons of various regulations on the components in exhaust gas and a more effective use of fossil energy resources which are derived from recent environmental problems. For this reason, the composition of an exhaust gas is analyzed so as to optimize the combustion efficiency and the operation conditions by, for example, feeding back and processing the exhuast gas. Also, the on-site tests and researches of a power generating system using a fuel cell having a higher energy conversion efficiency than that of a conventional power generating system using a turbine have steadily progressed. In such a fuel cell, a mixture gas of CO gas and hydrogen (H
2
) gas produced by reacting water steam under the presence of catalyst or a commercial gas mainly composed of methane (CH
4
) is used as fuel.
As described above, a variety of combustion equipments requires installation of sensors for measuring a concentration and detecting the generation of CO gas. Also, the maintenance and investigation of these combustion equipments requires portable CO gas concentration measurement devices. Also, in a chemical plant or a combustion engine or the like, it is preferable to always monitor a CO gas concentration for controlling suitably the CO gas concentration.
Main kinds of such CO gas sensors are classified into a semiconductor type, a catalyst combustion type, a solid electrolyte type and a thermal transfer type. Among those, the solid electrolyte type CO gas sensor is based upon the measurement principle, i.e., the electromotive force measurement for a rich/lean cell, is composed of a metal electrode and a stabilized zirconia having an oxygen ion transfer property, and is superior in heat resistance, shock resistance and poisoning resistance.
However, since the CO gas sensor using the stabilized zirconia is also an oxygen sensor, it is difficult to selectively measure a CO gas concentration in a gas in which oxygen coexists. Also, in a sensor using a platinum electrode which is used in general, the oxidation of CO gas is rapid on the platinum electrode surface at such a high temperature of 600 to 900° C.
Therefore, it is difficult to distinguish the measurement results attributed to oxygen and CO gases, in the case where oxygen is contained in a gas to be measured respectively.
SUMMARY OF THE INVENTION
In view of the foregoing defects, an object of the present invention is to provide a CO gas sensor for suitably measuring a concentration of CO gas contained in a gas containing oxygen, and a CO gas concentration measuring device using the CO gas sensor. Namely, according to the present invention, there are provided a carbon monoxide gas sensor having a solid electrolyte having an oxygen ion transfer property, and carbon monoxide gas measurement sensing and reference electrodes electrically connected to at least part of the surface of the solid electrolyte, characterized in that gold or gold alloy is used in the sensing electrode and an apparatus for measuring the concentration of CO gas equipped with said gas sensor.
Also, according to the present invention, there is provided a carbon monoxide gas sensor comprising: a solid electrolyte having an oxygen ion transfer property; carbon monoxide gas measurement sensing and reference electrodes electrically connected to at least part of the surface of the solid electrolyte; and oxygen measurement sensing and/or reference electrodes; wherein gold or gold alloy is used in the carbon monoxide gas measurement sensing electrode. Also, a carbon monoxide gas concentration measuring apparatus equipped with said gas sensor is provided.
Thus, by the CO gas sensor according to the present invention, in the case where the concentration of CO gas in the air or an exhaust gas emitted from the combustion engine is to be measured, Au or Au alloy that has a lower catalyst property than that of Pt having conventionally been used is used in the sensing electrode for measurement of CO gas, whereby it is possible to enhance the selectivity of CO gas. Also, CO gas measurement value is compensated by an oxygen measurement value by using an oxygen sensor, whereby it is possible to enhance the CO gas measurement precision. Furthermore, it is advantageous that the adverse affect of the oxygen concentration to the CO gas concentration measurement value can be extremely suppressed by using jointly an oxygen pump. In addition, in all of the embodiments of the CO gas sensors according to the present invention, it is possible to enhance the sensitivity to CO gas in the CO gas sensing electrode by causing the constant current to flow between the CO gas measurement electrodes or keeping the constant voltage therebetween. In general, it is possible to considerably enhance the measurement precision of the CO gas sensors. The surface of a solid electrolyte to be connected to a sensing electrode is chemically etched to be roughed or a fine particle layer made of Au or Au alloy is formed between a solid electrolyte and a electrode film so as to increase the area of a contact interface among a gas phase, a metal electrode and a solid electrolyte to thereby further enhance the CO gas detecting sensitivity. Furthermore, the sensor operates at such a high temperature of 600 to 900° C. and it is advantageous that an error by the other interference gases included in the measurement gas can be reduced. Also, a high temperature pre-treatment portion, i.e., a heater is provided for preheating a gas to be measured so as to obviate the adverse affect caused by NO or SO
2
, thereby a further enhance in the precision of the carbon monoxide concentration can be achieved.
REFERENCES:
patent: 3843400 (1974-10-01), Radford et al.
patent: 4190499 (1980-02-01), Pebler
patent: 4225634 (1980-09-01), Tanaka et al.
patent: 4264425 (1981-04-01), Kimura et al.
patent: 4502939 (1985-03-01), Holfelder et al.
patent: 4626337 (1986-12-01), Hotta et al.
patent: 4828673 (1989-05-01), Maeda
patent: 5366611 (1994-11-01), Ioannou et al.
patent: 5397442 (1995-03-01), Wachsman
patent: 5472580 (1995-12-01), Kennard et al.
patent: 5672811 (1997-09-01), Kato et al.
patent: 5716507 (1998-02-01), Tanaka et al.
patent: 5736028 (1998-04-01), Hjortsberg et al.
patent: 0 468 249 (1992-01-01), None
patent: 4-14302 (1992-03-01), None
patent: 4-208849 (1992-07-
Mizusaki Junichiro
Murase Takao
Yokota Minoru
NGK Insulators Ltd.
Parkhurst & Wendel L.L.P.
Tung T.
LandOfFree
Carbon monoxide gas sensor and measuring device using the... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Carbon monoxide gas sensor and measuring device using the..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Carbon monoxide gas sensor and measuring device using the... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2460385