Coating processes – Immersion or partial immersion – Inorganic base
Patent
1995-03-01
1996-11-19
Tung, T.
Coating processes
Immersion or partial immersion
Inorganic base
204424, 264 56, 427123, 427125, 4271263, 427226, 4273722, 4273831, 4273833, 427404, 4274192, G01N 2712, G01N 2726
Patent
active
055760678
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a carbon monoxide (CO) detecting sensor for detecting the existence and absence of carbon monoxide, and a manufacturing process therefor.
BACKGROUND OF THE INVENTION
Generally, a steel manufacturing plant generates gases which are harmful to the human body, and among these gases, CO gas is a dangerous one which can give a fatal inflict to the human body even at a concentration of less than 2000 ppm.
Conventionally there have been developed various CO gas detecting sensors for detecting the existence and absence of CO gas, but the SnO.sub.2 series CO gas detecting sensor which is currently used operates in the following manner. That is, an oxygen ion (O.sup.-) which has been adhered on the surface of the gas is desorbed by being reacted with a reactive gas, and therefore, the electron which has been captured by the oxygen ion is converted to a free electron, with the result that the conductivity of the gas is increased. This conductivity is measured, and the existence of CO gas is determined. However, this CO gas detecting sensor has a disadvantage that it is reacted with even hydrogen gas or propane gas (Japanese Chemical Journal 1987, No. 3, p447-488).
Meanwhile, recently, there has been developed another CO gas detecting sensor in which a p type semiconductor (CuO) and an n type semiconductor (ZnO) are physically contacted. According to Japanese Patent Laid-open No. Sho-62-90529, the CO gas detecting sensor has the advantage that it has the selectivity of reacting only with CO gas. However, it consists of two different semiconductors contacted together, and the two semiconductors are separated after the measurement. Therefore, when CO gas is to be measured again, a perfect contact realization of the two semiconductors are very low, with the result that the sensitivity for the measurement of CO gas is apt to be varied.
SUMMARY OF THE INVENTION
The present invention is intended to overcome the above described disadvantages of the conventional techniques.
Therefore it is the object of the present invention to provide a CO gas detecting sensor and a manufacturing process therefor, in which the CO gas preference is greatly improved compared with the conventional SnO.sub.2 series CO gas detecting sensor, and the measurement repeatability is greatly improved compared with the conventional p-n combination type CO gas detecting sensor.
In achieving the above object, the CO gas detecting sensor according to the present invention includes: a sintered zinc oxide (ZnO) body; a copper oxide (CuO) coating layer formed on a side of the sintered zinc oxide body; a positive metal electrode layer electrically connected to the copper oxide coating layer; and a negative metal electrode layer formed on the other side of the sintered zinc oxide body.
In achieving the above object, the process for manufacturing the CO gas detecting sensor according to the present invention comprises the steps of: press-forming a zinc oxide powder in the usual manner, and sintering it at 650-1000.degree. C. for 30 minutes to 3 hours; dipping a portion of the sintered zinc oxide body into an aqueous copper nitrate (Cu(NO.sub.3).sub.3 H.sub.2 O) solution to form a composite semiconductor; heat-treating the composite semiconductor for converting the copper nitrate of the composite semiconductor into copper oxide so as to form a thin copper oxide layer; spreading a metal on the copper oxide layer and on the portion of the sintered zinc oxide body where no copper oxide layer is formed, so as to form positive and negative electrodes; and heat-treating the positive and negative electrodes.
BRIEF DESCRIPTION OF THE DRAWINGS
The above object and other advantages of the present invention will become more apparent by describing in detail the preferred embodiment of the present invention with reference to the attached drawings in which:
FIG. 1A and 1B are respectively a perspective view and a sectional view showing the schematic constitution of the CO gas detecting sensor according to the pre
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Y. Nakamura, H. Yoshioka, M. Miyayama, H. Yanagida, T. Tsurutani and Y. Nakamura, "Selective CO Gas Sensing Mechanism with CuO/ZnO Heterocontact", J. Electrochem. Soc., vol. 137, No. 3, Mar. 1990, pp. 940-943.
Y. Nakamura, T. Tsurutani, M. Miyayama, O. Okada, K. Koumoto and H. Yanagida, "The Detection of Carbon Monoxide by the Oxide-Semiconductor Hetero-Contacts", The Chemical Society of Japan, 1987, month unavailable No. 3, pp. 477-483.
Miyayama Masaru
Shin Byoung C.
Pohang Iron & Steel Co. Ltd.
Research Institute of Industrial Science & Technology
Tung T.
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