Measuring and testing – Gas analysis – Detector detail
Reexamination Certificate
1999-03-11
2001-11-06
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Gas analysis
Detector detail
C422S088000
Reexamination Certificate
active
06311545
ABSTRACT:
BACKGROUND OF THE INVENTION
1 Field of the Invention
The present invention relates to an anhydrous zinc antimonate semiconductor gas sensor for detecting various reducing gases such as hydrogen sulfide, and to a method for producing the same.
2. Description of the Related Art
SnO
2
sintered bodies and thin films have been widely put to practical use as a detecting portion of a sensor for various reducing gases, such as hydrogen sulfide, hydrogen, and fuel gases (city gas, propane gas, etc). Japanese Patent Application Laid-open No. Hei 1-189553 describes a thin film sensor having SnO
2
and an oxygen activating adsorption catalyst made of a metal, such as Pd, Ru, or the like, simultaneously deposited thereon by sputtering can detect hydrogen gas, methane gas, and the like. In particular, with regard to hydrogen sulfide, JOURNAL OF MATERIALS SCIENCE LETTERS, vol. 14, p. 1391 (1995) describes an SnO
2
thin film sensor obtained by heat treatment at 700° C. after spin coating an SnO
2
sol; and Jpn. J. Appl. Phys., vol. 34, p. L455 (1995) discloses a thin film sensor comprising an SnO
2
thin film obtained by heat treatment at 600° C. after spin coating an SnO
2
sol, having carried thereon copper oxide. JOURNAL OF MATERIALS CHEMISTRY, vol. 4, p. 1259 (1994) describes that a sintered sensor comprising an SnO
2
sintered body having carried thereon copper oxide shows high sensitivity and high selectivity to H
2
S due to its specific high reactivity.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a thin film sensor for detecting hydrogen sulfide at high sensitivity.
As a result of intensive investigation, it has now been found that the above-described object of the present invention can be attained by use of an anhydrous zinc antimonate semiconductor in a detecting portion of a sensor. More particularly, the present invention is to provide a thin film sensor which can detect a gas, for example, hydrogen sulfide at high sensitivity and a method for producing the same, by mixing a zinc compound with colloidal antimony oxide in a ZnO/Sb
2
O
5
molar ratio of 0.8 to 1.2, coating, for example, dip coating, the resulting electroconductive anhydrous zinc antimonate sol obtained by calcining and grinding the mixture on a substrate of a device, and heating it.
Accordingly, the present invention provides a sensor for detecting a gas, comprising a gas detecting portion comprising an anhydrous zinc antimonate semiconductor
Here, the gas is preferably hydrogen sulfide.
Also, the present invention provides a method for producing the above-described sensor for detecting a gas, comprising the steps of:
mixing a zinc compound with colloidal antimony oxide in a ZnO/Sb
2
O
5
molar ratio of 0.8 to 1.2;
calcining the mixture at 300 to 680° C.;
grinding the calcined mixture to form electroconductive anhydrous zinc antimonate powder;
preparing a sol of the electroconductive anhydrous zinc antimonate;
coating the electroconductive anhydrous zinc antimonate sol on a substrate of a device; and
heating the substrate at the temperature above 680° C. but lower than 1,000° C.
The present invention provides a sensor for hydrogen sulfide gas having used anhydrous zinc antimonate semiconductor in a gas detecting portion thereof and a method for producing the same In particular, the anhydrous zinc antimonate semiconductor of the present invention has a sensitivity at least equivalent to that of SnO
2
sintered bodies and SnO
2
thin films fabricated by sputtering widely put in practical use, and can detect hydrogen sulfide at high sensitivity, even at a hydrogen sulfide concentration of 0.01 ppm. There is no other material that can detect to such a low level of hydrogen sulfide. Therefore, it is useful as a high performance gas sensor for malodorous gas. Further, the present invention enables fabrication of a high performance thin film gas sensor by a coating method, and therefore is low in cost as compared with the production method by deposition.
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Takahata, “Tin Dioxide Sensors—Development and Applications”, pp. 39-55.*
Chemical Abstracts, vol. 9, No. 10, Sep. 7, 1998 (1998-09-07), Columbus, Ohio, US; Y. Yamada et al.:Sensing properties to dilute hydrogen sulfide of zinc antimonate thick film sensor prepared from sol solution, p. 1334; col. r; XP002124214, *abstract*. & Chem Sens., vol. 14, 1998, pp. 1-4.
Y. Anno et al.,Zinc-oxide based semiconductor sensors for detecting acetone and capronaldehyde in the vapour of consommé soup, Sensors and Actuators B: Chemical, vol. B25, No. 1/3, Apr. 1995 (1995-04), pp. 623-627, XPOOO532848, ISSN 0925-4005, *Section 2. Experimental procedure*.
N. Jayadev Dayan et al., Effect of film thickness and curing temperature on the sensitivity of ZnO: Sb thick-film hydrogen sensor, Journal Of Materials Science: Materials In Electronics, vol. 8, No. 5, 1997, pp. 277-279, XP000730340, ISSN 0957-4522.
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Maekawa, Tomoki et al., “Improvement of Copper Oxide-Tin Oxide Sensor for Dilute Hydrogen Sulfide”, J. Matter. Chem., 1994, vol. 4, pp. 1259-1262.
Yoo, Do Joon et al., “Copper Oxide-Loaded Tin Dioxide Thin Film for Detection of Dilute Hydrogen Sulfide,” Jpn. J. Appl. Phys. , vol. 34, (1995), pp. L 455-L 457.
Yoo, D. J. Et al., “H2S sensing characteristics of SnO2thin film prepared from SnO2sol by spin coating” Journal of Materials Science Letters, vol. 14 (1995), pp. 1391-1393.
Ota Isao
Sakata Hideo
Tamaki Jun
Larkin Daniel S.
Nissan Chemical Industries Ltd.
Oliff & Berridg,e PLC
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