Measuring and testing – Gas analysis – Detector detail
Patent
1999-04-15
2000-08-22
Larkin, Daniel S.
Measuring and testing
Gas analysis
Detector detail
422 88, G01N 2700, G01N 2712
Patent
active
061054178
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to gas sensor materials.
BACKGROUND ARTS
A gas sensor responds to a specific gas contained in other gases such as air and produces an electric signal, a light signal and the like depending on the concentration of the specific gas. Currently, various gas sensors using a detection method wherein chemical properties such as adsorption, reaction, and light emission are often used to identify gas components have been known. As a conversion method into a signal, there is an energy-conversion method, for example using electromotive force, which directly obtains a sensing signal by contacting gases. However, an energy-control method which converts a change in device properties such as material properties, e.g., electrical resistance, transistor properties and the like, into a signal, is mainly used.
As typical materials for gas sensors, oxides having rather difficult reductiveness, such as SnO.sub.2 and ZnO types, are available. Among them, most current commercial devices use a porous sintered body of the SnO.sub.2 type, which is n type semiconductor. As semiconductor gas sensors which use such an oxide semiconductor, there are surface control types in which interactive reaction with a gas stays on the surface and bulk control types in which the reaction extends to a semiconductor itself. Among them, most are the surface control type like sensors of combustible gases- In such surface control type sensors, a chemical reaction occurs on a semiconductor surface. However, the activity is often not enough with a pure semiconductor. Therefore, the sensing function is improved by dispersing powder of a noble metal, a metal oxide and the like on the semiconductor particles.
However, to detect a gas by using these conventional gas sensors, it is required to heat the gas up to a temperature on the order of 200.degree. C. to 300.degree. C. Moreover, with those sensors there is insufficient selectivity of gas species because of difficulty in specifying gas species since these conventional gas sensors may respond to many species of gases. Therefore, further improvement is desired.
The main object of the present invention is to provide sensor materials which are able to sense gases at room temperature, and which also are superior in selectivity of the gases sensed.
DISCLOSURE OF THE INVENTION
As a result of a series of research efforts related to the above object, the inventors found that a carbon mixture containing fullerenes obtained by a carbon electrode arc method shows peculiar properties of adsorbing a polar gas and not adsorbing a nonpolar gas at room temperature, has larger surface area and electric conductivity so as to be electrically measured because it is composed of carbon grains. Based on these findings, the inventors evaluated the usefulness of the carbon mixture as a gas sensor material and found that the mixture can sense a gas at a room temperature and is superior in gas selectivity. Further, such a carbon mixture that contains metal obtained by arc discharge, wherein a carbon electrode arranged so as to contain a metal component is used, is improved in sensing ability of gases and has good selectivity, resulting in the present invention.
Namely, the present invention relates to providing the following gas sensor materials: matter by arc discharge which occurs by passing an alternating current or a direct current with electric current density 0.8 to 3.5 A/mm.sup.2 on discharge surfaces of carbon electrodes in an inert gas under a pressure of 0.1 to 600 torr. obtained as evaporated matter by arc discharge which occurs by passing an alternating current or a direct current with electric current density of 0.8 to 3.5 A/mm.sup.2 on discharge surfaces of carbon electrodes containing metal at 0.01 to 30% by weight in an inert gas under a pressure of 0.1 to 600 torr.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view illustrating an arc discharge apparatus used in EXAMPLE 1;
FIG. 2 is a graph showing test results for sensing an ammonia gas using the c
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Kawabata Shunsaku
Kiyama Hiromi
Mori Kiyohiro
Natsukawa Kazuki
Nishida Katsumi
Daido Hoxan Inc.
Larkin Daniel S.
Osaka Prefecture
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