Production of a sensor for carbon monoxide or water vapor includ

Measuring and testing – Gas analysis – With compensation detail

Patent

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

73 2331, 73 3105, 73 3106, 422 88, 422 94, 422 98, 334 34, G01N 2712

Patent

active

056294743

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a sensor for gases and vapours. For example, it may be used to detect carbon monoxide or water vapour. For convenience the invention will be described below with particular reference to the detection of carbon monoxide but it will be appreciated that its scope is not to be restricted thereto.
Detection of carbon monoxide is necessary in a number of different circumstances. For example, carbon monoxide is emitted when a fire starts to smoulder and can cause death before the fire begins to take hold. Most smoke detectors commercially available are based on one of two principles: diode;
In both cases a considerable quantity of smoke is needed before the alarm is triggered and in neither case is there detection of the early emission of carbon monoxide.


BACKGROUND OF THE INVENTION

Sensors for carbon monoxide have been previously proposed and one well known type is based on the; use of a metallic oxide semiconductor, usually tin oxide SnO.sub.2. The basic principle of their operation is the fact that the resistance of a layer of metallic oxide semiconductor changes in the presence of reactants such as organic vapours, carbon monoxide and even water vapour.
U.S. Pat. No. 4,453,151 discloses a sensor for detecting H.sub.2 S which is made from a mixture comprising metal oxides, activators, dopants and binders and which includes a molecular sieve material, e.g. a zeolite, to provide porosity in the product on a molecular scale.
However, previously proposed tin oxide sensors have not been entirely successful in that they have suffered from problems such as lack of sensitivity to very small amounts of the specific gases to be detected, over-sensitivity to surrounding conditions, e.g. humidity, and lack of specificity in operation. They are too readily poisoned by other extraneous gases and have a slow recovery time after an initial detection. The present invention, therefore, aims to provide an improved sensor of increased selectivity that can be used particularly for the detection of carbon monoxide emissions and that, unlike most previous sensors, can also be operated at room temperature.
Accordingly, the invention provides a sensor to detect emissions of gas or vapour, which comprises a substrate having a layer of a composition comprising a semiconductor metallic oxide, a catalyst and a rheological agent to induce porosity into the surface of the layer, the semiconductor metallic oxide being indium oxide or tannic oxide and the catalyst is present in the composition in an amount of from 3 to 30% by weight.
The invention also provides a method of making a sensor.
The substrate, which should be a good electrical insulator, may be, for example, a sheet of glass or ceramic material. A film of the sensor composition from 100 nanometres 1 mm thick is preferably formed on the substrate by applying a paste of the oxide, catalyst and rheological agent in water to the substrate and annealing at a temperature of e.g. from 500.degree. C. to 1000.degree. C. to form a hardened layer.
The proportions of the ingredients of the covering layer composition may be, for example, 3 to 30% catalyst by weight, 5 to 20% by weight theological agent, if desired additives (well known per se) to change the electrical conductivity of the layer, e.g. in an amount of from 0.5-5% by weight; and the balance stannic oxide or indium oxide.
The catalyst is chosen to give specificity of the sensitivity of the sensor to the gas, e.g. carbon monoxide, to be detected. It is preferably platinum, particularly in the form of platinum black, i.e. finely divided platinum, but other catalysts, e.g. palladium, rhodimn, ruthenium, osmium and irridium may be used.
The rheological aid may be chosen from, for example, kieselguhr and sepiolite. It is preferable to use Kieselguhr, (or diatomaceous earth), which is a mass of hydrated silica. It provides an improved open-pore structure surface for the sensing area of the: sensor and increases the available surface area for reaction with the gas to be detected.
To prep

REFERENCES:
patent: 3901067 (1975-08-01), Boardman, Jr. et al.
patent: 3933431 (1976-01-01), Trujillo et al.
patent: 4000089 (1976-12-01), Senda
patent: 4347732 (1982-09-01), Leary
patent: 4388272 (1983-06-01), Gesteland
patent: 4453151 (1984-06-01), Leary et al.
patent: 4457161 (1984-07-01), Iwanaga et al.
patent: 4575141 (1986-03-01), Burns
patent: 4601914 (1986-07-01), Barnes et al.
patent: 4703646 (1987-11-01), Muller et al.
patent: 4786476 (1988-11-01), Munakata et al.
patent: 4958514 (1990-09-01), Takami et al.
patent: 5086286 (1992-02-01), Yasukawa et al.
patent: 5296196 (1994-03-01), Takeshima
Techniques and Mechanisms in Gas Sensing 1991"Pattern Recognition in Gas Sensing", Gardner et al, pp. 347-379.
Solid Gas Sensors 1987, "Conduction and Gas Response of Semi-Conductor Gas Sensors", Williams, pp. 71-123.
Solid State Gase Sensors 1987, "The Role of Precious Metal Catalysts", Norris, pp. 124-138.
J. Chem. Soc., Faraday Trans. 1, 1987, "Tin Dioxide Gas Sensors", McAleer et al, pp. 1323-1346.
J. Chem. Soc., Faraday Trans. 1, 1988, "Tin Dioxide Gas Sensors", McAleer et al., pp. 441-457.
Electronics Ceramics: Properties, Devices and Applications, 1988, "Thick Film Technology", Cote et al, pp. 307 & 311.
Proc. Intl. Meeting on Chemical Sensors, 1983, "Sintered SnO.sub.2 Sensor for Methane", et al, pp. 57-59.
Sensors and Actuators 1985, "Effect of CH.sub.4, SO.sub.2 and NO on the CO . . . ", Romppainen et al, pp. 271-279.
Fire Safety Journal 1991 "The Use of Low Power Carbon Monoxide . . . ", Harwood et al, p. 431.
Proc. Intl. Meeting on Chemical Sensors, 1983, "Sensitivity and Sintering Temperature of SnO.sub.2 Gas Sensor," Murakami et al., pp. 18-23.

LandOfFree

Say what you really think

Search LandOfFree.com for the USA inventors and patents. Rate them and share your experience with other people.

Rating

Production of a sensor for carbon monoxide or water vapor includ does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Production of a sensor for carbon monoxide or water vapor includ, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Production of a sensor for carbon monoxide or water vapor includ will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFUS-PAI-O-1386899

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.