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Non Fire Yet But The Sensors Snap Into Action

December 06, 2004

Russian researchers offer a fundamentally new approach to the development of gas sensors for fire-prevention detecting devices. In contrast to already known ones, these sensors allow to detect unerringly fire occurrence at its earliest stage. However, this is not a single advantage of the innovation or a sole field of application.

Moscow scientists - specialists of the Institute of Molecular Physics (Russian Research Center) "Kurchatov Institute" have managed to teach fire-prevention detecting devices to promptly and precisely catch the carbon monoxide occurrence in the air. The new device would not be deceived either by cigarette smoke, or by stange scents which sometimes make traditional fire alarm systems snap into action. No device in the world is equal to the new one in terms of sensitivity and selectivity.

Alexey Vasiliev, senior staff scientist, manager of work (Kurchatov Institute), narrated about new sensors at the international "Chemical sensors" conference, which took place in July in a Japanese "town of science" - Tsukuba - located not far from Tokyo.

The appearance of the sensors, the first experimental specimens of which were demonstrated by A.A. Vasiliev to all comers, had been preceded by extensive experimental and theoretical work. The authors suggested an absolutely new approach to development of sensors, the approach relating both to the sensors' sensitive layer composition and their operating mode.

The point is that although the carbon oxide (CO - carbon monoxide) gas sensors have been known for quite a long time, their operation is not at all irreproachable. Principle of their operation is conventionally as follows: a layer of metal oxide, for example of tin or zinc, is the sensor. The determinate gas is sorbed on the oxide layer. Along with that, electroconductivity of the layer changes - it increases. That is the analytical response - the higher the conductivity of the sensitive layer gets, the higher the concentration of the sought gas is.

To increase the CO sensors selectivity, a catalyst - usually palladium - is introduced in the sensitive layer composition. When heated, the catalyst turns carbon monoxide into carbonic acid gas. This process, in its turn, affects the layer conductivity - therefore, these sensors are more sensitive, than the ones based simply on adsorption process.

The problem is that such sensors are easy to "deceive" - their readings are influenced by other gases as well, first of all by steam. And atmospheric humidity is known to be highly inconstant. That is why the fire safety systems are equipped with simplier sensors which are less sensitive but they snap into action "for sure" - when the room is already full of smoke or it is on fire, and the temperature exceeds all conceivable norms.

As for the sensors developed by the Moscow researchers, they would not be deceived either by steam or by any other gases, which impact the traditional sensors' readings. The sensitive layer based on tin oxide with addition of palladium and platinum (the latter accelerates the process of carbon monoxide oxidation through to carbonic acid gas) allows to perform this process most efficiently.

The temperature condition suggested by the developers provides for two more invaluable advantages. Firstly, the sensor response increases particularly at the CO concentration being close to the maximum permissible concentration. Secondly, the researchers managed to select the temperature of operation in such a way that other gases on the catalyst simply do not have time to oxidize. Therefore, neither steam, nor hydrogen, nor methane or other carbohydrates "misleading" traditional sensors do affect the new sensors' readings.

"Such sensors allow to detect occurrence of track concentrations of carbon monoxide at the initial stage of ignition, long before the fire appears as such, says Alexey Vasiliev. However, this is not their sole application. Sensors based on them may be used to identify the carbon monoxide concentration in motor exhausts."

Informnauka (Informscience) Agency