NAGPUR, May 27: Two city physicists have developed indigenous solid state gas sensors, first of their kind in the country, to detect the concentration of carbon and sulphur oxide pollutants in air.

These sensors, developed under a project granted by the Union ministry of forests and environment, uses sulphate and carbonate based solid electrolytes and appropriate silver and lithium based reference electrodes, which were also synthesised by these scientists. The project has been completed successfully and the sensors have since been patented.

Dr Ms Kamal Singh, professor and head, Department of Physics, Amravati University and principal investigator of the project, told The Indian Express that these sensors will be quite cheap as compared to similar imported sensors and would be even better than the few sensors developed elsewhere in the world, due to their improved performance. She said that the sensor will cost Rs 6,000 approximately while the imported sensors cost somewhere around Rs 80,000.

Singh said that pollution of air by oxides of sulphur and carbon is widespread since they come out during coal combustion or whenever any fossil fuels are burnt. Some specific industrial processes also produce mainly sulphur oxides as pollutants in large quantities. These gases, mainly sulphur oxides, although are not detectable in the normal atmosphere, as it is present in low quantity, due to its continuous presence in the atmosphere, manifests itself by corroding stonework and metalwork, it can damage plant tissues and aggravates illnesses like bronchitis.

It is also identified as a principal source for acid-rain. Since the presence of these gases in the atmosphere is harmful both from the health and economy point of view, a knowledge of their concentration in atmosphere becomes very important. Thus the use of gas sensors for pollution assessment and industrial process control, becomes imperative.

Gas sensing methods such as volumetric methods and electrochemical gas sensors have become redundant, as the former is time consuming, expensive and requires expert manpower and the later posed severe corrosion problems.

Singh said that the detection of gases using solid state electrolytes gained ground only recently due to their inherent simplicity, electrical readouts, high precision, inexpensive and less time consuming nature. These sensors could also be miniaturised.

However, these sensors had been developed only in some advanced countries and import elevated the cost to very high level. Dr Shyam Bhoga, lecturer in Physics at Hislop College and co-investigator in the project said that the sensors developed by them have come out better than those already in the market, as they are fast (better response time), can sustain changes in temperature a lot better and are very cheap.

Explaining the method in which the sensor works, Singh said that the most important part of the sensor is the `cell', which is mounted inside a quartz probe. The cell is made up of the solid electrolyte and reference electrodes (both synthesised during the project) covered on both sides by platinum foil.

The electrolyte of sulphate or carbonate based for sensing the sulphur oxide or carbon oxide gases respectively. The reference electrodes are made of silver and lithium for the two gases respectively.

The cell is mounted inside a probe, which has the inlet and outlet for the mixture of gases to be detected. The gas enters the probe, comes in contact with the electrolyte and undergoes chemical reaction. The reference electrode helps in establishing the equilibrium in the system and in developing potential.

Copyright © 1997 Indian Express Newspapers (Bombay) Ltd.