The workshop on new developments in semiconducting gas sensors

• H Meixner
• J Gerblinger
• U Lampe
• M Fleischer

• Siemens AG, Corporate Research and Development, Otto-Hahn-Ring 6, D-81730 Munich, Germany

Received 15 September 1993. Revised 26 July 1994. Accepted 1 August 1994. Available online 20 January 2000.

Abstract

In recent years, there has been a gradual realization that an intact environment and properly functioning ecosystems are essential to the continuance of human life; this has led to the tightening up of environmental legislation. As far as air pollution is concerned, gases like sulfur dioxide, the oxides of nitrogen (NOx ), carbon monoxide and carbon dioxide are considered to be the main culprits. Most sulfur dioxide is produced by the combustion of fossil fuels that contain sulfur (coal, oil and natural gas), the sulfur being oxidized to produce sulfur dioxide. This is why SO2 emissions can only be prevented by chemical binding. Oxides of nitrogen are also produced when fossil fuels are burnt. These oxides are largely the result of reactions between oxygen and nitrogen from the air. The main source of NOx emissions is automobiles. In 1986 alone, more than half (∼ 2 illion tonnes in the former FRG) of all NOx emissions could be directly attributed to this source. In the same year, somewhat less NOx (1 million tonnes in the former FRG) was produced by power stations, distant heating plants and other conversion areas. Air pollution by CO emissions from automobiles is an even more clear-cut case. As CO is produced by the incomplete combustion of fossil fuels, it is not surprising that automobiles alone produced 6.5 million tonnes of this gas in 1986 (former FRG), while the three other user groups (industry/households, trade and business/power stations and distance heating plant, other conversion areas) are only responsible for approximately 2.5 million tonnes (former FRG).

The presence of hydrocarbons (CHx ) in exhaust gases is also due to incomplete combustion. Hydrocarbons along with carbon dioxide and water vapour are also considered to be the main causes of the greenhouse effect. With hydrocarbons too, the main source of emissions is the automobile. The emission of CO and CHx from automobiles is particularly abundant when there is an excess of fuel (rich mixture, air coefficient λ 1). The introduction of catalytic converters only provides sufficient recombustion of these components in a very narrow range around λ =1. Therefore, to obtain the most efficient combustion and the least emission of pollutants, it would seem necessary to monitor the combustion process in each cylinder of a vehicle and to control it so that the exhaust gas expelled from each cylinder has a λ value corresponding to the maximum degree of conversion for the catalytic converter. Fast λ measurements are, therefore, of crucial importance, as they make regulation possible during non-stationary phases of engine operations (starting, braking, acceleration) that account for 80% of the total operating time. Attempts are also being made to introduce combustion regulation in incinerators by means of λ coefficients. This type of emission would also require sensors that are capable of continuously monitoring the concentration of pollutant components.

Sensor elements based on semiconducting metal oxides seem to be promising both for individual cylinder control in automobiles and for monitoring pollutant components.

Keywords

• Gas sensors
• Metal oxides
• Thin-film sensors

1995 Published by Elsevier B.V.

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Special Issue: 25th Anniversary of Sensors and Actuators B: Chemical

• N. Barsan
• D. Koziej
• U. Weimar .

• Institute of Physical and Theoretical Chemistry, University of Tübingen, Germany

Available online 27 October 2006.

Abstract

The paper critically reviews the state of the art in the field of experimental techniques possible to be applied to the study of conductometric gas sensors based on semiconducting metal oxides. The used assessment criteria are subordinated to the proposed RD approach, which focuses on the study, and subsequent modelling, of sensors’ performance in realistic operation conditions by means of a combination of phenomenological and spectroscopic techniques. With this viewpoint, the paper presents both the to-date achievements and shortcomings of different experimental techniques, describes – by using selected examples – how the proposed approach can be used and proposes a set of objectives for the near future.

Keywords

• Metal oxide
• Gas sensor
• Transduction
• Spectroscopy
• Operando

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Vitae

Nicolae Barsan received in 1982 his diploma in Physics from the Faculty of Physics of the Bucharest University and in 1993 his PhD in Solid State Physics from the Institute of Atomic Physics, Bucharest, Romania. He was a senior researcher at the Institute of Physics and Technnology of Materials, Bucharest between 1984 and 1995. Since 1995 he is a researcher at the Institute of Physical Chemistry of the University of Tübingen and actually is in charge with the developments in the field of metal oxides based gas sensors. He published about 150 papers and contributions to international conferences.

Dorota Koziej received in 2002 her diploma in Applied Physics from the Faculty of Mathematic and Physics of the Silesian University of Technology in Gliwice, Poland. Since 2002 a PhD student at the Department of Electron Technology of the Silesian University of Technology in Gliwice and since 2004 continuing her PhD studies at the Institute of Physical and Theoretical Chemistry of the University of Tübingen, Germany in the frame of Joint Doctoral Degree Program within the GOSPEL project.

Udo Weimar received his diploma in physics 1989, his PhD in chemistry 1993 and his Habilitation 2002 from the University of Tübingen. He is currently the head of Gas Sensors Group at the University of Tübingen. The research interest of Udo Weimar focuses on chemical sensors as well as on multicomponent analysis and pattern recognition. He is author of about 180 scientific papers and short notes. He is responsible for several European projects and for co-ordinating the Network of Excellence GOSPEL.

2006 Elsevier B.V. All rights reserved.

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