Development of a chemical gas sensor system [Elektronische Ressource] = Entwicklung eines chemischen Gas-Sensor-Systems / vorgelegt von Patrick Reichel

Patrick Lanneau

Informations

• Publié par: eberhard_karls_universitat_tubingen
• Publié le: 01 janvier 2005
• Nombre de lectures: 22
• Langue: Deutsch
• Poids de l'ouvrage: 3 Mo

Extrait

Development of a Chemical
Gas Sensor System

Entwicklung eines Chemischen Gas Sensor
Systems






DISSERTATION



der Fakultät für Chemie und Pharmazie
der Eberhard Karls Universität Tübingen
zur Erlangung des Grades eines Doktors
der Naturwissenschaften

2005



vorgelegt von

Patrick Reichel


















































Tag der mündlichen Prüfung: 07.10.2005
Dekan: Prof. Dr. Stefan Laufer
1. Berichterstatter: PD Dr. Udo Weimar
2. Berichterstatter: Prof. Dr. Günter Gauglitz

Table of Contents

1 Introduction ........................................................................................................................ 4
1.1 Motivation .................................................................................................................. 4
1.2 Gas Sensors ................................................................................................................ 5
1.2.1 Electrochemical Cells......................................................................................... 6
1.2.2 Microbalances .................................................................................................... 6
1.2.3 Metal Oxide Semiconductor Gas Sensors.......................................................... 7
1.3 Target and Outline of this Work ................................................................................ 9

2 Metal oxide gas sensors 11
2.1 Material Properties of Tin Dioxide .......................................................................... 12
2.1.1 Crystalline Structure......................................................................................... 12
2.1.2 Electronic Properties ........................................................................................ 12
2.1.3 Bulk Conductivity ............................................................................................ 13
2.2 Chemical and Physical Properties of Metal Oxide Surfaces.................................... 14
2.2.1 Physisorption and Chemisorption .................................................................... 15
2.2.2 Acidic and Basic Properties of Surface Sites................................................... 17
2.2.3 Space Charge Effects ....................................................................................... 19
2.2.4 From Charge Transfer to Sensor Signal........................................................... 20
2.2.5 Conduction in the Sensing Layer ..................................................................... 22
2.3 Interaction of Selected Adsorbants with SnO Surface............................................ 24 2
2.3.1 Adsorption of Oxygen (O ) .............................................................................. 24 2
2.3.2 Adsorption of Water (H O) 25 2
2.3.3 Adsorption of Carbon Monoxide (CO) ............................................................ 27
2.3.4 Adsorption of Methane (CH ) .......................................................................... 28 4
2.3.5 Adsorption of Nitrogen Dioxide (NO ) 29 2
2.4 Material Preparation and Sensor Fabrication ........................................................... 30
2.4.1 Effect of Dopants ............................................................................................. 33
2.4.2 Sensor Substrates.............................................................................................. 34
2.4.2.1 Alumina Substrates and Screen Printing...................................................... 34
2.4.2.2 Micromachined Substrates and Drop Coating ............................................. 35

3 Sensor System Development............................................................................................ 37
3.1 Concept..................................................................................................................... 37
3.2 Experimental ............................................................................................................ 38
3.2.1 Gas Mixing Bench 38
3.2.2 Sensor Heating ................................................................................................. 40
3.2.3 Data Acquisition............................................................................................... 40
3.2.4 Reference Instruments...................................................................................... 41
3.3 Development Stages and System Prototypes ........................................................... 42
3.3.1 Conventional Thick Film Sensor...................................................................... 42
3.3.2 AS-Sensor......................................................................................................... 42
3.3.3 ADA Sensor Chip............................................................................................. 43
3.3.4 First Steps: the Development Platform ............................................................ 45
3.3.4.1 Valves........................................................................................................... 45
3.3.4.2 Pump............................................................................................................. 46
3.3.4.3 Purge-and-Trap-Unit .................................................................................... 46
3.3.4.4 Sensor System Controller............................................................................. 46
3.3.4.5 Data Transmission Controller ...................................................................... 46
1


3.3.5 ADA Prototype................................................................................................. 46
3.3.5.1 Sensor System Controller............................................................................. 47
3.3.6 Sensor chip packaging...................................................................................... 48
3.3.7 Packaging................................................................................. 48
3.4 Solving the Selectivity Problem............................................................................... 49
3.4.1 Sensitive Materials and Dopants...................................................................... 50
3.4.2 Sensor Operation Temperatures....................................................................... 52
3.4.3 Temperature Modulation.................................................................................. 53
3.4.3.1 Pattern Recognition Methods 53
3.4.3.2 Selectivity Improvements 54
3.4.4 Gas Filters ........................................................................................................ 57
3.4.4.1 Adsorbants.................................................................................................... 59
3.4.4.2 Catalysts ....................................................................................................... 59
3.4.4.3 Molecular sieves........................................................................................... 60
3.4.4.4 Filter performance ........................................................................................ 60
3.4.5 Air Flow and Pressure Fluctuations ................................................................. 62
3.4.6 Strategies Discarded......................................................................................... 62
3.4.6.1 Pre-concentrator 62
3.4.6.2 Controlled Humidification ........................................................................... 63
3.5 Calibration Strategies ............................................................................................... 63
3.5.1 First Calibration................................................................................................ 63
3.5.2 Single Pollutant Prediction............................................................................... 64
3.5.3 Binary Mixture Prediction................................................................................ 65
3.5.4 Evaluation......................................................................................................... 67
3.5.5 Improved Calibration ....................................................................................... 68
3.6 System Operation ..................................................................................................... 70
3.7 Summary .................................................................................................................. 71

4 Laboratory Validation and Field Trials............................................................................ 73
4.1 ADA Sensor System................................................................................................. 73
4.1.1 Sensor Operation Temperature......................................................................... 73
4.2 Laboratory Validation .................................................................