Rene Lalauze is a Professor at the Ecole des Mines, St. Etienne, France.

• Preface xiiiChapter 1. Adsorption Phenomena 11.1. The surface of solids: general points 11.2. Illustration of adsorption 21.2.1. The volumetric method or manometry 31.2.2. The gravimetric method or thermogravimetry 41.3. Acting forces between a gas molecule and the surface of a solid 41.3.1. Van der Waals forces 41.3.2. Expression of the potential between a molecule and a solid 61.3.3. Chemical forces between a gas species and the surface of a solid 71.3.4. Distinction between physical and chemical adsorption 81.4. Thermodynamic study of physical adsorption 81.4.1. The different models of adsorption 81.4.2. The Hill model 91.4.3. The Hill-Everett model 101.4.4. Thermodynamics of the adsorption equilibrium in Hill’s model 101.4.4.1. Formulating the equilibrium 101.4.4.2. Isotherm equation 111.4.5. Thermodynamics of adsorption equilibrium in the Hill-Everett model 121.5. Physical adsorption isotherms 131.5.1. General points 131.5.2. Adsorption isotherms of mobile monolayers 151.5.3. Adsorption isotherms of localized monolayers 151.5.3.1. Thermodynamic method 161.5.3.2. The kinetic model 171.5.4. Multilayer adsorption isotherms 181.5.4.1. Isotherm equation 181.6. Chemical adsorption isotherms 231.7. Bibliography 27Chapter 2. Structure of Solids: Physico-chemical Aspects 292.1. The concept of phases 292.2. Solid solutions 312.3. Point defects in solids 332.4. Denotation of structural members of a crystal lattice 342.5. Formation of structural point defects 362.5.1. Formation of defects in a solid matrix 362.5.2. Formation of defects involving surface elements 372.5.3. Concept of elementary hopping step 382.6. Bibliography 38Chapter 3. Gas-Solid Interactions: Electronic Aspects 393.1. Introduction 393.2. Electronic properties of gases 393.3. Electronic properties of solids 403.3.1. Introduction 403.3.2. Energy spectrum of a crystal lattice electron 413.3.2.1. Reminder about quantum mechanics principles. 413.3.2.2. Band diagrams of solids 453.3.2.3. Effective mass of an electron 523.4. Electrical conductivity in solids 553.4.1. Full bands 553.4.2. Partially occupied bands 563.5. Influence of temperature on the electric behavior of solids 573.5.1. Band diagram and Fermi level of conductors 573.5.2. Case of intrinsic semiconductors 613.5.3. Case of extrinsic semiconductors 623.5.4. Case of materials with point defects 643.5.4.1. Metal oxides with anion defects, denoted by MO1x 653.5.4.2. Metal oxides with cation vacancies, denoted by M1xO 663.5.4.3. Metal oxides with interstitial cations, denoted by M1+xO 673.5.4.4. Metal oxides with interstitial anions, denoted by MO1+x 673.6. Bibliography 68Chapter 4. Interfacial Thermodynamic Equilibrium Studies 694.1. Introduction 694.2. Interfacial phenomena 704.3. Solid-gas equilibriums involving electron transfers or electron holes 714.3.1. Concept of surface states 724.3.2. Space-charge region (SCR) 734.3.3. Electronic work function 774.3.3.1. Case of a semiconductor in the absence of surface states 774.3.3.2. Case of a semiconductor in the presence of surface states 784.3.3.3. Physicists’ and electrochemists’ denotation systems 794.3.4. Influence of adsorption on the electron work functions 804.3.4.1. Influence of adsorption on the surface barrier VS 804.3.4.2. Influence of adsorption on the dipole component VD. 904.4. Solid-gas equilibriums involving mass and charge transfers 914.4.1. Solids with anion vacancies 924.4.2. Solids with interstitial cations 944.4.3. Solids with interstitial anions 944.4.4. Solids with cation vacancies 964.5. Homogenous semiconductor interfaces 974.5.1. The electrostatic potential is associated with the intrinsic energy level 1034.5.2. Electrochemical aspect 1044.5.3. Polarization of the junction. 1074.6. Heterogenous junction of semiconductor metals 1074.7. Bibliography 108Chapter 5. Model Development for Interfacial Phenomena 1095.1. General points on process kinetics 1095.1.1. Linear chain 1115.1.1.1. Pure kinetic case hypothesis 1145.1.1.2. Bodenstein’s stationary state hypothesis 1185.1.1.3. Evolution of the rate according to time and gas pressure 1195.1.1.4. Diffusion in a homogenous solid phase 1215.1.2. Branched processes 1255.2. Electrochemical aspect of kinetic processes 1265.3. Expression of mixed potential 1335.4. Bibliography 136Chapter 6. Apparatus for Experimental Studies: Examples of Applications 1376.1. Introduction 1376.2. Calorimetry 1386.2.1. General points 1386.2.1.1. Theoretical aspect of Tian-Calvet calorimeters 1396.2.1.2. Seebeck effect 1396.2.1.3. Peltier effect 1406.2.1.4. Tian equation 1406.2.1.5. Description of a Tian-Calvet device 1426.2.1.6. Thermogram profile 1446.2.1.7. Examples of applications 1466.3. Thermodesorption 1566.3.1. Introduction 1566.3.2. Theoretical aspect 1576.3.3. Display of results 1616.3.3.1. Tin dioxide 1616.3.3.2. Nickel oxide 1636.4. Vibrating capacitor methods 1726.4.1. Contact potential difference 1726.4.2. Working principle of the vibrating capacitor method 1766.4.2.1. Introduction 1766.4.2.2. Theoretical study of the vibrating capacitor method 1766.4.3. Advantages of using the vibrating capacitor technique 1796.4.3.1. The materials studied 1796.4.3.2. Temperature conditions 1796.4.3.3. Pressure conditions 1816.4.4. The constraints 1816.4.4.1. The reference electrode 1816.4.4.2. Capacitance modulation 1826.4.5. Display of experimental results 1826.4.5.1. Study of interactions between oxygen and tin dioxide 1846.4.5.2. Study of interactions between oxygen and beta-alumina 1856.5. Electrical interface characterization 1876.5.1. General points 1876.5.2. Direct-current measurement 1896.5.3. Alternating-current measurement 1916.5.3.1. General points 1916.5.3.2. Principle of the impedance spectroscopy technique 1916.5.4. Application of impedance spectroscopy – experimental results 1966.5.4.1. Protocol 1966.5.4.2. Experimental results: characteristics specific to each material 1976.5.5. Evolution of electrical parameters according to temperature 2026.5.6. Evolution of electrical parameters according to pressure 2086.6. Bibliography 212Chapter 7. Material Elaboration 2157.1. Introduction 2157.2. Tin dioxide 2167.2.1. The compression of powders 2167.2.1.1. Elaboration process and structural properties 2167.2.1.2. Influence of the morphological parameters on the electric properties 2177.2.2. Reactive evaporation 2197.2.2.1. Experimental device 2197.2.2.2. Measure of the source temperature 2227.2.2.3. Thickness measure 2227.2.2.4. Experimental process 2247.2.2.5. Structure and properties of the films 2247.2.3. Chemical vapor deposition: deposit contained between 50 and 300 Å 2367.2.3.1. General points 2367.2.3.2. Device description 2387.2.3.3. Structural characterization of the material 2427.2.3.4. Influence of the experimental parameters on the physico-chemical properties of the films 2457.2.3.5. Influence of the structure parameters on the electric properties of the films 2507.2.4. Elaboration of thick films using serigraphy 2527.2.4.1. Method description 2527.2.4.2. Ink elaboration 2537.2.4.3. Structural characterization of thick films made with tin dioxide 2547.3. Beta-alumina 2557.3.1. General properties 2557.3.2. Material elaboration 2577.3.3. Material shaping 2617.3.3.1. Mono-axial compression 2617.3.3.2. Serigraphic process 2627.3.4. Characterization of materials 2637.3.4.1. Physico-chemical characterization of the sintered materials 2637.3.4.2. Physico-chemical treatment of the thick films 2667.3.5. Electric characterization 2737.4. Bibliography 275Chapter 8. Influence of the Metallic Components on the Electrical Response of the Sensors 2778.1. Introduction 2778.2. General points 2788.2.1. Methods to deposit the metallic parts on the sensitive element 2788.2.2. Role of the metallic elements on the sensors’ response 2798.2.3. Role of the metal: catalytic aspects 2828.2.3.1. Spill-over mechanism 2838.2.3.2. Reverse spill-over mechanism 2848.2.3.3. Electronic effect mechanism 2848.2.3.4. Influence of the metal nature on the involved mechanism 2868.3. Case study: tin dioxide 2888.3.1. Choice of the samples 2888.3.2. Description of the reactor 2898.3.3. Experimental results 2918.3.3.1. Influence of the oxygen pressure on the electric conductivity 2918.3.3.2. Influence of the reducing gas on the electric conductions 2958.4. Case study: beta-alumina 2968.4.1. Device and experimental process 2978.4.2. Influence of the nature of the electrodes on the measured voltage 2988.4.2.1. Study of the different couples of metallic electrodes 2998.4.2.2. Electric response to polluting gases 3018.4.3. Influence of the electrode size 3038.4.3.1. Description of the studied devices 3038.4.3.2. Study of the electric response according to the experimental conditions 3048.5. Conclusion 3068.6. Bibliography 307Chapter 9. Development and Use of Different Gas Sensors 3099.1. General points on development and use 3099.2. Examples of gas sensor development 3109.2.1. Sensors elaborated using sintered materials 3109.2.2. Sensors produced with serigraphed sensitive materials 3129.3. Device designed for the laboratory assessment of sensitive elements and/or sensors to gas action 3169.3.1. Measure cell for sensitive materials 3179.3.2. Test bench for complete sensors 3199.3.3. Measure of the signal 3199.3.3.1. Measure of the electric conductance 3199.3.3.2. Measure of the potential 3229.4. Assessment of performance in the laboratory 3229.4.1. Assessment of the performances of tin dioxide in the presence of gases 3229.4.2. Assessment of beta-alumina in the presence of oxygen 3279.4.2.1. Device and experimental process 3279.4.2.2. Electric response to the action of oxygen 3279.4.3. Assessment of the performances of beta-alumina in the presence of carbon monoxide 3299.4.3.1. Measurement device 3299.4.3.2. Electric results 3299.5. Assessment of the sensor working for an industrial application 3329.5.1. Detection of hydrogen leaks on a cryogenic engine 3339.5.1.1. Context of the study 3339.5.1.2. Study of performances in the presence of hydrogen 3339.5.1.3. Test carried out in an industrial environment 3379.5.2. Application of the resistant sensor to atmospheric pollutants in an urban environment 3419.5.2.1. Measurement campaign conducted at Lyon in 1988 3429.5.2.2. Measurement campaign conducted at Saint Etienne in 1998 3459.5.3. Application of the potentiometric sensor to the control of car exhaust gas 3479.5.3.1. Strategy implemented to control the emission of nitrogen oxides 3479.5.3.2. Strategy implemented to control nitrogen oxide traps 3499.5.3.3. Results relative to the nitrogen oxides traps 3509.6. Amelioration of the selectivity properties 3529.6.1. Amelioration of the selective detection properties of SnO2 sensors using metallic filters 3529.6.1.1. Development of a sensor using a rhodium filter 3529.6.1.2. Development of a sensor using a platinum filter 3549.6.2. Development of mechanical filters 3569.6.2.1. Development of a sensor detecting hydrogen 3569.6.2.2. Development of a protective film for potentiometric sensors 3569.7. Bibliography 359Chapter 10. Models and Interpretation of Experimental Results 36110.1. Introduction 36110.2. Nickel oxide 36210.2.1. Kinetic model 36510.2.2. Simulation of a kinetic model using analog electric circuits 37010.2.2.1. Simulation of the curves displaying a maximum 37010.2.2.2. Simulation of the curves displaying a plateau 37710.2.3. Physical significance of the measured electric conductivity 38010.3. Beta-alumina 38010.3.1. Physico-chemical and physical aspects of a phenomenon taking place at the electrodes 38010.3.1.1. Oxygen species present at the surface of the device 38010.3.1.2. Origin of the electric potential 38410.3.2. Expression of the model 38510.3.2.1. The electrode potential 38510.3.2.2. Expression of the coverage degree 38910.3.2.3. Expression of the theoretical potential difference at the poles of the device 39410.3.3. Simulation of the results obtained with oxygen 39510.3.3.1. Behavior as a function of temperature and pressure 39510.3.3.2. Behavior as a function of electrode size 39710.3.3.3. Evolution of the surface potential 39910.3.4. Simulation of the phenomenon in the presence of CO 40110.3.4.1. Description of the mechanisms considered 40110.3.4.2. Oxidation mechanisms of carbon monoxide 40210.3.4.3. Results of the simulation 40510.4. Tin dioxide 40910.4.1. Introduction 40910.4.2. Proposition for a physico-chemical model 41010.4.3. Phenomenon at the electrodes and role of the thickness of the sensitive film 41510.4.3.1. Calculation of the conductance G as a function of the thickness of the film 41610.4.3.2. Mathematical simulation 42310.5. Bibliography 428Index 431

Rene Lalauze is a Professor at the Ecole des Mines, St. Etienne, France.

• Preface xiiiChapter 1. Adsorption Phenomena 11.1. The surface of solids: general points 11.2. Illustration of adsorption 21.2.1. The volumetric method or manometry 31.2.2. The gravimetric method or thermogravimetry 41.3. Acting forces between a gas molecule and the surface of a solid 41.3.1. Van der Waals forces 41.3.2. Expression of the potential between a molecule and a solid 61.3.3. Chemical forces between a gas species and the surface of a solid 71.3.4. Distinction between physical and chemical adsorption 81.4. Thermodynamic study of physical adsorption 81.4.1. The different models of adsorption 81.4.2. The Hill model 91.4.3. The Hill-Everett model 101.4.4. Thermodynamics of the adsorption equilibrium in Hill’s model 101.4.4.1. Formulating the equilibrium 101.4.4.2. Isotherm equation 111.4.5. Thermodynamics of adsorption equilibrium in the Hill-Everett model 121.5. Physical adsorption isotherms 131.5.1. General points 131.5.2. Adsorption isotherms of mobile monolayers 151.5.3. Adsorption isotherms of localized monolayers 151.5.3.1. Thermodynamic method 161.5.3.2. The kinetic model 171.5.4. Multilayer adsorption isotherms 181.5.4.1. Isotherm equation 181.6. Chemical adsorption isotherms 231.7. Bibliography 27Chapter 2. Structure of Solids: Physico-chemical Aspects 292.1. The concept of phases 292.2. Solid solutions 312.3. Point defects in solids 332.4. Denotation of structural members of a crystal lattice 342.5. Formation of structural point defects 362.5.1. Formation of defects in a solid matrix 362.5.2. Formation of defects involving surface elements 372.5.3. Concept of elementary hopping step 382.6. Bibliography 38Chapter 3. Gas-Solid Interactions: Electronic Aspects 393.1. Introduction 393.2. Electronic properties of gases 393.3. Electronic properties of solids 403.3.1. Introduction 403.3.2. Energy spectrum of a crystal lattice electron 413.3.2.1. Reminder about quantum mechanics principles. 413.3.2.2. Band diagrams of solids 453.3.2.3. Effective mass of an electron 523.4. Electrical conductivity in solids 553.4.1. Full bands 553.4.2. Partially occupied bands 563.5. Influence of temperature on the electric behavior of solids 573.5.1. Band diagram and Fermi level of conductors 573.5.2. Case of intrinsic semiconductors 613.5.3. Case of extrinsic semiconductors 623.5.4. Case of materials with point defects 643.5.4.1. Metal oxides with anion defects, denoted by MO1x 653.5.4.2. Metal oxides with cation vacancies, denoted by M1xO 663.5.4.3. Metal oxides with interstitial cations, denoted by M1+xO 673.5.4.4. Metal oxides with interstitial anions, denoted by MO1+x 673.6. Bibliography 68Chapter 4. Interfacial Thermodynamic Equilibrium Studies 694.1. Introduction 694.2. Interfacial phenomena 704.3. Solid-gas equilibriums involving electron transfers or electron holes 714.3.1. Concept of surface states 724.3.2. Space-charge region (SCR) 734.3.3. Electronic work function 774.3.3.1. Case of a semiconductor in the absence of surface states 774.3.3.2. Case of a semiconductor in the presence of surface states 784.3.3.3. Physicists’ and electrochemists’ denotation systems 794.3.4. Influence of adsorption on the electron work functions 804.3.4.1. Influence of adsorption on the surface barrier VS 804.3.4.2. Influence of adsorption on the dipole component VD. 904.4. Solid-gas equilibriums involving mass and charge transfers 914.4.1. Solids with anion vacancies 924.4.2. Solids with interstitial cations 944.4.3. Solids with interstitial anions 944.4.4. Solids with cation vacancies 964.5. Homogenous semiconductor interfaces 974.5.1. The electrostatic potential is associated with the intrinsic energy level 1034.5.2. Electrochemical aspect 1044.5.3. Polarization of the junction. 1074.6. Heterogenous junction of semiconductor metals 1074.7. Bibliography 108Chapter 5. Model Development for Interfacial Phenomena 1095.1. General points on process kinetics 1095.1.1. Linear chain 1115.1.1.1. Pure kinetic case hypothesis 1145.1.1.2. Bodenstein’s stationary state hypothesis 1185.1.1.3. Evolution of the rate according to time and gas pressure 1195.1.1.4. Diffusion in a homogenous solid phase 1215.1.2. Branched processes 1255.2. Electrochemical aspect of kinetic processes 1265.3. Expression of mixed potential 1335.4. Bibliography 136Chapter 6. Apparatus for Experimental Studies: Examples of Applications 1376.1. Introduction 1376.2. Calorimetry 1386.2.1. General points 1386.2.1.1. Theoretical aspect of Tian-Calvet calorimeters 1396.2.1.2. Seebeck effect 1396.2.1.3. Peltier effect 1406.2.1.4. Tian equation 1406.2.1.5. Description of a Tian-Calvet device 1426.2.1.6. Thermogram profile 1446.2.1.7. Examples of applications 1466.3. Thermodesorption 1566.3.1. Introduction 1566.3.2. Theoretical aspect 1576.3.3. Display of results 1616.3.3.1. Tin dioxide 1616.3.3.2. Nickel oxide 1636.4. Vibrating capacitor methods 1726.4.1. Contact potential difference 1726.4.2. Working principle of the vibrating capacitor method 1766.4.2.1. Introduction 1766.4.2.2. Theoretical study of the vibrating capacitor method 1766.4.3. Advantages of using the vibrating capacitor technique 1796.4.3.1. The materials studied 1796.4.3.2. Temperature conditions 1796.4.3.3. Pressure conditions 1816.4.4. The constraints 1816.4.4.1. The reference electrode 1816.4.4.2. Capacitance modulation 1826.4.5. Display of experimental results 1826.4.5.1. Study of interactions between oxygen and tin dioxide 1846.4.5.2. Study of interactions between oxygen and beta-alumina 1856.5. Electrical interface characterization 1876.5.1. General points 1876.5.2. Direct-current measurement 1896.5.3. Alternating-current measurement 1916.5.3.1. General points 1916.5.3.2. Principle of the impedance spectroscopy technique 1916.5.4. Application of impedance spectroscopy – experimental results 1966.5.4.1. Protocol 1966.5.4.2. Experimental results: characteristics specific to each material 1976.5.5. Evolution of electrical parameters according to temperature 2026.5.6. Evolution of electrical parameters according to pressure 2086.6. Bibliography 212Chapter 7. Material Elaboration 2157.1. Introduction 2157.2. Tin dioxide 2167.2.1. The compression of powders 2167.2.1.1. Elaboration process and structural properties 2167.2.1.2. Influence of the morphological parameters on the electric properties 2177.2.2. Reactive evaporation 2197.2.2.1. Experimental device 2197.2.2.2. Measure of the source temperature 2227.2.2.3. Thickness measure 2227.2.2.4. Experimental process 2247.2.2.5. Structure and properties of the films 2247.2.3. Chemical vapor deposition: deposit contained between 50 and 300 Å 2367.2.3.1. General points 2367.2.3.2. Device description 2387.2.3.3. Structural characterization of the material 2427.2.3.4. Influence of the experimental parameters on the physico-chemical properties of the films 2457.2.3.5. Influence of the structure parameters on the electric properties of the films 2507.2.4. Elaboration of thick films using serigraphy 2527.2.4.1. Method description 2527.2.4.2. Ink elaboration 2537.2.4.3. Structural characterization of thick films made with tin dioxide 2547.3. Beta-alumina 2557.3.1. General properties 2557.3.2. Material elaboration 2577.3.3. Material shaping 2617.3.3.1. Mono-axial compression 2617.3.3.2. Serigraphic process 2627.3.4. Characterization of materials 2637.3.4.1. Physico-chemical characterization of the sintered materials 2637.3.4.2. Physico-chemical treatment of the thick films 2667.3.5. Electric characterization 2737.4. Bibliography 275Chapter 8. Influence of the Metallic Components on the Electrical Response of the Sensors 2778.1. Introduction 2778.2. General points 2788.2.1. Methods to deposit the metallic parts on the sensitive element 2788.2.2. Role of the metallic elements on the sensors’ response 2798.2.3. Role of the metal: catalytic aspects 2828.2.3.1. Spill-over mechanism 2838.2.3.2. Reverse spill-over mechanism 2848.2.3.3. Electronic effect mechanism 2848.2.3.4. Influence of the metal nature on the involved mechanism 2868.3. Case study: tin dioxide 2888.3.1. Choice of the samples 2888.3.2. Description of the reactor 2898.3.3. Experimental results 2918.3.3.1. Influence of the oxygen pressure on the electric conductivity 2918.3.3.2. Influence of the reducing gas on the electric conductions 2958.4. Case study: beta-alumina 2968.4.1. Device and experimental process 2978.4.2. Influence of the nature of the electrodes on the measured voltage 2988.4.2.1. Study of the different couples of metallic electrodes 2998.4.2.2. Electric response to polluting gases 3018.4.3. Influence of the electrode size 3038.4.3.1. Description of the studied devices 3038.4.3.2. Study of the electric response according to the experimental conditions 3048.5. Conclusion 3068.6. Bibliography 307Chapter 9. Development and Use of Different Gas Sensors 3099.1. General points on development and use 3099.2. Examples of gas sensor development 3109.2.1. Sensors elaborated using sintered materials 3109.2.2. Sensors produced with serigraphed sensitive materials 3129.3. Device designed for the laboratory assessment of sensitive elements and/or sensors to gas action 3169.3.1. Measure cell for sensitive materials 3179.3.2. Test bench for complete sensors 3199.3.3. Measure of the signal 3199.3.3.1. Measure of the electric conductance 3199.3.3.2. Measure of the potential 3229.4. Assessment of performance in the laboratory 3229.4.1. Assessment of the performances of tin dioxide in the presence of gases 3229.4.2. Assessment of beta-alumina in the presence of oxygen 3279.4.2.1. Device and experimental process 3279.4.2.2. Electric response to the action of oxygen 3279.4.3. Assessment of the performances of beta-alumina in the presence of carbon monoxide 3299.4.3.1. Measurement device 3299.4.3.2. Electric results 3299.5. Assessment of the sensor working for an industrial application 3329.5.1. Detection of hydrogen leaks on a cryogenic engine 3339.5.1.1. Context of the study 3339.5.1.2. Study of performances in the presence of hydrogen 3339.5.1.3. Test carried out in an industrial environment 3379.5.2. Application of the resistant sensor to atmospheric pollutants in an urban environment 3419.5.2.1. Measurement campaign conducted at Lyon in 1988 3429.5.2.2. Measurement campaign conducted at Saint Etienne in 1998 3459.5.3. Application of the potentiometric sensor to the control of car exhaust gas 3479.5.3.1. Strategy implemented to control the emission of nitrogen oxides 3479.5.3.2. Strategy implemented to control nitrogen oxide traps 3499.5.3.3. Results relative to the nitrogen oxides traps 3509.6. Amelioration of the selectivity properties 3529.6.1. Amelioration of the selective detection properties of SnO2 sensors using metallic filters 3529.6.1.1. Development of a sensor using a rhodium filter 3529.6.1.2. Development of a sensor using a platinum filter 3549.6.2. Development of mechanical filters 3569.6.2.1. Development of a sensor detecting hydrogen 3569.6.2.2. Development of a protective film for potentiometric sensors 3569.7. Bibliography 359Chapter 10. Models and Interpretation of Experimental Results 36110.1. Introduction 36110.2. Nickel oxide 36210.2.1. Kinetic model 36510.2.2. Simulation of a kinetic model using analog electric circuits 37010.2.2.1. Simulation of the curves displaying a maximum 37010.2.2.2. Simulation of the curves displaying a plateau 37710.2.3. Physical significance of the measured electric conductivity 38010.3. Beta-alumina 38010.3.1. Physico-chemical and physical aspects of a phenomenon taking place at the electrodes 38010.3.1.1. Oxygen species present at the surface of the device 38010.3.1.2. Origin of the electric potential 38410.3.2. Expression of the model 38510.3.2.1. The electrode potential 38510.3.2.2. Expression of the coverage degree 38910.3.2.3. Expression of the theoretical potential difference at the poles of the device 39410.3.3. Simulation of the results obtained with oxygen 39510.3.3.1. Behavior as a function of temperature and pressure 39510.3.3.2. Behavior as a function of electrode size 39710.3.3.3. Evolution of the surface potential 39910.3.4. Simulation of the phenomenon in the presence of CO 40110.3.4.1. Description of the mechanisms considered 40110.3.4.2. Oxidation mechanisms of carbon monoxide 40210.3.4.3. Results of the simulation 40510.4. Tin dioxide 40910.4.1. Introduction 40910.4.2. Proposition for a physico-chemical model 41010.4.3. Phenomenon at the electrodes and role of the thickness of the sensitive film 41510.4.3.1. Calculation of the conductance G as a function of the thickness of the film 41610.4.3.2. Mathematical simulation 42310.5. Bibliography 428Index 431

Rene Lalauze is a Professor at the Ecole des Mines, St. Etienne, France.

• Preface xiiiChapter 1. Adsorption Phenomena 11.1. The surface of solids: general points 11.2. Illustration of adsorption 21.2.1. The volumetric method or manometry 31.2.2. The gravimetric method or thermogravimetry 41.3. Acting forces between a gas molecule and the surface of a solid 41.3.1. Van der Waals forces 41.3.2. Expression of the potential between a molecule and a solid 61.3.3. Chemical forces between a gas species and the surface of a solid 71.3.4. Distinction between physical and chemical adsorption 81.4. Thermodynamic study of physical adsorption 81.4.1. The different models of adsorption 81.4.2. The Hill model 91.4.3. The Hill-Everett model 101.4.4. Thermodynamics of the adsorption equilibrium in Hill’s model 101.4.4.1. Formulating the equilibrium 101.4.4.2. Isotherm equation 111.4.5. Thermodynamics of adsorption equilibrium in the Hill-Everett model 121.5. Physical adsorption isotherms 131.5.1. General points 131.5.2. Adsorption isotherms of mobile monolayers 151.5.3. Adsorption isotherms of localized monolayers 151.5.3.1. Thermodynamic method 161.5.3.2. The kinetic model 171.5.4. Multilayer adsorption isotherms 181.5.4.1. Isotherm equation 181.6. Chemical adsorption isotherms 231.7. Bibliography 27Chapter 2. Structure of Solids: Physico-chemical Aspects 292.1. The concept of phases 292.2. Solid solutions 312.3. Point defects in solids 332.4. Denotation of structural members of a crystal lattice 342.5. Formation of structural point defects 362.5.1. Formation of defects in a solid matrix 362.5.2. Formation of defects involving surface elements 372.5.3. Concept of elementary hopping step 382.6. Bibliography 38Chapter 3. Gas-Solid Interactions: Electronic Aspects 393.1. Introduction 393.2. Electronic properties of gases 393.3. Electronic properties of solids 403.3.1. Introduction 403.3.2. Energy spectrum of a crystal lattice electron 413.3.2.1. Reminder about quantum mechanics principles. 413.3.2.2. Band diagrams of solids 453.3.2.3. Effective mass of an electron 523.4. Electrical conductivity in solids 553.4.1. Full bands 553.4.2. Partially occupied bands 563.5. Influence of temperature on the electric behavior of solids 573.5.1. Band diagram and Fermi level of conductors 573.5.2. Case of intrinsic semiconductors 613.5.3. Case of extrinsic semiconductors 623.5.4. Case of materials with point defects 643.5.4.1. Metal oxides with anion defects, denoted by MO1x 653.5.4.2. Metal oxides with cation vacancies, denoted by M1xO 663.5.4.3. Metal oxides with interstitial cations, denoted by M1+xO 673.5.4.4. Metal oxides with interstitial anions, denoted by MO1+x 673.6. Bibliography 68Chapter 4. Interfacial Thermodynamic Equilibrium Studies 694.1. Introduction 694.2. Interfacial phenomena 704.3. Solid-gas equilibriums involving electron transfers or electron holes 714.3.1. Concept of surface states 724.3.2. Space-charge region (SCR) 734.3.3. Electronic work function 774.3.3.1. Case of a semiconductor in the absence of surface states 774.3.3.2. Case of a semiconductor in the presence of surface states 784.3.3.3. Physicists’ and electrochemists’ denotation systems 794.3.4. Influence of adsorption on the electron work functions 804.3.4.1. Influence of adsorption on the surface barrier VS 804.3.4.2. Influence of adsorption on the dipole component VD. 904.4. Solid-gas equilibriums involving mass and charge transfers 914.4.1. Solids with anion vacancies 924.4.2. Solids with interstitial cations 944.4.3. Solids with interstitial anions 944.4.4. Solids with cation vacancies 964.5. Homogenous semiconductor interfaces 974.5.1. The electrostatic potential is associated with the intrinsic energy level 1034.5.2. Electrochemical aspect 1044.5.3. Polarization of the junction. 1074.6. Heterogenous junction of semiconductor metals 1074.7. Bibliography 108Chapter 5. Model Development for Interfacial Phenomena 1095.1. General points on process kinetics 1095.1.1. Linear chain 1115.1.1.1. Pure kinetic case hypothesis 1145.1.1.2. Bodenstein’s stationary state hypothesis 1185.1.1.3. Evolution of the rate according to time and gas pressure 1195.1.1.4. Diffusion in a homogenous solid phase 1215.1.2. Branched processes 1255.2. Electrochemical aspect of kinetic processes 1265.3. Expression of mixed potential 1335.4. Bibliography 136Chapter 6. Apparatus for Experimental Studies: Examples of Applications 1376.1. Introduction 1376.2. Calorimetry 1386.2.1. General points 1386.2.1.1. Theoretical aspect of Tian-Calvet calorimeters 1396.2.1.2. Seebeck effect 1396.2.1.3. Peltier effect 1406.2.1.4. Tian equation 1406.2.1.5. Description of a Tian-Calvet device 1426.2.1.6. Thermogram profile 1446.2.1.7. Examples of applications 1466.3. Thermodesorption 1566.3.1. Introduction 1566.3.2. Theoretical aspect 1576.3.3. Display of results 1616.3.3.1. Tin dioxide 1616.3.3.2. Nickel oxide 1636.4. Vibrating capacitor methods 1726.4.1. Contact potential difference 1726.4.2. Working principle of the vibrating capacitor method 1766.4.2.1. Introduction 1766.4.2.2. Theoretical study of the vibrating capacitor method 1766.4.3. Advantages of using the vibrating capacitor technique 1796.4.3.1. The materials studied 1796.4.3.2. Temperature conditions 1796.4.3.3. Pressure conditions 1816.4.4. The constraints 1816.4.4.1. The reference electrode 1816.4.4.2. Capacitance modulation 1826.4.5. Display of experimental results 1826.4.5.1. Study of interactions between oxygen and tin dioxide 1846.4.5.2. Study of interactions between oxygen and beta-alumina 1856.5. Electrical interface characterization 1876.5.1. General points 1876.5.2. Direct-current measurement 1896.5.3. Alternating-current measurement 1916.5.3.1. General points 1916.5.3.2. Principle of the impedance spectroscopy technique 1916.5.4. Application of impedance spectroscopy – experimental results 1966.5.4.1. Protocol 1966.5.4.2. Experimental results: characteristics specific to each material 1976.5.5. Evolution of electrical parameters according to temperature 2026.5.6. Evolution of electrical parameters according to pressure 2086.6. Bibliography 212Chapter 7. Material Elaboration 2157.1. Introduction 2157.2. Tin dioxide 2167.2.1. The compression of powders 2167.2.1.1. Elaboration process and structural properties 2167.2.1.2. Influence of the morphological parameters on the electric properties 2177.2.2. Reactive evaporation 2197.2.2.1. Experimental device 2197.2.2.2. Measure of the source temperature 2227.2.2.3. Thickness measure 2227.2.2.4. Experimental process 2247.2.2.5. Structure and properties of the films 2247.2.3. Chemical vapor deposition: deposit contained between 50 and 300 Å 2367.2.3.1. General points 2367.2.3.2. Device description 2387.2.3.3. Structural characterization of the material 2427.2.3.4. Influence of the experimental parameters on the physico-chemical properties of the films 2457.2.3.5. Influence of the structure parameters on the electric properties of the films 2507.2.4. Elaboration of thick films using serigraphy 2527.2.4.1. Method description 2527.2.4.2. Ink elaboration 2537.2.4.3. Structural characterization of thick films made with tin dioxide 2547.3. Beta-alumina 2557.3.1. General properties 2557.3.2. Material elaboration 2577.3.3. Material shaping 2617.3.3.1. Mono-axial compression 2617.3.3.2. Serigraphic process 2627.3.4. Characterization of materials 2637.3.4.1. Physico-chemical characterization of the sintered materials 2637.3.4.2. Physico-chemical treatment of the thick films 2667.3.5. Electric characterization 2737.4. Bibliography 275Chapter 8. Influence of the Metallic Components on the Electrical Response of the Sensors 2778.1. Introduction 2778.2. General points 2788.2.1. Methods to deposit the metallic parts on the sensitive element 2788.2.2. Role of the metallic elements on the sensors’ response 2798.2.3. Role of the metal: catalytic aspects 2828.2.3.1. Spill-over mechanism 2838.2.3.2. Reverse spill-over mechanism 2848.2.3.3. Electronic effect mechanism 2848.2.3.4. Influence of the metal nature on the involved mechanism 2868.3. Case study: tin dioxide 2888.3.1. Choice of the samples 2888.3.2. Description of the reactor 2898.3.3. Experimental results 2918.3.3.1. Influence of the oxygen pressure on the electric conductivity 2918.3.3.2. Influence of the reducing gas on the electric conductions 2958.4. Case study: beta-alumina 2968.4.1. Device and experimental process 2978.4.2. Influence of the nature of the electrodes on the measured voltage 2988.4.2.1. Study of the different couples of metallic electrodes 2998.4.2.2. Electric response to polluting gases 3018.4.3. Influence of the electrode size 3038.4.3.1. Description of the studied devices 3038.4.3.2. Study of the electric response according to the experimental conditions 3048.5. Conclusion 3068.6. Bibliography 307Chapter 9. Development and Use of Different Gas Sensors 3099.1. General points on development and use 3099.2. Examples of gas sensor development 3109.2.1. Sensors elaborated using sintered materials 3109.2.2. Sensors produced with serigraphed sensitive materials 3129.3. Device designed for the laboratory assessment of sensitive elements and/or sensors to gas action 3169.3.1. Measure cell for sensitive materials 3179.3.2. Test bench for complete sensors 3199.3.3. Measure of the signal 3199.3.3.1. Measure of the electric conductance 3199.3.3.2. Measure of the potential 3229.4. Assessment of performance in the laboratory 3229.4.1. Assessment of the performances of tin dioxide in the presence of gases 3229.4.2. Assessment of beta-alumina in the presence of oxygen 3279.4.2.1. Device and experimental process 3279.4.2.2. Electric response to the action of oxygen 3279.4.3. Assessment of the performances of beta-alumina in the presence of carbon monoxide 3299.4.3.1. Measurement device 3299.4.3.2. Electric results 3299.5. Assessment of the sensor working for an industrial application 3329.5.1. Detection of hydrogen leaks on a cryogenic engine 3339.5.1.1. Context of the study 3339.5.1.2. Study of performances in the presence of hydrogen 3339.5.1.3. Test carried out in an industrial environment 3379.5.2. Application of the resistant sensor to atmospheric pollutants in an urban environment 3419.5.2.1. Measurement campaign conducted at Lyon in 1988 3429.5.2.2. Measurement campaign conducted at Saint Etienne in 1998 3459.5.3. Application of the potentiometric sensor to the control of car exhaust gas 3479.5.3.1. Strategy implemented to control the emission of nitrogen oxides 3479.5.3.2. Strategy implemented to control nitrogen oxide traps 3499.5.3.3. Results relative to the nitrogen oxides traps 3509.6. Amelioration of the selectivity properties 3529.6.1. Amelioration of the selective detection properties of SnO2 sensors using metallic filters 3529.6.1.1. Development of a sensor using a rhodium filter 3529.6.1.2. Development of a sensor using a platinum filter 3549.6.2. Development of mechanical filters 3569.6.2.1. Development of a sensor detecting hydrogen 3569.6.2.2. Development of a protective film for potentiometric sensors 3569.7. Bibliography 359Chapter 10. Models and Interpretation of Experimental Results 36110.1. Introduction 36110.2. Nickel oxide 36210.2.1. Kinetic model 36510.2.2. Simulation of a kinetic model using analog electric circuits 37010.2.2.1. Simulation of the curves displaying a maximum 37010.2.2.2. Simulation of the curves displaying a plateau 37710.2.3. Physical significance of the measured electric conductivity 38010.3. Beta-alumina 38010.3.1. Physico-chemical and physical aspects of a phenomenon taking place at the electrodes 38010.3.1.1. Oxygen species present at the surface of the device 38010.3.1.2. Origin of the electric potential 38410.3.2. Expression of the model 38510.3.2.1. The electrode potential 38510.3.2.2. Expression of the coverage degree 38910.3.2.3. Expression of the theoretical potential difference at the poles of the device 39410.3.3. Simulation of the results obtained with oxygen 39510.3.3.1. Behavior as a function of temperature and pressure 39510.3.3.2. Behavior as a function of electrode size 39710.3.3.3. Evolution of the surface potential 39910.3.4. Simulation of the phenomenon in the presence of CO 40110.3.4.1. Description of the mechanisms considered 40110.3.4.2. Oxidation mechanisms of carbon monoxide 40210.3.4.3. Results of the simulation 40510.4. Tin dioxide 40910.4.1. Introduction 40910.4.2. Proposition for a physico-chemical model 41010.4.3. Phenomenon at the electrodes and role of the thickness of the sensitive film 41510.4.3.1. Calculation of the conductance G as a function of the thickness of the film 41610.4.3.2. Mathematical simulation 42310.5. Bibliography 428Index 431