Table of Contents

Preface

Chapter 1. Adsorption Phenomena

1.1. The surface of solids: general points

1.2. Illustration of adsorption

1.3. Acting forces between a gas molecule and the surface of a solid

1.4. Thermodynamic study of physical adsorption

1.5. Physical adsorption isotherms

1.6. Chemical adsorption isotherms

1.7. Bibliography

Chapter 2. Structure of Solids: Physico-chemical Aspects

2.1. The concept of phases

2.2. Solid solutions

2.3. Point defects in solids

2.4. Denotation of structural members of a crystal lattice

2.5. Formation of structural point defects

2.6. Bibliography

Chapter 3. Gas-Solid Interactions: Electronic Aspects

3.1. Introduction

3.2. Electronic properties of gases

3.3. Electronic properties of solids

3.4. Electrical conductivity in solids

3.5. Influence of temperature on the electric behavior of solids

3.6. Bibliography

Chapter 4. Interfacial Thermodynamic Equilibrium Studies

4.1. Introduction

4.2. Interfacial phenomena

4.3. Solid-gas equilibriums involving electron transfers or electron holes

4.4. Solid-gas equilibriums involving mass and charge transfers

4.5. Homogenous semiconductor interfaces

4.6. Heterogenous junction of semiconductor metals

4.7. Bibliography

Chapter 5. Model Development for Interfacial Phenomena

5.1. General points on process kinetics

5.2. Electrochemical aspect of kinetic processes

5.3. Expression of mixed potential

5.4. Bibliography

Chapter 6. Apparatus for Experimental Studies: Examples of Applications

6.1. Introduction

6.2. Calorimetry

6.3. Thermodesorption

6.4. Vibrating capacitor methods

6.5. Electrical interface characterization

6.6. Bibliography

Chapter 7. Material Elaboration

7.1. Introduction

7.2. Tin dioxide

7.3. Beta-alumina

7.4. Bibliography

Chapter 8. Influence of the Metallic Components on the Electrical Response of the Sensors

8.1. Introduction

8.2. General points

8.3. Case study: tin dioxide

8.4. Case study: beta-alumina

8.5. Conclusion

8.6. Bibliography

Chapter 9. Development and Use of Different Gas Sensors

9.1. General points on development and use

9.2. Examples of gas sensor development

9.3. Device designed for the laboratory assessment of sensitive elements and/or sensors to gas action

9.4. Assessment of performance in the laboratory

9.5. Assessment of the sensor working for an industrial application

9.6. Amelioration of the selectivity properties

9.7. Bibliography

Chapter 10. Models and Interpretation of Experimental Results

10.1. Introduction

10.2. Nickel oxide

10.3. Beta-alumina

10.4. Tin dioxide

10.5. Bibliography

Index

First published in France in 2006 by Hermes Science/Lavoisier entitled “Physico-chimie des interfaces solide-gaz 1 et 2”

First published in Great Britain and the United States in 2008 by ISTE Ltd and John Wiley & Sons, Inc. Translated from the French by Zineb Es-Skali and Matthieu Bourdrel.

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:

ISTE Ltd | John Wiley & Sons, Inc.
6 Fitzroy Square | 111 River Street
London W1T 5DX | Hoboken, NJ 07030
UK | USA
www.iste.co.uk | www.wiley.com

© ISTE Ltd, 2008
© LAVOISIER, 2006

The rights of René Lalauze to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.

Library of Congress Cataloging-in-Publication Data

Lalauze, René.
   [Physico-chimie des interfaces solide-gaz. English]
   Physical chemistry of solid-gas interfaces : concepts and methodology for gas sensors development /
René Lalauze.
      p. cm.
   Includes bibliographical references and index.
   ISBN 978-1-84821-041-7
   1. Gas-solid interfaces. 2. Gas detectors. I. Title.
     QD509.G37L3513 2008
     681'.2--dc22

2008022737

British Library Cataloguing-in-Publication Data
A CIP record for this book is available from the British Library
ISBN: 978-1-84821-041-7

Preface

Produced with the collaboration of Christophe Pijolat and Jean Paul Viricelle, this book is the fruit of research carried out over a long period of time by the Microsystems, Instrumentation and Chemical Sensors department at the Ecole des Mines, Saint Etienne, France.

The abilities of this laboratory on the subject of modeling and instrumentation on heterogenous systems have enabled us to develop and study different devices for the detection of gas.

The theoretical models based on kinetic concepts constitute the course of reflection and progress in a scientific area that is still little understood.

A large part of this book refers to PhD and scientific reports. My thanks go out to all the authors.

I would also like to thank the translators of this book from French, Zineb Es-Skali and Matthieu Bourdrel.

Chapter 1

Adsorption Phenomena¹

1.1. The surface of solids: general points

The concept of form, which can be associated with that of surface, is characteristic of a solid.

On a crystallographic level, every solid can be identified by its atomic or molecular arrangement. This arrangement, which is specific to each solid, constitutes a solid phase.

Generally, the identification of such a structure (atomic positions, cohesive energy) is defined in the hypothesis of an infinite crystal, which implies a similar environment for all atoms. Near the surface, this is no longer true and it is important to imagine a new local structure of atoms or electrically charged species.

In the particular case of ionic species, to submit to the local electroneutrality, it will often be necessary to take the solid’s environment into account. The material and the different phases in contact with it will thus reach equilibrium.

Thus appears the concept of interface: a privileged area of the solid, from which all interactions likely to occur between a solid and different surrounding compounds upon its contact will start and develop.

Depending on the nature of these compounds, there will be talk of solid-solid, solid-liquid or gas-solid reactions.

To conceptualize the solid-gas reactions on which we will concentrate, it is essential to start by simply picturing a molecule of gas bonding with a solid. The bonded molecule could remain independent from its support or react with it.

In the first hypothesis, the reversible process at work is one of adsorption, which then constitutes the overall reaction. It is called the adsorption-desorption phenomenon (see Figure 1.1a).

In the second hypothesis, adsorption will be the first step of a more complex process. It has, in this case, a non-reversible character due to which a new compound, GS for instance, will form.

The nature of the observed phenomenon will depend on the thermodynamic conditions (pressure, temperature) as well as on the chemical affinity of the present species.

It is also possible in adsorption phenomena to distinguish between physical and chemical adsorption. Chemical adsorption or chemisorption is characterized by a simple electron transfer between the gas in physisorbed state and the solid. This transfer results in the forming of a reversible chemical bond between the two compounds (see Figure 1.1b). Once again, the appearance of the chemisorption process is directly related to the environment’s thermodynamic conditions.

Figure 1.1. The different interaction modes between a gas and a solid: a) physical adsorption, b) chemisorption, c) non-reversible reaction

1.2. Illustration of adsorption

Volumetric and gravimetric methods are the most explicit and common methods used to display and quantify adsorption.

1.2.1. The volumetric method or manometry

In a closed system, the bonding of a gas molecule with a solid contributes to lowering the partial pressure of the gas and measuring the variation of this pressure is enough to access the necessary information.

To conduct an experiment, one uses two containing vessels A and B (see Figure 1.2) are used. Vessel A is connected to a device that measures pressure in it or in vessel A+B if A and B are joined by a valve V1. Gas is introduced in vessel A using valve V2 under pressure Pa. The solid sample is put in vessel B. A simple gas expansion in vessel A+B is enough to allow us to measure pressure Pa₊b.

Figure 1.2. Adsorption-measuring device using the volumetric method

Generally, the number of gas molecules introduced, n, is given, either by:

when vessel A is isolated from vessel B, or by:

after the expansion of the gas in vessel A+B.

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