In situ monitoring of the internal stress evolution during titanium thin film anodising


Editie 1

Anodisation has been studied for almost eighty years, primarily in the field of corrosion science, as a simple and efficient way of producing thick protective oxide coatings on Al, Ti or Zr alloys. Anodisation is an electrochemical oxidation process which relies on the migration of ions across solid films under the action of a large electric field. From the fundamental point of view, many aspects regarding the growth of anodic films have been studied extensively. However, so far, little interest has been devoted to the mechanical aspects involved in the growth process, in spite of their considerable importance both from an applied as well as from a fundamental point of view. A solid understanding of internal stress development is indeed crucial in order to guarantee the durability of anodic coatings, their structural and functional properties. In addition, the stress evolution directly reflects the motion of the ions in the film and therefore provides a unique means to investigate in situ the growth mechanisms of anodic films. In this thesis, we have studied the evolution of the internal stresses in anodic TiO2 films in situ during their growth. The stresses have been obtained from changes in the curvature of cantilevered anode samples, measured using a high-resolution multibeam optical sensor. We demonstrate, for the first time, the capability of this type of curvature sensor for monitoring processes in liquid environments. Experimental data on the internal stresses developing in anodic TiO2 films is provided, and trends regarding the influence of the experimental conditions on the stress evolution are identified. In particular, the evolution of the internal stresses is shown to be strongly correlated with the evolution of the electrochemical variables, which directly demonstrates the interest of curvature measurements as a fundamental technique for investigating the details of the growth process of anodic oxide films. The reversible and irreversible stress contributions associated, respectively, with electrostriction and with growth-related ionic transport have been separated from one another and quantified. A novel constitutive model for the electrostriction stress is proposed which explicitly takes into account the effect of dielectrostriction.


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Gegevens


Uitgever
Presses universitaires de Louvain
Titel deel
Numéro 212
Auteur
Jean-François Vanhumbeeck,
Collectie
Thèses de l'École polytechnique de Louvain
Taal
Engels
BISAC Subject Heading
TEC000000 TECHNOLOGY & ENGINEERING
Onix Audience Codes
06 Professional and scholarly
CLIL (2013)
3069 TECHNIQUES ET SCIENCES APPLIQUEES
Voor het eerst gepubliceerd
2009
Type werk
Thesis

Paperback


Publicatie datum
01 januari 2009
ISBN-13
9782874631351
Omvang
Aantal pagina's hoofdinhoud : 280
Code
79255
Formaat
16 x 24 x 1,5 cm
Gewicht
450 grams
Aanbevolen verkoopprijs
23,00 €
ONIX XML
Version 2.1, Version 3

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Acknowledgements 3
General introduction 7
Scientific Production 9
1 State-of-the-art on Ti anodisation 11
1.1 General introduction to anodisation . . . . . . . . . . . . . . . 12
1.1.1 Definitions and concepts . . . . . . . . . . . . . . . . . . 12
1.1.2 Growth kinetics of anodic oxide films . . . . . . . . . . . 18
1.1.3 Breakdown of anodic oxide films . . . . . . . . . . . . . 31
1.2 The specific features of Ti anodisation . . . . . . . . . . . . . . 35
1.2.1 Influence of the semiconducting character of anodic TiO2 35
1.2.2 Crystallisation of TiO2 films . . . . . . . . . . . . . . . 40
1.2.3 Discussion of the validity of the breakdown models . . . 42
1.2.4 Influence of the processing conditions . . . . . . . . . . 43
1.2.5 Stability of anodic TiO2 films . . . . . . . . . . . . . . . 71
1.3 Growth stresses in anodic oxide films . . . . . . . . . . . . . . . 73
1.3.1 Stress measurements in anodic oxide films . . . . . . . . 73
1.3.2 State-of-the-art of stress measurements in TiO2 films . . 82
1.4 Characterisation of anodic oxide films . . . . . . . . . . . . . . 88
1.4.1 Thickness measurements . . . . . . . . . . . . . . . . . . 88
1.4.2 Morphological and functional characterisation . . . . . . 90
1.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
2 Experimental aspects 93
2.1 Stress measurements in thin films . . . . . . . . . . . . . . . . . 94
2.1.1 The Stoney equation . . . . . . . . . . . . . . . . . . . . 94
2.1.2 Methods for measuring curvatures . . . . . . . . . . . . 99
2.2 On the use of themulti-beam sensor . . . . . . . . . . . . . . . 104
2.2.1 Calibration equation for measurements in air . . . . . . 104
2.2.2 Calibration equation for measurements in a liquid . . . 116
5
6 CONTENTS
2.2.3 Calibration procedure . . . . . . . . . . . . . . . . . . . 124
2.2.4 Resolution of the sensor and optical perturbations . . . 127
2.3 Application to anodisation . . . . . . . . . . . . . . . . . . . . . 132
2.3.1 Description of the experimental cell and of the sample
preparation procedure . . . . . . . . . . . . . . . . . . . 132
2.3.2 Characterisation of the Ti thin film anodes . . . . . . . 139
2.3.3 Curvature-stress·thickness relationship for the specific case
of anodisation . . . . . . . . . . . . . . . . . . . . . . . . 149
2.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
3 Growth stress evolution in anodic TiO2. 153
3.1 Preliminary remarks . . . . . . . . . . . . . . . . . . . . . . . . 155
3.2 High-efficiency galvanostatic growth . . . . . . . . . . . . . . . 158
3.3 Growth stress transitions . . . . . . . . . . . . . . . . . . . . . 172
3.3.1 Transitions observed under galvanostatic growth conditions172
3.3.2 Transitions observed upon potentiostatic aging . . . . . 189
3.3.3 Discussion of the origin of the growth stress transitions 193
3.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
4 Electrostriction stresses 201
4.1 Introduction to electrostriction . . . . . . . . . . . . . . . . . . 202
4.2 Derivation of amodified constitutive equation . . . . . . . . . . 204
4.3 Experimental study . . . . . . . . . . . . . . . . . . . . . . . . . 207
4.4 Electrostriction stresses as a monitoring tool . . . . . . . . . . . 219
4.4.1 First series of experiments . . . . . . . . . . . . . . . . . 219
4.4.2 Second series of experiments: . . . . . . . . . . . . . . . 225
4.4.3 Common Discussion . . . . . . . . . . . . . . . . . . . . 232
4.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
5 Conductivity transitions in anodic TiO2 239
5.1 Growth kinetics of anodic TiO2 films . . . . . . . . . . . . . . . 240
5.2 Efficiency changes and cell voltage evolution . . . . . . . . . . . 240
5.3 Origin of the conductivity transitions . . . . . . . . . . . . . . . 251
5.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
General conclusions and perspectives 269