Plasma-material interaction and electrode degradation in high voltage ignition discharges [Elektronische Ressource] / von Nicolas Jeanvoine

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• Publié par: universitat_des_saarlandes
• Publié le: 01 janvier 2009
• Nombre de lectures: 65
• Langue: English
• Poids de l'ouvrage: 7 Mo

Extrait

PLASMA –MATERIAL INTERACTION
AND ELECTRODE DEGRADATION
IN HIGH VOLTAGE IGNITION DISCHARGES



DISSERTATION
zur Erlangung des Grades
des Doktors der Ingenieurwissenschaften
der Naturwissenschaftlich-Technischen Fakultät III
Chemie, Pharmazie, Bio- und Werkstoffwissenschaften
der Universität des Saarlandes



von
NICOLAS JEANVOINE



Saarbrücken
2009


















Tag des Kolloquiums:
Dekan: Prof. Dr.-Ing. Stefan Diebels
Berichterstatter: Prof. Dr.-Ing. Frank Mücklich
Prof. Dr.-Ing. Frank Berger



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Plasma seems to have the kinds of properties
one would like for life. It’s somewhat like
liquid water - unpredictable and thus able to
behave in an enormously complex fashion. It
could probably carry as much information as
DNA does. It has at least the potential for
organizing itself in interesting ways.

Freeman John Dyson


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Contents


Contents
Abstract ............................................................................................................................ xi
Kurzfassung .................... xii
Symbols and Abbreviations xiii
1 Introduction 1
2 Theoretical Background 5
2.1 Ignition Discharge Characteristics ........................................................................... 5
2.1.1 Breakdown Phase ........................................ 6
2.1.2 Breakdown to Arc Transition .................. 13
2.1.3 Arc and Glow Discharges ........................................................................................ 14
2.2 Cathode Processes ................................................................................................... 18
2.2.1 Cathode Layer ........... 18
2.2.2 Arc Discharge and Cathode Spot ............ 20
2.3 Energy Balance in Ignition Discharges ................................................................... 25
2.3.1 Energy Transferred to the Plasma ........... 25
2.3.2 Energy Balance at the Cathode Spot ...... 27
2.3.3 Energy Balance at the Cathode in Glow Discharges ............................................ 30
2.4 Erosion Mechanisms ................................................................ 30
2.4.1 Particle Ejection ........................................ 30
2.4.2 Vaporization .............. 32
2.4.3 Sputtering ................................................................................................................... 33
2.4.4 Oxide Layer Removal............................... 34
2.4.5 Plasma Assisted Oxidation ...................... 35
3 Experimental 37
3.1 Generation of Ignition Discharges .......................................................................... 37
3.1.1 Pressure Chamber ..................................... 37
3.1.2 Ignition System.......... 38
3.1.3 Oscilloscope Measurements .................................................................................... 39
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Contents
3.2 Preparation of Multilayered Electrodes .................................................................. 40
3.3 Electrode Surface Characterization ........ 40
3.3.1 White Light Interferometry ...................................................................................... 40
3.3.2 FIB/SEM Dual Beam Techniques .......... 42
4 Ignition Discharge Mode Analysis 45
4.1 Determination of the Arc and Glow Phase Fractions ............................................. 45
4.1.1 Introduction ................................................................................ 45
4.1.2 Measurement Methods ............................................................. 46
4.2 Results and Discussion ............................................................ 49
4.2.1 Arc Fraction Results ................................................................. 49
4.2.2 Plasma-Assisted Oxidation of Ag Cathode in Air ................................................ 51
4.2.3 The Arc to Glow Transition ..................................................... 54
4.3 Summary .................................................................................. 58
5 Microstructure Characterization of Craters 61
5.1 State of The Art ........................................................................................................ 61
5.2 Monitoring the Depth of Microstructure Modification ........... 63
5.2.1 Bulk Electrodes ......................................................................... 63
5.2.2 Immiscible Multilayer System ................................................ 64
5.2.3 Miscible Multilayer Systems ................................................... 65
5.2.4 Comparison between Craters on Bulk and Multilayered Electrodes ................. 70
5.3 Microstructure of Craters Produced at Different Pressures ................................... 73
5.3.1 Surface Characterization .......................................................................................... 73
5.3.2 Crater Cross Section Analysis ................. 74
5.3.3 Determination of the Molten Pool Volume ........................... 76
5.3.4 3D Reconstruction of the Molten Pool ................................................................... 77
5.3.5 Cross Section EBSD ................................. 79
5.4 Discussion ................................................................................ 82
5.4.1 Low and High Pressure Craters ............................................... 82
5.4.2 Crater Formation Mechanisms ................ 83
5.4.3 Displaced Molten Volume ....................................................................................... 86
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Contents

5.5 Summary .................................................................................................................. 87
6 Thermal Analysis of the Crater Formation 91
6.1 Analytical Models .................................................................................................... 92
6.1.1 Heat Conduction in a Semi-Infinite Electrode ...................... 92
6.1.2 Semi-Continuous Point Source ............... 93
6.1.3 Semi-Continuous Disk Source ................................................................................ 94
6.2 FEM Thermal Simulation ........................................................................................ 97
6.2.1 Description of the Physical Model.......................................... 98
6.2.2 Geometry and Boundary Conditions .................................... 103
6.2.3 Simulation Procedure ............................................................. 104
6.2.4 Results in Bulk Pt .................................... 105
6.2.5 Results in Pt/Ni Multilayer .................................................................................... 113
6.3 Discussion .............................................. 117
6.3.1 Comparison of the Results with Others Works ................................................... 117
6.3.2 Comparison with Arc Craters in Electrical Contacts ......... 119
6.3.3 Current-Time Characteristic of the Ignition Discharge ..................................... 120
6.3.4 Correlation between the Discharge Characteristic and the Crater Formation. 121
6.3.5 Effects of the Inductive Arc Discharge ................................ 122
6.3.6 Correlation with Cathode Wear ............................................ 124
6.4 Summary ................................................................................ 126
7 Conclusions and Outlook 129
References 135
Appendices 146
A Refractory and Non-Refractory Cathodes ............................................................. 146
B Fitting of the Electron Emission Current Density ................. 147
C Influence of the Simulated Region Size .................................. 148
D Determination of U and E .................................................................................... 149 i s
E Properties of Platinum Cathodes ........... 150

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Acknowledgments

Acknowledgments
I would like to express my gratitude to all the persons who supported my work and
encouraged me during this Ph.D. thesis:
 Prof. Dr. Frank Mücklich (Saarland University) for the opportunity to work under his
supervision in a very interesting research field, his scientific support and personal
advice which greatly contributed to the completion of this work;
 Prof. Dr. Frank Berger (TU Ilmenau) for the acceptance of the co-refereeing of this
thesis and the interesting discussions about electric arcs;
 All the industrial and academic partners of the project “Elektroerosion” Nr. 03X3500H
supported by the German Federal Ministry of Education and Research (BMBF) for the
efficient collaboration and the interesting discussions: Dr. Jürgen Oberle, Simone Baus,
Dr. Jochen Rager (Robert Bosch GmbH), Dr. Andreas Krätzschmar (Siemens AG),
Prof. Dr. David Lupton, Dr. Tanja Eckardt (W.C. Heraeus GmbH), Dr. Bernd Kempf
(Umicore AG & Co. KG), Prof. Dr. Frank Berger, Meik