Surface Chemistry and Corrosion Studies of Zn–Al and Zn–Mg–Al Alloy Coatings

149 Pages·2013·7.17 MB·English

by  Katharina Pohl

Surface Chemistry and Corrosion Studies of Zn–Al
and Zn–Mg–Al Alloy Coatings

PhD Thesis
Dr. rer. nat.

Faculty of Science
at the
University of Paderborn

submitted by
Katharina Pohl
from Nürtingen

Paderborn, 2013

Defence: 30.04.2013
First referee: Prof. Dr.–Ing. G. Grundmeier
Second referee: Prof. Dr. M. Tiemann

Ich versichere, dass ich diese Arbeit eigenständig verfasst und keine anderen als die
angegebenen Quellen und Hilfsmittel benutzt, sowie Zitate kenntlich gemacht habe.

Index
Acknowledgement ................................................................................................................. v
Abstract................................................................................................................................. vi
1 State of research and motivation .............................................................1
2 Fundamentals..........................................................................................4
2.1 Corrosion of zinc and zinc alloy coated steel ................................................................ 4
2.1.1 General corrosion mechanism under atmospheric conditions ............................. 4
2.1.2 General corrosion mechanism under full immersion ............................................ 9
2.1.3 In–situ Raman spectroscopic analysis of zinc corrosion products ...................... 13
2.2 Molecular adhesion on aluminum and zinc oxides .................................................... 14
2.2.1 Adsorption of monolayers ................................................................................... 15
2.2.2 Understanding of interfacial bond formation ..................................................... 18
2.3 Fundamentals of adhesion and de–adhesion of polymers on oxide covered metals 19
2.3.1 Wet de–adhesion ................................................................................................ 20
2.3.2 Corrosive de–adhesion of polymers on zinc substrates ...................................... 21
2.4 Raman spectroscopic analysis of polymer/metal interface ....................................... 22
3 Theoretical background of applied analytical techniques ........................ 25
3.1 Spectroscopic techniques ........................................................................................... 25
3.1.1 Raman spectroscopy ........................................................................................... 25
3.1.2 Infrared spectroscopy .......................................................................................... 27
3.1.3 X–ray photoelectron spectroscopy (XPS) ............................................................ 29
3.2 Electrochemical techniques ........................................................................................ 30
3.2.1 Scanning Kelvin probe (SKP) ................................................................................ 31
3.2.2 Cyclic voltammetry (CV) ...................................................................................... 32
3.2.3 Scanning Kelvin probe force microscopy (SKPFM) .............................................. 33
3.3 Microscopic techniques .............................................................................................. 35
3.3.1 Scanning electron microscopy (SEM) .................................................................. 35
3.3.2 Atomic force microscopy (AFM) .......................................................................... 36

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Index

3.4 Contact angle measurement ...................................................................................... 37
4 In–situ corrosion analysis of zinc alloy coated steel ................................ 39
4.1 Experimental .............................................................................................................. 39
4.1.1 Materials and sample preparation ..................................................................... 39
4.1.2 Surface Analysis................................................................................................... 40
4.1.3 In–situ Raman spectroscopy ............................................................................... 40
4.2 Surface morphology and microstructure ................................................................... 41
4.3 Bulk composition of the alloy ..................................................................................... 44
4.4 Electronic surface properties ...................................................................................... 47
4.5 Corrosion processes and mechanisms at different pH ............................................... 50
4.6 Conclusions ................................................................................................................. 58
5 In–situ corrosion analysis of zinc magnesium alloy coated steel .............. 59
5.1 Experimental .............................................................................................................. 59
5.1.1 Materials and sample preparation ..................................................................... 59
5.1.2 Surface Analysis................................................................................................... 60
5.1.3 In–situ Raman spectroscopy ............................................................................... 60
5.2 Surface morphology and bulk composition of the alloy ............................................. 60
5.3 Corrosion process and mechanisms at different pH .................................................. 63
5.4 Conclusions ................................................................................................................. 70
6 In–situ corrosion analysis of oxide covered iron/ zinc alloy cut edges ..... 72
6.1 Experimental .............................................................................................................. 72
6.1.1 Materials and sample preparation ..................................................................... 72
6.1.2 Surface Analysis................................................................................................... 72
6.1.3 In–situ Raman spectroscopy ............................................................................... 73
6.2 Cut edge morphology and chemistry ......................................................................... 73
6.3 Corrosion process and mechanism ............................................................................. 75
6.4 Conclusions ................................................................................................................. 79

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Index

7 Adsorption and stability of self–assembled organophosphonic acid
monolayers on plasma modified Zn–Mg–Al alloy surfaces ............................ 80
7.1 Experimental .............................................................................................................. 80
7.1.1 Materials and Sample Preparation ..................................................................... 80
7.1.2 Plasma Surface Chemistry ................................................................................... 81
7.1.3 Adsorption and Self–Organization of Organic Acids ........................................... 81
7.1.4 Surface Analysis................................................................................................... 81
7.2 Plasma surface chemistry........................................................................................... 83
7.3 Adsorption and self–organization of organic acids ................................................... 91
7.4 Stability of organic acids on Zn–Mg–Al alloys ........................................................... 96
7.5 Blocking of surface sites oxide covered on Zn–Mg–Al alloys by ODPA SAMs ............ 98
7.6 Conclusions ............................................................................................................... 100
8 Surface chemistry and adhesive properties of plasma modified Zn–Mg–Al
alloy coatings ............................................................................................ 101
8.1 Experimental ............................................................................................................ 101
8.1.1 Modification of the surface by plasma treatment ............................................ 101
8.1.2 Application of adhesion promoter and the model polymer coating ................. 102
8.1.3 Characterization of the surface chemistry after plasma treatments and APPA
adsorption ......................................................................................................... 102
8.1.4 Peel–test measurements ................................................................................... 103
8.2 Characterization of the plasma modified samples .................................................. 103
8.3 Adsorption of APPA on the plasma modified sample surface .................................. 108
8.4 The effect of plasma treatments and APPA adsorption on the adhesion of epoxy
amine coating on Zn–Mg–Al alloy surfaces ............................................................. 113
8.5 Conclusions ............................................................................................................... 115
9 Overall conclusions and outlook .......................................................... 116
References ................................................................................................ 119

iii
Index

Abbreviations and symbols ....................................................................... 127
List of Figures ............................................................................................ 129
List of Tables ............................................................................................. 134
List of Publications .................................................................................... 135
Curriculum Vitae ....................................................................................... 137

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