Corrosion Inhibition of Magnesium Alloys and Influence of Atmospheric Carbon Dioxide

216 Pages·2016·6.21 MB·English

Corrosion Inhibition of Magnesium Alloys and Influence of
Atmospheric Carbon Dioxide

THESIS

Presented in Partial Fulfillment of the Requirements for the Degree of Master of Science
in the Graduate School of The Ohio State University

By
Daniel Kaminski

Graduate Program in Materials Science and Engineering

The Ohio State University

2016

Master’s Examination Committee:
Rudy Buchheit, Advisor
Jerry Frankel
Copyright by
Daniel Kaminski
2016
Abstract
The widespread use of magnesium alloys as an engineering material is yet to be
realized due, in part, to poor corrosion resistance in condensing moisture environments.
Application of corrosion inhibitor compounds by way of coatings-based inhibitor systems
is one corrosion mitigation method that can be implemented to address this concern.
This work comprises a fundamental study of corrosion inhibitors for magnesium
alloys AZ31 and WE43. A broad array of corrosion inhibitors were examined at 1-100
mM concentration including transition metal oxyanions, group IVA through group VIIA
anions, as well as rare earth cations, and selected organic compounds.
Due to potent and rapid surface alkalization of magnesium alloys and the potential
application of inhibitors as functional pigment additives in organic coatings, it is of
concern whether atmospheric carbon dioxide absorbed within alkaline electrolytes could
interact with corrosion inhibitors in a favorable, negative, or neutral way. Reactive-
transport modeling of carbon dioxide gas absorption in such electrolytes was conducted
with respect to experimental conditions. From this, it was understood that equilibrium
concentration of dissolved inorganic carbon at experimentally observed pH values can be
realized in thin electrolyte layers upon time duration of several hours to days. Slow
absorption of carbon dioxide gas into alkaline aqueous solution of experimentally
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observed pH is primarily due to the rate limiting kinetics of carbon dioxide hydroxylation
at a given gas-liquid interface surface area and electrolyte volume.
To help develop an understanding of the interaction of corrosion inhibitors for
AZ31 and WE43 with ambient carbon dioxide, a novel closed-system test cell technique
was developed to decouple CO from the system. It was observed that ambient levels of
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CO play an important role in the corrosion of AZ31 and WE43 alloys and furthermore
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influences corrosion inhibitor effectiveness.
In the absence of corrosion inhibitors, experimental results showed that ambient
carbon dioxide acts to buffer the pH of the electrolyte in contact with either AZ31 or
WE43 during corrosion towards a lower pH than would develop if carbon dioxide was
absent. For AZ31, results showed that dissolved carbon dioxide affects the corrosion
morphology and surface films favorably and can lead to an approximately five times
decrease in corrosion rate. For WE43, dissolved ambient levels of CO slightly
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accelerated the corrosion rate and increased general surface corrosion compared to a
CO -free environment.
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In the presence of corrosion inhibitors, the critical concentration for inhibition by
the tested compounds was much better resolved by use of the novel closed-system test
cells compared to conventional methods. This proved to be an unanticipated advantage
of the novel test cell’s use. Side-by-side comparison of known, effective, corrosion
inhibitors in the presence and absence of ambient levels of CO indicated mostly neutral
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or negative interaction of test inhibitors with dissolved CO , although exceptions were
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documented. Additionally, film formation and corrosion inhibition was noted for 10mM
and 100mM sodium metavanadate on both alloys and all conditions tested. Significant
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corrosion inhibition was noted on AZ31 by sodium tungstate, particularly, in the absence
of ambient carbon dioxide. The information generated by this work can be utilized in the
future development of effective coatings-based corrosion inhibitors for magnesium
alloys.

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Dedicated to my grandfather, Ted Ignasiak.

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Acknowledgments
I would like to thank Dr. Rudy Buchheit of The Ohio State University for his
guidance and enthusiasm that ultimately allowed this work to be completed. I would also
like to thank Dr. Joe Labukas of United States Army Research Laboratory (US ARL) for
his support throughout the duration of this study.
I would like to extend gratitude for conversations pertaining to this study with Dr.
Jerry Frankel, Director of the Fontana Corrosion Center at The Ohio State University. In
addition, I owe special thanks to Dr. Ben Church and Dr. Steve Hardcastle at the
University of Wisconsin-Milwaukee for their support and use of key instrumentation that
made this work possible. Additionally, fellow graduate school colleagues at the Fontana
Corrosion Center including Jermain Onye, Dr. Santi Fajardo, Dr. Alejandro Samaniego,
Will Weimer, Kerrie Holguin, Sara Cantanwine, Jiheon Jun, Dr. Jinwook Seong, and Ben
Hanna provided valuable support.
Lastly, I would like to thank my family and fiancée, Annie Hochschild, for their
continuous encouragement. I could not have succeeded without their confidence during
best of times and difficult times. Above all, I would like to thank my grandfather for
being a pinnacle example of unwavering determination and hard work which I will never
forget and forever aim to reach.
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Vita

2006 …………………...…………………Technical Diploma (Automotive Maintenance)
Waukesha County Technical College

2007……………………………..…….......Technical Diploma (Machine Tool Operation)
Waukesha County Technical College

2012……………………………………..…B.S.E. Materials Engineering, B.S. Chemistry
University of Wisconsin-Milwaukee

2013 – Present ………………………………….M.S. Materials Science and Engineering
The Ohio State University

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PUBLICATIONS
1. B. Church, D. Kaminski, J. Jiang. “Corrosion of aluminum electrodes in aqueous
slurries for lithium-ion batteries” Journal of Materials Science (2014) 49: 3234-3241

Fields of Study

Major Field:
 Materials Science and Engineering

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Table of Contents

Abstract…………………………………………………………………………..…….....ii
Acknowledgments……………………………………………………….………….……vi
Vita………………………………………………………………………………….…...vii
List of Tables……………………………………………………………………………xiv
List of Figures……….…………………………………………………………………...xv
Chapter 1 Introduction…………………………...…................…………………....1
1.1 Research Goals……..…………………………………………………………..…3
1.2 Metallurgy of Magnesium Alloys AZ31 and WE43……………………..……..…4
1.3 Corrosion Theory of Magnesium Alloys…………………..……………………...5
1.3.1 Negative Difference Effect (NDE)……………………………………………..…7
1.4 Corrosion Inhibitor Theory…………………..…………………………………....8
1.4.1 Adsorption Inhibitors……………………………………………………………...8
1.4.2 Film Formation Inhibitors.…………………...………………………………...….9
1.4.3 Electrochemical Description of Corrosion Inhibition………........................……10
1.5 CO -Mg-Inhibitor Interactions……………...……………………….………..….11
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1.6 Figures………….....…………………………………..……………………...…..13
1.7 References………………………………………………..………………………16
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