Doctor of Philosophy
Intelligent Polymer Research Institute
Jamali, Sina S., Developing scanning electrochemical microscopy method for studying bio-corrosion of magnesium alloys and protective surface treatments, Doctor of Philosophy thesis, Intelligent Polymer Research Institute, University of Wollongong, 2016. http://ro.uow.edu.au/theses/4674
Ways of implementing scanning electrochemical microscope (SECM) for studying corrosion and degradation of Mg in simulated biological solution has been studied in this thesis. SECM was first employed in more conventional mode of operation, namely feedback mode, to provide a baseline for comparison with other imaging modes of SECM. Four modes of SECM were in total exploited including feedback, AC, potentiometric and surface generation/tip collection modes. In feedback and AC modes electro-activity and insulating properties of surface were examined at a local scale. In the AC mode variation in conductivity of solution that was caused by corrosion reactions was also examined. A solid-state pH sensing microelectrode based of iridium/iridium oxide was fabricated and used in potentiometric mode of SECM for measuring the near surface pH during corrosion of Mg.
A new method of sensing H2 at a solid surface has been introduced herein which is implemented to evaluate the H2 evolution during corrosion of Mg as a tool for acquiring mechanistic information about the corrosion process as well as measuring H2 evolution as an indicator of corrosion rate. Also a new Mg alloy named AZNd was specifically designed by Boston Scientific, funding body of this research, for use in fabrication of biodegradable coronary stents. Corrosion of AZNd in buffered media as well as effectives of surface treatments for protection against corrosion was investigated using SECM and other electrochemical and analytical methods.
Chapter 4 and 5 of this thesis were case studies showcasing capabilities of SECM as a powerful characterization tool for studying corrosion of Mg and protective properties of surface treatments. In chapter 4 effect of protein (i.e. albumin) on the corrosion of Mg in buffered media was investigated and it was shown that presence of protein may reduce the corrosion rate in the early stages of contact with corrosive media via formation of a barrier layer on the surface of Mg. However in the long term presence of protein may be detrimental due to formation of inhomogeneous surface layer and/or chelation of metal ions thus promoting localized corrosion. In chapter 5 surface treatments based on praseodymium conversion coating and a biodegradable conducting polymer were applied on AZNd and corrosion protection afforded by these surface treatments were investigated.