Passivity; the Enabler of Our Reactive Metals-Based Civilization



MON, 10/20/2014 - 4:00PM TO 5:00PM
Fall 2014 Colloquium Series

For more than forty years, the conditions for the existence of the passive state, and hence for the existence of our metals-based civilization, which is based upon the use of the reactive metals (Al, Cr, Fe, Ni, etc) to build machines, have been described in terms of equilibrium thermodynamics in the form of Pourbaix diagrams.  These diagrams plot equilibrium potential versus pH relationships for various reactions (e.g., Fe/Fe3O4, Fe/Fe2+, Fe3O4/Fe2+) to define regions of stability or predominance.  However, Pourbaix diagrams provide an equilibrium view of passivity, whereas passive films are non-equilibrium structures, whose existence depends upon an appropriate relationship between the rate of formation and the rate of destruction.  Accordingly, a more accurate and realistic description of the phenomena of passivity and passivity breakdown must be found in the field of electrochemical kinetics.  It is this kinetic theory for depassivation (loss of passivity) that is presented in this paper and which has led to the development of Kinetic Stability Diagrams.  KSDs are kinetic alternatives to the classical, thermodynamic equilibrium diagrams and provide a much more accurate view of passivity in highly acidic environments where the utility of Pourbaix diagrams is limited.  It is shown that the kinetic theory for depassivation not only accounts for transpassive dissolution, acid depassivation, flow-assisted corrosion, and fretting corrosion, and other “localized corrosion processes”, but it also led to the discovery of a new form of depassivation, which is termed “resistive depassivation”.  When applied to microscopic regions on a metal surface, at which cation vacancies that are generated at the film/solution interface by the absorption of chloride ion into surface oxygen vacancies condense at the metal/film interface, and hence cause cessation of the growth of the barrier layer into the metal, “depassivation” theory provides a natural account of blister formation and subsequent passivity breakdown.  This presentation will present the theory of passivity breakdown according to the point defect model and will show that the theory accounts essentially for all that is known about this important phenomenon.

About the Speaker:

Born in Thames, New Zealand, December 7 1943, Professor Macdonald gained his BSc and MSc degrees in Chemistry at the University of Auckland, New Zealand, and his Ph.D. degree in Chemistry from the University of Calgary in Canada.  He has served as Assistant Research Officer at Atomic Energy of Canada Ltd., Lecturer in Chemistry at Victoria University of Wellington, New Zealand, Senior Research Associate at Alberta Sulfur Research, Honorary Associate Professor at the Chemistry Department of the University of Calgary, Director and Professor of the Fontana Corrosion Center, Ohio State University, Vice President, Physical Sciences Division, SRI International, Menlo Park, California and has been Professor and later Distinguished Professor of Materials Science and Engineering at Pennsylvania State University since 1991.  On December 31, 2012, Professor Macdonald retired from Penn State and accepted Emeritus status at the university.  He then moved to California become Professor in Residence with a joint appointment between the Departments of Nuclear Engineering and Materials Science and Engineering at the University of California at Berkeley.

Professor Macdonald has received numerous awards and honors, including the 1991 Carl Wagner Memorial Award from The Electrochemical Society; the 1992 Willis Rodney Whitney Award from The National Association of Corrosion Engineers for “contributions to the science of corrosion”; the W. B. Lewis Memorial Lecture from Atomic Energy of Canada, Ltd., for his “contributions to the development of nuclear power in the service of mankind”; the H. H. Uhlig Award from The Electrochemical Society; the U. R. Evans Award from The Institute of Corrosion, UK; the 20th Khwarizmi International Award in fundamental science; and the Wilson Research and Teaching Awards of the Pennsylvania State University.  He is an elected fellow of NACE-International; The Electrochemical Society; the Royal Society of Canada; the Royal Society of New Zealand; ASM International; the World Innovation Foundation; the Institute of Corrosion (UK); and the International Society of Electrochemistry.  From 1993 to 1997 he was a member of the US Air Force Science Advisory Board with the protocol rank of Lieutenant General.  He was awarded the US Air Force Medal for Meritorious Civilian Service in 1997.  Dr. Macdonald was a Trustee of ASM International and has recently (2011) been inducted Doctuer Honoris Causa by INSA-Lyon, Lyon, France.  He was a recent (2011) recipient of the Lee Hsun Research Award of the Chinese Academy of Sciences.  More recently (2012), he received the Faraday Memorial Trust Gold Medal from the Central Electrochemical Research Institute in Karaikudi, India, for his work in electrochemistry and in particular on the phenomenon of passivity and passivity breakdown, and in 2013 he was awarded the Gibbs Award for his ground-breaking work on the properties of aqueous solutions at high temperatures [for example, he is the first and only person to measure the pH of an aqueous solution at supercritical temperatures (T > 374.15 oC), with the measurements being made at temperatures up to 528 oC].  In September 2014, he was awarded the Frumkin Memorial Medal by the International Society of Electrochemistry primarily for his work on passivity.


Dr. Macdonald has published more than 900 papers in peer-reviewed scientific journals, books, and conference proceedings, plus four books, one of which ("Transient Techniques in Electrochemistry") established an important area of electrochemical research, and has 11 patents and numerous invention disclosures credited to his name.