Electrochemical and Analytical Studies of Corroding and Reactive Surfaces

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Corrosion of materials is a major industrial and environmental issue with safety, environmental and major cost issues. The susceptibility of industrial materials to corrosion depends on a mixture of chemical, metallurgical and environmental factors. Localized corrosion (pitting, crevice corrosion, stress corrosion cracking) is particularly insidious since, while very little corrosion occurs, it is highly focussed at chemically and metallurgically vulnerable locations and can lead rapidly to structural failures. This makes it essential to understand both the corrosion mechanism and how the properties of the material influence damage distribution. The study of such processes requires a multidisciplinary approach involving chemical, metallurgical, physical and engineering techniques. The general goals of this research are to investigate the features that dictate susceptibility to localized corrosion, to determine how corrosion damage would be distributed, and to investigate the processes that might eventually lead to repassivation and the prevention of corrosion. Experimental techniques ranging from those able to resolve the mechanistic details of surface reactions at the atomic level to those able to determine the extent and location of materials damage over the scale of nanometers to centimeters will be applied. These techniques will range from electrochemical and surface analytical to analytical and microscopic. With these goals in mind the following areas will be studied. (a) The properties of the oxide films on which metals rely for passivity will be investigated with an emphasis on nickel-chromium-molybdenum superalloys. A combination of electrochemical, X-ray photoelectron and Auger spectroscopic, and time-of flight secondary ion mass spectrometric techniques will be used. (b) The factors influencing the evolution of crevice corrosion damage on Ni superalloys will be studied using Raman spectroscopy and confocal laser scanning microscopy. (c) The development and application of microscopic techniques (especially electron backscatter diffraction and atomic probe field-ion microscopy) will be undertaken to characterize corrosion controlling physical and chemical processes. (d) Key properties of oxide films and their metal substrates which are unavailable by other techniques will be determined using an in-situ combination of electrochemistry and neutron reflectometry. These properties include the dielectric constant, absolute film thickness and hydrogen content. Studies will concentrate on titanium and zirconium, the latter being an important in-reactor nuclear material. (d) The corrosion mechanisms occurring on gas transmission pipelines in sulphide-containing aqueous environments will be studied electrochemically using in-situ Raman spectroscopy. The primary goal is to determine how film properties change with the various pipeline exposure conditions.