Localized Corrosion Phenomena

Richard Alkire, Paul Kenis

An important consideration in the production of materials for industrial applications is the design lifetime of the material. Corrosion has been estimated to be responsible for approximately half of all industrial equipment failure. It is essential to understand the mechanism for failure, and then to design around it. Clearly, the design principles in this field are different from those used in designing products; success in corrosion engineering is achieved when nothing happens. The field of corrosion encompasses a myriad of interconnected phenomena that span a broad range of length and time scales, varying from micro-scale processes occurring at the metal/solution interface to the macro-scale events which directly lead to material failure. One of the most dangerous forms of corrosion is pitting corrosion, in which highly localized dissolution events that initiate at defects in the metal surface proceed much faster than corrosion associated with the passive metal surface. Improved understanding of pitting processes are necessary to increase the efficiency of corrosion failure prediction, and to allow better methods of providing corrosion protection to be developed, such as the design of new metal alloys and corrosion inhibitors.

images and inclusion dissolution graph

One of the major focuses of the corrosion research in Professor Alkire's laboratory is to identify and characterize critical parameters that are linked to the stability of corrosion pits. The leading theories which postulate the existence of critical parameters for pitting indicate that species in the local chemistry are among the dominant factors in pit stability. The research seeks to elucidate the role of such critical factors, using a complementary strategy of experimental investigation and computational simulation. Current research is focussed on stainless steel (arguably the most industrially significant metal alloy in current use) and pure nickel metal (a model system in which corrosion event interactions can be studied in controlled image and photo of micto electrodeenvironment). One of the main techniques used to study isolated events on metal alloys is a microelectrochemical cell apparatus, wherein a single sulfide inclusion on the stainless steel surface (average dimension: 10mm x 30mm x 15mm) may be isolated within a glass microcapillary fitted with electrical contacts. Another technique is a laser-initiation technique, which can be used to control the precise time and location of pit initiation. The laser-initiation technique cam be used to create arrays of corrosion pits as well as single isolated pits.