2007 W.R. Whitney Award Lecture: Molecular In Situ Studies of Atmospheric Corrosion

Atmospheric corrosion involves chemical, electrochemical, and physical processes in three phases (solid, liquid, and gas) and two interfaces (solid/liquid and liquid/gas). Because of inherent experimental and conceptual difficulties, scientific efforts to characterize this highly complex interfacial regime came relatively late into the field. With the access and development of surface and interface-sensitive analytical techniques, it has lately become possible to perform molecular in situ analyses of the interfaces involved in atmospheric corrosion. This Whitney Award paper presents some highlights from our fundamental research in atmospheric corrosion, including results from the most recent efforts in our research group to provide a molecular picture of the interfacial regime that governs atmospheric corrosion. Using copper or zinc as substrates, and formic acid (HCOOH), acetic acid (CH₃COOH), acetaldehyde (CH₃CHO) or propionic acid (C₂H₅COOH) as corrosion stimulators in the humidity-containing atmosphere, results will be presented with particular emphasis on probing the metal oxide/water interface (by infrared reflection absorption spectroscopy combined with the quartz crystal microbalance and sum frequency generation) and the water/gas interface (by sum frequency generation), respectively. Theoretical calculations are also presented, which aid in interpreting the in situ spectroscopy data. The multi-analytical effort provides evidence of the importance of the solid/liquid interface over the liquid/gas interface. In all, the results can be interpreted to follow the conceptual framework of GILDES, a general model for atmospheric corrosion. Taking copper as an example, identified surface species and reaction pathways include proton- and carboxylate-induced dissolution of the cuprous ion, followed either by formation and precipitation of cuprous oxide or by oxidation of cuprous to cupric ions and subsequent formation and precipitation of copper carboxylate.