Corrosion is a branch of materials research that is, by its nature, “schmutzy” (dirty). It has a reputation as an unglamorous subject and certainly suffers from an image problem in the materials community: the guest editors would like to have a dollar for every time we sat down and discussed “How can we make corrosion sound positive?” Solving corrosion problems requires an understanding of corrosion mechanisms, and corrosion mechanisms are infinitely subtle and interesting. Corrosion processes can often encompass concepts from a variety of disciplines, including thermodynamics, surface science, electrochemistry, physical metallurgy, and solid-state and statistical physics. While corrosion of metals is the subject of this issue of MRS Bulletin, ceramics, polymers, and geological materials are all greatly affected by corrosion.
Corrosion of metals is an electrochemical process, composed of anodic (metal oxidation) and cathodic (reduction) reactions occurring on a surface. The rates of these reactions are measured as current densities (in units of A m−2). On a single piece of metal, the anodic and cathodic current densities can vary arbitrarily from point to point, as long as the total anodic and cathodic currents are equal. This variation, which is associated with local differences in pH, surface composition, or defects in a surface film, leads to various localized phenomena, such as pitting and stress-corrosion cracking, and also to intriguing oscillatory dynamics.