Introduction

Corrosion of metals is understood to be degradation of metals by chemical surface reactions with aggressive components of the environment. The metals may be structural materials such as steel reinforcments in concrete structures, or steel cables of suspension bridges; or they may be functional materials such as dental alloys, or copper leads for printed circuits. A typical example of corrosion is rusting of iron: Rust, a mixture of oxides and hydroxides of iron, is the product of iron surface atoms reacting with oxygen and water, both present in the surrounding moist atmosphere, or else present in a surrounding aqueous solution. Corrosion thus differs from wear, which is degradation caused by mechanical friction, as for instance abrasion. The primary products of wear are metallic particles, whereas products of corrosion always are non-metallic chemical species either solid or dissolved.