Real solid surfaces
The properties of a material can vary significantly between the surface of the material and the bulk
region of the material. The differences seen can include energy variations, microstructural variations,
chemical variations and material strength variations.
The energy associated with atoms at the surface of a material differs significantly from the energy
associated with atoms in the material bulk. This is because atoms in the bulk of the material form bonds
with other atoms on all sides. Surface atoms, on the other hand, only have neighboring atoms on one
side.
Variations can have both negative effects (e.g. corrosion) on the overall utility of the material and
positive effects (e.g. surface hardening). Corrosion involves the degredation of a material as it interacts
with its environment, and is one of the major means by which metals deteriorate. As a major cause of
the breakdown of metal components, corrosion is often a primary factor in maintenance costs. The
process of corrosion is typically electrochemical in nature, and includes both oxidation and reduction. If
two metals are in contact in a given environment (e.g. seawater), one of the metals will be either more
noble or more active than the other. With the electrolyte (seawater) acting as a conduit for the flow of
ions, the active metal will provide electrons to the noble metal. An example of corrosion is shown
below.