adsorption - taking up one substance at the surface of another; tendency of all solids to condense on their
surfaces a layer of any gas or solute that contacts such solids.
aeration cell (oxygen cell) - electrolytic cell in which a difference in oxygen concentration at the electrodes
exists, producing corrosion.
amphoterics - materials subject to attack by both acid and alkaline environments; include aluminum, zinc, and
lead (commonly used in construction).
anaerobic - free of air or uncombined oxygen; anaerobic bacteria are those that do not use oxygen in their
anion - a negatively charged ion that migrates toward the anode under influence of a potential gradient.
*anode - electrode at which oxidation of its surface or some component of the solution is occurring
*bell hole - excavation to expose a buried structure.
cathode - electrode at which reduction of its surface or some component of the solution is occurring
cathodic corrosion - corrosion resulting from a structure's cathodic condition, usually caused by the reaction
of alkaline products of electrolysis with an amphoteric metal.
*cathodic protection - technique to prevent metal surface corrosion by making that surface the cathode
of an electrochemical cell.
cation - positively charged ion of an electrolyte that migrates toward the cathode under the influence of a
concentration cell - electrolytic cell in which a difference in electrolyte concentration exists between anode
and cathode, producing corrosion.
*continuity bond - metallic connection that provides electrical continuity.
*corrosion - deterioration of a material, usually a metal, because of a reaction with its environment.
* current density - current per unit area.
*electrical isolation - condition of being electrically separated from other metallic structures or the
*electrosmotic effect - passage of a charged particle through a membrane under the influence of a voltage;
soil can act as the membrane.
*electrode potential - potential of an electrode as measured against a reference electrode. The electrode
potential includes no loss of potential in the solution due to current passing to or from the electrodes (that
is, it represents the reversible work required to move a unit charged from the electrode surface through
the solution to the reference electrode).
electrolyte - chemical substance or mixture, usually liquid, containing ions that migrate in an electric field;
examples are soil and seawater.
electromotive force series (EMF series) - list of elements arranged according to their standard electrode
potentials; the sign is positive for elements with potentials cathodic to hydrogen and negative for those
elements with potentials anodic to hydrogen.
*foreign structure - any structure not intended to be part of the system of interest.
*galvanic anode - metal that, because of its relative position in the galvanic series, provides sacrificial
protection in the galvanic series when coupled in an electrolyte. These anodes are the current source in
one type of cathodic protection.
galvanic cell - corrosion cell in which anode and cathode are dissimilar conductors, producing corrosion
because of their innate difference in potential.
*galvanic series - list of metals and alloys arranged according to their relative potentials in a given
*holiday - coating discontinuity that exposes the metal surface to the environment.
hydrogen overvoltage - voltage characteristic for each metal-environmental combination above which
hydrogen gas is liberated.
*Definition is from NACE Standard RP-01.