GLOSSARY OF CORROSION TERMS

Active—a free corroding condition.
Aluminizing—a process for impregnating a metal's surface with aluminum to provide protection against oxidation and corrosion.
Anchor Pattern (Surface Profile)—the shape and amplitude of the profile of blast-cleaned or grooved steel, which influences the bond between metallic or paint films and the substrate.
Anion—negatively charged ions that migrate toward the anode of a galvanic cell.
Anode-the electrode at which oxidation of the surface or some com­ponent of the solution is occurring.
Anode Polarization—the difference between the potential of an anode passing current and the steady-state or equilibrium potential of the electrode with the same electrode reaction.
Anodic Inhibitor—a chemical constituent that reduces the rate of anodic or oxidation reaction.
Anodic Metallic Coating—a special coating usually comprised, either en­tirely or in part, of an anodic metal, which is electrically positive to the substrate to which it is applied.
Anodic Protection—a technique for reducing corrosion of a metal surface via passing sufficient anodic current to it to cause its electrode potential to enter into the passive state.
Anodizing—the formation of a hard, corrosion-resistant oxide film on metals via anodic oxidation of the metal in an electrolytic solution.
Base Potential—the potential toward the negative end of a scale of electrode potentials.
Blast Peening-a treatment for relieving tensile stress via inducing beneficial compressive stress in the surface by kinetic energy of rounded abrasive particles.
Breakaway Corrosion—a sudden increase in corrosion rate, particularly under conditions of high-temperature dry oxidation.
Cathode—the electrode of an electrolytic cell where reduction takes place. During corrosion, this is the area at which metal ions do not enter the solu­tion. During cathodic reactions, cations take up electrons and discharge them, hence reducing oxygen. That is, there is a reduction from a higher to a lower state of valency.
Cathodic Inhibitor-a chemical constituent that reduces the rate of cathodic reaction.
Cathodic Protection-a means of reducing the corrosion rate of a metal surface by passing sufficient cathodic current to it to cause its dissolution rate to become very low.
Cation—positively charged ions that migrate to the cathode in a galvanic cell.
Caustic Embrittlement—a form of stress corrosion cracking that occurs in steel exposed to alkaline solutions.
Composite Plate—an electrodeposit that consists of two or more layers of metals deposited separately.
Corrosion Fatigue Limit—the maximum stress that a metal can endure without failure. This is determined in a stated number of stress applications under defined conditions of stressing and corrosion.
Corrosion Potential—the potential of a corroding surface in an electrolyte relative to some reference electrode.
Corrosion Rate—the rate at which corrosion occurs. It is usually reported in units of inches of penetration per year (ipy), mils of penetration per year (mpy), milligrams of weight loss per square decimeter per day (mdd); microns per year (jimjyi), or millimeters per year (mmpy). Note that ljum = 0.0395 mils.
Couple—an electrical contact made between two dissimilar metals.
Critical Humidity—the relative humidity (RH) at and above which the atmospheric corrosion rate of a metal increases significantly.
Current Density—the average current flowing in an electrolyte (common units are amperes per square foot (A/ft ), amperes per square decimeter (A/dm ), amperes per square centimeter (A/cm ), or milliamperes per square centimeter (mA/cm ) of either cathode or anode surface.
Deactivation—in corrosion control refers to the removal of a constituent of a liquid that is active in promoting corrosion.
Deposit Attack—to localized corrosion under, and resulting from, a deposit on a metal surface.
Dielectric Strength—the magnitude of electrical nonconductance of a material.
Differential Aeration-the stimulation of corrosion at a localized area by differences in oxygen concentration in the electrolytic solution that is in contact with the metal surface.
Diffusion Coating-application of a metallic coating. The chemical compo­sition of the metal is modified by diffusing the coating into the substrate at the metal's melting temperature.
Electrogalvanizing  the process of galvanizing by electroplating.
Electrolysis-a reaction in which chemical change results in an electrolyte being produced from the passage of electric current.
Electrolyte-chemical constituent, usually a liquid, containing ions that migrate in an electric field.
Electrolytic Cleaning-method of degreasing/descaling metal surfaces via electrolysis. The metal is utilized as an electrode.
Electrophoretic Plating-the production of a layer of deposit as a result of discharge of colloidal particles in solution onto an electrode.
Electroplating—the process of electrodeposition onto a metallic substrate of a thin adherent layer of a metal or alloy having desirable chemical, physical and/or mechanical properties.
Exfoliation-also called lamination, refers to the falling away of metal in layers.
Filiform Corrosion—type of corrosion that takes place under a film in the form of randomly distributed hairlines.
Flame Plating-the deposition of a hard metal coating onto a substrate via application of molten metal at supersonic velocities.
Flash Corrosion-light surface oxidation of cleaned metals that are exposed to the environment for short times.
Fouling—deposition of scale materials on metal surfaces.
Galvanizing—the method of coating iron or steel with zinc by immersion of the metal in a bath of molten zinc.
Green Rot-a corrosion product particular to nickel alloys and greenish in color that normally results from carburization and oxidation of certain nickel alloys at temperatures around 1000°C (1832°F).
Hermetic Seal—an impervious seal made by the fusion of metals of ceramics, which prevents the passage of gas or moisture. The seal can be achieved by brazing, soldering, welding, fusing glass or ceramics.
Ion Erosion—the deterioration of materials caused by ion impact.
Iron Rot—the deterioration of wood caused by contact with iron.
Laminar Scale—rust formation in heavy layers.
Localized Attack—corrosion in which one area of the metal surface is primarily anodic and another predominantly cathodic.
Metal Cladding—the combination of two or more metal compounds bonded metallurgically face to face.
Metallic Coatings—coatings that consist fully or partially of metal applied
Design and Corrosion
to metals or nonmetals for the purpose of protection or to improve certain properties.
Metallizing-also called metal spraying; refers to the application of a metal coating to a surface (either metallic or nonmetallic) by means of a spray of molten particles.
Mill Scale—an oxide layer on metals produced by metal rolling, hot form­ing, welding or heat treatment.
Noble—positive direction of the electrode potential.
Noble Potential-a potential that is more cathodic (i.e., positive) than the standard hydrogen potential.
Oxidation-the loss of electrons by a constituent in a chemical reaction.
Parting—the selective attack of one or more constituents of a solid solution alloy.
Passivation-a reduction of the anodic reaction rate of an electrode in­volved in an electrochemical reaction, such as corrosion.
Passivity—a condition of a metal or alloy in which the material is normally thermodynamically unstable in a given electrolytic solution but remains visibly unchanged for a prolonged period. The electrode potential of a passive metal is always appreciably more noble than its potential in the active state.
Peen Plating-the deposition of the coating metal (in powder form) on the substrate via a tumbling action in the presence of peening shot.
Pickling—a form of chemical and electrolytic removal of mill scale and corrosion products from the surfaces of metals in an acidic solution. Electro­lytic pickling may be anodic or cathodic, depending on the polarization of the metal in the solution.
Plasma Plating—deposition on critical areas of metal coatings resistant to wear and abrasion; normally this is done by means of a high velocity and high-temperature ionized inert gas jet.
Rash Rusting—also called peak spotting; refers to a local corrosion due to inadequate coating of the peaks of a rough surface.
Reduction—the reverse of oxidation; a chemical change of state in which one constituent gains electrons.
Rust—a corrosion product consisting mainly of hydrated iron oxide; the term is used to describe the corrosion products of iron and ferrous ions.
Rust Creep—also called undcrfilm corrosion; refers to corrosive action that results in damaged or uncoated areas and extends subsequently under the surrounding inert protective coating.
Scaling—the formation of thick corrosion products as layers on a metal surface; in piping systems it is usually the deposition of water-insoluble con­stituents on a metal surface.
Season Cracking—stress corrosion cracking of brass.
Sherardizing—the process of coating iron or steel with zinc by heating the product to be coated in zinc powder at a temperature below the melting point of zinc.
Stress-Accelerated Corrosion—increased corrosion rate caused by applied stresses.
Surface Preparation-the cleaning of a surface prior to treatment.
Surface Treatment—any suitable means of cleaning and treating a surface that produces a desired surface profile that has required coating character­istics.
Tuberculation-the formation of localized corrosion products scattered over the surface in the form of knob-like tiles.
Vacuum Deposition—also vapor deposition or gas plating; the deposition of metal coatings by means of precipitation (sometimes in vacuum) of metal vapor onto a treated surface. The vapor may be produced by thermal de­composition, cathode sputtering or evaporation of the molten metal in air or an inert gas.
Weld Decay-localized corrosion of weld metal.