Glossary of Corrosion Related Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

absorption: A process in which Quid molecules are taken up by a liquid or solid and distributed throughout the body of that liquid or solid. Compare with adsorption..

accelerated corrosion test: Method designed to approximate, in a short time, the deteriorating effect under normal long-term service conditions.

acid: A chemical substance that yields hydrogen ions (H⁺) when dissolved in water. Compare with base..

acid embrittlement: A form of hydrogen embrittlement that may be induced in some metals by acid.

acid rain: Atmospheric precipitation with a pH below 3.6 to 5.7. Burning of fossil fuels for heat and power is the major factor in the generation of oxides of nitrogen and sulfur, which are converted into nitric and sulfuric acids washed down in the rain. See also atmospheric corrosion.

acicular ferrite: A highly substructured, non-equiaxed ferrite formed upon continuous cooling by a mixed diffusion and shear mode of transformation that begins at a temperature slightly higher than the transformation temperature range for upper bainite. It is distinguished from bainite in that it has a limited amount of carbon available thus, there is only a small amount of carbide present.

acrylic: Resin polymerized from acrylic acid, methacrylic acid, eaters of these acids, or acrylonitrile.

activation: The changing of a passive surface of a metal to a chemically active state. Contrast with passivation..
active: A state in which a metal tends to corrode; referring to the negative direction of electrode potential (opposite of passive or noble).

active Metal: A metal ready to corrode, or being corroded

active potential: The potential of a corroding material.

activity: A measure of the chemical potential of a substance, where chemical potential is not equal to concentration, that allows mathematical relations equivalent to those for ideal systems to be used to correlate changes in an experimentally measured quantity with changes in chemical potential.

activity (ion): The ion concentration corrected for deviations from ideal behavior. Concentration multiplied by activity coefficient. activity coefficient. A characteristic of a quantity expressing the deviation of a solution from ideal thermodynamic behavior; often used in connection with electrolytes.

addition agent: A substance added to a solution for the purpose of altering or controlling a process. Examples include wetting agents in acid pickles, brighteners or antipitting agents in plating solutions, and inhibitors.

additive: A substance added in a small amount, usually to a fluid, for a special purpose, such as to reduce friction, corrosion, etc.

adsorption: The surface retention of solid, liquid, or gas molecules, atoms, or ions by a solid or liquid. Compare with absorption..

aeration: (1) Exposing to the action of air. (2) Causing air to bubble through. (3) Introducing air into a solution by spraying, stirring, or a similar method. (4) Supplying or infusing with air, as in sand or soil.

aeration Cell: An oxygen concentration cell; an electrolytic cell resulting from differences in dissolved oxygen at two points. Also see differential aeration cell..

age hardening: Hardening by aging, usually after rapid cooling or cold working.
aging

A change in the properties of certain metals and alloys that occurs at ambient or moderately elevated temperatures after hot working or a heat treatment (quench aging in ferrous alloys, natural or artificial aging in ferrous and nonferrous alloys) or after a cold-working operation (strain aging). The change in properties is often, but not always, due to a phase change (precipitation), but never involves a change in chemical composition of the metal or alloy. See also age hardening, artificial aging, natural aging, averaging, precipitation hardening, precipitation heat treatment, quench aging, and strain aging..

alclad: Composite wrought product comprised of an aluminum alloy core having on one or both surfaces a metallurgically bonded aluminum or aluminum alloy coating that is anodic to the core and thus electrochemically protects the core against corrosion.

alkali metal: A metal in group lA of the periodic system - namely, lithium, sodium, potassium, rubidium, cesium, and francium. They form strongly alkaline hydroxides, hence the name.

alkaline: (1) Having properties of an alkali. (2) Having a pH greater than 7.

alkaline cleaner: A material blended from alkali hydroxides and such alkaline salts as borates, carbonates, phosphates, or silicates. The cleaning action may be enhanced by the addition of surface-active agents and special solvents.

alkyd: Resin used in coatings. Reaction products of polyhydric alcohols and polybasic acids.

alkylation: (1) A chemical process in which an alkyl radical is introduced into an organic compound by substitution or addition. (2) A refinery process for chemically combining isoparaffin with olefin hydrocarbons.

alligatoring: (1) Pronounced wide cracking over the entire surface of a coating having the appearance of alligator hide. (2) The longitudinal splitting of flat slabs in a plane parallel to the rolled surface. Also called fish-mouthing.

alloy plating: The codeposition of two or more metallic elements.

alpha ferrite: See ferrite..

alpha iron: The body-centered cubic form of pure iron, stable below 910C (l670F).

alternate-immersion test: A corrosion test in which the specimens are intermittently exposed to a liquid medium at definite time intervals.

aluminizing: Forming of an aluminum or aluminum alloy coating on a metal by hot dipping, hot spraying, or diffusion.

amalgam: An alloy of mercury with one or more other metals.

ammeter: An instrument for measuring the magnitude of electric current flow.

amorphous solid: A rigid material whose structure lacks crystalline periodicity; that is, the pattern of its constituent atoms or molecules does not repeat periodically in three dimensions. See also metallic glass..

amphoteric: A term applied to oxides and hydroxides which can act basic toward strong acids and acidic toward strong alkalis. Substances which can dissociate electrolytically to produce hydrogen or hydroxyl ions according to conditions.

anchorite: A zinc-iron phosphate coating for iron and steel.

anaerobic: In the absence of air or unreacted or free oxygen.

anion: An ion or radical which is attracted to the anode because of the negative charge. See also cation and ion.

annealing: A generic term denoting a treatment. consisting of heating to and holding at a suitable temperature, followed by cooling at a suitable rate, used primarily to soften metallic materials, but also to simultaneously produce desired changes in other properties or in microstructure. The purpose of such changes may be. but is not confined to. improvement of machinability, facilitation of cold work, improvement of mechanical or electrical properties, and/or increase in stability of dimensions. When the term is used by itself, full annealing is implied. When applied only for the relief of stress, the process is properly called stress relieving or stress-relief annealing.

anode: The electrode at which oxidation or corrosion of some component occurs (opposite of cathode). Electrons flow away from the anode in the external circuit.

anode corrosion: The dissolution of a metal acting as an anode.

anode corrosion efficiency: Ratio of actual to theoretical corrosion based on the total current flow calculated by Faraday's law from the quantity of electricity that has passed.

anode effect: The effect produced by polarization of the anode in electrolysis. It is characterized by a sudden increase in voltage and a corresponding decrease in amperage due to the anode becoming virtually separated from the electrolyte by a gas film.

anode efficiency: Current efficiency of the anode..

anode film: (1) The portion of solution in immediate contact with the anode, especially if the concentration gradient is steep. (2) The outer layer of the anode itself.

anodic cleaning: Electrolytic cleaning in which the work is the anode. Also called reverse-current cleaning.

anodic coating: A film on a metal surface resulting from an electrolytic treatment at the anode..

anodic inhibitor: A chemical substance or combination of substances that prevent or reduce the rate of the anodic or oxidation reaction by a physical, physico-chemical or chemical action.

anodic polarization: The change in the initial anode potential resulting from current flow effects at or near the anode surface. Potential becomes mode noble (more positive) because of anodic polarization.

anodic potential: An appreciable reduction in corrosion by making a metal an anode and maintaining this highly polarized condition with very little current flow.

anodic protection: A technique to reduce corrosion of a metal surface under some conditions by passing sufficient to it to cause its electrode potential to enter and remain in the passive region; imposing an external electrical potential to protect a metal from corrosive attack. (Applicable only to metals that show active-passive behavior.) Contrast with cathodic protection..

anodic reaction: Electrode reaction equivalent to a transfer of positive charge from the electronic to the ionic conductor. An anodic reaction is an oxidation process. An example common in corrosion is: Me ~ Me n+ + ne ..

anodizing: Forming a conversion coating on a metal surface by anodic oxidation; most frequently applied to aluminum.

anolyte: The electrolyte adjacent to the anode in an electrolytic cell.

anti-fouling: Intended to prevent fouling of under-water structures, such as the bottoms of ships; refers to the prevention of marine organism's attachment or growth on a submerged metal surface, generally through chemical toxicity caused by the composition of the metal or coating layer.

antipitting agent: An addition agent for electroplating solutions to prevent the formation of pits or large pores in the electrodeposit.

aqueous: Pertaining to water; an aqueous solution is made by using water as a solvent.

artificial aging: Aging above room temperature. See also aging. Compare with natural aging..

atmospheric corrosion: The gradual degradation or alteration of a material by contact with substances present in the atmosphere, such as oxygen. carbon dioxide, water vapor, and sulfur and chlorine compounds.

austenitic: The name given to the face-centered cubic crystal structure (FCC) of ferrous metals. Ordinary iron and steel has this structure at elevated temperatures; also certain stainless steels (300 series) have this structure at room temperature.

austenite: A solid solution of one or more elements in face-centered cubic iron. Unless otherwise designated (such as nickel austenite), the solute is generally assumed to be carbon.

austenitizing: Forming austenite by heating a ferrous alloy into the transformation range (partial austenitizing) or above the transformation range (complete austenitizing). When used without qualification, the term implies complete austenitizing.

auxiliary anode: In electroplating, a supplementary anode positioned so as to raise the current density on a certain area of the cathode and thus obtain better distribution of plating.

auxiliary electrode: An electrode commonly used in polarization studies to pass current to or from a test electrode, usually made of noncorroding material.

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