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CorrosionSource - Corrosion terms
Category: Earth and Environment > Corrosion
Date & country: 24/09/2008, USA
Words: 336

A process in which liquid 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

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 am..

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

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

The changing of a passive surface of a metal to a chemically active state. Contrast with passivation.

active potential
The potential of a corroding material

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

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

(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

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

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, d..

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

(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

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

(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

(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 910 ºC (l670 ºF)

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

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

An alloy of mercury with one or more other metals

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.

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

A zinc-iron phosphate coating for iron and steel

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. improvemen..

anode corrosion
The dissolution of a metal acting as an anode

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 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) + n(e-)

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

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

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

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

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

Material placed in a drilled hole to fill space around anodes, vent pipe, and buried components of a cathodic protection system

A metastable aggregate of ferrite and cementite resulting from the transformation of austenite at temperatures below the pearlite range but above M„ the martensite start temperature. Bainite formed in the upper part of the bainite transformation range has a feathery appearance; bainite formed in the lower part of the range has an acicular appe..

banded structure
A segregated structure consisting of alternating nearly parallel bands of different composition, typically aligned in the direction of primary hot working

A chemical substance that yields hydroxyl ions (OH ) when dissolved in water. Compare with acid

base metal
(1) The metal present in the largest proportion in an alloy; brass, for example, is a copper-base alloy. (2) An active metal that readily oxidizes, or that dissolves to form ions. (3) The metal to be brazed, cut, soldered, or welded. (4) After welding, that part of the metal which was not melted

beach marks
Macroscopic progression marks on a fatigue fracture or stress-corrosion cracking surface that indicate successive positions of the advancing crack front. The classic appearance is of irregular elliptical or semielliptical rings, radiating outward from one or more origins. Beach marks (also known as clamshell marks or arrest marks) are typically fou..

biaxial stress
See principal stress (normal)

biological corrosion
Deterioration of metals as a result of the metabolic activity of microorganisms

bipolar electrode
An electrode in an electrolytic cell that is not mechanically connected to the power supply, but is so placed in the electrolyte, between the anode and cathode, that the part nearer the anode becomes cathodic and the part nearer the cathode becomes anodic. Also called intermediate electrode

bituminous coating
Coal tar or asphalt-based coating

black liquor
The liquid material remaining from pulpwood cooking in the soda or sulfate paper-making process

black oxide
A black finish on a metal produced by immersing it in hot oxidizing salts or salt solutions

A raised area, often dome shaped, resulting from (1) loss of adhesion between a coating or deposit and the base metal or (2) delamination under the pressure of expanding gas trapped in a metal in a near-subsurface zone. Very small blisters may be called pinhead blisters or pepper blisters

blow down
(1) Injection of air or water under high pressure through a tube to the anode area for the purpose of purging the annular space and possibly correcting high resistance caused by gas blocking. (2) In connection with boilers or cooling towers, the process of discharging a significant portion of the aqueous solution in order to remove accumulated salt..

blue brittleness
Brittleness exhibited by some steels after being heated to a temperature within the range of about 200 to 370 ºC (400 to 700 ºF), particularly if the steel is worked at the elevated temperature

Whitening and loss of gloss of a usually organic coating caused by moisture. Also called blooming

brackish water
(1) Water having salinity values ranging from approximately 0.5 to l7 parts per thousand. (2) Water having less salt than seawater, but undrinkable

breakdown potential
The least noble potential where pitting or crevice corrosion, or both, will initiate and propagate

An agent or combination of agents added to an electroplating bath to produce a smooth, lustrous deposit

Seawater containing a higher concentration of dissolved salt than that of the ordinary ocean

brittle fracture
Separation of a solid accompanied by little or no macroscopic plastic deformation. Typically, brittle fracture occurs by rapid crack propagation with less expenditure of energy than for ductile fracture

(1) Permanently damaging a metal or alloy by heating to cause either incipient melting or intergranular oxidation. See also over-heating. (2) In grinding, getting the work hot enough to cause discoloration or to change the microstructure by tempering or hardening

calcareous coating
A layer consisting of a mixture of calcium carbonate and magnesium hydroxide deposited on surfaces being cathodically protected because of the increased pH adjacent to the protected surface

calomel electrode
An electrode widely used as a reference electrode of known potential in electrometric measurement of acidity and alkalinity, corrosion studies, voltammetry, and measurement of the potentials of other electrodes. See also electrode potential, reference electrode, and saturated calomel electrode

Imparting resistance to oxidation to an iron or steel surface by heating in aluminum powder at 800 to 1000 ºC (1470 to 1830 ºF)

A case hardening process in which a suitable ferrous material is heated above the lower transformation temperature in a gaseous atmosphere of such composition as to cause simultaneous absorption of carbon and nitrogen by the surface and, by diffusion, create a concentration gradient. The process is completed by cooling at a rate that produces the d..

The absorption of carbon atoms by a metal at high temperatures; it may remain dissolved, or form metal carbides; Absorption and diffusion of carbon into solid ferrous alloys by heating, to a temperature usually above Ac in contact with a suitable carbonaceous material. A form of case hardening that produces a carbon gradient extending inward from t..

case hardening
A generic term covering several processes applicable to steel that change the chemical composition of the surface layer by absorption of carbon, nitrogen, or a mixture of the two and, by diffusion, create a concentration gradient. The outer portion, or case, is made substantially harder than the inner portion, or core. The processes commonly used a..

CASS test
See copper-accelerated salt-spray test

The electrode of an electrolytic cell at which reduction is the principal reaction. (Electrons How toward the cathode in the external circuit.) Typical cathodic processes are cation' taking up electrons and being discharged, oxygen being reduced. and the reduction of an element or group of elements from a high Cl a lower valence state. Contrast wit..

cathode efficiency
Current efficiency at the cathode

cathode film
The portion of solution in immediate contact with the cathode during electrolysis

cathodic cleaning
Electrolytic cleaning in which the work is the cathode

cathodic corrosion
Corrosion resulting from a cathodic condition of a structure usually caused by the reaction of an amphoteric metal with the alkaline products of electrolysis

cathodic disbondment
The destruction of adhesion between a coating and its substrate by products of a cathodic reaction

cathodic inhibitor
A chemical substance or mixture that prevents or reduces the rate of the cathodic or reduction reaction by physical, physico-chemical or chemical action

cathodic pickling
Electrolytic pickling in which the work is the cathode

cathodic polarization
Polarization of the cathode; change of the electrode potential in the active (negative) direction due to current flow; a reduction from the initial potential resulting from current flow effects at or near the cathode surface. Potential becomes more active (negative) because of cathodic polarization. See also polarization

cathodic protection
(1) Reduction of corrosion rate by shifting the corrosion potential of the electrode toward a less oxidizing potential by applying an external electromotive force. (2) Partial or complete protection of a metal from corrosion by making it a cathode, using either a galvanic or an impressed current. Contrast with anodic protection

cathodic reaction
Electrode reaction equivalent to a transfer of negative charge from the electronic to the ionic conductor. A cathodic reaction is a reduction process. An example common in corrosion is: Ox + ne s Red

The electrolyte adjacent to the cathode of an electrolytic cell

A positively charged ion that migrates through the electrolyte toward the cathode under the influence of a potential gradient. See also anion and ion

(1) Burning or corrosive. (2) A hydroxide of a light metal, such as sodium hydroxide or potassium hydroxide

caustic dip
A strongly alkaline solution into which metal is immersed for etching. for neutralizing acid, or for removing organic materials such as greases or paints

caustic embrittlement
An obsolete historical term denoting a form of stress-corrosion cracking most frequently encountered in carbon steels or iron-chromium-nickel alloys that are exposed to concentrated hydroxide solutions at temperatures of 200 to 250 ºC (400 to 480 ºF)

The formation and instantaneous collapse of innumerable tiny voids or cavities within a liquid subjected to rapid and intense pressure changes. Cavitation produced by ultrasonic radiation is sometimes used to effect violent localized agitation. Cavitation caused by severe turbulent flow often leads to cavitation damage

cavitation corrosion
A process involving conjoint corrosion and cavitation

cavitation damage
The degradation of a solid body resulting from its exposure to cavitation. This may include loss of material, surface deformation, or changes in properties or appearance

Progressive loss of original material from a solid surface due to continuing exposure to cavitation

Electrochemical system consisting of an anode and a cathode immersed in an electrolyte. The anode and cathode may be separate metals or dissimilar areas on the same metal. The cell includes the external circuit, which permits the flow of electrons from the anode toward the cathode. See also electrochemical cell

A compound of iron and carbon, known chemically as iron carbide and having the approximate chemical formula Fe3C. It is characterized by an orthorhombic crystal structure. When it occurs as a phase in steel, the chemical composition will be altered by the presence of manganese and other carbide-forming elements