1、Designation: G 15 07Standard Terminology Relating toCorrosion and Corrosion Testing1This standard is issued under the fixed designation G 15; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revision. A number in pa
2、rentheses indicates the year of last reapproval. A superscriptepsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This terminology covers commonly used terms in thefield of corros
3、ion. Related terms may be found in Terminolo-gies D16, D 4538, G40, or other ASTM terminology stan-dards.All terms defined byASTM committees may be found inthe ASTM Dictionary of Engineering penetration per unit time.)counter electrodeelectrode in an electrochemical cell that isused to transfer curr
4、ent to or from a test electrode.couponspecimen, usually flat, but occasionally curved orcylindrical.crevice corrosionlocalized corrosion of a metal surface at,or immediately adjacent to, an area that is shielded from fullexposure to the environment because of close proximitybetween the metal and the
5、 surface of another material.critical anodic current densitymaximum anodic currentdensity observed in the active region for a metal or alloyelectrode that exhibits active-passive behavior in an envi-ronment.critical humidityrelative humidity above which the atmo-spheric corrosion rate of some metals
6、 increases sharply.critical pitting potentialleast noble potential where pittingcorrosion will initiate and propagate. (See breakdown poten-tial.)current densityelectric current to or from a unit area of anelectrode surface.current efficiencyratio of the electrochemical equivalentcurrent density for
7、 a specific reaction to the total appliedcurrent density.deactivationprocess of prior removal of the active corrosiveconstituents, usually oxygen, from a corrosive liquid bycontrolled corrosion of expendable metal or by other chemi-cal means, thereby making the liquid less corrosive.dealloyingSee pa
8、rting.depolarizationnot a preferred term. (See polarization.)deposit corrosionlocalized corrosion under or around adeposit or collection of material on a metal surface. (See alsocrevice corrosion.)dezincificationSee parting; specific to copper-zinc alloys.differential aeration cell (oxygen concentra
9、tion cell)concentration cell caused by differences in oxygen concen-tration along the surface of a metal in an electrolyte. (Seeconcentration cell.)diffusion limited current densitycurrent density, oftenreferred to as limiting current density, that corresponds to themaximum transfer rate that a part
10、icular species can sustaindue to the limitation of diffusion.electrochemical admittancereciprocal of the electrochemi-cal impedance, DI/DE.electrochemical cellelectrochemical system consisting of ananode and a cathode in metallic contact and immersed in anelectrolyte. (The anode and cathode may be d
11、ifferent metalsor dissimilar areas on the same metal surface.)electrochemical impedancefrequency dependent, complexvalued proportionality factor, DE/DI, between the appliedpotential (or current) and the response current (or potential)in an electrochemical cell. This factor becomes the imped-ance whe
12、n the perturbation and response are related linearly(the factor value is independent of the perturbation magni-tude) and the response is caused only by the perturbation.The value may be related to the corrosion rate when themeasurement is made at the corrosion potential.electrochemical noisefluctuat
13、ions of potential or current, orboth, originating from uncontrolled variations in a corrosionprocess.electrochemical potential (electrochemical tension)partialderivative of the total electrochemical free energy of thesystem with respect to the number of moles of the constitu-ent in a solution when a
14、ll other factors are constant.(Analogous to the chemical potential of the constituentexcept that it includes the electrical as well as the chemicalcontributions to the free energy.)electrode potentialpotential of an electrode in an electrolyteas measured against a reference electrode. (The electrode
15、potential does not include any resistance losses in potentialin either the solution or external circuit. It represents thereversible work to move a unit charge from the electrodesurface through the solution to the reference electrode.)electrolysisproduction of chemical changes of the electro-lyte by
16、 the passage of current through an electrochemicalcell.electrolytic cleaningprocess of removing soil, scale, orcorrosion products from a metal surface by subjecting it asan electrode to an electric current in an electrolytic bath.Electromotive Force Series (EMF Series)list of elementsarranged accord
17、ing to their standard electrode potentials,with “noble” metals such as gold being positive and “active”metals such as zinc being negative.embrittlementsevere loss of ductility or toughness or both,of a material, usually a metal or alloy.environmentally-assisted crackinginitiation or accelera-tion of
18、 a cracking process due to the conjoint action of aG15072chemical environment and tensile stress.equilibrium (reversible) potentialpotential of an electrodein an electrolytic solution when the forward rate of a givenreaction is exactly equal to the reverse rate. (The equilibriumpotential can only be
19、 defined with respect to a specificelectrochemical reaction.)erosionprogressive loss of material from a solid surface dueto mechanical interaction between that surface and a fluid, amulti-component fluid, or solid particles carried with thefluid.erosion-corrosionconjoint action involving corrosion a
20、nderosion in the presence of a moving corrosive fluid, leadingto the accelerated loss of material.exchange current densityrate of charge transfer per unitarea when an electrode reaches dynamic equilibrium (at itsreversible potential) in a solution; that is, the rate of anodiccharge transfer (oxidati
21、on) balances the rate of cathodiccharge transfer (reduction).exfoliationcorrosion that proceeds laterally from the sites ofinitiation along planes parallel to the surface, generally atgrain boundaries, forming corrosion products that forcemetal away from the body of the material, giving rise to alay
22、ered appearance.external circuitwires, connectors, measuring devices, cur-rent sources, and so forth, that are used to bring about ormeasure the desired electrical conditions within the test cell.filiform corrosioncorrosion that occurs under some coatingsin the form of randomly distributed threadlik
23、e filaments.fretting corrosiondeterioration at the interface betweencontacting surfaces as the result of corrosion and slightoscillatory slip between the two surfaces.galvanic corrosionaccelerated corrosion of a metal becauseof an electrical contact with a more noble metal or nonme-tallic conductor
24、in a corrosive electrolyte.galvanic couplepair of dissimilar conductors, commonlymetals, in electrical contact. (See galvanic corrosion.)galvanic currentelectric current between metals or conduc-tive nonmetals in a galvanic couple.galvanic serieslist of metals and alloys arranged accordingto their r
25、elative corrosion potentials in a given environment.galvanodynamicrefers to a technique wherein current, con-tinuously varied at a selected rate, is applied to an electrodein an electrolyte.galvanostaircaserefers to a galvanostep technique for po-larizing an electrode in a series of constant current
26、 stepswherein the time duration and current increments or decre-ments are equal for each step.galvanostaticexperimental technique whereby an electrodeis maintained at a constant current in an electrolyte.galvanosteprefers to a technique in which an electrode ispolarized in a series of current increm
27、ents or decrements.grain droppingdislodgement and loss of a grain or grains(crystals) from a metal surface as a result of intergranularcorrosion.graphitic corrosiondeterioration of metallic constituents ingray cast iron, which leaves the graphitic particles intact.(The term “graphitization” is commo
28、nly used to identify thisform of corrosion but is not recommended because of its usein metallurgy for the decomposition of carbide to graphite.)hot corrosionaccelerated corrosion of metal surfaces thatresults from the combined effect of oxidation and reactionswith sulfur compounds and other contamin
29、ants, such aschlorides, to form a molten salt on a metal surface whichfluxes, destroys, or disrupts the normal protective oxide.hydrogen blisteringformation of blisters on or below ametal surface from excessive internal hydrogen pressure.(Hydrogen may be formed during cleaning, plating, corro-sion,
30、and so forth.)hydrogen embrittlementhydrogen-induced cracking or se-vere loss of ductility caused by the presence of hydrogen inthe metal.immunitystate of resistance to corrosion or anodic dissolu-tion of a metal caused by thermodynamic stability of themetal.impingement corrosionform of erosion-corr
31、osion generallyassociated with the local impingement of a high-velocity,flowing fluid against a solid surface.impressed currentelectric current supplied by a deviceemploying a power source that is external to the electrodesystem. (An example is dc current for cathodic protection.)intensiostaticSee g
32、alvanostatic.intercrystalline corrosionSee intergranular corrosion.intergranular corrosionpreferential corrosion at or adja-cent to the grain boundaries of a metal or alloy.internal oxidationformation of isolated particles of corro-sion products beneath the metal surface. (This occurs as theresult o
33、f preferential oxidation of certain alloy constituentsby inward diffusion of oxygen, nitrogen, sulfur, and soforth.)knife-line attackintergranular corrosion of an alloy, usuallystabilized stainless steel, along a line adjoining or in contactwith a weld after heating into the sensitization temperatur
34、erange.local action corrosioncorrosion caused by local corrosioncells on a metal surface.local corrosion cellelectrochemical cell created on a metalsurface because of a difference in potential between adjacentareas on that surface.localized corrosioncorrosion at discrete sites, for example,pitting,
35、crevice corrosion, and stress corrosion cracking.long-line currentelectric current through the earth from ananodic to a cathodic area of a continuous metallic structure.(Usually used only where the areas are separated by consid-erable distance and where the current results fromconcentration-cell act
36、ion.)Luggin probe or Luggin-Haber capillarydevice used inmeasuring the potential of an electrode with a significantcurrent density imposed on its surface. (The probe mini-mizes the IR drop that would otherwise be included in themeasurement and without significantly disturbing the currentdistribution
37、 on the specimen.)macrocell corrosioncorrosion of a metal embedded inporous media (for example, concrete or soil) caused byconcentration or galvanic cells which exist on a scale at leastG15073as large as the smallest major dimension of the corrodingitem (for example, the diameter of a bar or pipe).m
38、etal dustingaccelerated deterioration of metals in carbon-aceous gases at elevated temperatures to form a dust-likecorrosion product.metallizingSee thermal spraying.microbial corrosioncorrosion that is affected by the actionof microorganisms in the environment.microbiologically influenced corrosion
39、(MIC)corrosioninhibited or accelerated by the presence or activity, or both,of microorganisms.mixed potentialpotential of a specimen (or specimens in agalvanic couple) when two or more electrochemical reac-tions are occurring simultaneously.noblepositive (increasingly oxidizing) direction of electro
40、depotential.noble metalmetal with a standard electrode potential that ismore noble (positive) than that of hydrogen.occluded cellelectrochemical cell created at a localized siteon a metal surface which has been partially obstructed fromthe bulk environment.open-circuit potentialpotential of an elect
41、rode measuredwith respect to a reference electrode or another electrodewhen no current flows to or from it.overvoltagechange in potential of an electrode from itsequilibrium or steady state value when current is applied.oxidationloss of electrons by a constituent of a chemicalreaction. (Also refers
42、to the corrosion of a metal that isexposed to an oxidizing gas at elevated temperatures.)partingselective corrosion of one or more components of asolid solution alloy.parting limitminimum concentration of a more noble com-ponent in an alloy, above which parting does not occur in aspecific environmen
43、t.passivationprocess in metal corrosion by which metalsbecome passive. (See passive.)passivatortype of inhibitor which appreciably changes thepotential of a metal to a more noble (positive) value.passivestate of the metal surface characterized by lowcorrosion rates in a potential region that is stro
44、ngly oxidizingfor the metal.passive-active cellcorrosion cell in which the anode is ametal in the active state and the cathode is the same metal inthe passive state.patinacorrosion product film, usually green, that forms onthe surface of copper and copper alloys exposed to theatmosphere. (Also used
45、to describe a weathered surface ofany metal.)pittingcorrosion of a metal surface, confined to a point orsmall area, that takes the form of cavities.pitting factorratio of the depth of the deepest pit resultingfrom corrosion divided by the average penetration as calcu-lated from weight loss.polarizat
46、ionchange from the open-circuit electrode poten-tial as the result of the passage of current.polarization admittancereciprocal of polarization resis-tance (di/dE).polarization resistanceslope (dE/di) at the corrosion poten-tial of a potential (E)current density (i) curve. (It isinversely proportiona
47、l to the corrosion current density whenthe polarization resistance technique is applicable.)potentiodynamicrefers to a technique wherein the potentialof an electrode with respect to a reference electrode is variedat a selected rate by application of a current through theelectrolyte.potentiostaircase
48、refers to a potentiostep technique for po-larizing an electrode in a series of constant potential stepswherein the time duration and potential increments ordecrements are equal for each step.potentiostatinstrument for automatically maintaining anelectrode in an electrolyte at a constant potential or
49、 con-trolled potentials with respect to a suitable reference elec-trode.potentiostatictechnique for maintaining a constant electrodepotential.potentiosteprefers to a technique in which an electrode ispolarized in a series of potential increments or decrements.poultice corrosionSee deposit corrosion.Pourbaix diagram (electrode potential-pH diagram)graphical representation showing regions of thermodynamicstability of species in metal-water electrolyte systems.primary passive potential (passivation pot
