Glossary -
A
acid.
A chemical substance that yields hydrogen ions (H+) when dissolved in water. Compare with base..
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.
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.
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.
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.
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.
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) + n(e-).
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.
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.
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.
Back to Top
B
base
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 found on service fractures where the part is loaded randomly, intermittently, or with periodic variations in mean stress or alternating stress. See also striation.
bimetallic corrosion
(Galvanic Corrosion) Corrosion resulting from dissimilar metal contact.
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 oxide
A black finish on a metal produced by immersing it in hot oxidizing salts or salt solutions.
blister
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 salts, deposits, and other impurities.
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.
Back to Top
C
calcareous coating or deposit.
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.
carbonitriding.
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 desired properties in the workpiece.
carburizing.
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 the surface, enabling the surface layer to be hardened either by quenching directly from the carburizing temperature or by cooling to room temperature then reaustenitizing and quenching.
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 are carburizing and quench hardening; cyaniding: nitrifying; and carbonitriding. The use of the applicable specific process name is preferred.
cathode.
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 with anode.
cathode efficiency.
Current efficiency at the cathode.
cathode film.
The portion of solution in immediate contact with the cathode during electrolysis.
cathodic cleaning.
Electrolyticcleaning
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.
catholyte.
The electrolyte adjacent to the cathode of an electrolytic cell.
cavitation.
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.
chalking.
The development of loose removable powder at the surface of an organic coating usually caused by weathering.
checking.
The development of slight breaks in a coating that do not penetrate to the underlying surface.
checks.
Numerous, very fine cracks in a coating or at the surface of a metal part. Checks may appear during processing or during service and are most often associated with thermal treatment or thermal cycling. Also called check marks. checking, or heat checks.
chromizing.
A surface treatment at elevated temperature, generally carried out in pack, vapor, or salt bath, in which an alloy is formed by the inward diffusion of chromium into the base metal.
cold cracking.
A type of weld cracking that usually occurs below 203 ºC (400 "F). Cracking may occur during or after cooling to room temperature, sometimes with a considerable time delay. Three factors combine to produce cold cracks: stress (for example, from thermal expansion and contraction). hydrogen (from hydrogen-containing welding consumables), and a susceptible micro.structure (plate martensite is most susceptible to cracking, ferritic and bainitic structures least susceptible). See also hot cracking, lamellar tearing and stress-relief cracking.
conductivity.
The ratio of the electric current density to the electric field in a material. Also called electrical conductivity or specific conductance.
contact corrosion.
A term primarily used in Europe to describe galvanic corrosion between dissimilar metals.
contact plating.
A metal plating process wherein the plating current is provided by galvanic action between the work metal and a second metal, without the use of an external source of current.
continuity bond.
A metallic connection that provides electrical continuity between metal structures.
conversion coating.
A coating consisting of' a compound of the surface metal, produced by chemical or electrochemical treatments of the metal. Examples include chromate coatings on zinc, cadmium, magnesium, and aluminum and oxide and phosphate coatings on steel. See also chromate treatment and phosphating.
corrosion.
The chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties.
corrosion effect.
A change in any part of the corrosion system caused by corrosion.
corrosion embrittlement.
The severe loss of ductility of a metal resulting from corrosive attack, usually inter,granular and often not visually apparent.
corrosion-erosion.
Corrosion which is increased because of the abrasive action of a moving stream; the presence of suspended particles greatly accelerates abrasive action.See erosion-corrosion.
corrosion fatigue.
The process in which a metal fractures prematurely under conditions of simultaneous corrosion and repeated cyclic loading at lower stress levels or fewer cycles than would be required in the absence of the corrosive environment.
Corrosion Fatigue Limit
The maximum cyclic stress value that a metal can with stand for a specified number of cycles or length of time in a given corrosive environment. See corrosion fatigue strength
corrosion fatigue strength.
The maximum repeated stress that can he endured by a metal without failure under definite conditions of corrosion and fatigue and for a specific number of stress cycles and a specified period of time.
corrosion potential (Ecorr).
The potential of a corroding surface in an electrolyte, relative to a reference electrode. Also called rest potential, open circuit potential, or freely corroding potential.
corrosion protection.
Modification of a corrosion system so that corrosion damage is mitigated.
corrosion rate.
Corrosion effect
on a metal per unit of time. The type of corrosion rate used depends on the technical .system and on the type of corrosion effect. Thus, corrosion rate may be expressed as an increase in corrosion depth per unit of time (penetration rate, for example, mils/yr.) or the mass of metal turned into corrosion products per unit area of surface per unit of time (weight loss, for example, g/m-/yr.). The corrosion effect may vary with time and may not be the same at all points of the corroding surface. Therefore. reports of corrosion rates should be accompanied by information on the type, time dependency, and location of the corrosion effect.
corrosion resistance.
Ability of a metal to withstand corrosion in a given corrosion system.
corrosion system.
System consisting of one or more metals and all parts of the environment that influence corrosion.
corrosivity.
Tendency of an environment to cause corrosion in a given corrosion system.
crazing.
A network of checks or cracks appearing on the surface.
crevice corrosion.
Localized corrosion
of a metal surface at, or immediately adjacent to, an area that is shielded from full exposure to the environment because of close proximity between the metal and the surface of another material.
critical anodic current density.
The maximum anodic current density observed in the active region for a metal or alloy electrode that exhibits active-passive behavior in an environment.
critical flaw size.
The size of a flaw (defect) in a structure that will cause failure at a particular stress level.
critical humidity.
The relative humidity above which the atmospheric corrosion rate of some metals increases sharply.
current.
The net transfer of electric charge per unit time. Also called electric current. See also current density.
current density.
The current flowing to or from a unit area of an electrode surface, generally expressed as amps per sq ft or milliamperes per sq ft (also milliamps per sq cm, etc).
current efficiency.
The ratio of the electrochemical equivalent current density for a specific reaction to the total applied current density.
Back to Top
D
deactivation.
The process of prior removal of the active corrosive constituents usuallyoxygen, from a corrosive liquid by controlled corrosion of expendable metal or by other chemical means, thereby making the liquid less corrosive.
dealloying.
The selective corrosion of one or more components of a solid solution alloy, usually in the form of ions. Also called parting or selective leaching. See also decarburization, decobaltification, denickelification, dezincification, and graphitic corrosion.
dealuminization
The selective leaching or corrosion of a specific constituent (Al, Ni, Mo, Ni) from an alloy.
decarburization.
Loss of carbon from the surface layer of a carbon-containing alloy due to reaction with one or more chemical substances in a medium that contacts the surface. See also dealloying.
decobaltification.
Corrosion in which cobalt is selectively leached from cobalt-base alloys, such as Stellite®, or from cemented carbides. See also dealloying and selective leaching.
decomposition potential (or voltage).
The potential of a metal surface necessary to decompose the electrolyte of a cell or a component/substance thereof.
denickelification.
Corrosion in which nickel is selectively leached from nickel-containing alloys. Most commonly observed in copper-nickel alloys after extended service in fresh water. See also dealloying, and selective Ieaching.
deoxidizing.
(1) The removal of oxygen from molten metals by use of suitable deoxidixers. (2) Sometimes refers to the removal of undesirable elements other than oxygen by the introduction of elements or compounds that readily react with them. (3) In metal finishing, the removal of oxide films from metal surfaces by chemical or electrochemical reaction.
depolarization.
A decrease in the polarization of an electrode; the elimination or reduction of polarization by physical or chemical means; depolarization results in increased corrosion.
deposit corrosion.
Corrosion occurring under or around a discontinuous deposit on a metallic surface. Also called poultice corrosion.
descaling.
Removing the thick layer of oxides formed on some metals at elevated temperatures.
dezincification.
Corrosion in which zinc is selectively leached from zinc-containing alloys. Most commonly found in copper-zinc alloys containing less than 83% copper after extended service in water containing dissolved oxygen; the parting of zinc from an alloy (in some brasses, zinc is lost leaving a weak, brittle, porous, copper rich residue behind) See also dealloying and
selective leaching
.
dichromate treatment.
A chromate conversion coating produced on magnesium alloys in a boiling solution of sodium dichromate.
diffusion.
(l) Spreading of a constituent in a gas, liquid, or solid, tending to make the composition of all parts uniform. (2) The spontaneous movement of atoms or molecules to new sites within a material.
diffusion coating.
Any process whereby a base metal or alloy is either (1) coated with another metal or alloy and heated to a sufficient temperature in a suitable environment or (2) exposed to a gaseous or liquid medium containing the other metal or alloy, thus causing diffusion of the coating or of the other metal or alloy into the base metal with resultant changes in the composition and properties of its surface.
diffusion coefficient.
A factor of proportionality representing the amount of substance diffusing across a unit area through a unit concentration gradient in unit time.
diffusion-limited current density.
The current density, often referred to as limiting current density, that corresponds to the maximum transfer rate that a particular species can sustain because of the limitation of diffusion.
dimple rupture.
A fractographic term describing ductile fracture that occurs through the formation and coalescence of microvoids along the fracture path. The fracture surface of such a ductile fracture appears dimpled when observed at high magnification and usually is most clearly resolved when viewed in a scanning electron microscope.
ductile fracture.
Fracture characterized by tearing of metal accompanied by appreciable gross plastic deformation and expenditure of considerable energy. Contrast with brittle fracture.
ductility.
The ability of a material to deform plastically without fracturing, measured by elongation or reduction of area in a tensile test, by height of cupping in an Erichsen test, or by other means.
dummy cathode.
(1) A cathode, usuully corrugated to give variable current densities, that is plated at low current densities to preferentially remove impurities from a plating solution. (2) A substitute cathode that is used during adjustment of operating conditions.
dynamic equilibrium
The condition of an electrode when the rate of anodic dissolution just balances the rate of cathodic plating.
Back to Top
E
elastic deformation.
A change in dimensions directly proportional to and in phase with an increase or decrease in applied force.
elasticity.
The property of a material by virtue of which deformation caused by stress disappears upon removal of the stress. A perfectly elastic body completely recovers its original shape and dimensions after release of stress.
elastic limits.
The maximum stress that a material is capable of sustaining without any permanent strain (deformation) remaining upon complete release of the stress.
elastomer.
A natural or synthetic polymer, which at room temperature can be stretched repeatedly to at least twice its original length, and which after removal of the tensile load will immediately and forcibly return to approximately its original length.
electrical isolation.
The condition of being electrically separated from other metallic structures or the environment.
electrical resistivity.
The electrical resistance offered by a material to the flow of current, times the cross-sectional area of current flow and per unit length of current path; the reciprocal of the conductivity. Also called resistivity or specific resistance.
electrochemical admittance.
The inverse of electrochemical impedance.
electrochemical cell.
An electrochemical system consisting of an anode and a cathode in metallic contact and immersed in an electrolyte. (The anode and cathode may be different metals or dissimilar areas on the same metal surface).
electrochemical corrosion.
Corrosion that is accompanied by a flow of electrons between cathodic and anodic areas on metallic surfaces.
electrochemical equivalent.
The weight of an element or group of elements oxidized or reduced at 100~ efficiency by the passage of a unit quantity of electricity. Usually expressed as grams per coulomb.
electrochemical impedance.
The frequency-dependent complex-valued proportionality factor (A£/Ai) between the applied potential or current and the response signal. This factor is the total opposition (0 or 0 - cm2) of an electrochemical system to the passage of charge. The value is related to the corrosion rate under certain circumstances.
electrochemical potential.
The partial derivative of the total electrochemical free energy of a constituent with respect to the number of moles of this constituent where all factors are kept constant. It is analogous to the chemical potential of a constituent except that it includes the electric as well as chemical contributions to the free energy. The potential of an electrode in an electrolyte relative to a reference electrode measured under open circuit conditions.
electrode.
(1) An electronic conductor used to establish electrical contact with an electrolytic part of a circuit. (2) An electronic conductor in contact with an ionic conductor.
electrode polarization.
Change of electrode potential with respect to a reference value. Often the free corrosion potential is used as the reference value. The change may be caused, for example, by the application of an external electrical current or by the addition of an oxidant or reductant.
electrodeposition.
The deposition of a substance on an electrode by passing electric current through an electrolyte.
electrode potential.
The potential of an electrode in an electrolyte as measured against a reference electrode. The electrode potential does not include any resistance losses in potential in either the solution or external circuit. It represents the reversible work to move a unit charge from the electrode surface through the solution to the reference electrode.
electrode reaction.
Interfacial reaction equivalent to a transfer of charge between electronic and ionic conductors. See also anodic reaction and cathodic reaction.
electrogalvanizing.
The electroplating of zinc upon iron or steels
electrolysis.
Production of chemical changes of the electrolyte by the passage of current through an electrochemical cell.
electrolyte.
(1) A chemical substance or mixture, usually liquid, containing ions that migrate in an electric field. (2) A chemical compound or mixture of compounds which when molten or in solution will conduct an electric current.
embrittlement.
The severe loss of ductility or toughness or both, of a material, usually a metal or alloy. Many forms of embrittlement can lead to brittle fracture. Many forms can occur during thermal treatment or elevated temperature service (thermally induced embrittlement).
epoxy.
Resin formed by the reaction of bisphenol and epichlorohydrin.
erosion.
Destruction of metals or other materials by the abrasive action of moving fluids, usually accelerated by the presence of solid particles or matter in suspension. When corrosion occurs simultaneously, the term erosion-corrosion is often used.
erosion-corrosion.
A conjoint action involving corrosion and erosion in the presence of a moving corrosive fluid, leading to the accelerated loss of material.
exfoliation.
Corrosion that proceeds laterally from the sites of initiation along planes parallel to the surface, generally at grain boundaries, forming corrosion products that force metal away from the body of the material, giving rise to a layered appearance.
Back to Top
F
Faraday's law.
(1) The amount of any substance dissolved or deposited in electrolysis is proportional to the total electric charge passed. (2) The amounts of different substances dissolved or deposited by the passage of the same electric charge are proportional to their equivalent weights.
filiform corrosion.
Corrosion that occurs under some coatings in the form of randomly distributed threadlike filaments.
Back to Top
G
Galvanic
Pertaining to the current resulting from the coupling of dissimilar electrodes in an electrolyte
galvanic anode.
A metal which because of its relative position in the galvanic series, provides sacrificial protection to metals that are more noble in the series, when coupled in an electrolyte.
galvanic corrosion.
Accelerated corrosion of a metal because of an electrical contact with a more noble metal or nonmetallic conductor in a corrosive electrolyte.
galvanize.
To coat a metal surface with zinc using any of various processes.
graphitic corrosion.
Deterioration of gray cast iron in which the metallic constituents are selectively leached or converted to corrosion products leaving the graphite intact. The term graphitization is commonly used to identify this form of corrosion, but is not recommended because of its use in metallurgy for the decomposition of carbide to graphite. See also dealloying and selective leaching.
graphitization.
A metallurgical term describing the formation of graphite in iron or steel, usually from decomposition of iron carbide at elevated temperatures. Not recommended as a term to describe
graphitic corrosion
.
Back to Top
H
huey test.
Corrosion testing in a boiling solution of nitric acid. This test is mainly used to detect the susceptibilty to intergranular corrosion of stainless steel.
hydrogen blistering.
The formation of blisters on or below a metal surface from excessive internal hydrogen pressure; Formation of blister-like bulges on a ductile metal surface caused by internal hydrogen pressures. Hydrogen may beformed during cleaning, plating, corrosion, and so forth.
hydrolysis.
(1) Decomposition or alteration of a chemical substance by water. (2) In aqueous solutions of electrolytes, the reactions of cations with water to produce a weak base or of anions to produce a weak acid.
Back to Top
I
immersion plating.
Depositing a metallic coating on a metal immersed in a liquid solution, without the aid of an external electric current. Also called dip plating.
inert anode.
An anode that is insoluble in the electrolyte under the conditions prevailing in the electrolysis.
interdendritic corrosion.
Corrosive attack that progresses preferentially along interdendritic paths. This type of attack results from local differences in composition, such as coring commonly encountered in alloy castings.
internal oxidation.
The formation of isolated particles of corrosion products beneath the metal surface. This occurs as the result of preferential oxidation of certain alloy constituents by inward diffusion of oxygen, nitrogen, sulfur, and so forth.
intumescence.
The swelling or bubbling of a coating usually because of heating (term currently used in space and fire protection applications).
ion.
An atom, or group of atoms, that has gained or lost one or more outer electrons and thus carries an electric charge. Positive ions, or cations, are deficient in outer electrons. Negative ions, or anions, have an excess of outer electrons.
Back to Top
J
Back to Top
K
Back to Top
L
lamellar tearing.
Occurs in the base metal adjacent to weldments due to high through-thickness strains introduced by weld metal shrinkage in highly restrained joints. Tearing occurs by decohesion and linking along the working direction of the base metal; cracks usually run roughly parallel to the fusion line and are steplike in appearance. Lamellar tearing can be minimized by designing joints to minimize weld shrinkage stresses and joint restraint. See also cold cracking, hot
cracking
,
and stress-relief cracking.
linear elastic fracture mechanics.
A method of fracture analysis that can determine the stress (or load) required to induce fracture instability in a structure containing a cracklike flaw of known size and shape. See also fracture mechanics and stress-intensity factor.
Back to Top
M
mole.
One mole is the mass numerically equal (in grams) to the relative molecular mass of a substance. It is the amount of substance of a system that contains as many elementary units (6.023 exp23) as there are atoms of carbon in 0.012 kg of the pure nuclide C12; the elemenary unit must be specified and may be an atom, molecule, ion, electron, photon, or even a specified group of such units.
moneypenny-strauss test.
Corrosion testing in a copper-sulfate solution containing sulfuric acid. Used to detect the susceptibility of stainless steel to intergranular corrosion.
monomer.
A molecule usually an organic compound, having the ability to join with a number of identical molecules to form a polymer.
Back to Top
N
Back to Top
O
oxidation.
(1) A reaction in which there is an increase in valence resulting from a loss of electrons. Contrast with reduction. (2) A corrosion reaction in which the corroded metal forms an oxide; usually applied to reaction with a gas containing elemental oxygen, such as air.
oxidized surface (on steel).
Surface having a thin, tightly adhering, oxidized skin (from straw to blue in color), extending in from the edge of a coil or sheet.
Back to Top
P
patina.
The coating, usually green, that forms on the surface of metals such as copper and copper alloys exposed to the atmosphere. Also used to describe the appearance of a weathered surface of any metal.
plasma spraying.
A thermal spraying process in which the coating material is melted with heat from a plasma torch that generates a nontransferred arc: molten coating material is propelled against the base metal by the hot, ionized gas issuing from the torch.
polarization.
(1) The change from the open-circuit electrode potential as the result of the passage of current. (2) A change in the potential of an electrode during electrolysis, such that the potential of an anode becomes more noble, and that of a cathode more active, than their respective reversible potentials. Often accomplished by formation of a film on the electrode surface.
polymer.
A chain of organic molecules produced by the joining of primary units called monomers.
potentiostat.
An instrument for automatically maintaining an electrode in an electrolyte at a constant potential or controlled potentials with respect to a suitable reference electrode.
Back to Top
Q
quenching.
Rapid cooling of metals (often steels) from a suitable elevated temperature. This generally is accomplished by immersion in water, oil, polymer solution, or salt, although forced air is sometimes used.
Back to Top
R
reactive metal.
A metal that readily combines with oxygen at elevated temperatures to form very stable oxides, for example, titanium, zirconium, and beryllium. Reactive metals may also become embrittled by the interstitial absorption of oxygen, hydrogen, and nitrogen.
rust.
A visible corrosion product consisting of hydrated oxides of iron. Applied only to ferrous alloys. See also white rust.
Back to Top
S
scaling.
(1) The formation at high temperatures of thick corrosion product layers on a metal surface. (2) The deposition of water-insoluble constituents on a metal surface.
sputtering.
A coating process whereby thermally emitted electrons collide with inert gas atoms, which accelerate toward and impact a negatively charged electrode that is a target of the coating material. The impacting ions dislodge atoms of the target material, which are in turn projected to and deposited on the substrate to form the coating.
subsurface corrosion.
Formation of isolated particles of corrosion products beneath a metal surface. This results from the prcferential reactions of certain alloy constituents to inward diffusion of oxygen, nitrogen, or sulfur.
sulfidation.
The reaction of a metal or alloy with a sulfur-containing species to produce a sulfur compound that forms on or beneath the surface on the metal or alloy.
Back to Top
T
temper.
(1) In heat treatment, to reheat hardened steel or hardened cast iron to some temperature below the eutectoid temperature for the purpose of decreasing hardness and increasing toughness. The process is also sometimes applied to normalized steel. (2) In tool steels, temper is sometimes inadvisably used to denote carbon content. (3) In nonferrous alloys and in some ferrous;alloys (steels that cannot be hardened by heat treatment), the hardness and strength produced by mechanical or thermal treatment, or both, and characterized by a certain structure, mechanical properties. Or reduction of area during cold working.
thermal spraying
A group of coating or welding processes in which finely divided metallic or nonmetallic materials are deposited in a molten or semimolten condition to form a coating. The coating material may be in the form of powder, ceramic rod, wire, or molten materials. See also flame spraying and plasma spraying.
thermocouple
A device for measuring temperatures, consisting of lengths of two dissimilar metals or alloys that are electrically joined at one end and connected to a voltage-measuring instrument at the other end. When one junction is hotter than the other, a thermal electromotive force is produced that is roughly proportional to the difference in temperature between the hot and cold junctions.
transition metal
A metal in which the available electron energy levels are occupied in such away that the d-band contains less than its maximum number of ten electrons per atom, for example, iron, cobalt, nickel, and tungsten. The distinctive properties of the transition metals result from the incompletely filled d-levels.
Back to Top
U
Back to Top
V
valence
A positive number that characterizes the combining power of an element for other elements, as measured by the number of bonds to other atoms that one atom of the given element forms upon chemical combination: hydrogen is assigned valence 1, and the valence is the number of hydrogen atoms, or their equivalent, with which an atom of the given element combines.
Back to Top
W
Back to Top
X
Back to Top
Y
Back to Top
Z
Back to Top
Source: corrosion source