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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 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.
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.
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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.
ually made of noncorroding material.
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.
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