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885-ºF
(475-ºC) embrittlement
Embrittlement of stainless steels upon extended exposure to
temperatures between 400 and 510 ºC (730 and 930 ºF). This type
of embrittlement is caused by fine, chromium-rich precipitates that
segregate at grain boundaries: time at temperature directly influences the
amount of segregation. Grain-boundary segregation of the chromium-rich
precipitates increases strength and hardness, decreases ductility and
toughness, and changes corrosion resistance. This type of embrittlement can
be reversed by heating above the precipitation range.
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
limit
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
conductivity
See conductivity.
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 (1 amp/s).
electrochemical
impedance
The frequency-dependent complex-valued proportionality
factor (SE/6i) between the applied potential or current and the response
signal. This factor is the total opposition (11 or Ill cm-) 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 at 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.
electrochemical
series
Same as electromotive force series.
electrode
(I) 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 on 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 steel.
electrokinetic
potential
This potential, sometimes called zeta
potential, is a potential difference in the solution caused by residual,
unbalanced charge distribution in the adjoining solution, producing a
double layer. The electrokinetic potential is different from the electrode
potential in that it occurs exclusively in the solution phase; that is,
it represents the reversible work necessary to bring a unit charge from
infinity in the solution up to the interface in question but not through
the interface.
electroless
plating
A process in which metal ions in a dilute aqueous
solution are plated out on a substrate by means of autocatalytic chemical
reduction.
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.
electrolytic
cell
An assembly, consisting of a vessel, electrodes, and
an electrolyte, in which electrolysis can be carried out.
electrolytic
cleaning
A process of removing soil, scale. or corrosion
products from a metal surface by subjecting it as an electrode to an
electric current in an electrolytic bath; process of cleaning, degreasing,
of a metal by making it an electrode in a suitable bath.
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electrolytic
protection
See cathodic protection.
electromotive
force
Electrical potential; voltage.
electromotive
force series (emf series)
A list of elements arranged according to their
standard electrode potentials (Hydrogen electrode is a reference point
nd given the value zero), with "noble" metals such as gold
being positive and "active" metals such as zinc being negative.
electron
flow
A movement of electrons in an external circuit
connecting an anode and cathode in a corrosion cell; the
current flow is arbitrarily considered to be in an opposite direction to
the electron flow.
electroplating
Electrodepositing a metal or alloy in an adherent form
on an object serving as a cathode.
electropolishing
A technique commonly used to prepare metallographic
specimens, in which a high polish is produced by making the specimen the anode
in an electrolytic cell, where preferential dissolution at high
points smooths the surface.
electrotinning
Electroplating tin on an object.
embrittlement
Loss of load carrying capacity of a metal or alloy;
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). Some of
these forms of embrittlement, which affect steels, include blue brittleness,
885 ºF (475 ºC) embrittlement, quench-age embrittlement,
sigma-phase embrittlement, strain-age embrittlement, temper embrittlement,
tempered martensite embrittlement, and thermal embrittlement. In
addition, steels and other metals and alloys can be embrittled by
environmental conditions (environmentally assisted embrittlement). The
forms of environmental embrittlement include acid embrittlement, caustic
embrittlement, corrosion embrittlement, creep-rupture embrittlement,
hydrogen embrittlement, liquid metal embrittlement, neutron
embrittlement, solder embrittlement, solid metal embrittlement, and stress-corrosion
cracking.
endurance
limit
The maximum stress that a material can withstand for
an infinitely large number of fatigue cycles; maximum cyclic stress level a
metal can withstand without fatigue failure. See also fatigue strength.
environment
The surroundings or conditions (physical, chemical, mechanical)
in which a material exists.
environmental
cracking
Brittle fracture of a normally ductile material
in which the corrosive effect of the environment is a causative factor.
Environmental cracking is a general term that includes corrosion fatigue,
high-temperature hydrogen attack, hydrogen blistering, hydrogen
embrittlement, liquid metal embrittlement, solid metal embrittlement,
stress-corrosion cracking, and sulfide stress cracking. The
following terms have been used in the past in connection with environmental
cracking, but are becoming obsolete: caustic embrittlement, delayed
fracture, season cracking, static fatigue, stepwise cracking, sulfide
corrosion cracking, and sulfide stress-corrosion cracking. See also embrittlement.
environmentally
assisted embrittlement
See embrittlement.
epoxy
Resin formed by the reaction of bisphenol and
epichlorohydrin.
equilibrium
(reversible) potential
The potential of an electrode in an
electrolytic solution when the forward rate of a given reaction is exactly
equal to the reverse rate. The equilibrium potential can only be defined
with respect to a specific electrochemical reaction.
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.
eutectic
(1) An isothermal reversible reaction in which a
liquid solution is converted into two or more intimately mixed solids on
cooling, the number of solids formed being the same as the number of
components in the system. (2) An alloy having the composition indicated by
the eutectic point on an equilibrium diagram. (3) An alloy structure of
intermixed solid constituents formed by a eutectic reaction.
eutectoid
(1) An isothermal reversible reaction in which a solid
solution is converted into two or more intimately mixed solids on cooling,
the number of solids formed being the same as the number of components in
the system. (2) An alloy having the composition indicated by the eutectoid
point on an equilibrium diagram. (3) An alloy structure of intermixed solid
constituents formed by a eutectoid reaction.
exchange
current
When an electrode reaches dynamic equilibrium in a
solution, the rate of anodic dissolution balances the rate of cathodic
plating. The rate at which either positive or negative charges are entering
or leaving the surface at this point is known as the exchange current.
exchange
current density
The rate of charge transfer per unit area when an
electrode reaches dynamic equilibrium (at its reversible potential) in a
solution; that is, the rate of anodic charge transfer (oxidation) balances
the rate of cathodic charge transfer (reduction).
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.
external
circuit
The wires, connectors, measuring devices, current
sources, etc. that are used to bring about or measure the desired
electrical conditions within the test cell. It is this portion of the cell
through which electrons travel.
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