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deactivation.
The process of prior removal of the active corrosive
constituents usually oxygen, 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.
deep
groundbed.
One or more anodes installed vertically at a
nominal depth of 15 m (50 ft) or more below the earth's surface in a
drilled hole for the purpose of supplying cathodic protection for an underground or submerged
metallic structure. See also groundbed.
delta
ferrite.
See ferrite.
demineralization
Removal of dissolved mineral matter, generally from
water.
dendrite.
A crystal that has a treelike branching pattern, being
most evident in cast metals, slowly cooled through the solidification
range.
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.
density
(of gases).
The mass of a unit volume of a gas at a stated
temperature and pressure.
density
(of solids and liquids).
The mass of unit volume of a material at a specified
temperature.
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.
depolarizer.
A substance that produces depolarization.
deposit
Foreign substance which comes from the environment,
adhering to a surface of a material
deposit
attack
Pitting corrosion resulting from deposits on a metal
surface which cause concentration cells.
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.
dielectric
shield.
In a cathodic
protection system, in electrically nonconductive
material, such as a coating, plastic sheet or pipe that is placed between
an anode and an adjacent cathode to avoid current wastage and
to improve current distribution, usually on the cathode.
differential
aeration cell.
An electrolytic cell, the electromotive
force of which is due to a difference in air (oxygen) concentration at
one electrode as compared with that at another electrode of the same
material; an oxygen concentration cell (a cell resulting from a potential
difference caused by different amounts of oxygen dissolved at two
locations). See also concentration cell.
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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.
disbandment.
The destruction of adhesion between a coating and the
surface coated.
discontinuity.
Any interruption in the normal physical structure or
configuration of a part, such as cracks, laps, seams, inclusions, or
porosity. A discontinuity may or may not affect the usefulness of the part.
dislocation.
A linear imperfection in a crystalline array of atoms.
Two basic types are recognized: (1) an edge dislocation corresponds to the
row of mismatched atoms along the edge formed by an extra, partial plane of
atoms within the body of a crystal; (2) a screw dislocation corresponds to
the axis of a spiral structure in a crystal, characterized by a distortion
that joins normally parallel planes together to form a continuous helical
ramp (with a pitch of one interplanar distance) winding about the
dislocation. Most prevalent is the so-called mixed dislocation, which is
any combination of an edge dislocation and a screw dislocation.
double
layer
The interface between an eletrode or a
suspended particle and an electrolyte created by charge-charge
interaction (charge separation) leading to an alignment of oppositely
charged ions at the surface of the electrode or particle. The simplest
model is represented by a parallel plate condenser of 2 x 10-8
cm in thickness. In general the electrode will be positively charged with
respect to the solution..
drainage.
Conduction of electric current from an underground
metallic structure by means of a metallic conductor. Forced drainage is
that applied to underground metallic structures by means of an applied
electromotive force or sacrificial anode. Natural drainage is that from an
underground structure to a more negative (more anodic) structure, such as
the negative bus of a trolley substation.
dry
corrosion.
See gaseous corrosion.
drying
oil.
An oil capable of conversion from a liquid to a solid
by slow reaction with oxygen in the air.
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, usually 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.
dummying.
Plating with dummy cathodes.
dynamic
equilibrium
The condition of an electrode when the rate of anodic
dissolution just balances the rate of cathodic plating.
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