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Corrosion Glossary - D
- 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.
- Dead flat: a
coating with no gloss or sheen.
- Deaeration: removal of air,
and gases from boiler feed water prior to its introduction to a boiler.
see parting or selective leaching.
- Dechlorination: the removal of chlorine
residual produced during
- Defect: a discontinuity or discontinuities
that by nature or accumulated effect (for example, total crack length) render
a part or product unable to meet minimum applicable acceptance standards or
- Degasification: removal of gases from
samples of steam taken for purity test. Removal of CO2 from water as in the
ion exchange method of softening.
- Degrease: to remove oil or grease from
the surface of the workpiece.
- Degreasing: the removal of grease and
oil from a surface. Degreasing by immersion in liquid organic solvents or by
solvent vapors condensing on the parts to be cleaned.
- Deionization: the removal of all ionized
minerals and salts from a solution
by a two-phase ion exchange process. Positively charged ions are removed by
a cation exchange resin in exchange for a chemically equivalent amount of hydrogen
ions. Negatively charged ions are removed by an anion exchange resin for a chemically
equivalent amount of hydroxide ions.
- Deliquescent: the process of melting
or becoming liquid by absorbing moisture from the air.
- Demineralization: the removal of
ionized minerals and salts from
a solution by a two-phase ion exchange procedure, similar to deionization, and
the two terms are often used interchangeably.
- 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.
- Density: the mass of a substance per
specified unit of volume; for example, pounds per cubic foot. True density is
the mass per unit volume excluding pores; apparent density is the mass per unit
volume including pores. (see specific gravity.)
- Deoxidizing: a) the removal of oxygen
from molten metals by use of suitable deoxidixers. b) Sometimes refers to the
removal of undesirable elements other than oxygen by the introduction of elements
or compounds that readily react with them. c) In metal finishing, the removal
of oxide films from metal surfaces by chemical or electrochemical reaction.
- Depolarization: not a preferred term.
- Deposit: foreign substance which comes
from the environment, adhering to a surface of a material
- Deposit corrosion:
localized corrosion under or around
a deposit or collection of material on a metal surface. (See also
- Depth gauge: see
- Descaling: removing the thick layer
of oxides formed on some metals at elevated temperatures.
- Desiccant: a chemical used to attract
and remove moisture from air or gas.
- Design load: the load for which a steam
generating unit is designed, considered the maximum load to be carried.
- Design pressure: the pressure used in
the design of a boiler for the purpose of calculating the minimum permissible
thickness or physical characteristics of the different parts of the boiler.
- Detergent: any material with cleaning
powers, including soaps, synthetic detergents, many alkaline materials and solvents,
and abrasives. In popular usage the term is often used to mean the synthetic
detergents such as ABS of LAS. (see alkyl benzene sulfonate, linear alkyl sulfonate,
- Detonation gun: a thermal spray process
in which the coating material is heated and accelerated to the workpiece by
a series of detonations or explosions from oxy-fuel gas mixtures.
- Dew point: temperature at which moisture
will condense from humid vapors into a liquid state. (see
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).
- Dialysis: the separation of components
of a solution by diffusion through a semi-permeable membrane which is capable
of passing certain ions or molecules while rejecting others. (see electrodialysis,
- Diamond-like carbon: a thin carbon-based
coating applied by either PVD or
PACVD. It has high hardness and
- Diaphragm pump: a type of positive displacement
pump in which the reciprocating piston is separated from the solution by a flexible
diaphragm, thus protecting the piston from corrosion and erosion, and avoiding
problems with packing and seals.
- Diatomaceous earth: a processed natural
material, the skeletons of diatoms, used as a filter medium.
- Diatomite: another name for diatomaceous
- Dielectric fitting: a plumbing fitting
made of, or containing, an electrical nonconductor, such as plastic; used to
separate dissimilar metals in a plumbing system to control galvanic corrosion.
- 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 (oxygen
concentration cell): a concentration cell caused by differences
in oxygen concentration along the surface of a metal in an electrolyte. (See
spreading of a constituent in a gas, liquid, or solid, tending to make the composition
of all parts uniform.
- Diffusion coating: any process whereby
a base metal or alloy is either a) coated with another metal or alloy and heated
to a sufficient temperature in a suitable environment or b) 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.
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 due to the limitation of diffusion.
- Digestion: the process in which complex
materials are broken down into simpler substances; may be due to chemical, biological
or a combination of reactions.
- Diluent: a liquid used in
coatings to reduce the consistency
and make a coating flow more easily. The
water in latex coatings is a diluent.
A diluent may also be called a "reducer," "thinner," "reducing agent" or "reducing
- Direct-reduced iron (DRI): a metallic
iron product made from iron ore pellets, lumps or fines that is reduced (by
removing only the oxygen) from the ore at a temperature below the melting point
of the iron. DRI is used as feedstock in electric-arc furnaces, blast furnaces
and in other iron and steelmaking processes.
- Disbondment: 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.
- Disinfection: a process in which vegetative
bacteria are killed; may involve disinfecting agents such as chlorine, or physical
processes such as heating.
- Dislocation: a linear imperfection in
a crystalline array of atoms. Two basic types are recognized: a) 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; b) 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
- Dissociation: the process by which a
chemical compound breaks down into simpler constituents, as do CO2 and H2O at
the weight of matter in true solution in a stated volume of water; includes
both inorganic and organic matter; usually determined by weighing the residue
after evaporation of the water.
- Distillate fuels: liquid fuels distilled
usually from crude petroleum.
- Distillation: vaporization of a substance
with subsequent recovery of the vapor by condensation. Often used in less precise
sense to refer to vaporization of volatile constituents of a fuel without subsequent
- Distilled water: water produced by vaporization
and condensation with a resulting higher purity.
- Dolomite: a specific form of limestone
containing chemically equivalent concentrations of calcium and magnesium carbonates;
the term is sometimes applied to limestone with compositions similar to true
- Double layer: the interface between
an electrode 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. (see also
Nernst diffusion layer)
- Downdraft booth: a spray booth in which
the air movement is from the ceiling through the floor.
- Downtime: the time that an item of equipment
is out of service, as a result of equipment failure. The time that an item of
equipment is available, but not utilized is generally not included in the calculation
- Drain: a pipe or conduit in a piping
system which carries liquids to waste by gravity; sometimes the term is limited
to liquids other than sewage.
- Drain line: a tube or pipe from a water
conditioning unit that carries backwash water, regeneration wastes and/or rinse
water to a drain or waste system.
- 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.
- Driers: various compounds added to coatings
to speed the drying.
- Dry colors: powder-type colors to be
mixed with water, alcohol or mineral spirits and resin to form a paint or stain.
- Dry corrosion: see gaseous or hot corrosion.
- Drying oil: an oil that when exposed
to air will dry to a solid through chemical reaction with air: linseed oil,
tung oil, perilla, fish oil, soybean oil.
- Dry to tape: the drying time required
to allow a coating the ability to resist marring of adhesive tape, after wiping
the panel clean.
- Dry steam: steam containing no moisture.
Commercially dry steam containing not more than one half of one percent moisture.
- 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
- Dynamic: active, alive, or tending to
produce motion, as opposed to static, resting or fixed.
- Dynamic system: a system or process
in which motion occurs, or includes active forces, as opposed to static conditions
with no motion.