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, dissolved oxygen, and gases from boiler feed water prior to its introduction to a boiler.
Dealloying: see parting or selective leaching.
Dechlorination: the removal of chlorine residual produced during chlorination.
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 specifications.
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. (see polarization).
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 crevice corrosion).
Depth gauge: see pit gauge
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, soap.)
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 TOW)
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).
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, semi-permeable membrane.)
Diamond-like carbon: a thin carbon-based coating applied by either PVD or PACVD. It has high hardness and low friction.
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 earth.
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 concentration cell).
Diffusion: 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.
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 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 solvent."
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 helical ramp.
Dissociation: the process by which a chemical compound breaks down into simpler constituents, as do CO2 and H2O at high temperature.
Dissolved solids: 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 condensation.
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 dolomite.
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 of downtime.
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 means.
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.

Link to glossary of corrosion and materials maintenance terms