Corrosion Terminology - E's

elastic deformation—changes of dimensions of a material upon the application of a stress within the elastic range. Following the release of an elastic stress, the material returns to its original dimensions without any permanent deformation.

elasticity—the property of a material that allows it to recover its original dimensions following deformation by a stress below its elastic limit.

elastic limit—the maximum stress to which a material may be subjected without retention of any permanent deformation after the stress is removed.

electrical interference—any electrical disturbance on a metallic structure in contact with an electrolyte caused by stray current(s).

electrical isolation—the condition of being electrically separated from other metallic structures or the environment.

electro-chemical admittance—the reciprocal of the electro-chemical impedance, DI/DE.

electro-chemical cell (1) an electro-chemical reaction involving two half reactions, one of which involves oxidation of the reactant(product) and the other of which involves reduction of the product (reactant).(The equilibrium potential of the electro-chemical cell can be calculated from the change in free energy for the overall electro-chemical reaction. The equilibrium potential of the electro-chemical cell can be measured by separating the oxidation and reduction half reactions into individual compartments and measuring the voltage that develops between them under conditions that virtually no charge passes between them.) [thermodynamic use] (2) an electro-chemical 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.) [common use]

electro-chemical corrosion potential—see  corrosion potential.

electro-chemical equivalent—the mass of an element or group of elements oxidized or reduced at 100 percent efficiency by the passage of a unit quantity of charge such as a Faraday(96,485 coulombs), ampere-hour, or coulomb.

electro-chemical impedance—the frequency dependent, complex valued proportionality factor, DI/DE, between the applied potential (or current) and the response current (or potential) in an electro-chemical cell. This factor becomes the impedance when the perturbation and response are related linearly (the factor value is independent of the perturbation magnitude) and the response is caused only by the perturbation.The value may be related to the corrosion rate when the measurement is made at the corrosion potential.

electro-chemical noise—fluctuations of potential or current, or both, originating from uncontrolled variations in a corrosion process.

electro-chemical potential—the partial derivative of the total electro-chemical free energy of the system with respect to the number of moles of the constituent in a solution when all other factors are constant. (Analogous to the chemical potential of the constituent except that it includes the electrical as well as the chemical contributions to the free energy.)

electrode—a material that conducts electrons, is used to establish contact with an electrolyte, and through which current is transferred to or from an electrolyte.

electrode potential—the potential of an electrode in an electrolyte as measured against a reference electrode.

electro-kinetic potential—a potential difference in a solution caused by residual, unbalanced charge distribution in the adjoining solution, producing a double layer. (The electro-kinetic potential is different from the electrode potential in that it occurs exclusively in the solution phase. This potential 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.) [also known as zeta potential]

electrolysis—production of chemical changes of the electrolyte by the current flowing through an electro-chemical cell.

electrolyte—a chemical substance containing ions that migrate in an electric field.

electrolytic corrosion—not a proper term, but sometimes incorrectly used to refer to galvanic corrosion, stray-current corrosion, or any form of electro-chemical corrosion.

electrolytic cleaning—aprocess for removing soil, scale, or corrosion products from a metal surface by subjecting the metal as an electrode to an electric current in an electrolytic bath.

electromotive force series—a list of elements arranged according to their standard electrode potentials, the sign being positive for elements whose potentials are more noble than hydrogen such as gold and negative for those more active than hydrogen such as zinc.[not to be confused with galvanic series]

electro-osmosis—the migration of water through a semipermeable membrane as a result of a potential difference caused by the flow of electric charge through the membrane.

ellipsometry—an optical technique wherein plane-polarized light is focused on a surface and the reflected beam is analyzed to determine the phase shift of the components of the light to provide information on the properties of films that may be present on the surface.

embrittlement—reduction of ductility, or toughness, or both, of a material (usually a metal or alloy).

EMF series—see electromotive force series.

enamel(1) a paint that dries to a hard, glossy surface. (2) a coating that is characterized by an ability to form a smooth, durable film.

end effect—the more rapid loss of anode material at the end of an anode, compared with other surfaces of the anode, resulting from higher current density.

endurance limit—the maximum stress that a material can withstand for an infinitely large number off atigue cycles.

environment—the surroundings or conditions (physical, chemical, mechanical) in which a material exists.

environmental cracking—cracking of a material wherein an interaction with its environment is a causative factor in conjunction with tensile stress, often resulting in brittle fracture of an otherwise ductile material. [also known as environmentally assisted cracking]Discussion—Environmental cracking is a general term that includes the terms listed below. The definitions of these terms are listed elsewhere in this document: caustic cracking, chloride stress corrosion cracking, corrosion fatigue, hydrogen embrittlement , hydrogen-induced cracking (stepwise cracking), hydrogen stress cracking,liquid metal cracking, stress corrosion cracking, sulfide stress cracking.Discussion—The following terms have been used in the past in connection with environmental cracking but are now obsolete and should not be used: caustic embrittlement, delayed cracking, liquid metal embrittlementseason cracking, static fatigue,  sulfide corrosion cracking, sulfide stress corrosion cracking.

environmentally assisted cracking—see  environmental cracking.

epoxy—type of resin formed by the reaction of aliphatic or aromatic polyols (such as bisphenol) with epichlorohydrin and characterized by the presence of reactive oxirane end groups.

equilibrium potential—the potential of an electrode in an electrolyte at which the forward rate of agiven reaction is exactly equal to the reverse rate. (The equilibrium potential can only be defined with respect to a specific electro-chemical reaction.) [also known as reversible potential]

erosion—the progressive loss of material from a solid surface resulting from mechanical interaction between that surface and a fluid, a multi-component fluid, or solid particles carried with the fluid.

erosion-corrosion—a conjointaction involving erosion and corrosion in the presence of a moving corrosive fluid or a material moving through the fluid, leading to accelerated loss of material.

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) is exactly equal to the rate of cathodic charge transfer (reduction).

exfoliation corrosion—subsurface corrosion that proceeds laterally from the sites of initiation along planes parallel to the surface forming corrosion products that force metal away from the body of the material, giving rise to a layered appearance resembling the pages of a book.

external circuit—the wires, connectors, measuring devices, current sources, etc., that are used to bring about or measure the desired electrical conditions within an electro-chemical cell. It is this portion of the cell through which electrons travel.