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Corrosion Glossary - E

  • Earth pigments: pigments used in paints and obtained from the earth, including barytes, ocher, chalk and graphite
  • Economic life: the total length of time that an asset is expected to remain actively in service before it is expected that it would be cheaper to replace the equipment rather than continuing to maintain it. In practice, equipment is more often replaced for other reasons, including because it no longer meets operational requirements for efficiency, product quality, comfort etc., or because newer equipment can provide the same quality and quantity of output more efficiently.
  • Economizer: utilizes waste heat by transferring heat from flue gases to warm incoming feedwater.
  • Effluent: the stream emerging from a unit, system or process, such as the softened water from an ion exchange softener.
  • Elasticity: the property of certain materials that enables them to return to their original dimensions after an applied stress.
  • Electrical steel: steel that includes silicon. The silicon content allows the steel to minimize energy loss during electrical applications.
  • Electric-arc furnace: an economical method of steelmaking that is energized by an electric arc flowing between two bottom electrodes. Furnace charges consist of purchased scrap.
  • Electrochemical admittance: the reciprocal of the electrochemical impedance, I/E.
  • 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 impedance spectroscopy (EIS): the frequency dependent, complex valued proportionality factor, E/I, between the applied potential (or current) and the response current (or potential) in an electrochemical 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.
  • Electrochemical potential (electrochemical tension): the partial derivative of the total electrochemical 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 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).
  • Electrodialysis: a process in which a direct current is applied to a cell to draw charged ions through ion selective semipermeable membranes, thus removing the ions from the solution.
  • Electroless nickel: the autocatalytic deposition of nickel/phosphorous and nickel/boron have many useful corrosion and corrosion wear applications. Unlike the electrolytic processes, they produce a deposit with completely uniform coverage. In the case of Ni P, deposits around 25 to 50 microns thick with a hardness of about 500Hv is obtained, but thermal ageing at temperatures around 400C can develop hardness values in excess of 1000Hv.
  • Electrolysis: production of chemical changes of the electrolyte by the passage of current through an electrochemical cell. (historical) 'Stray current corrosion'
  • Electrolyte: a nonmetallic substance that carries an electric current, or a substance which, when dissolved in water, separates into ions which can carry 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.
  • Electromotive force series (emf series): a list of elements arranged according to their standard electrode potentials, with "noble" metals such as gold being positive and "active" metals such as zinc being negative.
  • Electron: a fundamental particle found in the atom that carries a single negative charge.
  • Electron volt: unit equal to the energy of one electron moving through a potential difference of one volt.
  • Electrophorus (historical): a hand-held electrophorus can produce significant amounts of charge conveniently and repeatedly. It is operated by first frictionally charging a flat insulating plate called a "cake". In Volta's day, the cake was made of shellac/resin mixtures or a carnauba wax film deposited on glass.
  • 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 smooth the surface.
  • Electrostatic precipitator: a device for collecting dust, mist or fume from a gas stream, by placing an electrical charge on the particle and removing that particle onto a collecting electrode.
  • Electrostatic spraying: a deposition method of spraying and charging a coating so that it is deposited on a substrate usually grounded. A spray application process in which the coating and part to be coated are oppositely charged; process provides excellent "wrap" of coating around the part, even on sides opposite the spray gun. (See Corona Charge and Tribo Charging).
  • Element, chemical: atom that has a unique number of protons in its nucleus. Oxygen is an element with eight protons in the nucleus. There are more than 100 elemental substances that cannot be chemically separated into other elements. All matter is composed of one or more chemical elements. As of 1988, 105 of 109 known elements have been assigned a name.
  • Elution: the stripping of ions from an ion exchange material by other ions, either because of greater affinity or because of much higher concentration.
  • Embrittlement: the severe loss of ductility or toughness or both, of a material, usually a metal or alloy.
  • Emulsion: a mixture of solids suspended in a liquid.
  • Emulsion paint: coating in which resins are suspended in water, then flow together with the aid of an emulsifier. Example: latex paint.
  • Enamel: broad classification of paints that dry to a hard, usually glossy finish. Most equipment-coating enamels require baking. Enamels for walls do not.
  • Endpoint: the point at which a process is stopped because a predetermined value of a measurable variable is reached.
  • 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.
  • Energy conversion: process of changing one form of energy into another.
  • Environmental consequences: a failure has environmental consequences if it could cause a breach of any known environmental standard or regulation.
  • 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.
  • Environmental Protection Agency (EPA): established on December 2, 1970, the EPA is charged with protecting and enhancing the environment for present and future generations to the fullest extent possible under US Congressional law with responsibilities including the control of solid waste, pesticides, radiation, and toxic substances, and the abatement of air and water pollution.
  • Epoxy: extremely tough and durable synthetic resin used in some coatings. Epoxy coatings are extremely tough, durable and highly resistant to chemicals, abrasion, moisture and alcohol.
  • Equilibrium: the state in which the action of multiple forces produce a stead balance.
  • 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).
  • Equilibrium reaction: a chemical reaction which proceeds primarily in one direction until the concentrations of reactants and products reach an equilibrium.
  • Equivalent weight: the weight in grams of an element, compound or ion which would react with or replace 1 gram of hydrogen; the molecular weight in grams divided by the valence.
  • Erosion: the progressive loss of material from a solid surface due to mechanical interaction between that surface and a fluid, a multi-component fluid, or solid particles carried with the fluid.
  • Erosion-corrosion: a conjoint action involving corrosion and erosion in the presence of a moving corrosive fluid. Leading to the accelerated loss of material.
  • Estimated plant replacement value: the estimated cost of capital works required to replace all the existing assets with new assets capable of producing the same quantity and quality of output. This is a key value often used in benchmarking activities.
  • Etch: a roughened surface produced by chemical, electrochemical or mechanical means. To dissolve unevenly a part of the surface of a material to highlight microstructure in metallography.
  • Etching: the use of a chemical solution or primer to prepare a surface for priming or bonding by removing a layer of the base metal (e.g. Alodine).
  • Ettringite: A naturally occurring mineral characterized as a high sulfate calcium sulfoaluminate ( 3 CaO . Al3O3 . 3 CaSO4 . 30-32 H2O ). It is formed as a cement hydration product or by sulfate attack in mortar and concrete. It is also the product of the principal expansion-producing reaction in expansive cements. Was designated as "cement bacillus" in older literature.
  • Evaporation: the change of state from a liquid to a vapor.
  • Evaporation rate: the quantity of water of any other liquid that is evaporated in a unit of time.
  • 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).
  • Exempt solvents: solvents whose use is not subject to air pollution legislation.
  • 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.
  • Exothermic reaction or material: certain materials undergo chemical reactions when thermally sprayed and produce extra heating. This can be useful in improving adhesion of the coating to the substrate.
  • Expansion joint: The joint to permit movement due to expansion without undue stress.
  • Expert System: a knowledge based system which makes or evaluates decisions based on rules established within the software.
  • Extender: ingredients added to paint to increase coverage, reduce cost, achieve durability, alter appearance, control rheology and influence other desirable properties. Less expensive than prime hiding pigments such as titanium dioxide. Examples: barium sulfate, calcium carbonate, clay, gypsum, silica, talc.
  • 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.

Link to glossary of corrosion and materials maintenance terms