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Corrosion Source - Corrosion glossary
Category: General technical and industrial > Corrosion
Date & country: 11/12/2007, UK
Words: 619

metal dusting.
Accelerated deterioration of metals in carbonaceous gases at elevated temperatures to form a dustlike corrosion product; a unique form of high temperature corrosion which forms a dust-like corrosion product and sometimes develops hemispherical pits on a susceptible metal surface; simultaneous carburization is generally observed.

metal ion concentration cell
A galvanic cell caused by a difference in metal ion concentration at two locations on the same metal surface.

metallic glass.
An alloy having an amorphous or glassy structure. See also amorphous solid.

(1) The application of an electrically conductive metallic layer to the surface of nonconductors. (2) The application of metallic coatings by nonelectrolytic procedures such us spraying of molten metal and deposition from the vapor phase.

meteor perforation
Perforation of material in outer space resulting from meteor strikes.

microbial corrosion.
See biological corrosion.

Visible at magnifications above 25x.

The structure of a prepared surface of a metal as revealed by a microscope at a magnification exceeding 25x.

mill scale.
The heavy oxide layer formed during hot fabrication or heat treatment of metals.

mixed potential.
The potential of a specimen (or specimens in a galvanic couple) when two or more electrochemical reactions are occurring. Also called galvanic couple potential.

molal solution.
Concentration of a solution expressed in moles of solute divided by 1000 g of solvent.

molar solution.
Aqueous solution that contains 1 mole (gram-molecular weight) of solute in 1 L of the solution.

One mole is the mass numerically equal (in grams) to the relative molecular mass of a substance. It is the amount of substance of asystem that contains as many elementary units (6.023 exp23) as there are atoms of carbon in 0.012 kg of the pure nuclide C12; the elemenary unit must be specified and may be an atom, molecule, ion, electron, photon, or …

moneypenny-strauss test.
Corrosion testing in a copper-sulfate solution containing sulfuric acid. Used to detect the susceptibility of stainless steel to intergranular corrosion.

A molecule usually an organic compound, having the ability to join with a number of identical molecules to form a polymer.

natural aging
Spontaneous aging of a supersaturated solid solution at room temperature. See also aging. Compare with artificial aging.

Nernst equation
An equation that expresses the exact electromotive force of a cell in terms of the activities of products and reactants of the cell.

Nernst layer, Nernst thickness
The diffusion layer or the hypothetical thickness of this layer as given by the theory of Nernst, is defined by: id= n F D (Co - C)/d where, id = the diffusion limited current density, D = the diffusion coefficient, Co = the concentration at the electrode surface, and d= the Nernst thickness. It is a hypo…

neutron embrittlement
Embrittlement resulting from bombardment with neutrons, usually encountered in metals that have been exposed to a neutron flux in the core of a reactor. In steels, neutron embrittlement is evidenced by a rise in the ductile-to-brittle transition temperature.

Introducing nitrogen into the surface layer of a solid ferrous alloy by holding at a suitable temperature (below Ac1 for ferritic steels) in contact with a nitrogenous material, usually ammonia or molten cyanide of appropriate composition. Quenching is not required to produce a hard case.

Any of several processes in which both nitrogen and carbon are absorbed into the surface layers of a ferrous material at temperatures below the lower critical temperature and, by diffusion, create a concenteration gradient. Nitrocarburizing is performed primarily to provide an antiscuffling surface layer and to improve fatigue resistance. Comparc w…

The positive direction of electrode potential, thus resembling noble metals such as gold and platinum.

noble metal
(1) A metal whose potential is highly positive relative to the hydrogen electrode. (2) A metal with marked resistance to chemical reaction, particularly to oxidation and to evolution by inorganic acids. The term as often used is synonymous with precious metal.

noble potential
A potential more cathodic (positive) than the standard hydrogen potential.

normal solution
An aqueous solution containing one gram equivalent of the active reagent in 1L of the solution.

normal stress
The stress component perpendicular to a plane on which forces act. Normal stress may be either tensile or compresssive.

Heating a ferrous alloy to a suitable temperature above the transformation range and then cooling in air to a temperature substantially below the transformation range.

open-circuit potential
The potential of an electrode measured with respect to a reference electrode or another electrode when no current flows to or from it.

Being or composed of hydrocarbons or their derivatives, or matter of plant or animal origin. Contrast with inorganic.

organic acid
A chemical compound with one or more carboxyl radicals (COOH) in its structure; examples are butyric acid, CH3(CH2)2COOH; maleic acid, HOOCCH-CHCOOH; and benzoic acid, C6H5COOH.

organic zinc-rich paint
Coating containing zinc powder pigment andan organic resin.

Heating a metal or alloy to such a high temperature that its properties are impaired. When the original properties cannot be restored by further heat treating, by mechanical working, or by a combination of working and heat treating, the overheating is known as burning.

Aging under conditions of time and temperature greater than those required to obtain maximum change in a certain property, so that the property is altered in the direction of the initial value.,

The difference between the actual electrode potential when appreciable electrolysis begins and the reversible electrode potential.

(1) A reaction in which there is an increase in valence resulting from a loss of electrons. Contrast with reduction. (2) A corrosion reaction in which the corroded metal forms an oxide; usually applied to reaction with a gas containing elemental oxygen, such as air.

oxidized surface (on steel)
Surface having a thin, tightly adhering, oxidized skin (from straw to blue in color), extending in from the edge of a coil or sheet.

oxidizing agent
A compound that causes oxidation, thereby itself being reduced.

oxygen concentration cell
A galvanic cell resulting from difference in oxygen concentration between two locations; See differential aeration cell.

A powerfully oxidizing allotropic form of the element oxygen. The ozone molecule contains three atoms (O3). Ozone gas is decidedly blue, and both liquid and solid ozone are an opaque blue-black color, similar to that of ink.

partial annealing
An imprecise term used to denote a treatment given cold-worked material to reduce its strength to a controlled level or to effect stress relief. To be meaningful, the type of material, the degree of cold work, and the time-temperature schedule must be stated.

The selective attack of one or more components of a solid solution alloy; eg. dezincification, dealumination etc. See dealloying.

parts per billion
A measure of proportion by weight, equivalent to one unit weight of a material per billion (109) unit weights of compound. One part per billion is equivalent to 1 mg/kg.

parts per million
A measure of proportion by weight, equivalent to one unit weight of a material per million (10sup>6) unit weights of compound. One part per million is equivalent to l mg/g

(1) A reduction of the anodic reaction rate of an electrode involved in corrosion. (2) The process in metal corrosion by which metals become passive. (3) The changing of a chemically active surface of a metal to a much less reactive state. Contrast with activation.

A type of inhibitor that appreciably changes the potential of u metal to a more noble (positive) value.

(1) A metal corroding under the control of a surface reaction product. (2) The state of the metal surface characterized by low corrosion rates in a potential region that is strongly oxidizing for the metal. (3) The state of a metal when its behavior is much more noble than its position in the EMF series would predict. This is a surface phenomena.

passive-active cell
(1) A cell, the emf of which is due to the potential difference between a metal in an active state and the same metal in a passive state. (2) A corrosion cell in which the anode is a metal in the active state and the cathode is the same metal in the passive state.

A condition in which a piece of metal, because of an impervious covering of oxide or other compound, has a potential much more positive than that at the metal in the active state.

The coating, usually green, that forms on the surface of metals such as copper and copper alloys exposed to the atmosphere. Also used to describe the appearance of a weathered surface of any metal.

A metastable lamellar aggregate of ferrite and cementite resulting from the transformation of austenite at temperatures above the bainite range.

A measure of the acidity or alkalinity of a solution; The negative logarithm of the hydrogen-ion activity; it denotes the degree of acidity or basicity of a solution. At 25 ºC (77 ºF), 7.0 is the neutral value. Decreasing values below 7.0 indicate increasing acidity; increasing values above 7.0, increasing basicity.

Forming an adherent phosphate coating on a metal by immersion in a suitable aqueous phosphate solution. Also called phosphatizing. See also conversion coating.

physical vapor deposition
A coating process whereby the cleaned and masked component to be coated is heated and rotated on a spindle above the streaming vapor generated by melting and evaporating a coating material source bar with a focused electron beam in an evacuated chamber.

The binding of an adsorbate to the surface of a solid by forces whose energy levels approximate those of condensation. Contrast with chemisorption.

A solution or process used to loosen or remove corrosion products such as scale or tarnish.

Removing surface oxides from metals by chemical or electrochemical reaction.

Localized corrosion of a metal surface, confined to a point or small area, that takes the form of cavities or pits.

pitting factor
Ratio of the depth of the deepest pit resulting from corrosion divided by the average penetration as calculated from weight loss.

plane strain
The stress condition in linear elastic fracture mechanics in which there is zero strain in a direction normal to both the axis of applied tensile stress and the direction of crack growth (that is, parallel to the crack front); most nearly achieved in loading thick plates along a direction parallel to the plate surface. Under plane-strain conditions…

plane stress
The stress condition in linear elastic fracture mechanics in which the stress in the thickness direction is zero; most nearly achieved in loading very thin sheet along a direction parallel to the surface of the sheet. Under plane-stress conditions, the plane of fracture instability is inclined 45º to the axis of the principal tensile stress.

plasma spraying
A thermal spraying process in which the coating material is melted with heat from a plasma torch that generates a nontransferred arc: molten coating material is propelled against the base metal by the hot, ionized gas issuing from the torch.

plastic deformation
The permanent (inelastic) distortion of metals under applied stresses that strain the material beyond its elastic limit.

The property that enables a material to undergo permanent deformation without rupture.

(1) The change from the open-circuit electrode potential as the result of the passage of current. (2) A change in the potential of an electrode during electrolysis, such that the potential of an anode becomes more noble, and that of a cathode more active, than their respective reversible potentials. Often accomplished by formation of a film on the …

polarization admittance
The reciprocal of polarization resistance (di/dE).

polarization curve
A plot of r urrent density versus electrode potential for a specific electrode-electrolyte combination.

polarization resistance
The slope (dE/di) at the corrosion potential of a potential (E)/current density (i) curve. Also used to describe the method of measuring corrosion rates using this slope.

Resin formed by condensation of polybasic and monobasic acids with polyhydric alcohols.

A chain of organic molecules produced by the joining of primary units called monomers.

Any of various functions from which intensity or velocity at any point in a field may be calculated. The driving influence of an electrochemical reaction. See also active potential, chemical potential, corrosion potential, critical pitting potential, decomposition potential, electrochemical potential, electrode potential, electrokinetic potential, …

potential-pH diagram
See Pourbaix (potential-pH) diagram.

potentiodynamic (potentiokinetic)
The technique for varying the potential of an electrode in a continuous manner at a preset rate.

An instrument for automatically maintaining an electrode in an electrolyte at a constant potential or controlled potentials with respect to a suitable reference electrode.

The technique for maintaining a constant electrode potential.

poultice corrosion
A term used in the automotive industry to describe the corrosion of vehicle body parts due to the collection of road salts and debris on ledges and in pockets that are kept moist by weather and washing. Also called deposit corrosion or attack.

Pourbaix (potential-pH) diagram
A plot of the redox potential of a corroding system versus the pH of the system, compiled using thermodynamic data and the Nernst equation. The diagram shows regions within which the metal itself or some of its compounds are stable.

powder metallurgy
The art of producing metal powders and utilizing metal powders for production of massive materials and shaped objects.

precious metal
One of the relatively scarce and valuable metals: gold, silver, and the platinum-group metals. Also called noble metal(s).

precipitation hardening
Hardening caused by the precipitation of a constituent from a supersaturated solid solution. See also age hardening and aging.

precipitation heat treatment
Artificial aging in which a constituent precipitated from a supersaturated solid solution.

precracked specimen
A specimen that is notched and subjected to alternating stresses until a crack has developed at the root of the notch.

primary current distribution
The current distribution in an electrolytic cell that is free of polarization.

principal stress (normal)
The maximum or minimum value at the normal stress at a point in a plane considered with respect to all possible orientations of the considered plane. On such principal planes the shear stress is zero. There are three principal stresses on three mutually perpendicular planes. The state of stress at a point may be (1) uniaxial, a state of stress in w…

Anchor pattern on a surface produced by abrasive blasting or acid treatment.

protective potential
The threshold value of the corrosion potential that has to be reached to enter a protective potential range. The term used in cathodic protection to refer to the minimum potential required to supress corrosion.

protective potential range
A range of corrosion potential values in which unacceptable corrosion resistance is achieved for a particular purpose.

quench aging.
Aging induced by rapid cooling after solution heat treatment.

quench cracking.
Fracture of a metal during quenching from elevated temperature. Most frequently observed in hardened carbon steel, alloy steel, or tool steel parts of high hardness and low toughness. Cracks often emanate from fillets, holes, corners, or other stress raisers and result from high stresses due to the volume changes accompanying transformation to mart…

quench hardening.
(1) Hardening suitable a= balloys (most often certain copper or titanium alloys) by solution treating and quenching to develop a martensite-like structure. (2) In ferrous alloys, hardening by austenitizing and then cooling at a rate such that a substantial amount of austenite transforms to martensite.

quench-age embrittlement.
Embrittlement of low-carbon steels resulting from precipitation of solute carbon at existing dislocations and from precipitation hardening of the steel caused by differences in the solid solubility of carbon in ferrite at different temperatures. Quench-age embrittlement usually is caused by rapid cooling of the steel from temperatures slightly belo…

Rapid cooling of metals (often steels) from a suitable elevated temperature. This generally is accomplished by immersion in water, oil, polymer solution, or salt, although forced air is sometimes used.

radiation damage
A general term for the alteration of properties of a material arising from exposure to ionizing radiation (penetrating radiation), such as x-rays, gamma rays. neutrons, heavy-particle radiation, or fission fragments in nuclear fuel material.

rare earth metal
One of the group of l5 chemically similar metals with atomic numbers 57 through 7l, commonly referred to as the lanthanides.

reactive metal
A metal that readily combines with oxygen at elevated temperatures to form very stable oxides, for example, titanium, zirconium, and beryllium. Reactive metals may also become embrittled by the interstitial absorption of oxygen, hydrogen, and nitrogen.

(1) Formation of a new, strain free grain structure from that existing in cold worked metal, usually accomplished by heating. (2) The change from one crystal structure to another, as occurs on heating or cooling through a critical temperature.

redox potential
The potential of a reversible oxidation-reduction electrode measured with respect to a reference electrode, corrected to the hydrogen electrode, in a given electrolyte.

reducing agent
A compound that causes reduction, thereby itself becoming oxidized.

A reaction in which there is a decrease in valence resulting from a gain in electrons. Contrast with oxidation.

reference electrode
A nonpolarizable electrode with a known and highly reproducible potential used for potentiometric and voltammetric analyses. See also calomel electrode.

refractory metal
A metal having an extremely high melting point, for example, tungsten, molybdenum, tantalum, niobium, chromium, vanadium, and rhenium. In the broad sense, this term refers to metals having melting points above the range for iron, cobalt, and nickel.