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Corrosion Glossary C

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Corrosion Glossary C Corrosion Glossary calcareous coating or deposit clad metal A layer consisting of a mixture of A composite metal containing, two calcium carbonate and magnesium or more layers that have been hydroxide deposited on surfaces bonded together. The bonding may being cathodically protected because have been accomplished by co- of the increased pH adjacent to the rolling, co-extrusion, welding, protected surface. diffusion bonding, casting, heavy calomel electrode chemical deposition, heavy An electrode widely used as a electroplating, or explosive cladding. reference electrode of known cleavage potential in electrometric Splitting (fracture) of a crystal on a measurement of acidity and crystallographic plane of low index. alkalinity, corrosion studies, cleavage fracture voltammetry, and measurement of A fracture, usually of polycrystalline the potentials of other electrodes. metal, in which most of the grains See also electrode potential, have failed by cleavage, resulting in reference electrode, and saturated bright reflecting facets. It is calomel electrode. associated with low-energy brittle calorizing fracture. Imparting resistance to oxidation to cold cracking an iron or steel surface by heating in A type of weld cracking that usually aluminum powder at 800 to 1000 ºC occurs below 203 ºC (400 "F). (1470 to 1830 ºF). Cracking may occur during or after carbonitriding cooling to room temperature, A case hardening process in which a sometimes with a considerable time suitable ferrous material is heated delay. Three factors combine to above the lower transformation produce cold cracks: stress (for temperature in a gaseous example, from thermal expansion atmosphere of such composition as and contraction). hydrogen (from to cause simultaneous absorption of hydrogen-containing welding carbon and nitrogen by the surface consumables), and a susceptible and, by diffusion, create a micro.structure (plate martensite is concentration gradient. The process most susceptible to cracking, ferritic is completed by cooling at a rate and bainitic structures least that produces the desired properties susceptible). See also hot cracking, in the workpiece. lamellar tearing and stress-relief carburizing cracking. The absorption of carbon atoms by a cold working metal at high temperatures; it may Deforming metal plastically under remain dissolved, or form metal conditions of temperature and strain carbides; Absorption and diffusion of rote that induce strain hardening. carbon into solid ferrous alloys by Usually, hut not necessarily, heating, to a temperature usually conducted at room temperature. above Ac in contact with a suitable Contrast with hot working. carbonaceous material. A form of combined carbon case hardening that produces a The part of the total carbon in steel carbon gradient extending inward or cast iron that is present as other from the surface, enabling the than free carbon. surface layer to be hardened either complexation by quenching directly from the The formation of complex chemical carburizing temperature or by species by the coordination of cooling to room temperature then groups of atoms termed ligands to a reaustenitizing and quenching. central ion, commonly a metal ion. Carburization Generally, the ligand coordinates by The absorption of carbon into a providing a pair of electrons that metal surface; may or may not be forms an ionic or covalent bond to desirable. the central ion. See also chelate, case hardening coordination compound, and ligand. A generic term covering several compressive processes applicable to steel that Pertaining to forces on a body or change the chemical composition of part of a body that tend to crush or the surface layer by absorption of compress the body. carbon, nitrogen, or a mixture of the compressive strength two and, by diffusion, create a The maximum compressive stress a concentration gradient. The outer material is capable of developing. portion, or case, is made With a brittle material that fails in substantially harder than the inner compression by fracturing, the portion, or core. The processes compressive strength has a definite commonly used are carburizing and value. In the case of ductile, quench hardening; cyaniding: malleable, or semiviscous materials nitrifying; and carbonitriding. The (which do not fail in compression by use of the applicable specific process a shattering fracture), the value name is preferred. obtained for compressive strength is CASS test an arbitrary value dependent on the See copper-accelerated salt-spray degree of distortion that is regarded test. as effective failure of the material. cathode compressive stress The electrode of an electrolytic cell A stress that causes an elastic body at which reduction is the principal to deform (shorten) in the direction reaction. (Electrons How toward the of the applied load. Contrast with cathode in the external circuit.) tensile stress. Typical cathodic processes are concentration cell taking up electrons and being An electrolytic cell, the discharged, oxygen being reduced. electromotive force of which is and the reduction of an element or caused by a difference in group of elements from a high Cl a concentration of some component in lower valence state. Contrast with the electrolyte. This difference leads anode. to the formation of discrete cathode cathode efficiency and anode regions. Current efficiency at the cathode. concentration polarization cathode film That portion of the polarization of a The portion of solution in immediate cell produced by concentration contact with the cathode during changes resulting from passage of electrolysis. current through the electrolyte. cathodic cleaning conductivity Electrolytic cleaning in which the The ratio of the electric current work is the cathode. density to the electric field in a cathodic corrosion material. Also called electrical Corrosion resulting from a cathodic conductivity or specific conductance. condition of a structure usually contact corrosion caused by the reaction of an A term primarily used in Europe to amphoteric metal with the alkaline describe galvanic corrosion between products of electrolysis. dissimilar metals. cathodic disbondment contact plating The destruction of adhesion between A metal plating process wherein the a coating and its substrate by plating current is provided by products of a cathodic reaction. galvanic action between the work metal and a second metal, without cathodic inhibitor the use of an external source of A chemical substance or mixture current. that prevents or reduces the rate of contact potential the cathodic or reduction reaction by The potential difference at the physical, physico-chemical or junction of two dissimilar chemical action. substances. cathodic pickling continuity bond Electrolytic pickling in which the A metallic connection that provides work is the cathode. electrical continuity between metal cathodic polarization structures. Polarization of the cathode; change conversion coating of the electrode potential in the A coating consisting of a compound active (negative) direction due to of the surface metal, produced by current flow; a reduction from the chemical or electrochemical initial potential resulting from treatments of the metal. Examples current flow effects at or near the include chromate coatings on zinc, cathode surface. Potential becomes cadmium, magnesium, and more active (negative) because of aluminum and oxide and phosphate cathodic polarization. See also coatings on steel. See also chromate polarization. treatment and phosphating. cathodic protection coordination compound (1) Reduction of corrosion rate by A compound with a central atom or shifting the corrosion potential of ion bound to a group of ions or the electrode toward a less oxidizing molecules surrounding it. Also called potential by applying an external coordination complex. See also electromotive force. (2) Partial or chelate, complexation, and ligand. complete protection of a metal from copper-accelerated salt-spray (CASS) corrosion by making it a cathode, test using either a galvanic or an An accelerated corrosion test for impressed current. Contrast with some electrodeposits for anodic anodic protection. coatings on aluminum. cathodic reaction corrodkote test Electrode reaction equivalent to a An accelerated corrosion test for transfer of negative charge from the electrodeposits. electronic to the ionic conductor. A corrosion cathodic reaction is a reduction The chemical or electrochemical process. An example common in reaction between a material, usually corrosion is: Ox + ne s Red. a metal, and its environment that catholyte produces a deterioration of the The electrolyte adjacent to the material and its properties. cathode of an electrolytic cell. corrosion effect cation A change in any part of the A positively charged ion that corrosion system caused by migrates through the electrolyte corrosion. toward the cathode under the corrosion embrittlement influence of a potential gradient. See The severe loss of ductility of a also anion and ion. metal resulting from corrosive caustic attack, usually inter,granular and (1) Burning or corrosive. (2) A often not visually apparent. hydroxide of a light metal, such as corrosion-erosion sodium hydroxide or potassium Corrosion which is increased hydroxide. because of the abrasive action of a caustic dip moving stream; the presence of A strongly alkaline solution into suspended particles greatly which metal is immersed for accelerates abrasive action.See etching. for neutralizing acid, or
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