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Corrosion Glossary - C

  • Calcareous coating or deposit: a layer consisting of a mixture of calcium carbonate and magnesium hydroxide deposited on surfaces being cathodically protected because of the increased pH adjacent to the protected surface.
  • Cadmium plating: the electrolytic deposition of cadmium to provide galvanic corrosion protection. Restricted by environmental considerations.
  • Cadmium ion plating: the deposition of cadmium by a vacuum process to provide galvanic corrosion protection.
  • Calcium: one of the principal elements in the earth's crust. When dissolved, in water, calcium is a factor contributing to the formation of scale and insoluble soap curds that are a means of clearly identifying hard water.
  • Calcium carbonate equivalent: a common basis for expressing the concentration of hardness and other salts in chemically equivalent terms to simplify certain calculations; signifies that the concentration of a dissolved mineral is chemically equivalent to the stated concentration of calcium carbonate.
  • Calcium hypochlorite: a chemical compound, [Ca(ClO)2.4H2O], used as a bleach and as a source of chlorine in water treatment for chlorination. Specifically useful because it is stable as a dry powder and can be formed into tablets.
  • Calomel electrode: an electrode widely used as a reference electrode of known potential in electrometric measurement of acidity and alkalinity, corrosion studies, voltammetry, and measurement of the potentials of other electrodes. See also electrode potential, reference electrode, and saturated calomel electrode.
  • Calorie: the mean calorie is 1/100 of the heat required to raise the temperature of 1 gram of water from 0C to 100C at a constant atmospheric pressure. It is about equal to the quantity of heat required to raise one gram of water 1C. Another definition is, one calorie is 4.1860 joules.
  • Capillary action: a phenomenon in which water or many other liquids will rise above the normal liquid level in a tiny tube or capillary, due to attraction between molecules of the liquid for each other and the walls of the tube.
  • Carbide: a chemical compound formed between carbon and a metal or metals; examples are tungsten carbide, tantalum carbide, titanium carbide, chromium carbide.
  • Carbon chloroform extract: the matter adsorbed from a stream of water by activated carbon, and then extracted from the activated carbon with chloroform, using a specific standardized procedure; a measure of the organic matter in a water.
  • Carbon dioxide: a gas present in the atmosphere and formed by the decay of organic matter; the gas in carbonated beverages; in water it forms carbonic acid.
  • Carbonaceous: materials of or derived from organic substances such as coal, lignite, peat, etc.
  • Carbonaceous exchanger: ion exchange material produced by the sulfonation of carbonaceous matter.
  • Carbonate alkalinity: alkalinity due to the presence of the carbonate ion (CO32-).
  • Carbonate hardness: hardness due to the presence of calcium and magnesium bicarbonates and carbonates in water; the smaller of the total hardness and the total alkalinity. (see temporary hardness.)
  • Carbon dioxide: common gas molecule consisting of one carbon atom and two oxygen atoms made by burning carbon substances such as fossil fuels or by metabolism in the body.
  • Carbonitriding: similar to Carburizing. Diffusion of carbon and nitrogen at about 900oC (by pack, gas, salt bath or plasma process) into low carbon steel, followed by quenching and tempering to produce martensitic case (typically 1 mm thick).
  • Carbon steel: steel that has properties made up mostly of the element carbon and which relies on the carbon content for structure. Most of the steel produced in the world is carbon steel.
  • Carboxylic: an organic acidic group (COOH) which contributes cation exchange ability to some resins.
  • Carburizing (also called case hardening): diffusion of carbon at about 900oC (by pack, gas, salt bath or plasma process) into low carbon steel, followed by quenching and tempering to produce martensitic case (typically 1 mm thick).
  • Carburizing flame: a nonstandard term for reducing flame.
  • Carrier gas: usually nitrogen or argon gas that carries powder into the thermal spray process.
  • Casehardening: See Carburizing.
  • CASS test: see copper-accelerated salt-spray test.
  • Catalyst: substance whose presence increases the rate of a chemical reaction. (Paint) Acid catalyst added to an epoxy resin system to accelerate drying time.
  • Cathode: the electrode of an electrolytic cell at which reduction is the principal reaction. Electrons flow toward the cathode in the external circuit.
  • Cathodic coating: coatings which become the cathode in an electrochemical cell with the substrate (anode). This type of coating protects the substrate from corrosion only by being a complete barrier. If the coating allows the environment to reach the substrate, accelerated corrosion of the substrate will occur.
  • Cathodic corrosion: corrosion of a metal when it is a cathode. (It usually happens to metals because of a rise in pH at the cathode or as a result of the formation of hydrides).
  • Cathodic disbondment: the destruction of adhesion between a coating and its substrate by products of a cathodic reaction.
  • Cathodic inhibitor: an inhibitor that reduces the corrosion rate by acting on the cathodic (reduction) reaction.
  • Cathodic pickling: electrolytic pickling in which the work is the cathode.
  • Cathodic polarization: the change of the electrode potential in the active (negative) direction due to current flow. (See polarization).
  • Cathodic protection: a corrosion control system in which the metal to be protected is made to serve as a cathode, either by the deliberate establishment of a galvanic cell or by impressed current. (see anode.)
  • Cathodic reaction: electrode reaction equivalent to a transfer of negative charge from the electronic to the ionic conductor. A cathodic reaction is a reduction process.
  • Catholyte: the electrolyte adjacent to the cathode of an electrolytic cell.
  • Cation: a positively charged ion.
  • Cation exchange: ion exchange process in which cations in solution are exchanged for other cations from an ion exchanger.
  • Caustic: any substance capable of burning or destroying animal flesh or tissue. the term is usually applied to strong bases.
  • Caustic cracking: stress corrosion cracking of metals in caustic solutions. (See also stress corrosion cracking).
  • Caustic dip: a strongly alkaline solution into which metal is immersed for etching, for neutralizing acid, or for removing organic materials such as greases or paints.
  • Caustic embrittlement: see caustic cracking.
  • Caustic soda: the common name for sodium hydroxide.
  • Cavitation: the formation and rapid collapse within a liquid of cavities or bubbles that contain vapor or gas or both.
  • Cavitation damage:the degradation of a solid body resulting from its exposure to cavitation. (This may include loss of material, surface deformation, or changes in properties or appearance).
  • Cavitation-erosion: progressive loss of original material from a solid surface due to continuing exposure to cavitation.
  • Cementation coating: a coating developed on a metal surface by a high temperature diffusion process (as carburization, calorizing, or chromizing).
  • Cement bacillus: older term for ettringite.
  • Cementite: a compound of iron and carbon, known chemically as iron carbide and having the chemical formula Fe3C. It is characterized by an orthorhombic crystal structure.
  • Cermet: a physical mixture of ceramics and metals; examples are alumina plus nickel and zirconia plus nickel.
  • Chalking: the development of loose removable powder at the surface of an organic coating usually caused by weathering.
  • Charge, charging: putting raw materials into a furnace. For example, a blast furnace is charged with coke, coal, iron or scrap to make raw steel. The charge itself is the amount of material loaded into the furnace.
  • Checking: the development of slight breaks in a coating that do not penetrate to the underlying surface.
  • Checks: numerous, very fine cracks in a coating or at the surface of a metal part. Checks may appear during processing or during service and are most often associated with thermal treatment or thermal cycling. Also called check marks, checking, or heat checks.
  • Chelate: a molecular structure in which a heterocyclic ring can he formed by the unshared electrons of neighboring atoms or a coordination compound in which a heterocyclic ring is formed by a metal bound to two atoms of the associated ligand. See also complexation.
  • Chelating agent: a chemical compound sometimes fed to water to tie up undesirable metal ions, keep them in solution, and eliminate or reduce the normal effects of the ion. (see sequestering agent.)
  • Chelation: the process of forming complex chemical compounds in which certain metal ions are bound into stable ring structures, keeping the ions in solution and eliminating or reducing normal (and often undesirable) effects of the ions. Similar to the process of sequestration.
  • Chemical conversion coating: a protective or decorative nonmetallic coating produced in situ by chemical reaction of a metal with a chosen environment. (It is often used to prepare the surface prior to the application of an organic coating).
  • Chemical potential: in a thermodynamic system of several constituents, the rate of change of the Gibbs function of the system with respect to the change in the number of moles of a particular constituent.
  • Chemical stability: resistance to attach by chemical action.
  • Chemical vapor deposition: a coating process, similar to gas carburizing and carbonitriding, whereby a reactant atmosphere gas is fed into a processing chamber where it decomposes at the surface of the workpiece, liberating one material for either absorption by, or accumulation on the workpiece. A second material is liberated in gas form and is removed from the processing chamber, along with excess atmosphere gas.
  • Chemisorption: a process related to adsorption in which atoms or molecules of reacting substances are held to the surface atoms of a catalyst by electrostatic forces having about the same strength as chemical bonds. Chemisorption differs from physical adsorption chiefly in the strength of bonding, which is much greater in chemisorption than in adsorption.
  • Chloramination: the process of treating drinking water by applying chlorine before or after ammonia. This creates a persistent disinfectant residual.
  • Chlorides: salts of chloride are generally soluble. High concentrations contribute to corrosion problems.
  • Chlorination: the treatment process in which chlorine gas or a chlorine solution is added to water for disinfection and control of microorganisms. Chlorination is also used in the oxidation of dissolved iron, manganese, and hydrogen sulfide impurities.
  • Chlorinator: a device designed to feed chlorine gas or solutions of its compounds, such as hypochlorite, into a water supply.
  • Chlorine: a widely used gas used in the disinfection of water and an oxidizing agent for organic matter. (see chlorination)
  • Chlorinated rubber: a non-convertible binder used to produce single pack paints, with good resistance to acids, alkalies, humidity.
  • Chlorine demand: a measure of the amount of chlorine which will be consumed by organic matter and other oxidizable substances in a water before a chlorine residual will be found. Chlorine demand represents the difference between the total chlorine fed and the chlorine residual. (see chlorination)
  • Chlorinity: the total halogen ion (chloride, bromide, etc.) content as titrated by the addition of silver nitrate, expressed in parts per thousand, i.e. o/oo.
  • Chlorofluorocarbon (CFC): gas containing carbon and fluorine in various combinations. CFCs are generally volatile and are alleged to decrease the earth's protective ozone layer.
  • Chroma:a measure of color. The degree of saturation of a hue. A color at its full intensity has maximum chroma.
  • Chromadizing: improving paint adhesion on aluminum or aluminum alloys, mainly aircraft skins, by treatment with a solution of' chromic acid. Also called chromodizing or chromatizing. Not to be confused with chromating or chromizing.
  • Chromate treatment: a treatment of metal in a solution of a hexavalent chromium compound to produce a conversion coating consisting of trivalent and hexavalent chromium compounds.
  • Chromating: chromate conversion is a process which completely degreases and removes all traces of the oxide film, replacing it by immersion with a chromate coating which can then be painted. It is used as a post-treatment for cadmium, zinc and aluminum coatings.
  • Chromium: a steel-gray, lustrous, hard and brittle metallic element that takes its name from the Greek word for color (chrome) because of the brilliant colors of its compounds. It is found primarily in chromite. Resistant to tarnish and corrosion, it is a primary component of stainless steel and is used to harden steel alloys.
  • Chromizing: a surface treatment at elevated temperature, generally carried out in pack, vapor, or salt bath, in which an alloy is formed by the inward diffusion of chromium into the base metal.
  • Clad metal: a composite metal containing, two or more layers that have been bonded together. The bonding may have been accomplished by co-rolling, co-extrusion, welding, diffusion bonding, casting, heavy chemical deposition, or heavy electroplating.
  • Cladding: a surfacing variation that deposits or applies surfacing material, usually to improve corrosion or heat resistance.
  • Clear coating: a transparent protective and/or decorative film, generally the final coat of sealer applied to automotive finishes.
  • Cleavage: splitting (fracture) of a crystal on a crystallographic plane of' low index.
  • Cleavage fracture: a fracture, usually of polycrystalline metal, in which most of the grains have failed by cleavage, resulting in bright reflecting facets. It is associated with low-energy brittle fracture.
  • Coagulant: a material, such as alum, which will form a gelatinous precipitate in water and cause the agglomeration of finely divided particles into larger particles which can then be removed by settling and/or filtration.
  • Coagulant aid: a material which is not a coagulant, but which improves the effectiveness of a coagulant by forming larger or heavier particles, speeding the reactions, or by permitting reduced coagulant dosage.
  • Coagulation: the clumping together of very fine colloidal (less than 0.1 micron in size) and dispersed (0.1 to 100 microns in size) particles into larger visible agglomerates of these particles (usually between 100 and 1,000 microns in size) caused by the use of chemicals (coagulants). The chemicals neutralize the electrical charges of the fine particles and cause destabilization of the particles. This clumping together makes it easier to separate the solids from the water by settling, skimming, draining, or filtering.
  • Coalescence: the union or growing together of colloidal particles into a group or larger unit as a result of molecular attraction on the surfaces of the particles.
  • Coalescent aid: the small amount of solvent contained in latex coatings. Not a true solvent since it does not actually dissolve the latex resins, the coalescent aid helps the latex resins flow together, aiding in film formation.
  • Coal tar epoxy: a combination of epoxy, curing agent, and tar products which give a very water resistant film.
  • Coating: a paint, varnish, lacquer or other finish used to create a protective and/or decorative layer. Generally used to refer to paints and coatings applied in an industrial setting as part of the original equipment manufacturer (OEM) process.
  • Coating strength: a) a measure of the cohesive bond within a coating, as opposed to coating-to-substrate bond (adhesive strength), b) the tensile strength of a coating, usually expressed in kpa (psi).
  • Coating stress: the stresses in a coating resulting from rapid cooling of molten material or semimolten particles as they impact the substrate. coating stresses are a combination of body and textural stresses.
  • COD: the abbreviation for "chemical oxygen demand".
  • Cohesion: a bonding together of a single substance to itself. Internal adhesion.
  • Cold cracking: a type of weld cracking that usually occurs below 203C. Cracking may occur during or after cooling to room temperature, sometimes with a considerable time delay. Three factors combine to produce cold cracks: stress (for example, from thermal expansion and contraction), hydrogen (from hydrogen-containing welding consumables), and a susceptible microstructure (plate martensite is most susceptible to cracking, ferritic and bainitic structures least susceptible). (see also stress corrosion cracking)
  • Cold-rolling (CR): rolling steel without first reheating it. This process reduces thickness of the steel, produces a smoother surface and makes it easier to machine.
  • Cold welding: cohesion between two surfaces of a metal, generally under the influence of externally applied pressure at room temperature.
  • Cold working: deforming metal plastically under conditions of temperature and strain rote that induce strain hardening. Usually, hut not necessarily, conducted at room temperature. Contrast with hot working.
  • Coliform bacteria: a group of microorganisms used as indicators of water contamination, and the possible presence of pathogenic (disease producing) bacteria.
  • Colloid: very finely divided solid particles which do not settle out of a solution; intermediate between a true dissolved particle and a suspended solid which will settle out of solution. The removal of colloidal particles usually requires coagulation.
  • Colorant: concentrated color (dyes or pigments) that can be added to paints to make specific colors.
  • Colorfast: non-fading in prolonged exposure to light.
  • Color Retention: the ability of paint to keep its original color. Major threats to color retention are exposure to ultraviolet radiation and abrasion by weather or repeated cleaning.
  • Combined available chlorine: the chlorine present as chloramine or other chlorine derivatives in a water, but still available for disinfection and the oxidation of organic matter. Combined chlorine compounds are more stable than free chlorine forms, but are somewhat slower in disinfection action.
  • Combustion: The rapid chemical combination of oxygen with the combustible elements of a fuel resulting in the release of heat.
  • Combustion efficiency: The effectiveness of the burner to completely burn the fuel. A well designed burner will operate with as little as 10 to 20% excess air, while converting all combustibles in the fuel to useful energy.
  • Compatibility: the ability of two or more substances to mix with each other in a wet or dry state to form a homogeneous composition.
  • Compensated hardness: a calculated value based on the total hardness, the magnesium to calcium ratio and the sodium concentration of a water. It is used to correct for the reductions in hardness removal capacity caused by these factors in zeolite exchange water softeners.
  • Complexation: the formation of complex chemical species by the coordination of groups of atoms termed ligands to a central ion, commonly a metal ion. Generally, the ligand coordinates by providing a pair of electrons that forms an ionic or covalent bond to the central ion. See also chelate, coordination compound, and ligand.
  • Composite: mixture of two or more materials. Nearly all have a reinforcing material (wood, glass, etc.), called filler, and a natural or artificial resin, called matrix to achieve specific characteristics and required properties.
  • Composite coating: mixture of two or more materials. Many thermal spray coatings could be considered as composites.
  • Composite powder: a powder in which each particle consists of two or more distinct materials joined together.( Not the same as a powder blend.).
  • Computerized maintenance management system: a computerized system to assist with the effective and efficient management of maintenance activities through the application of computer technology.
  • Concentration cell: an electrolytic cell, the emf of which is caused by a difference in concentration of some component in the electrolyte. (This difference leads to the formation of discrete cathode and anode regions).
  • Concentration polarization: that portion of the polarization of a cell produced by concentration changes resulting from passage of' current through the electrolyte.
  • Condensate: Condensed water resulting from the removal of latent heat from steam.
  • Condition based maintenance: an equipment maintenance strategy based on measuring the condition of equipment in order to assess whether it will fail during some future period, and then taking appropriate action to avoid the consequences of that failure.
  • Condition monitoring: the use of specialist equipment to measure the condition of equipment. Vibration Analysis, Tribology and Thermography are all examples of Condition Monitoring techniques.
  • Conditional probability of failure: the probability that an item will fail during a particular age interval, given that it survives to enter that age.
  • Conductance: a measure of the ability of a material to conduct electrical current. The reciprocal of the resistance of the material, expressed in siemens (mhos).
  • Conductivity: a) a material property relating heat flux (heat transferred per unit area per unit time) to a temperature difference. b) The property of a water or soil sample to transmit electric current (inverse of resistivity) under a set of standard conditions. Usually expressed as microhms conductance.
  • Connate water: water deposited simultaneously with rock and held with essentially no flow; usually occurs deep in the earth, and usually is high in minerals due to long contact.
  • Contact resistance: the resistance in ohms between two objects in contact with each other.
  • Continuity bond: a metallic connection that provides electrical continuity between metal structures.
  • Continuous blowdown: the uninterrupted removal of concentrated boiler water from a boiler to control total solids concentration in the remaining water.
  • Convection: the transmission of heat by the circulation of a liquid or gas. It may be natural, with the circulation caused by buoyancy affects due to temperature differences, or forced with circulation caused by a mechanical device such as a fan or pump.
  • Conversion coating: a coating consisting of' a compound of the surface metal, produced by chemical or electrochemical treatments of the metal. Examples include chromate coatings on zinc, cadmium, magnesium, and aluminum and oxide and phosphate coatings on steel. See also chromate treatment and phosphating.
  • Cooling tower: structure in a power plant used to remove heat from cooling water from the condenser. The cooling tower prevents thermal pollution of lakes and rivers.
  • Copper cake: a by-product of electolytic zinc refining, usually containing a fair amount of cobalt.
  • Copper accelerated salt spray (CASS) test: an accelerated corrosion test for some electrodeposits for anodic coatings on aluminum.
  • Copper plating: the electrolytic deposition of copper to provide either a corrosion barrier (often as an undercoat for hard chrome plate) or for reclamation of worn parts.
  • Copper strip corrosion: a standard for the evaluation of an oil's tendency to corrode copper or copper alloys (see ASTM D130). Test results are based on the matching of corrosion stains. Non corrosiveness is not to be confused with rust inhibiting, which deals with the protection of a surface from some contaminant, such as water, rather than the oil itself.
  • Corona charge: an electrostatic charge induced on powder particles by passing them through an electrostatic field generated by a high-voltage device.
  • Corrective maintenance: any maintenance activity which is required to correct a failure that has occurred or is in the process of occurring. This activity may consist of repair, restoration or replacement of components.
  • Corrodkote test: an accelerated corrosion test for electrodeposits.
  • Corrosion: the chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties.
  • Corrosion fatigue: the process in which a metal fractures prematurely under conditions of simultaneous corrosion and repeated cyclic loading at lower stress levels or fewer cycles than would be required in the absence of the corrosive environment.
  • Corrosion fatigue strength: the maximum repeated stress that can be endured by a metal without failure under definite conditions of corrosion and fatigue and for a specific number of stress cycles and a specified period of time.
  • Corrosion inhibitive: a type of metal paint or primer that prevents rust by preventing moisture from reaching the metal. Zinc phosphate, barium metaborate and strontium chromate (all pigments) are common ingredients in corrosion-inhibitive coatings. These pigments absorb any moisture that enters the paint film.
  • Corrosion potential: the potential of a corroding surface in an electrolyte relative to a reference electrode measured under open-circuit conditions.
  • Corrosion product: substance formed as a result of corrosion.
  • Corrosion rate: the amount of corrosion occurring in unit time. (For example, mass change per unit area per unit time; penetration per unit time).
  • Corrosion resistance: ability of a metal to withstand corrosion in a given corrosion system.
  • Corrosive wear: wear in which chemical or electrochemical reaction with the environment is significant.
  • Corrosivity: tendency of an environment to cause corrosion in a given corrosion system.
  • Counter electrode: See auxiliary electrode.
  • Cratering: the formation of small bowl-shaped depressions in a coating film. These depressions frequently have drops or bands of material at their centers and raised circular edges. Some common causes of cratering are gel particles, oil droplets from air lines, and substrate contamination.
  • Crawling and dewetting: the tendency of a wet paint film to recede from certain areas of a painted surface. A frequent cause of dewetting is a dirty substrate that may result from poor wetting, contamination, fingerprints, or cutting oils.
  • Crazing: a network of checks or cracks appearing on a coated surface.
  • Creep: time-dependent strain occurring under stress. The creep strain occurring at a diminishing rate is called primary creep; that occurring at a minimum and almost constant rate, secondary creep; and that occurring at an accelerating rate, tertiary creep.
  • Crenothrix polyspora: a genus of filamentous bacteria which utilize iron in their metabolism, and cause staining, plugging and taste and odor problems in water systems. (see iron bacteria.)
  • Creosote: a liquid coating made from coal tar once used as a wood preservative. It has been banned for consumer use because of potential health risks.
  • Crevice corrosion: localized corrosion of a metal surface at, or immediately adjacent to, an area that is shielded from full exposure to the environment because of close proximity between the metal and the surface of another material.
  • Critical anodic current density: the maximum anodic current density observed in the active region for a metal or alloy electrode that exhibits active-passive behavior in an environment.
  • Critical flaw size: the size of a flaw (defect) in a structure that will cause failure at a particular stress level.
  • Critical humidity: the relative humidity above which the atmospheric corrosion rate of some metals increases sharply. (see TOW)
  • Criticality: the priority rank of a failure mode based on some assessment criteria.
  • Critical pitting potential: the least noble potential where pitting corrosion will initiate and propagate. (See breakdown potential ).
  • Cross-sectional area: the area of a plane at a right angle to the direction of flow through a tank or vessel; often expressed in square feet, and related to the flow rate. (example: 5 gallons per minute per square foot of ion exchanger bed area.)
  • Cure, curing: the process whereby a liquid coating becomes a hard film. Enamels cure. Lacquers do not cure.
  • Current density: the electric current to or from a unit area of an electrode surface.
  • Current efficiency: the ratio of the electrochemical equivalent current density for a specific reaction to the total applied current density.
  • CVD: See chemical vapor deposition.

Link to glossary of corrosion and materials maintenance terms