Corrosion Glossary - G

Galfan: A proprietary zinc alloy coating (5% aluminum) with improved corrosion resistance and formability compared to zinc alone.
Galling: damage to the surfaces of materials sliding in contact with each other, usually caused by the localized welding together of high spots. Common for materials like stainless steel, aluminum alloys and titanium.
Gallionella ferruginea: a genus of stalked, ribbon-like bacteria which utilize iron in their metabolism, and cause staining, plugging and odor problems in water systems. (see iron bacteria.)
Galvalume: A proprietary zinc alloy coating containing 55% aluminum with superior corrosion resistance.
Galvanizing: the process by which steel is coated with a layer of zinc. The zinc coating provides the steel with greater corrosion resistance.
Galvanic cell: a cell which generates an electrical current, consisting of dissimilar metals in contact with each other and with an electrolyte.
Galvanic corrosion: accelerated corrosion of a metal because of an electrical contact with a more noble metal or nonmetallic conductor in a corrosive electrolyte.
Galvanic couple: a pair of dissimilar conductors commonly metals in electrical contact. (See galvanic corrosion).
Galvanic current: the electric current between metals or conductive nonmetals in a galvanic couple.
Galvanic Series: a list of metals and allots arranged ac-cording to their relative corrosion potentials in a given environment.
Galvanizing: to coat a metal surface with zinc using any of various processes.
Galvanneal: to produce a zinc-iron alloy coating on iron or steel by keeping the coating molten after hot dip galvanizing until the zinc alloys completely with the base metal.
Galvanodynamic: refers to a technique wherein current is continuously varied at a selected rate. is applied to an electrode in an electrolyte.
Galvanostaircase: refers to a galvanostep technique for po-larizing an electrode in a series of constant current steps wherein the time duration and current increments or decrements are equal for each step.
Galvanostatic: an experimental technique whereby an electrode is maintained at a constant current in an electrolyte.
Galvanostep: refers to a technique in which an electrode is polarized in a series of current increments or decrements.
Gamma iron: the face-centered cubic form of pure iron, stable from 910 to l400ºC.
Gamma ray: high energy and speed, short wavelength electromagnetic radiation emitted in the radioactive decay of an unstable atom. Gamma radiation is highly penetrating and is stopped by lead. Similar to X-rays.
Gas carburizing: see carburizing.
Gas flow rate: the flow rate of gas (e.g. liters per minute) through the spraying torch.
Gas nitriding: see nitriding.
Gas nitrocarburizing: See nitrocarburizing.
Gas tungsten arc welding (GTAW): an arc welding process that uses an arc between a non-consumable tungsten electrode and the weld pool (base metal of strip). A high quality full fusion weld is achieved using no filler metal. The GTAW process is also commonly referred to as Tungsten Inert Gas (TIG) welding.
Gold plating: the electrolytic deposition of gold for decorative or electrical applications.
Gas pressure regulator: a spring loaded, dead weighted or pressure balanced device which will maintain the gas pressure to a supply line.
Gaseous corrosion: corrosion with gas as the only corrosive agent and without any aqueous phase on the surface of the metal, also called dry corrosion.
Gate valve: a valve with the closing element that is a disc which is moved across the stream, often in a groove or slot, for support against pressure.
Gauge pressure: the pressure above atmospheric pressure.
Gel zeolite: a synthetic sodium aluminoscilicate ion exchanger.
General corrosion: a form of deterioration that is distributed more or less uniformly over a surface; see uniform corrosion.
Generator: machine that makes electricity. The machine uses mechanical energy to spin a turbine that turns a coil of wire in the presence of a magnetic field. When this happens, an electric current is produced.
Gibbs free energy: thermodynamic function also called free energy, free enthalpy, or gibbs function.
Glass electrode: a glass membrane electrode used to measure pH or hydrogen-ion activity.
Glass transition temperature: the temperature at which polymer molecules are able to move freely, even in a solid state.
Globe valve: a valve in which the closing element is a sphere, or a flat or rounded gasket, which is moved into or onto a round port.
Gloss: the luster or shininess of paints and coatings. Different types of gloss are frequently arbitrarily differentiated, such as sheen, distinctness-of-image gloss, etc. Trade practice recognizes the following gloss levels, in increasing order of gloss:
- flat (or matte) - practically free from sheen, even when viewed from oblique angles (usually less than 15 on 60-degree meter)
- eggshell - usually 20-35 on 60-degree meter
- semi-gloss - usually 35-70 on 60-degree meter
- full-gloss - smooth and almost mirror-like surface when viewed from all angles, usually above 70 on 60-degree meter.
Gloss meter: an instrument to measure the light reflectance of coatings. Different brands with the same description (such as semi-gloss or flat) may have quite different ratings on the gloss meter.
Grab sample: a single sample of material collected at one place and one time.
Grain: an individual crystal in a polycrystalline metal or alloy; it may or may not contain twinned regions and subgrains. A portion of a solid metal in which the atoms are arranged in an orderly pattern.
Grain boundary: a narrow zone in a metal corresponding to the transition from one crystallographic orientation to another, thus separating one grain from another. The atoms in each grain are arranged in an orderly pattern. The irregular junction of two adjacent grains is known as a grain boundary.
Grain dropping: the dislodgment and loss of a grain or grains (crystals) from a metal surface as a result of intergranular corrosion.
Grain-boundary corrosion: same as intergranular corrosion. see also interdendritic corrosion.
Grains (water): a unit of measure commonly used in water analysis for the measurement of impurities in water (17.1 grains = 1 part per million ppm).
Grains per cu-ft: the term for expressing dust loading in weight per unit of gas volume (7000 grains equals one pound).
Gram (g): the basic unit of weight (mass) of the metric system, originally intended to be the weight of 1 cubic centimeter of water at 4oC.
Gram-milliequivalent: the equivalent weight of a substance in grams, divided by one thousand.
Granular powder: particles having approximately isotropic dimensions non-spherical shapes.
Graphitic corrosion: a form of selective leaching specific to the deterioration of metallic constituents in gray cast iron, which leaves the graphitic particles intact. (The term "graphitization" is commonly used to identify this form of corrosion but is not recommended because of its use in metallurgy for the decomposition of carbide to graphite).
Graphitization: a metallurgical term describing the formation of graphite in iron or steel, usually from decomposition of iron carbide at elevated temperatures. Not recommended as a term to describe graphitic corrosion.
Gravimetric: measurement of matter on the basis of weight.
Greenhouse effect: heating of the earth's atmosphere due to the presence of certain gases (e.g. carbon dioxide) that trap energy from sunlight striking the surface of the earth.
Green rot: a form of high-temperature corrosion of chromium-bearing alloys in which green chromium oxide (Cr₂O₃) forms, but certain other alloy constituents remain metallic; some simultaneous carburization is sometimes observed.
Grinding: the removal of material by the use of fixed abrasives like grinding wheels or emery paper.
Grit blasting: a pressurized stream of hard metal or oxide grit material used to clean and roughen surfaces prior to coating.
Gross national product (GNP): total economic output of the nation in a year (this includes national citizen output produced in foreign countries). Gross domestic product (GDP) is limited to productivity within the national borders.
Groundbed: a buried item, such as junk steel or graphite rods, that serves as the anode for the cathodic protection of pipelines or other buried structures.

Link to glossary of corrosion and materials maintenance terms