Glossary of Corrosion Related Terms

G

Galvanic

Pertaining to the current resulting from the coupling of dissimilar electrodes in an electrolyte

galvanic anode.

A metal which because of its relative position in the galvanic series, provides sacrificial protection to metals that are more noble in the series, when coupled in an electrolyte.

galvanic cell.

A cell in which chemical change is the source of electrical energy. It usually consists of two dissimilar conductors in contact with each other and with an electrolyte. or of two similar conductors in contact with each other and with dissimilar electrolytes.

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 also galvanic corrosion.

galvanic couple potential.

See mixed potential.

galvanic current.

The electric current that flows between metals or conductive nonmetal in a galvanic couple.

galvanic series.

A list of metals and alloys arranged according to their relative corrosion potentials in a given environment. Compare with electromotive series.

galvanize.

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.

galvanometer.

An instrument for indicating or measuring a small electric current by means of a mechanical motion derived from electromagnetic or electrodynamic forces produced by the current.

galvanostatic.

An experimental technique where by an electrode is maintained at a constant current in an electrolyte.

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.

gamma iron.

The face-centered cubic form of pure iron, stable from 910 to l400C (1670 to 2550F).

general corrosion.

A form of deterioration that is distributed more or less uniformly over a surface; See uniform corrosion.

Gibbs free energy.

The thermodynamic function 3G = 5H - TSS, where H is enthalpy, T is absolute temperature. and S is entropy. Also called free energy, free enthalpy, or Gibbs function.

glass electrode.

A glass membrane electrode used to measure pH or hydrogen-ion activity.

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 (usually a fraction of an inch in size), 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-boundary corrosion.

Same as intergranular corrosion. See also interdendritic corrosion.

graphitic corrosion.

Deterioration of gray cast iron in which the metallic constituents are selectively leached or converted to corrosion products leaving the graphite intact. The term graphic quotation 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; deterioration of gray cast iron in which the metallic constituents are selectively leached or converted to corrosion products leaving the graphite intact.See also dealloying and selective leaching.

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.

green liquor.

The liquor resulting from dissolving molten melt iron the kraft recovery furnace in water. See also kraft process and smelt.

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.

ground bed.

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. See also deep ground bed.

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