Galvanic corrosion

Galvanic corrosion is accelerated metal deterioration caused when dissimilar metals are electrically connected in an electrolyte, forming an electrochemical cell.

Galvanic series: A ranking of metals and alloys by their corrosion potentials in a specified environment. It predicts which connected metal becomes the anode in a particular electrolyte.
Electrode potential: The voltage difference between an electrode and a reference electrode under specified conditions. Differences in potential help drive current between electrically connected metals.
Cathodic protection: A corrosion-control method that makes a metal structure the cathode of an electrochemical cell. It deliberately uses galvanic current to protect a structure from dissolution.
Uniform corrosion: Corrosion distributed relatively evenly over an exposed metal surface. It lacks the sharply localized attack often produced at the galvanic anode.
Electrochemical cell: A system in which redox reactions and charge transfer convert chemical energy into electrical energy or vice versa. Galvanic corrosion is an unintended electrochemical cell operating at a metal surface.
Oxidation-reduction reaction: A chemical reaction involving electron transfer, with oxidation and reduction occurring together. Metal dissolution and cathodic reactions are paired redox processes.
Sacrificial anode: A more active metal electrically connected to a structure so it corrodes preferentially. This is a controlled use of galvanic corrosion to protect the less active structure.
Pitting corrosion: Localized corrosion that forms small cavities or pits in a metal surface. Pits can resemble galvanic damage, but arise from local breakdown of surface protection.
Anode: The electrode at which oxidation occurs in an electrochemical cell. The anodic metal loses atoms to corrosion as it supplies electrons.
Corrosion potential: The mixed potential at which anodic and cathodic reaction rates on a corroding surface balance. Coupling metals shifts their potentials and changes their corrosion rates.

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