Editing Corrosion (section)

== Galvanic corrosion ==
{{Main|Galvanic corrosion}}
[[File:Galvanic corrosion of aluminum and steel in seawater.jpg|thumb|Galvanic corrosion of an [[aluminium]] plate occurred when the plate was connected to a mild steel structural support.]]
Galvanic corrosion occurs when two different metals have physical or electrical contact with each other and are immersed in a common [[electrolyte]], or when the same metal is exposed to electrolyte with different concentrations. In a [[galvanic cell|galvanic couple]], the more active metal (the anode) corrodes at an accelerated rate and the more [[noble metal]] (the cathode) corrodes at a slower rate. When immersed separately, each metal corrodes at its own rate. What type of metal(s) to use is readily determined by following the [[galvanic series]]. For example, zinc is often used as a sacrificial anode for steel structures. Galvanic corrosion is of major interest to the marine industry and also anywhere water (containing salts) contacts pipes or metal structures.

Factors such as relative size of [[anode]], types of metal, and operating conditions ([[temperature]], [[humidity]], [[salinity]], etc.) affect galvanic corrosion.<ref>{{Cite web |last=Nwagha |first=Nzube |title=Statistical study on the corrosion of mild steel in saline mediums |url=https://www.academia.edu/40855993}}</ref> The surface area ratio of the anode and [[cathode]] directly affects the corrosion rates of the materials. Galvanic corrosion is often prevented by the use of [[sacrificial anode]]s.

=== Galvanic series ===
{{Main|Galvanic series}}
In any given environment (one standard medium is aerated, room-temperature [[seawater]]), one metal will be either more ''noble'' or more ''active'' than others, based on how strongly its ions are bound to the surface. Two metals in electrical contact share the same electrons, so that the "tug-of-war" at each surface is analogous to competition for free electrons between the two materials. Using the electrolyte as a host for the flow of ions in the same direction, the noble metal will take electrons from the active one. The resulting mass flow or electric current can be measured to establish a hierarchy of materials in the medium of interest. This hierarchy is called a ''galvanic series'' and is useful in predicting and understanding corrosion.