Sacrificial metal

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A sacrificial metal is a metal used as a sacrificial anode in cathodic protection that corrodes to prevent a primary metal from corrosion or rusting. [1] It may also be used for galvanization.



When two metals touch each other and water is present, electrolysis occurs. [2] One well known example is the reaction between zinc (Zn) and iron (Fe). Zinc atoms will lose electrons in preference to the iron as they are more electropositive and therefore zinc is oxidized and corrodes.

(aq) +2e (oxidation)

Capacity derivation from 1st Principles

The capacity of a sacrificial metal may be calculated from first principle as follows:

By similar calculations Zinc and Magnesium have a capacity of 825 and 2206 Amp.Hours per Kg respectively.


Sacrificial metals are widely used to prevent other metals from corroding: for example in galvanised steel. [3] Many steel objects are coated with a layer of zinc, which is more electronegative than iron, and thus oxidises in preference to the iron, preventing the iron from rusting. [4] Similarly, sacrificial bars of a metal such as aluminium or aluminium alloys can be attached to an oil rig or to the hull of a ship to prevent it from rusting and breaking down. Magnesium may similarly be used on dry land for installations such as pipelines and oil refineries, where its high driving voltage is better for overcoming the resistance of soils found on dry land. [5] [6]

See also

Related Research Articles

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Galvanization Process of coating steel or iron with zinc to prevent rusting

Galvanization or galvanizing is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in which the parts are submerged in a bath of hot, molten zinc.

Magnesium Chemical element, symbol Mg and atomic number 12

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Rust Type of iron oxide

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Zinc Chemical element, symbol Zn and atomic number 30

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Redox Chemical reaction in which oxidation states of atoms are changed

Redox is a type of chemical reaction in which the oxidation states of substrate change.

Corrosion Gradual destruction of materials by chemical reaction with its environment

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Magnesium alloy

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Corrosion in Ballast Tanks is the deterioration process where the surface of a ballast tank progresses from microblistering, to hydroscaletric electration, and finally to cracking of the tank steel itself.

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Galvanic corrosion Electrochemical process

Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. A similar galvanic reaction is exploited in primary cells to generate a useful electrical voltage to power portable devices.


  1. "Galvanic Corrosion". Archived from the original on 2018-12-22. Retrieved 2018-12-21.
  2. Brett, Christopher M. A. (1993). Electrochemistry : principles, methods, and applications. Ana Maria Oliveira Brett. Oxford: Oxford University Press. ISBN   0-19-855389-7. OCLC   26398887.
  3. Fontana, Mars G. (1987). Corrosion engineering (3rd ed.). New York: McGraw-Hill. ISBN   0-07-100360-6. OCLC   77545140.
  4. Trethewey, Kenneth R.; Chamberlain, John (1988). Corrosion for students of science and engineering. Harlow, Essex, England: Longman Scientific & Technical. ISBN   0582450896. OCLC   15083645.
  5. Romanoff, Melvin (1964). "Exterior Corrosion of Cast-Iron Pipe". Journal AWWA. 56 (9): 1129–1143. doi:10.1002/j.1551-8833.1964.tb01314.x. ISSN   1551-8833.
  6. Romanov, Melvyn. "Monograph - underground soil corrosion" (PDF). NIST US Government.{{cite web}}: CS1 maint: url-status (link)

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