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.
Zn(s)→Zn2+ (aq) +2e (oxidation)
Capacity derivation from 1st Principlesedit
The capacity of a sacrificial metal may be calculated from first principle as follows:
1 kg Al = 1000/27 moles Al
1 kg Al = 3 x 1000/27 moles of electrons
1 kg Al = 3 x 1000/27 x 96494 coulombs of charge (by Faraday principles)
= 10.72 x 106 Amp.seconds of charge per Kg Al (1 Coulomb = 1 Amp.Second)
= 10.72 x 106/3600 = 2978 Amp.Hours per Kg
By similar calculations Zinc and Magnesium have a capacity of 825 and 2206 Amp.Hours per Kg respectively.
Usesedit
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]
^"Galvanic Corrosion". www.nace.org. from the original on 2018-12-22. Retrieved 2018-12-21.
^Brett, Christopher M. A. (1993). Electrochemistry : principles, methods, and applications. Ana Maria Oliveira Brett. Oxford: Oxford University Press. ISBN0-19-855389-7. OCLC 26398887.
^Fontana, Mars G. (1987). Corrosion engineering (3rd ed.). New York: McGraw-Hill. ISBN0-07-100360-6. OCLC 77545140.
^Trethewey, Kenneth R.; Chamberlain, John (1988). Corrosion for students of science and engineering. Harlow, Essex, England: Longman Scientific & Technical. ISBN0582450896. OCLC 15083645.
sacrificial, metal, sacrificial, metal, metal, used, sacrificial, anode, cathodic, protection, that, corrodes, prevent, primary, metal, from, corrosion, rusting, also, used, galvanization, contents, equation, capacity, derivation, from, principles, uses, also,. 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 Contents 1 Equation 2 Capacity derivation from 1st Principles 3 Uses 4 See also 5 References 6 Further readingEquation editWhen 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 Zn s Zn2 aq 2e oxidation Capacity derivation from 1st Principles editThe capacity of a sacrificial metal may be calculated from first principle as follows 1 kg Al 1000 27 moles Al 1 kg Al 3 x 1000 27 moles of electrons 1 kg Al 3 x 1000 27 x 96494 coulombs of charge by Faraday principles 10 72 x 106 Amp seconds of charge per Kg Al 1 Coulomb 1 Amp Second 10 72 x 106 3600 2978 Amp Hours per Kg By similar calculations Zinc and Magnesium have a capacity of 825 and 2206 Amp Hours per Kg respectively Uses editSacrificial 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 editMetal in electrochemical series Corrosion engineeringReferences edit Galvanic Corrosion www nace org Archived from the original on 2018 12 22 Retrieved 2018 12 21 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 Fontana Mars G 1987 Corrosion engineering 3rd ed New York McGraw Hill ISBN 0 07 100360 6 OCLC 77545140 Trethewey Kenneth R Chamberlain John 1988 Corrosion for students of science and engineering Harlow Essex England Longman Scientific amp Technical ISBN 0582450896 OCLC 15083645 Romanoff Melvin 1964 Exterior Corrosion of Cast Iron Pipe Journal AWWA 56 9 1129 1143 Bibcode 1964JAWWA 56i1129R doi 10 1002 j 1551 8833 1964 tb01314 x ISSN 1551 8833 Romanov Melvyn 17 October 2019 Monograph underground soil corrosion PDF NIST US Government Further reading editBrett CMA Brett AMO ELECTROCHEMISTRY Principles methods and applications Oxford University Press 1993 ISBN 0 19 855389 7 nbsp This electrochemistry related article is a stub You can help Wikipedia by expanding it vte Retrieved from https en wikipedia org w index php title Sacrificial metal amp oldid 1213164419, wikipedia, wiki, book, books, library,
