[DML] Zinc as a Sacrificial Electrode

[Bob Brandys <BobB@xxxxxxxxxxxxxx>]

Ian is correct, J C Whitney used to sell zinc as a sacrificial electrode.

Did is work?  A single device as proposed here does not work. 

Why?  Because of the resistance of the base steel and resistance at weld joints.  Corrosion is driven by electrical differential.  It takes less electrical potential to corrode zinc than steel so it corrodes first.  However, as you get further from the sacrificial zinc, the potential goes up and the steel corrodes. 

Galvanized steel works to "prevent" steel corrosion, but after the zinc is gone(corroded) then the steel corrodes.   It only slows corrosion down but does not stop it. Note: the Zn is right next to the steel and so it works.  There is not a distance resistance problem. 

Keeping oxygen and water (which donates oxygen) away from the steel surface is the only way to stop corrosion.  Under coating retards water.  Epoxy and similar coating can stop both water and oxygen permeation to a very low level.  

These coatings are used on newer vehicles, instead of galvanized steel, because they work so much better.   However, you have to treat the steel with a chemical to change any invisible surface rust that has occurred before you apply these coatings.  At best, you convert Fe2O3 to Fe3O4 before you apply the coating. This is a more stable form of steel oxidation. 


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