Galvanic Corrosion – An Introduction
Galvanic Corrosion is an age old problem where one metal corrodes in preference to another.
Put simply different metals and alloys have varying electrical properties and potentials. When the two come into contact one will act as an anode and the other a cathode.
There must be an electrolyte and an appropriate conduction pathway present for corrosion to occur.
What is Galvanic Corrosion?
The two metals will be in electrical contact with each other and have the presence of an electrolyte.
An example of this process would be that of rust on a corrugated iron sheet.
Here the sheet of steel or iron will typically have a zinc based corrosion protection layer which is attacked primarily as it is less of a noble metal to the iron or steel itself.
Compare this to a typical tin can where the outer tin layer is attacked immediately and quickly, because it is considered to be more of a noble metal than the underlying steel.
This galvanic reaction is actually encourage and utilised in household batteries to produce the electrical voltage itself.
Where does Galvanic Corrosion occur?
All metals can be considered ‘Galvanic’ to some degree and so have the ‘electrical potential to produce rust and corrosion.
Statue of Liberty – Case Study
The most well known example would be the corrosion that has occurred on the Statue of Liberty.
This was revealed in the 1980’s following maintenance checks on it’s build quality but of course this would have slowly been building over the previous 100 years.
This had taken place between the outer copper layer of the shell and the wrought iron superstructure.
These kind of problems had long been expected since the statues design due to the shellac insulatory layers not beeing very effective, but following an extensive restoration these were replaced with a PTFE material.
USS Independence Case Study
Severe corrosion has been reported on this ship since it’s inception. It has become a primary example for the detrimental effects that can be caused by Galvanic Corrosion.
It has been caused due to the contact between the steel jet water propellor systems and the aluminum hull itself.
In this case the aluminium acts as a anode whilst the stainless steel plays the part of the cathode.
This problem has since been rectified by the US Navy.
However it was a costly refit and demonstrated the cost of aggressive Galvanic Corrosion.
Preventing Galvanic Corrosion
There are numerous ways to prevent galvanic corrosion build. Most of the time solutions focus around insulating the protected material with a metal that has different properties.
– More often than not you can insulate the two metal from each other. Using a non conductive material like PTFE can be effective for corrosion prevention due to it’s different electrode potential properties.
– Using antioxidant paste has proved a successful method for insulation between copper and aluminium connectors. It has a lower nobility rating than both these metals.
– Electroplating put simply is where a metal with superior corrosion resistance is chosen to insulate against Galvanic current. These are usually metals like Chrome, Nickel and Gold.
– Cathodic Protection is also commonly used on metal items that may be buried or immersed under water. This is where a ‘more active’ metal is used on the sacrificial anode itself like Zinc, Magnesium and aluminium.
– The best preventative method however is to simply choose metals for use that hve similar similar electro potentials and so a less volatile galvanic current.
The Corrosion X™ anti corrosion spray is a highly effective rust treatment product.
It’s market leading for corrosion prevention and has excellent penetrant, prevention and lubricant properties.
It’s also safe to use on electronics like batteries, fans and motor engines.
Furthermore it conforms to the United States Navy’s strict corrosion prevention and performance guidelines meeting MIL–PRF-8109F.
For more information on Galvanic Corrosion please visit our partner website.