What Is Galvanic Corrosion?
It is a phenomenon which occurs when two dissimilar metals are put in conductive solution. Of course, this happens when you connect the metals electronically.
Implying, for galvanic corrosion to occur, there should be an electrolyte allowing for movement of ions.
Galvanic Corrosion Causes
Galvanic corrosion takes place when more than one metal that is not similar is put in a conductive solution.
Corrosion of the anode happens faster and does not stop while that of the cathode is slow and it eventually stops.
Metals with an oxidation potential that is higher will start losing electrons and act as anodes while those with low oxidation potential will act as cathodes.
Galvanic Corrosion Mechanism
In the presence of an electrolyte, two metals can come in contact with each other. One metal can be more reactive than the other.
The more reactive metal serves as the anode while the less reactive metal serves as the cathode.
The electrolyte makes way for the particles to pass through. This results in the fast eroding of the anodic metal.
Galvanic corrosion can be beneficial too. It can help prevent corrosion of a cathodic metal.
As an example, the zinc in batteries promotes the corrosion of zinc to make a potential difference.
Preventing Aluminum From Galvanic Corrosion
Aluminum has many desirable qualities but its ability to resist corrosion is one of its major qualities.
Although aluminum can resist corrosion it does not mean it cannot corrode.
To prevent aluminum from galvanic corrosion, you should ensure that any unfinished aluminum is stored in a dry controlled environment.
It should also not at any chance be handled with bare hands.
Another way to prevent aluminum from galvanic corrosion includes applying a pretreatment of chrome phosphate (a single coat).
Then following it with a primer and a high-quality paint.
You can also apply a one field-applied coat of a dense-bodied bituminous paint.
How To Prevent Galvanic Corrosion
Galvanic corrosion takes place when two metals that are not similar are immersed in a conductive solution.
There are several ways that you can use to prevent galvanic corrosion and they include;
Pick Metals That Have Same Corrosion Potential
From the definition above we see that the main cause of galvanic corrosion is metals with dissimilar corrosion potentials.
When the metals have a higher difference when it comes to corrosion potential, the galvanic current becomes greater.
This results in a severe corrosion rate.
Insulating The Two Metals
You can also prevent galvanic corrosion by insulating the two metals from each other. This breaks the electrical connection between them.
Breaking the electrical connection will ensure the metals do not corrode easily. To break the electrical connection you place a non-conductive material between the contact point of the two metals.
Placing the non-conductive material ensures there is no flow of electrons which causes oxidation and reduction reactions from taking place.
Coating the materials can be another solution. The coating has always come in handy when preventing corrosion.
The cathode must have a good coating since it is the one that corrodes faster.
Use Spacer To Separate The Two Metals
Inserting a good-sized spacer into the conductive solution to separate the two metals is another way of preventing galvanic corrosion.
The spacer ensures the two materials do not connect at any point. Remember , the degree and seriousness of galvanic corrosion are determined by the propotion of the cathode area to the anode area.
When the cathode has a larger ratio compared to the anode, the rate of reduction at the anode is greater. At the same time, when the cathode proportion to the anode is smaller, the degree of reduction at the anode is smaller.
Consider Sacrificial Anode
A sacrificial anode is also another prevention solution. The anode should be anodic to both materials. Also, putting up a sacrificial anode can help prevent galvanic corrosion.
Add Corrosion Inhibitor
Another way of preventing galvanic corrosion is by adding a corrosion inhibitor to the environment. The main purpose of a corrosion inhibitor is to prevent corrosion. You add corrosion inhibitors to the electrolyte to inhibit the chemical reactions that cause galvanic corrosion.
Examples Of Galvanic Corrosion
Copper Is Cathode While Zinc Is Anode
The circuit is completed when copper and zinc metal are immersed in an electrolyte. The electrolyte can be an aqueous solution that has any salt such as copper sulfate. Zinc begins to oxidize now due to its higher oxidation potential than the cathode.
As a result, zinc begins to corrode and form zinc ions gradually.
Copper ions, on the other hand, begin to gain electrons and are reduced, allowing them to be protected. The procedure is repeated until the zinc electrode is completely dissolved. Also, the hydrogen ions in the electrolyte are also reduced to hydrogen gas, which is visible as bubbles at the cathode.
Steel And Aluminum
When you place both steel and aluminum in an electrolyte, aluminum will act as an anode and will start corroding faster. On the other hand, steel as a cathode will be protected and hence will not corrode.
Iron And Zinc
A sheet of iron, galvanized iron or steel that has a zinc coating can be another example of galvanic corrosion. When the coating that protects the zinc is interfered with, the underlying steel is safe from attack. What happens is the zinc undergoes corrosion and after that, the base metal starts rusting.
Tin And Steel
Regarding a conventional tin can, the complete opposite happens. Here tin is nobler than steel, the steel below is attacked as soon as the tin coating breaks. You can also take an example of the statue of liberty.
The corrosion took place between the support structure made of iron and the exterior made up of copper. That is, the iron support structure went through corrosion.
Galvanic corrosion also occurred in the combat ship.
There was an aluminum hull in the ship that had a steel water jet propulsion system connected to it.
In this corrosion, the aluminum hull played as an anode toward steel.
People Also Ask:
In an instance where two metals that are not similar are put in a conductive solution and are connected electronically galvanic corrosion takes place. Galvanic corrosion takes place when an electrolyte that gives a medium for the movement of ions is present and when there is an electric conducting path connecting the metals.
No, galvanic corrosion is not the same as rusting. Rust only affects iron and its alloys while corrosion affects so many objects.
You can prevent galvanic corrosion using several ways including;
- Insulation breaks the electrical path
- Corrosion inhibitors inhibit the chemical reactions that cause galvanic corrosion
- Breaking the electrical connection of the materials
- Coating the materials
- Selecting materials with the same corrosion potential
- Inserting a good-sized spacer
Yes, you can reverse galvanic corrosion. You can reverse the corrosion by using a sacrificial anode.
The main conditions for galvanic corrosion to happen is:
- Both the cathode, the anode, an electrolyte, and a return current path have to be present.
- There should be the presence of an electrolyte.
- The two metals should be in electrical continuity.
- Metals that are not similar should be present.