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Galvanic Corrosion

Define Galvanic Corrosion, and how does it work?

Experience has shown that when two different metals are in immediate contact in a conducting liquid, one of them will corrode. Galvanic corrosion is the term for this type of corrosion. When two metals with varied electrode potentials come into contact in the presence of an electrolyte, one becomes a cathode and the other becomes an anode. The anode is then melted into the electrolyte as a result of an electrochemical process. Galvanic corrosion of metals is the name for this electrochemical process.

Only when an electric conducting path connects the metals and an electrolyte that can provide a conduit for ion migration is present can galvanic corrosion occur.

Galvanic Corrosion Examples

  • Galvanic corrosion affected the Statue of Liberty in New York, USA. Corrosion had taken place between the wrought iron support framework and the statue's copper exterior. The support structure of iron rusted as a result.
  • The fighting cruiser 'USS Independence' was another victim of galvanic corrosion. A water jet propulsion system made up of steel was fitted to the ship's aluminium body. In this corrosion, the aluminium body worked as an anode against the steel.

Galvanic Corrosion Mechanism

The more reactive metal acts as an anode in the presence of an electrolyte. The less reactive metal works as a cathode. The electrolyte provides a passage for particles to flow through, resulting in fast erosion of the anodic metal. Galvanic corrosion can be helpful in preventing corrosion of a cathodic metal. The use of zinc in batteries to induce zinc corrosion in order to create a potential difference is a good example of this.

Galvanic Corrosion: What Causes It?

When two different metals are electrically submerged and linked in a conductive fluid, this form of corrosion develops. The cathode metal remains corrode-free, but the anode corrodes. When compared to the uncoupled metal rate, the anode attack rate is accelerated. What will happen if you put aluminium and carbon steel together and submerge them in seawater? The aluminium will corrode quickly but the steel will be protected.

Galvanic Corrosion Prevention

There are a variety of approaches that can be used to prevent galvanic corrosion. A handful of these techniques are mentioned below:

  • Galvanic corrosion can be reduced by electroplating the metal with a thin layer of an inert metal.
  • Placement of electrical insulation between the two metals to avoid galvanic interaction and stop the electron flow between them.
  • A Galvanic isolator can be made up of two series-semiconductor diodes connected in series with two diodes conducting in the opposite way.
  • The use of an impermeable coating on the metal surface, such as paint, can help ensure that the metal does not come into contact with an electrolyte. This helps in preventing galvanic corrosion.
  • The quantity of galvanic current that flows through metals with equal potentials is reduced. As a result, the rate of galvanic corrosion of metals is reduced.

Frequently Asked Questions

Q1. Is it possible for galvanic corrosion to occur without the presence of an electrolyte?
A: When all of these criteria are absent, galvanic corrosion does not occur. Galvanic corrosion accelerates a metal's natural corrosion in an electrolyte. Uniform corrosion, pitting, crevice corrosion and other forms of corrosion can occur in metals, especially without galvanic corrosion.

Q2. Is it possible for galvanic corrosion to occur in the presence of air?
A: Galvanic corrosion is an electrochemical mechanism in which one metal preferentially corrodes when it is in electrical contact with another in the presence of an electrolyte. Galvanic cells can occur in any electrolyte, including soil or moist air, and under any chemical circumstances.

Q3. What does galvanic corrosion necessitate?
A: For galvanic corrosion to occur, three conditions must be met:
1. Electrochemically different metals must be present
2. They must be in contact with these metals electrically
3. An electrolyte must be used to expose the metals.

Q4. What happens when galvanic corrosion takes place?
A: Galvanic corrosion occurs when two different metals are dissolved in a conductive fluid and electrically linked. One metal (the cathode) is completely covered, while the other (the anode) is corroded. The attack rate on the anode is accelerated when compared to when the metal is uncoupled.

Q5. How do you keep metal from corroding due to galvanic corrosion?
A: Galvanic corrosion can be easily avoided on aluminium by applying a single coat of chrome phosphate pretreatment followed by primer and a high-performance coating. Instead, a single coat of heavy-bodied bituminous paint can be applied in the field. Anodic coatings alone are usually ineffective for galvanic isolation.

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