Galvanic Corrosion | Forms of Corrosion

Summary

In this video, Maido, a materials scientist specializing in nanotechnology, explains the concept of galvanic corrosion. This type of corrosion occurs when two metals with different electrochemical activities are in contact, leading to the accelerated degradation of the more active metal. Maido discusses how this process happens, even in open air, and its impact on materials like aluminum and steel in corrosive environments. He also provides practical solutions, such as choosing compatible materials or applying coatings, to prevent galvanic corrosion and protect devices from damage.

Takeaways

• 😀 Galvanic corrosion is an accelerated form of corrosion caused by the interaction of two dissimilar metals.
• 😀 It occurs when two metals with different electrochemical activity are in electrical contact with each other.
• 😀 The more passive metal (less reactive) remains unharmed, while the active metal (more reactive) undergoes corrosion.
• 😀 This electrochemical process continues until the active metal is completely corroded or the electrical connection is broken.
• 😀 A real-world example of galvanic corrosion is an aluminum frame connected to steel screws, where the steel screws cause the aluminum frame to corrode.
• 😀 Galvanic corrosion can happen not only in electrolytes but also in open air, where metals are often covered with a thin layer of water.
• 😀 The process is faster near the sea due to the presence of moisture and chloride in the air.
• 😀 At the microscopic scale, water reacts with oxygen and hydroxide ions at the cathode, while electrons flow from the more active anodic metal.
• 😀 The corrosion results in the formation of stable compounds like oxides and hydroxides, commonly referred to as rust.
• 😀 To prevent galvanic corrosion, one should refer to the galvanic series and combine materials with a voltage difference of less than 0.2 volts.
• 😀 If using dissimilar materials is unavoidable, coating the metals or adding an insulating layer can prevent the corrosion process.

Q & A

What is galvanic corrosion?

Galvanic corrosion is an accelerated form of corrosion that occurs when two metals with different electrochemical activities are in electrical contact with each other. The more active metal corrodes, while the passive metal remains unharmed.

How does galvanic corrosion differ from regular corrosion?

Regular corrosion is a slow process of material degradation, while galvanic corrosion is an accelerated form that happens due to the electrochemical interaction between two metals with different electrochemical activities.

Why does the more active metal corrode in galvanic corrosion?

The more active metal becomes anodic and loses electrons, which leads to its corrosion. These electrons are transferred to the more passive metal, which remains unaffected.

What happens at the cathode in the galvanic corrosion process?

At the cathode, water reacts with oxygen to produce hydroxide ions, and this reaction is facilitated by electrons provided by the anode (the more active metal).

Can galvanic corrosion occur in open air?

Yes, galvanic corrosion can occur in open air because, at the microscopic scale, materials are always covered with a thin layer of water, which can facilitate the electrochemical process.

What role does chloride play in galvanic corrosion?

Chloride, especially in sea air, accelerates the corrosion process by increasing moisture and providing ions that contribute to the electrochemical reactions that lead to corrosion.

How can galvanic corrosion be prevented?

Galvanic corrosion can be prevented by using materials with similar electrochemical activities, typically with a difference of less than 0.2 volts, or by applying coatings, insulating layers, or ensuring no direct contact between the metals.

What is the galvanic series and why is it important?

The galvanic series is a list that ranks metals according to their electrochemical activity. It's important because it helps in selecting materials that are less likely to cause galvanic corrosion when used together.

What happens if the electrical connection between two metals is broken?

If the electrical connection is broken, the galvanic corrosion process will stop because there is no longer an electron flow between the metals, thus halting the corrosion of the active metal.

What is the result of galvanic corrosion on a material?

The result of galvanic corrosion is the degradation and eventual failure of the more active metal, which is consumed by the corrosion process, leading to the loss of structural integrity.