Galvanic corrosion: trying to understand

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In summary, Galvanic corrosion occurs when two dissimilar metals are in contact and connected electrically, causing a flow of electrons from one metal to the other. This results in one metal losing electrons and becoming positively charged ions, while the other metal gains electrons and becomes negatively charged. These ions then break away and float through the electrolyte, causing corrosion. Understanding anodic and cathodic reactions and the ranking of metals in the galvanic series is important in preventing and understanding galvanic corrosion. Resources such as the website provided can help in learning more about this process.
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Lsos
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Hi, in the course of designing a heat exchanger for my company, I've ran into the problem of galvanic corrosion. I've managed to somehow figure out what to do to prevent it from happening, but I don't fully understand WHY. In other words, I don't have an exact feeling for what happens at the basic level. Let me try to explain the way I understand it, and hopefully I will get some feedback with where I am wrong:

In this example, we have aluminum and stainless steel, electrically connected and bathed in an electrolyte:

Since there is a voltage potential difference between the Al and SS, the electrons flow from the Al along the electrical connection to the SS.

Due to this electrical flow, the Al is now missing some electrons, which means that the Al atoms turn into positively charged ions. These positively charged ions are then attracted to the negatively charged SS. They therefore break away from the Al and float their way through the electrolyte towards the SS. The breaking away from the Al is corrosion.

Is there anything wrong with the above description of the process?

If so, please let me know. If not, please let me know also...because I still have many things about the above process which I don't understand.
 
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On has to understand the anodic and cathodic reactions, or reduction-oxidation reactions, and it helps to know the ranking of metals in the galvanic series. One should have learned this in an introductory chemistry course - redox equations are rather fundamental.

Two metals in contact form a circuit in conjuction with the electrolyte, which could be water with various ionic species, e.g., saltwater, or other conductive medium.

One metal will preferentially reduce, while the other will oxidize.

These guys have a really good site from which one can learn about corrosion.

http://corrosion-doctors.org/Modules/Modules.htm

http://corrosion-doctors.org/Definitions/galvanic-series.htm
 

1. What is galvanic corrosion?

Galvanic corrosion is a type of corrosion that occurs when two different metals are in contact with each other in the presence of an electrolyte. It is also known as bimetallic corrosion or dissimilar metal corrosion.

2. How does galvanic corrosion occur?

Galvanic corrosion occurs when there is an electrical potential difference between two metals in contact with each other. This creates a flow of electrons from the more active metal (anode) to the less active metal (cathode), resulting in the anode corroding at a faster rate.

3. What are some common examples of galvanic corrosion?

Some common examples of galvanic corrosion include the corrosion of iron nails in a wooden structure, the corrosion of aluminum flashing on a copper roof, and the corrosion of a copper pipe connected to a steel water tank.

4. How can galvanic corrosion be prevented?

Galvanic corrosion can be prevented by using metals that are close in the galvanic series, meaning they have similar electrical potentials. Other methods of prevention include using corrosion-resistant coatings or sacrificial anodes, which are metals that are more active and will corrode in place of the main metal.

5. Can galvanic corrosion be reversed?

Galvanic corrosion cannot be reversed. However, it can be stopped by separating the two metals, removing the electrolyte, or adding a third metal that is more active than the anode to act as a sacrificial anode. In some cases, the damage caused by galvanic corrosion can be repaired by replacing the corroded metal with a new one.

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