20 Questions
What is galvanic corrosion?
The corrosion that occurs when two dissimilar metals are surrounded by an electrolyte.
What causes electrons to flow in galvanic corrosion?
The difference of electrochemical potential between dissimilar metals.
What can cause galvanic corrosion even in a single type of metal?
All of the above
What is the role of stress in stress corrosion cracking?
It makes the area under stress anodic to the rest of the metal.
What is the electromotive series?
A series that lists the electrochemical potential of various metals in descending order.
What is the role of soluble metal ions in galvanic corrosion?
They enter solution with the electrolyte and cause the anodic metal to waste away.
How does a scratch or a dent contribute to galvanic corrosion?
It causes one location to be more anodic, leading to corrosion
What happens when two metals with a greater potential difference are coupled in a galvanic cell?
The rate of corrosion is greater
What do noble metals listed at the top of Table 2 do in a galvanic cell?
Receive electrons from anodic metals
In a zinc-copper galvanic cell, which metal acts as the cathode?
Copper (Cu)
What forms bubbles of H2 gas in a zinc-copper galvanic cell?
H+ ions
What is a sacrificial anode used for?
To prevent galvanic corrosion
What is recommended to minimize galvanic corrosion when joining different alloys?
Using electrically insulated dissimilar metals
What is the role of sacrificial anodes in preventing galvanic corrosion?
They corrode instead of the protected cathodic materials
In a zinc-copper galvanic cell, which metal acts as the anode?
Zinc
What do noble metals listed at the top of Table 2 do in a galvanic cell?
Receive electrons from anodic metals
What causes electrons to flow in galvanic corrosion?
The potential difference between the metals
What happens when two metals with a greater potential difference are coupled in a galvanic cell?
The rate of corrosion increases
What forms bubbles of H2 gas in a zinc-copper galvanic cell?
$H+$ ions combining with electrolyte
What is recommended to minimize galvanic corrosion when joining different alloys?
Using materials with similar electrochemical potential
Study Notes
Galvanic Corrosion
- Galvanic corrosion occurs when two dissimilar metals with a potential difference are in contact in the presence of an electrolyte, resulting in the flow of electrons.
- The flow of electrons in galvanic corrosion is caused by the difference in electrode potential between the two metals.
Electromotive Series
- The electromotive series is a ranking of metals based on their electrode potential, with noble metals having a higher potential and more reactive metals having a lower potential.
Role of Soluble Metal Ions
- Soluble metal ions, such as copper ions, can accelerate galvanic corrosion by increasing the conductivity of the electrolyte.
Effect of Scratches or Dents
- Scratches or dents on a metal surface can create a localized galvanic cell, leading to accelerated corrosion.
Galvanic Cell Reaction
- When two metals with a greater potential difference are coupled in a galvanic cell, electrons flow from the more reactive metal (anode) to the less reactive metal (cathode).
- In a zinc-copper galvanic cell, zinc acts as the anode and copper acts as the cathode.
- Hydrogen gas is formed at the cathode, causing bubbles to form.
Noble Metals
- Noble metals, listed at the top of the electromotive series, act as cathodes in a galvanic cell, attracting electrons.
Prevention of Galvanic Corrosion
- To minimize galvanic corrosion when joining different alloys, it is recommended to use a sacrificial anode, which corrodes in place of the more noble metal.
- Sacrificial anodes, such as zinc, are used to protect more noble metals from corrosion by corroding themselves instead.
- Stress can contribute to galvanic corrosion by creating micro-cracks in the metal, allowing electrolytes to penetrate and accelerate corrosion.
Test your knowledge about the process of galvanic corrosion, which occurs when two dissimilar metals come into contact with an electrolyte. Understand the electrochemical potential and the flow of electrons between the anode and cathode.
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