Question

Which type of corrosion protection involves connecting the metal to be protected to a more reactive "sacrificial" metal?

• A. Anodic protection
• B. Cathodic protection
• C. Passivation
• D. Galvanizing

Hint:

Zinc, Magnesium, and Aluminum are commonly used as sacrificial anodes because they lie lower (more active/reactive) in the galvanic series compared to steel.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the name of the corrosion prevention technique where a target metal is connected to a more reactive (less noble) metal that corrodes preferentially to protect the target.

Step 2: Key Formula or Approach:
The galvanic series dictates which metal will act as an anode when coupled.
The sacrificial metal (more active, e.g., Zinc or Magnesium) oxidizes:
\[ M_{\text{sacrificial}} \rightarrow M_{\text{sacrificial}}^{n+} + n e^- \]
The electrons flow to the protected metal (e.g., Iron), making it cathodic and protecting it:
\[ \text{O}_2 + 2\text{H}_2\text{O} + 4e^- \rightarrow 4\text{OH}^- \]

Step 3: Detailed Explanation:

• Cathodic Protection (Sacrificial Anode): In this method, the protected metal is made the cathode of an electrochemical cell.
By connecting it electrically to a more active, sacrificial anode (like Zinc or Magnesium), the sacrificial anode undergoes oxidation (corrosion) instead of the protected structural metal.

• Comparison with Other Options:
-

Anodic protection (Option A) involves applying an external anodic current to shift the metal potential into its passive region.
-

Passivation (Option C) refers to the spontaneous formation of a protective oxide film (like on stainless steel) without external electrical connection.
-

Galvanizing (Option D) is a specific method of applying a zinc coating on steel. While it utilizes cathodic protection principles, the overall engineering practice of using connected blocks of reactive metals is termed Cathodic Protection.


Step 4: Final Answer:
Thus, the correct answer is Cathodic protection, which corresponds to Option (B).