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Difficulty: MediumCorrosion of Metals and Prevention Methods

An offshore oil platform made of steel is submerged in seawater. To protect the submerged steel structure from corrosion, an impressed current cathodic protection system is installed using an external direct current source and an inert anode. Which of the following best describes the electrochemical role and behavior of the steel structure in this system?

  1. It acts as the cathode, receiving electrons from the external power source to prevent iron from oxidizing.Answer
  2. B
    It acts as the anode, releasing electrons into the DC power source to corrode preferentially.
  3. C
    It acts as the cathode, undergoing continuous oxidation to form a protective metal oxide layer.
  4. D
    It acts as the anode, attracting hydroxide ions to passivate the steel surface.

Answer

The steel structure acts as the cathode, receiving electrons from the external DC power source to prevent iron from oxidizing.
In impressed current cathodic protection (ICCP), an external DC power source supplies electrons to the steel structure. By forcing electrons into the steel, the structure becomes the cathode of the electrochemical cell, preventing the oxidation of iron (Fe→Fe2++2e−Fe \rightarrow Fe^{2+} + 2e^-) and effectively stopping corrosion.

Step-by-Step Solution

1
Identify the electrochemical mechanism of Cathodic Protection via Impressed Current (ICCP).
An external direct current (DC) power source forces electrons onto the metal structure to be protected.
Corrosion of iron occurs via an anodic oxidation process (Fe→Fe2++2e−Fe \rightarrow Fe^{2+} + 2e^-). Supplying electrons reverses/prevents this oxidation.
2
Determine the electrode polarities in the cathodic protection circuit.
The negative terminal of the DC power source is connected to the steel structure, making it the cathode. The positive terminal is connected to an inert material, making it the anode.
Reduction or electron supply occurs at the cathode, ensuring the protected metal remains in its unoxidized elemental state.

Key Concept

Impressed Current Cathodic Protection (ICCP)
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Topics

Corrosion of Metals and Prevention Methods

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