Step 1: Understanding the Concept:
This question relates to the topic of corrosion, which is an electrochemical process. Different types of electrochemical cells can form on a metal surface, leading to corrosion. The question asks to identify the specific type of cell that forms in a bent section of a metal pipe.
Step 2: Detailed Explanation:
When a metal pipe is bent, the metal in the bent region is subjected to mechanical stress. This stress is not uniform. The outer part of the bend is under tensile stress (stretched), while the inner part is under compressive stress.
- A region of a metal that is under higher stress is more chemically active and has a lower electrode potential. It tends to act as the anode.
- A region under lower stress is less active and has a higher electrode potential. It tends to act as the cathode.
This difference in electrode potential due to variations in mechanical stress creates a corrosion cell. Such a cell, where the potential difference is caused by differences in stress on the metal, is called a Stress Cell.
In a bent pipe, the bent, stressed area will act as the anode and corrode faster than the straight, unstressed parts of the pipe, which act as the cathode.
Let's analyze the other options:
- (A) Concentration Cell: Corrosion is driven by differences in the concentration of the electrolyte or dissolved oxygen. For example, a water droplet on steel.
- (B) Composition Cell: This term is less common, but would imply a cell formed by two different metals or alloys (galvanic corrosion), not differences within the same piece of metal.
- (D) Electrolytic Cell: This is a cell where an external power source is used to drive a non-spontaneous reaction (like in electroplating). Corrosion cells are galvanic (spontaneous) cells.
Step 3: Final Answer:
The electrochemical cell formed due to differences in mechanical stress, such as in a bent pipe, is an example of a Stress Cell. Therefore, option (C) is correct.