Question

In the Fe-C system, the invariant reaction Liquid + $\delta$ $\rightleftharpoons$ $\gamma$ takes place at 1493 °C. This type of reaction is called ______.

• A. eutectic
• B. eutectoid
• C. peritectic
• D. monotectic

Hint:

In phase diagrams, a peritectic reaction involves a liquid and a solid phase reacting to form a second solid phase, which is characteristic of certain alloy systems like Fe-C.

Answer 1

The Correct Option is C

The reaction described in the question, where a liquid phase reacts with the $\delta$ phase to form the $\gamma$ phase at a specific temperature, is an example of a peritectic reaction in the Fe-C system. 
Step 1: Understanding the types of reactions - Eutectic (Option A): The eutectic reaction occurs when a liquid phase transforms into two solid phases at a specific temperature and composition. This is not the reaction described in the question. 
- Eutectoid (Option B): The eutectoid reaction involves the transformation of a single solid phase into two solid phases, which does not match the description of the reaction. 
- Peritectic (Option C): Correct — A peritectic reaction occurs when a liquid phase reacts with a solid phase to form a different solid phase. In the Fe-C system, the reaction Liquid + $\delta$ $\rightleftharpoons$ $\gamma$ at 1493°C is a peritectic reaction. 
- Monotectic (Option D): A monotectic reaction involves the transformation of one liquid phase into two distinct liquid phases, which does not apply to this case. 
Step 2: Conclusion The reaction described in the question is a peritectic reaction, so the correct answer is Option C.