Question

Addition of ________ to alumina increases its toughness.

• A. Magnesia
• B. Silica
• C. Chromia
• D. Calcia

Hint:

The addition of Chromia (\( \text{Cr}_2\text{O}_3 \)) to alumina enhances fracture toughness by refining the grain structure and improving crack resistance.

Answer 1

The Correct Option is C

Alumina (\( \text{Al}_2\text{O}_3 \)) is a widely used ceramic material known for its high hardness, thermal stability, and wear resistance. However, pure alumina has low fracture toughness, making it brittle.
Step 1: Understanding Toughness Enhancement in Alumina - To increase toughness, reinforcing agents or additives are introduced to modify the microstructure and improve fracture resistance. - Chromia (\( \text{Cr}_2\text{O}_3 \)) is commonly used as an additive to alumina to enhance its fracture toughness and mechanical strength.


Step 2: Evaluating the Options - Option (A) - Incorrect: Magnesia (\( \text{MgO} \)) improves sintering but does not significantly enhance toughness.
- Option (B) - Incorrect: Silica (\( \text{SiO}_2 \)) reduces thermal conductivity but does not increase toughness.
- Option (C) - Correct: Chromia (\( \text{Cr}_2\text{O}_3 \)) increases toughness by forming a solid solution with alumina.
- Option (D) - Incorrect: Calcia (\( \text{CaO} \)) helps in densification but does not enhance toughness.


Step 3: Conclusion Since Chromia (\( \text{Cr}_2\text{O}_3 \)) is used to improve the toughness of alumina, the correct answer is option (C).