Question

Which of the following materials exhibits the lowest thermal expansion at high temperatures?

• A. Fused silica
• B. Quartz
• C. Cristobalite
• D. Tridymite

Hint:

Amorphous materials like fused silica generally have lower thermal expansion than crystalline forms of silica because they lack sharp phase transformations.

Answer 1

The Correct Option is A

Step 1: Understanding Thermal Expansion.
Thermal expansion refers to the increase in dimensions of a material when temperature risesThe coefficient of thermal expansion (CTE) indicates how much a material expands per degree increase in temperatureMaterials with lower CTE exhibit better dimensional stability at high temperatures
Step 2: Properties of the Given Materials.
(A) Fused silica: It is a non-crystalline (amorphous) form of silicon dioxideIt has an extremely low coefficient of thermal expansion and excellent thermal shock resistanceBecause of its amorphous structure, it shows minimal structural change with temperature
(B) Quartz: Crystalline quartz undergoes phase transformation (alpha to beta quartz) around 573^\circ C, leading to noticeable expansion
(C) Cristobalite: It has a high coefficient of thermal expansion and undergoes significant volume change during phase transformation
(D) Tridymite: Though it has lower expansion than cristobalite, it still expands more than fused silica at elevated temperatures
Step 3: Comparison and Conclusion.
Among all the listed materials, fused silica exhibits the lowest thermal expansion at high temperatures due to its amorphous structure and very low coefficient of thermal expansion