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

To determine which material exhibits the lowest thermal expansion at high temperatures, it's essential to understand the properties of each listed material. The options given are:

• Fused silica
• Quartz
• Cristobalite
• Tridymite

Each of these materials is a form of silica (SiO₂), but they exhibit different structural properties that affect their thermal expansion:

1. Fused Silica: Fused silica is a non-crystalline form of silicon dioxide. It is highly prized for its low thermal expansion, which means it retains its shape better even at high temperatures. This property makes it ideal for applications requiring high thermal stability.
2. Quartz: Quartz is a crystalline form of silica that has a moderate thermal expansion. While it has several industrial applications, its thermal expansion is greater than that of fused silica.
3. Cristobalite: Cristobalite is another crystalline form of silica that has a high thermal expansion compared to fused silica. At higher temperatures, it undergoes phase transitions that increase its thermal expansion significantly.
4. Tridymite: Tridymite is similar to cristobalite and exhibits significant thermal expansion properties. It also undergoes phase changes at high temperatures, further increasing its expansion.

Conclusion: Among the materials listed, fused silica exhibits the lowest thermal expansion at high temperatures. This makes it particularly useful in applications where minimal thermal deformation is required. The unique structure of fused silica, being non-crystalline, allows it to maintain stability across a wide temperature range.

The correct answer is: Fused silica.