Which property of borosilicate glass makes it suitable for thermal shock resistance?
🔬 Understanding Thermal Shock
Thermal shock is the stress that builds up in a material when it is subjected to a rapid change in temperature. If you pour boiling water into a cold, regular glass, the inside surface heats up and tries to expand instantly, while the outside surface is still cold and has not expanded. This difference in expansion creates immense internal stress, which can cause the glass to crack.
Borosilicate Glass: A type of glass that includes boron trioxide, which gives it very different properties from standard soda-lime glass. It is famous for its use in laboratory equipment (beakers, test tubes) and high-end kitchenware (like Pyrex), all applications where it must withstand rapid temperature changes.
⚖️ Detailed Analysis of the Options
Let's analyze which property is responsible for resisting this thermal shock.
(c) Low thermal expansion coefficient
Why it's correct: The coefficient of thermal expansion is a measure of how much a material expands or contracts for each degree of temperature change. Borosilicate glass has a very low coefficient of thermal expansion (about one-third that of regular soda-lime glass). This means that when it is heated or cooled rapidly, it expands or contracts very little. Because there is minimal change in size, the internal stresses created are also minimal, and the glass does not crack. This is the single most important property for thermal shock resistance.
(a) Low density
Why it's incorrect: Density relates to the mass per unit volume. While borosilicate glass is slightly less dense than regular glass, this property makes it lightweight but has no direct bearing on its ability to withstand thermal stress.
(b) High transparency
Why it's incorrect: Transparency is an optical property, describing how well light passes through the material. This is useful for labware and cookware so you can see the contents, but it is unrelated to the material's response to heat.
(d) High refractive index
Why it's incorrect: Refractive index is another optical property that describes how much light bends when it enters the material. It is a critical property for making lenses but is irrelevant to thermal shock resistance.
💡 Study Tips for Material Properties
- Low Expansion = Low Stress: This is the key relationship to remember. If a material doesn't try to expand much, it won't build up stress when heated unevenly.
- Think Pyrex: The most famous brand of borosilicate glass is Pyrex. Its main selling point is that you can take it from a hot oven to a cool countertop without it shattering. This is a real-world example of thermal shock resistance.
- Thermal vs. Optical: Learn to separate properties related to heat (thermal conductivity, thermal expansion) from properties related to light (transparency, refractive index). The question asks about a thermal problem, so the answer must be a thermal property.