Consider two glasses. Glass A has a composition of 5% CaO - 95% B2O3. Glass B has a composition of 15% CaO - 85% B2O3. Both samples are cooled from their molten state to room temperature at rates that result in an identical glass transition temperature. Given this information, identify which melt was cooled at a higher cooling rate to achieve identical Tg.

a)Glass A
b)Glass B

Glass B

Thank you

To determine which glass was cooled at a higher rate, we need to understand the concept of glass transition temperature (Tg) and its relationship with cooling rate.

Glass transition temperature is the temperature at which a glass changes from a supercooled liquid state to a more rigid, glassy state. It is an important property as it affects the mechanical and thermal properties of glass.

In general, a higher cooling rate typically results in a higher Tg. This is because a faster cooling rate allows the atoms in the glass to arrange themselves in a more ordered and rigid structure, leading to a higher Tg.

Now, let's analyze the given compositions:

Glass A: 5% CaO - 95% B2O3
Glass B: 15% CaO - 85% B2O3

Comparing the compositions, we can see that Glass B has a higher concentration of CaO compared to Glass A. It is known that the introduction of network modifiers, such as CaO in this case, tends to lower the Tg of glass.

Since both glasses have achieved identical Tg values, it means that the higher cooling rate was applied to Glass B (15% CaO - 85% B2O3). The higher concentration of CaO in Glass B would lower its Tg, and a faster cooling rate compensates for this effect to achieve the same Tg as Glass A.

Therefore, the answer is:
b) Glass B was cooled at a higher cooling rate to achieve identical Tg.