Glass A has a composition of 90% SiO2 - 10% Na2O. Glass B has a composition of 99% SiO2 - 1% Na2O. Both glasses are cooled to room temperature at the same rate.
(a) Which glass has the higher Tg?
Glass A
Glass B
(b) Which glass has the lower free volume?
A) glass B
B) glass A
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Which of the following will increase the strength of a sample of 90% SiO2 - 10% MgO
To determine which glass has the higher Tg (glass transition temperature) and which glass has the lower free volume, we need to understand the properties of SiO2 (silicon dioxide) and Na2O (sodium oxide) in glass composition.
(a) The glass transition temperature (Tg) is the temperature at which an amorphous material, like glass, changes from a hard and brittle state to a more flexible and rubbery state. The Tg is influenced by the chemical composition of the glass. In general, the presence of modifiers, such as Na2O, lowers the Tg, while the presence of network formers, such as SiO2, increases the Tg.
Comparing the compositions of Glass A and Glass B, we can see that Glass A has 90% SiO2 and 10% Na2O, while Glass B has 99% SiO2 and 1% Na2O. Since SiO2 is a network former and Na2O is a modifier, we can conclude that Glass B has a higher SiO2 content and therefore a higher Tg compared to Glass A. Therefore, Glass B has the higher Tg.
Answer: Glass B
(b) Free volume refers to the spaces or voids between atoms or molecules in a solid material. In crystalline materials, the free volume is limited by the regular arrangement of atoms in a crystal lattice. In amorphous materials like glass, however, the arrangement is more random, allowing for the presence of more free volume.
Comparing the compositions of Glass A and Glass B, we can see that Glass A has a higher Na2O content (10%) compared to Glass B, which has a lower Na2O content (1%). Since sodium ions are larger than silicon and oxygen ions, the inclusion of Na2O causes the glass structure to become more open and have more free volume. Therefore, Glass A has a higher free volume compared to Glass B.
Answer: Glass A