CaO-SiO2 glasses (lime)

Question 1

What does Ca2+ do in CaO-SiO2 glasses?

Answer 1

~ each Ca2+ forms two non-bridging oxygens
~ Ca2+ is more tightly bound compared to Na+, not as easily extracted
~ gives good chemical durability
~ Ca2+ powerfully attracts O2-, facilitating liquid immiscibility and a PHASE SEPARATED glass upon cooling

Question 2

What causes phase separation in CaO-SiO2 glasses?

Answer 2

~ undulating composition, differing ratio of CaO/SiO2

Question 3

What is the effect of differences in index of refraction between phase separated regions?

Answer 3

~ light scatters, causes a TURBID glass (translucent rather than transparent)