Properties of Sodium Silicate glass

Question 1

What happens as more non-bridging oxygens are formed?

Answer 1

~ viscosity DECREASES

Question 2

What are the effects of increasing alkali oxide concentration in sodium silicate glass?

Answer 2

~ lower viscosity
~ higher DENSITY
~ higher CTE (bigger cation = greater effect)
~ higher index of refraction (Li is small, pull NBO together, increasing conc of oxygen)

Question 3

What’s the difference between NBO and bridging oxygens?

Answer 3

~ NBO have a looser tied e- tied
~ bridging oxygens have outer e- more tied to the nucleus

Question 4

What is the effect of open volume in fused silica?

Answer 4

~ very low CTE
~ plenty of room for ions to vibrate without pushing neighbors

Question 5

What’s the effect of adding Na2O?

Answer 5

~ increased ionic bonding
~ more efficient atomic packing
~ higher density
~ increased CTE
~ turn bridging oxygens into NBO, making more polarizable and thus higher index of refraction

Question 6

What happens as light interacts with the glass?

Answer 6

~ as light interacts with the dieletric, it slows down due to the electrically insulating solid

Question 7

What causes a high index of refraction?

Answer 7

~ if the e- clouds are easily polarized by the light electric field
~ light is significantly slowed down by the medium

Question 8

Are anions or cations more easy to polarize?

Answer 8

~ anions because cations have e- more tightly held by the nucleus

Question 9

Why are NBO more polarizable than bridging oxygens?

Answer 9

~ with bridging oxygens, the e- cloud is permanently deformed by the partial covalent bond, making it less polarizable by an external electric field
~ Na2O additions increase index of refraction (light slows down more)