Effect of choice of alkali cation

Question 1

What is viscosity a function of?

Answer 1

~ number of NBO’s formed

Question 2

What’s the effect of heavier cations?

Answer 2

~ heavier cations like Na+ and K+ give HIGHER DENSITY than with Li+
~ although K+ is heavier than Na+, it dialates the network more
~ the larger the cation, the greater the hard-sphere type ionic packing = higher CTE

Question 3

Why is the index of refraction of Li2O-Si2O higher?

Answer 3

> the small Li+ ions pull network ions closer together
higher conc of NBO give higher increase in index of refraction with R2O additions with Li2O