Durability and Ionic conductivity

Question 1

Why is Na+ diffusivity in a silicate glass significantly greater than in NaCl?

Answer 1

~ in NaCl, Na+ diffusion needs the adjacent Na+ site be vacant and that Cl- ions move out of the way
~ an open glass network facilitates easy motion of Na+
~ higher conc of Na2O PUSHES NETWORK OPEN, facilitating Na+ migration

Question 2

How do alkali containing glasses become electrically conductive at high temp?

Answer 2

~ mobile Na+ ions, not e-
~ more Na2O dialates network, more Na+ mobility

Question 3

What trend is shown between alkali silicate glasses and high ionic conductivity?

Answer 3

~ Rb+<K+<Li+<Na+
~ ionic conductivity increases with decreasing cation size (smaller cations move with less displacement of surrounding ions)