Alkali-lead glasses

Question 1

What are the characteristics of lead oxide glasses?

Answer 1

~ lead oxide additions VASTLY INCREASE DENSITY

~ PbO substitution for Na2O DECREASES ionic conductivity via less mobile Na+ conc.

Question 2

Why is lead an exception to the rule for cations?

Answer 2

~ the e- cloud for Pb2+ polarizes in response to electric field

Question 3

What happens at high conc. of PbO?

Answer 3

~ Pb4+ takes the role of a network former w/ tetrahedral coordination of oxygen

Question 4

What are applications for alkali-lead glasses?

Answer 4

~ highly reflective
~electrical feedthrough and sealing
~ high XRAY absorption, crt/tv screens

Question 5

What happens when lead acts as a network former?

Answer 5

~ as a network former, glass has more covalent bonding and more open network to vibrate = LOW CTE

Question 6

What is the equation for reflectance?

Answer 6

= [(nair - nglass)/(nair+nglass)]^2