Phase separated glass

Question 1

When does phase separation occur?

Answer 1

~ when enthalpy of mixing is ENDOTHERMIC, giving a gibbs energy of mixing with two minima

Question 2

What glasses have phase separation? Can they have a continuous phase?

Answer 2

~ sodium borosilicate

~ with appropriate comp and heat treatment, the B2O3-Na2O rich regions can be continuous

~ this phase ccan be etched/leeched out with acid, giving a porous glass with a very narrow pore size range aka thirsty glass

Question 3

What is porous glass used for?

Answer 3

~ gas component separation

~ dessicator

~ catalysis (acceration of gaseous rxns)

Question 4

What is Vycor glass?

Answer 4

~ glass after etching is very silica rich, porosity can be sintered out

~ pore free glass is very similar to pure fused silica

~ more economical to fabricate than pure fused silica