Question

Composition A: 5% MgO - 95% SiO2

Composition B: 20% MgO - 80% SiO2

The two glasses above are soaked in molten calcium chloride (CaCl2) at the same temperature for a time long enough for the properties of the two glasses to approach a steady value.

What glass will have the larger increase in strength after treatment?
A
B
No change in either glass
Both glasses will be weaker

Composition C: 5% K2O - 95% SiO2

Composition D: 20% K2O - 80% SiO2

The two glasses above (C and D) are soaked in molten sodium chloride (NaCl) at the same temperature for a time long enough for the properties of the two glasses to approach a steady value.

What glass will have the larger increase in strength after treatment?
C
D
No change in either glass
Both glasses will be weaker

Answer 1

i think the former CaCl2 is A, not sure about Nacl

Answer 2

whoops i am so sorry its B

Answer 3

B and both glasses will be weaker

Answer 4

The principle behind this is to incorporate compressive stresses in the surface of your glass.

When you immerse your glass into a molten salt, the positive ions of the molten salt will migrate into your glass.

If the cation from the molten salt is greater in size than the cation modifier in the glass then it will strengthen the glass.

Since in the first question Glass B has more MgO modifier to exchange for Ca then it should be harder!!!

Now for the second one, notice than the molten salt cation is Na+ which is smaller than K+ so you should expect that this process would weaken your glass, both glasses because both of them contains K+ ions.