Composition A: 25% CaO - 75% B 2 O 3 Composition B: 5% Cao - 95% B 2 O 3 Two gla

Question

Composition A: 25% CaO - 75% B2O3

Composition B: 5% Cao - 95% B2O3

Two glass forming melts, A and B whose composition is noted above, are each cooled from molten state to room temperature at rates that result in identical values of glass transition temperature (Tg).

(a) Identify which melt was subjected to a higher cooling rate.

(b) Choose ALL of the following statements that are true.

(1) The composition with the higher cooling rate is more heavily modified.

(2) The composition with the higher cooling rate is less modified.

(3) The composition with the higher cooling rate has longer chains.

(4) The composition with the higher cooling rate has shorter chains.

(5) The composition with the higher cooling rate has less excess volume.

(6) The composition with the lower cooling rate has more excess volume.

(7) The composition with the higher cooling rate would have had a lower Tg if both glasses were cooled at the same rate.

   (8) The composition with the lower cooling rate would have had a lower Tg if both glasses were cooled at the same rate.

(c) Why are oxide glasses brittle (no ductility at room temperature)? Hint: Remember why metals are ductile. Check ALL correct answers.

(1) Oxide glasses have a plethora of slip systems for dislocations to travel.

(2) Oxide glasses lack any slip systems for dislocations to travel.

(6) How would you increase the density of the glass with composition you answered in the first part of this problem? Check ALL correct answers.

(1) Heat rapidly to melt, then cool rapidly.

(2) Heat slowly to melt, then cool rapidly.

(3) Heat rapidly to melt, then cool slowly.

(4) Heat slowly to melt, then cool slowly.

Explanation / Answer

Melting point of CaO =2,572

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