Thermal behaviour of glasses

The behavior of entropy and enthalpy of glass-forming melts is very similar. Discrete changes are observed at T in both enthalpy (A//) and entropy (A5) for the crystalline phase, but for the glass, a continuous change occurs at Tg with only a change of slope. 

The supercooled melt and the glass are in the metastable states, which are well separated from the corresponding crystalline states by large barriers. We may therefore assume that equilibrium thermodynamics can be applied to such metastable states. Hence the free energy variation of a glass is also represented by equation (2.04) and we may therefore write, 

AS - ACpdXnT. This is the entropy frozen into the glass. At this 

In many examples, particularly in fragile glass-forming liquids discussed in detail in chapter 3, the entropy lost by the time the system arrives at Tg is such a large fraction of AS m that the entropy crisis is imminent in just under 20 K below Tg. Therefore, any suggestion that the remaining entropy may be lost so slowly that Tk becomes equal to 0 K appears impossible. Kauzmann s own resolution of this paradox has been 

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Abrahams, I. and Hadzifejzovic, E., Lithium ion conductivity and thermal behaviour of glasses and crystallised glasses in the system Li20-Al203-Ti02-P205, Solid State Ionics, 134, 249, 2000. 

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