Brasil
| Tesis
Cristalização e relaxação em vidros óxidos uma tentativa de solução do Paradoxo de Kauzmann
Fecha
2021-09-03Registro en:
Autor
Passos, Rodrigo Cardoso dos
Institución
Resumen
The quest for a solution to Kauzmann’s Paradox has been a lifelong
journey for many glass scientists over the last seventy years. The idea that this
paradox may violate the Third Law of Thermodynamics is what makes it such an
exciting topic for study, even more so, with some possible solutions proposed on
the literature. The aim of this work is to find a possible solution to the paradox
formulated by Kauzmann in his 1948 paper by using his very same hypothesis. If
Kauzmann’s extrapolations of entropy were correct, then a supercooled liquid
would have the same entropy as the stable isochemical crystalline phase at some
temperature below the laboratory glass transition temperature, Tg, known as
Kauzmann’s temperature, TK. If we extrapolate the liquid’s entropy even further,
it becomes zero at a temperature above zero Kelvin, which violates the Third Law
constituting a paradox. By comparing the relaxation kinetics with crystallization
rates, both extrapolated down to TK, if the crystallization kinetics are faster than
the relaxation kinetics there is no liquid at Kauzmann’s temperature, which would
deny the paradox. In this case, the liquid stability limit or kinetic spinodal
temperature should be higher than TK. We tested two fragile glass-forming liquids
(diopside and wollastonite) and two strong liquids (silica and germania). For the
fragile substances, Tks >> TK, so a supercooled liquid cannot exist at TK, and the
entropy crisis is averted. On the other hand, the results for the strong liquids were
inconclusive. We hope these findings entice glass researchers to further
investigate the crystallization and relaxation dynamics of different strong glassforming systems at deep supercoolings.