Relaxation and crystallization kinetics: an attempt to solve Kauzmann's paradox

Abstract

Seventy years after its proposal, Kauzmanns paradox remains as an amusing subject in glass science due to its association with a possible violation on the third laaw of thermodynamics. If his smooth extrapolations are correct, then a super-cooled liquid would have the same entropy as its stable isochemical crystal in a finitu temperature well below the laboratorial glass transition temperature. The Kauzmann temperature, Tk,is where this unexpected equality takes place. This work as an attempt to propose a solution to this intriguing problem by compairing the relaxation and crystal growth kinetics down to Tk. In this study, two different vitreous systems are going to be used: diopside glass (CaO.MgO.2SiO2) and a bariumsilicate glass (3SiO2.2BaO). These glasses were chosen because each presents one of the main crystallization mechanism, which allow us to decide a general solution for the paradox for the class of stechiometric oxide glasses.In order to do so, structural relaxation experiments, crystal nucleation and crystallization are to be conducted. The relaxation in these glasses will be evaluated using refractive index measurements after isothermal heat treatments below Tg while the nucleation and crystal growth kinetics will be monitored by optical microscopy, also after isothermak heat treatments. The viscosity, at low temperatures and high temperatures, will be measured as well. In this work, the solution to the paradox rests on the hypothesis that glasses must crystallize before reaching the paradoxal state. (AU)