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Materials 2011, 4(5), 869-892; doi:10.3390/ma4050869
Article

Thermodynamic Origin of the Vitreous Transition

Received: 22 March 2011; in revised form: 19 April 2011 / Accepted: 5 May 2011 / Published: 9 May 2011
(This article belongs to the Special Issue Advances in Bulk Metallic Glasses)
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Abstract: The vitreous transition is characterized by a freezing of atomic degrees of freedom at a temperature Tg depending on the heating and cooling rates. A kinetic origin is generally attributed to this phenomenon instead of a thermodynamic one which we develop here. Completed homogeneous nucleation laws reflecting the energy saving due to Fermi energy equalization of nascent crystals and their melt are used. They are applied to bulk metallic glasses and extended to inorganic glasses and polymers. A transition T*g among various Tg corresponds to a crystal homogeneous nucleation temperature, leading to a preliminary formation of a cluster distribution during the relaxation time preceding the long steady-state nucleation time of crystals in small samples. The thermally-activated energy barrier ΔG*2ls/kBT at T*g for homogeneous nucleation is nearly the same in all glass-forming melts and determined by similar values of viscosity and a thermally-activated diffusion barrier from melt to cluster. The glass transition T*g is a material constant and a linear function of the energy saving associated with charge transfers from nascent clusters to the melt. The vitreous transition and the melting temperatures alone are used to predict the free-volume disappearance temperature equal to the Vogel-Fulcher-Tammann temperature of fragile glass-forming melts, in agreement with many viscosity measurements. The reversible thermodynamic vitreous transition is determined by the disappearance temperature T*g of the fully-relaxed enthalpy Hr that is not time dependent; the observed specific heat jump at T*g is equal to the proportionality coefficient of Hr with (T*g − Ta) for T ≤ T*g as expected from the enthalpy excess stored by a quenched undercooled melt at the annealing temperature Ta and relaxed towards an equilibrium vitreous state. However, the heat flux measurements found in literature over the last 50 years only gave an out-of-equilibrium Tg since the enthalpy is continuous at T*g without visible heat jump.
Keywords: 64.70 kj glasses; 64.70 P glass transitions; 64.70 pe metallic glasses; 64.70 ph. non metallic glasses; 64.70 pj polymers; 64.60 Q-nucleation 64.70 kj glasses; 64.70 P glass transitions; 64.70 pe metallic glasses; 64.70 ph. non metallic glasses; 64.70 pj polymers; 64.60 Q-nucleation
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Tournier F., R. Thermodynamic Origin of the Vitreous Transition. Materials 2011, 4, 869-892.

AMA Style

Tournier F. R. Thermodynamic Origin of the Vitreous Transition. Materials. 2011; 4(5):869-892.

Chicago/Turabian Style

Tournier F., Robert. 2011. "Thermodynamic Origin of the Vitreous Transition." Materials 4, no. 5: 869-892.


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