Thermodynamics of viscous flow and elasticity of glass forming liquids in the glass transition range
Résumé
The elastic moduli of glasses from different chemical systems, including oxide, chalcogenide, oxynitride, and metallic, were investigated through the glass transition (T(g)), typically from 0.4 to 1.3 T(g). These data were used to interpret the temperature sensitivity of the shear viscosity coefficient obtained on the same materials. The relevant Gibbs free activation energy was estimated from the apparent heat of flow by means of the temperature dependence of the shear elastic modulus. The activation entropy associated with the viscous flow was also derived and was found to correlate with the fragile versus strong character of the glass forming liquids. Finally, the physicochemistry of the flow process was described on the basis of the glass network de-structuration which shows up through the temperature dependence of Poisson's ratio, and an expression for the shear viscosity coefficient is proposed which is chiefly based on the high temperature elastic behavior. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3656695]
Mots clés
aluminium alloys
aluminium compounds
aluminosilicate glasses
calcium compounds
chalcogenide glasses
copper alloys
elasticity
entropy
free energy
germanium compounds
glass transition
magnesium compounds
nickel alloys
palladium alloys
phosphorus alloys
plastic flow
Poisson ratio
shear modulus
silicon compounds
viscosity
vitrification
yttrium compounds
zirconium alloys