Thermodynamic aspects of the glass transition of silicates

The marked increase in second-order thermodynamic properties observed at th e glass-transition signals the onset of configurational changes in viscous liquids. Experimental determinations in the glass-transition range will ill ustrate this point for thermal expansivity and demonstrate that the kinetic s of volume, enthalpy and structural relaxation are identical for silicate liquids. Within the framework of the Adam-Gibbs theory, heat capacity and v iscosity data may be combined to calculate configurational entropies and ga in insights into the potential energy barrier to viscous flow. Finally, the considerable effect of water on the glass transition temperature of geolog ically relevant silicates is presented. (C) 2001 Academie des sciences/Edit ions scientifiques et medicales Elsevier SAS.