Parametrization of viscosity-temperature relations of aluminosilicate melts

A new approach to parameterize the viscosity-temperature relationships of silicate melts is applied to a data set for 28 aluminosilicate melts based on a haplogranitic chemistry. The approach is based on the introduction of a crossover temperature Tc Such a crossover temperature has been predicted by the recently developed mode coupling theory (MCT). For simple liquids, this temperature distinguishes a fluid regime with power-law temperature dependence of viscosity from a viscous regime with Vogel-Fulcher-Tammann temperature dependence of viscosity. The viscosities of melts used in the present application, have been obtained in a temperature range from 1650° to 450°C at 1-atm pressure. The viscosity was determined with three different methods (concentric cylinder, micropenetration and centrifuge assisted falling sphere), which span a measurable viscosity range from 100 to 1012 Pa s. roducing the crossover temperature Tc we are able to collapse these data onto a master curve, which has been already obtained for simple glass formers like o-terphenyl. The resulting systematic variation of the fragility and Tc can be related to cationic properties such as electronegativity. The success of the master plot raises the possibility that an universal viscosity behavior exists for all liquids between Tc and Tg. The question remains as to whether Tc for non-fragile systems can be linked with the critical temperature of the mode coupling theory.