Fragility degree evaluation of glass formic from Na2O-SiO2

The way in which the viscosity of glass forming melts vary with temperature leads to classify them in two extreme limits, called "strong" and "fragile" glasses. Strong glasses have on Arrhenius behavior. For the majority of melts the viscosity dependence on temperature is described by the Vogel - Fulcher - Tammann equation (V F T). A careful analysis of log viscosity vs inverse temperature plots has led to the concept of fragility. In this work is presented an original method to evaluate the fragility of glass forming melts. The defined fragility parameter is used to characterize some glasses from Na2O- SiO2 system.