Viscosity, Fragility, and Specific Heat of Glasses

Viscosity (tj) indicates the resistance to flow or shear deformation of a liquid. The ease of glass formation is dependent on the temperamre and the viscosity of the glass. Viscosity is the determining factor whether the glass will be homogeneous, bubble free, and devitrified. Mathematically, viscosity may be defined as the ratio of applied shearing force to the rate of flow of liquid, i.e., 

The constant A is tjQ, and T and To are temperamres (°C). The VFT equation provides a good fitting of data over a wide range of temperamres. Anyhow, near the lower end of the transformation region, it should be used with caution because the activation energy of viscosity AE ) is almost constant and hence viscosity values may be overestimated. When To 0, then the VFT equation changes to the Arrhenian equation, i.e.. 

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