Viscosity of Glass and Glass-Forming Melts

Abstract

Beginning with a selection of commercial glasses, the typical temperature course of the shear viscosity of inorganic glasses is discussed. The significance of the different temperature ranges for the different production steps (melting, hotforming, annealing) is explained. The viscosity-based typology of glasses as long or short is introduced and discussed with respect to glass composition. The glass viscosity measurement methods conforming to ISO 7884 1-7 are described. This includes the individual rules for the determination of the shear viscosity fix points. Special shear viscosity measurement techniques applying to extremely high or low viscosity values are also described. Concerning viscosity theory and modeling, Adams–Gibbs theory, Angell's fragility concept, and the semiempirical models after Vogel–Fulcher–Tammann (Vogel–Fulcher–Tammann (VFT)), Avramov–Milchev (Avramov–Milchev (AM)), and Waterton–Mauro–Yue–Ellison–Gupta–Allan (Waterton–Mauro–Yue–Ellison–Gupta–Allan (W-MYEGA)) are presented, applied to different glasses, and compared. Viscoelastic behavior is discussed with respect both to shear and bulk deformation, including Boltzmann's superposition principle, the particular effect of delayed elasticity, the special viscoelastic models after Maxwell, Kelvin–Voigt, Burger etc. as well as special mathematics, i. e., the stretched exponential or Kohlrausch(–Williams–Watts) function. Viscoelastic characterization by dynamic mechanical analysis and by reversible compression in a quasi-isostatic device are discussed considering experimental data.