Viscosity of glass‐forming systems

Abstract

As one of the most important properties of glass-forming liquids, viscosity has drawn significant attention in both glass manufacturing and fundamental research.We review the recent scientific progress in viscosity of glass-forming systems, including both the liquid and glassy states. After the Vogel-Fulcher-Tammann (VFT) equation was introduced, many more efforts have been made to develop more accurate models to describe the temperature dependence of viscosity. In addition to the VFT equation, we also discuss three other viscosity models, viz., the Adam-Gibbs, Avramov-Milchev, and Mauro-Yue-Ellison-Gupta-Allan models. We compare the four viscosity models in terms of their theoretical underpinnings and ability to fit measured viscosity curves. The concept of fragility and the universality of the high-temperature viscosity limit are also discussed. Temperaturedependent constraint theory is introduced in detail as a powerful tool for predicting the composition dependence of viscosity. Some examples of the application of this approach to predict the glass transition temperature and fragility of various glass systems are shown. Topological constraint theory is not only of scientific interest, but also has important industrial applicability. We also discuss the thermal history dependence of viscosity in the glassy state. Some phenomenological models are briefly reviewed, while the main focus is given to the modified Mauro-Allan-Potuzak model, which can accurately predict the nonequilibrium viscosity as a function of temperature, thermal history, and composition. The correlation of viscosity with elasticity is described in terms of the shoving model. Some theoretical implications of the various viscosity models are discussed, including the concepts of the Kauzmann paradox and the ideal glass transition. Some of the evidence against the existence of these phenomena are discussed. We also review the link between glass relaxation and viscosity, that is, emphasizing that the viscosity equations presented in this review can also be used to model different types of relaxation effects based on the Maxwell relation. K E Y W O R D Sglass, modeling/model, theory, viscosity

Quantitative estimation of crystallization kinetics in GeGaS and Au‐doped GeGaS glass‐ceramics

“…The best fitting parameters of C , η ∞ , T g , and m , are 7.97, 10 −2.93 Pa s, 674 K, 163 for GGS, and 8.10, 10 −2.93 Pa s, 694 K, 213 for GGS‐Au, respectively. It should be noted that, here we follow Mauro's suggestion that, the value of η ∞ is converged as 10 −2.93 Pa s …”

Maxwell relaxation time for nonexponential α‐relaxation phenomena in glassy systems

“…Phenomenological models for the equilibrium (Mauro‐Yue‐Ellison‐Gupta‐Allan, MYEGA) and nonequilibrium (Mauro‐Allan‐Potuzak, MAP) viscosity of glass were used to calculate the viscosities for the experimental stress and structural relaxation experiments, respectively. Fragility ( m ) and glass transition temperature ( T g ), as defined by Angell, were directly measured by conducting equilibrium viscosity measurements in the vicinity of the glass transition by using three‐point beam bending method as previously shown in Gulbiten et al The temperature dependence of the nonequilibrium viscosity of the glass was calculated using RelaxPy, a Python script that returns viscosity and fictive temperature components for any thermal history input by implementing a Prony series fit to approximate the stretched exponential form .…”

STRUCTURE, GLASS STABILITY AND RHEOLOGICAL PROPERTIES OF Na₂O-CaO-Al₂O₃-SiO₂ GLASSES DOPED WITH Y₂O₃

“…In order to describe the relationship between viscosity and temperature for silicate melts, various models, such like Arrhenius equation, VogeleFulchere-Tamman (VFT) equation, Adame Gibbs equation and Mauro-Yue-Ellison-Gupta-Allan (MYEGA) equation, are commonly used for fitting and describing the temperature dependence of viscosity [6,12,33,34]. Among them, the MYEGA equation is more precisely to describe the temperature dependence of viscosity in the long temperature range, as shown below [34]: (2) where η ∞ is the high-temperature limit of the liquid viscosity, and K and C are constants.…”