Determining the liquidus viscosity of glass‐forming liquids through differential scanning calorimetry

Abstract

Viscosity at the liquidus temperature (TL), ηL, is a critical parameter for the design of new glasses, particularly for industrial glass production where crystallization must be suppressed. However, a direct viscometric determination of ηL for a glass‐forming system is difficult due to crystallization. Here we propose an alternative approach for determining ηL through differential scanning calorimetry (DSC). Specifically, DSC is used to measure both the viscosity curve and liquidus temperature of a glass‐forming system and then derive its ηL value. The ηL values determined using DSC are found to be in excellent agreement with those measured through viscometry. The DSC approach is applicable to various glass‐forming systems covering a wide range of fragilities and ηL values spanning over five orders of magnitude. Other advantages of this approach are its accuracy and small sample requirements.

Mechanical, thermal, and structural investigations of chemically strengthened Na2O–CaO–Al2O3–SiO2 glasses

“…The sub-T g step coincides well to the point where stresses start to relax, i.e., slightly above the strain point. The Al8-CS glass manifests 2 T g peaks, which is attributed to the presence of two separate segments/phases of each glass particle they presumably differ primarily in their glass modifier composition, constituting ion-exchangeinduced K + -bearing outer segment and a core/bulk of the pristine Al8 glass (similar to a liquid-liquid phase separation (Zheng et al, 2020)). Such inhomogeneities rationalize the ill-defined T g values of the CS glasses.…”

On Viscous Flow in Glass-Forming Organic Liquids

“…At intermediate temperatures, the activation energy of the viscous flow Q(T) is a function of the temperature, e.g., it can be used in an Arrhenius-type equation η(T) = A·T·exp(Q/RT), where it formally depends on the temperature. There are many effective models of viscosity to account for this [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 39 , 40 , 41 , 42 , 43 ], with two of the most frequently used models being the Williams–Landel–Ferry (WLF) equation for polymers and the Vogel–Fulcher–Tammann (VFT) equation for inorganic materials. The WLF equation typically used for polymers is [ 39 ]: η(T) = η 0 ·exp[−C 1 ·(T − T 0 )/(C 2 + T − T 0 )] where η 0 is a constant and T 0 is taken as T g , whereas C 1 and C 2 are universal constants for most polymeric materials.…”

“…Equation (4) can be further exploited, as it explicitly relates the viscosity to the glass transition temperature. The T g in (4) is the temperature, which is found via differential scanning calorimetry measurements, however here it is not presumed to result in log[η(T g )] = 12, as typically is the case in other models (e.g., [ 18 ]).…”

“…In 1949, Ronald W. Douglas of the University of Sheffield (UK) devised a model of viscous flow based on the dual roles of oxygen in glasses, which resulted in a two-exponential equation for the temperature dependence of viscosity [ 25 ]. Although the equation gave a very good description of viscosity, it has not become popular compared with Vogel–Fulcher–Tammann (VFT), Williams–Landel–Ferry (WLF), Avramov–Milchev, Nemilov, Sanditov, Mauro–Yue–Ellison–Gupta–Allan (MYEGA), and other often used models [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. It is considered that the two-exponential equations such as that obtained by Douglas can exactly describe the viscosity of amorphous materials, as the two-exponential equations with two activation energies can properly account for the asymptotic Arrhenius-type dependences of the viscosity on temperature, having different activation energies at low and high temperatures (compared with T g )—low Q L at high and high Q H at low temperatures [ 1 ].…”

“…The salient feature characterizing a supercooled liquid is the dramatic increase of viscosity η(T) with decreasing temperature T, which may encompass some 15 orders of magnitude over a temperature range of almost several hundred K [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. The interest in analyzing the viscous flow in glass-forming materials is not diminishing, with many novel findings having occurred over the last decade [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. There are many theoretical models that can describe the viscous flow of glass-forming materials, which provide reasonably exact descriptions of viscosity–temperature relationships [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ].…”