Elastic interpretation of the glass transition in aluminosilicate liquids

Abstract

One of the remaining puzzles of the glass transition is the origin of a glass-forming liquid's "fragility," which quantifies the departure of its relaxation time from Arrhenius activated kinetics. According to the shoving model proposed by Dyre, fragility is controlled by the instantaneous shear modulus of the liquid, since any flow event requires a local volume increase and the related activation energy is equal to the work done in shoving aside the surrounding atoms. Here, we present an in situ high-temperature Brillouin spectroscopy test of the shoving model near the glass transition of eight aluminosilicate glass-forming systems. We find that the measured viscosity data agree qualitatively with the measured temperature dependence of shear moduli, as predicted by the shoving model. However, the model systematically underpredicts the values of fragility for our aluminosilicate liquids. This suggests that the dynamics of the glass transition are governed by additional factors beyond the evolution of the shear modulus, such as configurational entropy. We have also compared the glass transition temperature T g,vis obtained from viscosity (temperature at 10 12 Pa s) with the onset temperatures of the decrease in elastic moduli (T g,elas ) and increase in the thermal expansion coefficient (T g,CTE ) during heating. While we find an approximate one-toone correlation between T g,vis and T g,CTE , it is clear that the elastic moduli probe a different frequency response of the glass structure since T g,elas is systematically lower than T g,vis .2

Microscopic Origins of Compositional Trends in Aluminosilicate Glass Properties

“…We prepared two sets of sodium aluminosilicate glasses with either calcium or magnesium (in mol%): (76− x )SiO 2 – x Al 2 O 3 –16 Na 2 O–8 RO with x = 0, 2.7, 5.3, 8, 10.7, 13.3, 16, 18.7, 21.3, and 24 for R = Ca and Mg . We included 0.15 mol% SnO 2 as fining agent in all compositions.…”

“…We prepared two sets of sodium aluminosilicate glasses with either calcium or magnesium (in mol%): (76Àx)SiO 2 -x Al 2 O 3 -16 Na 2 O-8 RO with x = 0, 2.7, 5.3, 8, 10.7, 13.3, 16, 18.7, 21.3, and 24 for R = Ca and Mg. [31][32][33] We included 0.15 mol% SnO 2 as fining agent in all compositions. The batch materials (SiO 2 , Al 2 O 3 , Na 2 CO 3 , CaCO 3 , MgO, and SnO 2 ) were first thoroughly mixed for 60 min using a ball mill.…”

Viscosity of glass‐forming systems

“…The shoving model works well for predicting viscosity of a number of molecular and metallic glass‐forming liquids . However, some aspects of the shoving model have been challenged by both modeling and experimental studies. Moreover, most of the prior studies have focused on the connection between elasticity and the equilibrium viscosity of the glass‐forming liquids.…”

Double‐Torsion Measurements of the Brittle‐to‐Ductile Transition Temperature in Calcium Aluminosilicate Glasses

“…K Ic is proportional to for brittle fracture, where E is Young's modulus and γ is the surface energy. The Young moduli of alkaline earth boroaluminosilicate glasses, as well as other related glasses, decrease in the range from room temperature to about 700°C, consistent with the drop in K Ic that we measure.…”