Inadequacies of Viscosity Theories for B2O3

Abstract

The viscosity of B.Oa glass was measured from 10 1L I0 14 P by the fiber-elongation method and found to be Arrhenius with an activation energy of 94 kcal/mol. These new data were combined with previously reported rotation data (10 L lO 10 P) and gave a smooth plot. The complete viscosity data were used to test the equations of the best-known viscosity theories but no reasonable fits were found. Therefore, an examination of the validity of the basic assumptions underlying these theories was made. As a result of this study, it was found that the temperature dependence of the viscosity is not controlled by structural effects such as free volume, configuration entropy, etc., but by activation energy effects in the viscous flow process. The onset of the non-Arrhenius region is a direct consequence of the appearance of a symmetric distribution of relaxation times and/or a distribution of activation energies which cannot be explained by existing viscosity theories. Finally, all theories are in error in predicting that the viscosity goes to infinity (in the annealing region) much faster than the measured values indicate.

String model for the dynamics of glass-forming liquids

“…This length scale is consistent with empirical CRR size estimates obtained from specific heat measurements in small-molecule liquids and estimates of the change in the activation energy in GF liquids. 40,73,74 This range of length scales The experimental data emphasize the similarity to our simulation data. We compare the equilibrium polymer model data both isobaric and isochoric simulation data to show that change does not alter the qualitative trend.…”

“…Assuming that relaxation can be Table 2 of Ref. 40. Note that, while these data are well known, it is the first time that this form of data reduction has been considered.…”

Communications: Comparison of activation barriers for the Johari–Goldstein and alpha relaxations and its implications

“…Attempts to correct for this changing structure have used the Adam-Gibbs equation, 19 in which the dependence of the barrier height on the configurational entropy provides an explicit expression for the spurious term. 20,21 More recent model-independent estimates have been proposed, from experimental studies of hyperquenched glasses, 22 from the simple requirement that the prea͒ Electronic mail: ifg2@columbia.edu.…”

Prediction of the viscosities of ""soda-lime"" silica glasses

“…It has limitations. Macedo and Napolitano [15] comment that, in general, if the data are limited to viscosity values between 10 2 and 10 12 a good fit can be obtained to the Fulcher equation. A more serious practical problem arises if the equation is used for extrapolation.…”