Inadequacies of Viscosity Theories for B2O3

Abstract

The viscosity of B2O3 glass was measured from 1010–1014 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 (101–1010 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.