Inadequacies of Viscosity Theories for a Vitreous KNO 3 ‐Ca(NO 3 ) 2 Melt

The viscosity of a 0.60KNO 3 ‐0.40Ca(NO 3 ) 2 melt was measured from 10 9.6 to 10 14 P by a beam‐bending method. In this range, the viscosity exhibited Arrhenius behavior, with an activation enthalpy of 138 kcal/mol. These data joined smoothly with capillary and rotational viscometer data from 10 −2 to 10 8 P previously reported for this system. The temperature dependence of shear sound wave velocities at 75.2 MHz was measured, and the temperature dependence of the shear modulus from 60° to 120°C was calculated for this melt. The Fulcher equation, In n =A+B/(T‐T 0 ), described the temperature dependence of the viscosity of this melt poorly, indicating severe deficiencies in the viscosity theories which predict an equation of this form.