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The rate-theory approach of Eyring and the free-volume theory of Cohen and Turnbull for liquid viscosities have been reconsidered. The rate theory has been reformulated using the Cohen and Turnbull expression for the probability of finding a vacant site and yields an equation of the form η=A0exp[Ev*/RT+γV0/Vf].This result has been applied to many liquids ranging from fused silica to liquid argon and including polyatomic van der Waals as well as hydrogen-bonded liquids. Consistent fits to both temperature and pressure dependence of viscosity were obtained. A significant conclusion is that the free volume of liquids is considerably higher than that suggested by the WLF and Cohen and Turnbull equations.

The dielectric constant e' and electrical conductivity of a glass-forming 40 mol % Ca(NC>3)2-60 mol % KNO3 melt were measured over a frequency range of 0.02 Hz-1 MHz and a temperature range of 25-96°. Measurements were carried out both on the equilibrium liquid above 60°and the nonequilibrium glass below 60°. The observed frequency dispersions in t' and were attributed to a nonexponential decay of the electric field via the ionic diffusion process and analyzed as such. It was found that the electric field relaxation was well described by the decay function ( ) = exp[-(£/ro)á], 0 < ß < 1. The mean electric field relaxation time, ( ), for the liquid was found to be faster than the mean shear stress relaxation time, (ts), by a factor ranging from 10 to 104 over the temperature range 96-60°, indicating a solid-like ionic conductivity mechanism in the highly viscous melt. The activation enthalpy for the electrical conductivity dropped from 78 kcal/mol for the equilibrium liquid to 24 kcal/mol for the glass. The difference between liquid and glass activation enthalpies was attributed to thermally induced structural chánges in the equilibrium liquid. The width of the spectrum of electric field relaxation times was temperature independent for the glass but broadened with increasing temperature for the liquid. From this it was concluded that the source of the spectrum of relaxation times was the microscopic heterogeneity of the vitreous system and that the temperature dependence of the width of the spectrum for the liquid reflected thermally induced structural changes.

A method was developed to determine the kinetic parameters controlling structural relaxation in the glass transition region from data acquired during continuous heating or cooling. The nonexponential character of the relaxation is accounted for by assuming an equilibrium isothermal relaxation function of the form exp [−(t/Toe)ß], where Toe is a relaxation time and 0<β1. The data are linearized using the method of Narayanaswamy, and the continuous temperature variation during heating or cooling is dealt with by invoking the superposition principle. The analysis yields the kinetic parameters A, the relaxation‐time preexponential term; Δh★, the relaxation‐time activation enthalpy; x, a term describing the relative effects of temperature and structure on the rate of relaxation; and β. The method was applied to analysis of the variation of the enthalpy of vitreous B2O3 during rate heating through the transition region following rate cooling through the same region at a variety of rates.