The electrical conductivity and freezing point of molten (n hexyl)4NBF4 as a function of pressure and temperature

Abstract

The electrical conductance and freezing point of (n hexyl)4NBF4 have been studied as a function of pressure to 1000 bar, and temperature over a range of 110°. The specific conductance is given by the empirical equation, log K = 0.322(1 - Px10-4) 779.4 + 0.068P/T - 160 The compressibility is estimated and used to discuss the relative importance of volume and temperature in determining the conductance. The volume dependence is small and nearly independent of temperature, whilst the temperature dependence is larger and increases with decreasing temperature, both at constant pressure and at constant volume. This result is interpreted qualitatively in terms of the theory of Adam and Gibbs. The activation volume is small relative to the small ion volume, which supports the view of Naghizadeh and Rice, that the pressure dependence of transport is small when the repulsive potential is steep. The results suggest that the free volume theory of Cohen and Turnbull does not account correctly for transport in molten salts, even though it predicts the form of the isobaric temperature dependence.