Conductivity of (C4H9)4N BF4 in liquid and supercritical hydrofluorocarbons

The conductivity of tetrabutylammonium tetrafluoroborate in 1,1,1,2-tetrafluoroethane (HFC 134a) in the liquid state at 30 degrees C and in difluoromethane (HFC32) in the liquid, near critical and supercritical states is presented as a function of concentration and pressure. The data are fitted to a Fuoss-Kraus model and the ion pair and triple ion dissociation constants are analyzed as a function of temperature and pressure. It is shown that the ionic equilibria are controlled by the relative permittivity of the media irrespective of the state of the fluid. The change in ion pair and triple ion dissociation constants with pressure are used to discuss the solvation of charged and neutral species in liquid and supercritical fluids.