Electrical Conductivity of Decamethylferrocenium Hexafluorophosphate and Tetrabutylammonium Hexafluorophosphate in Supercritical Trifluoromethane

Abstract

The electrical conductivity of tetrabutylammonium hexafluorophosphate (TBAPF6) and decamethylferrocenium hexafluorophosphate (Fe(Cp*)2PF6) in supercritical trifluoromethane (CHF3) was measured as a function of density (at pressures of 6−16 MPa) at 323.15 K. The concentration dependence of the molar conductivity was fitted using the Fuoss−Kraus equations, including ion pairs and triplets, and the molar conductivities at infinite dilution and the ion-pair formation constants were calculated as a function of the solvent density for both salts. The results were analyzed and explained by resorting to the peculiar properties of supercritical fluids in the low-density region. A comparison with the continuum model of ion mobility was conducted to demonstrate the inability of such a hydrodynamic model to describe the transport properties of salts in supercritical media. Also, the compressible continuum model applied to these systems seems to describe the limiting conductivity behavior in the high-density region rather well.