Thermodynamic Properties of Sulfur Hexafluoride

We present new vapor phase speed-of-sound data u(P, T), new Burnett density pressure temperature data \(P, T), and a few vapor pressure measurements for sulfur hexafluoride (SF6). The speed-of-sound data spanned the temperature range 230 K T 460 K and reached maximum pressures that were the lesser of 1.5 MPa or 800 of the vapor pressure of SF6 . The Burnett \(P, T) data were obtained on isochores spanning the density range 137 mol } m&3 \ 4380 mol } m&3 and the temperature range 283 K T 393 K. (The corresponding pressure range is 0.3 MPa P 9.0 MPa.) The u(P, T) data below 1.5 MPa were correlated using a model hard-core, Lennard Jones iIntermolecular poten- tial for the second and third virial coefficients and a polynomial for the perfect gas heat capacity. The resulting equation of state has very high accuracy at low densities; it is useful for calibrating mass flow controllers and may be extrapolated to 1000 K. The new u(P, T) data and the new \(P, T) data were simultaneously correlated with a virial equation of state containing four terms with the temperature dependences of model square-well potentials. This correla- tion extends nearly to the critical density and may help resolve contradictions among data sets from the literature.