STATIC RELATIVE PERMITTIVITY OF SULFUR-HEXAFLUORIDE UP TO 30-MPA

The static relative permittivity epsilon(r) of sulfur hexafluoride, SF 6, has been measured along ten isotherms from 273.15 to 353.15 K at pr essures up to 30 MPa. The experimental epsilon(r)-values obtained were accurate to within +/-0.02 per cent, except for some values in the vi cinity of the critical point. The critical relative permittivity epsil on(r,c) was estimated to be 1.281+/-0.001 by application of the rectil inear diameter law. The epsilon(r)-values were combined with densities obtained from the equation of state in the literature to calculate th e molar polarization P(m) given by the Clausius-Mossotti equation. The results Of epsilon(r) and P(m) as a function of fluid density are dis cussed; the volume polarizability alpha' of SF6 was evaluated to be 6. 67x10(-30) m3 and 6.59x10(-30) M3 using the values of the first dielec tric virial coefficient A(epsilon) determined by two methods. Further, the values of alpha' for carbon dioxide and nitrous oxide were recalc ulated to be 2.94x10(-30) m3 and 3.20x10(-30) m3, respectively, from A (epsilon)-values obtained by the newly employed method.