Meßwerte des zweiten Virialkoeffizienten und Bestimmung des zwischenmolekularen Wechselwirkungspotentials von gasförmigem Uranhexafluorid

Abstract

Es wird über eine Apparatur berichtet, mit der der Temperaturverlauf des zweiten Virialkoeffizienten chemisch aggressiver Gase und Gasmischungen von 300500 K gemessen werden kann. Für Uranhexafluorid werden die Virialkoeffizienten angegeben. Im Gegensatz zu Meßdaten anderer Autoren sind unsere Meßergebnisse sehr gut mit theoretisch berechneten Virialkoeffizienten vereinbar, die mit einem Lennard‐Jones‐n26‐Potential erhalten wurden. Die Parameter des benutzten Potentials wurden mit Hilfe von Literaturdaten der Viskosität, des Selbstdiffusionskoeffizienten und des Thermodiffusionsfaktors für Isotope ermittelt.

The isotropic temperature-dependent potential describing the binary interactions in gaseous and

“…Therefore we considered separately the values measured by Malyshev at low temperature B1 and high temperature B2. These two groups of data are mainly responsible for the calculated temperature dependence of B since they are the only values measured at T < 313 K and T > 453 K. The smooth transition of B(T ) results from the simultaneous consideration of all three experiments (Morizot et al 1973, Malyshev 1974, 1973, Heintz and Lichtenthaler 1976. As was observed for UF 6 , the results of Heintz and Lichtenthaler (1976) deviate the most, particularly for WF 6 .…”

“…With a variation of the parameters by ±5% the change in RMS deviation σ is about 250-300% for r m , 70-80% for ε, and 10-15% for n and δ. . Full curves: our potential curves for 0, 400 and 1000 K; short broken curve: Heintz et al (1976); medium broken curve: Malyshev (1974); long broken curve: Morizot et al (1973).…”

“…The Lennard-Jones potential form is applicable only in a narrow temperature range (Morizot et al 1973) and is not appropriate when the parameters in it are derived from a single experiment (Malyshev 1974). Heintz and Lichtenthaler (1976) have introduced (18-6) model potentials to approximate their measurements of B in the range T = 320-460 K together with those of Morizot et al (1973) for B and η. An anisotropic model including the hexadecapole contribution (Ursu et al 1987) has been proposed too; the drawback of this model is that no hexadecapole moments have been experimentally measured to date for WF 6 and MoF 6 , and our evaluations for SF 6 show that the values of the hexadecapole moment needed for the simultaneous approximation are several orders of magnitude larger than the measured ones.…”

Modeling of Some Thermodynamic Properties of UF6 at Low Pressure Using Correlation Function

“…So far, several researchers have studied virial coefficients of UF6 and some of them have presented its correlation function of the second virial coefficient [32][33][34][35][36][37][38][39]. Some of the important ones consist of Weinstock in 1959 [32], Dewitt in 1960 [33], Malyshev in 1973 [34], Dymond [37] and Zarkova [38] in 2002.…”

pVT –Second Virial Coefficients B(T ), Viscosity η(T ), and Self-Diffusion ρD(T) of the Gases: BF3, CF4, SiF4, CCl4, SiCl4, SF6, MoF6, WF6, UF6, C(CH3)4, and Si(CH3)4 Determined by Means of an Isotropic Temperature-Dependent Potential

“…This approach explains the existence of a big variety of different -r m pairs for one specific molecule extracted from different experi-ments ͑see, e.g., the review given by Aziz et al 6 for SF 6 ͒. In the 1970s the Heidelberg group 7,8 has tried to fit simultaneously both transport and equilibrium properties of quasisymmetric molecules and have reported a repulsive parameter n higher than 12 for some of them ͑SF 6 , UF 6 , MoF 6 , WF 6 ͒. In some cases calculations for octahedral hexafluorides 9,10 have taken into account hexadecapole moments which lead to anisotropic potentials.…”