Thermophysical properties of binary mixtures containing oxygen and noble gases

This work deals with the determination of reliable transport and equilibrium thermophysical properties of binary mixtures of O2 and the noble gases Ar, Kr, and Xe. The second virial coefficients B(T), the viscosities η(T), and the binary diffusion coefficients D12(T) were calculated for each mixture in the temperature range between 200 K and 1000 K using a a temperature dependent (n-6) Lennard-Jones intermolecular interaction potential model. The properties of the mixtures were obtained by using the Lorentz-Berthelot and Hohm-Zarkova-Damyanova mixing rules. Our results were compared to other theoretical and experimental data and acceptable agreement was found in all cases. Fitting formulae for the calculation of the intermolecular potential parameters and equilibrium and transport properties of the examined mixtures are recommended proposed.


Introduction
Binary mixtures containing molecular oxygen and the noble gases Ar, Kr, and Xe are used in many industrial processes, e.g. Ar/O 2 is applied as a shielding gas in weldings [1]; Ar/O 2 , Kr/O 2 , and Xe/O 2 are used in magnetron sputtering [2]; Ar/O 2 or Kr/O 2 are applied in etching processes [3]. Recently, medical applications became popular; e.g., a Xe/O 2 mixture is used as a respiratory and anesthetic gas mixture [4][5] and Ar/O 2 [6] is used in tissue regeneration. In all applications, reliable information is needed on the equilibrium and transport properties at different concentrations and in a wide range of temperatures. The variety of possible constituents of mixtures, as well as various experimental difficulties, stimulate the calculation of thermophysical data by different models.
Our calculations were based on the (n-6) Lennard-Jones temperature dependent potential (LJTDP). By using the Lorentz-Berthelot [7] and Hohm-Zarkova-Damyanova [8] mixing rules, the intermolacular interaction potentials of the binary mixtures were obtained from the pure component data. Subsequently, these potentials were used to calculate the second virial coefficients (B 12 , B mix ), the viscosities  12 ,  mix and the binary diffusion coefficients (D 12 ) for all three mixtures in the temperature range betwen 200 K and 1000 K. Our findings were compared to available theoretical and experimental data.

Theoretical background
All thermophysical properties of gas mixtures in the low pressure (under 1 atm ) range depend on the binary intermolecular interaction energies between like and unlike constituents of the corresponding mixture. In our model, the intermolecular interactions between molecule 1 and 2 are described by the (n-6) Lennard-Jones potential with the characteristic potential parameters R m12 (equilibrium distance),  12 (potential well depth), and n 12 (repulsive parameter). In the case of molecules, we consider to be R m12 and  12 as being functions of the temperature T, which leads us to using the Lennard-Jones temperature-dependent potential (LJTDP) [9].
The intermolecular interaction potential parameters R m11 ,  11 , and n 11 for the pure gases have already been determined by Damyanova et al. and are given in Ref. [10] for pure O 2 and Ref. [11] for the noble gases.
The fitting constants are given in table 2. Here ΔP is the standard error of the fit.