The thermodynamic properties and the transport coefficients of thermal plasmas formed in SF6-copper vapour mixtures were calculated as a function of temperature and pressure for molar concentrations of copper between 0 and 10%. The material property that is most affected by the presence of copper is the electrical conductivity for temperatures up to 10000 K. The results given in this paper enabled a data bank to be built up for modelling arcs in SF6 seeded with copper vapour.

In this paper we discuss the use of generalized Saha and Guldberg-Waage equations for calculating the composition of a two-temperature SF 6 plasma in a pressure range 0.1-1.6 MPa, for an electron temperature in the range 300-20 000 K. We compare two sets of two-temperature laws and we recommend the expressions proposed by the team from Eindhoven. Furthermore, knowing the great influence of the choice of the excitation temperature on the plasma composition, we propose, on the basis of a chemical kinetics approach, a simple general relation allowing the calculation of this temperature versus the electron temperature, the heavy particle temperature and the electron number density. The application of these relations to a real case of a two-temperature SF 6 arc plasma gives a realistic radial profile of the electron number density.

The electrical conductivity of SF6-Cu and Ar-Cu plasmas has been calculated by using new values of the cross section of the electron-copper momentum transfer. The comparison between the new values of the electrical conductivity and the previous ones, in the temperature range 2500-15000 K, shows the actual influence of copper vapour on this transport coefficient and allows quantification of the errors made with the various approximations.

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