Study of the dielectric breakdown properties of hot SF6-CF4 mixtures at 0.01-1.6 MPa

The dielectric breakdown properties of SF6-CF4 mixtures were investigated at different ratios of SF6, 0.01-1.6 MPa, and gas temperatures up to 3000 K. Initially, the equilibrium compositions of SF6-CF4 mixtures were calculated by minimizing the Gibbs free energy under the assumptions of local thermodynamic and chemical equilibrium. Then the electron energy distribution function was obtained based on those data by solving the Boltzmann equation under the zero-dimensional two-term spherical harmonic approximation. Finally, the critical reduced electric field strength (E/N)(cr) of SF6-CF4 mixtures, which is defined as the value for which total ionization reaction is equal to total attachment reaction, were determined and analyzed. The results confirm the superior breakdown properties of pure SF6 at relatively low gas temperatures. However, for higher gas temperatures (i.e., T > 2200 K at 0.4 MPa), the (E/N)(cr) in SF6-CF4 mixtures are obviously higher than that in pure SF6 and the values of (E/N)(cr) increase with the reduction of the ratio of SF6. (C) 2013 AIP Publishing LLC.