Equation of state for partially ionized carbon and oxygen mixtures at high temperatures

A. Y. Potekhin,1 G. Chabrier,2 G. Massacrier2
1Ioffe Physical-Technical Institute, 194021 St. Petersburg, Russia
2Ecole Normale Supérieure de Lyon, CRAL (UMR CNRS No. 5574), 69364 Lyon Cedex 07, France

Equation of state for partially ionized carbon, oxygen, and carbon-oxygen mixtures at temperatures T ∼ 105—107 K is calculated in a wide range of densities, using the method of free energy minimization in the framework of the chemical picture of plasmas. The free energy model is an improved extension of our model previously developed for pure carbon [Phys. Rev. E 72, 046402 (2005)]. The internal partition functions of bound species are calculated by a self-consistent treatment of each ionization stage in the plasma environment taking into account pressure ionization. The long-range Coulomb interactions between ions and screening of the ions by free electrons are included using our previously published analytical model, which has been recently improved, in particular for the case of mixtures. We also propose a simple but accurate method of calculation of the EOS of partially ionized binary mixtures based on detailed ionization balance calculations for pure substances.


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