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

TL;DR

This paper presents an improved equation of state model for partially ionized carbon, oxygen, and their mixtures at high temperatures, incorporating pressure ionization, Coulomb interactions, and a new method for binary mixture calculations.

Contribution

It extends previous pure carbon models to mixtures, including pressure ionization and Coulomb effects, with a new simplified method for binary mixture EOS calculations.

Findings

Accurate EOS for carbon and oxygen mixtures at high temperatures.

Inclusion of pressure ionization effects in the model.

A new method for binary mixture EOS calculation.

Abstract

The equation of state (EOS) for partially ionized carbon, oxygen, and carbon-oxygen mixtures at temperatures 3\times10^5 K <~ T <~ 3\times10^6 K is calculated over 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; arXiv:physics/0510006). 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, 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.