Modelling of Ar-CO₂ thermal plasma

Abstract

<p>A chemical kinetic model has been constructed to predict the pressure and gas and electron temperature dependency of the neutral and ionic species composition in Ar-CO₂ mixtures under thermal plasma conditions. Pure Ar and Ar-C models have also been constructed as a part of this investigation. The models include electron impact, thermal impact, ion-molecule, and recombination reactions as well as accounting for diffusion. Important metastable and excited states of species have been accounted for as well as the presence of neutral molecules, radicals, and atoms, positive and negatively charged atoms and molecular ions as well as electrons. All relevant electron temperature, gas temperature and pressure terms have been included, and primarily experimentally derived reaction rate constants were utilized. Electron and gas temperature dependent species concentrations were obtained under both thermodynamic equilibrium and non-equilibrium conditions for gas temperatures from 300 to 15000 K, electron temperatures from 300 to 20000 K, and pressures from 1 Torr to 15200 Torr. Percentage mixtures of C and CO₂ in Ar were varied between 0.1 and 40%. Results indicate that the neutral and excited species Ar, Ar*, Ar**, C, CO, CO₂, O, O₂ and O₃, positive ions Ar⁺, Ar₂⁺, C⁺, CArO⁺, CO⁺, CO₂⁺, CO₄⁺, C₂O₂⁺, O⁺, O₂⁺, O₄⁺, and O₅⁺ and negative ions CO₃⁻, CO₄⁻, O⁻, O₂⁻, and O₃⁻ and electrons are observed. Under thermodynamic equilibrium conditions, Ar, C, CO, CO₂, and O were found to be the dominant neutral species, C⁺, CO₄⁺, O⁺, and O₂⁺ the dominant positive ions, and O⁻ and electrons the dominant negatively charged species under certain gas temperature ranges. The introduction of thermodynamic non-equilibrium conditions, changes in gas pressure, and percentage mixture of C or CO₂ were observed to have a significant influence on the temperature dependent concentrations of these species. The results were found to be in good agreement with previous experimental and theoretical results. Comparison of the present results with the results of the Saha equation seem to indicate that the simple Saha equation type approach may mispredict the plasma density of Ar, Ar-C, and Ar-CO₂ mixtures under thermal plasma conditions.</p>