Thermodynamic and transport properties of an aluminum-nitrogen plasma

The thermodynamic and transport properties of an aluminum-nitrogen plasma arc have been calculated at atmospheric pressure at temperatures up to 25,000 K and at different mole fractions of aluminum. At higher temperatures 11 species are produced in the in the plasma, namely, Al, Al⁺, Al²⁺, Al³⁺, N₂, N₂⁺, N, N⁺, N²⁺, AlN, and e. The thermodynamic properties include the number densities, enthalpy, and total heat capacity of the mixture. The number density of AlN reaches a maximum at temperatures around 5000 K and a mole fraction of 67% of aluminum. The transport properties have also been calculated as a function of temperature and mole fraction of Al. The momentum transfer cross sections between the ions and neutrals have been estimated using a polarization potential. The collision cross sections between the electrons and neutrals have been determined using a semiphenomenological effective potential that is based on the self-consistent Dirac-Hartree-Fock-Slater field and accounts for exchange and polarization effects in a simple way. For neutral-neutral and charge-charge interactions, the cross sections have been calculated by the Leonard-Jones and shielded Coulomb potentials, respectively. At temperatures below 8000 K, the electrical conductivity is increased by the presence of a small mole fraction of Al in the nitrogen plasma. However, the viscosity is less sensitive to the presence of Al.