Spectroscopic analysis of Ar-H_2 and Ar-N_2 plasmas revealed that the population density of the excited states of each species (Ar, H and N) followed a Boltzmann distribution, but each species had its own respective temperature. The temperature of argon atom was lower than that of hydrogen atom in the plasma of Ar-H_2 mixture. The temperature of nitrogen atom was close to that of argon atom in the plasma of Ar-N_2 mixture under one atmospheric pressure. There was a deviation from local thermodynamic equilibrium (LTE) in these plasmas under one atmospheric pressure. The deviations from LTE in these plasmas are explained by the differences in the energy flow in the plasmas .
The in-flight reductions of Fe_2O_3, Cr_2O_3, TiO_2 and Al_2O_3 were carried out in the Ar-H_2 plasma. The plasma reduces Fe_2O_3 and Cr_2O_3 to their metals. TiO_2 is reduced to Ti_2O_3 and Ti_3O_5 . Al_2O_3 isn't reduced. The products contain non-spherical and spherical particles, which are quenched and cooled from gas and liquid respectively. The reaction mechanisms are explained as follows. The oxide particles in the plasma are heated quickly, and then they melt and vaporize.
Fe_2O_3 and Cr_2O_3 are vaporized as a metallic state in the plasma. They are quenched and precipitated as non-spherical particles of their metals. TiO_2 and Al_2O_3 are vaporized as their suboxides such as TiO, AlO and Al_2O. They are precipitated as non-spherical particles and oxidized to stable oxides such as Ti_2O_3, Ti_3O_5 and Al_2O_3 during the cooling. The particles which are not vaporized completely are cooled from liquid phase as spherical particles.