Plasma analysis using emission spectroscopy has been carried out in the cathode fall and the negative glow of N2-H2 abnormal glow discharges for steel surface nitriding. The spatial distributions of the selected excited states of N2, N, N2+, N+, NH, H2, H and Fe have been measured in terms of their dependence on the main process parameters, such as the cathode temperature (400-550 degrees C), H2 percentage in the gas mixture (10-70%) and total pressure in the nitriding reactor (400 and 800 Pa), corresponding to the given values of the discharge current (115-260 mA) and applied voltage (465-635 V). The experimental data presented yield reliable information on the occurrence of excited states in the cathode region and on the effect of the process parameters on the cathode fall thickness, which determines the energy distributions of ions bombarding the cathode and is an important input parameter in plasma process modelling.

For pt.II see ibid., vol.22, p.632 (1989). The extensive collisional-radiative model for an argon atom plasma is applied to atmospheric and subatmospheric pressure wall-stabilised arcs in order to clarify the mechanisms by which the excited levels are populated in the axial region of these discharges. Computations are carried out for various sets of input parameters, such as the electron kinetic temperature Te, the atom temperature Ta, the ion temperature Ti, the electron number density ne, the ground-state atom population n1, the plasma column radius R and the escape factors Lambda mn and Lambda m, characterising the non-equilibrium plasmas under consideration. The predicted values of the populations in the excited levels and the qualities derived from them, as well as the values of the critical electron densities for establishing the local thermodynamic equilibrium in the axial region of the arcs investigated, are in good agreement with the corresponding experimental results. The effect of the changes in the discharge parameters Te, Ta, ne, R and Lambda 1n on the population mechanism, together with the role played by the recombination flow of electrons from a continuum, the deviations of the actual electron distribution function from the corresponding Maxwellian form and by the atom-atom inelastic collisions, are also shown.