Characteristics of supersonic nitrogen/hydrogen-mixture and ammonia plasma jets and nitrided material properties

Spectroscopic and electrostatic probe measurements were made to examine plasma characteristics under nitriding for a 10-kW-class direct-current arc plasma jet generator with a supersonic expansion nozzle in a low pressure environment. Heat fluxes into the plate from the plasma were also evaluated. Ammonia and mixtures of nitrogen and hydrogen were used as a working gas. The H-atom electronic excitation temperature and the N(2) molecule-rotational excitation temperature intensively decreased downstream in the nozzle although the NH molecule-rotational excitation temperature did not show an axial decrease. As approaching the titanium plate, the thermodynamical non-equilibrium plasma came to be a temperature-equilibrium one. Both the electron number density near the plate and the heat flux increased with H(2) mole fraction for mixtures gases. In cases with mixtures of N(2) and H(2), a radical of NH with a radially wide distribution was considered to contribute to the better nitriding as a chemically active and non-heating process. (C) 2003 Elsevier B.V. All rights reserved.