Plasma plume characteristics of supersonic ammonia and nitrogen/hydrogen-mixture DC plasma jets for nitriding under low-pressure environment

Abstract

Spectroscopic and electrostatic probe measurements were made to examine plasma exhaust plume characteristics with or without a titanium plate under nitriding for a 10-kW-class direct-current arc plasma jet generator with a supersonic expansion nozzle under a low-pressure environment. Ammonia and a mixture of nitrogen and hydrogen were used as the working gas. The NH 3 and N 2+3H 2 plasmas in the nozzle and in the downstream plume without substrate plates were in thermodynamic nonequilibrium states. As a result, 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. On the other hand, each temperature was kept in a small range in the plume without a substrate plate under 130 Pa except for the NH rotational temperature for NH 3 working gas, although with a titanium plate the nonequilibrium plasma tended to have an equilibrium temperature as it approached the plate.