Behaviors of excited N, N2+ and NH in modulated induction thermal plasmas

Summary form only given. High-power high-pressure induction thermal plasmas have been widely used in many material processing fields such as syntheses of nanopowders and thermal barrier coatings etc, because they have advantages such as remarkably higher enthalpy and higher radical density than cold plasmas, and also little contamination. To functionalize induction thermal plasmas, we have developed a pulse-modulated induction thermal plasma (PMITP). This PMITP offers the possibility of controlling temperature, chemical reaction and gas flow fields in thermal plasmas, and then is expected as a radical and heat source for material processing. Recently we found that one can create more nitrogen atomic density in Ar-N₂ PMITP than in a non-modulated convectional thermal plasma under the same power condition. In this report, time variation in radiation spectra from Ar, N, N₂ ⁺ and NH was measured to study dynamic behaviors of these particles in Ar PMITP with N₂/H₂ additional gases. The radiation intensities were observed using a time resolved CCD. In thermal plasma material processing, the densities of N and NH are considered to be crucial for rapid surface nitriding process of materials. From this measurement, their inherent periodical behaviors were found in the radiation intensities of these spectra following the pulse modulation of the coil current sustaining PMITP. Furthermore, we compared the time-averaged radiation intensities for N, N₂ ⁺ and NH in a PMITP with those in a non-modulated conventional induction thermal plasma under the same input power condition. Results showed increases in the time- averaged radiation intensities of N and NH by the pulse- modulation of the coil current compared with that in a non- modulated thermal plasma.