Optical emission spectroscopy of plasma of electric spark discharge between metal granules in liquid

This work is devoted to the plasma diagnostics of an underwater electric spark discharge, specially developed for the synthesis of metal nanoparticles by electro erosion of metal granules immersed into water. To improve the process of metal nanoparticle generation, the main plasma parameters for different modes of discharges between molybdenum and, separately, iron granules were investigated. The optical emission spectroscopy as a non-perturbing method was used. Namely, the Boltzmann plots on the basis of metal atomic lines’ (in particular Fe I and Mo I) intensities are used to determine the electron temperatures in plasma. Profile of H α spectral line, exposed to the Stark mechanism of spectral lines’ broadening, is used to determine the electron density in such plasma. The black-body radiation is found in the spectrum of the discharge between molybdenum granules. It was found that the background emission in the spectral regions with densely spaced spectral lines can be caused by the overlapping of spectral lines’ contours for the underwater discharge between metal granules.