Plasma spectroscopy of electric spark discharge between silver granules immersed in water
This work is devoted to optical emission spectroscopy of plasma of underwater electric discharge, which is used for the synthesis of silver nanoparticles. The main aim of this work is to investigate the possibility and validity of using plasma optical emission spectroscopy to determine its main physical characteristics, such as excitation temperature, electron density, the degree of ionization, etc. The specially developed pulse power source was used to initiate a discharge between silver granules immersed into the deionized water. Typical values of voltage vary from 40 to 200 V, the current is up to 150 A, and pulse frequency is in the range of 0.2–2 kHz. Applied to electrodes, the voltage caused a current flow along the chain of closely arranged granules in the stochastic switching mode. Special attention is paid to methods of spectrum treatment of underwater discharge plasma between silver granules. The method of Boltzmann plots and the method of relative intensities on the basis of both atomic and ionic silver spectral lines are used in order to determine the excitation temperature. The spectral lines, which were investigated and treated in detail, were used. Exposed to the Stark mechanism of spectral line broadening, the spectral profile of Hα spectral line is used to determine the electron density. The degree of ionization of the studied plasma was calculated using the obtained values of the electron density and temperature.