Comparison of the Characteristics of DC Discharges with a Liquid Anode and a Liquid Cathode over Aqueous Solutions of Zinc Nitrate

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Results of systematic measurements of the electric and energy characteristics of a dc gas-discharge plasma in contact with a liquid are presented. The discharge was excited in atmospheric-pressure air over aqueous solutions of Zn(NO₃)₂. The experiments were carried out with two types of discharge: with a liquid anode and a liquid cathode. An H-shaped plasma–solution cell was used, whose branches were separated by a membrane to exclude the effect of possible chemical and/or electrochemical processes at the electrode immersed in the solution in one part of the cell on the characteristics of the metal–plasma–solution system in the other part of the cell. The discharge current was varied from 20 to 80 mA, and the zinc nitrate concentration in the solution was varied from 5 to 100 mmol/L. The current–voltage characteristic of the discharge, the electric field strength, and the near-electrode potential drops were measured. Using the geometrical characteristics of the discharge, the current densities are calculated in both the positive column and the region of the contact between the discharge and the solution. From results of spectral measurements, the vibrational temperatures of vibrationally excited nitrogen molecules in the N₂(C³Π_u) state and the temperature of the neutral plasma component are determined. The reduced electric field is calculated in the entire ranges of zinc nitrate concentrations and discharge currents under study. The results obtained for discharges with a liquid cathode and a liquid anode are compared. The results of this work can be used to simulate gas-discharge plasmas over aqueous solutions, in particular, to calculate the densities and fluxes of active particles from the plasma to the solution.