Electric Discharge between a Jet Electrolytic Cathode and a Metal Anode

Introduction. Gas discharges with liquid electrodes are considered as a promising tool for improving adhesion properties and preparing surfaces for coating application. Glow and arc discharges with electrolytic electrodes have been investigated in detail in the literature, but most studies focus on configurations with a stationary electrolyte. For “jet electrolytic cathode–metal anode” systems at atmospheric pressure, the discharge combustion modes, their stability limits, and the energy characteristics of the process are insufficiently systematized. This hinders the scalability of localized aluminum processing technologies. The objective of this study is to experimentally classify combustion modes and their stability regions, determine the electrical, spectral, and thermal parameters of the discharge, and substantiate practical modes for localized aluminum surface preparation for adhesion and coating. Materials and Methods. To achieve this goal, a laboratory setup was built: a 3% NaCl jet served as the cathode, and an AMTs-40 (aluminum-manganese alloy in the RU system, ISO analog: AW-3003) aluminum plate served as the anode. The jet-anode assembly was placed in a temperature-controlled electrolytic cell with closed circulation of the solution. Typical conditions: U ≈ 600 V, v k ≈ 0.6–0.7 m/s, d ≈ 2 mm, σ ≈ 0.10–0.12 Ω –1 ·cm –1 . A power supply of up to 4 kV/10 A provided a wide range of settings. The diagnostics included oscillographic measurements, high-speed video recording (Casio EX-F1, 600–1200 fps), thermal imaging (FLIR A6500sc), and optical emission spectroscopy (OES) on a PLASUS EC 150201 MC spectrometer with electron density n e estimated from Stark broadening of H α . Results. Two plasma localization topologies were detected: a contact zone on the triple gas-liquid-solid line and a jet breakup region. The current was pulsed with an amplitude of 0.8–1.6 A. The spectra were dominated by the Na I doublet (~589 nm), the OH(A–X) bands, and the H α line; from Δλ L ( H α ) ≈ 0.64 nm, an estimate of n e ≈ 6.4 × 10 16 cm –3 was obtained. Thermal imaging maps showed a maximum effective temperature of ~47°C at the point of contact, and an energy deposition zone elongated along the jet with a length of ~7 mm (diameter ~2 mm). Discussion. The pulsed nature of the current with an amplitude of 0.8–1.6 A at 600 V indicates the periodic formation and breakdown of the current channel, which is typical for discharges with a nonstationary geometry of the cathode region and has been previously noted in studies on discharges with flowing jets. The estimate of the electron density nₑ ≈ 6.4×10 16 cm –3 based on the Stark broadening of Hα falls within the range of 10 15 –10 17 cm –3 , characteristic of atmospheric discharges with liquid electrodes, and indicates a relatively dense plasma sufficient for effective surface activation. The dominance of Na I lines in the spectrum confirms the intense transfer of electrolyte components into the discharge gap, which is consistent with the aerosol sputtering mechanism in the near-cathode region. The compactness of the temperature spot on the anode (transverse size ~2 mm, maximum 47°C) confirms the localized nature of the energy deposition without global overheating of the component. However, the true surface temperature may be higher than the measured one due to the uncertainty in the emissivity of the growing oxide film. Conclusion. A discharge between a jet electrolytic cathode and an aluminum anode at atmospheric pressure has been experimentally characterized. Two stable combustion topologies, the pulsed nature of the current, spectral markers, and a thermal energy deposition pattern are demonstrated. The results form the basis for constructing operational maps for local aluminum processing and expanding technology applications. The data obtained form the basis for constructing a map of aluminum processing modes and can be expanded through varying the flow rate, nozzle diameter, electrolyte composition, and using faster diagnostics. Future work includes standardizing the energy metrics, quantitatively decomposing the radiation sources, and scaling the methodology.