Abstract
In this work, micro-arc discharge is investigated using a needle-to-plane electrode system placed with a micro-gap in highly conductive artificial seawater. A major problem with microarc discharge is the erosion of electrodes caused by the high current of the arc; however, it was found that erosion of the needle electrode did not have any effect on the discharge process in the case of precise control of the discharge gap. A simple mathematical model was developed for a more detailed study of the preheating phase of the discharge. The modeling showed good agreement with the experimental results and confirmed that the needle electrode could be reused to generate reproducible micro-arc discharges even after the erosion caused by the arc. Moreover, it was found that, in certain conditions, the preheating phase could be simulated using a simple inductor-capacitor-resistor (LCR) oscillator model with a resistor instead of electrodes immersed in the liquid. It was confirmed that the shape of the needle electrode’s tip did not affect the measurement of optical emission spectra in the case of precise focusing, which could be used in the development of compact analytical tools for on-site analysis of deep-sea water using atomic emission spectroscopy.
Highlights
Plasma processes in liquids have been gaining a lot of attention owing to their wide range of possible applications, such as nanoparticle and nanocarbon production, water cleaning, plasma medicine, and plant growth promotion [1,2,3,4,5,6,7,8,9]
One promising application is the use of optical emission spectroscopy (OES) of various plasmas generated in liquid or in contact with liquid for elemental composition analysis of the liquid [10,11,12,13,14]
Micro-arc discharges were reproducibly operated in the 10ASW using a needle-to-plane electrode system using needle electrodes with various tip shapes
Summary
Plasma processes in liquids have been gaining a lot of attention owing to their wide range of possible applications, such as nanoparticle and nanocarbon production, water cleaning, plasma medicine, and plant growth promotion [1,2,3,4,5,6,7,8,9]. Considering the requirements of strong optical emission and the possibility of generation of the plasma in highly-conductive liquid at high pressure, arc discharge is looking promising owing to the increase in the intensity of optical emission with the increase in pressure [12,15,24,27]. Micro-arc discharges generated directly in liquids, especially highly-conductive liquids (such as seawater), have not been well studied and reproducible operations and reliable measurement are still a challenge [12,32,33]. For the operation of plasma in such highly-conductive liquid, it is advantageous to focus the current in the small volume within the micro-sized electrode to reduce the energy required for formation of the bubbles and breakdown [12,19,32]. Considering that the arc discharges in a gaseous medium have been studied extensively, this study mostly focuses on the preheating of seawater within the electrode gap required for the formation of the bubbles
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