engleski

Immersion of single electrode atmospheric pressure plasma jet into deionized water

Various designs of plasma sources and choice of operational parameters are used to tailor plasma content suitable for specific application. For example, using typical dielectric barrier discharge with high voltage and grounded electrode around the glass tube leads to plasma plumes with smaller concentration of radicals and weaker emission intensity compared to the case when a single electrode plasma jet is used [1]. On the other hand, when a one electrode system is used, the presence of a substrate and its dielectric properties can influence the way a discharge operates [2, 3]. In our work, a single electrode atmospheric pressure plasma jet was used for treatment of deionized water. Voltage frequency was around 30 kHz with variable amplitude. Helium 5.0 was used as a working gas at 2 slpm. The first part of the experiment was optical emission spectroscopy for different electrode-water distances and different voltage amplitudes, while measuring voltage and current waveforms. RMS values of current and voltage along with power exhibit local maximum versus electrode-water distance. These maxima are dependent on initial voltage amplitude. Observed spectral features show different dependence versus electrode-water distances. The second part of the experiment was measuring pH of treated water at fixed distance for different treatment times and applied voltage amplitudes, every day for a week to check for ageing effects. The results showed that longer treatment time lowers pH of the water more (for example, at 11 kV pH drops from 5.6 to 3.8 for 10 minute treatment instead of 4.9 for 1 minute treatment. Likewise, higher voltage amplitudes can lower the pH more than lower voltages (for example, treatment of 5 minutes at 19 kV lowers pH to 3.7 instead of 4.2 at 11 kV). Regarding the ageing, samples treated for shorter time and lower voltages recover the initial pH over a week, while those treated for longer time and with higher voltage amplitudes maintain their pH or decrease even further. This work was supported in part by Croatian Science Foundation under the project #2753. [1] CT. Liu et al., IEEE T. Plasma Sci. 44 (2016) 12. [2] V. Prysiazhnyi et al., Braz. J. Phys. 46 (2016) 496. [3] R. Zaplotnik et al., Spectrochim. Acta 103-104 (2015) 124-130

Atmospheric pressure plasma jet ; spectroscopy ; pH change

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