Applying pulsed corona discharge in hypersaline droplets

Abstract

Crystallization of salts in droplets of hypersaline solution placed on a glass slide was monitored and evaluated under controlled conditions of temperature and humidity. Pulsed corona discharge (PCD) was applied over sessil droplets on a glass surface, and its effect in the crystallization is demonstrated for the first time. These results were compared with natural evaporation. Under natural evaporation, crystals are firstly formed on surface, near edges of the drop and grow towards the center, eventually acquiring a pyramidal morphology. Under PCD, a Taylor cone is formed between electrode and droplet surface and then, 4 s after the beginning of the discharge, small crystals were formed on the cone besides a dense crystal film around the discharge incidence point in the droplet. These results are discussed considering existing knowledge about plasma–liquid interaction (PLI) and dynamical of crystal growth. This paper explores an interesting aspect of PLIs, which has both fundamental and practical usefulness, for understanding desalination processes, salt crystallization on water surface and biomedical science for advances in electrosurgical methods.

Investigating the Influence of the Pulsed Corona Discharge Over Hypersaline Water

“…In addition to local heating, another possible mechanism that occurs during plasma-activated precipitation can be attributed to the alignment of the dipoles in the solvation layer towards the opposites, in order to facilitate the breaking of the solvation shell and consequent precipitation 12,34 . When NaCl (for example) is dissolved in water, the Na+ and Clions are hydrated by the polar water molecules, forming double-layer structure with opposite signs of charges 10 .…”

“…As for the cathodic plasma, unlike anodic, precipitation will proceed by the already discussed water vapor/droplet formation. This is true because when cathode pulsed corona discharge is applied over conductive solutions, an avalanche of electrons is driven towards water, producing vapour bubbles 12,42 . As mentioned before, the salts formed that remained in solution are similar for to the anodic ones, differing by the fact that in the anodic configuration more magnesium salts are obtained.…”

“…Among the mineral extraction commercial from seawater without organic waste, the electrolytic processes are more economic 9 . Recently there has been keen interest in the physics and chemistry occurring in electrical discharges through liquids and plasmas formed in saline environments [10][11][12][13] . Cold atmospheric plasma (CAP) over liquids has led to various established industrial implementations, as well as promising applications, including chemical analysis, nanomaterials synthesis, plasma medicine and water desalination [14][15][16][17] .…”

“…In the case of expected oxidation, removal of harmful compounds from water, for example, the anodic configuration is preferred because it can create and deliver more oxidative species towards the plasma-liquid interface. In the case of HSW, the expected results should differ for each configuration, but even considering the great amount of literature about plasma-liquid interaction that has already been published 12,17,[26][27][28][29] very little is currently known about interaction plasma -HSW. Therefore, in the present study, we use plasma produced by PCD over HSW surface, in helium atmosphere, to evaluate its extracting and/or separating capacity of salts from HSW.…”

Plasma–Saline Water Interaction: A Systematic Review

“…When plasma touches the surface of saline water, the reactive species interact with the solvated charges in the saline water and induce additional physicochemical transformations, having as one of the consequences the accelerated and selective crystallization of salts, for example, which opens up possibilities for use in desalination processes, chemical extraction, and others [ 19 ]. To date, the effects of the interaction of plasma with saline water have been reported for sterilization and disinfection [ 20 , 21 , 22 , 23 ]; desalination, precipitation, and crystallization of salts [ 19 , 24 , 25 , 26 ]; catalysis of oxidative processes [ 27 , 28 , 29 ]; decontamination of organic pollutants [ 30 ]; alternative sources of nitrites/nitrates [ 31 , 32 ]; etc. There are different applications and different types of plasma sources, which differ strongly from each other, making it difficult to summarize or even compare the results of different types of sources from a chemical and physical point of view.…”