The effect of liquid target on a nonthermal plasma jet−imaging, electric fields, visualization of gas flow and optical emission spectroscopy

International audienceThe article describes the complex study of the interaction of a helium plasma jet with distilled water and saline. The discharge development, spatial distribution of the excited species, electric field measurement results and the results of the Schlieren imaging are presented. The results of the experiments showed that the plasmaliquid interaction could be prolonged with the proper choice of the gas composition between the jet nozzle and the target. This depends on the gas flow and the target distance. Increased conductivity of the liquid does not affect the discharge properties significantly. An increase of the gas flow enables an extension of the plasma duration on the liquid surface up to 10 µs, but with a moderate electric field strength in the ionization wave. In contrast, there is a significant enhancement of the electric field on the liquid surface, up to 30 kV cm−1 for low flows, but with a shorter time of the overall plasma liquid interaction. Ignition of the plasma jet induces a gas flow modification and may cause turbulences in the gas flow. A significant influence of the plasma jet causing a mixing in the liquid is also recorded and it is found that the plasma jet ignition changes the direction of the liquid circulation

Plasma-surface interaction: dielectric and metallic targets and their influence on the electric field profile in a kHz AC-driven He plasma jet

International audiencePlasma catalysis, biomedical applications or atomic layer deposition at atmospheric pressure all make use of non-thermal plasmas in contact with a wide variety of surfaces. As the presence of a target (substrate) has been shown to modify the plasma in addition to the plasma modifying the target, it is reasonable to describe and study the plasma-surface as one system. This work shows how the presence of dielectric and metallic targets influences a kHz AC-driven discharge in a He plasma jet. Next to bringing the absolute values of the axial electric field along the plume of the jet, the presence of the surface has been shown to significantly elongate both the plume and the electric field profile. In addition, when a dielectric target is placed closer than the maximum length of the freely expanding jet, the electric field profile is enhanced only in the vicinity of the dielectric, typically between 0.3 and 2 mm above the target surface. The maximum measured relative increase is 31%, for 1000 SCCM flow with the target at 7 mm distance, when the electric field increased from 14.1 kV cm−1 for the freely expanding jet to 32.6 kV cm−1 when the jet was impinging on glass. Finally, a grounded metallic target enhances the electric field compared to the glass target only within a very thin layer just above the surface, typically about 0.2 mm. The highest measured electric field was 40.1 kV cm−1 at a grounded metallic target 12 mm away from the nozzle, for 1000 SCCM of helium flow. The discussion on the effects of the flow on the electric field profile are supported by the visualization of the flow. The discussion brings, among other, the comparison of properties between the 30 kHz AC-driven system and the 5 kHz pulsed jet

Electric field measurements in a kHz-driven He jetthe influence of the gas flow speed

International audienceThis report focuses on the dependence of electric field strength in the effluent of a vertically downwards-operated plasma jet freely expanding into room air as a function of the gas flow speed. A 30 kHz AC-driven He jet was used in a coaxial geometry, with an amplitude of 2 kV and gas flow between 700 sccm and 2000 SCCM. The electric field was measured by means of Stark polarization spectroscopy of the He line at 492.19 nm. While the minimum and the maximum measured electric fields remained unchanged, the effect of the gas flow speed is to cause stretching of the measured profile in spacethe higher the flow, the longer and less steep the electric field profile. The portion of the effluent in which the electric field was measured showed an increase of electric field with increasing distance from the capillary, for which the probable cause is the contraction of the plasma bullet as it travels through space away from the capillary. There are strong indications that the stretching of the electric field profile with increase in the flow speed is caused by differences in gas mixing as a function of the gas flow speed. The simulated gas composition shows that the amount of air entrained into the gas flow behaves in a similar way to the observed behaviour of the electric field. In addition we have shown that the visible length of the plasma plume is associated with a 0.027 molar fraction of air in the He flow in this configuration, while the maximum electric field measured was associated with a 0.014 molar fraction of air at gas flow rates up to 1500 SCCM (4.9 m s−1). At higher flows vortices occur in the effluent of the jet, as seen in Schlieren visualization of the gas flow with and without the discharge

Adsorption and inhibition effect of 2,4-diamino-6-hydroxypyrimidine for mild steel corrosion in HCl medium: experimental and theoretical investigation, Ionics

2,4-Diamino-6-hydroxypyrimidine (2D6H) was examined as corrosion inhibitor of mild steel (MS) in 0.1 M HCl using potentiodynamic measurements, linear polarization resistance (LPR), scanning electron microscopy, electrochemical experiments, and quantum chemical calculations. All measurements show that the corrosion inhibition effectiveness is forthright compared to the concentration of 2D6H ranging from 0.5 to 10.0 mM. Adsorption of 2D6H on the MS surface in the presence of HCl is determined to obey Langmuir adsorption isotherm. The electronic features elucidated by quantum chemical calculations were associated with the experimental inhibition productivities. The mechanism of inhibition was revealed by Epzc measurements