The effect of potassium addition on plasma parameters in argon dc plasma arc

Abstract

The effect of potassium addition on the radial distribution of temperature and electron number density in a U-shaped direct current (dc) argon plasma operating at different arc currents has been studied by optical emission spectroscopic techniques and the power interruption method. Spatially resolved electron number densities (n e) have been determined from measured radial profiles of Balmer-Hβ spectral line. The obtained electron number densities have been used for thermodynamic temperature (T LTE) evaluation with the assumption that the arc plasma is in a state of local thermodynamic equilibrium. The excitation temperatures (T exc) have been determined from the absolute integral emissivity of the argon line at 430.01 nm. For heavy particle temperature (T h) evaluations we have used a power interruption method. The obtained results have shown that an addition of KCl decreases both electron number density and temperature of the arc column. The magnitude of such an influence on plasma parameters increases with an increase in the KCl concentration and decreases with an increase in the arc current.

Properties of Argon–Nitrogen Atmospheric Pressure DC Arc Plasma

“…For a plasma in LTE, another criterion must be satisfied: the gradient length of electron density should be so large that transport processes do not affect the local Saha equilibrium. The pure argon DC arc plasma at atmospheric pressure is found to be well described by the LTE model if the arc operates at currents above 30 A [13,20]. The currents used in this study were in the range 5-10 A.…”

“…The Characteristics of the Plasma Source A detailed description of the plasma source, atmospheric pressure argon U-shaped DC arc, was given in previous papers [13,15]. However, some of the arc characteristics that are relevant to the present study are briefly summarized here.…”

“…As the pressure was assumed constant across the plasma column (atmospheric), temperature and electron number density were interrelated by a series of equations defined by Plasma Chem Plasma Process the local electrical neutrality principle, Dalton's law, and the Saha equations [13,21]. A set of equations describing the plasma in LTE was solved iteratively to obtain the composition of the plasma at atmospheric pressure.…”

“…Electron number densities obtained from the measured Stark profiles of H b line were used to evaluate T LTE [13,21,22]. The uncertainty of the temperature determination is estimated at about 10 %.…”

“…The reduction of the radial electric field allows for better penetration of the analyte into the hotter plasma zones, which results in the enhancement of the analyte spectral emission. Higher concentrations of KCl produce lowering of temperature and electron number density of the arc core [13]. Based on the results obtained for ICP [14], and the similarities between the two plasma sources, we assumed that the addition of molecular gas might improve the analytical performance of DC arc source as well.…”