Parametric study of atmospheric pressure microwave-induced Ar∕O2 plasmas and the ambient air effect on the plasma

Abstract

A torch type microwave-induced afterglow plasma was produced at atmospheric pressure using an open-ended fused silica concentric double tube assisted by Ar and O 2 supply gases. The plasma emerged from the end of the discharge tube and was exposed to ambient air. A parametric study of the plasma characteristics was performed by measuring the temperature, density, and plasma volume as the operational parameters such as microwave power, gas flow rate, and its composition were varied. The excitation temperature ͑T exc ͒ obtained from the Ar I emission spectrum ranged from 3010 to 4350 K and the rotational temperature ͑T rot ͒ measured from the OH and O 2 diatomic molecular spectra ranged from 2250 to 3550 K. The electron density ͑n e ͒ from the H ␤ Stark broadening width at the plasma core was in the range of 6.6 to 7.6ϫ 10 14 cm −3 . The two-dimensional distribution of T exc and T rot was also obtained. Experiments while varying the Ar and O 2 gas flow rate and the O 2 / Ar ratio showed that n e was reduced but T exc was increased as the O 2 flow rate was increased. Using an additional dielectric tube for shielding the plasma from the ambient air demonstrated a significantly enlarged plasma length and lower T rot due to the nitrogen entrainment, as compared to the unshielded case.

Effects of argon on the analytical properties of a microwave-sustained, inductively coupled, atmospheric-pressure plasma

“…Particularly the onset of filamentation was found to be troublesome, as the plasma discharge tends to expand towards the wall causing torch damage. Contrary to previously reported microwave discharges, 1,5,12,13 the MICAP does not form long, arc-like filaments but rather a thin, highly luminous ring. This ring is located in close proximity to the inner wall of the torch outer glass tube – a region that is commonly occupied by the outer gas flow.…”

“…Moon and Choe 12 extended their investigation to the characteristics of an oxygen/argon plasma in 2006. They used again an 18 mm ID torch, quite similar to an ICP torch with the exception that no injector tube and consequently no inner gas stream were present.…”

Electron characterization in weakly ionized collisional plasmas: from principles to techniques

“…The line broadening method has been widely used for most electron studies in atmospheric-pressure plasmas, particularly in microwave-and radio-frequency-excited plasmas because of their high n e . Moon et al [83] investigated a variation in electron density of up to 0.75 × 10 15 cm −3 in an Ar + O 2 microwave torch (which present different characteristics from kHz-and MHz-driven plasma jets) using H β Stark broadening under different conditions, such as microwave power, gas flow rate, and gas composition ratio. Hofmann et al [80] estimated the electron density in 11.7 MHz argon and helium plasma jets based on the Stark broadening of H α and H β lines, which yielded n e values between 10 13 and 10 14 cm −3 .…”

Spectroscopic Investigation of a Microwave‐Generated Atmospheric Pressure Plasma Torch

“…On the one hand they can be used for the treatment of surfaces, for example for cleaning, etching, or activation to enhance the adhesion of lacquer, colours, or glue. Compared to discharges in noble gases, which have been explored widely and in detail [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31], moleculare gas discharges have only been investigated very seldom and incomplete [13,14,16,[32][33][34]. In this field the decomposition of waste gases has to be named, where destruction and removal efficiencies (DRE) of waste gases of over 99% were achieved in recent years [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16].…”

“…On the other hand these plasma sources can be applied for chemical synthesis like the conversion of gases. At present, there are several microwave plasma torches operating at atmospheric pressure, like for example the surfatron, the surfaguide, or the TIA(torchà injection axiale) just to name a few [1,[3][4][5][6][7][8][9][13][14][15][16][17][18][19][20][21][32][33][34][35][36][37][38][39][40][41]. Thus microwavegenerated plasma processes at atmospheric pressure provide a promising alternative to conventional oil or gas combustions for the abatement of perfluorinated compounds (PFC) [3][4][5][6][7][8][9][10][11][12], which are widely used for etching processes in growing industries like the production of semiconductor components and which have very high green house potentials.…”