Spectroscopic Study of a Helium Plasma Jet with Hydrocarbon Additives
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MA INVESTIGATIONS
Spectroscopic Study of a Helium Plasma Jet with Hydrocarbon Additives M. B. Shavelkinaa, R. Kh. Amirova, D. I. Kavyrshina, *, and V. F. Chinnova a
Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, 125412 Russia *e-mail: [email protected] Received June 17, 2019; revised October 22, 2019; accepted December 24, 2019
Abstract—The results of a spectroscopic study of the conversion of acetylene and methane in a helium plasma jet produced by a direct current plasma torch are presented. The operating mode of the plasma torch corresponds to conditions that provide a high yield of carbon nanostructures. In the emission spectra recorded during the transverse observation of a 20-mm jet section following the outlet of the anode channel of the plasma torch, high-intensity Swan bands of the С2 molecule are the dominant component in the visible wavelength range. The spectra show atomic hydrogen lines of the HI Balmer series from Hα to Hε, numerous CI carbon lines from ultraviolet 247.9 nm to infrared 962–966 nm, and a number of HeI helium lines. The axial temperature values of the plasma jet were spectrally determined by the observed ionized carbon CII lines 283.7 nm, 392.0 and 426.7 nm. A joint analysis of the emission spectra and the mixture composition calculated in the Saha–Boltzmann approximation revealed the nature of the spatial heterogeneity of the studied He : C : H plasma jet. It is manifested by the difference in the electron temperature of the axial region of the jet, which is measured with ionized carbon lines CII (Te(0) = 12000–14000 K) from the vibrational and rotational temperatures of C2 molecules (TV = TR ≅ 5000 K) that emit intensely at the jet periphery. The electron density measured along the Hβ and Hγ line widths, which varies in the range of the observed jet region of ne = (4–2) × 1016 cm–3, corresponds to the ionization equilibrium in a plasma He : C : H mixture with an electron temperature close to Te measured by carbon-ion lines. DOI: 10.1134/S0018151X20030165
INTRODUCTION Plasma jets are an effective medium for the synthesis of carbon nanostructures [1–5]. The high-performance synthesis of graphene and carbon nanotubes in plasma jets produced by a direct-current plasma torch with an expanding anode channel [7, 8] was demonstrated in [6]. The use of a plasma torch has several advantages as compared to the synthesis of carbon nanotubes in a free arc burning between graphite electrodes with catalysts pressed into them [9, 10], where the temperature field, the distribution of the carbonvapor concentration, and the plasma cooling rate are controlled by the choice of the plasma-forming medium (argon, nitrogen…), the arc current, and the discharge-gap geometry. These advantages include the wide range of changes in the input power and the associated possibility of a significant increase in facility productivity; the ability to work with the starting materials in various states of aggregation (powders, gases, liquids); the ability to optimize the process due to the i
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