Role of metallic neutrals and gaseous molecular ions in a copper cathodic arc operated with oxygen gas

Abstract

The plasma-neutral gas structure generated in a copper cathodic arc operated with oxygen gas at a constant current level of 100 A has been investigated by employing a Langmuir spherical probe and a calorimetric technique. The plasma potential and electron temperature at several axial distances (between 10 and 25 cm) from the cathode surface and for different O2 pressure values (between 0.5 and 5 Pa) have been measured. A simplified one-dimensional model which incorporates the relevant atomic processes of the problem (charge-exchange, lateral diffusion loses, electron impact ionization, and dissociative recombination) is developed. This model allows calculating densities and drift velocities of the different species and, in particular, predicts the creation of a considerable number of metallic neutrals and gaseous ions. A comparison of the experimental ion saturation probe current and the heat source term derived from the calorimetric measurements with the corresponding quantities predicted by the model is performed. We found good agreement between theory and experiment, notwithstanding the fact that the physical quantities presented large variations, and the atomic reaction rates varied for several orders of magnitude, over the range of gas pressure and axial position values investigated.

Spectroscopic measurements in a titanium vacuum arc with different ambient gases

“…Besides, the absence of this line is also consistent with the lack of excited particle levels by electron impact, since visible transitions of Ti-III correspond to highly excited levels (with bound energies of about 20 eV) while the electron temperature in the inter-electrode space is ∼ 1.8 eV (or less, depending on the gas pressure value) [8], too low for that ion excitation energy level.…”

Differences in the metallic plasma-neutral gas structure in a vacuum arc operated with nitrogen and argon

“…The metallic ion temperature was chosen to be 0.3 eV, 13 and the gas temperature 0.025 eV. 5 The metallic ion current ejected from the cathode was taken as 8% of the total discharge current in the whole pressure range. 22,23 The average velocity and ,charge state of the metallic ions at the cathode surface were taken according to published experimental results for a Ti cathode, resulting in 1 ϫ 10 6 cm/ s and z m = 1.8.…”

“…Some of them, [3][4][5] working in a pressure range of 5 ϫ 10 −5 -10 −2 mbar observed a monotonic decrease in the ion current with increasing pressure for reactive gases such as nitrogen or oxygen, or the presence of a maximum in the ion current in noble gases such as argon, helium, and neon. 3,4,6 In Refs.…”

Features of the process of vacuum-arc produced Ti-plasma flux deposition under gas pressure of 1 to 10 Pa

“…The gas pressure influence on the deposition parameters and the properties of coatings obtained are extensively studied (for example, Refs. [3][4][5][6][7][8][9][10][11][12][13]). Most of the experimental results' evidences on the coating deposition rate decrease under gas pressure above 1 Pa.…”