The parameters of a non-pulsed dc arc discharge of atmospheric pressure in argon were experimentally studied, and the chemical composition of the cathode surface in the arc binding zone was studied. The measurements were performed for thoriated tungsten cathodes (W-2% ThO2) for currents of 200 and 300 A. During the operation of the plasma torch, the temperature and electron concentration in the positive column and the surface temperature of the cathode were measured. A computational and theoretical analysis was performed on the distribution of current density and electric field strength in the arc binding zone. As a result, three fundamentally different zones of the arc binding area were identified, and their size and chemical composition were determined.

Abstract Using the automated system of high-speed visualization and spatial-temporal spectral diagnostics, the destructive effect of an atmospheric pressured nitrogen plasma jet with a temperature of 0.7 - 1.0 eV on samples of isotropic and anisotropic graphite was studied. Measurements of the electron, vibrational, and rotational temperatures of the plasma in the zone of destructive interaction were performed, and the pattern of the spatial-temporal distribution of the products of graphite destruction (carbon atoms and cyanogen molecules) was revealed. The efficiency of local spectral analysis of near-surface plasma is shown using a combination of longitudinal and transverse periodic scanning of the emission spectra and recording of instantaneous 2D spectra of the selected spectral region containing the CN and N2 + bands. The spectral estimate of the concentration of the graphite destruction main product (carbon atoms) is in quantitative agreement with the results of measuring the mass loss rate of the sample material, made by two-positioned visualization of its surface. In the zone of realizable heat loads of 0.5-1.5 kW/cm2, heating of the graphite surface to temperatures of 2800 ÷ 3600 K was achieved and the rate of loss of its material was 3-15 mg/cm2s, which is consistent with the literature data.

Local and average values across the cross section of a plasma jet of the velocity and temperature of Al2O3, Ti, and Mo particles heated by plasma are determined as a result of data processing on high-speed registration of particle tracks; the velocity changes of these particles along the axis of a plasma jet at different modes of operation of the experimental setup of plasma spraying are also determined. These data made it possible to choose the optimal spraying mode, wherein the particles collide with the surface of the substrate in a molten state, where the fields of velocities and temperature are homogeneous. Calculation of all the parameters of particles mentioned is carried out with regard to their dynamic and thermal delay relative to carrying flow, nonisothermality of particles of low-heat-conducting oxides, as well as matter evaporation from the particles’ surfaces. Calculation results are in satisfactory agreement with the experimental data.