Boron, calcium and silicon in an arc plasma in air with chlorine: calculation of the plasma composition

Abstract

The composition of an air plasma in the presence of chlorine (0.1%), and boron, calcium or silicon (at concentrations in the plasma of 0.0001%), was calculated assuming thermal equilibrium, in the temperature range 298–6000 K. The calculated plasma composition reproduces the composition of the d.c. arc plasma free burning in air, as the plasma is assumed to be in (local) thermal equilibrium. Assuming that an arc is usually operated between graphite electrodes, the presence of carbon in the plasma (1%) was also taken into account. It was found that the presence of chlorine in the plasma caused a decrease in the atomic, ionic and molecular forms of calcium, boron and silicon and their spectral line and band intensities (compared with observations in the absence of chlorine) only at temperatures <3000 K. The presence of carbon in the plasma (under the conditions investigated) had almost no influence on the partial pressures of calcium, boron and silicon species and on the partial pressures of compounds of chlorine with oxygen and nitrogen. Also, the change in partial pressures of CN, C₂etc.(the radiation of these molecules produces the background band spectra in the graphite arc), in the presence of chlorine, cannot be observed.