Axial segregation of additives in mercury–metal-halide arcs

In most arcs burning vertically in a gas mixture, axial segregation of the components is observed. This segregation can be explained by the combined action of radial diffusion and axial convection. The effect is very strong in arc plasmas which consist of large amounts of a chemically inert component together with a molecular additive of high thermal stability. For mercury arcs with admixtures of TlI, InI, NaI, and SnI2, axial concentration profiles have been calculated numerically from the theoretical model and are compared with experimental data derived from spectroscopic measurements.