Change of Ionization Mechanism in the Welding Fume Plasma from Gas Metal Arc Welding

Abstract

Ionization mechanisms in welding fumes from gas metal arc welding are studied. Welding fume is a low-temperature thermal plasma with ultra-violet radiation as external ionization source, where ionization occurs via gas particles’ collisions and photoionization. The plasma cooling causes heterogeneous ion-induced nucleation, which provides large number of nuclei. Nucleus number density is much greater than equilibrium number density of charge carriers. Electrons are captured by nuclei. As a result, the dust–ion plasma is formed, in which electron number density is much less than ion and nucleus number densities and it can be neglected. The surface atom ionization and ion recombination becomes predominant processes. Calculation of the plasma component number densities are presented as their evolution during welding fume cooling.