Coagulation of charged particles in self-organizing thermal plasmas of welding fumes

• The self-organization of the dusty plasma of welding fumes is studied.
• Formation of the ordered structures of the primary particles leads to their rapid coagulation.
• Agglomerates are presented by two types: chain-like and cluster-like spatial structures.
• The inhalable particles have the bimodal size distribution with different chemical compositions.

The dusty plasma behavior is studied in the process of coagulation of the primary particles, which are formed as a result of the nucleation and nuclei growth in the condensable high-temperature vapors. The study is concentrated to the example of the thermal plasma formed in the welding fume in the arc welding process where the electrodes covered with carbonate–fluorite are used. The tendency to self-organization of such a plasma and formation of the ordered spatial structures of primary particles is demonstrated. The number densities of the primary particles in these structures are much higher than at uniform spatial distribution that causes the rapid coagulation of the fine nano-sized primary particles. The coagulation of the particles with size more 10 nm into cluster-like agglomerates occurs during almost all cooling period of aerosol up to the ambient air temperature. The coagulation of the ultra-fine particles (~2 nm) occurs in two stages: at first the chain-like agglomerates are formed rapidly, and then they associate with the cluster-like agglomerates. As a result, the final agglomerates (inhalable particles) have the bimodal size distribution with different chemical compositions and fractal dimensions.