Influence of an Argon/Silane Atmosphere on the Temperature of a Thermal Plasma

One promising approach to keep the residual oxygen level in welding at extremely low levels is to add monosilane to the argon shielding gas. However, its effect on the plasma itself is not clear, and thus this study examines the influence of a silane-doped argon atmosphere on the chemical components and temperature within a nontransferring, thermal argon plasma in comparison to an atmosphere of pure argon and air. For this purpose, the emitted radiation of the plasma was analyzed using optical emission spectroscopy. The spectra show that the Ar I lines are most prominent in all atmospheres. Compared to the air atmosphere, the plasma in the argon atmosphere exhibits a stronger H I line and an OH emission band. A slight doping of the argon atmosphere with silane (0.01 vol.%) leads to strongly pronounced Si I and H I lines and a clearly recognizable H₂ emission band. The high amount of free electrons resulting from the stepwise ionization and dissociation of the silane molecule leads to an increase in plasma temperature from about 7,600 to 9,000 K.