Shielding and oxide reduction on steel surfaces using an Ar/H₂ non-thermal plasma jet

This study explores the application of a dielectric barrier discharge (DBD) plasma jet in an Ar/H 2 gas flow for oxide reduction and shielding on E235 steel surfaces. We detail the construction of the non-thermal plasma jet system, including the operational parameters and characterization of reactive species present in the plasma phase using optical emission spectroscopy (OES). Notably, the presence of atomic hydrogen species in the plasma highlights the oxide-reducing capability of this method. Subsequently, analytical techniques such as optical microscopy, field-emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS) were employed to evaluate the treatment's effectiveness. The application of the Ar/H 2 plasma jet at 25 °C produced partial deoxidation and cleaning effects on the steel surface, indicating its potential under these conditions. Furthermore, we assessed the plasma jet’s efficiency during rapid thermal processing of steel, where the surface temperature reached approximately 1000 °C within 1 s – a condition relevant to high-temperature metal-joining applications. Our findings revealed that the center of the area directly interacting with the plasma jet was largely protected from oxidation, exhibiting an oxygen concentration of 7 at.% compared to 53 at.% on the untreated surface. The metallic appearance of this central interaction zone was largely preserved, and it measured approximately 2.5 mm 2 . In contrast, processing with a non-ionized Ar/H 2 gas under identical conditions produced a smaller central area of 0.7 mm 2 with a higher oxygen concentration of 19 at.%. Importantly, both treatments were conducted using the same setup, ensuring that observed differences resulted from the presence of the plasma jet. These results suggest that the DBD plasma jet process offers improved shielding and oxide reduction over a larger surface area than a non-ionized gas flow. Therefore, this study highlights the potential of Ar/H 2 non-thermal plasma jet treatment for enhancing steel surface quality in metal-joining applications.