Surface Cleaning with Atmospheric Pressure Plasma Jets investigated by in-situ Optical Emission Spectroscopy and by LIBS chemical imaging

Atmospheric pressure plasma jets (APPJs) are employed for surface cleaning, modification of surfaces, deposition of coatings. etc. We investigate the plasma of an industrial APPJ (Acerios, Fronius International GmbH) and apply it to the cleaning of contaminated metals. The device operates a spark discharge in Argon gas flow resulting in a continuous plasma jet of kW power expanding into ambient air (Fig. 1, left). The plasma parameters are measured by Optical emission spectroscopy (OES). For surface cleaning the samples are coated with oil layers of 0.5 μm to 10 μm thickness. The plasma cleaning is monitored in-situ by OES and ex situ by chemical imaging using Laser-induced breakdown spectroscopy (LIBS). The APPJ plasma cleaning efficiency is alculated from measured spectra and the intensities of atomic lines and molecular bands of species originating from the contamination layer. Spatial profiles of the cleaning efficiency are measured by LIBS (Fig. 1, right). We find a strong influence of the plasma parameters and of the type and thickness of contamination layer on the APPJ cleaning efficiency. For instance, cleaning becomes more efficient at higher power of the plasma generator (CN violet band emission measured in situ by OES).