Modified stainless steel surfaces targeted to reduce fouling––surface characterization

Abstract

The surface properties of several modified stainless steel samples were characterized according to their chemical composition, roughness, topography and wettability. The modifications tested were SiF 3 + and MoS 2 2+ ion implantation; diamond-like carbon (DLC) sputtering; DLC, DLC–Si–O and SiO x plasma enhanced chemical vapor deposition (PECVD); autocatalytic Ni–P–PTFE and silica coating. X-ray photoelectron spectroscopy (XPS) and X-ray microanalysis were applied to determine the surface chemical composition. Atomic force microscopy (AFM) and stylus-type instruments were used for roughness determination, and the surface topography was imaged with AFM and scanning electron microscopy (SEM). The contact angle and surface tension were measured with the Wilhelmy plate method and the sessile drop method. For thick modified layers, only the elements of the coating were detected at the surface, whereas for thin layers the surface composition determined was that of the stainless steel substrate. The roughness of the 2R (cold rolled and annealed in a protective atmosphere) surfaces was not altered by the modification techniques (except for the Ni–P–PTFE coating), while for the 2B (cold rolled, heat treated, pickled and skinpassed) surfaces an increase in roughness was observed. The silica coating produced surfaces with consistent roughness, independent of which steel substrate was used. DLC sputtering and Ni–P–PTFE coating produced surfaces with the highest roughness. All modified surfaces revealed a similar surface topography with the exception of the Ni–P–PTFE coating, for which the coating masked the underlying steel topography. In terms of wettability, the SiO x -plasmaCVD and Ni–P–PTFE coating techniques produced the most hydrophilic and hydrophobic surfaces, respectively.