Controlling the bulk and surface properties of TiOx coatings synthesized by High Power Impulse Magnetron Sputtering (Hi-PIMS) for antifouling applications

A non-common application of titanium oxide coatings is studied: the antifouling properties of this material and its capacity to mitigate the deposition and/or the growth of calcium carbonate, CaCO3, on heated stainless steel plates. These phenomena are mainly related to surface parameters such as the elemental composition, the surface energy, the roughness. Molecular modeling with CFD calculations predicted that the fouling kinetic on TiO2 could be higher or lower than on uncoated stainless steel, depending on the crystallinity of the films. Controlling the bulk and the surface properties of TiOx coatings becomes then of prime interest. In this work, titanium oxide thin films (100 nm) were synthesized on flat substrates using a High Power Impulse Magnetron Sputtering (HiPIMS) deposition system. The interest for this emerging technology is growing as it allows depositing crystalline layers at low temperature, with or without polarization of the substrate. Among the numerous tunable parameters of the deposition process, the influence of the duty cycle, i.e. the pulses duration and delay, on the coatings characteristics (bulk and surface properties) is presented. Thus, XRD and TEM investigations of the films revealed that the microstructure and the crystallinity depend on the duty cycle, and that the coexistence of anatase, rutile and amorphous micro-domains with preferential orientation can be obtained. The films present various roughness, grain size and morphologies too. The surface of the titanium oxide coatings were characterized by mean of XPS in order to correlate their composition and the presence of defects with the deposition parameters. At last, fouling tests at the laboratory scale highlighted that the fouling kinetic can be reduced by a factor of three compared to bare stainless steel.