Environmentally friendly plasma treatments for surface nano-functionalization and protection of metals

Plasma Enhanced Chemical Vapour Deposition (PECVD) is a clean and environmentally friendly surface treatment for the protection of metallic artefacts. In particular, among the different plasma-based processes, PECVD can be used for the production of high-purity and high-performances conformal coatings in the form of thin nano-structured films, due to its high versatility. In this research project, PECVD is employed for the deposition of diamond-like carbon (DLC) coatings, which are proposed as safe and innovative materials for the long-term conservation of archaeological bronzes, in order to ensure the chemical-physical stability of the ancient artefacts against the dangerous post-burial corrosion phenomena. DLC is an amorphous material composed by hydrogen and carbon, whose properties, strongly affected by the sp2/sp3 ratio and hydrogen content, depend on the deposition parameters and test conditions of the PECVD process. DLC films are widely used for several industrial applications, including wear resistant and chemical barrier for metals. Hence the potential to employ this material even in the Cultural Heritage safeguard field; however compliance with the following specific requirements must be verified: I) transparency, i.e. no change to the aesthetic appearance of the artifacts; II) long-term protection; III) treatment reversibility. An accelerated degradation methodology for evaluating the protective effectiveness of the DLC films has been purposely developed and the combined use of Optical Microscopy observation (OM), Colorimetric analysis, Raman Spectroscopy, X-ray Spectroscopy (XPS), X-ray Diffraction (XRD), Scanning Electron Microscopy coupled with Energy Dispersive Spectrometry (FEG, SEM-EDS) and wettability measuremets have been carried out in order to validate the protective properties of the DLC coatings and any color changes in the aesthetic appearance of reference Cu-based alloys used for the investigations, whose chemical composition, metallurgical features and patina are very similar to that of the real archeological artefacts.