Sustainable conservation of outdoor metallic artworks by natural corrosion inhibitors

Summary In this work 'green' products derived from natural extracts of some common and widespread plants in the Mediterranean basin were tested as potential corrosion inhibitor for outdoor iron-based artworks. The alcoholic extract of Brassica campestris L. was investigated as corrosion inhibitor for COR-TEN, a "weathering steel" used in modern artworks. A new formulation based on the oil extracted from the seeds of Nigella sativa L. was tested as corrosion inhibitor for archaeological iron-based artifacts. The electrochemical properties and the surface chemical composition were monitored as a function of corrosion in different media, i.e. in chlorides and acidic solutions, simulating a marine environment and rainwater in an urban polluted context, respectively. Motivation Environmental protection and preservation of the health of professionals in the Conservation of Cultural Heritage is a key issue to be addressed for a sustainable scientific approach. The development of safe, reliable, non-toxic and long-lasting corrosion inhibitors for the conservation of metallic artifacts has become mandatory for replacing the presently used hazardous materials. Results Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were performed both in presence and in absence of the natural inhibitors. The surface chemical characterization of the coating was performed by X-ray Photoemission Spectroscopy (XPS), both before and after submission to the corrosion attacks. The best performance of Brassica campestris extracts was observed on COR-TEN steel in chlorides solution, with an inhibitor efficiency up to 88-84% for a concentration of 80 ppm. The best performance of the green formulation of Nigella sativa was ascertained in the case of iron corrosion by the acidic medium, with an inhibitor efficiency of 99% for a concentration of 2500 ppm. Acknowledgements. This work was financially supported by the PON03PE_00214_1 TECLA Project: "Nanotecnologie e nanomateriali per i Beni Culturali", Distretto di Alta Tecnologia per l'Innovazione nel settore dei Beni Culturali della Regione Sicilia