An in situ investigation of the corrosion behaviour of a weathering steel work of art

An in situ investigation of the atmospheric corrosion phenomena affecting weathering steels has been performed on a large outdoor sculpture dated back to 1983, the 'Reditus ad origines' by Agapito Miniucchi. The sculpture is exposed in the Scientific and Technological Pole of the University of Ferrara, and is an interesting example of architectural recovery of an industrial area. The assessment of the corrosion behavior was performed by means of an in situ, nondestructive approach based on electrochemical impedance spectroscopy measurements. The ultimate goal is to understand the corrosion mechanisms that affect outdoor immovable metallic artefacts to develop tailored and long-lasting conservation strategies. The impedance measurements were carried out by means of a portable equipment specifically designed by the authors to work as a stand-alone device connected to a personal computer. Polymeric electrodes were employed instead of the traditional electrochemical cell to avoid any acceleration of the corrosion process; the applied stimulus was in the range 0.001Hz-100kHz, while the measurement range could span from about 100Ω to 1GΩ. Furthermore, chemical analyses were carried out by means of X-ray photoelectron spectroscopy on samples obtained with a microsampling technique to correlate the electrochemical impedance spectroscopy results with the chemical composition of the corrosion layer and to identify the presence of electrochemically active species.