An Electrochemical and Spectroscopic Study of Surfaces on Bronze Sculptures Exposed to Urban Environment

Protection of Patinated Bronze with Long-Chain Phosphonic Acid/Organic Coating Combined System

Bronze cultural heritage in urban areas is susceptible to decay due to the significant amount of pollutants present in the air. This causes the dissolution of bronze and the patina on its surface. The efficient protection of outdoor bronze cultural heritage is still an unresolved problem. The aim of this work is to investigate 16-phosphonohexadecanoic acid as an environmentally friendly and non-toxic corrosion inhibitor for patinated bronze. The corrosion protection of sulphide-patinated bronze by phosphonic acid alone and in combination with acrylic coating Paraloid B-72 is examined. In order to achieve efficient corrosion protection, various parameters of the phosphonic acid application were studied. The efficiency of protection is examined by electrochemical impedance spectroscopy (EIS) during the immersion in simulated acid rain solution and after exposure to a corrosion chamber. It was found that the studied phosphonic acid provides corrosion protection to patinated bronze and significantly improves the protective properties of Paraloid B72. This was also confirmed by scanning electron microscopy (SEM) examination of the coating surface after exposure to a corrosive environment.

The Effect of Corrosion Conditions on Aging of Artificial Patina on Three Bronzes

The new bronze objects of art are almost always patinated before their exposure outdoors or indoors. Among the many patination methods used by practitioners, sulphide patination is one of the most common techniques. The aim of this work is to examine the corrosion behaviour of sulphide patinated bronzes under various aging conditions, including continuous immersion in simulated urban rain, alternating wet/dry cycles, and exposure to corrosion chamber with NO2 gas. The study was conducted on three types of bronzes with varying tin content. Corrosion characterisation of patinated bronze samples was performed by the means of electrochemical impedance spectroscopy and polarization measurements. Chemical composition and morphology of sulphide patinated bronze surface was examined by infrared spectroscopy and scanning electron microscopy. Obtained results show that freshly patinated bronze surfaces exhibit low corrosion resistance that gradually improves over time. An increase in corrosion resistance strongly depends on aging conditions, and it appears to be the highest under continuous immersion conditions.