Coating Protection of Metal Objects in Cultural Heritage

Metals such as copper, silver and its alloys have played a key role in the course of civilization. They have had a profound influence on the evolution of human societies and they are central to many technologies. Metals and its alloys have been valued as precious materials since time memorial with shiny brightness and wide use in daily life for jewellery, fine utensils, coinage and photography. As those metals are exposed to different indoor and outdoor atmospheres the function of the material can be affected or even destroyed by the interaction of the metal surface with the ambient chemicals. For this reason it is of special interest to develop methods and strategies in order to prevent those atmospheric attacks. In conservation-restoration, nitrocellulose coatings are often used to prevent metals from tarnishing, however non-uniform coatings and degradation limit their effectiveness over time.

A new method for creating uniform and dense coatings e.g. atomic layer deposition (ALD) with aluminium oxide will be explored. The main objective of this project is to apply ALD coatings on different metal substrates and explore their effectiveness under ambient aging conditions. Artificial aging will be performed under different relative humidity content (50 – 90 %RH) and concentration of corrosive gases: H2S, SO2, NOx and O3. During sample weathering chemical reactions will be tracked in-situ and in a time-resolved way by Infrared Reflection Absorption Spectroscopy (IRRAS) and simultaneous Quartz Crystal Microbalance (QCM). Furthermore, Raman spectroscopy, Scanning Kelvin Probe (SKP) and Atomic Force Microscopy (AFM) will be applied. For visual effects of material fading Light Microscopy (LM) and Spectrophotometry (SPM) will be the methods of choice. To evaluate the anti-corrosion properties of the coating Electrochemical Impedance Spectroscopy (EIS) and real-time Polarization Curve Tests will be performed.