Naturwissenschaften und Technologie in der Kunst; Akademie der bildenden Künste Wien; Schillerplatz 3; 1010 Wien
Research > Projects > Degradation and Stability of Materials > Corrosion of Metals > Early stages of corr. Print

Surface Sensitive Analytical Methods for the In-Situ Investigation of the
Metal - Atmosphere Interface

Zelle
In-situ weathering cell for simultaneous IRRAS and QCM measurements.

 

Metals such as gold, copper or iron and their alloys have played a key role in the course of civilization. The Golden, Silver, Bronze and Iron Age of human history signalled a major intellectual leap for each civilisation that achieved it. These metals had a profound influence on the evolution of human societies and they are still central to many technologies. Silver and its alloys has been valued as a precious metal too, used for many objects of our cultural heritage such as statues, ornaments, jewelry, high-value utensils, currency coins and silverware. Today, silver metal is also used in electrical contacts and conductors, mirrors and optical devices. Unfortunately, the chemical stability of silver and its alloys is not as high as of gold, and exposed to different atmospheres the function of silver devices can be affected or even destroyed by the interaction of their surfaces with the ambient atmosphere.

Conventional atmospheric parameters that affect silver comprise weathering factors (temperature, moisture, solar radiation, wind velocity, etc.), air pollutants (H2S, SO2, CO2, etc.) and aerosols. The increasing concentration of anthropogenic caused corrosive gases such as H2S, SO2, CO2 and O3 mainly present in urban environment atmospheres is challenging corrosion scientists as well as scientists and conservators dealing with art objects in museums, private collections or archaeological findings. As our cultural heritage is inherited from the past generations, unique and irreplaceable, it is our responsibility to preserve and protect this cultural property for future generations. Therefore, a fundamental understanding of the chemistry occurring on the surfaces is needed in order to be able to control material degradation in the near future. For this reason it is of special interest to study the occurring reactions in-situ and in a time-resolved way in order to develop methods and strategies to reduce or even stop and prevent those atmospheric attacks. Due to their various applications in works of art the metals Ag and Cu but also Fe are of special interest for such investigations.  The complexity of atmospheric corrosion of different metals is caused by the occurrence of different physical and chemical surface reactions. As many macroscopic long-term investigations of the atmospheric corrosion of metals have been devoted in the past, the knowledge of the exact chemical reactions occurring on the surface during the early stages of corrosion is still rudimentary.

Mechanismus

Atmospheric corrosion of silver

In this project highly sensitive analytical methods are applied to investigate in-situ the atmospheric corrosion behaviour of silver and its alloys exposed to controlled atmospheres containing different amounts of relative humidity (%RH), SO2, H2S and O3 in the ppb range, as well as CO2 in the ppm range. Additionally, the influence of photo catalytic reactions caused by UV-light will be investigated. In order to obtain information concerning the chemical reactions and the species formed on the surfaces, in-situ InfraRed Reflection Absorption Spectroscopy (IRRAS), Raman spectroscopy, Atomic Force Microscopy (AFM) and Scanning Kelvin Probe (SKP) are applied. A Quartz Crystal Microbalance (QCM) set-up can be used for gravimetric information of changing chemistry on the sample surface and bulk composition. Two of these in-situ methods (IRRAS and QCM) were already combined in a self-designed and self-built environmental cell allowing simultaneous time-resolved measurements. Besides identifying the exact reaction mechanisms on the surface a main goal is to study synergistic effects in order to decrease or even stop corrosion on silver surfaces of art objects. Scientists working in the field of conservation-restoration as well as archaeology are often confronted with questions of cleaning corroded silver artefacts and their preventive conservation (e.g. coatings and/or storage conditions). Furthermore, the increasing activities of exhibiting art objects all around the world makes a clear standardisation of the conditions during transportation and exhibition necessary and definition of certain thresholds levels for those factors influencing mostly the corrosion of silver, such as the relative humidity, temperature, concentrations of acidifying gases (pollutants), ozone, and exposure time to UV light are of great importance for the preservation of such objects for the next generations.

Papers:

R. Wiesinger, Ch. Kleber, J. Frank, M. Schreiner:
A new experimental set-up for in-situ IRRAS studies of atmospheric corrosion on metal surfaces considering the influence of UV-light.
Applied Spectroscopy 63 (2009) 465-470

R. Wiesinger, J. Schnöller, H. Hutter, M. Schreiner, Ch. Kleber:
About the formation of basic silver carbonate on silver surfaces – an in-situ IRRAS study.
Open Corrosion Journal 2 (2009) 96-104

R. Wiesinger, M. Schreiner, Ch. Kleber:
In situ investigations of the interaction of CO2, O3 and ultraviolet light with silver surfaces by means of IRRAS and QCM.
Applied Surface Science 256 (2010), 2735-2741

R. Wiesinger, Ch. Kleber, M. Schreiner:
Surface and Interface Analytics as a tool in atmospheric corrosion research
Global Journal of Physical Chemistry 1 (2010) 59-78

Dissertation:

Rita Wiesinger:
Development and application of surface sensitive methods for the in-situ investigation of
atmospheric corrosion processes on non-transparent materials.

Vienna University of Technology, October 2009