Multianalytical in-situ investigation of corrosion processes on copper and copper alloys

Corrosion phenomena on copper and copper based alloys have been the subject of great interest because of the numerous use of these materials in structural, architectural, artistic, electrical and electronic devices. The first part of this thesis focuses on the activities within the IMMACO-Project (Improvement of Means of Measurement on Archaeological Copper Alloys for Characterization and Conservation) of the European Union. This project aims the production of certified reference materials (CRM) for the investigations of archaeological alloys. Within the scope of the second part of the presented thesis a new set-up of different techniques for in-situ investigations was applied to pure copper and bronze in order to obtain information about the initial stages of atmospheric corrosion. Atomic force microscopy (AFM) was used for the investigation of topographical changes of the surface upon exposure to a defined atmosphere. A combination of infrared reflection and adsorption spectroscopy (IRAS) and quartz crystal microbalance (QCM) delivered chemical and kinetic information about the corrosion process. The influence of humidity, SO2, O3, and NO2 to the corrosion behavior of pure copper is investigated. At 60 % relative humidity (RH) small cuprous oxide features partly covering the surface are observed, whereas a fast formation of a layer of cuprous oxide entirely covering the copper surface was obtained at 80 % RH. Copper exposed to humidified air with SO2 yielded in the formation of cuprous oxide as well as copper sulfite. A detailed investigation of the influence of O3 to the corrosion process of pure copper showed that copper sulfite is further oxidized to copper sulfate and the formation of cuprous oxide is promoted. NO2 enables also an oxidation of sulfite to sulfate, but not in the same extent as O3 and reduces the formation rate of cuprous oxide. In addition to the weathering experiments carried out on pure copper investigations by means of AFM and IRAS were also performed on samples of the CRMs of the IMMACO-Project. Some of these samples were also used for ex-situ investigations with X-ray photoelectron spectroscopy (XPS). In synthetic humidified air a slower weathering process was observed for the copper alloys than for pure copper, which is obviously caused by the formation of a protective Pb oxide layer. In SO2 containing humidified air the formation of large copper sulfite features was observed. Furthermore, the formation of cuprous oxide was detected 486 min after adding SO2 to the gas stream with IRAS. This fact and the decreased amount of Pb on the surface during the exposure in SO2 containing atmosphere gives evidence that the formed lead oxide layer has protective properties and must be destroyed before any surface reaction can occur between the bronze sample and the ambient atmosphere. (author)