engleski

Use of XRF for quantitative analysis on corroded metallic artefacts

One of the most often used non-destructive methods for elemental analysis on metallic artifacts is X-ray fluorescence (XRF) analysis based on portable instrumentation. However, when performing routine in-situ XRF analysis on very corroded objects the obtained results are sometimes considerably influenced by the corrosion surface products. In this work capability of portable XRF for quantitative analysis of bulk bronze with consideration of specific corrosion layers on data reliability was investigated. As it is known, the influence of corrosion processes on data reliability in some cases (archaeological bronzes with thick corrosion layers) can be significant [1]. However, if the thickness of the corrosion layer is very small, analytical techniques revealing the chemical composition of the bulk, like X-ray fluorescence, may be applied [2–5].Corrosion layers formed on the surface of some artifact can affect data reliability due to different X-ray attenuation through the changed matrix (corrosion layers) or due to different concentration profiles of alloying elements trough the corrosion layer (de-alloying) [6]. Therefore, there is a reasonable concern that measurements can be affected by the presence of corrosion product layers which could not be removed due to conservation–restoration requirements. Thus, ability to analyze bulk metal composition of bronze artifacts without disrupting patina formed on surface would be great achievement in restoration-conservation practice. For this purpose samples of ternary bronze alloy (Cu-Sn-Pb), similar in composition to ancient alloys, were artificially aged in controlled conditions by exposure to specified corrosive media for different time periods, to obtain well defined corrosion layers. In that way artificial corrosion layers (patinas) of different thickness and chemical composition were formed. The samples were then investigated using sophisticated laboratory techniques (SEM-EDX, PIXE and RBS), in order to gain precise information on the formation of the corrosion product layers for different aging parameters. In this way a correlation was established between the portable XRF results and the results obtained with ion beam techniques. Additionally, a few ancient bronzes with naturally formed corrosion layer were investigated using XRF and correlated with obtained results. Results from this paper can lead to better understanding of bulk metal analysis of bronze objects covered with different corrosion layers.

XRF ; PIXE ; bronze ; corrosion

nije evidentirano