Characterisation of corrosion products on copper-based artefacts: potential of MA-XRF measurementsties of MA-XRF measurement

Elisabetta Di Francia,Sabrina Grassini,Sergio Augusto Barcellos Lins,Stefano Ridolfi,Giovanni Ettore Gigante

doi:10.21014/acta_imeko.v10i1.859

Abstract

The use of macro-X-ray fluorescence (MA-XRF) scanners is now widespread in cultural heritage applications. However, its use for the characterisation of metallic works of art is still limited. In this study, a novel portable MA-XRF scanner prototype was tested on artificially corroded copper samples to assess its analytical capabilities on corroded metals, yielding information on the spatial distribution of the corrosion products grown on the metal’s surface. A multi-analytical approach was used to thoroughly characterise the copper samples and compare the obtained results to verify the reliability of the MA-XRF data. The prototype was able to obtain distribution maps of different elements, such as sulphur and chlorine, which can be directly correlated to different corrosion products. With the use of imaging filtering techniques, it was possible to investigate the stratification of the corrosion product layers and observe gradients in the distribution of certain elements.

Highlights

The study of corrosion products, their morphology and chemical, physical and microstructural characterisation, is of considerable interest to heritage and conservation sciences
The accelerated corrosion procedures applied to the copper reference samples led to the growth of different artificial corrosion product layers
Looking at the surface and the high-resolution image, the corrosion product layer formed by exposing the Cu reference samples to the ASTM D1384 solution appears uniformly green in colour, with a corrosion product layer that is quite homogenous and well adhered to the metal surface (Figure 2A)

Summary

Introduction

The study of corrosion products, their morphology and chemical, physical and microstructural characterisation, is of considerable interest to heritage and conservation sciences. It is of the utmost importance to study and preserve such objects. To achieve this goal, a transdisciplinary approach is always preferable; measurement, instrumentation and material sciences find a point of commonality in conservation science. Metrological and material characterisation are combined in measuring and quantifying the conservation state of artefacts and the aggressiveness of the surrounding environment with a common final goal, the preservation, restoration and safeguarding of objects [1]-[6]. Numerous studies on ancient and historical copper (Cu)-based artefacts have tried to establish the chemical characteristics and structure of the natural patinas that grow on objects that have been buried in soil for long periods. The long-time corrosion of Cu-based alloys leads to structural alloy transformations and to the growth of surface corrosion product layers with complex and stratified structures, the investigation of which allows important information on degradation mechanisms to be obtained [7], [8]

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Results

Conclusion