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|Title: ||Development and optimisation of protocols for surface cleaning of cultural heritage metals|
|Authors: ||Quintana, Carla Lucía Soto|
|Advisors: ||Angelini, Emma|
Espinosa, Ruth Lahoz
|Issue Date: ||27-Sep-2016|
|Publisher: ||Universidade de Évora|
|Abstract: ||The conservation and valorisation of cultural heritage is of fundamental importance for
our society, since it is witness to the legacies of human societies. In the case of metallic artefacts,
because corrosion is a never-ending problem, the correct strategies for their cleaning and
preservation must be chosen. Thus, the aim of this project was the development of protocols
for cleaning archaeological copper artefacts by laser and plasma cleaning, since they allow
the treatment of artefacts in a controlled and selective manner. Additionally, electrochemical
characterisation of the artificial patinas was performed in order to obtain information on the
protective properties of the corrosion layers. Reference copper samples with different artificial
corrosion layers were used to evaluate the tested parameters.
Laser cleaning tests resulted in partial removal of the corrosion products, but the lasermaterial
interactions resulted in melting of the desired corrosion layers. The main obstacle
for this process is that the materials that must be preserved show lower ablation thresholds
than the undesired layers, which makes the proper elimination of dangerous corrosion products
very difficult without damaging the artefacts. Different protocols should be developed
for different patinas, and real artefacts should be characterised previous to any treatment to
determine the best course of action.
Low pressure hydrogen plasma cleaning treatments were performed on two kinds of patinas.
In both cases the corrosion layers were partially removed. The total removal of the undesired
corrosion products can probably be achieved by increasing the treatment time or applied
power, or increasing the hydrogen pressure. Since the process is non-invasive and does not
modify the bulk material, modifying the cleaning parameters is easy.
EIS measurements show that, for the artificial patinas, the impedance increases while the
patina is growing on the surface and then drops, probably due to diffusion reactions and a slow
dissolution of copper. It appears from these results that the dissolution of copper is heavily
influenced by diffusion phenomena and the corrosion product film porosity.
Both techniques show good results for cleaning, as long as the proper parameters are used.
These depend on the nature of the artefact and the corrosion layers that are found on its surface.|
|Appears in Collections:||BIB - Formação Avançada - Teses de Mestrado|
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