Historic and modern alloys: atmospheric corrosion and development of accelerated ageing methodologies

The atmospheric corrosion of modern and historic alloys used in cultural heritage has been investigated by applying specific accelerated ageing methods. Three main research lines were carried out, involving different materials. In the first part, the atmospheric corrosion of a modern Cu-3Si-1Mn bronze was investigated through accelerated ageing tests simulating outdoor runoff conditions. The corrosion processes were evaluated through different analyses, and the results obtained were compared to those of a traditional quaternary bronze. The second line was carried out to characterise historic aluminium alloys used in aeronautics to develop and apply innovative protection strategies for their conservation. Historic wrecks were identified and characterised through micro and macroscale observations. Moreover, accelerated ageing tests were performed on both historic and modern alloys to compare their behaviour and select the best modern substrate to be used for the development of effective coatings. The third research line aimed to develop accelerate sampling and ageing methods to investigate the role of particulate matter (PM) in the atmospheric corrosion of bronzes and metals in general. The first approach consisted in the fine-tuning of an efficient accelerated method for ambient PM sampling on bronze specimens followed by their accelerated ageing, in order to establish a correlation between the PM and the substrate’s corrosion. After the accelerated ageing of the specimens, the corrosion was evaluated by surface characterisation and correlated to the PM features. The second approach consisted in the development of a synthetic PM formulation and of an artificial deposition method, which was performed by spraying mixtures containing the main PM inorganic fractions on a G-85 bronze with an airbrush. The deposition efficiency was assessed, and the effect of synthetic PM on the bronze corrosion was evaluated. The results were compared to those obtained by ambient PM deposition

Atmospheric corrosion of Cu-Si-Mn bronze for contemporary art under simulated runoff and continuous immersion conditions

Silicon bronze is widely used for monuments: corrosion of Cu-3Si-1Mn was studied with respect to Cu-5Sn-5Zn-5Pb during ageing tests (runoff/full immersion) in acid rain. Surface characterisation (FEG-SEM/EDS elaborated through PCA, TEM, Raman, FTIR, profilometry), metal release and EIS measurements were performed. Under runoff conditions, where mechanical action plays a role, the alloys showed comparable corrosion resistance. In full immersion the corrosion rate of Cu-3Si-1Mn was slightly higher than that of Cu-5Sn-5Zn-5Pb, due to the different nature of the corrosion products. Results showed that, compared to Sn oxide/hydroxide, Si tends to form less protective amorphous products, detaching from the surface

Atmospheric corrosion of Silicon Bronze for contemporary art

Artistic foundries are increasingly requested to select new bronze compositions, with improved aesthetic features and resistance toward the different corrosive agents. The development of industrial copper-based alloys led to less toxic, lead-free bronzes, such as Cu-Si-Mn bronze. Due to its excellent corrosion resistance, good weldability, remarkable castability and golden colour, this silicon bronze is now widely used by artistic foundries for bronze monuments [1]. This work aims to study mechanisms of atmospheric corrosion and durability of an as-cast Si- Mn bronze. The bronze, supplied by Livartis Foundry d.o.o, Slovenia, corresponds to the copper casting alloy UNS C87300 [2] and contains 3.1±0.4 Si and 0.9±0.1 Mn (wt%) as main alloying elements; Sn and Zn (< 0.1 wt%) as well as P (0.02 wt%) are also present as trace elements. As-cast plates (5 mm thick) were obtained by sand casting. Metallographic analyses were performed by optical (OM) and electron (SEM and FEG) microscopy. The corrosion behaviour was studied through both electrochemical and accelerated ageing tests simulating outdoor conditions. Electrochemical impedance spectroscopy (EIS)was used to monitor the evolution of corrosion process during 10 days of exposure to synthetic acidic rain and potentiodynamic polarization tests were carried out at the end of exposure. Surface analyses (OM, SEM-EDS, FEG, TEM, Raman and FT-IR spectroscopy, profilometric measurements) were performed, together with analyses of Cu, Si and Mn released in the ageing environment (MP-AES). Corrosion rates were determined. Metallographic examination revealed a typical dendritic microstructure with Si coring and a few shrinkage cavities within interdendritic spaces. Coring also led to localised precipitation of Si-, Mn- and P-containing phases in interdendritic spaces. The role of microstructural constituents was examined during accelerated tests. Both electrochemical and accelerated ageing tests showed that modern and traditional quaternary bronzes exhibited similar corrosion rates at the end of exposure, however relevant differences were observed in the metal release trends and in the corrosion products formations, suggesting different corrosion mechanisms

Atmospheric corrosion of Silicon Bronze for contemporary art

Artistic foundries are increasingly requested to select new bronze compositions, with improved aesthetic features and resistance toward the different corrosive agents. The development of industrial copper-based alloys led to less toxic, lead-free bronzes, such as Cu-Si-Mn bronze. Due to its excellent corrosion resistance, good weldability, remarkable castability and golden colour, this silicon bronze is now widely used by artistic foundries for bronze monuments [1]. This work aims to study mechanisms of atmospheric corrosion and durability of an as-cast Si- Mn bronze. The bronze, supplied by Livartis Foundry d.o.o, Slovenia, corresponds to the copper casting alloy UNS C87300 [2] and contains 3.1±0.4 Si and 0.9±0.1 Mn (wt%) as main alloying elements; Sn and Zn (< 0.1 wt%) as well as P (0.02 wt%) are also present as trace elements. As-cast plates (5 mm thick) were obtained by sand casting. Metallographic analyses were performed by optical (OM) and electron (SEM and FEG) microscopy. The corrosion behaviour was studied through both electrochemical and accelerated ageing tests simulating outdoor conditions. Electrochemical impedance spectroscopy (EIS)was used to monitor the evolution of corrosion process during 10 days of exposure to synthetic acidic rain and potentiodynamic polarization tests were carried out at the end of exposure. Surface analyses (OM, SEM-EDS, FEG, TEM, Raman and FT-IR spectroscopy, profilometric measurements) were performed, together with analyses of Cu, Si and Mn released in the ageing environment (MP-AES). Corrosion rates were determined. Metallographic examination revealed a typical dendritic microstructure with Si coring and a few shrinkage cavities within interdendritic spaces. Coring also led to localised precipitation of Si-, Mn- and P-containing phases in interdendritic spaces. The role of microstructural constituents was examined during accelerated tests. Both electrochemical and accelerated ageing tests showed that modern and traditional quaternary bronzes exhibited similar corrosion rates at the end of exposure, however relevant differences were observed in the metal release trends and in the corrosion products formations, suggesting different corrosion mechanisms

Galvanic corrosion over World War II aircraft wrecks

International audienceAluminium usually exhibits a better corrosion resistance than other common metals when exposed to outdoor environments. However, wrecks components made of aluminium alloys, particularly Al-Cu alloys, can be strongly affected by corrosion. The observation of different objects from WWII wrecks indicates more significant degradation in the presence of ferrous parts because of galvanic corrosion. The study focused on two WWII aircraft objects recovered from French coasts: a Supermarine Spitfire aircraft wing, found in 1988 at sea less than 3 miles from the coast of Plérin, and an aircraft propeller found offshore near the beach of Fécamp. We investigated the galvanic corrosion effect over these objects and the influence of their Fe/Al areas ratio between the more noble material (usually ferrous alloy) and the less noble material (usually aluminium alloy). This deterioration was severe due to their exposure to the marine environment and the relatively high amount of Cu (3.4-4.5 wt. %) in the Al alloys, provoking pitting, intergranular, and exfoliation corrosion. This study aims to help understanding active corrosion on aircraft wrecks, with the final aim to improve their conservation

Galvanic corrosion over World War II aircraft wrecks

International audienceAluminium usually exhibits a better corrosion resistance than other common metals when exposed to outdoor environments. However, wrecks components made of aluminium alloys, particularly Al-Cu alloys, can be strongly affected by corrosion. The observation of different objects from WWII wrecks indicates more significant degradation in the presence of ferrous parts because of galvanic corrosion. The study focused on two WWII aircraft objects recovered from French coasts: a Supermarine Spitfire aircraft wing, found in 1988 at sea less than 3 miles from the coast of Plérin, and an aircraft propeller found offshore near the beach of Fécamp. We investigated the galvanic corrosion effect over these objects and the influence of their Fe/Al areas ratio between the more noble material (usually ferrous alloy) and the less noble material (usually aluminium alloy). This deterioration was severe due to their exposure to the marine environment and the relatively high amount of Cu (3.4-4.5 wt. %) in the Al alloys, provoking pitting, intergranular, and exfoliation corrosion. This study aims to help understanding active corrosion on aircraft wrecks, with the final aim to improve their conservation

Galvanic corrosion over World War II aircraft wrecks

International audienceAluminium usually exhibits a better corrosion resistance than other common metals when exposed to outdoor environments. However, wrecks components made of aluminium alloys, particularly Al-Cu alloys, can be strongly affected by corrosion. The observation of different objects from WWII wrecks indicates more significant degradation in the presence of ferrous parts because of galvanic corrosion. The study focused on two WWII aircraft objects recovered from French coasts: a Supermarine Spitfire aircraft wing, found in 1988 at sea less than 3 miles from the coast of Plérin, and an aircraft propeller found offshore near the beach of Fécamp. We investigated the galvanic corrosion effect over these objects and the influence of their Fe/Al areas ratio between the more noble material (usually ferrous alloy) and the less noble material (usually aluminium alloy). This deterioration was severe due to their exposure to the marine environment and the relatively high amount of Cu (3.4-4.5 wt. %) in the Al alloys, provoking pitting, intergranular, and exfoliation corrosion. This study aims to help understanding active corrosion on aircraft wrecks, with the final aim to improve their conservation

Historical primers and paints used for aeronautical protection and colouring during WWII: A multi-techniques approach on archaeological parts

International audienceAeronautics for military or civil applications effectively pushed scientists, engineers and industrial leaders to invent and produce increasingly efficient materials. Aluminium alloys are among the most important strategic materials used in aircraft manufacturing. Consequently, so are the protective coatings (primers and paints). After decades of burial, World War II (WWII) wrecks provide a tremendous amount of archaeological information on this period of intense technological research. In this article, the original protective coatings of ten samples collected on WWII wrecks and one collection aircraft were studied. Information was retrieved thanks to a multi-techniques approach: SEM-EDS, Raman spectroscopy and XRD to identify the nature of the mineral compounds (fillers and pigments) and FTIR, Py-GC-MS and NMR to identify the organic binders of the paints and primers. This information will help conserve this valuable 20 th century Industrial Heritage