Patina Layer Research Articles

Fatty Imidazolines as a Green Corrosion Inhibitor of Bronze Exposed to Acid Rain

Acid rain is one of the primary corrosive agents on bronze exposed to the atmosphere. Bronze naturally forms a layer of oxides on its surface called patina, protecting it from corrosion. However, when exposed to acid rain, this layer dissolves, making it necessary to use a corrosion inhibitor or stabilize the patina. This study investigated fatty imidazolines derived from agro-industrial waste bran as a corrosion inhibitor of SAE-62 bronze in simulated acid rain (pH of 4.16 ± 0.1). Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curve (PC) measurements were used to evaluate corrosion inhibition efficiency, which was 90% for an inhibitor concentration of 50 ppm. The EIS measurements showed that the fatty imidazolines formed a protective film that stabilized the patina on the bronze surface to a certain extent by hindering the charge transfer process. SEM–EDS analyzed the morphology and composition of the protective oxide layer. The results were complemented by Raman spectroscopy and XRD analysis, indicating cuprite, tenorite, cassiterite, and covellite in the patina layer formed on the bronze surface. The SEM analysis showed that the protective coating on the bronze surface was homogeneous using a 50-ppm inhibitor concentration. The XRD analysis suggested the presence of an organic complex that stabilizes the corrosion products formed on the bronze surface.

Insight into patina formed on beryllium-bronze after 29 years of exposure in an industrial environment and DFT research

This research explores the corrosion behavior of beryllium bronze over a period of 29 years in an industrial atmosphere, revealing an average corrosion rate of 0.557 μm·a−1. The skyward patina layer primarily consists of Cu2O, Cu4SO4(OH)6 and CuSO4, while the field-ward patina layer contains Cu2O, CuO, Cu4SO4(OH)6 and CuSO4. Density functional theory (DFT) calculations and XPS analysis show that Be oxidizes preferentially, providing early-stage corrosion protection. DFT and open circuit potential measurements suggest that the patina layer on the field-ward surface is more thermodynamically stable, but cracks serve as pathways for mass transport, accelerating corrosion.

Corrosion Behaviors of Artificial Chloride Patina for Studying Bronze Sculpture Corrosion in Marine Environments

Copper trihydroxychlorides, which are known as “bronze disease”, are dangerous corrosion products that compromise the stability and conservation of bronze sculptures. Here, we performed artificial patina corrosion experiments on quaternary bronze (Cu-Zn-Sn-Pb) to examine the corrosion behavior of the chloride patina commonly found in bronze objects in marine environments. The chromaticity and reflectance of the patina in the context of the corrosion products indicate that copper trihydroxychloride, which is commonly found in a single color in marine environments, was produced early in the corrosion experiment. Furthermore, the corrosion of bronze had different effects on the alloying elements, contrary to pure copper corrosion. The chloride patina formed a single patina layer of copper trihydroxychlorides. This patina layer was divided into the outer porous powder and inner uniform layers. Furthermore, the interaction of oxygen in the atmosphere with the corrosion layer and internal oxidation of tin in the alloy promoted powdering. These results provide important basic data for research on sculpture conservation and corrosion characteristics, such as changes in color, chemical composition, and corrosion products on the patina surfaces of outdoor bronze sculptures.

Corrosion Behaviors of Outdoor Bronze Sculptures in an Urban–Industrial Environment: Corrosion Experiment on Artificial Sulfide Patina

Copper alloys interact with air pollutants to form corrosion products and, consequently, a patina on outdoor bronze sculptures. In this study, corrosion experiments were conducted to clarify the corrosion behaviors of artificial sulfide patina in an urban–industrial environment on a quaternary bronze alloy (Cu–Zn–Sn–Pb) with a composition and metallurgical properties similar to those of outdoor bronze sculptures. The correlation between the chromaticity and reflectance of the patina revealed increasing brochantite with the corrosion of the patina and an association between the chromaticity a* and patina growth. Cuprite and brochantite were distinguished, and the point at which brochantite covered the patina surface was determined. The quantitative changes in brochantite were mainly influenced by physical causes such as the crystal size and patina layer thickness as well as by Cu2+ ions working as color formation ions moving to the outermost layer. Atmospheric corrosion of the alloy resulted in reduced Cu and Zn contents and increased Sn and Pb contents. The patina consisted of brochantite in the outermost layer and cuprite and cassiterite in the inner layers. These findings should clarify corrosion characteristics such as the surface color, composition, and changes in corrosion products of outdoor bronze sculptures and contribute toward their preservation.

Electrochemical Polarization as a Sustainable Method for the Formation of Bronze Patina Layers on a Quaternary Copper Alloy: Insight into Patina Morphology and Corrosion Behaviour

The bronze patina is aesthetically pleasing and enhances the corrosion resistance of the metallic object. This corrosion product layer can develop naturally, through aging or artificially. However, artificial methods require substances that are hazardous to human health and the environment. In this study, a sustainable approach to patina development, based on the anodic polarization of a 85.5Cu-4.2Pb-4.5Sn-5.7Zn copper alloy immersed in 0.1 M NaCl + 0.01 M NaHCO3 were characterized using polarization curves, chronoamperometry, electrochemical impedance spectroscopy, electrochemical noise measurements, X-ray diffraction, and scanning electron microscopy. The results indicate that the anodic potential modifies the current density as well as the diffusion coefficient of oxygen associated with a thicker corrosion product layer. Electrochemical Impedance spectroscopy and electrochemical noise show that the porous behaviour and corrosion resistance increases as the potential becomes more anodic due to the formation of a protective layer. This behaviour corresponded with the results acquired by chronoamperometry. The surface characterization shows that the potential applied changes the surface morphology and composition of the corrosion products, being identified the crystalline phases of nantokite and atacamite although Cu, Cl, O, Zn, and Pb elements were also detected.

Characterization of yellow patina on stone surfaces by instrumental analysis including LIBS

ABSTRACT Yellow patina formed on the stone surfaces of historical buildings, monuments, and archaeological structures due to weathering is considered a value of the building in the conservation of cultural heritage studies. Although yellow patina layers can be easily distinguished on white marble surfaces, it is not possible to distinguish them on the yellow travertine surfaces with the naked eye. It should be taken into account in yellow travertines as well as marble surfaces before conservation treatments of the stone. In this study, mineralogical and chemical compositions and the thicknesses of yellow patina layers formed on yellow travertine and marble surfaces in Aizanoi, Aphrodisias, and Hierapolis archaeological sites in Turkey were analyzed in order to constitute a conservation approach in the archaeological sites. In this respect, XRD, FT-IR, SEM-EDX, and LIBS were used in the determination of compositions and thicknesses of yellow patina. Although LIBS analysis is a more convenient method to investigate patina layers on stone surfaces, this technique is not as well known as the others. Yellow patina layers contained calcium oxalate in the form of whewellite (CaC2O4.H2O). Their thicknesses were between 15 and 100 μm and should be protective against weathering on travertine and marble surfaces. Highlights LIBS analysis seems to be the most convenient micro-destructive method to estimate the thickness of the yellow patina layers on the marble and yellow travertine surfaces. The determination of the thickness of the yellow patina is critical to keep irreversible cleaning interventions, especially for the yellow travertines due to their similar colors. Yellow patina is mainly composed of calcium oxalate with clay minerals and organic compounds.

Characterization of the corrosion products formed on Michael the Brave’s equestrian statue in urban atmosphere

The present work is focusing on the study of the corrosion products (natural patina) formed on the surface of the equestrian statue of Michael the Brave, Principe of Walachia, and on the patina formed on the bas-reliefs that decorated the marble of the statue pedestal. The statue is placed in the Mihai – Viteazul Square in the center of Cluj-Napoca, Romania, since 1976 and was restored in 2018 after 42 years of exposure in the urban atmosphere. The morphology and the chemical composition of the statue and of the natural patina formed on the statue’s surface, on the bas-reliefs surrounding the statue, as well as on one assembling element exposed in the urban atmosphere for almost 50 years, were determined by SEM - EDX supported by micro-Raman and XRD analyses. The X-ray maps pictured the distribution of various elements in the patina samples collected from the equestrian statue’s surface. The selective dissolution of the Cu, Zn, and Sn observed in the patina layer, was quantified by the dissolution factor based on EDX analysis. The corrosion products indicated the presence of malachite and brochantite, along with other various minerals. It was concluded that the analyzed patinas were affected by the pollution of the urban atmosphere, but their composition was mostly influenced by the composition of the different copper alloy substrates (high-leaded tin bronze or brass).

Surface, Elemental and Electrochemical Characterizations of Ancient Coins By Non – Destructive Techniques

Abstract The cultural heritage field represents a witness to artifacts values in a continuous evolution, it strongly influences our sense of identity and our behavior as people. To protect these archaeological treasures, different conservation and restoration methods are required. Considering the field of priceless artifacts, our research direction led us to preliminary studies of metallic coins from 20th century through non–destructive techniques. Copper–based coins were subjected to the surface characterization through optical microscopy (OM) in transmitted light, elemental composition analysis using Wavelength Dispersive X-ray Fluorescence (WDXRF) and electrochemical corrosion using Tafel extrapolarization technique. The microscopic investigations showed that the patina layer is due to presence of copper content in coins composition confirmed by X-ray fluorescence spectroscopy technique. Also, the electrochemical tests disclosed different corrosion rate according to each chemical composition of coins. This study provide a broad overview of ancient coins to preserve their value in the future.

Determination of optimal electrochemical parameters to reproduce copper artistic patina on quaternary alloys

A copper patina provides both a pleasing aesthetical appearance and corrosion protection to artistic artworks so the electrochemical features for restoring metallic artifacts need to be studied. In this study, the potentiodynamic scan rate consisting of 0.5, 1, 3, 5, 7 10 mV/s to develop artistic patinas on a quaternary copper alloy was studied. The results obtained by SEM/EDS indicate that the patina on the surface is a porous layer mainly composed of copper/chloride corrosion products. The X-Ray analysis identified the formation of nantokites and atacamites depending on the scan rate that was applied. The morphology appearance shows a greenish patina and a more porous structure for scan rates lower than 5 mV/s. Polarization curves and electrochemical impedance spectroscopy determined that the corrosion protection increases at lower scan rates due to higher barrier properties of the patina layer.

An Electrochemical and Spectroscopic Study of Surfaces on Bronze Sculptures Exposed to Urban Environment.

Polluted urban environment enhances dissolution of patina and underlying bronze material of recent and historical bronze sculptures exposed outdoors. In this work, two bronze statues, situated in one of the most polluted Croatian cities, were examined in order to characterize composition of patina and its electrochemical stability. The composition of patina on several positions on each sculpture was determined by EDS, Raman spectroscopy, and FTIR measurements. Electrochemical impedance spectroscopy measurements were conducted in order to evaluate the corrosion stability of both patina and underlying bronze. Results obtained in this work show that the two examined bronze sculptures were covered with patina layer that was mainly composed of copper sulfides and sulphates, which is in accordance with the high concentrations of H2S and SO2 in the atmosphere. However, the variations in the appearance of FTIR and Raman spectra revealed that the amount of each species differed from spot to spot, as well as the fact that other compounds, such as carbonates, were present at some areas. This difference in patina composition was reflected in electrochemical behavior as observed by electrochemical impedance spectroscopy.

Long-term outdoor exposure of artificial copper patina based on brochantite

Abstract A typical green layer of patina starts to cover copper in atmosphere condition, which is aesthetically acceptable and also provides protective properties. This work investigates stability of the artificial patina layer based on sulphates prepared from a gaseous phase during two-year exposure in atmosphere condition. XRD and SEM were employed to verify the composition and morphology of artificial patina. Colour and patina coverage were compared before and after exposure also. According to results after 1 and 2 years of exposure, it is possible to see changing of hydroxyl sulphates to more stable brochantite and filling pores in the patina layer. There is almost no colour change, however lower patina coverage is slightly evident due to precipitation and abrasive effect.

Copper and sulphur depth profile in patina layers using NRA and RBS

A combination of nuclear reaction analysis (NRA) and Rutherford backscattering spectroscopy (RBS) were utilized in order to obtain information on the depth distribution of sulphur and copper in artificially produced and natural patina layers. The copper profiling was performed by using the reaction 63Cu(p,p'y)6 3Cu and detecting the 1327 keV γ-ray deexciting the third excited state to the ground state of 6 3Cu produced. For the determination of sulfur the 2230 keV γ-ray was used, deexciting the first excited state to the ground state of 32S formed through the reaction 3 2S(p,p'y)3 2S, which exhibits three sharp resonances at projectile energies 3.094, 3.195 and 3.379 MeV. The relevant cross-sections were measured in the energy range between 3.0 and 3.7 MeV in steps of 20 keV at 125° to the incident proton beam direction. Supporting information on the depth distribution of oxygen and the other elements of the patina samples was obtained by p-RBS (Ep = 1.5 MeV; θ = 160°).

Non-destructive thickness measurement as a tool to evaluate the evolution of patina layer formed on weathering steel exposed to the atmosphere

This work considers the magnetic induction method on rough surfaces (ABNT NBR 10443) to determine the thickness of the patina layer formed on weathering steel (WS) sheets exposed for up to two years at São Paulo atmosphere and on WS sculptures exposed for sixteen and twenty-four years at the same site. A good agreement was found with SEM measurements. It was also found that patina thickening followed a two slopes bilogarithmic law, with a steeper slope for short exposure periods, in agreement with increased corrosion rate. For long-term exposure, it was found a low thickening rate (<2μmyear−1), suggesting stabilization of the patina layer. The increase in goethite (α-FeOOH) content over time reinforces the hypothesis of a more protective layer as indicated by Protective Ability Index (PAI) for 24 years old sculpture.

EIS investigation and patina characterization of weathering steel exposed to each of the four seasons in the São Paulo metropolitan area

Weathering steel (WS) is a low alloy steel particularly suitable for outdoor exposures. When exposed to wet and dry cycles, they develop a protective patina layer with complex composition, effectively reducing the corrosion rate. However, several years are necessary to completely develop this layer. Aiming to investigate the seasonal dependence on the climatic parameters and concentration of pollutants in the atmosphere in the patina development at early stages, the present study investigates the corrosion behavior of patina layers formed on WS exposed to the atmosphere of the São Paulo metropolitan area during a period corresponding to each of the four seasons, employing open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and electric equivalent circuit (EEC) fitting. SEM, Raman spectroscopy and thicknesses evaluation were used to characterize the patinas. The results showed that, while the patina compositions were independent of the exposure period, their thicknesses and corrosion resistances were extremely dependent on this variable. Excessive rain and wetting periods, as well as the presence of pollutants, proved to be deleterious, leading to the development of non-protective patinas. Based on the EEC fitting procedure, a model was proposed to explain the EIS responses of the patina layers based on the porous electrode theory initially developed by de Levie.

Electrochemical study of the corrosion behavior of bronze under acetic acid-containing thin electrolyte layers

The corrosion behavior of bare bronze, bronze with Cu2O patina and bronze with CuCl patina under acetic acid-containing thin electrolyte layers (TELs) with various thickness was studied by electrochemical tests, SEM-EDS and XRD analysis. The results indicated that the corrosion rate of these three bronze samples under different TEL thicknesses is lower than that in bulk solutions. Besides, the corrosion rate of bare bronze increases as TEL thickness increases, and as for the bronze with Cu2O patina or bronze with CuCl patina, the critical thickness is about 198 μm or 152 μm. Moreover, the Cu2O patina layer can protect the bronze matrix, while the CuCl patina layer will accelerate the corrosion process. The major corrosion products of bare bronze and bronze with Cu2O patina in the acetic acid vapor are Cu2O and hydrate of copper acetate, but for bronze with CuCl patina, the corrosion products on the surface is mainly Cu2Cl(OH)3.

Corrosion kinetics and patina evolution of galvanized steel in a simulated coastal-industrial atmosphere

The corrosion kinetics and patina (corrosion products) layer evolution of galvanized steel submitted to wet/dry cyclic corrosion test in a simulated coastal-industrial atmosphere was investigated. The results show that zinc coating has a greater corrosion rate during the initial period and a lower corrosion rate during the subsequent period, and the patina composition and structure can greatly affect the corrosion kinetics evolution of zinc coating. Moreover, Zn5(OH)6(CO3)2 and Zn4(OH)6SO4 are identified as the main stable composition and exhibit an increasing relative amount; while Zn12(OH)15Cl3(SO4)3 cannot stably exist and diminish in the patina layer as the corrosion develops.

The origin and evolution of copper patina colour

The copper patina colour has been systematically explored through a large set of short- and long-term exposed copper metal samples. The initial brown-black appearance is attributed to semiconducting properties of cuprite (Cu2O) and fully attained at thickness 0.8 ± 0.2 μm. The characteristic green-blue appearance is due to the colour forming Cu(II)-ion in the outer patina layer which needs to be 12 ± 2 μm to fully cover the inner cuprite layer. No significant influence of atmospheric environment on patina colour is discerned. The green-blue patina colour on historic copper was attained after shorter exposures than in modern copper due to more inhomogeneous microstructure.

CVD Synthesis of Monodisperse Graphene/Cu Microparticles with High Corrosion Resistance in Cu Etchant

Copper powder has broad applications in the powder metallurgy, heat exchanger, and electronic industries due to its intrinsically high electrical and thermal conductivities. However, the ease of formation of surface oxide or patina layer raises difficulty of storage and handling of copper powder, particularly in the case of Cu microparticles. Here, we developed a thermal chemical vapor deposition chemical vapor deposition (CVD) process for large-scale synthesis of graphene coatings on Cu microparticles, which importantly can remain monodisperse without aggregation after graphene growth at high temperature by using removal spacers. Compared to other protective coating methods, the intrinsic electrical and thermal properties of Cu powder would not be degraded by uniform growth of low defect few-layer graphene on each particle surface. As a result, when the anticorrosion performance test was carried out by immersing the samples in Cu etchant, the corrosion rate of graphene/Cu microparticles was significantly improved (ca three times slower) compared to that of pristine Cu powder, also showing a comparable anticorrosion ability to commercial CuZn30 alloy.

Convenient extraction method for quantification of thin zinc patina layers

Synthetic zinc patina was grown on galvanized steel sheets in supercritical carbon dioxide atmosphere. Different patina compounds were dissolved and quantified using a stepwise immersion and dissolution procedure. The distinct patina components, namely anhydrous zinc carbonate (a dense layer adjacent to metallic zinc) and zinc hydroxy carbonate (nanowires on the surface), were dissolved in glycine solutions, followed by quantification of Zn2+ in the solutes by X‐ray fluorescence. The zinc hydroxy carbonate nanowires were readily glycine soluble, and the anhydrous zinc carbonate showed scarce glycine solubility, which enabled their selective quantification. The amount of the remaining (anhydrous) zinc carbonate after glycine extraction was determined from the glycine‐soluble zinc oxide after calcination (heat treatment for 10 minutes at 350°C). The results were verified by scanning electron microscopy imaging and Fourier transform infrared spectroscopy measurements.

Use of Monte Carlo Simulation as a Tool for the Nondestructive Energy Dispersive X-ray Fluorescence (ED-XRF) Spectroscopy Analysis of Archaeological Copper-Based Artifacts from the Chalcolithic Site of Perdigões, Southern Portugal.

This work is part of a broader research line that aims to develop and implement a nondestructive methodology for the chemical characterization of archaeological metals based on a protocol that combines energy dispersive X-ray fluorescence spectrometry (ED-XRF) with a Monte Carlo (MC) simulation algorithm. In this paper, the ED-XRF-MC protocol has been applied to estimate the chemical composition of a selected group of 26 copper-based artifacts and fragments recovered at Perdigões, one of the larger Chalcolithic sites of southwest Iberia. All the analyzed artifacts have a multilayered structure composed of the alloy substrate and of a superficial layer common in each metal buried for hundreds of years and consisting of the patina mixed with soil. Due to the difficulty in determining the quantitative composition of these alloys in the presence of this complex patina/encrustation layer, the spectrometric protocol applied in this paper allows to simulate and to determine the composition of the bulk alloy without any prior removal of the overlying corrosion patina layer and soil-derived crust, even in the presence of rough and irregular surfaces, thus preserving the physical integrity of the artifacts. The overall results obtained with the ED-XRF-MC protocol indicates that the artifacts from Perdigões are almost pure coppers with a low amount of arsenic (<3.0 wt%) and reduced concentration of elements such as Pb, Bi, and Sb, in agreement with the third millennium metallurgy known in southwestern Iberia. Also based on previously theoretical-experimental studies, the data presented in this paper show how the applied analytical methodology can be a fast and completely nondestructive analytical tool reliable for routine and large-scale chemical analysis of archaeological metals, thus representing a major advance to be broadly applied within the field of cultural heritage studies.