Characterization of a heavily corroded bronze statue from Pharaonic Egypt

The current study aims to characterize a heavily corroded bronze statue from Pharaonic Egypt, in terms of the morphology and mechanism of corrosion. The characterization was carried out by a combination of methods, including the scanning electron microscope equipped with energy dispersive X-ray spectroscopy (SEM–EDS), USB digital microscope, X-ray micro-diffraction, and Raman micro-spectroscopy. Insights into the morphology and corrosion mechanisms of two corrosion stages are presented. Specifically, the metallic-wall layer was first converted into grayish-brown corrosion mottled with green and gray spots in the central part, in which a greenish-white corrosion phase was formed in the second stage. The EDS analysis of the greenish-white phase revealed the predominance of tin, copper, oxygen, and carbon and a low chlorine content. The greenish-white phase consisted of four corrosion products: romarchite, cassiterite, malachite, and a small amount of atacamite. The morphology developed upon corrosion was attributed to the selective dissolution and depletion of copper in the central layer, internal oxidation of tin, and conversion of cuprite into malachite. Moreover, the usual bronze corrosion products were formed as a superficial layer on the statue.     

Non-invasive surface analysis of ancient bronze arrowheads with scanning electron microscopy and X-ray powder diffractometry

In this research, surfaces of eight ancient metal arrowheads were investigated regarding chemical composition, homogeneity, and products of corrosion. To perform that, two nondestructive techniques were applied: Scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), and X-ray powder diffractometry (XRPD). Importantly, both methods did not require sampling, cutting, nor significant cleaning of the historical artifacts, which made the measurements not only nondestructive but noninvasive too. SEM-EDS measurements provided information on the morphology and elemental composition of the surfaces of the studied objects as well as the distribution of chemical elements on the surfaces and supported crystalline phase analysis. It was revealed that the arrowheads were cast of tin bronze, but some of them contained high amounts of lead and admixtures of antimony and arsenic while copper and tin oxides and lead carbonates were found as the major corrosion products. In some cases, distribution of elements in the surface exhibited serious nonhomogeneity, probably resulting from limited solubility of the casting metals and degradation processes. Based on the obtained results, authenticity and declared provenience of the arrowheads were assessed in reference to the characteristics of similar objects described in literature.     

Multianalytical study of corrosion layers in some archaeological copper alloy artefacts

Corrosion layers in some copper and bronze archaeological objects from Haft Tappeh archaeological site, southwest Iran, were studied. For this purpose, optical microscopy, scanning electron microscopy with energy dispersive X‐ray microanalysis, micro‐Raman spectroscopy and X‐ray diffraction methods were applied to observe corrosion stratigraphy and their characteristics as well as identification of chemical composition and phase determination of different corrosion layers. Based on optical and electron microscopy, three different corrosion strata were identified in cross section of different metallic objects including various red, green, white‐grey powdery and dark internal compact layers. Scanning electron microscopy with energy dispersive X‐ray microanalysis on different corrosion layers revealed that Cu, Sn and Cl are the main elements in the chemical composition of different layers. Tin‐rich phases were detected in white‐grey and dark layers that may be formed because of the internal oxidation of tin as well as the decuprification (selective dissolution of copper) phenomena occurring during long‐term burial period in the soil. Also, the XRD and micro‐Raman spectroscopy results proved that the main corrosion products are nantokite (CuCl), copper trihydroxychlorides and copper oxides. The combination of these analytical methods allows us to explore the surface and internal corrosion layers of the archaeological copper and bronze samples, and major interest is on studying their chemistry, microstructural properties and corrosion stratigraphy. Copyright © 2015 John Wiley & Sons, Ltd.     

Plasma reduction of bronze corrosion developed under long-term artificial ageing

Reference Cu-based alloy with chemical composition and micro-chemical structure similar to that of ancient alloys has been used for carrying out the artificial long-term degradation test based on chloride enriched soil (chemical + soil) degradation. The results show that such degradation procedure produces natural like “patinas” as the ones grown on archaeological artefacts, from a chemical, structural and micro-morphological point of view. Glow discharge plasma technique has been employed for the treatment of the as-corroded bronze coupons. The gradual elimination of chloride-containing corrosion products in favour of the formation of more stable species and even the complete reduction back to copper has been observed. The chemical and metallurgical features have been determined by combined use of different analytical techniques such as scanning electron microscopy with energy dispersive X-ray micro-analysis (SEM-EDS), X-ray diffraction (XRD) and optical microscopy.     

Characterization of the patina formed on a low tin bronze exposed to aqueous hydrogen sulfide

The dark gray corrosion layer (patina) formed on the surface of a polished low tin bronze alloy following exposure to a deoxygenated and saturated aqueous solutions of H₂S has been characterized by X‐ray photoelectron spectroscopy, scanning electron microscopy‐energy dispersive spectroscopy and X‐ray diffraction. The system represents a model for bronze corrosion in reducing conditions where sulfate‐reducing bacteria in soils or deoxygenated seawater may generate H₂S during respiration. The initial surface was dominated by metallic copper together with Sn, Pb and Zn oxides and hydroxides. Surface enrichment of Pb and Zn was noted because of a smearing effect during polishing. At least some of the lead was crystalline. In contrast, the corrosion layer formed by H₂S(aq) exposure was dominated by polycrystalline Cu₂S (low and high chalcocite) and smaller concentrations of CuSO₄ · nH₂O. This surface was enriched with Zn as Zn(OH)₂. Lead was present as redeposited PbS (galena) crystallites in at least two different morphologies. Unlike bronzes exposed to oxidizing conditions, which develop protective SnO₂ layers, the H₂S(aq)‐exposed surface was considerably depleted in Sn. Copyright © 2014 John Wiley & Sons, Ltd.     

Electrochemical Characterization of Corrosion Products in Leaded Bronze Sculptures Considering Ohmic Drop Effects on Tafel Analysis

The characterization of corrosion products in leaded bronze based on the voltammetry of immobilized particles methodology is described. Voltammetric data, supported by Fourier transform infra‐red spectroscopy, field emission scanning electron microscopy‐energy dispersive X‐ray microanalysis (FESEM‐EDX) and scanning electrochemical microscopy (SECM) allow the identification of copper and lead corrosion materials. The mutual influence of such products is modeled upon considering uncompensated ohmic drops in the Tafel analysis of the rising portion of the respective voltammetric signals for their electrochemical reduction.     

Bronze degradation processes in simulating archaeological soil media

The purpose of this study is to establish reliable procedure reproducing the degradation processes that occurred on the archaeological artefacts before their excavation. Two simulating soil media are chosen, the first one (FJ) is made from archaeological soil filtrate and the second is a chloride- and/or sulphate-containing solution (CSJ) taken at the same soil amounts of aggressive ions. According to stationary studies, corrosion mechanism in CSJ medium is catalysed by the presence of chloride at the surface of tin bronze electrode, but sulphate products tend to stabilise the surface of bronze sample immersed in soil filtrate. In FJ, the trend of impedance spectra remains unchanged during the immersion period. Adjusted impedance parameters prove that passivation and depassivation can occur simultaneously on bronze surface with different expansion. In CSJ, impedance data evolve according to the immersion time. The evolution of adjusted parameters according to the immersion time describes well the surface state of the bronze sample. The corrosion process is more difficult while the metallic surface is covered with a bronze corrosion layer “patina” which explain the capacitance decreasing and the resistance increasing (after 50 days). Scanning electron microscopy observations coupled with energy-dispersive X-ray spectrometry analysis approve our electrochemical results.     

The electrochemical behaviour of bronze in synthetic seawater

This paper reports a voltammetric study of bronze in synthetic seawater (SSW). The effects of buffering and deoxygenating were particularly visible in the transpassive region. The breakdown of the anodic passive film on bronze leads to a well-defined activation peak in the transpassive region typical of a nucleation and growth of pits. The breakdown potential of the passivity was shown to vary with the experimental conditions, namely, with buffering and deoxygenating. Buffering has shown to lead to more stable passive films and deoxygenating to higher oxidation currents. Scanning electron microscopy with energy dispersive spectrometer (SEM/EDS) studies of bronze samples with 1-month exposure in non-deoxygenated buffered and non-buffered SSW under open circuit potential have shown significant differences in their morphology: a uniformly cracked surface and a surface showing large and spherical precipitates of about 50 μm uniformly distributed along the surface, respectively, for bronze coupons in buffered (pH 9) and in non-buffered SSW. The EDS technique has identified Cu, O, Cl and Na on the corrosion products of bronze in non-buffered SSW, whilst in buffered media, Sn was also identified. In non-buffered media, open circuit potentials have shown to be all the time less negative than in the buffered media. After 1-month exposure the E _OCP of bronze samples in both media seem to converge to −0.131 and −0.155 V vs Ag|AgCl, respectively. This potential can be assigned to the formation of cuprite, Cu₂O and nantokite, CuCl. The analysis of the SEM images after the removal of the corrosion products has shown descuprification with higher intensity on the surface from coupons in non-buffered SSW.     

Quantitative Analysis of Ti-Si-Ge/Si-Ge/Si Structures by EDS and AES

 A method for quantitative analysis of Ti-Si-Ge/Si-Ge/Si structures with submicron thick layers by energy dispersive spectroscopy (EDS) in transmission electron microscopy (TEM) and Auger electron spectroscopy (AES) was developed. Quantitation of the results of both AES and EDS techniques was performed on the basis of a single reference specimen for the Ti-Si-Ge system comprising a uniform layer of the Ti(Si_0.85Ge_0.15)₂ phase on a silicon substrate. The reference sample was prepared by the same procedure as the samples used in the study, and was thoroughly characterized by X-ray diffractometry, transmission electron microscopy and energy dispersive spectroscopy in scanning electron microscopy. Using this reference sample the elemental sensitivity factors relative to Si were found for both techniques, which enable us to obtain the elemental depth distributions for the studied samples. Good agreement between the results obtained by EDS/TEM, AES and supplementary techniques was found.     

Copper corrosion in soil: influence of chloride contents, aeration and humidity

The corrosion of copper in a typical Portuguese soil was studied. The original soil was characterised, and modifications were produced by adding chloride, and HClO₄ solutions, or by increasing its relative humidity. The aggressiveness degree of the various soil samples was determined. Copper coupons exposed for 3 months in the original and in the modified soil samples were analysed. The average corrosion rates determined from gravimetric data were in good correlation with the soil aggressiveness. The morphology of the corroded copper surfaces, with and without corrosion products, was analysed by visual observation, optical microscopy and scanning electron microscopy. Energy dispersive spectroscopy was used for the semi-quantitative analysis of the corrosion products and X-ray diffraction spectroscopy to identify the crystalline products. Cuprite has been identified on the copper samples corresponding to the interfaces Cu|S6 and Cu|S8, plus paratacamite on the copper coupon exposed to the soil with higher concentration of chloride (S6). Polarisation curves of copper samples in neutral solutions made by adding different amounts of chloride ions to the soil washing water, under deaereated conditions, were recorded and analysed. The passivity breakdown potential has shown, as expected, a displacement to the cathodic direction as the Cl⁻ ion concentration increases.     

Corrosion resistance of zinc electrodeposited from acidic and alkaline electrolytes using pulse current

Corrosion resistance of zinc coatings was investigated in an accelerated corrosion test in a condensation chamber. Zinc was electrodeposited from alkaline and acidic electrolytes using direct current (DC) or pulse current (PC). The zinc coating was subsequently protected against corrosion with a chrome (III) layer. Morphology and structure of the coatings was investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction analysis (XRD) before and after the corrosion test. Corrosion resistance of alkaline zinc coatings electrodeposited with DC and PC under test conditions was found to be comparable. The corrosion resistance of zinc coatings deposited from acidic electrolytes by PC was lower in comparison with corrosion resistance of zinc coatings deposited using DC. Presented at the 8th Conference on Solid State Chemistry, Bratislava, Slovakia, 6–11 July 2008.     

Preparation of Cd-doped SnO<Subscript>2</Subscript> nanoparticles by sol–gel route and their optical properties

Nanocrystalline cadmium doped tin oxide (SnO₂) powders of about 2.5–4.5 nm in size have been synthesized by using different solvents via sol–gel method. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDX), Transmission electron spectroscopy (TEM), UV-Vis absorption and Photoluminescence (PL) spectroscopy. The PL emission spectra revealed that the band centered at 452 nm might be related with oxygen vacancies. A spherical, small rod and slice like morphologies of the prepared Cd-SnO₂ nanoparticles were observed in the SEM and TEM studies. The presence of Cd modifies the structural, morphological and optical properties of the tin oxide nanoparticles.     

Characterization of “oil on copper” paintings by energy dispersive X-ray fluorescence spectrometry

Energy dispersive X-ray fluorescence is a common analytical tool for layer thickness measurements in quality control processes in the coating industry, but there are scarce microanalytical applications in order to ascertain semi-quantitative or quantitative information of painted layers. “Oil on copper” painting becomes a suitable material to be analysed by means of X-ray fluorescence spectrometry, due to the metallic nature of substrate and the possibility of applying layered models as used in coating industry. The aim of this work is to study the suitability of a quantitative energy dispersive X-ray fluorescence methodology for the assessment of the areal distribution of pigments and the characterization of painting methods on such kind of pictorial artworks. The method was calibrated using standard reference materials: dried droplets of monoelemental standard solutions laid on a metallic plate of copper. As an example of application, we estimated pigment mass distribution of two “oil on copper” paintings from the sixteenth and eighteenth centuries. Pictorial layers have been complementarily analysed by X-ray diffraction. Apart of the supporting media made of copper or brass, we could identify two different superimposed layers: (a) a preparation layer mainly composed by white lead and (b) the pictorial layer of variable composition depending on the pigments used by the artist on small areas of the painting surface. The areal mass distribution of the different elements identified in the painting pigments (Ca, Cr, Mn, Fe, Zn, Cd, Hg and Pb) have been determined by elemental mapping of some parts of the artworks.     

Identification of ancient gilding technology and Late Bronze Age metallurgy by EDXRF, Micro-EDXRF, SEM-EDS and metallographic techniques

A combination of analytical techniques capable of elemental and microstructural characterisation was used for the identification of ancient gilding technology and bronze metallurgy. EDXRF, micro-EDXRF, SEM-EDS analysis and metallographic examinations were applied in the study of artefacts dating to the end of the second millennium BC from Crasto de São Romão in Central Portugal. Results report to the finding of an exceptional gilded copper nail among bronze artefacts with 9 wt.% to15 wt.% tin and minute other metallic impurities. Additionally, analysis of a crucible fragment points out for bronze production at the archaeological site. EDXRF and micro-EDXRF analysis made on the copper nail showed that it was gilded only on the front side of the head, and that the gold layer has been lost in the most exposed areas. SEM-EDS analysis showed that the gold layer has 5–8 µm in thickness and is covered with a thick corrosion layer. The gilding technique is discussed based on the gold layer composition and gold/copper substrate interface. So far, this object seems to be the first diffusion gilded artefact identified in the Portuguese territory dated to Late Bronze Age.     

Surface analysis of epitaxially grown GeSn alloys with Sn contents between 15% and 18%

Metastable Germanium–tin (GeSn) layers with rather high Sn content between 15% and 18% grown on Si substrates by molecular beam epitaxy were analyzed for the morphological changes on a surface before and after reaching critical layer parameters (thickness, Sn content, and growth temperature) for surface roughening. Atomic‐force microscopy investigations were performed as a function of thickness and separately for varying Sn concentrations in the GeSn layer. Epitaxial growth of metastable, uniform GeSn (15% Sn content) layers is obtained up to a critical thickness which increases from about 80 to above 200 nm by reducing the nominal growth temperature from 160 to 140 °C. Phase separation of the complete layer into tin‐rich surface protrusions and a Ge‐rich matrix takes place beyond the critical thickness. This surface roughening via phase separation was not observed in earlier investigations with lower Sn concentrations (<6%). Tin depletion in the GeSn matrix was confirmed by using energy‐dispersive X‐ray spectroscopy measurements showing residual Sn concentration below 5%. Additionally, creation of droplets with high concentration of tin on the surfaces was confirmed by energy‐dispersive X‐ray spectroscopy. Copyright © 2016 John Wiley & Sons, Ltd.     

In vitro corrosion behavior of electrodeposited calcium phosphate coatings on Ti6Al4V substrates

Calcium phosphate coatings on titanium alloy substrates are synthesized by pulsed electrodeposition and characterized by scanning electron microscopy associated to energy dispersive X-ray spectroscopy and by X-ray diffraction. The corrosion behavior of CaP/Ti6Al4V systems and uncoated Ti6Al4V are investigated using electrochemical methods in three physiological solutions and simulated with an equivalent circuit. The results reveal that the calcium phosphate coatings act as a protective layer especially when electrodeposition is carried out in the presence of hydrogen peroxide into the electrolyte which is used to control the chemical composition of the coatings and which implies a control of the corrosion behavior of the prosthetic material.     

Energy Dispersive X-Ray Fluorescence Analysis and X-Ray Microanalysis of Medieval Silver Coins

 Austrian medieval silver/copper coins were investigated at their surfaces by energy dispersive X-ray fluorescence analysis (EDXRF) and at the cross-sections by X-ray microanalysis in the scanning electron microscope (SEM/EDX) in order to estimate the error occurring when corroded objects of art and archaeology are analyzed on the surface by non-destructive methods. Additionally, Ag/Cu-standards were treated in diluted sulphuric acid and the depletion of copper on the surface was measured by EDXRF. By calculating the ratio of the Ag-K/Ag-L intensity the process of blanching could be studied.     

Effect of reduction treatment on copper modified activated carbons on NO(x) adsorption at room temperature

Activated carbon was impregnated with copper salt and then exposed to reductive environment using hydrazine hydrate or heat treatment under nitrogen at 925 °C. On the obtained samples, adsorption of NO(2) was carried out at dynamic conditions at ambient temperature. The adsorbents before and after exposure to nitrogen dioxide were characterized by X-ray diffraction (XRD), thermal analysis, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectroscopy (XPS), N(2)-sorption at -196 °C, and potentiometric titration. Copper loading improved the adsorption capacity of NO(2) as well as the retention of NO formed in the process of NO(2) reduction on the carbon surface. That improvement is linked to the presence of copper metal and its high dispersion on the surface. Even though both reduction methods lead to the reduction of copper, different reactions with the carbon surface take place. Heat treatment results in a significant percentage of metallic copper and a reduction of oxygen functional groups of the carbon matrix, whereas hydrazine, besides reduction of copper, leads to an incorporation of nitrogen. The results suggest that NO(2) mainly is converted to copper nitrates although the possibility to its reduction to N(2) is not ruled out. A high capacity on hydrazine treated samples is linked to the high dispersion of metallic copper on the surface of this carbon.     

Study of corrosion on copper strips by mixtures of mercaptans, sulphides and disulphides with elemental sulphur in the ASTM D-130 test by means of electron microscopy (SEM) and energy dispersive X-ray (EDX)

Summary The corrosivity of sulphur compounds present in petroleum products is measured by means of the ASTM D-130 copper strip test, which is based on discoloration of a standard copper strip immersed into the petroleum products at 50°C for 3 h. This paper studies the influence that mercaptans, sulphides or disulphides exert on corrosion produced by elemental sulphur in synthetic naphtha in the ASTM D-130 test by means of scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques. The synergistic effect of mercaptans on corrosion produced by elemental sulphur is an inverse function of the number of carbon atoms in linear mercaptans. For mercaptans with 6 carbon atoms corrosion activity follows the order: hexylmercaptan > cyclohexylmercaptan > thiophenol. In general, sulphides and disulphides decrease the corrosion produced by elemental sulphur. Among all the chemicals tested diphenyl disulphide is the best inhibitor of corrosion produced by elemental sulphur.     

Effect of biofilm on naval steel corrosion in natural seawater

The behaviour of steel in natural environments is not only dependent on material properties and environmental aggressiveness, but also on micro-organisms which can exist within it. The electrochemical evolution of the interface formed on BV-grade A naval steel exposed to natural seawater in the presence and absence of marine micro-organisms has been studied over 30?days. The results obtained by electrochemical techniques including linear polarisation and electrochemical impedance spectroscopy revealed that a heterogeneous layer formed by a mixture of corrosion products and biofilm grew on the material surface in natural seawater, producing an increase of the corrosion rate and then a decrease in the corrosion resistance under diffusion process. In this case, the protective layer formed by the corrosion products can be subject to the localised breakdown. In sterile seawater, the formation of two layers at the metal surface generated by organic and/or inorganic compounds deposits (outer layer) and corrosion products (inner layer) is concluded. Using our experimental data, electrical models are proposed. They describe the impedance distribution for carbon steel exposed to both environments. Scanning electron microscopy, energy dispersive X-ray spectrometry analysis and optic microscope reproductions were obtained. They allowed an interpretation of the effect of the marine biofilm on the behaviour of the carbon steel in seawater.