Linear sweep voltammetry: a cheap and powerful technique for the identification of the silver tarnish layer constituents

The potentialities of linear sweep voltammetry (LSV) for the characterization of the tarnish layer formed on pure and sterling silver samples exposed in the chapel and in the museum, at the Cathedral of Porto, in Portugal, are well demonstrated in this study. The technique allows the identification of the constituents of the thin tarnishing layers and also its relative abundance. A much more complex composition than the silver sulphide commonly associated with silver tarnish has been found, namely, silver chlorides, silver oxides and minor amounts of silver sulphide on the pure silver, plus copper oxides and a mixed copper–silver sulphide on the sterling silver samples. The tarnishing films were very thin mainly composed by silver chloride and silver oxides layers with estimated thicknesses ranging between 0.22 and 9.63 nm.     

Investigating the tarnish and corrosion mechanisms of Chinese gold coins

In order to investigate the gold coin's tarnish mechanism, the tarnish and corrosion mechanism on Chinese gold coins was investigated by optical microscopy (OM), scanning electron microscope energy dispersive spectrometry (SEM‐EDS), electron microprobe analysis (EMPA), XPS and X‐ray diffraction (XRD). The results indicated that the tarnish on the gold coin was caused by silver on its surface. The main component of the tarnish stain on the gold coin was silver sulfide and silver sulfate. The stain and the contamination originate from the polishing procedure, which accelerated the tarnish process. Two measures can be taken to prevent the gold coin's tarnish. First, the mintage of gold and silver coins should be separated and, second, a chemical cleaning procedure should be introduced. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

Investigation of copper patinas using ion beam analysis and scanning electron microscopy

Ion beam analysis (IBA) techniques were applied successfully to the investigation of non‐corroded and artificially corroded patina layers grown on copper substrates in order to explore their potential use in the study of degradation phenomena of copper and copper alloys subjected to chemical treatment and exposed to selected environmental conditions. Rutherford backscattering spectroscopy (RBS) with deuterons as projectiles and the nuclear reactions ¹⁶O(d,p)¹⁷O and ³²S(p,p′γ)³²S were applied to the investigation of the depth distribution of oxygen and sulphur in near‐surface layers of synthetic patina consisting of mineral phases corresponding to chalcanthite as well as to cuprite + chalcanthite and antlerite + brochantite + chalcanthite. Electrochemical techniques (potentiodynamic polarization and cyclic voltammetry in 0.5 M Na₂SO₄) were used for artificial acceleration and study of the corrosion processes, and scanning electron microscopy (SEM/EDS) was used for examination of the surface morphology of the samples. A patinated roof sample from the Vienna Hofburg also was investigated using the same techniques. The measurement showed that IBA can provide valuable information for the study of patina near‐surface layers of thickness up to a few micrometres and indicated that cuprite was the mineral phase primarily formed on the copper substrates and the main component of the interface between the patina layer and the metallic substrate. The investigated copper patinas looked rather heterogeneous and were characterized by high porosity. Mixed patinas exhibited considerable stability to further corrosive attack. Copyright © 2005 John Wiley & Sons, Ltd.     

Surface characteristics of titanium–silver alloys in artificial saliva

Titanium and its alloys are widely used in biomedical and dental fields because of their excellent corrosion resistance and biocompatibility. It is well known that titanium is protected from corrosion because of the stability of the passive film that controls and determines the corrosion resistance and biocompatibility of titanium and its alloys. The purpose of this study was to evaluate the electrochemical properties of titanium–silver alloys and the surface characteristics of passive film in artificial saliva. We designed titanium–silver alloys with silver contents ranging from 0 to 5 at.%, in 1% increments. These alloys were arc‐melted, homogenized, hot‐rolled to 2 mm thickness, and finally solution heat‐treated for 1 h and quenched. Potentiostatic testing was performed, and the open circuit potentials of the alloys were measured in artificial saliva, at 37 °C. The passive films of the titanium–silver alloys were analyzed via XPS. Titanium–silver alloys maintained low current density and showed stable passive region and also had high open circuit potential as compared with pure titanium. The open circuit potential of titanium–silver alloys increased as silver addition increased. With regard to the fraction of oxygen species, a component of over 80% was found to be comprised of oxide. Therefore, the titanium surface mainly consisted of titanium oxide and, on the titanium–silver alloys, this film was composed of TiO₂, Ti₂O₃, and TiO. As silver content increased, the TiO₂ fraction also increased, as did the thickness of the titanium oxide layer formed. Copyright © 2005 John Wiley & Sons, Ltd.     

Examination and analysis of Indian silver punch‐marked coins employing WD‐XRF and other noninvasive techniques

The archaeometallurgical analysis of ancient silver coins provides useful information regarding fabrication methodology, provenance, and trade route and explains large diversification in elementary composition, weight, and physical features. The present investigation deals with the chemical analysis and examination of the processing history of Indian punch‐marked silver coins dating to 400–200 bc . The chemical analysis was carried out by wavelength dispersive X‐ray fluorescence and X‐ray Diffraction (XRD). The microstructural examination was performed using field emission scanning electron microscope (FE‐SEM) and different phases were identified by Scanning Electron Microscopy coupled with Energy Dispersive X‐ray (SEM‐EDX) Spectroscopy. It was observed that all eight coins were manufactured with silver‐copper alloy. The ore used for obtaining silver was argentiferous galena, and cupellation was carried with perfection. The absence of slag inclusions as revealed by SEM examination indicated that coins (numbers 2, 4, 5, and 7) were cast from a molten state. The presence of Cu₂O, CuO, and Ag₂O on the surfaces of the coins was confirmed by XRD. The formed oxide layers provided protection and saved the coins from bulky corrosion products. The data reveal great divergence of coin surface from the composition of the core with the far better metallurgical process for refining of silver for this hoard.     

Plasma chemical synthesis. II. Effect of wall surface on the synthesis of ammonia

The plasma synthesis of ammonia was stuided at pressures of 1–5 torr and flow rates of up to 200 torr cm³ min^–1 using Pyrex and silver surfaces cooled to 77 K. The N conversion to ammonia was about 13% in experiments in which the afterglow was trapped on the Pyrex surface. By quenching the plasma rather than the afterglow, the percent N conversion could be doubled using the Pyrex surface and quadrupled using the silver surface. Increasing the hydrogen pressure and/or hydrogen discharge cleaning decreased the percent N conversion; nitrogen discharge conditioning had no significant effect. With increasing nitrogen flow rate the percent N conversion decreased linearly in the quenched plasma reaction on the silver surface, suggesting nitriding and reduction by hydrogen to form ammonia. The exponential decrease of the percent N conversion in the quenched afterglow reaction on the Pyrex surface is explained by the formation and/or dissociation of adsorbed N₂ determining the ammonia yield at 77 K.     

Atmospheric corrosion of copper and silver influenced by particulate matter

The atmospheric corrosion of copper and silver influenced by graphite and alumina as particulate matter (PM) in an environment containing 200 μg m^?3 SO₂ + 150 μg m^?3 NO₂ at 85% RH and 25 °C was analyzed. Different proportions of PM mixture conditions were used, and the corrosion rate was followed using gravimetric analysis. Results of linear sweep voltammetry (LSV) and coulometric reduction (CR) indicated that larger corrosion rates were obtained in the presence of deposited PM. Under present exposure conditions, copper corrosion rate was larger than silver corrosion rate. X-ray diffraction (XRD) shows the presence of cuprite (Cu₂O) and brochantite (Cu₄SO₄(OH)₆) in the case of copper and achantite (Ag₂S) in the case of silver.     

Enhanced Carbon Dioxide Electroreduction to Carbon Monoxide over Defect‐Rich Plasma‐Activated Silver Catalysts

Efficient, stable catalysts with high selectivity for a single product are essential if electroreduction of CO₂ is to become a viable route to the synthesis of industrial feedstocks and fuels. A plasma oxidation pre‐treatment of silver foil enhances the number of low‐coordinated catalytically active sites, which dramatically lowers the overpotential and increases the activity of CO₂ electroreduction to CO. At −0.6 V versus RHE more than 90 % Faradaic efficiency towards CO was achieved on a pre‐oxidized silver foil. While transmission electron microscopy (TEM) and operando X‐ray absorption spectroscopy showed that oxygen species can survive in the bulk of the catalyst during the reaction, quasi in situ X‐ray photoelectron spectroscopy showed that the surface is metallic under reaction conditions. DFT calculations reveal that the defect‐rich surface of the plasma‐oxidized silver foils in the presence of local electric fields drastically decrease the overpotential of CO₂ electroreduction.     

Novel use of glow discharge optical emission spectroscopy (GDOES) to study corrosion of AA2024‐T3 in the presence and absence of inhibitors – part 3: investigating the effects of various proportions of inhibitor in the coating matrix or in nanocontainers

Elemental depth profiling by glow discharge optical emission spectroscopy has been used to characterize the corrosion products on AA2024‐T3. In previous work, the aluminium, oxygen and copper depth profiles were shown to provide information regarding surface roughening, the thickness of corroded layers and extent of copper de‐alloying/relocation. Nitrogen, sulfur, phosphorus and chromium depth profiles were examined in the hope of detecting inhibitor species within the corroded/altered layers after 5 h of exposure to a corrosive solution. In the present work, the study is extended to longer exposure time. The work presents a further study of the leaching of benzotriazole from the coating matrix or from nanocontainers during various times of exposure to a corrosive environment. Copyright © 2016 John Wiley & Sons, Ltd.     

In situ investigations of the interaction of small inorganic acidifying molecules in humidified air with polycrystalline metal surfaces by means of TM‐AFM,IRRAS, and QCM

Initial atmospheric corrosion of copper, silver, and iron induced by humidity and oxidizing agents was studied in situ by three highly surface‐sensitive and complementary techniques: infrared reflection‐absorption spectroscopy (IRRAS), quartz crystal microbalance (QCM), and tapping‐mode atomic force microscopy (TM‐AFM). These techniques deliver information about the change of the topography of the sample surfaces with emphasis on the shape and lateral distribution of the corrosion products grown within the first 1300–2800 min of weathering (TM‐AFM), as well as chemical (IRRAS) and kinetic (QCM) data. A completely different mechanism of the initial stages of atmospheric corrosion of the three investigated metals could be observed. A uniform growth of corrosion products was seen on the copper surface (identified by IRRAS and XPS to be cuprite‐like) during exposure to synthetic air with 80% relative humidity (RH), whereas the iron surface remained unattacked. The investigations of the silver surface exposed to humidity revealed that silver is attacked by humidity and tends to form oxide and hydroxide surface species. While an increased humidity content of the surrounding atmosphere causes higher corrosion rates on copper, on the exposed silver sample only a change in the degradation mechanism could be observed. The addition of SO₂ to the humidified air causes the growth of so‐called ‘second‐order’ features on copper, identified to be CuSO₃ · xH₂O‐like, which reveals the formation of a new chemical species on the investigated surface. These features are placed on top of the homogeneous formed oxide layer and tend to form well‐defined islands. In contrast to copper, on a silver surface exposed to humidity and SO₂ no new chemical species are formed; nevertheless an increased corrosion rate could be observed owing to a change of the chemistry in the physisorbed water layer. Iron exposed to humidity and SO₂ still remains unattacked. An iron surface is attacked only if exposed to humidity and SO₂ and NO₂, which show a synergistic effect by the oxidation of four‐valent sulfur‐oxygen species by NO₂. Such an attack leads to the formation of pitting corrosion, which was observed in situ and time‐resolved. The pits mainly occur on predamaged surface structures, such as scratches caused from the polishing process of the samples, and therefore promote the initiation of the corrosion. The results obtained demonstrate the high potential of the surface‐sensitive methods applied for investigating the early stages of corrosion of different metals and for obtaining a better understanding of the molecular mechanisms during degradation. Copyright © 2007 John Wiley & Sons, Ltd.     

Use of portable X-ray fluorescence instrument for bulk alloy analysis on low corroded indoor bronzes

One of the most often used non-destructive methods for elemental analysis when performing field measurements on bronze sculptures is X-ray fluorescence (XRF) analysis based on portable instrumentation. However, when performing routine in-situ XRF analysis on corroded objects obtained results are sometimes considerably influenced by the corrosion surface products.In this work the suitability of portable XRF for bulk analysis of low corroded bronzes, which were initially precisely characterized using sophisticated and reliable laboratory methods, was investigated and some improvements in measuring technique and data processing were given. Artificially corroded bronze samples were analyzed by a portable XRF instrument using the same methodology and procedures as when performing in-situ analysis on real objects. The samples were first investigated using sophisticated complementary laboratory techniques: Scanning Electron Microscopy, Proton-Induced X-ray Emission Spectroscopy and Rutherford Backscattering Spectrometry, in order to gain precise information on the formation of the corrosion product layers and in-depth elemental profile of corrosion layers for different aging parameters. It has been shown that for corrosion layers of up to ca. 25 μm a portable XRF can yield very accurate quantification results.     

Surface enhanced Raman spectroscopic studies on 1H-1,2,4-triazole adsorbed on silver colloidal nanoparticles

1H-1,2,4-triazole is a very effective corrosion inhibitor for copper. The adsorption of this compound on silver colloidal nanoparticles has been studied by means of surface enhanced Raman scattering (SERS). SERS data are interpreted with the help of DFT calculations of models of the surface complex formed by 1H-1,2,4-triazole on the silver colloidal nanoparticles surface. It was found that this compound is adsorbed on metal surface in its anionic form and that it interacts with silver through the N₁ and N₂ atoms. The molecular plane assumes a tilted orientation with respect to the silver surface.     

TOF-SIMS investigations on weathered silver surfaces

Silver-coated quartz crystal microbalance (QCM) disks were treated under different environmental conditions (including changes in parameters such as relative humidity (%RH) and SO₂/H₂S content) in atmospheres of synthetic air and pure N₂ for 24 h in a weathering chamber. The corroded surfaces were subjected to depth profiling by a time of flight (TOF) secondary ion mass spectrometry (SIMS) instrument, equipped with a Bi⁺ analysis gun and Cs⁺ sputter gun. The evaluation of the in-depth distribution of several elements and species provides evidence for the formation of a corrosion layer containing Ag₂SO₃, even in the absence of oxidizing agents, such as H₂O₂ or NO₂. Furthermore it could be elucidated that the thickness of the formed Ag₂SO₃ layer does not depend on the SO₂ concentration but rather on the humidity and oxygen content of the ambient atmosphere. In weathering experiments in atmospheres composed of synthetic air, humidity, and H₂S, the presence of different oxygen species (surface and bulk) and silver sulfide could be detected by TOF-SIMS depth profiling experiments. The obtained results for both acidifying gases are in good correlation with the corresponding tapping mode atomic force microscopy (TM-AFM) investigations and in situ QCM measurements.     

Spectroscopic study of decontaminated corroded carbon steel surfaces

Removal of uranium from contaminated carbon steel surfaces by chelation with hydroxycarboxylic acid has been tested as a cleaning process for decommissioning and decontaminating contaminated surfaces. Comparison of contaminated surfaces prior to decontamination with subsequently cleaned surfaces was done in order to study the effectiveness of this cleaning technique. This was accomplished using various spectroscopic techniques, including x‐ray photoelectron spectroscopy, synchrotron infrared microspectroscopy, Rutherford backscattering spectroscopy and scanning electron microscopy/energy‐dispersive spectroscopy. Mild carbon steel (1010) coupons were exposed to uranyl nitrate solution, which led to the formation of a lightly corroded surface. Some contaminated samples underwent further cyclic humidity treatment, during which additional corrosion took place. In this study, it was found that a citric acid–hydrogen peroxide–citric acid cleaning method successfully removed uranium in lightly corroded areas. However, the method but incompletely decontaminated some heavily corroded areas where more highly crystallized corrosion products are found or where complex surface structure can occlude contaminants. Use of complementary analytical techniques is essential to provide an accurate model of surface chemistry before and after decontamination. Copyright © 2004 John Wiley & Sons, Ltd.     

Electroless deposition of silver on poly(3, 4-ethylenedioxythiophene): role of the organic ions used in the course of electrochemical synthesis

The electroless deposition of silver is studied on poly(3, 4-ethylenedioxythiophene) (PEDOT) layers synthesized in the presence of excess of perchlorate ions with and without the addition of two organic dopants: dodecylsulfate (DDS) or polystyrenesulfonate (PSS). Silver deposition is carried out at the expense of oxidation of the pre-reduced PEDOT layers using either Ag⁺ cation or [AgEDTA]^3? complex anion solutions. The amount of deposited silver is monitored by voltammetric stripping. The type of the metal deposit is imaged by SEM. It is found that there are marked differences between the three types of PEDOT with respect to the amount of deposited silver and size distribution of the metallic species. In both silver plating solutions, the largest amount of silver is deposited on PEDOT/DDS, followed by PEDOT/PSS and PEDOT/ClO₄ ^?. These results are discussed in the context of possible structural difference of the three types of PEDOT layers. The comparison between the silver deposits obtained in the two silver plating solutions shows finer dispersion and larger amount of the metallic phase obtained in the presence of the silver complex anions. This solution presents a better opportunity to obtain homogeneous distribution of silver crystalline species on the PEDOT surface.     

Synthesis of silver (II) oxide by oxidation of silver or silver oxide by means of ozone

The oxidation by ozone of a suspension of silver or silver oxide in an aqueous solution of sodium hydroxide is described. It has been shown that the oxidation proceeds in two steps:Ag^O₃→Ag₂O^O₃→AgO.The experimental results are in good agreement with a mechanism of dissolution and precipitation. The silver (II) oxide obtained has remarkable properties of stability in alkaline solution and of reducibility to metallic silver. These special properties are probably due to the large size of the particles.     

Paramagnetic behaviour of silver nanoparticles generated by decomposition of silver oxalate

Silver oxalate Ag₂C₂O₄, was already proposed for soldering applications, due to the formation when it is decomposed by a heat treatment, of highly sinterable silver nanoparticles. When slowly decomposed at low temperature (125 °C), the oxalate leads however to silver nanoparticles isolated from each other. As soon as these nanoparticles are formed, the magnetic susceptibility at room temperature increases from −3.14 10⁻⁷ emu.Oe⁻¹.g⁻¹ (silver oxalate) up to −1.92 10⁻⁷ emu.Oe⁻¹.g⁻¹ (metallic silver). At the end of the oxalate decomposition, the conventional diamagnetic behaviour of bulk silver, is observed from room temperature to 80 K. A diamagnetic-paramagnetic transition is however revealed below 80 K leading at 2 K, to silver nanoparticles with a positive magnetic susceptibility. This original behaviour, compared to the one of bulk silver, can be ascribed to the nanometric size of the metallic particles.     

Nitride layers on uranium surfaces

Uranium as an important energy material plays a significant role within the field of material sciences and nuclear industrial applications. However, metallic uranium is chemically active in ambient environment and is easily oxidized and corroded, leading to not only deterioration of its properties and failure of performance as working components but also nuclear pollution of the environment. Therefore, the development of corrosion protection systems for metallic uranium is an issue of prime importance. In view of the nitridation technology in Ti and Fe-based alloys, the successful application to improve the surface wear hardness and corrosion resistance, several nitridation methods have been developed for the surface modification of metallic uranium. Many studies have shown that the surface nitridation of metallic uranium can efficiently improve its corrosion resistance. The surface oxidation layer thickness is as thin as several nanometers even if placed 4?years in the atmosphere. At the present, nitridation of uranium surface is considered as the most promising surface modification way to protect uranium from corrosion. To design and fabricate nitride layers on uranium surface with reliable long-term protective effects, however, one needs deep understanding on the relationships among the physical and chemical properties of the nitride layers, the composition and structure of the layers, and the dependence on the techniques and the processing parameters. One also needs deep understanding on the corrosion behavior of the prepared nitride layers in the environment, and the related corrosion mechanism.In this review, we bring to the readers the achievements and recent advances on the uranium nitridation in the world, including the processing techniques and the related studies on the formation mechanism of the nitride layers, and the understanding on the property-processing-corrosion performance relationship of the layers, aiming at the development of high-performance resistance layers for metallic uranium by the surface nitridation technique. In the review (1) the surface nitridation techniques developed recently, the relationship between the preparation parameters and the composition as well as the structure of the surface layer are summarized; (2) the fundamental physical properties of the uranium nitrides are summarized, depicted and discussed; (3) the influence of the nitrides structure and composition and of the environment on resistance to corrosion as well as the formation mechanism of corroded products in oxidizing environments are depicted and discussed; (4) the potential application of uranium nitrides in other application field such as the application of thermal-electrical conversion is also discussed. Finally, the prospective on the investigations of nitride layers is suggested.     

Ag2Cu2O3: The First Silver Copper Oxide

An efficient low‐temperature route provides the first mixed oxide of silver and copper. Ag₂Cu₂O₃ represents an important precedent in the search for silver‐containing superconductors. It has an open structure with three‐dimensional tunnels displaying square‐planar CuO₄ units, linerly coordinated silver ions, and vacant oxygen sites (see picture; Ag, Cu, and O are represented by white, large black, and small black spheres, respectively). The last feature allows for a rich solid‐state redox chemistry.