Tarnish Layer Research Articles

Effectiveness of three auxiliary irrigation methods for cleaning the internal walls of root canals of curved isolated teeth.

This study aimed to compare the effectiveness of ultrasound and acoustic and laser cleaning of curved root canals. A total of 92 molars with independent root canals with a curvature of 20°-40° were prepared and standardized at 04 25# and stained with gentian violet solution for 72 h. Among them, 52 were randomly divi-ded into four groups for final rinsing (n=13): NI group, PUI group, EDDY group, and PIPS group. Ten samples in each group were cut horizontally along the long axis perpendicular to the root and divided into curved upper, curved, and apical segments. Images were taken with a stereomicroscope and Image J measurements were taken to calculate the depth of rinse penetration. The remaining three samples from each group were split along the long axis of the dentin, photographed by scanning electron microscope to record the dentin tubule exposure and staining layer, and scored for staining layer by double-blind method. SPSS 26.0 software was used to perform statistical analysis and select the best flushing method. An extra 40 samples were randomly divided into four groups for detection of flushing fluid penetration depth (n=10): 10, 20, 30, and 40 s. In the upper part, the mean depth of infiltration was not significantly different between the experimental and control groups (P>0.05). The PIPS group had a significantly lower smear layer score than the control group and the EDDY group (P<0.01). In the curved segment, the mean depth of infiltration was significantly greater in the PUI group than in the control group (P<0.05); the tarnish layer score was lower in each experimental group than in the control group. At the top, the mean depth of infiltration was greater in the PUI and PIPS groups than in the control group (P<0.05), and the smear layer score was lower in the PIPS group than in the other groups (P<0.05). After the time was changed, the depth of infiltration of PUI increased only in the apical segment as the flushing time increased. The PUI and PIPS methods facilitate the penetration of irrigation solution into the dentin canal in curved root canals, especially in the apical segment. The PIPS technique is effective in removing the smear layer in curved root canals.

Selective Electrochemical Treatment of Naturally Aged Silver Alloy Artefacts

ABSTRACT Conservation interventions on silver tarnish and corrosion layers include mechanical, chemical, and electrolytic techniques. Electrolytic reduction is still disputed among metal conservators. The prevailing conviction with many is that mechanical cleaning methods are more likely to maintain control over the result than electrochemical methods. A survey on this subject undertaken in Germany and Austria suggested that this may be due to the traditional approaches of academic education. An electrolytic pencil was further developed and has been applied on naturally aged silver artefacts of the nineteenth and twentieth centuries. The influence of the electrochemical potential difference between artefact and counter electrode as well as of the tip diaphragm material was evaluated. A minimized material loss and a good controllability of conservation interventions on silver alloys were demonstrated.

Erratum to the Influence of Gaseous Pollutants on Silver Artifacts Tarnishing, Vol. 6 (2017), 135-148

The original online version of this article Salem, Y. (2017) The Influence of Gaseous Pollutants on Silver Artifacts Tarnishing. Open Journal of Air Pollution, 6, 135-148. doi: 10.4236/ojap.2017.64011 unfortunately contains grammar mistakes. The author wishes to correct the errors. The present work investigated the effect of common gaseous pollutants on silver artifacts. The study was carried out on coupons made of a silver alloy (91 silver and 9% copper) with chemical composition similar to ancient Egyptian silver artifacts. These coupons were exposed to gaseous pollutants such as sulfur dioxide, nitrogen dioxide, carbon dioxide, hydrogen sulfide and chlorine, each gas separately. The exposure period was four weeks inside a climate chamber with 10 PPM concentration of each gas. After each test, examinations by SEM and PM were used to evaluate the effect of each gas and observe the formed tarnish layers. The results revealed that all gases reacted with the surface except carbon dioxide. The formed tarnish layers varied in coverage and density rate, and the heaviest layer was of H2S coupons. The tested coupons were analyzed by XRD and the results revealed Ag2S, AgCl, Ag2SO4, Ag(NO3)3(NO)3, AgO and Ag2O as corrosion products.

The Cleaning of Silver Objects With a Basic Solution of Sodium Glycinate: A Study on Artificially and Naturally Tarnished Silver

ABSTRACT The appearance of silver objects deteriorates due to the formation of a brown-to-black tarnish layer. Several methods are available for removing these tarnished layers, ranging from polishing through chemical cleaning to electrochemical methods. This study presents a low-cost and low-toxicity method that uses sodium glycinate to clean silver. Cleaning tests were performed on both artificially tarnished prototypes and naturally tarnished objects after characterizing them; scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX) were used to characterize the artificially tarnished prototypes, and X-ray fluorescence (XRF) was used to characterize the naturally tarnished objects. The aggressiveness of the baths was analyzed by measuring the leached amount obtained through atomic absorption spectroscopy (AAS) and SEM. The procedures used for cleaning the artificially tarnished prototypes served as a guide for cleaning two naturally tarnished objects: a halo and a crown. Cleaning was guided by the presented method’s characteristics as well as the object’s unique characteristics and condition.

How effective are reducing plasma afterglows at atmospheric pressure in removing sulphide layers: Application on tarnished silver, sterling silver and copper

A plasma afterglow from a gas mixture of 5 vol% H2 in He is able to remove tarnish layers on pure silver in a matter of seconds. This dry, localized, and noncontact cleaning technique is a promising method to clean historical objects where silver is combined with organic materials and where traditional cleaning techniques are not recommended. However, historical objects are often manufactured with silver alloys but somehow their tarnish layers are removed less effectively with plasma treatments. To understand the different impact of the afterglow, the surfaces of corroded silver, sterling silver, and copper coupons are characterized before and after plasma treatment by a multianalytical approach combing optical and confocal microscopy, scanning electron microscopy coupled to energy dispersive X‐ray analysis and chronopotentiometry. The analyses demonstrate that the few hundred nanometre‐thick tarnish layer on pure silver is transformed through the whole thickness resulting in a porous metallic film. On top of that metallic film, some isolated remnant Ag2S particles are found. For sterling silver, a yellowing of the surface occurs. The Ag‐rich corrosion products are reduced to a large extent, while the Cu‐rich corrosion products are only partially reduced. For corroded copper, no apparent visual change is observed at a macroscopic scale, although the morphology of the surface changed. The results allow an evaluation of the cleaning efficiency and provide a deeper understanding of hydrogen plasma effects on the transformation of sulphide corrosion layers at atmospheric pressure.

Tribo‐electrochemical study of stainless steel surfaces during chemical–mechanical polishing

AbstractChemical–mechanical polishing combines the synergistic effect of chemical etching and mechanical abrasion to achieve surface planarisation. These effects are discussed in this paper based on a tribocorrosion study of stainless steel (SS) immersed in two different acidic polishing slurries containing iron oxide nanoparticles. The effect of slurry chemistry and contact area on depassivation–repassivation phenomena are investigated and discussed. In case of the point‐contact geometry it was found that high friction and wear caused by formation of third body particles in the contact contributed to slow repassivation time of the SS, and wear accelerated corrosion was the dominant mechanism under these conditions. An increase in the contact area caused a removal of oxides from a larger surface area, leading to much slower repassivation rates and the appearance of a tarnish layer on the SS immersed in a slurry with high acid content. Surface chemistry investigations revealed an enrichment of chromium oxide. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Protecting silver cultural heritage objects with atomic layer deposited corrosion barriers

Silver, prized throughout history for its luster and shine, develops a black Ag2S tarnish layer that is aesthetically displeasing when exposed to atmospheric pollutants. Tarnishing, and subsequent polishing, leads to irreversible material loss and object damage. Currently, nitrocellulose coatings are often used to prevent silver from tarnishing, however non-uniform coatings and degradation over time limit their effectiveness. Atomic layer deposition (ALD) has been explored as a new method for creating dense, uniform, and conformal coatings on 3-dimensional (3D) objects that are more effective than nitrocellulose in preventing silver from tarnishing. To create high quality ALD coatings on 3D objects, slowing down the ALD process is critical to ensure proper precursor exposure. Non-ideal deposition of organo-oxy-metallic compounds can occur with fast deposition rates that do not allow sufficient flow around 3D objects. The coatings can be removed by dissolving the Al2O3 ALD films in aqueous NaOH. Thicker ALD films prevent defects from occurring on non-ideal surfaces and effectively prevent silver objects from tarnishing under ambient aging conditions. Thick ALD films, deposited with sufficiently long precursor pulse and purge times, may be effective in preventing complex, 3D non-mixed media silver cultural heritage objects from tarnishing.

On the Behavior of Surface Plasmons at a Metallo-Dielectric Interface

In an attempt to shed additional light on the extraordinary transmission of an electromagnetic wave through a subwavelength aperture, we undertake a more detailed analysis of the canonical problem of the magnetic field of a line source located at a silver-dielectric interface at optical wavelengths. In particular, we present a closed-form asymptotic evaluation of the branch cut integral and show that the branch cut term initially decays as x <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1/2</sup> , where x is the distance between the source and the field point along the interface, but for larger distances, it falls off more rapidly as x <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3/2</sup> . We also address the effect on a surface plasmon of a tarnished silver substrate. Our analysis supports the extraordinary transmission surface plasmon electromagnetic interaction model, explains the origin of the so-called “creeping wave,” and shows that the tarnish layer has a significant damping effect on the surface plasmon polariton.

Electrochemical study of the tarnish layer of silver deposited on glass

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the tarnished thin layer of silver deposited on glass. Instead of natural tarnishing in air environment, an acceleration of tarnishing process was realized by immersion of Ag covered glass in 10μMK2S medium. The X-ray photoelectron spectroscopy (XPS) shows that tarnishing product formed on the silver surface consisted of Ag2S and Ag2O. As electrochemical characterization, the measurements were carried out in aerated 0.5M Na2SO4 solution adjusted at pH 10. The impedance spectra collected in sulphate medium at the open-circuit potential show one capacitive loop in parallel with a high resistance, which reflects a blocking electrode behaviour. However, the equivalent electrical circuit, Rs-(CPE//R) is insufficient to reproduce the experimental results correctly. To minimize the dispersion between the experimental and fitted data, the CPE contribution is replaced by two normal power-law distributions of the local resistivity to interpret the tarnishing process in K2S medium with respect to the immersion time. These distributions are associated with the Ag2S and Ag2O layers.

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.

Reduction of silver tarnishing and protection against subsequent corrosion

The kinetics of tarnishing formation was examined on a polished silver dipped in a 10 mM Na 2S. The recovery of an initial bright surface was then obtained by cathodic reduction of the tarnish layer in a 5% sesqui-carbonate solution. Two protection methods to prevent a further formation of a dark deposit were tested: an electrodeposited poly(amino-triazole) film and the surface treatment in hexadecane-thiol. The protection by poly(amino-triazole) is not reliable for all nuances of silver. In contrast, the film formed with hexadecane-thiol showed satisfactory properties. The formations of tarnish and protective films were examined by electrochemical methods, the reflectance measurements, and the quartz crystal microbalance.

Tarnish protection of silver jewels by plasmapolymer coatings

The major problem of silver and silver coatings is the tendency to get a tarnish layer with sulphuric compounds out of the air on the surface. The previous methods to protect the silver has several disadvantages. The plasmapolymer coating system developed by the Fraunhofer Institute (IFAM) in Bremen works without these disadvantages. This system was checked under production conditions for silver jewellery. The results compared with the previous state of the art were excellent. Therefore, the plasmapolymer coating is a suitable tarnish protection process for silver jewels.

Laser characterization and cleaning of 19th century daguerreotypes II

Recently, we have made tremendous progress in the spectroscopic analysis and laser restoration of tarnished daguerreotypes. Laser induced breakdown spectroscopy (LIBS) has been applied for the first time to both modern and 150-year-old daguerreotypes. In addition to surface and depth profiling, the analysis of colors on “tinted” samples allowed identification of the pigment. These results complement the previous analysis by laser ionization mass spectrometry of the surface composition of clean and tarnished examples of the old photographs. Laser ablation cleaning of the submicrometer tarnish layers has now been clearly demonstrated on numerous daguerreotypes with various extents and types of tarnish. The use of computer controlled XY translation and stable laser beam quality have allowed decisive proof-of-principle examples of laser restoration. The best parameters of laser wavelength, power and pulse duration have been determined. Using digital files of daguerreotype images, straightforward models have been developed that allow for the digital mapping of the surface tarnish. In principle, such maps could guide the computer control of the laser cleaning process.

Application of SIMS to silver tarnish at the British Museum

The tarnishing of silver in a museum environment is a perennial problem. Silver reacts with atmospheric gases generating a thin disfiguring surface layer. In order to elucidate the nature of the tarnish layer formed in showcase environments in the British Museum, a number of silver coupons were exposed in different situations inside showcases. SIMS analysis with the Millbrook Chemical Microscope has identified a number of compounds within the tarnish layers. It has indicated a much more complex composition than the silver sulphide commonly associated with silver tarnish.

X-Ray Photoelectron Spectroscopy Study on the Chemical Composition of Copper Tarnish Products Formed at Low Humidities

This work studies the chemical composition of copper tarnish products formed at 40, 60, and 80% relative humidity (RH) in an uncontaminated environment, for 21 days experimentation at 30°C. The experimental method used was X-ray photoelectron spectroscopy (XPS) in conjunction with -ion sputtering. The main compounds found were cuprite and copper hydroxide Differences were observed between 40, 60, and 80% RH. Copper specimens exposed to 40% RH show the thickest tarnish layers, while the thinnest correspond to the 80% RH specimens. The tarnish layer of the copper specimen exposed to 80% RH is constituted mainly by copper hydroxide. For the 40 and 60% RH copper specimens the tarnish layer is a mixture of copper hydroxide and cuprite. © 2000 The Electrochemical Society. All rights reserved.

Artificial Neural Network and Fuzzy Clustering - New Tools for Evaluation of Depth Profile Data?

Depth profiling has been performed by using Auger electron spectrometry (AES) and X-ray photoelectron spectrometry (XPS) in combination with Ar-ion sputtering. The data obtained by both surface-analytical methods have been evaluated by means of factor analysis and afterwards by applying an artificial neural network or fuzzy clustering in order to determine the compositional layering of different samples such as a Cr2O3/CrN sandwich layer, tarnish layers on a nickel based alloy and on steel, and the coating of a Si3N4 ceramic powder. The applied artificial neural network was a Kohonen network. It turned out that the method of fuzzy c-means clustering was more successful than Kohonen network due to the fact that fuzzy c-means clustering starts with more input information which can be obtained from factor analysis.

Examinations on the morphology of tarnish layers grown on stainless 18-10 chromium nickel steels

18-10 chromium nickel steels are generally valid as well weldable. However, during thermal joining oxides are formed in the heat affected zone, whose structure and composition essentially differs from the morphology of passive layers. The steel qualities X6 CrNiTi 18-10 (materials no. 1.4541) and X5 CrNiMoTi 17-12-2 (materials no. 1.4571) were examined on their tarnish growing behaviour by means of XPS/sputtering, transmission electron microscopy and atomic force microscopy. Information on the pitting corrosion resistance of annealed metal sheets was received by ageing them in iron chloride solution and by measuring the current density-potential curves under quasi-stationary conditions in artificial sea water.

Cleaning of daguerreotypes with an excimer laser

The cleaning of daguerreotypes is a process that must remove tarnish layers and debris without altering the optical properties of the daguerreotype. This means that (1) the polished silver layer substrate must not be etched or pitted and (2) the image particles must not be altered or damaged. Electro cleaning is the only known method of cleaning gilded daguerreotypes; however, it is not suitable for the treatlnent of ungilded and coloured daguerreotypes. This article describes a new laser method for cleaning daguerreotypes. A model is developed for the cleaning process and testing procedures are discussed. This method permits (1) the cleaning of gilded and ungilded plates, (2) local treatment and (3) removal of tarnish without immersion in solvents and chemicals.

Surface analytical examinations of welded nickel alloys by XPS, SNMS and SEM/EDX

Tarnish layers are formed in the heat affected zone during the welding of steels and nickel based alloys. They commonly consist of oxides of the alloying elements. The corrosion behaviour of welded components is generally influenced by the thickness and composition of the oxide films. In the following the corrosion behaviour of annealed samples cut from NiMo28 and NiMo16Cr16Ti is investigated, correlating XPS, SNMS and SEM/EDX data to their pitting corrosion potentials.

Composition of Copper Tarnish Products Formed in Moist Air with Trace Levels of Pollutant Gas: Hydrogen Sulfide and Sulfur Dioxide/Hydrogen Sulfide

The objective of the work reported here was to characterize the tarnish products formed on copper during the early stages of exposure to moist air with trace levels of pollutant gas, in particular hydrogen sulfide and sulfur dioxide/hydrogen sulfide. As determined by x‐ray photoelectron spectroscopy and coulometric reduction (chronopotentiometry), the exposure of copper to 50 ppb hydrogen sulfide at 23°C and 70% relative humidity was found to produce a tarnish layer consisting of and . Addition of 75 ppb sulfur dioxide to a 50 ppb hydrogen sulfide, moist air environment at 23°C and 70% relative humidity encouraged the growth of a thicker tarnish product layer, with proportionally more in the structure.