[Show abstract][Hide abstract] ABSTRACT: This paper concerns a time lapse spectroelectrochemical study of the growth of lead dodecanoate layers on a lead substrate in an aqueous solution using cyclic voltammetry. In-situ synchrotron radiation X-ray diffraction measurements were carried out on station BM26A (DUBBLE) at the European Synchrotron Radiation Facility (ESRF) in France. The diffraction pattern images were taken using a two-dimensional Mar CCD camera. After deposition of the coating, a spectroelectrochemical study of a linear sweep voltammetry experiment using an acetic acid electrolyte, simulating ‘active’ lead corrosion, was carried out on both a bare and lead dodecanoate coated sample. The results show that the coating inhibits the formation of new lead corrosion products.
[Show abstract][Hide abstract] ABSTRACT: Several heritage systems have been studied using state-of-the-art synchrotron techniques. The cultural heritage value of silver is documented in museum collections across the globe. However, the silver surface is not as chemically stable as that of other precious metals, and is susceptible to corrosion by atmospheric gases. It is therefore of special interest to clarify these surface reactions by using in-situ, time-lapse chemical and structural analysis in controlled ambients in order to develop strategies to reduce or even prevent the atmospheric attacks. In order to study the initial corrosion processes of silver in the presence of corrosive gases in-situ time-lapse X-ray diffraction experiments were performed on the XMaS beamline at the European Synchrotron Radiation Facility, Grenoble. Highly pure silver samples were weathered with synthetic air containing 500 ppb of both H2S and ozone, at relative humidity (RH) levels, and XRD patterns were tracked every 10 min over a total weathering time of 24h. The time-lapse Synchrotron Radiation (SR)-XRD data show that pure silver exposed to those atmospheres starts to form crystalline corrosion products after only 10 minutes. Silver sulfates, silver oxides, intermediates and mixed species are formed on the sample surface over the duration of the experiment. The data collected using a newly combined environmental cell/gas flow set up introduces a set of highly useful tools for scientists who wish to study time-lapse gaseous corrosion at ambient temperature and pressure.
Journal of Analytical Atomic Spectrometry 01/2015; · 3.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Figure: Cyclic voltammograms of GCEs in 0.5 M H2SO4 at 5 mV/s in N2: i) pristine and ii) modified with poly(PdTAPc). The polymeric palladium tetraaminephthalocyanine has been prepared by electropolymerization. The polymer is characterized and showed very good supercapacitance behavior in 0.5 M H2SO4.
Dyes and Pigments 01/2015; 112:192–200. · 3.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The hydrolysis of nantokite to form cuprite could be a reaction step in the progression of bronze disease on cupreous objects d'art. In this paper, this transformation is visualized for the first time using a time-resolved synchrotron X-ray diffraction experiment. Complete conversion of nantokite to cuprite was observed on a nantokite patina over 5 h in water using time-resolved synchrotron X-ray diffraction.
[Show abstract][Hide abstract] ABSTRACT: The application of a modular system for the non-destructive chemical imaging of metal and other surfaces is described using heritage metals as an example. The custom-built X-ray-excited optical luminescence (XEOL) microscope, XEOM 1, images the chemical state and short-range atomic order of the top 200 nm of both amorphous and crystalline surfaces. A broad X-ray beam is used to illuminate large areas (up to 4 mm²) of the sample, and the resulting XEOL emission is collected simultaneously for each pixel by a charge-coupled device (CCD) sensor to form an image. The input X-ray energy is incremented across a range typical for XANES and an image collected for each increment. The use of large-footprint beams combined with parallel detection allows the power density, to be kept low and facilitates complete non-destructive XANES mapping on a reasonable timescale. In this study the microscope was evaluated by imaging copper surfaces with well-defined patterns of different corrosion products (cuprite Cu2O and nantokite CuCl). The images obtained show chemical contrast, and filtering the XEOL light allowed different corrosion products to be imaged separately. Absorption spectra extracted from software selected regions of interest exhibit characteristic XANES fingerprint spectra for the compounds present. Moreover, when the X-ray absorption edge positions were extracted from each spectrum an oxidation state map of the sample could be compiled. The results show that this method allows one to obtain non-destructive and non-invasive information at the micron-scale whilst using full-field imaging.
[Show abstract][Hide abstract] ABSTRACT: Objective
To assess the site-specific corrosive behaviour of the frameless IUD following long-term exposure to the uterine environment.
A qualitative and morphological study using X-ray diffraction (XRD) and scanning electron microscopy (SEM).
Three GyneFix® IUDs which were in site up to 150 months were examined. In utero corroded copper sleeves were divided into 10 different groups based on their shape (U or O), orientation (inside or outside) and in utero residence time. X-ray diffraction indicated the presence of solely cuprite (Cu2O) as corrosion product on both the inside and the outside of the copper sleeves, regardless of their shape. These results were confirmed by backscattered electron micrographs recorded on the inside, the outside and the cross-section of the IUD sleeve. SEM results suggest that shape and orientation slightly affect the corrosion rate.
The apparent copper loss from both sides of GyneFix copper tubes proves that both sides are a potential copper source and therefore justifies the design of GyneFix IUD. This could be beneficial for women as the IUD could be reduced in size and therefore better tolerated. The impact on bleeding could also be minimized.
[Show abstract][Hide abstract] ABSTRACT: Background: Ethanolic solutions of long-chain carboxylic acids can be applied to lead metal substrates to form a coating of lead carboxylate which provides protection against atmospheric pollutants. Results and conclusions: In this paper we describe the optimal inhibitor concentration for the coating on lead. Electrochemical impedance data taken before and after immersion in media modelling oak emitted volatile organic compounds (VOCs) polluted atmospheres show that coating effectiveness decreases after exposure, but the effect is lessened if longer chain carboxylates are used.
[Show abstract][Hide abstract] ABSTRACT: This work presents the application of voltammetry of microparticles (VMP) to the characterization of metallic artefacts. The paper illustrates the principle of the technique and the methods for the identification of metals and copper minerals. VMP can be considered a non-invasive technique as it requires a minimum amount of material for performing the analyses. To emphasize the efficacy of this technique regarding characterization of cultural heritage materials, two bronze artefacts of different historical periods were investigated. By using a paraffin-impregnated graphite electrode, the composition of the alloy and the copper minerals present in their patinas were analysed and identified. The results obtained from the electrochemical characterization were confirmed by complementary analysis carried out with X-ray fluorescence and X-ray diffraction.
[Show abstract][Hide abstract] ABSTRACT: Capillary–based microcells, also known as
microcapillary electrochemical droplet cells, have proved their
capabilities in various electrochemical surface investigations
in recent decades. Due to the large measured current density
and the high limiting current, this technique provides high–
resolution electrochemical responses. Current densities in the
range from a few femto to pico Acm−2 to hundreds of Acm−2
can be measured using this technique. Various applications for
microcapillary cells have been reported. Technical limitations,
such as the Ohmic drop and changes in the composition of the
measurement area near the tip of the microcapillary have also
been considered by some researchers. The rapid increase in
the application of microcells and the increase in the number of
related reports published in the literature have paralleled recent
attempts to develop and improve microcell setups, showing
that this technique is already well established for electrochemical
Journal of Solid State Electrochemistry 01/2014; · 2.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Polarization and impedance measurements in a corrosive environment have been used to investigate the adsorption and corrosion inhibition characteristics of sodium dodecanoate on lead. Results show that the concentration of sodium dodecanoate has an important effect on the anodic lead dissolution. Monolayer adsorption occurs at low inhibitor concentrations. The equilibrium constant (Kads), calculated using the Frumkin model, is about 10−5 M−1. Multilayer formation at concentrations above the critical micelle concentration ensures the formation of a lead dodecanoate coating following the dissolution-precipitation mechanism. These lead complexes are formed on top of the surface, which has been conﬁrmed by secondary electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS).
Journal of The Electrochemical Society 01/2014; 161(3):C126-C137. · 2.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In order to understand the corrosive and morphological characteristics of lead dodecanoate protective coatings on real samples, three pipe organ samples were studied using optical microscopy (OM), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS). The corrosion products and elemental composition of the top layer of the different pipe organ samples were investigated. The results indicate that the three pipe organ samples are made of an alloy composed mainly of lead and tin. After immersion and the deposition of the protective coating, only lead and no tin is detected, which indicates the formation of a thick coating containing lead dodecanoate complexes.
[Show abstract][Hide abstract] ABSTRACT: In experiments preliminary to the design of an x-ray excited optical luminescence (XEOL) based chemical mapping tool we have used x-ray micro (4.5 μm × 5.2 μm) and macro (1 mm × 6 mm) beams with similar total fluxes to assess the effects of a high flux density beam of x-rays at energies close to an absorption edge on inorganic surfaces in air. The near surface composition of corroded cupreous alloys was analysed using parallel x-ray and optical photoemission channels to collect x-ray absorption near-edge structure (XANES) data at the Cu-K edge. The x-ray fluorescence channel is characteristic of the composition averages over several microns into the surface, whereas the optical channel is surface specific to about 200 nm. Whilst the x-ray fluorescence data were mostly insensitive to the x-ray dose, the XEOL-XANES data from the micro beam showed significant dose-dependent changes to the superficial region including surface cleaning, changes in the oxidation state of the copper, and destruction of surface compounds responsible for pre-edge fluorescence or phosphorescence in the visible. In one case there was evidence that the lead phase in a bronze had melted. Conversely, data from the macro-beam were stable over several hours. Apart from localized heating effects, the micro-beam damage is probably associated with the O3 loading of the surface and increased reaction rate with atmospheric water vapour.
[Show abstract][Hide abstract] ABSTRACT: We report the use of voltammetry of immobilized microparticles for the quantification of metallic copper and nickel in their binary mixtures. Twenty-two electrolytes were investigated in order to obtain well-separated oxidation peaks. An experimental design strategy was employed to study the effect of the electrolyte concentration and the scan rate on the resolution of the oxidation peaks. With the optimum experimental parameters, a quantification was performed and the linear results of percentage of anodic currents in term of their relative amount in the binary mixture were obtained. Finally, the prediction of two mixture samples was performed and gave satisfactory results.
International journal of electrochemical science 02/2013; 8:2576 - 2585. · 1.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Tetra-substituted palladium phthalocyanine complexes with different electron withdrawing and electron donating substituents (–H, –NO2, –NH2, –Cl, –COOH, aryl thio) have been synthesized with a good yield. The synthesized complexes were characterized using XPS, UV–Vis, IR, Raman, XRD, TGA and electrochemistry. The XPS spectra show that the central metal ion is in the +2 state, while the UV–Vis spectra demonstrate split absorption peaks in the Q-band region 600–700 nm due to the presence of dimeric and oligomeric molecules in addition to the monomeric species. The UV–Vis and Raman spectra demonstrate a shift in the peaks/bands which is a result of the electron withdrawing and electron donating substituents at the periphery of the benzene ring compared to the parent palladium phthalocyanine. The thermogravimetic stability studies show that these complexes undergo two separate decomposition processes. The thermal stability for different complexes are in the order: PdPc < PdTPSPc < PdTClPc < PdTAPc < PdTCAPc = PdTNPc, indicating that the substituents at the periphery have an effect on the thermal stability. The cyclic voltammetric data in DMSO show that the central metal ion Pd does not undergo a redox process and the redox behaviour observed is mainly due to the macrocyclic ring reduction process.
Dyes and Pigments 01/2013; 96(1):269–277. · 3.47 Impact Factor