Quantification of metallic copper and nickel in their binary mixtures by voltammetry of immobilized microparticles

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

Quantification of tin and lead in binary alloys using voltammetry of immobilized microparticles

Voltammetry of immobilized microparticles (VMP) has been used in this work for the quantitative determination of tin and lead particles in their binary alloys. Carbon paste electrodes, which contained small amounts of tin and lead or their mixtures, were used as working electrodes and square wave voltammograms of each electrode were recorded. Quantification was performed using optimum experimental conditions, obtained by an experimental design technique. The calibration was made by measuring the percentage peak height of each metal taking the sum of peak currents of the both metals as 100%. The results were compared with quantitative results of X-ray fluorescence (XRF) technique to evaluate the capability of VMP method in its quantitative determination of solid samples

Electrochemical quantification of copper-based alloys using voltammetry of microparticles : optimization of the experimental conditions

Voltammetry of microparticles (VMP) has been used in this work for the qualitative and quantitative analysis of zinc, tin, lead and copper in binary, ternary or quaternary alloy samples. The analyses were carried out by spiking small amounts of the metals into a carbon paste electrode, after which they were anodically stripped off using differential pulse voltammetry. The work involved four separate experiments. The first one examined the type of electrolyte, which is suitable to identify the four elements. More specifically the aim was to examine in which electrolyte all elements can be measured simultaneously - as would be the case in a quaternary copper alloy - without seeing any overlap in their current peaks. The second experiment focused on optimizing the measurement conditions with the aim of having the current peaks of each element well separated from the others. For this part we made use of the central composite design. The aims were to: (i) maximize the separation between current peaks; (ii) to determine which variable has a higher impact on the response; (iii) give an insight in the robustness of the method close to the optimum conditions and (iv) eventually show interactions between variables. In the third experiment the four elements were quantified in their binary mixtures. Here, the percentage of the oxidation current for each metal, which is directly related to the ratio of the metal in the binary matrices, was employed for the calibration. Finally in the last experiment the elements were quantified in two real quaternary samples: a brass and a lead bronze

Microelectrochemical investigation of the effect of cathodic polarisation on the corrosion resistance of 304L stainless steel in a 1 M NaCl solution

304L stainless steel was cathodically polarised in a 1 M sodium chloride solution using a microcapillary electrochemical droplet cell. During the cathodic polarisation the produced hydrogen atoms penetrate into the sample and accumulate at sites of the steel surface. We observed that the pitting potential (E-pit), the anodic current density (I-corr) and the corrosion potential (E-corr) of the polarised steel are strongly influenced by the applied cathodic potential and therefore by the amount of charged hydrogen atoms which penetrate into the sample. Local electrochemical impedance spectroscopy (LEIS) using different applied cathodic potentials shows lower corrosion resistance for cathodically polarised steel and reveals a different behaviour on a microscale level

Electrochemical discrimination of mints: The last Chinese emperors Kuang Hsu and Hsuan T'ung monetary unification

[EN] An electrochemical methodology for discriminating monetary emissions, a recurrent problem in much archaeological studies, is introduced. The method is based on the record of voltammetric signatures of cuprite and tenorite corrosion products in the patina using a minimally invasive nanosampling following the voltammetry of immobilized particles methodology. A model for the depth variation of voltammetric electrochemical parameters characterizing the composition of the corrosion patinas is presented. This model permits to rationalize electrochemical data and discriminate different monetary emissions. The application of this technique, corroborated by electrochemical impedance spectroscopy (EIS) and focusing ion beam-field emission scanning electron microscopy (FIB-FESEM-EDX), to a series of 10 cash copper coins produced around the Kuang Hsu and Hsuan Tung last Chinese emperors permits to discern different provincial mints and reveals that the monetary unification developed in this period was not uniform.Financial support from the Spanish MINECO Projects CTQ2014-53736-C3-1-P and CTQ2014-53736-C3-2-P which are also supported with ERDF funds. The Universita degli Studi di roma "La Sapienza" has granted a six-months research-scholarship (d.r.n. 965/2016 prot.n.0022041 del 31/03/2016) to the graduated Elena Montagna. The authors also wish to thank Dr. Jose Luis Moya Lopez and Mr. Manuel Planes Insausti (Microscopy Service of the Universitat Politecnica de Valencia) for technical supportDomenech-Carbo, A.; Domenech Carbo, MT.; Montagna, E.; Álvarez-Romero, C.; Lee, Y. (2017). Electrochemical discrimination of mints: The last Chinese emperors Kuang Hsu and Hsuan T'ung monetary unification. Talanta. 169:50-56. https://doi.org/10.1016/j.talanta.2017.03.025S505616

Characterizing archaeological bronze corrosion products intersecting electrochemical impedance measurements with voltammetry of immobilized particles

[EN] Application of electrochemical impedance measurements to microparticulate deposits of copper corrosion products attached to graphite electrodes in contact with 0.10 M aqueous HClO4 electrolyte is described. The impedance measurements were sensitive to the applied potential and the amount of solid sample and were modeled taking into account the contribution of the uncovered base electrode. Several pairs of circuit elements provide monotonic variations which are able to characterize different corrosion compounds regardless the amount of microparticulate solid on the electrode. Application to a set of archaeological samples from the archaeological Roman site of Gadara (Jordan, 4th century AD) permitted to establish a grouping of such samples suggesting different provenances/manufacturing techniques.Financial support from the MINECO ProjectsCTQ2014-53736-C3-1-P and CTQ2014-53736-C3-2-P which are also supported with ERDF funds and Grants ES-2012-052716 and EEBB-I-16-11558 is gratefully acknowledgedRedondo-Marugan, J.; Piquero-Cilla, J.; Domenech Carbo, MT.; Ramírez-Barat, B.; Al Sekhaneh, W.; Capelo, S.; Doménech Carbó, A. (2017). Characterizing archaeological bronze corrosion products intersecting electrochemical impedance measurements with voltammetry of immobilized particles. Electrochimica Acta. 246:269-279. https://doi.org/10.1016/j.electacta.2017.05.190S26927924

On-line database of voltammetric data of immobilized particles for identifying pigments and minerals in archaeometry, conservation and restoration (ELCHER database)

[EN] A web-based database of voltammograms is presented for characterizing artists' pigments and corrosion products of ceramic, stone and metal objects by means of the voltammetry of immobilized particles methodology. Description of the website and the database is provided. Voltammograms are, in most cases, accompanied by scanning electron microphotographs, X-ray spectra, infrared spectra acquired in attenuated total reflectance Fourier transform infrared spectroscopy mode (ATR-FTIR) and diffuse reflectance spectra in the UV-Vis-region. For illustrating the usefulness of the database two case studies involving identification of pigments and a case study describing deterioration of an archaeological metallic object are presented. (C) 2016 Elsevier B.V. All rights reserved.Research was conducted within the "Grupo de analisis cientifico de bienes culturales y patrimoniales y estudios de ciencia de la conservacion" Microcluster of the University of Valencia Excellence Campus. Financial support is gratefully acknowledged from the MINECO Projects CTQ2014-53736-C3-1-P and CTQ2014-53736-C3-2-P which are also supported with ERDF funds. The authors would like to thank to Gonzalo Girones Sarrio manager of GongDisseny Co. by the technical support for building the site structure and the structure of the database, Archbishop of Valencia, Dr. Ignacio Bosch Reig and Dr. Pilar Roig Picazo directors of the intervention project in the Basilica de la Virgen de los Desamparados de Valencia, the conservator Estrella Arcos Von Haartman (Quibla Restaura Company) and City Council Town of Malaga, the Museum of Archaeology of Xativa, its director Angel Velasco and the conservators Isabel Martinez Lazaro and Betlem Martinez for facilitating access to samples as well as Manuel Planes Insausti and Dr Jose Luis Moya Lopez technical supervisors of the Electron Microscopy Service of the Universitat Politecnica de Valencia where were carried out SEM-EDX analyses.Domenech-Carbo, A.; Domenech Carbo, MT.; Valle-Algarra, FM.; Gimeno-Adelantado, J.; Osete Cortina, L.; Bosch-Reig, F. (2016). On-line database of voltammetric data of immobilized particles for identifying pigments and minerals in archaeometry, conservation and restoration (ELCHER database). Analytica Chimica Acta. 927:1-12. https://doi.org/10.1016/j.aca.2016.04.052S11292

Microcapillary electrochemical droplet cells: applications in solid-state surface analysis

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 re- cent attempts to develop and improve microcell setups, show- ing that this technique is already well established for electro- chemical surface studies