An Impedance Investigation of the Mechanism of Pure Magnesium Corrosion in Sodium Sulfate Solutions

The corrosion behavior of pure magnesium in sodium sulfate solutions was investigated using voltammetry and electrochemical impedance spectroscopy with a rotating disk electrode. The analysis of impedance data obtained at the corrosion potential was consistent with the hypothesis that Mg corrosion is controlled by the presence of a very thin oxide film, probably MgO, and that the dissolution occurs at film-free spots only. This hypothesis was substantiated both by the superposition of the EIS diagrams, obtained for different immersion times and for two Na2SO4 concentrations once normalized, and by use of scanning electrochemical microscopy in the ac mode to sense the local conductivity of the material. On the basis of the electrochemical results, a model was proposed to describe magnesium corrosion at the open-circuit potential. Simulation of the impedance diagrams was in good agreement with the experimental results

Local Mass Transfer in Turbulent Flow by Electrochemical Methods

Mass transfer to the surface of rotating electrodes during turbulent flow was studied by electrochemical methods under steady and non-steady state diffusion conditions. The flow was due to a large rotating disk made from insulating material, flush with the surface of which was mounted a ring shaped electrode of platinum or nickel. A local study of the radial component of the convective diffusion in turbulent flow was carried out with very thin ring electrodes (width ΔR ~ 0,05 mm). The diffusion layer thickness was varied relatively to the diffusion sublayer thickness by changing the ring width or the rotation speed so as to determine the eddy diffusivity in the viscous sublayer. The local viscous friction was measured at the wall by a steady state method. As an application, the drag reduction phenomenon was studied in the presence of high polymer additives. Using a non-steady state method which yields the electrochemical impedance, we examined the possibility of adsorption of polymers at the wall- fluid interface

Electrochemical synthesis of polypyrrole doped with graphene oxide and its electrochemical characterization as membrane material

Polypyrrole (PPy) doped with graphene oxide (GO) has been electrochemically obtained by potentiostatic synthesis and its electrochemical behavior as membrane material has been studied for the first time. Fourier transform infrared spectroscopy with attenuated total reflection showed the formation of the hybrid material due to presence of PPy and GO bands. Field emission scanning electron microscopy micrographs showed the effective incorporation of GO sheets and the formation of a 3-D porous material with high surface area. Scanning electrochemical microscopy of PPy/GO films showed positive feedback close to the ideal conducting behavior, indicating a good electroactivity. Electrochemical impedance spectroscopy (EIS) was employed to measure the electrochemical properties of the coatings by two-, three-, and four-electrode configurations. The electronic conductivity of PPy/GO film, measured between two metallic conductors, was 4.7·10−6 S/cm. Its ionic conductivity was superior (1.6·10−3 S/cm) due to the high porosity of the material as demonstrated by cyclic voltammetry and EIS measurements, where the PPy/GO film was employed as a free-standing membrane. The diffusion-migration rate of tetramethylammonium chloride was very similar to sodium chloride when present in the same concentration, which indicated no influence of the size of the electrolyte conductor due to the high porosity. © 2016 Elsevier B.V. All rights reserved.Authors wish to thank the Spanish Ministerio de Ciencia e Innovacion (contract CTM2011-23583) for the financial support. J. Molina is grateful to the Conselleria d'Educacio, Formacio i Ocupacio (Generalitat Valenciana) for the Programa VALi+D Postdoctoral Fellowship (APOSTD/2013/056). A.I. del Rio is grateful to the Spanish Ministerio de Ciencia y Tecnologia for her FPI fellowship. Electron Microscopy Service of the UPV (Universitat Politecnica de Valencia) is gratefully acknowledged for help with FESEM and EDX characterization.Molina Puerto, J.; Bonastre Cano, JA.; Fernández Sáez, J.; Del Río García, AI.; Cases Iborra, FJ. (2016). Electrochemical synthesis of polypyrrole doped with graphene oxide and its electrochemical characterization as membrane material. Synthetic Metals. 220:300-310. https://doi.org/10.1016/j.synthmet.2016.06.028S30031022

Interaction Model of the Interface Nasicon with Aqueous Solution

Complex impedance spectroscopy (CIS) study was carried out using the 4-electrodes cell arrangement with NASICON membrane. The physical model developed in this work was based on own CIS characteristic of the system NASICON/solution, and it accurately described the experimental diagrams. The electronic parameters could be determined from the fittings with the designed model

Polycarbonate microchannel network with carpet of Gold NanoWires as SERS-active device

A polycarbonate (PC) microchannel network supporting gold nanowires was developed to be a SERSactive microchip. Observations of large increases in a Raman cross-section, allowed us to collect vibrational signatures which are not easily detectable by Raman techniques due to the high fluorescence level of bare PC. Compared to other SERS experiments, this study relies on the use of dielectric polymer/metal surfaces which are well defined at microscale and nanoscale levels. This device seems a promising tool for sensing the adsorption of biomolecules

Electroacoustic Polymer Microchip as an Alternative to Quartz Crystal Microbalance for Biosensor Development

Laser photoablation of poly(ethylene terephthalate) (PET), a flexible dielectric organic polymer, was used to design an acoustic miniaturized DNA biosensor. The microchip device includes a 100-μm-thick PET layer, with two microband electrodes patterned in photoablated microchannels on one side and a depressed photoablated disk decorated by gold sputtered layer on the other side. Upon application of an electric signal between the two electrodes, an electroacoustic resonance phenomenon at ∼30 MHz was established through the microelectrodes/PET/ gold layer interface. The electroacoustic resonance response was fitted with a series RLC motional arm in parallel with a static C0 arm of a Buttlerworth-Van Dyke equivalent circuit: admittance spectra recorded after successive cycles of DNA hybridization on the gold surface showed reproducible changes on R, L, and C parameters. The same hybridizations runs were performed concomitantly on a 27-MHz (9 MHz, third overtone) quartz crystal microbalance in order to validate the PET device developed for bioanalysis applications. The electroacoustic PET device, ∼100 times smaller than a microbalance quartz crystal, is interesting for the large-scale integration of acoustic sensors in biochips

On the Corrosion Resistance of Porous Electroplated Zinc Coatings in Different Corrosive Media

The corrosion resistance of an electroplated (EP) Zn coating whose surface was chemically etched to produce surface defects (pores) is investigated in this work. Impedance and DC polarisation measururements were employed to study the behaviour of such coating in various corrosive media (NaCl, NaOH and rain water). Four different faradaic relaxation processes were clearly revealed in different NaCl concentrations (from 0.1M to 1M). In the most concentrated solutions at least three relaxation processes at low frequencies (LF) appeared and were related to zinc deposition and dissolution. At lower concentrations and depending on the pH, only one process was observed. The charge transfer resistance (Rct) and the corrosion current (Icorr) were practically stable in the pH range 5 to 10. In deaerated NaCl 0.1M, the EIS diagrams showed two time-constants at very close frequencies. From the EIS diagrams the porous nature of the coating was highlighted and showed that the dissolution mechanisms occurred at the base of the pores

Electrochemical Oxidation Assessment and Interaction of 2-aminoethanol and N, N-diethylethanamine Propagation in Acidic Medium

Electro�oxidation and inhibitor performance of copper specimens in 1 M hydrochloric acid solu� tion was investigated at room temperature by linear potentiodynamic polarization and gravimetric method in the presence of 2�aminoethanol (A) and N, N�diethylethanamine (D) as an inorganic inhibitor. The effect of the inhibitory concentration on the corrosion behavior of copper was studied over 288 hrs at 298°K. The inhibitory efficiency rise up to 96% for single induced and 98% for synergistic behavior. The adsorption mechanism characteristic was supported by SEM/EDX analysis and adsorption isotherm. From all indica� tion, the inhibitive efficiency of these compounds majorly depends on their molecular structure and concen� tration. The blocking effects of the surface interface were also explained on the basis of the inhibitor active action. 2�aminoethanol and N, N�diethylethanamine inhibits copper in 1 M HCl by strictly affecting both the anodic and cathodic sites. Portion of the surface covered calculated was also found to follow Langmuir adsorption isotherm

Thermogalvanic effects on the corrosion of copper in heavy brine LiBr solutions

Thermogalvanic corrosion of copper in heavy brine LiBr solutions has been investigated using a zero-resistance ammeter (ZRA). The temperature gradients between copper electrodes immersed in the same LiBr solution result in the formation of thermogalvanic cells with hot anodes, leading to high and sustained thermogalvanic currents. Copper loss rates, calculated using Faraday's law, substantially exceed 0.025 mm year−1, a value regarded as the threshold of low corrosion rates. The effects of thermogalvanic coupling on the surface properties of the anode and the cathode have been analysed by means of electrochemical impedance spectroscopy (EIS). The results obtained in this analysis have been related to the process of copper electrodissolution in bromide media