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

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

Carctérisation d'un composé tensioactif réducteur de frottement hydrodynamique et application à l'inhibition de l'érosion-corrosion du cuivre en présence d'écoulements forts

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Étude du transport de matière dans des solutions concentrées de polyoxyéthylène à l’aide d’une électrode à disque tournant

La mesure du courant limite de diffusion id dans les liquides non-newtoniens a permis l’étude de trois types d’écoulements lents caractérisés à vitesse de rotation Ω croissante par :

Mass transfer in elongational laminar and turbulent flows of drag reducing solutions of quaternary ammonium surfactants. Influence of the counter-ion to surfactant concentrations ratio

International audienceElectrochemical method was used to study in elongational laminar and turbulent flows the mass transfer toward a rotating disk in different drag reducing solutions of two cationic surfactants (Arquad 16-29, Arquad S50) together with counter ions (Para-chloro benzoate, Nasal) by varying the concentrations of their mixture. The mass transfer in laminar flow conditions displays a first order transition characterized by a significant drop accompanied by strong instabilities and a hysteresis cycle at a critical angular velocity which depends on the counter ion to surfactant concentrations ratio ζ.The local wall shear stress in turbulent flow was measured using a microelectrode inserted flush with the cross-section of the rotating disk. The ζ ratio influences the drag reduction onset: Arquad 16-29 was shown to be more efficient at lowest concentration values than the Arquad S50 for both the critical velocity transition in laminar flow and the onset of drag reduction in turbulent flow

ETUDE DU TRANSPORT DES IONS CHROME TRIVALENTS A TRAVERS DES MEMBRANES ION-SELECTIVES ORIGINELLES OU MODIFIEES

PARIS7-Bibliothèque centrale (751132105) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Élaboration de films de polypyrrole par électropolymérisation sur un substrat fer et caractérisation de leurs propriétés de protection contre la corrosion

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

pH sensing in aqueous solutions using a MnO2 thin film electrodeposited on a glassy carbon electrode

International audienceAn electrolysis technique at a constant potential was used to develop a highly reproducible and fast elaboration method of adherent manganese dioxide thin films on a glassy carbon electrode from aqueous solutions containing sulfuric acid and manganese sulfate. The resulting films were found to have a nanostructured character presumably due rather to birnessite (delta-MnO2) than to gamma-MnO2, as suggested by their Raman and XRD signatures. They lead to modified electrodes that present an obvious although complex pH dependent potentiometric response. This sensor indeed showed a single slope non-Nernstian linear behaviour over the 1.5-12 pH range for increasing pH direction ("trace"), whereas a Nernstian two slopes linear behaviour was observed for decreasing pH direction ("re-trace"). Preliminary EIS experiments carried out at a pH value of 1.8 seem to reveal a sensitivity mechanism based on proton insertion process at least at highly acidic pH values