The mean ionic activity coefficients of NaCl were experimentally determined in ethylene carbonate (EC) + water at 298.15 K from potential difference measurements of the following electrochemical cell containing two ion-selective electrodes (ISEs):The molality (m) varied between 0.02 mol • kg -1 and almost saturation, while the mass fraction of EC in the mixture (w) was varied between 0 and 0.8 in 0.1 unit steps. Values of the standard potential difference, E 0 (molal scale), were determined using a routine method of extrapolation together with the extended Debye-Hu ¨ckel, Pitzer, and Scatchard equations. The results obtained produced good internal consistency, within the normal limits of experimental error encountered in these types of measurement. Once E 0 was determined, the mean ionic activity coefficients of the NaCl, the Gibbs energy of transfer of the NaCl from the water to the EC + water mixture, standard solubility product of NaCl in EC + water, and the NaCl primary hydration number were estimated. The results were comparatively analyzed with those of the NaF previously obtained in similar mixtures.

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Corrosion processes occurring on stainless steel 304 surfaces under anodic polarization have been characterized using scanning electrochemical microscopy (SECM) and the scanning vibrating electrode technique (SVET), complemented with conventional potentiodynamic polarization curves. Stable pit formation has been detected by SVET on the samples as result of surface modification under electrochemical control, which may include the previous electrochemical reduction of passive oxide layer if the media is not aggressive enough to induce pitting at small overpotentials. Additionally, the sample generation -tip collection operation mode of the SECM has enabled the detection of local release of iron (II) ions, as well as their conversion to iron (III), both processes being greatly affected by the potential applied to the substrate.

The activity coefficients of NaClO 4 in water were experimentally determined at (288.15, 298.15, and 308.15) K from electromotive force (emf) measurements of the following electrochemical cell without transference containing two ion-selective electrodes (ISEs): Na-ISE|NaClO 4 (m)|ClO 4 -ISE. The molality m varied between about (0.02 and 12) mol 3 kg À1 . The determination of E 0 *, which is necessary to calculate the activity coefficients, was carried out following a method similar to that of Hitchcock, using the Pitzer, extended DebyeÀH€ uckel, and Scatchard equations to represent the dependency of log γ on molality.The electrode system employed shows good Nernstian behavior. The activity and osmotic coefficients obtained in this study at 298.15 K were contrasted to those from the literature and show a good agreement.