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In this study, the impedance response of a passive material is investigated, attributing it to a normal time constant distribution caused by resistivity variations within the passive film. Two models, namely the Power Law Model (PLM) and the recently developed Dielectric Bi-Layer Model (DBLM), are employed to express the impedance data. The PLM considers an oxide film as a single layer with a power-law distribution of resistivity, while the DBLM incorporates two distinct layers: an inner layer with constant resistivity (ρ 0) and an outer layer with resistivity following Young's theory. Application of both models to 316L stainless steel immersed in a borate buffer solution exhibit that PLM and DBLM fitting results are in good agreement with experimental data. While the models differ mainly in resistivity profiles at the vicinity of the outer interface, the results suggest that deviations in regressed parameters indicate similar ranges for resistivity profiles calculated by both models. DBLM, in particular, is highlighted as promising for interpreting impedance data of passive materials due to its reliance on physical concepts. [ABSTRACT FROM AUTHOR]

Corrosion tests of metallic materials for biomedical applications are generally carried out in highly simplified solutions and are often disapproved by direct or indirect cytotoxicity tests. Cell culture medium is then the better alternative to get robust biocompatibility assessments. The specific intrinsic reactivity of a Roswell Park Institute Medium cell culture medium (RPMI-1640) was studied here using a platinum electrode inside and outside a dedicated CO 2 incubator. Electrochemical tests and surface analyses revealed that organic compounds of the RPMI-1610 are forming an organic adsorbed layer on the surface which is electrochemically active in a wide potential range. Precipitations of inorganic salts (calcium phosphate) are also promoted by organic species. The effect of the 5% content of CO 2 in the incubator was also discussed, relative to the fact that carbonate and bicarbonate ions are involved in the charge transfer and mass transport processes. All these features were taken into account when performing biocompatibility tests for material design and selection. [ABSTRACT FROM AUTHOR]

• Substituting few percents of Cu in TiZrCuPd BMG improves its passive behavior. • Sn and Si elements play a beneficial role on the metallurgical quality of BMG. • Heterogeneity within solid solution and casting defects act as weakening sites. • Adding Sn and Si elements limit the susceptibility to pitting corrosion. In this work, the effect of substituting Cu with small amounts of Sn and Si on the passive behavior and pitting resistance of the bulk metallic glass Ti 40 Zr 10 Cu 36 Pd 14 was investigated. The Sn/Si substitution promoted homogenization of the solid solution and limited the presence of casting defects. In addition, unlike the heterogeneous passive film grown on TiZrCuPd, the passive films of the micro-alloyed materials were homogeneous, implying less sensitivity to film weakening and breakdown. Thus, alloying with small amounts of Sn and Si appears to be a viable approach to drastically improve the corrosion resistance of TiZrCuPd. [ABSTRACT FROM AUTHOR]

The passive behavior of a Ni–20Cr binary alloy was studied using an original methodology, based on successive electrochemical impedance spectroscopy (SEIS), over a wide potential range. The proposed method was first validated by comparing the resulting potentiostatic polarization curves with more conventional potentiodynamic polarization curves and determining the effect of the dwell time (30, 120, and 600 s) and potential step size (25 and 50 mV). Using the optimized parameters from this preliminary work, the passive behavior of the Ni–Cr alloy was then studied in solutions of varying pH: 10 g/L Na 2 SO 4 with H 2 SO 4 (pH = 2), 0.01 M Na 2 SO 4 (pH = 5.8), and 0.05 M H 3 BO 3 + 0.075 M Na 2 B 4 O 7 10H 2 O (pH = 9.2). The obtained impedance diagrams were interpreted using enhanced graphical representation and fitted using the power-law model to determine the resistivity distribution throughout the passive film during polarizations. The results demonstrated that SEIS provides complementary information to conventional potentiodynamic curves. The evolution of the passive film properties was monitored in situ within the potential range corresponding to stable passivity. With the help of this original method, complementary to the evolution of the current density (measured at each potential step), the thickness, chemical composition, and reactivity changes were also highlighted. Image 1 • Successive electrochemical impedance technique was validated to study passivity. • Accuracy of enhanced graphical method and fit using power law model was evidenced. • Evolution of passive film's properties was assessed on a wide potential range. • This original methodology permits the in-situ monitoring of passive behavior. [ABSTRACT FROM AUTHOR]

Barrier properties of innovative epoxy coatings containing 10 or 20 phr of phosphate/phosphonium ionic liquid (IL) were investigated using mainly electrochemical impedance spectroscopy. The impedance diagrams revealed quasi-pure capacitive behavior and the impedance modulus at low frequency, related to corrosion resistance, remains at around 1012 Ω cm2 during immersion time in 0.1 M NaCl solution. The capacitances were graphically extracted from Cole–Cole representations, and the resistances were determined using R//C electric equivalent circuits. Both epoxy–IL coatings were free of porosity and impeded the hydration of the matrix. The results were also compared to those of conventional epoxy coatings, for which hydration occurs owing to their porosity. Results indicate that this new epoxy–IL coating system would offer excellent anticorrosion protection for metallic substrates. • Innovative epoxy coatings containing phosphate/phosphonium ionic liquid developed as an alternative to epoxy–amine coatings • Quasi-pure capacitive behavior during the entire immersion, • Epoxy-ionic liquid coatings are free of porosities • Epoxy-ionic liquid network is characterized by very high barrier properties preventing the hydration of the coating [ABSTRACT FROM AUTHOR]