Development of quantitative Local Electrochemical Impedance Mapping: an efficient tool for the evaluation of delamination kinetics

International audienceLocal Electrochemical Impedance Mapping (LEIM) methodology was adopted to quantify the propagation of electrochemically active regions with a micrometric precision. The method consisted in the use of the gradient modulus of the admittance map as a parameter for the spatial quantifi-cation. Numerical simulations were used to optimize the experimental conditions, namely the AC frequency, the distance between the local bi-probe and the working electrode, and the distances between the probes for the local bi-probe used for the local current mapping. This analysis was reinforced by experimental verifications on coated electrodes. The quantitative LEIM methodology was successfully applied to follow the delamination kinetics on Zn coated with the polyvinyl butyral polymer in NaCl solutions. At 1 kHz, the LEIM response only reflected the position of the anodic front beneath the polymer because oxygen reduction reaction was diffusion limited and hence, independent of the applied potential. This novel LEIM methodology completes the set of usual tools used to investigate the delamination mechanisms on metal substrates

MoO42- as a soluble inhibitor for Zn in neutral and alkaline solutions.

International audienceThe inhibitive action of soluble Na2MoO4 on the spontaneous reactivity of hot dip galvanized steel in 0.5 M NaCl was studied at pH 4–13 by a direct measurement of Zn dissolution rate in the flowing electrolyte and postmortem surface analysis. The stability and the composition of Mo-rich films depended on the solution pH and flow conditions. The inhibition efficiency of soluble Mo(VI) correlated with the composition of the films: Mo(V)-rich films were immediately formed under uniform flow at pH 6–12, and the inhibition efficiency of Mo(VI) in these conditions (>92%) was comparable with the efficiency of Cr(VI)

Factors affecting MoO42- inhibitor release from Zn2Al based layered double hydroxide and their implication in protecting hot dip galvanized steel by means of organic coatings.

International audienceZn2Al/-layered double hydroxide (LDH) with intercalated MoO42– was investigated as a potential source of soluble molybdate inhibitor in anticorrosion coatings for hot dip galvanized steel (HDG). The effect of solution pH, soluble chlorides, and carbonates on the release kinetics of the interleaved MoO42– ions from the LDH powder immersed in solutions containing different anions was studied by X-ray diffraction, in situ attenuated total reflectance infrared (ATR-IR) spectroscopy, and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The effect of the solution composition on the total release and the release kinetics was demonstrated. Less than 30% of the total amount of the intercalated MoO42– was released after 24 h of the immersion in neutral 0.005–0.5 M NaCl and 0.1 M NaNO3 solutions whereas the complete release of MoO42– was observed after 1 h in 0.1 M NaHCO3 or Na2SO4 and in alkaline solutions. The in situ ATR-IR experiments and quantification of the released soluble species by ICP-AES demonstrated the release by an anion exchange in neutral solutions and by the dissolution of Zn2Al/-LDH in alkaline solutions. The anion exchange kinetics with monovalent anions was described by the reaction order n = 0.35 ± 0.05 suggesting the diffusion control; for divalent anions, n = 0.70 ± 0.06 suggested the control by a surface reaction. Dissolution of Zn from coated HDG with and without Zn2Al/-MoO42– fillers, leaching of MoO42– from the coating, and the electrochemical impedance spectroscopy response of the coated systems were measured during the immersion in 0.5 M NaCl solutions with and without 0.1 M NaHCO3. Without carbonates, the release of soluble MoO42– was delayed for 24 h with no inhibiting effect whereas with 0.1 M NaHCO3 the immediate release was accompanied by the immediate and strong inhibiting effect on Zn dissolution. The concept of controlling the inhibition performance of LDH hybrid coatings by means of the environment composition is discussed

Data for High pressure high temperature synthesis of highly boron doped diamond microparticles and porous electrodes for electrochemical applications

High pressure high temperature (HPHT) synthesis of crystallographically well-defined boron doped diamond (BDD) microparticles, suitable for electrochemical applications and using the lowest P and T (5.5 GPa and 1200 °C) growth conditions to date, is reported. This is aided through the use of a metal (Fe–Ni) carbide forming catalyst and an aluminum diboride (AlB2) boron source. The latter also acts as a nitrogen sequester, to reduce boron-nitrogen charge compensation effects. Raman microscopy and electrochemical measurements on individual microparticles reveal they are doped to metal-like levels, contain negligible sp2 bonded carbon and display a large aqueous solvent window. A HPHT compaction process is used to create macroscopic porous electrodes from the BDD microparticles. Voltammetric analysis of the one-electron reduction of Ru(NH3)6 3+ is used to identify the fundamental electrochemical response, revealing large capacitive and resistive components to the current-voltage curves, originating from solution trapped within the porous material. Scanning electrochemical cell microscopy (SECCM) is employed to map the local electrochemical activity and porosity at the micron scale. Such electrodes are of interest for applications that require the electrochemical and mechanical robustness properties of BDD, e.g. when operating under high applied potentials/currents, but with the additional benefits of a large, electrochemically accessible, surface area

Factors Affecting MoO₄^2– Inhibitor Release from Zn₂Al Based Layered Double Hydroxide and Their Implication in Protecting Hot Dip Galvanized Steel by Means of Organic Coatings

Zn₂Al/-layered double hydroxide (LDH) with intercalated MoO₄^2– was investigated as a potential source of soluble molybdate inhibitor in anticorrosion coatings for hot dip galvanized steel (HDG). The effect of solution pH, soluble chlorides, and carbonates on the release kinetics of the interleaved MoO₄^2– ions from the LDH powder immersed in solutions containing different anions was studied by X-ray diffraction, in situ attenuated total reflectance infrared (ATR-IR) spectroscopy, and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The effect of the solution composition on the total release and the release kinetics was demonstrated. Less than 30% of the total amount of the intercalated MoO₄^2– was released after 24 h of the immersion in neutral 0.005–0.5 M NaCl and 0.1 M NaNO₃ solutions whereas the complete release of MoO₄^2– was observed after 1 h in 0.1 M NaHCO₃ or Na₂SO₄ and in alkaline solutions. The in situ ATR-IR experiments and quantification of the released soluble species by ICP-AES demonstrated the release by an anion exchange in neutral solutions and by the dissolution of Zn₂Al/-LDH in alkaline solutions. The anion exchange kinetics with monovalent anions was described by the reaction order <i>n</i> = 0.35 ± 0.05 suggesting the diffusion control; for divalent anions, <i>n</i> = 0.70 ± 0.06 suggested the control by a surface reaction. Dissolution of Zn from coated HDG with and without Zn₂Al/-MoO₄^2– fillers, leaching of MoO₄^2– from the coating, and the electrochemical impedance spectroscopy response of the coated systems were measured during the immersion in 0.5 M NaCl solutions with and without 0.1 M NaHCO₃. Without carbonates, the release of soluble MoO₄^2– was delayed for 24 h with no inhibiting effect whereas with 0.1 M NaHCO₃ the immediate release was accompanied by the immediate and strong inhibiting effect on Zn dissolution. The concept of controlling the inhibition performance of LDH hybrid coatings by means of the environment composition is discussed