The adsorption and corrosion protection of 1-pyrrolidinedithiocarbamate (PDTC) and 2,5-dimercapto-1,3,4thiadiazole (DMTD) on bare Pb were investigated. Surface analyses revealed that for high concentration (i.e 10 mM), the organic molecules are strongly adsorbed on Pb surface. In 30 g.L-1 NaCl, Pb corrosion current was highly decreased and anodic passivation was very efficient. EIS measurements and simulations enabled to evaluate organic films thickness, anodic charge transfer resistance Rta and metal/film interface resistivity rho 0. Efficient Pb corrosion protection was confirmed. Results obtained from Young and power law models showed that EIS parameters are not much dependent on the chosen analytical expression.

The oxidation behaviour of a ferritic stainless steel containing 17%Cr in dry or wet air was examined during exposures of less than one minute at 1200°C. The extent of attack was assessed by direct weight measurement complemented by nuclear reaction analysis of the oxygen uptake. The phases produced were identified by Laser Raman and Glow Discharge spectroscopy. The oxidation mechanism appeared to be a competition between chromia formation, its evaporation as CrO3 and spinel oxide formation.

In a context of ageing reinforced concrete structures, electrochemical chloride extraction (ECE) is an interesting treatment for structures damaged by chloride-induced corrosion. This paper summarises the state of the art by presenting the concept of ECE, assessing available measurement techniques and discussing influencing factors. The determination of ECE efficacy requires the consideration of different results, and particularly those pertaining to chloride extraction, corrosion mitigation and evolution of pH. This literature review also highlights the potential side effects and risks to the concrete structure. Further work is needed to ascertain the long-term performance of ECE.

The stiction phenomenon which results in the adhesion of the brake pad to the disc brake of a vehicle has been investigated from a corrosion point of view. Asbestos-free organic pad that contains copper associated with a cast iron disc was investigated and compared to a model system which consisted in a ceramic pad (chemically inert) associated with the same cast iron disc. The whole system was described as a thin-layer cell of electrolyte and was studied using different electrochemical methods including polarization curves and impedance spectroscopy. The influence of the cell geometry was pointed out, but the corrosion of the system is enhanced due to the presence of copper in the pad. Indeed, the copper dissolves from the pad and redeposits on the disc. This was confirmed by scanning electron microscopy observations and Raman spectroscopy. A mechanism taking into account the thin-layer geometry was then proposed to account for the role of metallic additive (in this case copper) on the corrosion of the disc.

Gold electrodes were modified by silver and gold nanocrystals (NCs) that self-organize onto the surface. Their optical properties were explored by measuring electroreflectance spectra as a function of electrode potential. Below their oxidation potential, no shift of the reflectance maximum was observed for Ag NCs. This can be explained by a low interfacial capacitance resulting from the impossibility for the electrolyte to penetrate into the hydrophobic layer created by the NCs dodecanethiol ligands. Conversely, a non-monotonous evolution was observed with the electrode potential for oleylamine capped Au NCs. This behavior is suggesting a less dense hydrophobic layer, allowing significant electrolyte penetration. Next, electroactive compounds were adsorbed on the the Au NCs assemblies and characterized by Raman spectroelectrochemistry. In the first system displaying a single electron transfer with no coupled chemical reaction, only the spectrum intensity changed, because oxidation generated a Raman resonant radical cation. The second study considered 4-nitrothiophenol, for which up to 6 electrons and 6 protons may be transferred. In this case, the nitro band disappeared upon reduction, and the spectrum displayed typical features of the formed 4-aminothiophenol.

Effect of 2,5-dimercapto-1,3,4-thiadiazole (DMTD) concentration on the electrochemical behaviour of bronze was studied in 30 g L−1 sodium chloride (NaCl) by means of surface analyses and electrochemical techniques. Scanning electron microscopy (SEM) was used to observe surface morphology. Raman micro-spectroscopy was carried out to study chemical structure of deposited layers. X-ray photoelectron spectroscopy enabled elemental characterization as well as molecular structure investigation. Finally, electrochemical polarization and impedance permitted a thorough study of corrosion protection behaviour reached through the presence of DMTD-based organic layers on the surface. Above 1 mM, a fast adsorption of DMTD on copper (Cu) and lead (Pb) allows a thin and blocking film to be formed on bronze surface. DMTD prevents oxide formation at high concentrations, and the surface film is mainly composed of CuI-DMTD and CuII-DMTD complexes as evidenced by spectroscopic techniques, with a bidentate adsorption at 1 mM and monodentate adsorption at 10 mM.

The increasing international interest in contemporary architecture has drawn attention to the numerous listed buildings made of reinforced concrete in Europe, and especially in France. The main source of deterioration of this cultural heritage is the corrosion of rebars through carbonation or chloride contamination, but also often by a combination of both. The present study explored this combined corrosion mechanism in reinforced concretes, and investigated Electrochemical Chloride Extraction (ECE) as a technique to stop or decrease corrosion. The analytical approach was based on physico-chemistry, electrochemical measurements, Raman spectroscopy and SEM examinations. The results evidenced the aggressiveness of the combined carbonation and chloride-induced corrosion, and demonstrated the efficiency of the ECE treatment in terms of chloride extraction and reduction of corrosion rate. It appears that ECE treatment only reduces corrosion activity by increasing pH to a value of 10. Nevertheless, the long term durability of the treatment is questionable as the return to a sound concrete passivity is not obtained.

The corrosion inhibition of nickel in 0.5 M H2SO4 by cysteine was investigated with various electrochemical methods and surface observations by SEM. The cyclic voltammetry revealed that the current density is the highest in absence of the cysteine and decreases with increasing inhibitor concentration. The cysteine is an anodic inhibitor. The polarization and electrochemical impedance spectroscopy showed that the cysteine has a poor inhibitive effect. The surface observation by scanning electron microscope corroborates the addition of cysteine has no significant improvement of the surface morphology of nickel electrode in 0.5 M H2SO4. Results obtained by different methods corroborate each other.

Herein, we report tip-enhanced Raman spectroscopy (TERS) hyperspectral imaging under electrochemical control of a non-Raman-resonant molecular compound. A new setup combining a Scanning Tunneling Microscope (STM) and an optical coupling with high signal excitation and collection efficiency enables fast chemical imaging of an opaque functionalized electrode surface upon polarization. Variations in the TERS signal intensity up to 1.8 were observed across the surface, and correlated with topographic heterogeneities. These fluctuations, attributed to enhancement of the local electromagnetic field below the TERS tip, were used to estimate the lateral resolution of the produced hyperspectral image, which was found greater than 8 nm. This work represents an important step towards the use of electrochemical TERS imaging as a unique tool to unravel electrochemical processes at the nanoscale.

Civil engineering structures and historical buildings can suffer from corrosion of the embedded reinforcing steel once the concrete cover is totally carbonated and/or when chloride ions have reached the steel/concrete interface. In practice, these two types of contamination can be encountered separately or combined requiring implementation of proper repair methods. In this research, carbonated and chloride-contaminated reinforced concrete specimens were studied by three main analysis means: electrochemical characterizations, Raman microspectrometry and scanning electron microscopy (SEM). The specimens were contaminated in a two-step process involving addition of chlorides followed by carbonation of the complete cover. Electrochemical chloride extraction (ECE) was then performed as a repair treatment (1 A/m(2) of steel surface during 8 weeks). The efficiency of the treatment and its impact on the steel/concrete interface and cement matrix were studied during the treatment, after steel depolarization and on the long term (several months) in order to evaluate the durability of the treatment. Electrochemical characterizations showed an increase of corrosion rates comparing the specimens after fabrication and after carbonation (from a negligible level of 0.1 mu A/cm(2) to values in excess of 10 mu A/cm(2)). SEM observations confirmed this significant increase with the identification of a corrosion layer on most of the steel/concrete interface after carbonation. The ECE efficiency was evidenced by a decrease of chloride content below the practical threshold value of 0.4% by weight of cement after a two weeks treatment. Simultaneously a realkalisation ring was observed around the reinforcement bar having a diameter of about 1 cm after four weeks. Results obtained after depolarization showed that a two weeks ECE treatment allowed the stabilization of the corrosion state of the rebar.

Prediction of material lifetime such as stainless steels requires a clear understanding of passivation, corrosion, and pitting mechanisms. Despite its ubiquity and its history, the mechanisms of pitting are poorly understood, mainly because the stochastic behavior of the phenomenon, which results in many individual processes occurring simultaneously on the material surface. It is thus necessary to devise experiments which allow to work on a single pit for a better understanding of mechanisms governing pitting from its initiation to the propagation or its repassivation. Different experimental setup allowing the local injection of aggressive species such as chloride ions, have thus been developed [1-3], including a flow micro-device allowing a single pit to be initiated and then propagated over long time [4-6]. In this work, we show that we were able to reproduce, at will, the pitting of 316L stainless steel in order to study its propagation at various stages and to revisit the different parameters involved in the pitting process. Thanks to a statistical analysis performed on identical experiments, it was possible to build some zone diagrams showing the stability of pits as a function of the chloride concentration, the pit dimensions, and the electrode potential. Interestingly, the chemistry inside the pit was also studied as a function of the electrode potential. These experiments were performed with a specific experimental setup in order to measure the pitting current of a single pit simultaneously with the Raman spectrum thus opening new insight in the identification of species inside the pit. It was also possible to link the sulphate concentration (and thus the pH variation) inside the pit to the current as a function of time. [1] K. Fushimi, K. Azumi, M. Seo, Use of a liquid-phase ion gun for local breakdown of the passive film on iron, J. Electrochem. Soc., 147 (2000) 552-557. [2] K. Fushimi, M. Seo, Initiation of a local breakdown of passive film on iron due to chloride ions generated by a liquid-phase ion gun, J. Electrochem. Soc., 148 (2001) B450-B456. [3] C. Gabrielli, S. Joiret, M. Keddam, H. Perrot, N. Portail, P. Rousseau, V. Vivier, Development of a Coupled SECM-EQCM Technique for the Study of Pitting Corrosion on Iron, J. Electrochem. Soc., 153 (2006) B68-B74. [4] N. Aouina, F. Balbaud-Celerier, F. Huet, S. Joiret, H. Perrot, F. Rouillard, V. Vivier, A flow microdevice for studying the initiation and propagation of a single pit, Corros. Sci., 62 (2012) 1-4. [5] S. Heurtault, R. Robin, F. Rouillard, V. Vivier, Initiation and propagation of a single pit on stainless steel using a local probe technique, Faraday Discuss., 180 (2015) 267-282. [6] S. Heurtault, R. Robin, F. Rouillard, V. Vivier, On the Propagation of Open and Covered Pit in 316l Stainless Steel, Electrochim. Acta, 203 (2016) 316-325.

A rotaxane scaffold incorporating two dithiolane anchoring units for the modification of gold surfaces has been functionalized with multiple copies of a redox unit, namely ferrocene. Surface modification has been first assessed at the single molecule level by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) imaging, while tip enhanced Raman spectroscopy (TERS) provided the local vibrational signature of the ferrocenyl subunits of the rotaxanes grafted onto the gold surface. Finally, oxidation of the redox moieties within a rotaxane scaffold grafted onto gold microelectrodes has been investigated by ultrafast cyclic voltammetry. Intramolecular electron hopping is indeed extremely fast in this system. Moreover, the kinetics of charge injection depends on the molecular coverage due to the influence of intermolecular contacts on molecular motions.

Through the characterization of functional nanomaterials or of molecular architectures under operating conditions (in situ, operando), new insights in their working mechanism will be accessible. In this context, tip-enhanced Raman spectroscopy (TERS) which enables the extraction of precise chemical signatures at the nanoscale represents a great alternative to ultra-high vacuum analytical techniques. This review compiles the recent advances in in situ TERS characterizations and focuses on the strong potential of TERS to characterize the electrochemical processes taking place at the electrode/electrolyte interface.

In the quest for analytical tools which enable the characterization of materials at the nanoscale and under the condition of their operation (in situ, operando), the emerging tip-enhanced Raman spectroscopy (TERS) now enters the spotlight. We demonstrate in this work that a TERS tip can be functionalized and partially insulated to be used as a microelectrode enabling electrochemical substrate enhanced Raman sectroscopy (EC-SERS) at a single hotspot. This "SERS at a tip" experiment enables one to capture the electrochemical transformation of a molecular layer self-assembled on a tapered gold microelectrode. The proposed setup and protocol open new perspectives in the characterization and development of complex redox architectures for molecular devices.

Interaction between ammonium pyrrolidinedithiocarbamate (PDTC) and bronze in 30 g L-1 NaCl was investigated at several concentrations between 0.1 and 10 mM by means of various electrochemical and spectroscopic techniques. Electrochemical measurements revealed a fast adsorption process of PDTC on Cu and Pb and the formation of a thick insulating and protective film with a high surface coverage. At high concentrations, PDTC prevents oxides formation. Surface analyses confirm PDTC adsorption on bronze mainly via interaction between sulphur atoms and Cu sites to form Cut-PDTC complex.

Herein we present new substrates for surface-enhanced Raman spectroscopy (SERS). The synthesis of colloidal nanoparticles through an organometallic route allowed us to obtain gold, silver, or copper nanoparticles with well-controlled shapes and sizes (5-12 nm in diameter). The organization of these nanoparticles into large-scale 3D superlattices produces a very large number of "hot spots" at the origin of the signal enhancement. Each superlattice was studied individually to correlate its optical and SERS properties to the thickness, the nanoparticle sizes, and the interparticle distance. This experimental and theoretical study provides insights for the optimization and tuning of the SERS activity. Indeed, significant SERS amplification could be observed regardless of the nature of the metal. In addition, the SERS signal was homogeneous at the surface of the superlattices, which opens the route for a new approach in analytical SERS detection.

Intermetallic compounds A(2)B(7) (A = rare earth, B = transition metal) are of interest for Ni-MH batteries. Indeed they are able to absorb hydrogen reversibly and exhibit good specific capacity in electrochemical route. To understand the effect of rare earth on properties of interest such as thermodynamic, cycling stability and corrosion, we synthesized and studied three compounds: Y2Ni7, Gd2Ni7 and Sm2Ni7. Using Sieverts' method, we plot P-c-isotherms up to 10 MPa and study hydride stability upon solid-gas cycling. Electrochemical cycling was also performed, as well as calendar and cycling corrosion study. Corrosion products were characterized by means of X-ray diffraction, electron diffraction, Raman micro spectroscopy and scanning and transmission electron microscopies. Magnetic measurements were also performed to calculate corrosion rates. A corrosion mechanism, based on the nature of corrosion products, is proposed. By combining results from solid-gas cycling, electrochemical cycling and corrosion study, we attribute the loss in capacity either to corrosion or loss of crystallinity. (C) 2016 Elsevier B.V. All rights reserved.

Adsorption of ammonium pyrrolidine dithiocarbamate (PDTC) on copper surface in 0.2 and 30 g L-1 NaCl media was investigated by different electrochemical methods and surface analyses. The results from electrochemical measurements showed that PDTC adsorbs rapidly on copper surface and revealed a marked effect of mixed inhibition. Surface analyses confirm the adsorption of PDTC on copper and the formation of a Cu-PDTC complex through the S atoms of PDTC. At high concentrations PDTC prevents oxides and cuprous chloride formation. XPS results showed that PDTC bonds with cuprous species indicating the formation of Cu-I-PDTC complex. (C) 2016 Elsevier Ltd. All rights reserved.

Implementation of Tip Enhanced Raman Spectroscopy in liquid is still a challenge. We demonstrate herein its feasibility in an upright illumination/collection configuration. Through a thin layer of organic solvent covering the sample, laser focussing on the tip is possible, enabling TERS imaging in liquid.

The electrochemical behavior of hydride-forming A(2)B(7) alloys (Y2Ni7, LaSmNi7, and Gd2Ni7) is investigated in KOH solution. The evolution of the material performance is shown to strongly depend on the A elements. Electrochemical impedance spectroscopy (EIS), SEM observations, XRD, and Raman spectroscopy showed that Y2Ni7 is mainly sensitive to calendar corrosion and decrepitation, whereas LaSmNi7 and Gd2Ni7 are sensitive to the concomitant effect of both cycling and calendar corrosion. It is also shown that the capacity loss of Gd2Ni7 can be ascribed to amorphization on cycling, which is not the case for Y2Ni7. The formation of both an thin oxide film (a few tens of nanometers thick) at the material surface, measured by EIS, and the dissolution products formed during long-term immersion, analyzed by Raman spectroscopy, is in agreement with the decrease in material activity evaluated by EIS during cycling at different depths of charge.