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After passage of a delamination front at a polymer/zinc interface, pH oscillations and oscillations in the quantity of corrosion products are observed. The reason for these oscillations is the low quantity of water in the confined reaction volume, water consumption by oxygen reduction, and water regeneration after precipitation of ZnO.

Rust Resistance The rusting of iron and steel can be prevented through the addition of 11% or more chromium. The addition of molybdenum can enhance the corrosion resistance, with a complex interplay between the Cr and Mo atoms. However, if chemical variations exist, corrosion can still occur in localized regions or if the surface layer is mechanically abraded. Duarte et al. (p. 372 ) studied the corrosive failure of an iron-based glassy alloy. A combination of atom probe tomography, electron microscopy, and x-ray diffraction was used to build up a near atomistic picture of local variations in the metal as it was heated and allowed to crystallize, and the impact these processes have on the corrosion resistance.

The scanning Kelvin probe (SKP) is a versatile method for the measurement of the Volta potential difference between a sample and the SKP-tip (ΔψsampleSKP-tip). Based on suitable calibration, this technique is highly suited for the application in corrosion science due to its ability to serve as a very sensitive noncontact and nondestructive method for determining the electrode potential, even at buried interfaces beneath coatings or on surfaces covered by ultrathin electrolyte layers, which are not accessible by standard reference electrodes. However, the potential of the reference (i.e., the SKP-tip) will be influenced by variations of the surrounding atmosphere, resulting in errors of the electrode potential referred to the sample. The objective of this work is to provide a stable SKP-tip which can be used in different or changing atmosphere, e.g., within a wide range of relative humidity (approximately 0–99%-rh) or varying O2 partial pressure, without showing a change of its potential (note that the wor...

Iron (Fe(0) ) corrosion in anoxic environments (e.g. inside pipelines), a process entailing considerable economic costs, is largely influenced by microorganisms, in particular sulfate-reducing bacteria (SRB). The process is characterized by formation of black crusts and metal pitting. The mechanism is usually explained by the corrosiveness of formed H(2) S, and scavenge of 'cathodic' H(2) from chemical reaction of Fe(0) with H(2) O. Here we studied peculiar marine SRB that grew lithotrophically with metallic iron as the only electron donor. They degraded up to 72% of iron coupons (10 mm × 10 mm × 1 mm) within five months, which is a technologically highly relevant corrosion rate (0.7 mm Fe(0) year(-1) ), while conventional H(2) -scavenging control strains were not corrosive. The black, hard mineral crust (FeS, FeCO(3) , Mg/CaCO(3) ) deposited on the corroding metal exhibited electrical conductivity (50 S m(-1) ). This was sufficient to explain the corrosion rate by electron flow from the metal (4Fe(0) → 4Fe(2+) + 8e(-) ) through semiconductive sulfides to the crust-colonizing cells reducing sulfate (8e(-) + SO(4) (2-) + 9H(+) → HS(-) + 4H(2) O). Hence, anaerobic microbial iron corrosion obviously bypasses H(2) rather than depends on it. SRB with such corrosive potential were revealed at naturally high numbers at a coastal marine sediment site. Iron coupons buried there were corroded and covered by the characteristic mineral crust. It is speculated that anaerobic biocorrosion is due to the promiscuous use of an ecophysiologically relevant catabolic trait for uptake of external electrons from abiotic or biotic sources in sediments.

As we could recently show, scanning Kelvin probe force microscopy (SKPFM) is a very promising and powerful tool for the in situ investigation of filiform corrosion. Here we present how the underlying processes, namely the galvanic coupling of active head and intermetallic particles, can be visualised by performing SKPFM experiments under gas change conditions, i.e. by switching the atmosphere between nitrogen and air. It will be shown that, the different activity of the active particles can be detected by SKPFM at the buried coating/alloy interface and that these differences in activity play a role in determining the course of the FFC.

Hydrogen uptake by metals is of high interest for many applications. Hydrogen storage may be a crucial factor for shaping the energy management of the future, but hydrogen absorption in some metallic materials, such as high strength steels, may also cause so called hydrogen induced embrittlement, which constitutes a serious operational safety problem in technical applications. Hence, hydrogen uptake into and permeation through metals is an important field of research. However, what is missing is a ready to use technique with high lateral resolution. Here a novel approach will be presented, based on a potentiometric hydrogen detection at high lateral resolution. Keywords: Scanning Kelvin probe, H2 permeation, Duplex steel, Palladium, High resolution

A wide range of high-performance X-ray surface/interface characterization techniques are implemented nowadays at every synchrotron radiation source. However, these techniques are not always `non-destructive' because possible beam-induced electronic or structural changes may occur during X-ray irradiation. As these changes may be at least partially reversible, anin situtechnique is required for assessing their extent. Here the integration of a scanning Kelvin probe (SKP) set-up with a synchrotron hard X-ray interface scattering instrument for thein situdetection of work function variations resulting from X-ray irradiation is reported. First results, obtained on bare sapphire and sapphire covered by a room-temperature ionic liquid, are presented. In both cases a potential change was detected, which decayed and vanished after switching off the X-ray beam. This demonstrates the usefulness of a SKP forin situmonitoring of surface/interface potentials during X-ray materials characterization experiments.

In many technical processes, high temperature wetting of a liquid metal phase on a solid substrate occurs via an extensive chemical reaction and the formation of a new solid compound at the interface. For instance, good adhesion of the zinc coating to the steel surface is one of the most important requirements that the hot-dip galvanizing process has to fulfill. Good adhesion directly depends on the formation of a defect-free Fe2Al5 inhibition layer at the interface. The complex surface chemistry of oxides on the steel surface which is a result of segregation and selective oxidation upon recrystallization annealing significantly influences the kinetics of the correlated reactive wetting. This article presents the development of a novel advanced technique for the investigation of high temperature wetting process up to a temperature of 1100 K and provides first new insights in the mechanisms of the reactive wetting process in presence of oxides on the surface. The method is based on the sessile drop method with an additional spinning technique to get rid off the liquid metal phase at any chosen wetting time, thusly opening the way to access the interfacial reaction layer directly. The presented work focuses on model alloys of interest which are mainly relevant to the industrial steel grades. Emphasis is put both on the wettability of liquid Zn and on the interfacial reactions during reactive wetting process. Insights into such reactive phenomena are fundamental demand to improve the hot-dip galvanizability of advanced high strength steel grades.

Due to their promising corrosion properties, metallic coatings containing magnesium are currently widely investigated for use as protective coatings for steel sheet. Particularly, alloying zinc coatings with magnesium results in a remarkable improvement of the corrosion resistance of the painted system. While some aspects of this improvement have been understood, the progress of the corrosive degradation of the alloy coating/paint interface has not been reported in detail. In this paper, the delamination of a model polymer from the intermetallic MgZn2 is described and a degradation mechanism proposed. Aspects for the design of stable interfaces are discussed.

Kelvin Probes can be modified to control as well as monitor potential. The design and operation of two different Kelvin Probe Potentiostats (KPPs) are described in this paper. One approach uses a permanent magnet and double coil to oscillate the needle at a fixed frequency, an AC backing potential, and software analysis and control schemes. This technique can also control the distance between the tip and sample, thereby tracking the topography of the sample. Both KPPs were used to make measurements on Type 304L stainless steel under thin layers of electrolyte. Cathodic polarization curves exhibited a limiting current density associated with oxygen reduction. The limiting current density varied with solution layer thickness over a finite range of thickness. Anodic polarization curves on 304L in a thin layer of chloride solution resulted in pitting corrosion. The breakdown potential did not vary with solution layer thickness. However, the thin layer was observed to increase in volume remarkably during pit growth owing to the absorption of water from the high humidity environment into the layer with ionic strength increased by the pit dissolution. The open circuit potential (OCP) and solution layer thickness were monitored during drying out of a thin electrolyte layer. Pitting corrosion initiated, as indicated by a sharp drop in the OCP, as the solution thinned and increased in concentration.

Model thin film coated substrates were developed to investigate the functionality of Zn-phosphates, the polymeric binder and emulsifiers during the interface formation on iron substrates. By means of grazing incidence FTIR-spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy, it was observed that ultra-thin films of zinc phosphates and hydroxides, with a thickness of less than 2 nm, adsorb on the iron surface during the formation of the latex coating/metal interface. Moreover, film formation conditions were developed for the deposition of hexagonal closed packed defect-free-monolayers of latex particles over large areas. This allowed the application of time of flight SIMS for the analysis of the monolayer-metal interface and the study of its morphology before and after film annealing. After annealing, the monolayer film showed an enrichment of surfactants at the particle boundaries and at the interface to the phosphate and hydroxide covered metal substrate.

Defined mono- and multilayer styrene/acrylate latex films were applied on model oxide covered iron substrates. Unmodified and chemically modified Zn-phosphate pigments were investigated with regard to corrosion inhibiting properties in combination with the model latex films. The nature of these pigments and their location in the coating influencing the de-adhesion kinetics in corrosive environments were studied by means of in situ scanning Kelvin probe measurements, which were correlated with the composition of the coating/metal interface. As shown by means of ATR-FTIR spectroscopy, Zn-phosphates improve the barrier properties. Due to the application of Zn-phosphate containing latex coatings an about 2–3 nm thin inorganic interface layer was formed containing Zn-hydroxides, phosphates, chromates and molybdates in different quantities, depending on the chemical modification of the pigment. The release of pigment ions through the binder matrix is responsible for the inhibition of the cathodic de-adhesion process at the interface. At distances larger than few tenths of nanometers the release effect of the pigments is significantly reduced. Chromate and molybdate modified Zn-phosphates showed a fast release and interfacial enrichment of these ions thereby leading to improved corrosion resistance.

This paper presents studies on the efficacy and on the limits of polypyrrole (Ppy) doped with either MoO42- or [PMo12O40]3− as self-healing corrosion protecting coatings. The kinetics of the cathodic delamination were studied by means of the Scanning Kelvin Probe (SKP). This method, in combination with cyclic voltammetry, UV–visible spectroscopy (UV–vis) and X-ray photoelectron spectroscopy (XPS), shows a potential driven anion release from the Ppy coating that results in an inhibition of the corrosion process taking place in the defect. Thus, an intelligent release of inhibitor occurs only when the potential at the interface decreases. Inhibitor anions are released only due to an active defect. However, the release mechanism can be easily negatively affected by the presence of small cations and/or by too high pH values at the buried interface. Hence, such a self-healing coating has to be carefully designed in order to ensure an effective performance.

▪ Abstract The review highlights the state-of-the-art research regarding the application of modern in situ spectroscopic, microscopic, and electrochemical techniques to improve the understanding of the interaction of organic molecules with metal surfaces. We also consider the chemical and electrochemical processes that lead to a de-adhesion of polymers from metal surfaces. Spectroscopic techniques such as surface-enhanced infrared or Raman spectroscopy provide molecular understanding of organic molecules and water at buried metal surfaces. This information is complementary to adhesion studies by means of atomic force microscopy and de-adhesion studies of polymer layers from metals by means of a scanning Kelvin probe. Adhesion and de-adhesion mechanisms are discussed, especially those involving humid and corrosive environments, which are the predominant and most important for metal/polymer composites in engineering applications.

Increased alkalinity during oxygen reduction contributes largely to corrosion and polymer degradation on galvanized steel. In these investigations, studies have been carried out to quantify the pH dependence of the electrochemical properties for pure zinc under alkaline conditions. In contrast to theoretical predictions, a strong kinetic influence is observed for intermediate to high alkaline pH values, resulting in an anodic shift of the corrosion potential and corresponding changes in the electrochemical properties of the surface layer. Also, a significant delay in the potential stabilisation is observed for pH values assigned to the increase, respectively, decrease to this found potential maximum. As an explanation a precipitant layer of various zinc complexes is suggested that changes its structure and composition with variation of the pH. For pH values below 12 it has a more homogeneous and compact structure. In the pH range between 12 and 13 the structure becomes inhomogeneous and porous. For higher pH values than 13 it changes back to the homogenous and compact structure. Keywords: Zinc, pH-Dependence, Precipitate, EIS, Alkaline solution

MAXNET Energy is an initiative of the Max Planck society in which eight Max Planck institutes and two external partner institutions form a research consortium aiming at a deeper understanding of the electrocatalytic conversion of small molecules. We give an overview of the activities within the MAXNET Energy research consortium. The main focus of research is the electrocatalytic water splitting reaction with an emphasis on the anodic oxygen evolution reaction (OER). Activities span a broad range from creation of novel catalysts by means of chemical or material synthesis, characterization and analysis applying innovative electrochemical techniques, atomistic simulations of state-of-the-art x-ray spectroscopy up to model-based systems analysis of coupled reaction and transport mechanisms. Synergy between the partners in the consortium is generated by two modes of cooperation – one in which instrumentation, techniques and expertise are shared, and one in which common standard materials and test protocols are used jointly for optimal comparability of results and to direct further development. We outline the special structure of the research consortium, give an overview of its members and their expertise and review recent scientific achievements in materials science as well as chemical and physical analysis and techniques. Due to the extreme conditions a catalyst has to endure in the OER, a central requirement for a good oxygen evolution catalyst is not only its activity, but even more so its high stability. Hence, besides detailed degradation studies, a central feature of MAXNET Energy is a standardized test setup/protocol for catalyst stability, which we propose in this contribution.

In the third part of this series of papers a kinetic analysis of the experimental data shown in Parts 1 and 2 are presented. Further experiments demonstrate the strong influence of CO2 on the delamination kinetics. For CO2 concentrations lower than 1 vol% the rate of delamination is reduced drastically without changing the reaction, between 1 vol% and 2 vol% the overall delamination rate is no longer controlled by diffusion of irons but by a charge transfer controlled O2-reduction. The results are interpreted by thin zinc carbonate layers formed at the interface, which inhibit the rate of the ETR.

The basic mechanism of the cathodic delamination of polymer films from zinc-coated steel starting from a defect with an intact zinc layer has been derived. Scanning Kelvinprobe and ESCA measurements have been carried out with a very simple model system. The delamination is presented as the formation of a galvanic element between the active defect and the delamination front with electrons and cations being transported to the local cathode. The oxygen reduction in the delaminated area leads to an alkalinisation of the zinc/polymer interface resulting in a significant growth of the oxide layer.

The present investigations were carried out to understand the role played by nitrogen in affecting the passivation and pitting kinetics of Fe-N model alloys. Synthetic alloys of Fe-N, Fe-10%Ni-N and Fe-10%Ni-3%Mo-N were prepared by surface nitriding process with 0.9 wt% nitrogen on the surface. Pit initiation studies were conducted on pure Fe and Fe-N alloy in an acidic sulphate solution (0.01 M H2SO4 and 0.99 M Na2SO4) containing 0.0007, 0.001, 0.007 and 0.07 M NaCl at three different electrode potentials, namely, +800, +1000 and +1200 mV (NHE). Pit growth kinetics was assessed by studying the dissolution behaviour of these alloys during potentiostatic transient in an acidic sulfate solution containing 0.5, 1, 2 and 4.5 M NaCl. The steady state dissolution current was considered as the parameter reflecting the pit dissolution behaviour of the alloys. Potentiodynamic anodic polarisation of the alloys was also carried out in the acidic sulphate solution at room temperature. The results of the investigation indicated that as the chloride content increased nitrogen addition delayed the pit initiation as well as reduced the dissolution kinetics of the pits. The polarisation study of the model alloys indicated that nitrogen played a greater role in reducing the corrosion behaviour of the alloys by reducing the active peak current density and widening the passive range in which pitting is less probable.

The effect of gallic acid on the corrosion reactions underneath paint films on steel during immersion experiments in the presence and absence of oxygen is investigated using Moessbauer spectroscopy. The mass evolution as a function of immersion time is measured for different solid phases such as iron, lepidocrocite, magnetite and ferrous hydroxide. Results show that in the presence of oxygen, gallic acid enhances the initial dissolution of iron due to complexation with ferrous ion. The ferrous complex is subsequently oxidized into an insoluble ferric complex leading to a reduction in the anodic reaction rate. No magnetite is formed under these conditions. In the absence of oxygen, magnetite is formed by reduction of lepidocrocite on precorroded steel coated with films not containing gallic acid. When gallic acid is present in the paint film the reductive transformation of lepidocrocite to magnetite is inhibited.

In the second part of this paper, the model presented in Part 1 is verified by several key experiments. For the simple, non-pigmented polymer used in this study, the migration of cations along the substrate/polymer interface is the rate-determining step for the overall delamination reaction The delaminated area therefore increases with time The larger the size of the hydrated cation the slower is the observed delamination rate which increases in the order Li + + + + The type of the anion does not significantly influence the delamination rate The delamination rate also depends on the concentration of cations at the defect: the higher the concentration the faster the rate of delamination This is interpreted by a threshold concentration of ions at the intact substrate/polymer interface which is detected by the Kelvinprobe The threshold concentration must be exceeded in order to galvanically couple the intact interface with the defect and to allow the reduction of oxygen just in front of the delaminated zone which will result in the loss of adhesion in this zone The pH-change accompanied by the reduction of oxygen is measured in situ by pH-sensitive pigments incorporated into the polymer film and by an Auger-analysis of the substrate/polymer interface A large excess of cations in comparison to anions is observed Finally the first stages of delamination are analyzed In contrast to steady state conditions the delaminated area increases linearly with time which is interpreted by charge-transfer controlled kinetics of the oxygen reduction

In the first part of this study are presented the theory and the experimental techniques which are necessary to investigate the delamination of model coatings on steel. It is shown that the electrochemical reactions taking place at the substrate/electrolyte and substrate/polymer interfaces are responsible for delamination. Due to the fact that the electrochemical reactions are accompanied by changes in the corrosion potential, it is possible to identify and follow the delamination by measuring the corrosion potential as a function of time and local position. Furthermore, it is demonstrated that the Volta-potential difference between a reference metal and the model polymer surface is determined by the corrosion potential, whereas the influence of the Donnan-potential is small and constant. By combining several experimental techniques, like the Scanning Kelvinprobe, Auger electron spectroscopy and mechanical de-adhesion tests, the delamination process is studied in detail and a model is presented, which is based on the existence of a galvanic element at the substrate/polymer interface. The uncoated iron is the local anode, where the iron dissolution predominates, whereas the delaminated part represents the local cathode and, within this area, only the oxygen reduction takes place. The second and third part of this paper deal with an experimental verification of this model.

International audience; Materials science in general, and surface/interface science in particular, have greatly benefited from the development of high energy synchrotron radiation facilities. Irradiation with intense ionizing beams can however influence relevant sample properties. Permanent radiation damage and irradiation-induced sample modifications have been investigated in detail during the last decades. Conversely, reversible sample alterations taking place only during irradiation are still lacking comprehensive in situ characterization. Irradiation-induced surface charging phenomena are particularly relevant for a wide range of interface science investigations, in particular those involving surfaces of solid substrates in contact with gaseous or liquid phases. Here, we demonstrate partially reversible radiation-induced surface charging phenomena, which extend far beyond the spatial dimensions of the X-ray beam mainly as a consequence of the interaction between the surface and ionized ambient molecules. The charging magnitude and sign are found to be surface chemistry specific and dependent on the substrates' bulk conductivity and grounding conditions. These results are obtained by combining a scanning Kelvin probe with a synchrotron surface diffractometer to allow simultaneous in situ work function measurements during precisely controlled hard X-ray micro-beam irradiation

The electrochemical oxygen reduction reaction (ORR) on a n-Ge(100) surface in 0.1 M HClO4 was investigated in situ and operando using a combination of attenuated total reflection infrared (ATR-IR) spectroscopy and density functional (DFT) calculations. The vibrational modes of the detected intermediates were assigned based on DFT calculations of solvated model clusters such as Ge-bound superoxides and peroxides. ATR-IR shows the Ge-bound superoxide with a transition dipole moment oriented at (28 ± 10)° with respect to the surface normal. At slightly negative potentials, the surface-bound peroxide is identified by an OOH bending mode as a further intermediate, oriented at a similar angle. At strongly negative potentials, a surface-bound perchlorate is found. The findings indicate a multistep mechanism of the ORR. The reaction is furthermore coupled with the hydrogen evolution reaction (HER).

To investigate the chemical modification of metal surfaces by silanes and mercaptans used as molecular adhesion promoters between metal surfaces and polymer films, the adsorption of chlorosilanes and n-propylmercaptan has been examined on iron surfaces under ultra high vacuum conditions (UHV). The adsorption of silanes directly from the vapour phase has been impossible in UHV, however, a simultaneous condensation of water and silane leads to a stable silane layer. The hydrolysis reaction is rate determining. Stable mercaptan monolayers have been obtained only on oxygen covered iron surfaces. On pure iron the mercaptan molecules have been cracked, so that methyl groups as well as sulphur atoms could be found. The characterization of the surface layers has been performed by XPS and AES.

Oxygen reduction is a major cathodic partial reaction during the corrosion of iron. The reaction is greater than the H+ reduction reaction for pH values >4. In the same pH range the iron surface is covered by insoluble oxide layers like rust scales. As rust scales are reduced in the potential range of the oxygen reduction, it was the aim of this study to analyse the relation between the kinetics of the oxygen reduction and the reduction of the rust layer. The results presented in this paper show that oxygen is predominantly reduced within the rust scale and not at the metal/electrolyte phase boundary. In order to allow any oxygen reduction, the rust layers have to be reduced. Oxidized rust scales, which are nearly free of Fe2+ states, inhibit the reduction of oxygen completely.

The corrosion of rusted iron coated by organic lacquers is analysed. The rates of metal dissolution and oxide reduction are measured by in situ Moβbauer spectroscopy, the rate of oxygen reduction by a gas volumetric type of technique. For the first 100 h after wetting, rust reduction is more important than oxygen reduction as the cathodic partial reaction. Due to rust reduction, the morphology of the oxide scale is changed, which results in a loss of adhesion between the polymer and the substrate. The stability of the rust layer can be increased significantly after suitable surface treatments. Most effective is the chemisorption of organophosphates on to the surface of γ-FeOOH. After this treatment rust reduction is nearly completely inhibited and no loss of adhesion is observed after exposure of the modified and polymer coated material to aerated electrolytes.

Stress corrosion cracking (SCC) behavior of two high nitrogen steels, P900 (0.58 wt% N) and P900N (0.90 wt% N), in 1 wt% NaCl solution under an applied potential condition was investigated by slow strain rate testing (SSRT). The experimental results showed that there exists a critical potential for SCC for each of these two materials in the above solution. At applied potentials of 500 and 650 mV(SHE), SCC assisted by pitting corrosion was found to occur in P900 and P900N, respectively. The results also indicated that P900N is more resistant than P900 to SCC in 1 wt% NaCl solution. Electrolyte analyses after SSRT tests showed that during SCC tests most nitrogen from the steels is converted to NH 4 + .

Several new techniques have recently been introduced in order to analyse the corrosion of metals covered by very thin or even adsorbed electrolyte layers. In this study the same techniques are used for the first time to investigate the inhibition mechanism of a typical vapour phase inhibitor (ammonium benzoate) on iron under atmospheric corrosion conditions. During wet/dry transitions the corrosion potential and the corrosion rate are measured without touching the surface under investigation, the kinetics of the metal dissolution and the oxygen reduction are analysed in bulk electrolytes as well as below very thin electrolyte layers and the corrosion rate and the chemical composition of the inhibitor covered surface are determined under non-condensing reaction conditions, where the surface is covered by monolayers of water only. It is shown that the rate of the anodic and the cathodic partial reactions of the corrosion process are strongly effected by the thickness of the electrolyte layer. Due to the presence of the inhibitor the surface is passivated, but stable passivity is observed only for very thin electrolyte layers. The inhibitor efficiency, therefore, cannot be deduced from conventional electrochemical experiments in bulk electrolytes, but only from studies on a metal surface which is covered either by very thin layers or even adsorbed electrolyte layers.

The mechanism by which an alloy corrodes into a potentially useful porous sponge is understood qualitatively, but quantitative predictions of its final structure have been lacking. A model for this has now been proposed.

A new technique is presented, which is able to detect directly the corrosion induced delamination of polymer coatings from metallic substances. The technique is based on a local measurement of Volta-potentials. The defamination in the vicinity of local defects and the delamination caused by local contaminations below intact polymer layers can be determined quantitatively.

Room-temperature ionic liquids (RTILs) are promising candidates for a broad range of "green" applications, for which their interaction with solid surfaces plays a crucial role. In this high-energy x-ray reflectivity study, the temperature-dependent structures of three ionic liquids with the tris(pentafluoroethyl)trifluorophosphate anion in contact with a charged sapphire substrate were investigated with submolecular resolution. All three RTILs show strong interfacial layering, starting with a cation layer at the substrate and decaying exponentially into the bulk liquid. The observed decay length and layering period point to an interfacial ordering mechanism, akin to the charge inversion effect, which is suggested to originate from strong correlations between the unscreened ions. The observed layering is expected to be a generic feature of RTILs at charged interfaces. Refereed/Peer-reviewed

In this series of three papers new techniques are described, which allow the investigation of the corrosion kinetics of metal surfaces which are covered by very thin or even adsorbed electrolyte layers. In this first part the experimental arrangement is discussed in detail, which is used to measure simultaneously corrosion rates and corrosion potentials of atmospherically corroding iron surfaces during several wet/dry transitions without touching the surface under investigation. The theoretical basis for the measurement of electrode potentials using a Kelvin probe as a reference electrode is evaluated. Additional experiments have been performed to check the validity of the measured Volta potential and its correlation to the corrosion potential of the metal/electrolyte interface. The results prove that the potential drop across the oxide scale formed on top of the iron surface is small if the surface is kept in a humid environment (e.g. 95% relative humidity). Then, the Volta potential difference between surface and Kelvin probe can be directly correlated to the corrosion potential of the corroding metal surface.

In this study for the first time a circuit is presented which allows the measurement of polarisation curves on metal surfaces which are covered by electrolyte layers as thin as 2 μm. The circuit does not need any Luggin capillary but uses a Kelvin probe as a reference electrode which does not touch the surface under investigation. Results are discussed which have been obtained with platinum and iron as working electrodes. On iron electrodes, during drying the rate of the oxygen reduction is accelerated due to a faster transport of oxygen through the thin electrolyte layer. The surface is passivated either due to the precipitation of corrosion products or due to pH-changes inside the thin electrolyte layer. This confirms the model of the atmospheric corrosion of iron and steel presented in part 2 of this paper.

Corrosion of iron presents a serious economic problem. Whereas aerobic corrosion is a chemical process, anaerobic corrosion is frequently linked to the activity of sulphate-reducing bacteria (SRB). SRB are supposed to act upon iron primarily by produced hydrogen sulphide as a corrosive agent and by consumption of 'cathodic hydrogen' formed on iron in contact with water. Among SRB, Desulfovibrio species--with their capacity to consume hydrogen effectively--are conventionally regarded as the main culprits of anaerobic corrosion; however, the underlying mechanisms are complex and insufficiently understood. Here we describe novel marine, corrosive types of SRB obtained via an isolation approach with metallic iron as the only electron donor. In particular, a Desulfobacterium-like isolate reduced sulphate with metallic iron much faster than conventional hydrogen-scavenging Desulfovibrio species, suggesting that the novel surface-attached cell type obtained electrons from metallic iron in a more direct manner than via free hydrogen. Similarly, a newly isolated Methanobacterium-like archaeon produced methane with iron faster than do known hydrogen-using methanogens, again suggesting a more direct access to electrons from iron than via hydrogen consumption.

A Langmuir-Blodgett-Film-Balance was modified, in order to obtain electrochemical potential control of metal substrates during film deposition. With this balance octadecylmercaptan (ODM) was brought onto gold substrates under different potentials. The mercaptan monolayer was investigated by means of surface analytical techniques (XPS, ARXPS). Initial results concerning the potential dependence of the LB-layer are presented.

The adsorption of methyl and butyl-trimethoxysilane onto iron surfaces from the gas phase at different humidity levels has been investigated in situ with a quartzcrystal micro-balance and with ATR-IR spectroscopy. The thickness of the resulting siloxan polymer depends on the humidity during the film preparation. The polymer coating inhibits the corrosion of iron in an SO2-containing atmosphere.

The 83 institutes and research facilities of the Max Planck Society, established in 1948, include some of the world's leading scholars in the life sciences, including 17 Noble Prize winners, and publish 15,000 research papers annually. For the past 18 years, biologists have stood at the helm of the prestigious German organization. But last month, an electrochemist and materials scientist, Martin Stratmann, began a six-year term as president of the Munich-based society.Stratmann, who is 60, served as the director of the Max Planck Institute for Iron Research in Dusseldorf since 2000, where he helped develop self-healing coatings that can protect steels and other metals from rust. Stratmann spoke with David Levine about his vision for the Max Planck Society and about what the change of guard will mean for biomedical research. The conversation has been edited for clarity.

The reduction of oxygen has been studied on octadecylmercaptan self-assembled monolayers adsorbed on gold substrates in borate buffer solutions with a rotating disc electrode. A great inhibition of the oxygen reduction and other electrochemical reactions by these monolayers has been found. However, after polarisation at −0.80 V she the protecting properties of the film against electron transfer reactions are lost, and a behaviour similar to bare gold is observed. Ex situ XPS indicates that the thiol monolayer has not been desorbed to a large extent during oxygen reduction. Disorders of the monolayer structure and desorption of thiol molecules are proposed as the main reasons for the accessibility of electrochemical reactions to the surface.

The applicability of a new experimental technique - the Scanning Kelvinprobe - for the analysis of the delamination of polymer films from galvanized steel is discussed. Defect ions having direct access to the zinc/ polymer interface will diffuse along this interface, a process, which can be monitored by the Kelvinprobe in a very early state with a high local resolution. After incorporation of ions a galvanic element is formed, the local cathode being at the delamination front, where oxygen is reduced, and the local anode at the zinc coated defect. For the model polymer under investigation the interaction between the film and the substrate is weak and the rate determining step for the delamination is the diffusion of cations from the local anode to the local cathode. An exposure to a highly CO(2)-containing atmosphere before the delamination prolongs the incubation time of delamination. If there is no zinc layer at the defect, an anodic delamination mechanism occurs. Zinc is dissolved under the polymer film, while the steel surface is cathodically protected.

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Combinatorial material development was combined with high throughput microelectrochemistry to allow an efficient but comprehensive investigation of the interface chemistry of Al rich Al–Fe alloys as a function of their chemical composition. Composition spread thin films with a linear composition gradient were produced by thermal codeposition. A scanning droplet cell was used to determine the open circuit potential and to perform successive anodic oxide formation with intermittent impedance spectroscopy. The film formation factor, the relative permittivity of the oxides and the onset potential of oxide formation were determined quantitatively as function of the composition with a resolution of 0.5 at.%. An unexpected synergistic effect is found in a very narrow composition range between 9 and 12 at.% Fe. This effect, which shifts the onset potential by nearly 1 V, is discussed in terms of a local accumulation of Fe resulting in a redox stabilisation of space charge layer formation during high-field oxide growth. The results are supported by composition and depth dependent XPS measurements.

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