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Lithium Ion batteries have to be significantly improved to fulfill the challenging needs in electromobility or large scale energy storage technology. In this context the use of model electrodes such as single-crystals or thin films allows well-defined mechanistic studies. Here we present a detailed electrochemical investigation of the lithiation–delithiation behavior of Au thin film model electrodes in ionic liquid electrolyte. Cyclic voltammetry, galvanostatic-, stepwise potentiostatic lithiation–delithiation cycles, as well as galvanostatic intermittent titration technique, GITT, measurements were performed. We found nearly identical mechanism of Li insertion and extraction in these three types of measurements at different current levels. The mechanism of alloying or lithiation deviated from the mechanism of dealloying or delithiation. While during the lithiation process two main plateaus related to phase transformations occur in the potential–time curves three main plateaus appear during delithiation. First results of theoretical simulations confirm a high number of possible metastable phases in the Li–Au system. The measurements also point to the influence of SEI-film formation on the cycling behavior. Based on these insights a mechanistic sequence and a phase evolution diagram for the electrochemical alloying of Li with Au are presented.

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.

For an understanding of the four electron transfer mechanism of the electrochemical oxygen reduction reaction (ORR), a direct detection of intermediates on well-defined working electrode surfaces is crucial, as it bridges the gap between electrochemistry and computation. Here, the ORR is studied on the crystalline semiconductor n-Ge(1 0 0) by electrochemical attenuated total reflection infrared (ATR-IR) spectroscopy in aqueous NaClO4 and NaCl solutions at pH 10.5. Germanium-bound superoxide at a tilt angle of ∼45° with respect to the surface normal is found as an intermediate in both electrolytes. The frequency of the superoxide O O stretching mode differs by 25 cm−1 between the two electrolytes, hinting at a complex formation between at least one of the anions and the superoxo-intermediate. This complex formation may be related to the different surface terminations of germanium in the two electrolytes. The surface concentration of the superoxide intermediate is proportional to the ORR current. Analysis of the relation between absorbance and current shows that the rate constant of the second electron transfer step in the ORR, i.e. the step from superoxide to peroxide, in NaCl is three times as high as in NaClO4.

Electrochemical frequency modulation (EFM) is a rather novel technique to monitor corrosion rates in situ, providing direct access to Tafel slopes with only minor polarization. So far EFM has been applied mainly for electrochemical corrosion monitoring in purely chemical corrosion systems with predominant uniform corrosion, but it has also great potential for monitoring microbially influenced corrosion (MIC). Thus, in this study MIC induced by different cultures of sulfate-reducing bacteria (SRB) was monitored with EFM, and compared to results from linear polarization resistance (LPR) and measurements of the free corrosion potential E corr . The electrochemical results obtained in small scale bioreactors with a three electrode setup were complemented by chemical analysis and SEM observations. SRB featuring high corrosion rates were compared to non-corrosive but still H 2 -consuming control SRB, sterile controls and abiotic sulfide corrosion controls. Corrosion rates determined with EFM and LPR were accurate and precise in all cases as long as the system was based on uniform corrosion. However with the onset of localized corrosion both methods fail to predict accurate rates. Unlike other electrochemical corrosion rate measurements, EFM has the advantage to provide indicating ratios in the current response at different frequencies, so-called causality factors, which allow identifying changes in the corrosion system and therefore assessing the accurateness of the obtained results. As a consequence EFM is a promising electrochemical corrosion monitoring technique for MIC in fundamental and applied studies.

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...

A probe head for Raman spectroscopy was installed in the sample chamber of a height-regulated Kelvin probe (KP) in order to focus a laser beam beneath the KP needle and to detect light scattered at the sample surface. This allowed a simultaneous spectroelectrochemical analysis of buried polyvinylbutyral/sodium sulfate/steel interfaces during exposure to humid and dry air. Alterations of sulfate spectra, Volta potential shifts and variations of the polymer surface topography were monitored and found to be interrelated. Bulging of the polymer layer during humidification lowered the Volta potential and thereby indicated a reduction of the interface stability. Partial solvation of sulfate particles manifested in the evolution of the symmetric S O stretching vibration peak at ∼980 cm −1 , but was retarded and did not induce a volume increase at the polymer/sulfate interface that was detectable at the sample surface. Drying of water saturated PVB/Na 2 SO 4 /steel interfaces instantaneously induced a depression of the polymer surface and increased Volta potentials. Pronounced potential shifts in the range of several hundred millivolts, however, were not observed before de-solvation of sodium sulfate initiated. These observations confirmed that the combined KP-Raman spectroscopy approach provides valuable complementary information that is not available from each technique separately.

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.

We present an electrochemical study of Au3Cu (0 0 1) single crystal surfaces in 0.1 mol dm−3 H2SO4 and 0.1 mol dm−3 H2SO4 + 0.1 mmol dm−3 HCl, and of Cu3Au (0 0 1) in 0.1 mol dm−3 H2SO4. The focus is on in situ scanning tunneling microscopy experiments. The changes of the surface morphology, which are time- and potential-dependent, have been observed, clearly resolving single atomic steps and mono-atomic islands and pits. Chloride additives enhance the surface diffusion and respective morphologies are observed earlier. All surfaces have shown considerable roughening already in the passive region far below the critical potential.

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.

From corrosion to batteries and super-capacitors, mobility of ions at interfaces, a pre-requisite for many electrochemical processes, plays a key role in a great number of applications. In this paper we show for the first time that the Scanning Kelvin Probe (SKP) technique can be applied for studying ion mobility along any kind of insulator/insulator interface. As across these interfaces high biases can be applied, the determination of the mobility constants should be possible. Since for practically all kinds of interfaces model samples based on insulating substrate can be prepared, this is a break-through for studying ion mobility along any kind of interface, as well as mobility of ions adsorbed on a surface. While it has been shown nearly two decades ago that delamination of polymer/metal interfaces and also diffusion or migration of ions along such interfaces can be monitored in situ by SKP, no attempts have been made so far to apply this technique for investigating the mobility of ions also along interfaces between insulating materials. Here we show that this is possible. This opens up the use of SKP for a vast field of research that is of critical importance for many applications.

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.

The study of ion transport processes on non-polymer coated bare oxide covered iron and zinc surfaces showed that the presence of adsorbed ions determines the ion distribution on oxide/metal surfaces in humid atmosphere. For fundamental studies of ion ingress at polymer/oxide/metal interfaces, already the transport analysis in the absence of the polymer reveals important mechanistic aspects. Sophisticated spectroscopic techniques were applied for the correlation of electrochemical data with local surface chemistry. In-situ Scanning Kelvin Probe (SKP) measurements of the local interfacial potentials of oxide covered iron and zinc substrates and ex situ time-of-flight secondary ion mass spectroscopy (ToF-SIMS) analysis showed that the surface layer charge influences the ion transport processes. A model is proposed to explain the basic mechanism of hydrated ion transport on oxide covered zinc and iron.

Localised electrochemical and spectroscopic techniques were jointly applied for the evaluation of hydrated ion transport processes along polymer/oxide/metal interfaces. In situ Scanning Kelvin Probe (SKP) studies of the local interfacial potentials of organically coated oxide covered zinc and iron substrates were performed in humid nitrogen atmospheres. They were supported by ex situ small spot X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) analysis of the interfacial ion distribution. Based on the experimental results it is concluded that also in atmospheres of strongly reduced oxygen partial pressure at which no corrosive delamination takes place, a negatively charged layer of adsorbed hydroxide ions determines ion transport processes along interfaces between polymer films and oxide covered metals. No ion transport was observed for zinc substrates while hydrated cations were selectively transported along the polymer/iron interface. The reduction of oxygen molecules on the highly reactive iron oxide surface is assumed to be responsible for the generation of adsorbed interfacial hydroxide ions. On the other hand such oxygen reduction induced hydroxide formation in humid nitrogen atmospheres with strongly reduced oxygen partial pressure does not seem to take place on oxide covered zinc. The variation of free volumes at the polymer/substrate interface did not lead to a principal change of this phenomenon.

Titanium alloy (TiAl6V4) surfaces were treated with ultraviolet (UV) radiation to remove organic “contamination” molecules which remained on the surfaces after conventional cleaning processes. The UV-technique simultaneously revealed reactive surface hydroxyl groups at the metal surface which were monitored by the reaction with perfluorooctanoylchloride and application of Fourier-Transform infrared reflection-absorption spectroscopy and contact angle measurements, respectively. Two different cellulose polymers each made soluble in methanol by functionalized hydroxylalkyl-spacer groups and their mixtures were deposited on UV-treated TiAl6V4 surfaces. Atomic force microscopy measurements could reveal polymer films which covered the metal surfaces completely without defects. Differences were indicated in the surface structure, especially between the pure cellulose phosphate films and cinnamate containing cellulose films.

A new device for performing accelerated cyclic immersion tests is described. The main achievement is to realise a high cycling rate without a proportional increase in the test duration. The device is also capable of performing tests according to EU ISO 11130 specification. A minimal invasive drying system is used that neither heats air nor sample and the flow rate is still low as to prevent a mechanical delamination of paints or loose corrosion products. A multiple sample set-up is realised that provides individual reference electrodes. The random access through a multiplexer allows individual investigation of the samples even by electrochemical impedance spectroscopy under immersion conditions. The device and its test principle are applicable in both industrial and laboratorial scale applications. Two application examples are given to demonstrate the versatility of the alternating immersion tester. One addresses the corrosion protection performance of different zinc-coated steel sheets; the other quantifies the patina formation kinetics of low-alloyed steels with weathering properties.

Aminopropylphosphonic acid was investigated as a short-chain bi-functional adhesion promoter between an aluminium alloy and an epoxy amine adhesive. Benefits of the short-chain adhesion promoter are its high solubility in water and epoxy resins, and the formation of densely packed monolayers on the aluminium substrate during the adsorption from both media. Application of the adhesion promoter as an adhesion promoting monolayer adsorbed from aqueous solution and as an additive to the adhesive bulk was investigated. By means of XPS and SAM analysis, monolayer formation on the aluminium passive layer and, at lower coverage, on intermetallic particles was demonstrated. Formation of ionic bonds to the aluminium oxihydroxide surface via acid/base interactions in bi-dentate conformation was proven by means of FTIR-RAS. Filiform corrosion tests, utilized as probe for interfacial stabilization, showed a strong inhibition of this anodic de-adhesion process for both variations of application.

This paper presents the first results of a project aimed at investigating the arrangement of polyelectrolyte layers on unalloyed steel. We studied the structure of double and single polymer layers consisting of cellulose phosphate (HP-PP-C) and polyethyleneimine (PEI). Layers were characterized by variable angle ellipsometry, AFM and XPS. In particular, XPS indicated the incorporation of iron ions into cellulose phosphate layers, but, in contrast, these ions could not be observed in PEI layers. Results indicated that the homogeneity and qualitative corrosion performance of double layers (HP-PP-C/PEI) on unalloyed steel depend on the deposition of cellulose phosphate at the interface with steel.

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.

The electropolishing of NiTi shape memory alloys was surveyed electrochemically. Anodic polarization of NiTi up to 8 V was performed in various aqueous and methanolic H2SO4 solutions. The passivity could be overcome in methanolic solutions with 0.1 mol d m − 3 ≤ C H 2 S O 4 ≤ 7 mol d m − 3 . The dissolution kinetics was studied in dependence of the polarization potential, the H2SO4-concentration, the water concentration and the temperature. For lower concentrations of sulfuric acids ( C H 2 S O 4 ≤ 0.3 mol d m − 3 ) electropolishing conditions were not observed for potentials up to 8 V. The dissolution remained under Ohmic control. In the concentration range from 1 to 7 mol dm−3 a potential independent limiting current was registered depending linearly on the logarithm of concentration. The best results were obtained with a 3 mol dm−3 methanolic sulfuric acid at 263 K which yielded an electropolishing current of 500 A m−2 at a potential of 8 V. Surface roughness as well as current efficiency showed an optimum under these conditions.

Using highly sensitive measurement and analog digital conversion devices it was possible to detect the repassivation transients after particle impingement on aluminium. Simultaneous use of a newly constructed slurry-jet and μ-electrodes as targets allowed the highly reproducible detection of single-particle impacts. This, in turn, allowed correlating the charge consumed during repassivation in a potentiostatic experiment with the damage caused. Variation of the experimental geometry allowed tuning the impingement angle to predetermined values. Current transients and the craters resulting from the particle impact were analyzed for impingement angles between 30° and 90°. It was found that both peak current and charge increase with decreasing angle. As a result of the nano-roughness of the impacting zirconia particles used it was possible to ascribe the crater morphologies to the different mechanisms of indentation and scratching. A model that links the normal and lateral components of the kinetic energy to these two wear mechanisms is proposed.

Slurry impingement is a type of tribocorrosion resulting from simultaneous mechanical and electrochemical surface degradation. In order to understand the elementary process of slurry impingement and the effect of mechanical damage on passive films, electrochemical responses associated with passive film breakdown by particle impacts and following repassivation were measured during slurry impingement on Al and Al–1wt%Si alloy microelectrodes. Measurements were made using a slurry jet system which consists of a pump, a microelectrode, a potentiostat suited for measurements of fast transients of small currents and a high frequency data acquisition system. Current transients corresponding to separated single particle impacts have been successfully measured. The current transient sharply rises and gradually decays following a high field model of oxide growth. It is shown that pure Al repassivates faster after particle impact than the Al–1 wt% Si alloy. This type of erodent particle had an influence on the apparent repassivation rate of these electrodes, and both Al and Al–1 wt% Si alloy showed slower current decay after the impact of angular SiC particle than after the impact of spheroidal zirconia particle. The SiC particles made deep scars and scratches, and the zirconia particles made shallow depressions.

In order to improve the corrosion resistance of a NiTi shape memory alloy, thick oxide films were fabricated on the surface by an anodic oxidation process. The microscopic observation showed the films had a porous nature and the structural analyses indicated that the films are amorphous. From the chemical analyses, the oxide films mainly contained titanium as metal component, the nickel content of the oxide films depends on pH of the electrolyte and anions could be incorporated from the electrolyte into the films. The asymmetrically rectangle waveform was effective to increase the density of the films. The electrochemical technique showed that the corrosion resistance of the anodised films could improve the resistance against localized corrosion of NiTi.

Scanning Kelvin probe and electrochemical impedance spectroscopy were used to study the release behaviour of inhibitor anions doped in polypyrrole film (e.g. molybdate, 3-nitro salicylate). The polypyrrole coatings were formed on mild steel and zinc substrates in aqueous solution. It was shown that the release behaviour of the molybdate and 3-nitro salicylate anions depends on the size of cations in the electrolyte. The delamination is determined with the migration and incorporation of small cations.

Scanning ATR-spectroscopy and scanning Kelvin probe studies are introduced as new analysis techniques for the study of water and ion transport at polymer/metal interfaces. The new approach of scanning ATR spectroscopic analysis of water transport at the adhesive/metal interface is combined with scanning measurements in transmission mode of water transport along adhesive joints and non-scanning ATR-measurements of the water transport in a vertical direction through the adhesive. D2O was chosen in some cases instead of water due to its excellent traceability in the infrared spectra. A scanning Kelvin probe was chosen for the detection of the transport kinetics of hydrated alkali ions along the adhesive/metal interface based on the local measurement of interfacial electrode potentials. The complimentary FT-IR techniques showed that the interfacial diffusion of water, in the case of epoxy adhesives on iron, is about two orders of magnitude faster that the transport through the adhesive itself. Similar transport kinetics at the interface is also shown by hydrated ions. Moreover, the here presented FT-IR–ATR and SKP results reveal more information on how adhesion promoting organosilane layers and organosilanes as additives act at polymer/metal interfaces in the presence of water incorporated in the interphase zone.

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.

Polycrystalline Fe7.5Al7Cr is a ferritic light weight steel that shows a strong anisotropic dissolution behaviour. This electrochemical phenomenon was investigated by use of a scanning droplet cell (SDC). The crystallographic orientation of the single grains was determined by electron back scatter diffraction (EBSD). The fraction of grains with a near 〈1 1 1〉 orientation (

The effect of surface treatments on the surface characteristics of aluminium alloy 2024-T3 before the appearance of filiform corrosion (FFC) is investigated. The nature of the surface prior to coating and initiation of FFC, with particular respect to the intermetallics is investigated in this work. The SKPFM (Scanning Kelvin Probe Force Microscopy), ToF-SIMS (Time of Flight Secondary Ion Mass Spectroscopy), XPS (X-Ray Photo Electron Spectroscopy) and SEM (Scanning Electron Microscopy) surface analysis techniques were used to characterize polished AA2024-T3 before and after etching or after etching with subsequent chromating treatments. The etching pretreatment is intended to remove surface intermetallics and increase the oxide layer thickness. In these respects, the treatment was partially successful: some, not all, of the particles were eliminated from the surface and the oxide thickness increased by abont 25%. In addition, XPS depth profiling showed a copper and iron enrichment at the oxide-metal interface from this treatment. The oxide thickness is drastically increased following the application of the chromate conversion coating. Furthermore, XPS and ToF-SIMS analysis revealed that Cu and Fe were enriched on the oxide surface indicating that either Cu is complexed into the Cr-Al layer following chromating or that the chromating coating is insufficiently formed on the Cu-containing intermetallics. SKPFM analysis provided further information on the distribution of these complexes on seen by distinct points of high potential on the treated alloy surface.

▪ 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.

The metals commonly used as reference tip in scanning Kelvin probe (SKP) devices experience a change in their work function when initially present in inert atmosphere and then exposed to oxygen. This change in work function biases the signal measured on a substrate submitted to a variation in environmental O 2 partial pressure and prohibits a wide range of kinetic investigations on reactional mechanisms involving oxygen. In this paper, reference probes based on the Ag/AgCl/KCl reference electrode structure are described and validated in regards to their use for SKP measurements in humid atmosphere. A validation example is presented where such a silver reference tip is used to measure on a gold substrate the potential change induced by introduction of oxygen in the investigation atmosphere.

A laser beam focused beneath a Kelvin probe needle allows for evaluation of laser-induced Volta potential shifts that can be used to identify (ir)reversible structural rearrangements at the sample surface. This work investigates the impact of laser irradiation on different substrate materials and the influence of laser power and wavelength to explore possible additional areas of analytical applications. Complete and instantaneous potential recovery was achieved with a 785 nm beam, whereas inverse and less meaningful potential shifts result for highly reflective Si wafers. Moreover, similarities to photovoltage transients recorded on solar cell devices are discussed.

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

Forming of pre-coated sheet metal becomes of increasing importance in various fields of industrial application. In the recent years, ultra-thin plasma-polymer films have emerged as promising candidates as pre-treatments for steel sheet. Not much, however, is known about the forming behaviour of ultra-thin polymer coatings on ductile substrates, while an extensive literature exists for the reverse case, metal films on polymer, or brittle films on deformable substrates in general. For these cases, advanced models exist, mostly based on the so-called shear lag approximation. The heterogenous, highly localized strain and stress distribution, typical of ductile substrates, as well as out of plane displacements at the interface are disregarded, but cannot be neglected at the high strain levels of interest for elastic polymer films. This paper will focus on the role of slip bands on cracking of ultra-thin polymer films.

Complimentary spectroscopic, microscopic and electrochemical studies were performed to characterise the barrier properties as well as the interface structure of model iron substrates covered with thin plasma polymer films. Cathodic plasma polymers were deposited which show high barrier properties. The metal surface was pre-treated by a reducing or oxidising plasma. This allowed the adjustment of the oxidation state of the interface layer. The interface structure was characterised by means of X-ray photoelectron sputter profiles, infrared spectroscopy and the application of a Kelvin probe. The investigations show that the measured Voltapotential on the plasma polymer surface can be correlated with the oxidation state of the interface. Reducing plasmas lead to an almost oxide free surface. After deposition of the plasma polymer, this reduced state of the oxide is sensitive to re-oxidation of the interface by oxygen that diffuses through the plasma polymer. It could be shown that the increase in the plasma polymer thickness leads to an improved barrier effect as indicated by the more negative Voltapotential. The barrier properties of the organosilicon plasma polymer layers on iron were further quantified by means of electrochemical impedance spectroscopy (EIS). The morphology of the plasma polymer surface was studied using atomic force microscopy (AFM) to support the evaluation of the impedance data. A water diffusion coefficient of 4×10−14 cm2/s was found for the plasma polymer. Moreover, the water uptake of the film was measured to be 0.13%. These values illustrate the high barrier properties of these thin films.

The growth of thin microwave organosilicon plasma polymers on model zinc surfaces was investigated as a function of the film thickness and the oxygen partial pressure during film deposition. The evolution of the topology of the film was studied by atomic force microscopy (AFM). The nano- and micro-roughness was investigated at the inner and the outer surfaces of the plasma polymers. A special etching procedure was developed to reveal the underside of the plasma polymer and thereby its inner surface. Rough films contained voids at the interface, which reduced the polymer/metal contact area. The increase in oxygen partial pressure led to a smoother film growth with a perfect imitation of the substrate topography at the interface. The chemical structure of the films was determined by infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). ToF-SIMS at the outer and the inner surface of the plasma polymers showed that the density of methylsilyl groups increases in the outer surface layer of the plasma polymer and depends on the oxygen partial pressure. The chemical composition of the films could be altered to pure SiO 2 without changing the morphology by using oxygen-plasma post-treatment. This was proved by means of IRRAS and AFM. Chemistry and topology of the films were correlated with the apparent water contact angle. It was found that a linear relationship exists between the nanoscopic roughness of the plasma polymer and the static contact angle of water. Superposition of a nanoscopic roughness of the metal surface and the nanoscopic roughness of methylsilyl-rich films led to ultra-hydrophobic films with water contact angles up to 160°.

Alloying zinc coatings with elements such as magnesium and titanium increases the corrosion resistance in industrial tests. Based on the fundamental mechanism of cathodic delamination, a simple concept how alloying zinc with specific elements might improve its resistance to cathodic delamination is presented in this paper. As an example, results concerning the delamination of a simple polymer from the zinc-magnesium intermetallic MgZn 2 are presented. From electrode potential measurements obtained with the Scanning Kelvin Probe it can be concluded that cathodic delamination from this alloy is completely inhibited. This behaviour is attributed to the electronic properties of the magnesium-rich oxidic passive layer, that inhibits the oxygen reduction reaction at the metal oxide/polymer interface.

While the basic mechanisms of anodic and cathodic delamination, i.e. the de-adhesion of polymer coatings from the metal substrate, are already well understood [Industrial Adhesion Problems, Orbital Press, Oxford (1985); Polymeric Materials for Corrosion Control, American Chemical Society, Washington (1986); Corrosion Control by Organic Coatings, NACE, Houston, TX; MRS Bull. 24 (1999) 43; Corros. Sci. 43 (2001) 207; Corros. Sci. 43 (2001) 229; Corros. Sci. 43 (2001) 243; Corros. Sci. 41 (1999) 547; Corros. Sci. 41 (1999) 579; Corros. Sci. 41 (1999) 599], only little is known about the microscopic and submicroscopic aspects of delamination. The main difficulty for a detailed investigation of delamination with a suitably high resolution is that the de-adhesion is a process occurring at a buried interface. On the macroscopic scale Scanning Kelvin Probe Microscopy (resolution of about a few 10 μm) has been the most important method to elucidate the fundamental processes of cathodic and anodic delamination, which in combination with other methods such as photoelectron spectroscopy (XPS) and measurement of the adhesion strength in dependence on distance from the defect helped to develop detailed models [MRS Bull. 24 (1999) 43; Corros. Sci. 43 (2001) 207; Corros. Sci. 43 (2001) 229; Corros. Sci. 43 (2001) 243; Corros. Sci. 41 (1999) 547; Corros. Sci. 41 (1999) 579; Corros. Sci. 41 (1999) 599]. The development of the scanning Kelvin probe force microscopy (SKPFM) opened application of the Kelvin probe technique to the submicroscopic scale. In this paper, first results of these submicroscopic investigations are presented and discussed in view of the earlier results.

This paper is part of a study on filiform corrosion (FFC) on aluminum alloy 2024-T3 and focuses on the surface characterization of corroded samples. Untreated samples were used as well as samples which had undergone pretreatments including polishing, surface etching and chromated conversion coatings (CCC). These samples were coated with both pigmented and non-pigmented epoxy-based coatings. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) analysis were used to investigate the nature of the surface as well as optical images to gauge the rate of FFC advancement. FFC corrosion rates decreased on samples which had received a surface etching pretreatment and a chromate conversion coating. Pigmented coatings reduced the rate of FFC further and led to two different types of corrosion surface morphology. On pretreated samples, the corrosion appeared deeper and pit-like, possibly due to an enhanced polymer-substrate bond. On untreated samples, widespread FFC developed. SEM and EDX analysis of various intermetallic particles (IMPs) on all samples, inside and outside of corroded regions, revealed that Cr from pigments was found deposited on Cu-containing intermetallics in corroded areas while Fe/Mn-containing particles were free from all pigment traces. These results suggest that the Cr deposition on Cu particles hinders the cathodic reduction of oxygen necessary for FFC advancement. For this reason, the coating pigments proved, under FFC conditions, to be a more effective inhibitor than the Cr originating from a chromate conversion coating.