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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.

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.

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

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.

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.

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.

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.

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.

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

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.

The effect of cold plasmas of oxygen, hydrogen, water and carbon dioxide on zinc samples was investigated. Oxygen plasma is known for its cleaning effect, hydrocarbons and water are removed from metal surfaces and the oxide layer is thickened. It was found that other oxygen-containing gases had a similar effect. In addition, surface layers of other compounds were produced. The samples were investigated using XPS, Kelvin probe measurements and in situ infrared reflection absorption spectroscopy. Copyright © 2003 John Wiley & Sons, Ltd.

In der Korrosionsschutzpraxis wird ein deutlicher Einfluss der Oberflachenvorbereitung und der Pigmentierung der Grundbeschichtung auf die Unterwanderung am Defekt gefunden. Zur Aufklarung der Mechanismen wurde in der vorliegenden Arbeit die Raster-Kelvinsonde eingesetzt, mit der ortliche Korrosionspotentiale auch unter isolierenden, organischen Beschichtungen beruhrungslos gemessen werden konnen. Folgende Ergebnisse wurden erzielt: Auf gestrahltem Stahlsubstrat findet bei Systemen mit Zinkphosphat-Grundbeschichtung kathodische Delamination statt, bei Systemen mit Zinkstaub-Grundbeschichtung wird insbesondere der Randbereich des Defekts zunachst durch anodische Auflosung von Zink der Zinkstaubgrundbeschichtung kathodisch geschutzt. Durch Bildung von Zinkkorrosionsprodukten kann bei zunehmender Belastungsdauer Deaktivierung des Zinkstaubs und Fortschreiten der Korrosion unter die Beschichtung stattfinden. Auf handentrostetem Stahl findet unabhangig von der Pigmentierung der Grundbeschichtung am Rand des Defekts Rostreduktion als kathodische Teilreaktion statt, die durch Elementbildung noch verstarkt wird. Bei zyklischer Belastung wird reduzierter Rost in Trockenphasen reoxidiert und kann so bei Befeuchtung erneut am Prozess teilnehmen. Als Ergebnis nimmt die Dicke der Rostschicht zu und Phasenumwandlungen im Rost fuhren zum Adhasionsverlust der Beschichtung vom Rand des Defektes ausgehend. Corrosion-protective effect of organic coatings at the defect – influence of surface preparation and anti-corrosive pigments of base coating In practice of corrosion protection a clear influence of surface preparation and pigments of base coating has been widely observed on defect-induced delamination of organic coatings. In the presented paper this mechanism was studied using the Scanning Kelvin-Probe. This instrument enables determination of the corrosion potential by high resolution contactless measurements even with presence of insulating organic coatings. During these investigations the following results were obtained: Cathodic delamination takes place in case of coatings with zinc phosphate primers on blast cleaned steel substrates. Using zinc dust primers, especially the edges of the defect are cathodically protected by anodic dissolution of zinc as part of the zinc dust primer. Because of the formation of zinc oxides, increasing load duration can lead to a deactivation of zinc dust and a progression of the corrosion process below the coating. On hand-cleaned steel surfaces rust reduction takes place at the edge of the defect in form of a cathodic partial reaction which is independent from pigments of the base coating. This reduction is increased by the galvanic cell. In case of cyclic loading reduced rust is reoxidized during dry phases and can re-participate in the process during wetting. In the result the thickness of the rust-layer is growing and phase transformations in the rust lead to the loss of adhesion of the coating starting from the edge of the defect

Cellulose as natural and non-toxic material is very interesting for biological applications. Its poor solubility in organic solvents can be improved by introduction of long alkyl chains. Phosphate-substituted cellulose derivatives form ultra-thin layers on several metal surfaces [1, 2]. The layers were applied on the surfaces via dip coating from dilute solutions and characterised by contact angle measurements. Initial corrosion tests were performed. These polymers were applied as adhesion promoters for steel-, titanium- and hydroxy apatite surfaces. Medical implants were pre-treated by UV irradiation, coated with the cellulose derivatives and activated by hot water treatment. The adhesion of the implants surpassed that of conventionally used PMMA systems.

Reduction of carbon dioxide to methane by microorganisms attached to electrodes is a promising process in terms of renewable energy storage strategies. However the efficient and specific electrosynthesis of methane by methanogenic archaea on cathodes needs fundamental investigations of the electron transfer mechanisms at the microbe-electrode interface without the addition of artificial electron mediators. Using well-defined electrochemical techniques directly coupled to gas chromatography and surface analysis by scanning electron microscopy, it is shown that a pure culture of the marine lithoautotrophic Methanobacterium-like archaeon strain IM1 is capable to utilize electrons from graphite cathodes for a highly selective production of methane, without hydrogen serving as a cathode-generated electron carrier. Microbial electrosynthesis of methane with cultures of strain IM1 is achieved at a set potential of -0.4V vs. SHE and is characterized by a coulomb efficiency of 80%, with rates reaching 350 nmol d(-1) cm(-2) after 23 days of incubation. Moreover, potential step measurements reveal a biologically catalyzed hydrogen production at potentials more positive than abiotic hydrogen evolution on graphite, indicating that an excessive supply of electrons to strain IM1 results in proton reduction rather than in a further increase of methane production.

The adhesion of polymeric coatings on iron and steel is interesting especially for industrial applications. Lacquers are important because of their optical properties but also because they protect the metallic surface e.g. from corrosion. The new concept of using adhesion promoters between the polymeric coating and the metallic surface was introduced recently. But the adhesion of polymeric coatings is a difficult task on iron since the surface must be oxide free. This problem can be avoided by covering the iron surface with a thin film of silicon, silicides and SiO 2 . Silane molecules chemisorb on top of it and act as adhesion promoters. The silicon reacts with the iron in a CVD process and the silane via a self-assembly process. We describe the electrochemical properties and the stability of the iron covered by silicon and by silicon-organic molecules. Impedance and current-voltage measurements are used for this. The influence of oxygen and nitrogen solved in the electrolyte is described. Also the time dependence of the stability of the surface layer was measured.

Oxidized silicon is a promising candidate for the adhesion promotion of polymeric coatings on iron and steel. Therefore, the surface of iron must be covered by silicon and silicon oxide. This can be done by the chemical vapor deposition (CVD) of silane gas, a process which might be applied in industry easily. Because of these reasons the CVD of Si on the Fe(100) surface was studied at the deposition temperature of 770°C. The silane partial pressure ranged from 0.02 to 0.2 mbar while the total pressure was constant 990 mbar. It was found that the morphology of the surface changes from a very thin two-dimensional (2D)- to a complex and thick three-dimensional (3D)-structure with increasing deposition time. This is connected with a change of the chemical structure and a change in the reaction mechanism. Different processes like passivation of the surface by oxidation and surface diffusion influence the deposition. Models are proposed to describe the mechanism of growth of the surface layer.

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.

In recent works the self-assembly process has been investigated to replace the present chromating procedure on reactive metals like aluminium and the improve the lacquer adhesion and corrosion inhibition. These self-assembling layers were formed of small bifunctional organic molecules with phosphate or phosphonic acid groups attached to the metal substrate. The idea of this work was to apply these results and techniques to cellulose derivatives on implant metals. The formation of ultra-thin layers of phosphorylated cellulose derivatives has been reported previously. These ultrathin layers were built on metal substrates like aluminium, titanium or steel for adhesion promotion and corrosion inhibition. Hydroxypropyl-2-phosphatepropyl cellulose was synthesised for adhesion on hydrophilic metallic surface. Hydroxypropyl-2-cinnamoylpropylester cellulose was prepared in order to crosslink the adsorbed layers. The layers were formed on metal surfaces via dip coating from dilute solutions and characterised by means of contact angle measurements, SEM investigations and FT-IR spectroscopy. Initial corrosion tests were performed.

New hairy-rod like cellulose polymer layers were developed as a model system for corrosion protection and adhesion promotion in medical technology. Using the Langmuir-Blodgett technique a mixture of a cinnemate containing and a phosphate containing cellulose were transferred on titanium and steel surfaces. The cinnemate can be crosslinked by ultraviolet light (UV). Differences in the formation of multilayers were found and analyzed by atomic force microscopy, scanning auger microscopy and ellipsometric measurements. Phosphate cellulose forms homogenous layers at all substrate surfaces. With increasing layer thickness a mixture with low phosphate content becomes homogenous, too. Only mixtures with high content of phosphate keep imperfections with increasing layer thickness. For the pure component cinnemate cellulose the imperfections arise only in the case of titanium surfaces.

The paper reveals structural changes of the iron surface during the plasma oxidation in an oxygen glow discharge. For this purpose, an in-situ set-up which combines IR-spectroscopy under grazing incidence and quartz crystal micro weighing was used. A Scanning Kelvin Probe was used to measure the influence of the glow discharge on the electronic properties of the iron oxide surface. The glow discharge was initiated by a low power audio frequency voltage source. The results show that an oxygen plasma on iron which is already covered by a natural oxide layer leads to an effective removal of organic contaminations and an increased thickness of the oxide of about 5 to 6 nm. In agreement with the spectroscopic data, the Voltapotential measurements show that the oxide surface is depleted in Fe 2+ states. The structure of the additionally grown oxide is most likely to be γ-Fe 2 O 3 . This means that the n-semiconducting properties of the oxide are changed. Within an subsequent argon discharge, the Fe 3+ in the oxide surface is again reduced to Fe 2+ . The paper illustrates the importance of the consideration of the electronic properties while structuring oxide covered metals and the usefulness of the Scanning Kelvin Probe measurement to reveal electronic properties of semiconducting oxide layers.

Silicon and iron silicides are promising candidates as adhesion promoters on iron. The formation of silicon and iron silicides films on polycrystalline iron is studied in a CVD process with monosilane. The process is performed between 475°C and 800°C with a silane partial pressure of 0.2 to 10 mbar to a total pressure of the silane–hydrogen mixture of 100 to 990 mbar. A model of the reaction mechanism is presented which includes the transport of the gases, the adsorption on the surface, the chemical decomposition of the silane and the interdiffusion between Si and Fe.

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.

Film formation processes of ultrathin films of a curable model polymer system in the presence of a metallic substrate were studied. The structure of prepolymerized films strongly depends on the relative humidity during the spin-coating process. With increasing atmospheric humidity, typical defect structures were observed which never healed during full curing. A mathematical simulation shows that condensation of water forming liquid drops can be excluded as source of holes in the films. We propose that these defects are caused by physisorbed water layers on the substrate surface resulting in a dewetting of the polymer.

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

The self-assembly process has been investigated for the replacement of the present chromating procedure on reactive metals like aluminium and to improve the lacquer adhesion and corrosion inhibition. It will be shown, that self-assembled layers can affect adhesion and corrosion inhibition on aluminium and its alloys. For self-assembly molecules (SAMs) substances are required which are able to react spontaneously on the surface for which terminated alkyl-phosphonic and phosphoric acid monoalkyl esters have been synthesised. The best anchor groups for aluminium were ascertained by pH-dependent flotation tests, dynamic contact angle measurements and corrosion tests. Grazing angle Fourier transform infrared spectroscopy (FTIR), angle dependent X-ray photoelectron spectroscopy (XPS) and Auger measurements show the existence and orientation of these new molecular structures. Model surface reactions with isocyanates demonstrate the binding capability to the lacquer.

The adsorption and self-organisation process of alkyl-phosphonic acids and phosphoric acid monoalkyl esters on technical aluminium surfaces have been investigated by different surface sensible techniques: Grazing angle FT-IR- spectroscopy, angle dependent XPS and Auger- spectroscopy. The aim of these studies was to replace the present technical procedure for pretreatment of aluminum surfaces with chromate acid in order to improve the corrosion inhibition and the coating adhesion. The ability for self-assembly is given by substances which have a surface reactive group and a long-aliphatic or aromatic spacer and a supramolecular order is built-up between these spacers. The results show that these molecules are able to adsorb spontaneously onto the aluminum surface and subsequently a structured molecular order is formed. These effects were confirmed by industrial linked adhesion and corrosion tests.

The electrochemical quartz crystal microbalance (EQCM) is applied in order to study the technical pretreatment processes of galvanized steel such as alkaline cleaning, chromating and phosphating in modern trication solutions. The mass change associated with these reactions is monitored insitu under conditions which are very similar to those of a coil-coating line. It is shown that cleaning of the zinc surface in an alkaline cleaning solution is a two-step process: removal of the zinc oxide layer by a chemical dissolution followed by electrochemical dissolution of zinc, the rate of which is controlled by the diffusion of zincate ions into the electrolyte. During phosphating of the sample, three subsequent steps are observed: zinc dissolution during the first seconds followed by precipitation of a phosphate layer and then cementation of Ni, which leads again to increasing dissolution of the base material.

The atmospheric corrosion of zinc in the presence of (NH{sub 4}){sub 2}SO{sub 4} particles has been investigated at 300 and 373 K in air-water vapor mixtures. The development of corrosion products was followed by several in situ techniques, including Fourier transform infrared-spectroscopy, X-ray diffraction, pH measurements, and scanning Kelvin probe measurements. Unlike earlier work on copper and aluminum, zinc reacts with the particles below the critical relative humidity (CRH) of (NH{sub 4}){sub 2}SO{sub 4}. At 300 K reaction was observed at 65% relative humidity (RH), but not at 60% /RH. This is attributed to the presence of basic zinc carbonate on the surface, which absorbs sufficient water at this low RH to make electrochemical reactions possible. At and above the CRH of (NH{sub 4}){sub 2}SO{sub 4}, zinc reacts with (NH{sub 4}){sub 2}SO{sub 4} forming mixed ammonium zinc sulfate and later on basic zinc sulfate, and at 373 K additionally zincite (ZnO). Above the CRH of (NH{sub 4}){sub 2}SO{sub 4}, the corrosion potential decreases directly after formation of droplets surrounding the particles and zinc becomes active. Corrosion mechanisms are proposed to explain the observations.

The corrosion mechanism of copper at 373 and 300 K in the presence of submicron (NH[sub 4])[sub 2]SO[sub 4] particle deposits has been investigated. Several in situ techniques have been used to monitor the corrosion process in real time. At and above the critical relative humidity of (NH[sub 4])[sub 2]SO[sub 4], dissolution of Cu is followed by formation of Cu[sub 2]O, oxidation of Cu(I) ions to Cu(II) ions, and precipitation of antlerite [Cu[sub 3](SO[sub 4])(OH)[sub 4]], brochantite [Cu[sub 4](SO[sub 4])(OH)[sub 6]], or posnjakite [Cu[sub 4](SO[sub 4])(OH)[sub 6][center dot]H[sub 2]O]. The amount of corrosion product formed increases with amount of (NH[sub 4])[sub 2]SO[sub 4] particles, relative humidity (RH), and temperature. The in situ techniques allowed the authors to confirm and refine the individual steps in the multistep mechanism proposed in earlier work.

A comparative study of O 2 reduction on well defined iron oxides Fe 3 O 4 and γ-FeOOH is presented. The Fe(III)/Fe(II) surface stoichiometry strongly depends on potential and determines the electronic conductivity and electron transfer rate to soluble redox species. A common feature of O 2 reduction on both oxides is the occurrence of Fe 2+ surface sites simultaneous to O 2 reduction, which is necessary for the specific interaction between Fe(II) and O 2 . The electrocatalytic differences for γ-FeOOH and Fe 3 O 4 are related to differences in oxide structure and different structure of the oxide-electrolyte interface.

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.

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 + .

The corrosion mechanism of copper at 373 and 300 K in the presence of submicron (NH[sub 4])[sub 2]SO[sub 4] particle deposits has been investigated. Several in situ techniques have been used to monitor the corrosion process in real time. At and above the critical relative humidity of (NH[sub 4])[sub 2]SO[sub 4], dissolution of Cu is followed by formation of Cu[sub 2]O, oxidation of Cu(I) ions to Cu(II) ions, and precipitation of antlerite [Cu[sub 3](SO[sub 4])(OH)[sub 4]], brochantite [Cu[sub 4](SO[sub 4])(OH)[sub 6]], or posnjakite [Cu[sub 4](SO[sub 4])(OH)[sub 6][center dot]H[sub 2]O]. The amount of corrosion product formed increases with amount of (NH[sub 4])[sub 2]SO[sub 4] particles, relative humidity (RH), and temperature. The in situ techniques allowed the authors to confirm and refine the individual steps in the multistep mechanism proposed in earlier work.

The atmospheric corrosion of zinc in the presence of (NH{sub 4}){sub 2}SO{sub 4} particles has been investigated at 300 and 373 K in air-water vapor mixtures. The development of corrosion products was followed by several in situ techniques, including Fourier transform infrared-spectroscopy, X-ray diffraction, pH measurements, and scanning Kelvin probe measurements. Unlike earlier work on copper and aluminum, zinc reacts with the particles below the critical relative humidity (CRH) of (NH{sub 4}){sub 2}SO{sub 4}. At 300 K reaction was observed at 65% relative humidity (RH), but not at 60% /RH. This is attributed to the presence of basic zinc carbonate on the surface, which absorbs sufficient water at this low RH to make electrochemical reactions possible. At and above the CRH of (NH{sub 4}){sub 2}SO{sub 4}, zinc reacts with (NH{sub 4}){sub 2}SO{sub 4} forming mixed ammonium zinc sulfate and later on basic zinc sulfate, and at 373 K additionally zincite (ZnO). Above the CRH of (NH{sub 4}){sub 2}SO{sub 4}, the corrosion potential decreases directly after formation of droplets surrounding the particles and zinc becomes active. Corrosion mechanisms are proposed to explain the observations.

It is possible to measure the work-function of polymer coated materials with a Kelvin-probe. In a humid atmosphere this work-function is mainly given by the corrosion-potential of the metal substrate. The use of a scanning Kelvinprobe then allows to map the corrosion potential of polymer coated material with a local resolution of approx. 20 μm and to follow the delamination of polymer coatings as well in the vicinity of defects as on metal substrates, which are contaminated at the metal/polymer interface. Simultaneously, the diffusion of oxygen can be followed with a high local resolution after a jump of the oxygen activity within the gas phase.—The same techniques are used to analyse intrinsic defects within monomolecular LB-films. In a dry gas phase the Volta potential map corresponds to the distribution of dipole-potentials and therefore allows to distinguish between covered and uncovered parts of the substrate, as the ordered LB-film shows rather large dipole-potentials. In a humid atmosphere the Volta potential map again is dominated by the corrosion potential of the substrate and therefore the delamination of the LB-film in the vicinity of defects can be studied as well as the stability of the film on the metal substrate far away from any defect.

Die auf Fe-Basislegierungen gebildeten Rostschichten sind elektronisch sehr reaktiv. Durch Polarisation dieser Oxidschichten werden Festkorperreaktionen ermoglicht, die zur Reduktion der 3-wertigen Oxidhydrate fuhren. Diese Redox-Reaktionen erlauben eine Eisenauflosung ohne Reduktion von Sauerstoff und erhohen damit den Metallabtrag insbesonders bei periodisch variierenden Korrosionsbedingungen und bei polymerbeschichteten Werkstoffoberflachen. Durch die Oxidreduktion werden elektronenleitende Oxide gebildet, die die Kinetik von Sauerstoffreduktion bestimmen. Schlieslich andert sich bei der Reduktion der Rostschicht die Rostmorphologie. Dies fuhrt zu einem Haftungsverlust bei polymerbeschichteten oxidbelegten Metalloberflachen. Influence of rust layers on corrosion reactions of low alloy steels Rust layers formed on iron base alloys are electrochemically highly reactive. Due to a polarisation of these oxide scales solid state reactions are induced, by which the 3-valent iron oxides are reduced. These redox reactions allow the dissolution of iron without the reduction of oxygen and therefore increase the corrosion rate, if the corrosion conditions vary periodically or if the material is coated by a polymer layer. Due to the oxide reduction electron-conducting oxides are formed, which determine the rate of the oxygen reduction. This causes the loss of adhesion for polymer coated and oxide covered iron substrates.

The principle of operation and the design of a scanning Kelvin microprobe for the determination of corrosion potential profiles are described. The profiles of Volta potentials on galvanically coupled metals under humidity films were determined and are compared to profiles for the same metals under dry nitrogen. The relation between the Volta potential and the corrosion potential and some of the difficulties involved in studying corrosion under humidity films are discussed

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.

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.

bMax-Planck-Institut fur Eisenforschung, D-40237, Dusseldorf, Germany In an attempt to improve the corrosion resistance of a NiTi shape memory alloy, thick oxide films were fabricated on the surface by an anodic oxidation process. High-voltage square shape pulse anodization was carried out in various electrolytes over the whole range of pH values from sulfuric acid, acetate buffer, ammonium pentaborate, sodium diphospho heptoxide, sodium aluminate, and potassium hydroxide. Microscopic observation showed that the films are porous or tile structured in nature and the structural analyses by X-ray diffraction and Raman spectroscopy demonstrated their amorphous nature. From the chemical analyses, the oxide films were determined to consist mainly of titanium as the metal component, whereas the nickel content of the oxide films depends on the pH value of the electrolyte as well as the amount of anions incorporated from the electrolyte. The application of an asymmetrical rectangle waveform was effective in increasing the density of the films. An electrochemical technique was used for screening the corrosion resistance of the anodized films and demonstrating the improvement in the resistance against localized corrosion of NiTi.

A height-regulated scanning Kelvin probe (HR-SKP) that is capable of measuring the sample/needle distance and the interfacial electrode potential at the same time was constructed for the study of rough or curved surfaces in humid environments. Moreover, the height regulation led to an improvement of the spatial resolution because the distance between the vibrating needle (i.e., the reference electrode) and the substrate surface was kept to a minimum. The height regulation was performed by a double modulation of the external voltage at different frequencies. The mechanical part of the height regulation is comprised of a piezoelectric translator and a stepping motor in combination, so that both a fine adjustment of the height and a large height range of several millimeters was possible. The z-resolution of the system was about 200 nm, while the lateral spatial resolution was about 15 μm. The HR-SKP was applied to different forms of corrosion including filiform corrosion on organically coated aluminum samples. Moreover, a combination of a pressurized blister test and the HR-SKP was applied for the study of adhesives under both corrosive and mechanical stress.