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The delamination of polymeric coatings (pc) on iron and steel is a phenomena everybody knows e.g. from his rusting car. The damage caused by it costs the Western countries hundreds of millions Euro every year. Hence it is a very important task for the steel industry and also for scientists to improve the stability of the pc on iron and steel. The authors developed a new corrosion protection of iron by covering it with a thin layer of a-SiO2:Fe. An adhesion promoter sticks on top of it so that the pc adhers well. The delamination of the pc as function of the surface preparation (roughness, adhesion promoter) is described in this paper. The Scanning Kelvin Prove (SKP) is utilized to detect the delamination. Unterwanderung von Lacken auf Eisen mit einer SiO2-Schicht Jeder kennt das Phanomen der Unterwanderung von Lacken (pc, engl. polymeric coatings) auf Eisen und Stahl, z. B. vom eigenen rostenden Auto. Der dadurch verursachte Schaden kostet den westlichen Landern jedes Jahr hunderte von Millionen Euro. Daher ist es sowohl fur die Stahlindustrie als auch fur Wissenschaftler eine wichtige Aufgabe, die Haftung der Lacke auf Eisen und Stahl zu verbessern. Die Autoren entwickelten einen neuartigen Korrosionsschutz fur Eisen, indem sie dieses mit einer dunnen Schicht aus a-SiO2:Fe bedecken. Ein Haftvermittler bindet sich gut daran, so das Lacke sehr gut auf der Oberflache haften. In diesem Artikel wird die Unterwanderung von Lack als eine Funktion der Oberflacheneigenschaften (Rauhigkeit, Haftvermittler) beschrieben. Eine Raster-Kelvin-Sonde (SKP, engl. Scanning Kelvin Probe) wird fur diese Untersuchungen eingesetzt, um die Unterwanderung zu messen.

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.

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

The delamination of organic coatings from reactive metal surfaces has been examined by different kinds of techniques. The electrochemical behavior of the delaminating system has been proven by the Scanning Kelvin Probe technique to be a combination of localized electrodes between the defect, delamination front and intact interface. A first idea of the extent of the delamination front could be gained. To achieve an even deeper insight in the characteristics of the delamination, Scanning Kelvin Probe Force Microscopy (SKPFM) has been used for in situ delamination experiments for the first time. This technique permits a high lateral resolution of the potential distribution and, at the same time, detection of the topographic changes of the substrate. An overview of the development of delamination research from macroscopic to submicroscopic resolution is given here.

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

It is shown that aminomethoxysilane (AEAPSi) forms almost a monolayer thick film during a hydrolysis on silicidized iron. The molecules chemisorb from a solution in water within a few minutes in a self-assembly (SA) process. IR and X-ray photoelectron spectroscopy measurements provide evidence for a chemical reaction of AEAPSi with the surface. The surface is covered by more than a half and less than one monolayer after 10 min duration of the self-assembly process (0.5 < θ < 1). The resulting SA film is ordered with the silicon-containing head of the AEAPSi molecules at the interface and the amino group at the outer surface. The AEAPSi molecules have a small tilt against the normal axis.

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.

An investigation of plasma-polymers of hexamethyldisilane and oxygen was conducted, to allow optimization of the interfaces and surfaces of these plasma-polymers. For this study galvanized steel was used as a substrate. During this work the chemical structure (X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy), morphology (atomic force microscopy) and water contact angles of films deposited at different pressures and oxygen partial pressures were measured. These studies have shown that gas pressure and oxygen partial pressure can be used independently to determine the surface roughness of plasma polymer films derived from hexamethyldisilane (HMDS). At high pressures and low oxygen partial pressures roughness of the films increased. The roughness is then also shown to determine the water contact angle within a certain range of oxygen concentrations although the chemical structure of the films changed. With a high roughness a contact angle of 160° was observed. The roughness was determined only by the plasma-polymer layer. Despite this high contact angle the samples could be painted; the adhesion of rough films onto the substrate was, however, reduced.

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.

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.

The corrosion behaviour of zinc- and polymer-coated steel has been investigated from a very fundamental standpoint of view in order to be able to derive the important parameters for suitable short-term corrosion tests, which are capable of simulating outdoor exposure behaviour. A very simple model system has been investigated mainly by in situ Scanning Kelvinprobe measurements and surface analysis after removal of the polymer. Both types of defect have been considered. The delamination from a defect with an intact zinc layer is due to the formation of a galvanic element. The oxygen reduction in the delaminated area leads to an alkalinization of the interface and therefore to an anodic reaction with the consequence of oxide growth. Cathodic delamination is strongly influenced by the CO2-concentration in the atmosphere. The delamination starting from a defect down to steel has shown to be a complex combination of anodic undermining and cathodic delamination, the latter one becoming more important with increasing corrosion time and therefore influencing the cathodic protection of the defect.

The application of electrochemical techniques for corrosion studies of organic coatings on reactive metals is considered from the analytical and mechanistic standpoint. Techniques such as electrochemical impedance spectroscopy (EIS), scanning vibrating electrode and scanning Kelvinprobe (SKP) are powerful tools to better understand the fundamental processes of corrosion at defects and underneath coatings. In the first part of this paper these three techniques are discussed in more detail as they present a very complementary approach to understand the ensemble of coating degradation, processes in defects and corrosion underneath coatings, respectively. The second part of this paper focuses on the two important mechanisms of cathodic delamination and filiform corrosion (FFC). Since both forms of corrosion are characterised by certain electrochemical reactions underneath coatings and are localised in nature, the discussion focuses on the application of the SKP to give new insights in these corrosion phenomena.

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 gives an insight into the interfacial processes at the iron oxide/polymer interface during the plasma polymer deposition from hexamethyldisilane ((CH 3 ) 3 Si–Si(CH 3 ) 3 ). For this purpose an in situ set-up which combines IR-spectroscopy under grazing incidence and quartz crystal micro weighing was used. The deposited plasma polymers had a thickness of less than 10 nm. The surface morphology of the films deposited on flame annealed gold could be visualized by means of atomic force microscopy. The plasma polymers deposited in this study form laterally homogeneous films even at film thicknesses lower than five nanometer. The features of the plasma polymers have a diameter of about 20 nm and a height of about 0.5 nm. During the initial growth of the plasma polymer a formation of covalent bonds at the interface was indicated by IR-spectroscopy. First voltapotential measurements of the plasma modified surface by means of a scanning Kelvin probe show that Fe 3+ states in the iron oxide surface are partly reduced to Fe 2+ during the formation of the first plasma polymer layers.

Metal/polymer composites are used in numerous technical applications. For example, polymer coatings on metal surfaces are used for corrosion protection, metal films on polymers inhibit static buildup, and polymers between two metals can serve as a “glue” for connecting materials that cannot be welded. Polymer/metal composites also play an important role in modern electronics. In condensers, polymers serve as insulating layers between metallic leads and are used to encapsulate entire electronic circuits. In all circumstances, interfaces are formed between the two different materials, and since the chemistry and structure change abruptly, interfacial failure is frequently observed.The cause of failure may just be mechanical (e.g., shrinkage of the polymer during curing), or the interface stability may be degraded by attack of aggressive species, resulting in delamination. More specifically, loss of adhesion is directly caused by interfacial electrochemical reactions that nucleate at a defect and progress into intact regions of the interface. This occurs for encapsulated electronic parts in humid atmospheres as well as for lacquers on automotive parts.Thus the investigation of corrosion reactions at a buried interface is an important area of research, but it is made very difficult by the fact that most electrochemical methods do not give information on localized reaction kinetics at a buried (metal/polymer) interface. This situation has changed with the invention and development of the scanning Kelvin probe (SKP). This method allows, for the first time, local analysis of reactions occurring at a buried metal/polymer interface. Based on the results obtained with the SKP, a detailed reaction model for the delamination process has been developed. This understanding has led to the development of new approaches that protect the interface from delamination. The idea is to chemically modify the interface using Afunctional molecules that promote adhesion between metal and polymer 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.

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

The self-assembly of thiol molecules from ethanolic solution on Au(111) depends significantly on the electrode potential. Especially at cathodic potentials, chemisorption of thiol molecules and the development of the highly ordered structure are slowed down significantly. At potentials near the point of zero charge, first a disordered thiol film of already high thiol density is formed, and then domains of the highly ordered phase develop and grow together. At cathodic potentials, first a disordered film of very low density of predominant flat adsorbed thiol molecules is formed; the formation of ordered domains takes time three orders of magnitude longer than at potentials near the point of zero charge.

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

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

In this paper the glow discharge process is used for the deposition of ultrathin (d < 10 nm) plasma polymers on iron specimens. The plasma polymer serves as an interfacial polymeric layer between the passive iron surface and a conventional pigment free water based 1-component primer. Sample, were fixed in the grounded electrode of an audio frequency discharge (4 kHz). Cleaning of the iron surface was achieved by an oxygen plasma treatment and Plasma polymers were deposited from a mixture of hexamethyldisilane ((CH 3 ) 3 Si-Si(CH 3 ) 3 ) and argon. The modification of the surface structure was investigated by the use of quartz crystal microweighing (QCM) and infrared spectroscopy under grazing incidence (IRRAS) as in-situ methods. Both the iron oxide as well is the plasma polymer are characterized in detail by infrared spectroscopy and photoelectron spectroscoopy (XPS). The corrosion performance of primer coated samples was tested according to the kinetics of cathodic delamination which was measured in-situ by the Scanning Kelvinprohe (SKP). While the pure oxygen plasma treatments leading to a contamination free and thickened oxide layer, does not influence the delamination kinetics the existence of an only 5 nm thick plasma polymer at the metal-primer interface leads to a significantly decreased rate of undermining.

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.

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

The adsorption and self organization of phosphonic acids on oxidized aluminum surfaces has been investigated by surface sensible techniques: ARXPS, AES and FTIR. The analysis has been performed on Al 99.999 samples and on surfaces of a technical alloy whose surfaces contain iron inclusions. The results obtained lead to the conclusion that self organization is not only possible on perfect defect free surfaces but also on inhomogeneous ones.

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 sections in this article are Introduction Experimental Investigation of Corrosion Reactions by Analysis of the Corrosion Products Experimental Investigation of Corrosion Reactions by Following the Chemical Reaction Rate Experimental Investigation of Corrosion Reactions by Following the Rate of the Electrochemical Corrosion Reaction Electrochemical Impedance Spectroscopy and Noise Analysis Introduction The Principle of Dynamic System Analysis Measurement of the Electrochemical Impedance Presentation of Impedance Data Interpretation of Impedance Data The Polarization Resistance Frequency Dispersion Surface Inhomogeneities Single Layer Impedance Model Sandwich Layer Impedance Model Equivalent Circuit Versus Transfer Function The Transport Impedance Iron Corrosion in Neutral Solution Impedance Model of Passive Films Metal Dissolution and Active-to-Passive Transition Electrochemical Noise Noise Sources in Electrochemical Systems Noise Measurement Techniques Data Processing Noise Resistance and Polarization Resistance The Scanning Vibrating Electrode Technique Introduction History of Scanning Reference Electrodes Basic Principles of Localized Potential Mapping Localized Electrochemical Impedance Spectroscopy (LEIS) Applications of Modern Scanning Electrode Techniques Local Breakdown of Passivity Galvanic Corrosion Inhibition Microbiologically Influenced Corrosion Protective Polymeric Coatings Concluding Remarks Scanning Kelvinprobe Introduction Theory of the Vibrating Condenser Method The Relation between the Volta Potential Difference and Corrosion-Relevant Properties Electrolyte Covered Metal Surfaces Metals in Humid Air Polymer-Coated Metals Calibration of the Kelvinprobe Application of the Kelvinprobe: Atmospheric Corrosion Experimental Results Application of the Kelvinprobe: Corrosion Protection by Organic Coatings Experimental Polymer-Coated Steel Polymer Coated Galvanized Steel Polymer Coated Aluminum Alloys Industrial Coatings Application of the Kelvinprobe: Corrosion Protection by Modified Metal Surfaces Metal Surfaces Modified by Monolayers of Organic Molecules Metal Surfaces Modified by Ultra-Thin Plasma Polymers Metal Surfaces Modified by Inorganic and Organic Layers

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.

A combination of quartz crystal microweighing (QCM) and infrared reflection absorption spectroscopy (IRRAS) was used to investigate the formation of ultrathin polysiloxane films on iron oxide surfaces by the adsorption of alkyltrimethoxysilanes in a humid atmosphere. It was shown that in the absence of a catalyst, only the most reactive methyltrimethoxysilane led to film formation. These films are not completely polymerized and incorporate silanols and water. The addition of n-propylamine to the reactive gas phase as an alkaline catalyst enables one to use even the butyltrimethoxysilane as a starting material and leads to a much higher deposition rate. In addition, these films are completely condensed and very hydrophobic. Layers of both alkoxysilanes even with a thickness corresponding to only a few monolayers showed high stability in the presence of a corrosive atmosphere (SO2, H2O, O2), leading to significant inhibition of the corrosion process. Corrosion started at local defects in the film, whereas t...

Corrosion reactions which take place during delamination in the vicinity of defects have not been understood up to now. In this paper the delamination of a simple model coating from clean steel and the delamination of technical coatings from petreated steel substrates are analysed with a scanning Kelvin probe. It is possible, with this technique, to follow the delamination in situ and to understand the basic corrosion mechanism at the metal/polymer interface.

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

XPS and AES are suitable techniques for studying organic monolayers on metals if radiation doses are kept low. The adsorption of self-assembled (SA) mercaptan monolayers on gold is a process in two stages. The adsorption to near completeness is very rapid. However, the process of orientation of the carbon chains, which is responsible for the blocking of electrochemical reactions takes much longer, as could be shown by ARXPS (angle resolved X-ray photo electron spectroscopy). Adsorption under potential control allows electrochemical experiments during the adsorption process as e.g. the measurement of the capacity of the electric double layer. Furthermore the control of the potential guarantees sure that the metal/liquid interface is well defined during the adsorption process.

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

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.

Langmuir—Blodgett films of octadecylmercaptan (ODM) were formed on an aqueous subphase and transferred to gold substrates under electrochemical potential control by means of a modified LB Balance. The monolayers were investigated by surface analytical techniques (XPS, ARXPS, AES, IRRAS) and by electrochemical methods (cyclic voltammetry, impedance spectroscopy). The results are compared to self-assembled films (SA) of ODM on gold.

The corrosion reactions which take place at a defect free metal/polymer interface and the delamination in the vicinity of defects are not yet understood. In this paper several recently developed experimental techniques are applied to such corrosion systems to elucidate the fundamental corrosion processes for polymer coated metals. The transport of water and oxygen through the coating and the electrochemical reactivity of the coated metal are investigated using a quartz-crystal microbalance, FTIR spectroscopy and electrochemical dc and ac techniques with a special reference electrode positioned at the metal—polymer interface. The delamination of the polymeric coating in the vicinity of defects is analysed by the scanning Kelvin-probe. The combined application of these techniques leads to a corrosion model, which explains the corrosion protection of metals by polymers.

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.