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

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

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

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 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.

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

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.

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.

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.

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 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 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.

A new technique is presented, which is able to detect corroding parts of a metal surface below technical polymercoatings. The technique (vibrating reference electrode) is based on the observation, that the local corrosion potential – which in turn is given by the rates of the anodic and cathodic partial reactions of the corrosion process– is quite different for an intact and for a delaminated metal/polymer interface. In this paper two different coatings are analysed, which are used in technical flue gas desulfurisation (FGD) plants. It is shown, that the different stability of the two coatings can clearly be elucidated by mapping the corrosion potential of the surface in a humid atmosphere. Uberwachung der Blasenbildung bei organischen Beschichtungen durch kontaktlose Messung Es wird eine neue Technik vorgestellt, die in der Lage ist, korrodierende Stellen unterhalb technischer Polymerbeschichtungen nachzuweisen. Das Verfahren (vibrierende Referenzelektrode) basiert auf der lokalen Messung von Korrosionspotentialen, die ihrerseits durch die Kinetik der anodischen und kathodischen Teilreaktion der Korrosion gegeben sind. Die Korrosionspotentiale intakter Metall/Polymer-Grenzflachen unterscheiden sich deutlich von solchen Potentialen, die an delaminierten Metall-Polymer-Verbunden gemessen werden. In dieser Arbeit werden zwei technische Beschichtungen untersucht, die auch in Rauchgasentschwefelungsanlagen eingesetzt werden. Es wird gezeigt, das die unterschiedliche Stabilitat der Beschichtung durch die Abbildung von Korrosionspotentialen in einer feuchten Atmosphare deutlich herausgearbeitet werden kann.

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.

Die Kinetik der Korrosion von polymerbeschichtetem Reineisen in 0,1 M NaCl wurde untersucht. Durch die Praparation von Proben mit einer unter der Beschichtung positionierten Referenzelektrode konnte eine direkte Polarisation der Phasengrenze Metall/Polymer bei Gleich- und Wechselspannungsmessungen erreicht werden. Die Kombination dieser Messung mit den Ergebnissen nicht elektrochemischer Techniken, wie z.B. Kelvin-Sonde, Mosbauerspektroskopie und O2-Verbrauchsmessungen, liefert neue Erkenntnisse zur Korrosionskinetik unter einer Polymerbeschichtung. Die Metalloberflache ist von einem gequollenen Polymerfilm bedeckt, und bei der Korrosion werden primar im Polymer geloste Eisenkationen gebildet. Dies fuhrt zu einer extremen Hemmung der anodischen Metallauflosung (Tafelneigungen mehrere 100 mV). Auch die kathodische Teilreaktion (O2-Reduktion) lauft nicht unter transportkontrollierten Bedingungen, sondern aufgrund ihrer gehemmten Kinetik durchtrittskontrolliert ab. Die Diffusionskoeffizienten von Wasser und Sauerstoff in einer haftenden Beschichtung wurden bestimmt. New model of corrosion protection of organic coatings on iron The corrosion kinetics of polymer-coated iron is investigated in 0.1 M NaCl. As special samples are prepared with the reference electrode located at the metal/polymer interface a direct polarization of this interface is possible by AC and DC techniques. A combination of these measurements with results obtained by non-electrochemical techniques like Kelvin-probe, Mosbauerspectroscopy and O2-consumption allows to derive a new model of the corrosion kinetics below a polymer coating. The metal surface is covered by a swollen polymer layer and during corrosion at first iron cations are dissolved in the organic matrix. This results in a strong inhibition of the anodic partial reaction (Tafel-slope several 100 mV). Also the cathodic partial reaction (O2-reduction) is not transport-limited but its rate is given by the electron transfer reaction. The diffusion of water and oxygen is investigated on adherent polymer films.

In dieser Arbeit werden neue Wege vorgeschlagen, organische Polymere auf Metalloberflachen uber chemische Hauptvalenzbindungen zu verankern. Zwischen Polymer und Metall sollen bifunktionelle organische Molekule angeordnet werden, die uber chemische Bindungen mit reaktiven Zentren der Metalloberflache und uber konventionelle (C-C)-Bindungen mit dem Polymer verknupft sind. Als einen ersten Schritt in dieser Richtung wird die Anbindung von einfachen aliphatischen Mercaptanen an Eisenoberflachen untersucht. Oberflachenanalytische Experimente zeigen, das Mercaptane an metallisch blanken Eisenoberflachen unter Ausbildung von (Fe-S-R)-Bindungen anbinden. Die Reaktion selbst mus unter elektrochemisch kontrollierten Bedingungen durchgefuhrt werden. Die Stabilitat der Bindung ist sehr gros sowohl in Luft als auch in zahlreichen Elektrolyten. Sie wird begrenzt durch eine massive Sauerstoffreduktion, bei der die chemisorbierten Mercaptanmolekule wahrscheinlich durch das bei der Sauerstoffreduktion gebildete H2O2 chemisch aufoxidiert werden und anschliesend desorbieren. Binding behaviour of organic monomers on iron surfaces and corrosion of the resultant chemically modified surfaces In this study a new concept is discussed, to anchor polymers onto metal surfaces by primary chemical bonds. Organic molecules with two functional groups are positioned between polymer and substrate, which should be bonded to reactive centers of the metal surface by one functional group and to the polymer by conventional C-C bonds. As a first in this direction, the reaction between simple aliphatic mercaptanes and iron surfaces has been studied in detail. Surface analytical investigations have proven, that mercaptane molecules can be bonded to metallic clean iron surfaces by Fe-S-R bonds. The reaction itself has to be performed under well controlled electro-chemical conditions. The stability of the bonds is quite large as well in air as in many different electrolytes. The stability is limited by a prolonged oxygen reduction at large cathodic overpotentials. Probably, the mercaptane molecules are chemically oxidised by the H2O2 formed during the reduction of oxygen and the resulting sulfonic acid desorbs from the electrode surface.

In order to develop new composite materials between reactive metals and polymers, it is proposed to place organic monomers at the metal/polymer phase boundary, which can be coupled by covalent/ionic bonds to reactive centres of the metal substrate and later by covalent bonds to the polymer itself. As a first step, the model system iron/n-decanethiol (n-decylmercaptan, C10H21SH) has been investigated by AES and XPS. It is shown that the mercaptan binds to metallic clean iron surfaces through the sulphur atom, probably by cleavage of the SH bond. The S 2p3/2 peak has a binding energy of 162.4 ± 0.2 eV. Anodic polarization and ageing in the laboratory atmosphere do not oxidize these chemisorbed molecules; the oxidation reactions of the substrate are suppressed too. After cyclovoltammetry (−1.0 VSHE⩽ U ⩽ + 0.6 VSHE), better oriented chemisorbed molecules are packed more densely on top of the surface.

This promising method of chemically modifying reactive metal surfaces with organic molecules prior to the attachment of polymers could have a significant impact on work aimed at the optimization of the performance of composite materials. Strong chemical bonds can be formed between a suitably prepared metal surface and certain monomers, which resist even an electrochemical polarization of the interface at large cathodic or anodic overpotentials. These chemical bonds can, however, only be achieved if a suitable structure and reactivity is generated, for example, by using electrochemical techniques. Therefore, further technological progress in this important area requires the cooperation of scientists from rather different scientific disciplines like electrochemistry, surface science and organic chemistry, in order to optimize the structure of the organic monomers and to provide the best possible bonds to the different metals in use, taking into account the rather different reactivity of technologically important media.

Phase transformations in oxide layers below organic coatings have been investigated by in-situ Mossbauer spectroscopy. During wetting of preoxidized iron surfaces iron can further corrode without diffusion of O 2 through the polymer film. The anodic iron dissolution is compensated by cathodic rust reduction. The reactive rust component γ-FeOOH can be reduced to the spinel-phase Fe 3− δO-4 changing the rust morphology and causing the loss of adhesion of the organic coating. This reaction is controlled by the ionic conductivity below the organic coating which is caused e.g. by impurities adsorbed from the atmosphere before the application of the organic coating. ― In order to retard the redox reactions in oxide scales below organic coatings the oxide surface has been chemically modified e.g. by silanes, phosphates and phosphor-organic compounds. This decreases the rate of rust reduction significantly

Bei Laborversuchen zur atmospharischen Korrosion von Reineisen wurde der Metallabtrag eines dunnen Bleches uber magnetische Messungen und der Sauerstoffverbrauch gasvolumetrisch bestimmt. Die Meswerte zeigten, das nach einer kurzen Befeuchtung zuerst eine Auflosung des Eisens unter Reduktion der Rostschicht ablauft. Die Korrosionsstromdichte betragt dabei kurzfristig bis zu 500 m/cm2, fallt aber zeitlich rasch ab. Neben dieser Korrosion unter Rostreduktion spielt die Korrosion bei kritischer Befeuchtung der Metalloberflache wahrend des Austrocknens des Korrosionssystems eine dominierende Rolle. Die Korrosionsstromdichte erreicht hier Werte bis zu 1 mA/cm2. Investigations towards understanding of the atmospheric corrosion processes of pure iron In an investigation of the atmospheric corrosion of pure iron the metal loss of a foil was determined by magnetic measurements and the oxygen consumption gasvolumetrically. The results showed that in the period immediately following short wetting iron dissolution takes place with reduction of the rust layer. The corrosion current density thereby reaches a value of 500 mA/cm2 temporarily falling rapidly with time. Apart from this the corrosion under conditions of critical humidity of the metal surface during the drying-out of the corrosion system plays a dominant role. The corrosion current density reaches here values up to 1 mA/cm2.