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

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

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

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.

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

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

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

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

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.

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 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.

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.

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.

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.

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.

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 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.

Monomolecular LB films of n-octadecyltrichlorosilane (n-OTS) and chlorodimethyloctadecylsilane (CODS) have been produced on metal substrates like Fe and Ni in order to protect the reactive metal surface against corrosive species like H2O, O2 and SO2. To characterize defects within the monomolecular LB films, they were studied by UHV methods such as scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and scanning Auger microscopy (SAM). In dry or humid air atmospheres it is possible to measure a work function topography of the LB film covered materials with a scanning Kelvin microprobe. In dry air the work function topography corresponds to the distribution of dipole potentials. Therefore it is possible to analyze intrinsic defects within the monomolecular LB film on the metal surface. In a humid atmosphere the work function is mainly given by the local corrosion potential of the metal substrate and therefore delamination processes of the monomolecular film can be studied as well as the stability of the LB film coated metal substrate.

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.

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

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.

A key parameter that controls the formation of a local galvanic element during the deadhesion of paint from base metals is the potential gradient between a defect in the paint and the intact metal oxide/polymer interface. The suitable development of zinc coatings allows for control of the potential at the intact interface and thus improvement of the delamination behavior. However, no systematic in-depth study on the origin and meaning of electrode potentials at polymer/metal interfaces or even bare metal surfaces has been presented yet, although in many recent publications Volta potential differences between inclusions and matrix measured on the surfaces of alloys are often interpreted as providing information on the galvanic activity during corrosion. It is the focus of this paper to present a detailed analysis of the origin of the potentials measured on the different materials and to point out what conclusion can be drawn from their values. Special focus is given to the technologically important system Zn-Mg.

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.

Scanning Kelvin probe force microscopy (SKPFM) is used to study the initial stages of atmospheric corrosion of an AlMg alloy and of physical vapor deposition (PVD) deposited 2 μm Al dots on pure Mg. The latter system is used as a model of a two-phase AlMg alloy. The influence of CO2 was studied in situ in humid air using SKPFM. This method allows for the in situ investigation of the evolution of the Volta potential during exposure, the resolution being in the submicrometer range. The temperature was 22.0°C, and the relative humidity was 85 or 95%. The concentration of CO2 was

Tip-induced metal deposition was employed to fabricate nanometer sized Cu clusters on electrodes using an electrochemical scanning tunneling microscope (EC-STM). Due to the mixed Au and Cu termination of the substrate surface, an underpotential deposition (UPD) layer of copper covers only Au sites. Investigation of the anodic oxidation and dissolution of the Cu clusters give evidence for a strong inhibition of surface diffusion reactions due to this partial UPD layer. Based on a comparison of the nanocluster dissolution behavior with dealloying reactions of the substrate, it is concluded, that the nanostructures consist of a mixture between copper and gold due to interfacial alloying effects. This offers a novel explanation for the unexpected and unusually high stability of the clusters frequently reported in literature. © 2003 The Electrochemical Society. All rights reserved.

The effect of the surface concentration of submicrometer ammonium sulfate (NH 4 ) 2 SO 4 dust particles on the mechanism of atmospheric corrosion of copper has been investigated at 298 K and 93% relative humidity (RH). For surface concentrations from 1 μg/cm 2 to 10 mg/cm 2 , the same corrosion products are formed at relative humidities well above the critical relative humidity of (NH 4 ) 2 SO 4 . Initially, a Cu(NH 3 ) 2+ complex is formed. The basic copper sulfate posnjakite precipitates when its solubility product is exceeded while NH 3 evaporates. Posnjakite may be converted to antlerite or brochantite if higher amounts of (NH 4 )SO 4 particles were deposited. The basic copper sulfates then decompose at the inner interface to form Cu 2 O. With low amounts of (NH 4 ) 2 SO 4 particles, the conversion is 100%. With high amounts of particle deposits, residual copper sulfate remains on top of a Cu 2 O-layer. With increasing amounts of deposited (NH 4 ) 2 SO 4 particles on copper, the sequence of corrosion products that are formed takes more time. The mechanism proposed in earlier work for the corrosion of copper with (NH 4 ) 2 SO 4 particles in humid air is improved to explain the new experimental findings.

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.

New primer molecules have been synthesized to increase the adhesion strength between a copper leadframe and an epoxy molding compound in microelectronical devices. The coupling agents were preliminarily chemisorbed at the surface of copper plates via special binding groups like thiol, disulfide, ethylene diamine and phthalocyanine. Binding to the epoxy resin was performed via an hydroxyl group. Linear hydrocarbon spacers with various chain lengths connected the copper- and epoxy-binding groups. The self-assembled layers of the organic coupling agents at the metal surface were characterized by X-ray photoelectron spectroscopy. Thermogravimetric analysis was used to study the coating with respect to its corrosion oxidation inhibition. Shear tests clearly indicated that the coupling agents increase adhesion strength and are stable even in extreme humidity and thermal conditions in analogy to IPC-Level-1 pretreatment. Thus, delamination of the microelectronical packages was prevented.