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

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.

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

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

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

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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.

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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.

It is possible to generate small metal clusters on a metal surface in an electrochemical environment by tip-induced metal deposition using an electrochemical scanning tunneling microscope (STM). So far, it has only been possible to observe the clusters in situ over a period of a few hours. The present work shows for the first time, that copper clusters of 2-3 atomic layers height, consisting of 100-1000 atoms, can be prepared under electrochemical in situ conditions on a Au(111) surface and remain observable after removing the electrolyte. The clusters show no Ostwald ripening but the imaged heights of the clusters decrease continuously with time. Only traces of the nanostructures can be imaged with the STM 2 days after exposure to ex situ conditions in air. The results open a new perspective for further investigations of the properties of electrochemically created nanostructures with ex situ analytical methods.