Mario Sahre

In-situ grazing incidence X-ray diffractometry observation of pitting corrosion of copper in chloride solutions

Abstract In-situ Grazing Incidence X-Ray Diffractometry (in-situ GIXD) by means of common laboratory equipment, in combination with a potentiostated three-electrode cell, revealed the conversion film dynamics during the alkaline chloride pitting action on copper. Several hours of oxidation in the potential range of Cu(OH) 2 formation resulted in the formation of crystalline CuCl and Cu 2 O. The attack of chloride ions initially replaces the outer amorphous Cu(OH) 2 layer, forming soluble CuCl 2 . Then the chloride ions start replacing the oxygen in the Cu 2 O layer, forming a CuCl phase. At transient times, only CuCl occurs before corrosion currents increase due to copper dissolution and crystalline Cu 2 O formation. Ultrasonic treatment shows that CuCl has poor adhesion, whereas Cu 2 O crystals persist at the pitted copper surface.

Multi-method Analysis of the Metal/Electrolyte Interface: Scanning Force Microscopy (SFM), Quartz Microbalance Measurements (QMB), Fourier Transform Infrared Spectroscopy (FTIR) and Grazing Incidence X-ray Diffractometry (GIXD) at a Polycrystalline Copper Electrode

The successful application of various in situ and ex situ analytical techniques has been demonstrated at the buried interface between a metal and an electrolyte. Scanning force microscopy (SFM), electrochemical quartz microbalance measurements (EQMB), grazing incidence x-ray diffractometry (GIXD), Fourier transform infrared spectroscopy (FTIR) in the specular reflection absorption mode and electrochemical charge measurements proved complementary in the characterization of a polycrystalline copper electrode in alkaline 0.1 M sulphate, perchlorate, fluoride and chloride electrolyte contact at pH 12. The surface exhibited a mixture of Cu(111) and Cu(200) grains of the order of 100 nm. Repeated potential scanning in the double layer and passive oxide region, between -1.4 and +0.1 VMSE, resulted in a complete reorganization of the surface morphology but no detectable corrosion. The electrochemical exchange of H2O and OH− between the electrolyte and the oxide film took place reversibly in accordance with a solid-state growth mechanism. The copper atoms were redeposited at crystallographically preferred sites, generating comparatively homogeneously oriented, narrow Cu(111)-edged grain ridges of length 200 nm. In the Cu(I) potential range, the formation of several monolayers of amorphous Cu2O could be confirmed. Only after extended time periods in the Cu(II) oxide potential region, Cu2O recrystallized to a (111) phase accompanied by Cu2O(200) and Cu2O(110). In this region, one observed the formation of amorphous Cu(OH)2 concurrent with further growth of Cu2O. Strong CuOH IR stretching bands excluded the existence of CuO. At corrosive potentials of +0.25 VMSE, high anodic currents and substantial mass losses led to an electropolished surface with isolated features of <300 nm width and <70 nm height.© 1997 John Wiley & Sons, Ltd.

Electrochemistry of nano-scale bacterial surface protein layers on gold

The mechanism of the recrystallization of nano-scale bacterial surface protein layers (S-layers) on solid substrates is of fundamental interest in the understanding and engineering of biomembranes and e.g. biosensors. In this context, the influence of the charging state of the substrate had to be clarified. Therefore, the electrochemical behaviour of the S-layers on gold electrodes has been investigated by in-situ electrochemical quartz microbalance (EQMB) measurements, scanning force microscopy (SFM) and small-spot X-ray photoelectron spectroscopy (SS-XPS) of potentiostatically emersed substrates. It was shown that the negatively charged bonding sites of the S-layer units (e.g. carboxylates) can bond with positively charged Au surface atoms in the positively charged electrochemical double layer region positive of the point of zero charge ( approximately -0.8 V vs. saturated mercury-mercurous sulphate electrode). Surface conditions in other potential regions decelerated the recrystallization and fixation of S-layers. Time-resolved in-situ and ex-situ measurements demonstrated that two-dimensional S-layer crystal formation on gold electrodes can occur within few minutes in contrast to hours common in self-assembled monolayer (SAM) generation. These results proved that the recrystallization and fixation of 2D-crystalline S-layers on an electronic conductor can be influenced and controlled by direct electrochemical manipulation.

In-situ grazing incidence X-ray diffractometry investigation of phase change processes at the silver/aqueous-halogenide interface

Abstract In-situ grazing incidence X-ray diffractometry has been successfully applied to monitor phase change processes at silver in an aqueous halogenide interface. Crystalline silver halogenide films and islands equivalent to homogeneous films of several nanometers thick could be resolved. Major crystalline orientations independent of pH are AgI (002), AgBr (200), AgCl (200). Grain sizes increase with growth time (at fixed overpotential), but the crystalline percentage decreases with anodic overpotential and formation rate. The crystalline portion of the AgX phases is maximum in neutral electrolyte. The amorphous or nanocrystalline phases dominate at high pH. A dissolution–precipitation mechanism is valid. A strong pH dependence of the overall generation rate and the crystalline percentage of the AgX phases has been observed in contrast to thermodynamic expectations. A mechanistic model involving the modification of silver surfaces covered with specifically adsorbed halogenides species by hydroxyl ions is suggested.

Modelling and simulation of a fibre Bragg grating strain sensor based on a magnetostrictive actuator principle

A new concept for the self-diagnosis of embedded fiber Bragg grating (FBG) strain sensors was developed, simulated and experimentally tested. This concept is based on a magnetostrictive metallic layer directly coated on the fibre cladding over the grating segment of the FBG sensor, so that an on-demand external magnetic field in a millitesla scale can produce a controllable artificial strain as an indication signal for the remote optical interrogator. The relationship between the pre-defined magnetic field and its induced Bragg wavelength shift characterizes this validation concept. Any deviation of the local bonding state of the interfaces from the initial or/and any change of shear strain transferring mechanism from composite matrix to the optical fibre core will result in alterations in this sensitive relationship, and thus triggers an immediate alert for a further inspection. The finite element method is used to simulate the strain of this configuration as result of different values of the magnetic field in order to optimize the geometrical sensor parameters. The simulations are verified by experiments results.