Ingolf Scharf

Effect of additive and current mode on surface morphology of palladium films from a non-aqueous deep eutectic solution (DES)

Electrodeposition of palladium from a non-aqueous electrolyte solution [choline chloride/urea/palladium(II)chloride] has been carried out by direct and pulse current electroplating. In this study, the influence of an organic additive (nicotinic acid amide), current mode (direct current or pulse current deposition) and hydrodynamic on the surface morphology of electroplated palladium films was investigated. In order to determine the surface morphology and thickness of the electrodeposited palladium layers, a scanning electron microscope and an energy dispersive X-ray fluorescence spectroscope were used. In addition, the cell voltage during the different electrodeposition experiments was recorded and analysed. The experimental results showed that the surface morphology of the palladium deposits could be remarkably affected either by addition of the additive or by applying pulse current. Pulse plating and the selected inhibitor mutually interfere with each other, causing changes in the microstructure of the palladium deposits (e.g. smoothening or forming of micro-cracks). It was possible to optimise the palladium deposit quality by applying pulse current or by addition of the appropriate inhibitor.

Electrodeposition of palladium films from ionic liquid (IL) and deep eutectic solutions (DES): physical–chemical characterisation of non-aqueous electrolytes and surface morphology of palladium deposits

Abstract The physical and electrochemical characteristics such as density, viscosity, electrical conductivity and cyclic voltammetry of three different non-aqueous palladium electrolytes were analysed. The cyclic voltammetry behaviour showed typical reduction and oxidation peaks corresponding to the deposition and stripping of palladium in the electrolytes employed. The electrodeposition of palladium films from choline chloride/ethylene glycol (ChCl-EG), choline chloride/urea (ChCl-urea) and 1-butyl-3-methylimidazolium chloride-tetrafluoroborate (BMIM-Cl-BF4) solutions was demonstrated. Compact deposits were obtained with galvanostatic electrolysis. The scanning electron micrographs of the deposits revealed predominantly nodular Pd particles.

Experimental and Theoretical Characterization of the Aromatization, Epimerization, and Fragmentation Reactions of Bi‐2H‐azirin‐2‐yls Prepared from 1,4‐Diazidobuta‐1,3‐dienes

1,4-Diazidobuta-1,3-dienes (Z,Z)-10, 17, and 21 were photolyzed and thermolyzed to yield the pyridazines 13, 20, and 23, respectively. To explain these aromatic final products, the generation of highly strained bi-2H-azirin-2-yls 12, 19, and 22 and their valence isomerization were postulated. In the case of meso- and rac-22, nearly quantitative formation from diazide 21, isolation as stable solids, and complete characterization were possible. On the thermolysis of 22, aromatization to 23 was only a side reaction, whereas equilibration of meso- and rac-22 and fragmentation, which led to alkyne 24 and acetonitrile, dominated. Prolonged irradiation of 22 gave mainly the pyrimidine 25. The change of the configuration at C-2 of the 2H-azirine unit was observed not only in the case of bi-2H-azirin-2-yls 22 but also for simple spirocyclic 2H-azirines 29 at a relatively low temperature (75 °C). The fragmentation of rac-22 to give alkyne 24 and two molecules of acetonitrile was also studied by high-level quantum chemical calculations. For a related model system 30 (methyl instead of phenyl groups), two transition states TS-30-31 of comparable energy with multiconfigurational electronic states could be localized on the energy hypersurface for this one-step conversion. The symmetrical transition state complies with the definition of a coarctate mechanism.

Calculation approach for current–potential behaviour during pulse electrodeposition based on double-layer characteristics

Abstract This paper introduces a phenomenological calculation approach for the electrolytic pulse deposition of nickel under high polarisation based on an equivalent electrical circuit. In a quasistationary state of the deposition, the electrolyte resistance and double layer parameters are identified by electrochemical impedance spectroscopy and galvanostatic polarisation. The charge–transfer resistance of both the anodic and cathodic electrode double layer is inversely proportional to the current density. This means the overpotentials over the electrode double layers are independent of the current density. For short pulse on-times and off-times (up to 10 ms), the behaviour of the electrolytic cell is mainly determined by the double layer characteristics and the calculation approach therefore allows the prediction of the current–potential behaviour during pulse deposition under high polarisation. For larger pulse widths, the time-dependent evolution of the overpotentials occurring at the electrode/electrolyte interface becomes a determining factor for the cell potential.

EBSD und STEM an hochgradig plastisch verformten Aluminiumlegierungen

Abstract After aluminum alloys undergo severe plastic deformation there is an interest in what grain refining is obtained and is determined from the orientation data detected from backscatter electron diffraction in lateral resolution. The quality of backscatter diffraction depends on the fraction of successful indexings, which presupposes an appropriate preparation of the surface. Vibration polishing results in a matrix nearly free of deformation and excellent levelling of the precipitates whereas relief formation (often occurring in oxide polishing) and dissolution (often occurring in electro-polishing) of those phases will reduce the band contrast and indexing quality. The results thus obtained from backscatter electron diffraction are backed by scanning electron microscopy images in transmission.

On the development of an intrinsic hybrid composite

Hybrid parts, which combine low weight with high strength, are moving into the focus of the automotive industry, due to their high potential for usage in the field of crash-relevant structures. In this contribution, the development of an intrinsic hybrid composite is presented, with a focus on the manufacturing process, complex simulations of the material behaviour and material testing. The hybrid composite is made up of a continuous fibre- reinforced plastic (FRP), in which a metallic insert is integrated. The mechanical behaviour of the individual components is characterised. For material modelling, an approach is pointed out that enables modelling at large strains by directly connected rheological elements. The connection between the FRP and the metallic insert is realised by a combination of form fit and adhesive bonds. On the one hand, adhesive bonds are generated within a sol gel process. On the other hand, local form elements of the metallic insert are pressed into the FRP. We show how these form elements are generated during the macroscopic forming process. In addition, the applied sol gel process is explained. Finally, we consider design concepts for a specimen type for high strain testing of the resulting interfaces.

Anodisation with dynamic current control for tailored alumina coatings

The anodic oxidation process is commonly used to refine the surface of aluminium and its alloys. Compared to the substrate, the alumina layers produced by anodising exhibit an increased hardness and chemical resistance. Thus, the corrosion and wear resistance are generally improved. The coatings are also electrically isolating and may serve decorative purposes. Applying a time-variant, dynamic electrical process control by pulse-current or current-steps is a promising approach to improve the coating properties, which is partially deployed in an industrial scale. In the present work, the influence of dynamic electrical process control on the coating properties is examined by means of a design of experiments (DOE). The effects of various electrolyte compositions and temperatures as well as processing time are considered with regard to coating thickness, hardness, wear resistance and the electrical energy consumption during the formation of the coatings. Information about the statistical significance of the effects of the parameters on the considered properties is obtained by an analysis of variance (ANOVA).

Anodisation of Aluminium Alloys by Micro-Capillary Technique as a Tool for Reliable, Cost-Efficient, and Quick Process Parameter Determination

Anodisation is essential for improving surface properties of aluminium alloys and composites regarding wear and corrosion behaviour. Optimisation of the anodising process depends on microstructural constituents contained in aluminium alloys and represents a key task, consisting of the control of process parameters and electrolyte formulation. We applied the micro-capillary technique known from corrosion studies and modified it to form anodic aluminium oxide films on high-strength aluminium alloys in comparison to pure aluminium in sulphuric acid. A glass capillary with an opening of 800 μm in diameter was utilized. Corresponding electrochemical measurements during potentiodynamic and potentiostatic anodisation revealed anodic current responses similar to conventional anodisation. The measurement of film thickness was adapted to the thin anodised spots using ellipsometry and energy dispersive X-ray analysis. Cross sections prepared by focused ion beam milling confirm the thickness results and show the behaviour of intermetallic phases depending on the anodising potential. Consequently, micro-capillary anodising proved to be an effective tool for developing appropriate anodisation conditions for aluminium alloys and composites because it allows quick variation of electrolyte composition by applying low electrolyte volumes and rapid film formation due to short process durations at small areas and more flexible variation of process parameters due to the used set-up.

Anodic Oxidation of AMCs: Influence of Process Parameters on Coating Formation

Aluminium matrix composites (AMCs) consisting of high-strength, age-hardenable aluminium alloys and homogeneously dispersed hard particles open up new possibilities in designing light-weight material based security related structures. The susceptibility of the matrix alloy to selective corrosion can be reduced significantly by anodic oxidation. A powder-metallurgical processed alloy AlCu4MgMn with hard particles and a commercial wrought alloy for reference were used for the investigations.In order to control the microstructure of anodic aluminium oxide (AAO) formed on AMCs, it is necessary to understand the formation mechanism and the influencing parameters. Therefore in a first run, the anodizing behaviour of matrix alloy was separated from the behaviour of hard particles. The AAO coatings show small growth rates on the matrix and the reference alloy accompanied by a complex pore structure which differs from the ordered vertical pore structure on pure aluminium. Depending on the type and the size as well as the anodizing parameters, the particles are either incorporated into the AAO coating unchanged or partly resp. completely oxidized. The AAO microstructure changes significantly in dependence of the anodizing parameters. It is shown that a technically relevant coating thickness can be achieved on AMCs by choosing appropriate process parameters.

A process and load adjusted coating system for metallic inserts in hybrid composites

According to the concept of an intrinsic hybrid composite, adhesive bonding is designed for generating the connection between the applied fiber reinforced polymer and a metallic insert. To induce adhesive bonding, a metallic insert, made of aluminum, is coated. This contribution focusses on the development of a suitable coating system. To this end, the coating system must meet certain requirements. On one hand, demands on the coating like ductility can be deduced from analyzing the manufacturing process. On the other hand, requirements like corrosion protection as well as high static and dynamic strength arise from specific applications under considerations. The utilized coating system is based on organically modified silicate layers (Ormosil) applied using a sol–gel process. To prove that this coating system fulfils the requirements, the corrosion protection is analysed by impedance spectroscopy. Furthermore, different mechanical experimental investigations are performed to verify the ductility of the coating as well as the strength of the resulting interface. Hence, it is shown that the considered coating system can be applied for the analysed intrinsic hybrid composite manufactured in series.