Caterina Zanella

Effect of ultrasound vibration during electrodeposition of Ni–SiC nanocomposite coatings

Abstract The deposition of pure Ni and Ni/SiC nanocomposite coatings was carried out using an additive free Watts type bath. In order to avoid porosity and defects induced by the hydrogen evolution ultrasonic vibration was used during the electrodeposition. The effects of the ultrasound treatment on both pure Ni and Ni/SiC nanocomposite codeposition was investigated by means of coatings microstructure and surface morphology study and SiC content measurements. Moreover, it was demonstrated that the ultrasonic vibration reduced the layer porosity. The role of ultrasounds in reducing porosity was shown.

Ultra-Fine Grained Degradable Magnesium for Biomedical Applications

Abstract Properties of commercially available purity magnesium and wrought ZM21 Mg alloy were investigated in view of their biodegradable applications. In particular, the opportunities offered by grain size refinement down to the ultra-fine scale achieved by equal channel angular pressing (ECAP) and warm extrusion were discussed and material properties were analyzed. Results show that the grain refinement will lead to a significant improvement in compression strength. The tension strength of the coarse grained alloy is always significantly higher than that measured in compression due to the sharp texture of the starting wrought alloy. ECAP also causes an attenuation of the above texture effects, promoting marked changes in plastic flow behavior. The corrosion behavior of the investigated materials are affected by a combination of microstructural effects such as chemistry, grain size and the extent of lattice distortion inherited from previous processing stages. ECAP leads to refinement of grain size and to increased lattice defect density which apparently produce counterbalancing effects on corrosion performance. The improved dispersion of second-phase particles brings positive effects on development of pitting.

Effect of pulse current on the electrodeposition of copper from choline chloride-ethylene glycol

Deep eutectic solvents (DESs) have been considered as alternatives to classic aqueous deposition baths used at room temperature. This work describes a preliminary study about the copper deposition process from a bath based on choline chloride/ethylene glycol deep eutectic solvents. The physical properties, such as viscosity and conductivity of the bath, are compared before and after the addition of CuCl2 · 2H2O. The process kinetics during copper deposition was investigated. By optimizing the concentration of metallic salts and operating temperature, deposits with compact surfaces and small grain size were obtained. However, the process has a very limited current efficiency. Pulse plating was applied to improve the mass transport and refine grain size. In this case, an important improvement was achieved. Current efficiency (CE) increased significantly compared to the results obtained in direct current. This proves that pulse plating can be used as an effective method to reduce deposition time and costs. Surface morphology of deposits was observed by scanning electron microscopy (SEM), and compositional analysis was quantified by energy-dispersive X-ray spectroscopy (EDXS).

Resistance to localized corrosion of pure Ni, micro- and nano-SiC composite electrodeposits

The aim of this work was the production and characterization of composite Ni matrix electrodeposits. Pure Ni, micro- and nano-SiC Ni matrix composite deposits have been produced from a Watts’s-type electroplating bath under both direct (DC) and pulse current (PC) conditions. The obtained deposits have been characterized regarding their microstructure by scanning electron microscopy (SEM) observations on both top surface and cross-section and their SiC content by energy-dispersive X-ray spectrometry (EDXS) and glow discharge optical emission spectrometry (GDOES) analyses. The resistance to localized corrosion has been evaluated by exposing the samples in a salt spray cabinet and performing visual observation as well as electrochemical impedance spectroscopy (EIS) measurements every five days. Both the use of PC and the codeposition of the nanoparticles lead to a grain refinement of the Ni matrix. The use of the PC did not influence in a significant way the resistance of the pure Ni deposits to the localized corrosion. The incorporation of micro-SiC led to a decrease of the corrosion resistance for the deposits produced under DC, while the microcomposites produced under PC presented a corrosion resistance comparable to the pure Ni deposits. The nanocomposites presented the highest corrosion resistance due to the more compact and fine-grained microstructure. EIS revealed the presence of a localized corrosion attack earlier than the visual observation, giving useful information about the failure mechanism.

Study of the influence of sonication during the electrod­eposition of nickel matrix nanocomposite coatings on the protective properties

Abstract The interest in the electrocodeposition has been revived due the development of new nanotechnology methods for the production of nano-particles. The codeposition of nanoparticles might enhance the mechanical properties of composite deposits without penalizing the corrosion resistance and avoid the formation of an abrasive third body during the wear process. On the other hand, the volume fraction of codeposited nano-particles is generally low and usually inversely proportional to their size. Many efforts have been done in order to improve the codeposition rate of nanoparticles. Most of the research on nickel composites is focused on the electrodeposition process or on the mechanical and wear properties rather than on the corrosion resistance. In this work, the protective properties of nickel matrix nanocomposite coatings have been studied by means of potentiodynamic curves and electrochemical impedance spectroscopy. Two different nanopowders, i.e., silicon carbide and alumina, were added to a Watts type galvanic bath in order to deposit the nanocomposites coatings on steel substrate. Ultrasonic vibrations have been considered as new process parameter to improve the dispersion of the powder into both the plating bath and metal matrix coating and to substitute pitting control agents for the production of defect-free coatings. Unique, functional properties of composite coatings are derived not only from the presence of the particles dispersed in the bulk of the metallic matrix but also on the matrix microstructural changes induced by the interaction between particles and electrocrystallization process. It has been demonstrated that the codeposition of the silicon carbide particles induces an important microstructural refinement. On the contrary, the aluminum oxide powder is strongly agglomerated and only under ultrasonic vibrations can be dispersed. Ultrasounds have a positive effect not only in hindering the porosity but also in dispersing the ceramic powder and increasing the codeposition rate leading thus to the production of protective and very refined coatings. Moreover, the better dispersed powder induces an improvement also in the corrosion protection leading to the formation of a more stable and resistant passive nickel oxide.

Influence of anodic pulses and periodic current reversion on electrodeposits

Abstract This paper discusses how anodic pulses and periodic current reversion influence electrodeposition. Depending on the involved metal and electrolyte, very different effects can be observed and taken advantage of. The Wagner number, Wa, describing the current distribution is shown to be useful for predicting the throwing power at low frequencies of current reversion, even in complex electrochemical systems, but is less useful at higher frequencies. Passivation can occur due to oxide formation, super-saturation of metal salts or depletion of complexing agents at the electrode surface. Furthermore, dissolution and desorption processes in the anodic period can have strong influence on the succeeding cathodic electrocrystallisation affecting preferred crystal orientation, intrinsic stress and current efficiency. A literature survey is combined with experiments from silver plating from a cyanide bath.

Stress corrosion cracking (SCC) failure in marine areas of fixed guards for climbing

Abstract This work studies the particular mechanism of environmental stress corrosion cracking (SCC) that has been described to interest stainless steel products, like climbing anchors, installed in sea areas. The failure analysis of several broken anchors was carried out. The samples were collected in different parts of the world, always from climbing structures close to the sea. The analysis confirmed the stress corrosion mechanism of degradation, giving also important information about the specific environments causing the metal fracture. These results are in agreement with a few previous works about this subject and are in the frame of the larger topic of SCC of austenitic stainless steel at room temperature. Moreover, some corrosion tests were carried out on stainless steel samples simulating the operation conditions, after contamination with electrolytes at different concentration. The tests are performed in order to better understand the degradation mechanism and to evaluate the influence of some environmental parameters over the susceptibility to SCC. With these experimental data, a possible interpretation model has been proposed together with some reasonable solutions for the material selection process, considering the problem’s characteristics and the multiple alternatives available nowadays for climbing materials.

Promotion of young European scientists in surface technology

This contribution is an extension of two earlier reports in Transactions on EAST activities in which the imminent start-up of the e-MINDS program, involving training courses for early stage surface technology researchers in electrochemical processing in the development of miniaturised systems and devices, was noted. The first of these courses recently took place in Brno, the Czech Republic, in April of this year, and this is reported here, together with the Schwäbisch Gmünd Prize for young scientists in our field.

Control of silver throwing power by pulse reverse electroplating

The influence of electroplating parameters on throwing power (TP) is studied in additive-free silver cyanide solutions under direct current and pulse reverse electroplating conditions. It is found that the best TP is obtained when no agitation of the electrolyte is applied. The most important parameters for controlling the TP are the cathodic current density, the anodic to cathodic charge ratio, and the ratio between the anodic and cathodic current densities. Guidelines for process optimisation are given.

6th European Pulse Plating Seminar

Abstract Over the past decade the European Pulse Plating Seminar has been established as the most important event for discussing research and applications of pulse plating. Now it is organised every second year in the area of Vienna by the company Happy Plating. For the past two years it has been co-organised with the European Academy of Surface Technology, EAST. The pulse plating seminars have made it possible to follow how the application of pulse plating has increased and widened during the last decade since the first seminar in 2006.