Teodor Visan

Electrodeposition of Co and CoMo alloys coatings using choline chloride based ionic liquids - evaluation of corrosion behaviour

This study deals with the electrodeposition of Co and CoMo alloys from various ionic liquids based on choline chloride (ChCl) – urea and ChCl – ethylene glycol eutectic mixtures. The Co and Co–Mo (with 1–8 wt-% Mo content) deposits obtained were adherent, compact and uniform onto copper substrates. A decrease of the Mo content in the alloy has been shown as the applied current density increased in the range of 7–25 mA cm−2, at 90–100°C. Some peaks assigned to MoO3 or Co3Mo phases have been identified in the XRD patterns. The average size of crystallites has been estimated to be in the range of 7–9.2 nm (nanocrystalline deposits). Atomic Force Microscopy analysis gave evidence that Co deposits were formed by multiple compact almost rounded crystallites, while Co–Mo alloy ones consisted of multiple relatively compact grains with cylindrical shape. The coatings’ corrosion performance has been also measured by continuous immersion testing in 0.5M NaCl solution, and potentiodynamic polarisation and electrochemical impedance spectra.

Studies Regarding the Nickel Electrodeposition from Choline Chloride Based Ionic Liquids

The electrochemical technologies are extensively applied in a large range of industrial fields, from decorative/protective coatings in electrical engineering, electronics, automotive or machine building domains towards the manufacturing of microelectronic components, of micro-electro-mechanical systems (the so-called MEMS) or of the high precision microand nanostructures, including biological ones (Data & Landolt, 2000; Gurunathan et al., 1999). Due to the fact that electrochemical deposition is an atomic/molecular level process, the formed layer entirely takes the three-dimensional shape of the substrate with a very high accuracy. As a result of the last years scientific progress, the theoretical aspects of electrochemical engineering principles applicable for electrochemical micro-processing have significantly developed so that, associated with performance techniques and equipment lead to the new and innovative materials development having controlled microor nanostructures. In spite of a long history and experience, the metals surface finishing industry still has not been successful in extending the range of the metals able to be electrodeposited towards some of them with a promising technical potential, such as Al, W, Mo, Ti. Their capability to form stable oxides represents an obstacle against their application as coating layers, especially from classical aqueous electrolytes. Moreover, in the last decade sustained efforts have been made to preserve the environment and to minimize the toxic effects of certain electrochemical technologies on human health. Thus, certain metallic coatings have been and still are subjected to some use restrictions such as Cr, Ni, but Cu, Ag and Au as well, due to the involvement of aqueous cyanide electrolytes. Taking into account the above mentioned considerations, in the last 10 years investigations to develop and promote alternative more environmentally friendly electrochemical media have been reported, including the class of the so-called “ionic liquids”, defined as “ionic materials in liquid state for temperatures lower than 100oC” (Endres et al., 2008; Wasserscheid & Welton, 2007). The ionic liquids have some properties which make them adequate as metal electrodeposition electrolytes, such as:

Electrochemical Deposition of PbSe1-xTex Nanorod Arrays Using Ion Track Etched Membranes as Template

Lead chalcogenides(PbS, PbSe, PbTe)are narrow band gap semiconductors which have been studied in the field of IR detection and thermoelectric devices. The template method is a general approach for synthesizing nanomaterials within the pores of membranes. The membranes employed contain cylindrical pores with monodisperse diameters, and corresponding cylindrical nanostructures are obtained. The aim of the present study was to prepare PbSe1-xTexnanorod arrays using electrodeposition. The process was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The resulted PbSe1-xTexnanostructures were characterized using scanning electron microscopy(SEM)as well as energy dispersive X-ray analysis(EDAX).

Lithium-AluminIum Hydroxide Hydrate thin Layers on Al Based Substrates - New Ecological Process for Corrosion Resistance Increase

Some preliminary experimental results on development of non-conventional, environmentally friendly procedures to form new corrosion protective thin films on Al, based on lithium-aluminium hydroxides known as hydrotalcite coatings, are presented. Chemical conversion films on pure Al and AU4G1 Al alloy have been formed involving LiNO3-KNO3-LiOH based solutions, with/without a second step involving Ce(III)and Mn(VII)compounds. SEM pictures revealed a uniform layer, formed by crystallites with 200–300 nm walls length. Corrosion experiments showed their excellent performances, materialised in corrosion currents of 0.1–0.2 μA/cm2and at least 168 hours of salt mist exposure with no aspect modification.

Electrochemical Growth of Eosin Y/Manganese Doped ZnO as Hybrid Films and Nanowires

Abstract The electrodeposition process of Eosin Y/ZnO: Mn as films and nanowires performed using a solution containing zinc and manganese nitrates + lactic acid mixture was studied by linear voltammetry. The films and wires grown by polarization at −1.1 V/SCE electrode potential were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). Additionally, the Eosin Y presence was evidenced by optical measurements as absorption and photoluminescence spectroscopy. The manganese content in films depends on the nature of support electrode used. On the other hand, the presence of Eosin Y species in the deposition bath increased significantly the manganese concentration in the ZnO: Mn nanowires electrodeposited at −1.1 V/SCE.

Polypyrrole Films Doped with Phosphomolybdate Anions on Al Surfaces – Formation and Corrosion Protection Characterisation

Abstract The present paper deals with some preliminary experimental results regarding electrodeposition of polypyrrole films doped with phosphomolybdate anions onto Al substrates involving an initial anodizing in nitric acid electrolyte; early studies proved that this stage offers a very good adherence of the further layer on Al surfaces. The phosphomolybdate doped polypyrrole films have been formed both galvanostatically and involving cyclic voltammetry, in aqueous solutions containing phosphomolybdic acid and pyrrole. In several experiments Tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt) has been added, acting as mediator and improving the layer morphology and aspect. The films exhibited a very good adherence on the metallic substrate, with a uniform black color and showed classical cauliflower morphology, more dense and ordered in the presence of Tiron, according to SEM investigations. Raman spectroscopy and EDX analysis revealed the presence of doping anion within polypyrrole layer. Also EDX measurements suggested that the film incorporates a 1 : 9 ratio of phosphomolybdate anion to PPy units. When both Tiron and phosphomolybdate anions are present in the solution, phosphomolybdate and other related anions are preferentially incorporated within the layer. Based on the continuous immersion test in NaCl 0.5M solution for 240 h, the phosphomolybdate entrapping into the polymer matrix was shown to provide a better corrosion protection in chloride medium.

Cathodic deposition of BiTe as thermoelectric films using choline chloride based ionic liquids

This paper reports the electrodeposition of BiTe by potential control electrolysis using a ionic liquid based on choline chloride and malonic acid mixture (1:1 moles) in the 25-60°C temperature range. From cyclic voltammetry and impedance experiments carried out in order to characterize the cathodic process on Pt electrode it was found that the deposition of BiTe from electrolytes occurs on a Te-covered Pt substrate at less negative potentials than for deposition of singular Bi or Te films. Nyquist and Bode impedance spectra showed differences in Pt behavior due to its polarization at various cathodic potentials. The morphology and chemical composition of BiTe films deposited on Cu were determined by AFM, SEM and TEM microscopy.