Nuno Miguel Oliveira Pereira

Abstract An alternative route is proposed for direct electrodeposition of TiO2 films. The electrochemical behaviour of Ti (IV) species in the deep eutectic solvent formed between choline chloride (ChCl) and ethylene glycol (EG) was studied by chronoamperometry and cyclic voltammetry. It was discussed that during the cathodic scan soluble subvalent TiCl chi species were formed using the eutectic system 1ChCl:2EG. Using ethylenediamine or LiF as additives it was possible to obtain a titanium dioxide thin film in the orthorhombic variant named brookite. Chronoamperometric investigations revealed a nucleation mechanism involving the simultaneous presence of 2D instantaneous nucleation process including lattice incorporation and a 3D diffusion-limited nucleation and growth process.

Abstract The effect of the addition of a group of organic additives on the electrodeposition behavior of zinc was investigated in choline chloride:ethylene glycol (ChC1:EG) eutectic mixture in the molar ratio of 1:2. Cyclic voltammograms recorded on steel electrode showed a cathodic peak is only observed after reversing of the scan. Chronoamperometric measurements indicated that the deposition of zinc occurs through 3D progressive nucleation mechanism. The morphology of the zinc deposits and was evident that additives influence the deposits morphologies. X-ray diffraction confirmed the presence of crystalline zinc and reveal the grain refinement effect obtained by using the additives selected where the smallest grain size of 31.7 nm was obtained in the presence of Dimethyl sulfoxide (DMSO). Moreover the XRD data showed that the addition of additives modified the preferential growth plane. The corrosion resistance properties of the electrodeposited Zn coatings were evaluated in 3% NaCI aqueous solution using potentiodynamic polarization. The results showed that the zinc film deposited with DMSO was the best corrosion resistant coating.

Abstract Co-Sn alloy films were electrodeposited from choline chloride (ChC1)-ethylene glycol (EG) and choline chloride (ChCl1)-urea (U) eutectic mixtures. The deposition of Co-Sn alloy on a copper electrode was studied by cyclic voltammetry, which demonstrates that the coelectrodeposition was achieved. For comparison of properties, Co-Sn alloys were deposited from electrolytes with different Co/Sn ratios. The X-ray diffraction patterns (XRD) showed that the phase structure was affected by the Co/Sn ratio; nevertheless, Co3Sn2 was always the predominant phase. Traces of metallic cobalt were also detected. The nature of the electrolyte used and the metallic composition affected the morphologies of the deposits and their corrosion resistance. The best corrosion resistant coating, with a corrosion potential of -617 mV, was composed by 44.4 wt % of Co and 55.6% of Sn, and it was obtained from the ChCl-EG electrolyte. The magnetic properties of the analyzed samples did not present an evident relationship with the metallic ions ratio in solution.

Abstract The paper presents experimental results regarding the electrodeposition and characterization of cobalt and cobalt composites with carbon nanotubes from a choline-chloride-based deep eutectic solvent. Dispersion stability of multi-walled carbon nanotubes (MWCNTs) was excellent in the eutectic solvent used. According to Raman and XRD analysis, the carbon nanotubes were successfully inserted into the metallic matrix. Furthermore, XRD results suggested that the incorporation of CNTs on the deposit promoted a preferred orientation of the Co crystallites on (220) plane. The Co and Co-composites coatings obtained onto a copper substrate are adherent and uniform. Pure Co deposit was formed by sharp edge grains, Co-composites appeared to be less compact and formed by relatively spherical particles connected by MWCNTS. Furthermore, it was found that the presence of MWCNTs contributed to decreasing the deposit's roughness. From corrosion tests, Co-composite films exhibit a comparable or slightly better corrosion performance as compared to pure Co films.

Abstract The deposition of Mn and Mn-Sn alloy from two deep eutectic solvents (DES) was investigated. Pure Mn deposits were powdery and amorphous regardless the DES used. In contrast, the manganese-tin deposits obtained from the two DES used were adherent. The morphology of the deposits obtained from the different DES was analyzed by SEM, which showed that pure Mn films were fibrous. The morphology of Mn-Sn deposits changed upon changing on the amount of tin in solution or the DES used. The phase composition of the Mn-Sn films were investigated by X-Ray diffraction, which showed that the deposits were formed by different MnxSny intermetallic phases. The metallic content in the deposit changed upon changing the bath composition or the DES used. Using the urea (U) based DES Mn-Sn deposits with a Sn content between 1.8 and 6.7 wt% were obtained. In contrast, using the ethylene glycol (EG) based DES the Sn content in the deposits varied between 33.2 and 59.0 wt%.