Browsing by Author "Vilar, Rui"
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- Electrodeposition of black chromium from CR(III) ionic liquid solutionPublication . Eugénio, S.; Rangel, C. M.; Vilar, RuiBlack chromium is an important coating material used in solar thermal systems as a spectrally selective surface. This coating is usually obtained by electrodeposition from sulphate free chromium (VI) aqueous solutions which represent a health and environmental hazard due to the presence of Cr(VI), a known toxic and carcinogenic agent. Recent developments in green chemistry have shown that ionic liquids can be used as electrolytes, allowing the deposition of a wide range of materials with negligible environmental and health impacts. In the present study, the electrodeposition of black chromium films from a solution of ionic liquid containing chromium (III) has been investigated by cyclic voltammetry and chronoamperometry. Homogeneous and well adherent black Cr films have been obtained on several substrates, by potentiostatic electrodeposition. The films morphology and composition have been characterised by SEM/EDS and GI-XRD.
- Electrodeposition of black chromium thin films from trivalent chromium-ionic liquid solutionPublication . Eugénio, S.; Vilar, Rui; Rangel, C. M.; Baskaran, I.In the present study, black chromium thin films were electrodeposited from a solution of 1-butyl-3- methylimidazolium tetrafluoroborate ([BMIm][BF4] ionic liquid containing trivalent chromium (Cr(III)). Homogeneous and well adherent coatings have been obtained on nickel, copper and stainless steel substrates. The nucleation and growth of the films were investigated by cyclic voltammetry and current-density/time transient techniques. SEM/EDS, XPS and XRD were used to study the morphology, chemical composition and structure of the films. The coatings consist of a mixture of metallic chromium and chromium oxides (black chromium) and present a sub-micrometric granular structure.
- Towards an electroless deposition of gold on metallic substrates using ionic liquids as electrolytesPublication . Sá, A.I. De; Quaresma, S.; Eugénio, S.; Rangel, C. M.; Vilar, RuiRecent research has suggested a number of applications for gold in fuel cells and related hydrogen fuel processing, which include light weight corrosion resistance bipolar plates and the incorporation of gold as catalyst to provide improvements in electrode conductivity, among others. This paper reports on the electroless deposition of gold on copper substrates from a HAuCl4.3H2O solution in 1-butyl-1- methylpyrrolidinium dicyanamide (BMP-DCA), in laboratory atmospheric conditions. The electrochemical behaviour of the plating solution was studied by potential sweep techniques. Results suggest that gold ions are reduced and deposited on copper without the aid of external polarization, probably by displacement deposition involving copper dissolution, since no other oxidation reaction was identified. Preliminary studies using SEM/EDX showed that compact gold thin films, deposited on copper substrates at 333 K, present a granular nanostructured morphology.
- Towards an electroless deposition of gold on metallic substrates using ionic liquids as electrolytesPublication . Sá, A.I. De; Eugénio, S.; Quaresma, S.; Rangel, C. M.; Vilar, RuiRecent research has suggested a number of applications for gold in fuel cells and related hydrogen fuel processing, which include coatings for light weight corrosion resistance bipolar plates and the incorporation of gold as catalyst to provide improvements in electrode conductivity, among others. This paper reports on the electroless deposition of gold on copper substrates from a HAuCl4.3H2O solution in 1-butyl-1-methylpyrrolidinium dicyanamide (BMP-DCA), in normal atmospheric conditions. The electrochemical behaviour of the plating solution was studied by potential sweep techniques. Results indicate that gold ions are deposited on copper without the aid of external polarization. The deposition process probably involves a displacement reaction involving copper dissolution, since no other oxidation reaction was identified. Preliminary studies using SEM/EDX showed that gold thin films, deposited on copper substrates at 333 K, present a granular nanostructured morphology, typical of electrodeposited films from DCA containing ionic liquids.