Electrodeposition of metals, alloys and composite materials from acetamide-dimethyl sulfone eutectic melts

The aim of this PhD thesis is the study of a new eutectic melts based on acetamide and dimethyl sulfone for the electrodeposition of metals, alloys and composites. Mixtures of acetamide and dimethylsulfone (DMSO2) with dissolved anhydrous transition metal chlorides are introduced as new non-aqueous electrolytes for the preparation of luminescent composite metal coatings. Red-emitting (Eu2O3 and Y2O3:Eu3+), yellow-emitting (Y3Al5O12:Ce3+), green-emitting (Gd2O2S:Tb3+) and blue-emitting (BaMg2Al16O27:Eu2+) rare-earth phosphor particles and yttrium oxide particles have been embedded into nickel and cobalt coatings. The metal coatings with the rare-earth phosphor particles have a metallic luster, but show at the same time photoluminescence upon irradiation with UV light. The spectroscopic and photophysical properties of the rare-earth phosphors are not modified by embedding them in the metallic host matrix. Different electrodeposition parameters were optimized in order to obtain well-adherent coatings with a uniform particle distribution. By preparing mixtures of the Y2O3:Eu3+ and Gd2O2S:Tb3+ phosphors, the emission color could be varied from red over orange and yellow to green, depending on the mixing ratios. Embedding mixtures of yellow and blue phosphors in the metal layer made it possible to produce coatings with white photoemission.Acetamide-dimethyl sulfone eutectic melts containing metal chlorides were used as non-aqueous electrolytes for the codeposition of oxide particles (ceria, silica and alumina) with nickel, cobalt, nickel-cobalt and zinc-nickel alloys. For all types of particles, very high particle incorporation was observed. Scanning electron microscopy and energy dispersive X-ray analysis showed that the particles are uniformly distributed inside the coating. The influence of current density, stirring speed and particle concentration on particle incorporation was examined for nickel-ceria coatings. X-ray diffraction patterns of ceria particles and nickel-ceria or cobalt-ceria composites indicated that the particles in the coatings remained unchanged. Agglomerate-free, homogeneously well dispersed silica composites were obtained from surfactant-free melt with suspended unmodified hydrophilic silica particles. Alloy codeposition of nickel-cobalt-ceria and zinc-nickel-ceria was also demonstrated from acetamide-dimethyl sulfone eutectic melts containing dissolved metal chlorides.Gauze-supported skeletal nickel catalysts were successfully prepared by electrodeposition of nickel-zinc alloys on copper gauzes from an acetamide-DMSO2-ZnCl2-NiCl2 quaternary melt, followed by chemical and electrochemical leaching of zinc from the deposited alloys. The nickel content of the alloys was varied with deposition potential and deposition temperature during the electrolysis. The nickel content in the alloys increases from 17 wt.% to 89 wt.% when the temperature was increased from 70 °C to 150 °C. The surface morphology and BET surface area of the activated zinc-nickel alloy varied markedly for the chemical and electrochemically leached alloys. The activity and selectivity of the structured Raney nickel catalysts surpass those of commercially available porous nickel in the hydrogenation of acetophenone. Characterization by XRD and SEM revealed that the electrodeposited zinc-nickel alloys have very fine grain size, combined with excellent adhesion to the supporting gauze.Zinc-cobalt precursor alloys were electrodeposited from an acetamide-DMSO2-ZnCl2-CoCl2 quaternary electrolyte for the preparation of gauze-supported skeletal cobalt. Alloys with various compositions were obtained by changing the experimental parameters. In comparison to the aqueous plating bath, non-anomalous zinc-cobalt alloy deposition was found in this melt. The deposited zinc-cobalt alloys were used for the preparation of Raney cobalt after the preferential dissolution of zinc either chemically and/or electrochemically. The chemical leaching of the zinc-cobalt alloys was carried out in concentrated or diluted sodium hydroxide solutions, whereas the electrochemical leaching of the alloys was carried out in the same electrolyte as used for the electrodeposition. The activated alloy was used as a catalyst for hydrogenation of acetophenone. The activity of the catalyst prepared by the dealloying method was higher than that of the commercially available chromium-promoted Raney cobalt catalyst. The catalytic activities of chemically and electrochemically leached alloy were 0.47 h-1 and 0.95 h-1, respectively, whereas the activity of commercial catalyst was only 0.37 h-1. The surface area of electrochemically leached sample was higher than the one of the chemically leached and the commercial sample. From this study, it was found that the activities and surface morphologies of the catalysts depend on the initial composition of the alloys and on the leaching conditions.nrpages: 163status: publishe