Electrodeposition of Nb, Ta, Zr and Cu from Ionic Liquid for Nanocomposites Preparation

MAIS, LAURA

2015-03-26

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Abstract

Multilayer metal materials with nanometric scale are important in modern engineering applications. Composite materials based on metals with different characteristics give rise to new materials with unique properties. Among the others, nanostructured composites constituted by immiscible metals can present interfaces able to control defects produced by high doses of radiation, stress and temperature: their properties can be exploited in nuclear power reactor. Immiscible systems constituted by Cu/Nb or Cu/Ta multilayers exhibit higher thermal stability and improved mechanical properties with respect to bulk Nb, bulk Ta and bulk Cu. Refractory metals present high melting point, high hardness and high resistance against strong acids and bases. The electrodeposition of these metals presents several limitations: the most important is the very negative deposition potential that makes difficult the deposition of metals such as niobium, tantalum and zirconium. Since both oxygen reduction and hydrogen evolution from water splitting occur at potential values much less cathodic than the metals reduction, at the low potential requested to obtain niobium, tantalum and zirconium in metal form it is necessary the use of electrolytes free of water and oxygen and characterized by high stability in large potential windows. To overcome this limitation, the electrodeposition from molten salts or ionic liquids as solvents have been proposed. In the present project the electrochemical coating of niobium, tantalum zirconium and copper has been investigated in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide([BMP][TFSA]) on both boron doped diamond (BDD) and metal substrates in order to determine the reduction path for both single metal and nanometric composites electrodeposition. Electrochemical experiments have been performed at different temperatures in a glove box, under nitrogen atmosphere. Galvanostatic runs and cyclic voltammograms performed at different scan rates and different potential windows have been carried out in order to determine the behaviour of the systems employed. Potentiostatic experiments were performed at the potential values corresponding to the voltammetric peaks and the samples obtained were analysed by SEM-EDX analyses. Regarding the electrodeposition of refractory metals nanometric crystallites have been obtained at 125 °C. Cu/Nb and Cu/Ta composites have been prepared by a dual bath deposition technique; the deposits were constituted by fine crystallites with average sizes in the range 50-100 nm. The elemental maps indicate a different distribution of Cu/Nb and Cu/Ta in the composites obtained with the different substrates.