Estudo da eletrodeposição de cobre-indio sobre platina em meio de cloreto de colina e de etilenoglicol

Abstract

The electrodeposition of CuIn alloys on platinum was investigated using 2 individual solutions, a 0.050 mol L−1 of CuCl2.2H2O (Sol. 1) and a 0.050 mol L−1 of InCl3 (Sol. 2), 5 more solutions containing the two salts, varying their concentrations in 0.050 mol L−1 of CuCl2.2H2O + 0.050 mol L−1 of InCl3 (Sol. 3), 0.075 mol L−1 of CuCl2.2H2O + 0.050 mol L−1 of InCl3 (Sol. 4), 0.100 mol L−1 of CuCl2.2H2O + 0.050 mol L−1 of InCl3 (Sol. 5), 0.050 mol L−1 of CuCl2.2H2O + 0.075 mol L−1 of InCl3 (Sol. 6) and 0.050 mol L−1 of CuCl2.2H2O + 0.100 mol L−1 of InCl3 (Sol. 7), dissolved in eutectic solvent (DES) in a 1: 2 molar ratio of choline chloride (ChCl) and ethylene glycol (EG). The experiments with cyclic voltammetry showed three peak reduction potentials (Epc), the first two referring to Cu2+/Cu+ (Epc ≅ 0.95 V) and Cu+/Cu(s) (Epc ≅ −0.45 V) and the third to In3+/In(s), the latter, ranging from Epc ≅ −0.95 V at 296.5 K to Epc ≅ −0.75 V at 353 K, obtaining an approximate variation of 0.200 mV, moving to values of potential less negatives. The values of the diffusion coefficients of the Cu2+ and In3+ ions were calculated by the Cottrell model using Sol. 1 and Sol. 2, respectively, obtaining the values of 1.19 ± 0.05 × 107 /cm2 s−1 at 296.5 K and 10,03 ± 0,33 × 107 /cm2 s−1 at 353 K, for the Cu2+ ion and 0.77 ± 0.01 × 107 /cm2 s−1 at 296.5 K and 7.66 ± 0.07 × 107 /cm2 s−1 at 353 K, for the In3+ ion. For the other solutions, the values of the apparent diffusion coefficients were estimated. The values of the diffusion coefficients and the dynamic viscosities of Sol. 1 and Sol. 2 were adjusted by an equation similar to Arrhenius, where, the apparent activation energies calculated were 32.52 kJ mol−1 for the species of Cu2+ (Sol. 1) and 35.10 kJ mol−1 for the species of In3+ (Sol. 2). Scanning electron microscopy (SEM) analyzes for CuIn deposits from Sol. 3 showed a uniform distribution of deposits, however with the increase in temperature it is possible to observe the formation of clusters with an increase in grain size and the appearance of a new layer with greater porosity. The deposits made from the solutions with higher Cu2+ ions contents presented a compact and circular morphology while the deposits made from the solutions with higher contents of In3+ ions presented a morphology of plate clusters. The X-ray diffraction analysis (XRD) showed three distinct crystalline phases: a first phase referring to the platinum substrate, a second phase referring to the CuIn alloy and a last phase referring to the Cu2In alloy. It is also possible to notice an increase in the intensity of the peaks related to the CuIn phases with temperature.