Anodic dissolution of metals in ionic liquids
thesisposted on 2016-11-21, 13:41 authored by Wrya Othman Karim
Anodic dissolution of 12 metals and alloys was carried out in ionic liquids, a deep eutectic solvent comprising of 1:2 molar ratio mixture of choline chloride, [(CH₃)₃NC₂H₄OH] Cl, (ChCl) and ethylene glycol (EG) and C₄mimCl using electrochemical techniques, such as anodic linear sweep, chronoamperometry and chronopotentiometry. To study the dissolution mechanism electrochemical impedance spectroscopy (EIS) was used, in addition, a wide range of spectroscopic, for instance, UV-Visible and X-ray photoelectron spectroscopy (XPS) and microscopic techniques, such as scanning electron microscopy (SEM), atomic force microscopy (AFM) and 3D Optical microscopy were used. The anodic dissolution of copper in Ethaline and C₄mimCl was studied. It is shown that the speciation of dissolved copper at the interface region are [CuCl₃]⁻ and [CuCl₄]²⁻ and the EG controls the structure of interface. A super-saturated solution forms at the electrode-solution interface and CuCl₂ was deposited on the metal surface. The impact of additives, such as water and CuCl₂.2H₂O on the copper dissolution in Ethaline were examined. The former affected the quality of electropolished copper and the latter decreased the dissolution rate. The second stage of the study involved the study of eight metals, Ag, Au, Co, Fe, Ni, Pb, Sn and Zn in Ethaline and C4mimCl at 20 °C and 70 °C. Film formation occurred on almost all metals surface. It was only when the film that formed led to a diffusion controlled dissolution rate that electropolishing occurred. This was the case with nickel and cobalt in Ethaline at 20C producing a mirror finished surface. In the final section the anodic dissolution of three alloys; Cu₀.₆₃Zn₀.₃₇, Cu₀.₉₄Sn₀.₀₆, and Cu₀.₅₅Ni₀.₄₅ was studied in Ethaline at 20 °C. The Cu₀.₉₄Sn₀.₀₆ and Cu₀.₅₅Ni₀.₄₅ showed electropolishing whereas Cu₀.₆₃Zn₀.₃₇ displayed dealloying. The redox potential difference and the elemental composition of the alloys controlled the dissolution mechanism. The electropolishing mechanism was shown to be consistent with the model developed in Chapter 4.