engleski

Electrochemical Deposition of Gold in Cotrate Solution Containing Thallium

Process of electrochemical deposition of gold from citrate solution, with and without thallium, has been studied using a rotating disc electrode (RDE) and linear sweep voltammetry. RDE was made of monocrystal silicon wafer, layered by a thin film of vaporized gold as a substrate. Obtained results shown that the limiting current density is not achieved in citrate and thallium free electrolyte. The rotation speed had significant influence on the process rate at lower temperatures. At elevated temperatures gold deposition occurred in a kinetic domain. Tafel slopes confirmed that the electrochemical reaction occurs in two steps depending on electrode potential and the presence of thallium ions in the electrolyte. The reaction kinetics is changed in the presence of thallium ions, as well. The mechanism of gold deposition is predominantly dependent on the electrolyte composition. In the citrate solution, free of thallium, the adsorption of Au(CN)- and CN- on the electrode surface is presumed, resulting in the formation of AuCNad species, which afterwards are reduced to the metallic gold. In the citrate solution containing thallium, an adsorption of Tl+ ion on the surface is presumed at the potential of -750 mV/SCE, including its catalytic effect as an adatom. The presence of thallium was not confirmed by AES and SEM analyses. Simultaneously, the presence of thallium in a citrate solution shifts the deposition potential to the positive values.

AES and SEM analysis; Citrate Solution; Cyclic Voltammetry; Electrodeposition of Gold; Thallium Ions

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