Miroslav Gojo,a* Velizar D. Stankovićb and Sanja Mahović Poljačeka
aFaculty of Graphic Arts, University of Zagreb, HR 10000 Zagreb, Getaldićeva 2
Croatia,
E-mail: miroslav.gojo@grf.hr; sanja.mahovic@grf.hr
bTechnical Faculty Bor, University of Belgrade, VJ 12, Yu 19210 Bor, Serbia,
E-mail: vstankovic@tf.bor.ac.yu
* Corresponding author: E-mail: miroslav.gojo@grf.hr
In memoriam to professor Nada Ciković (1939–2005)
Abstract
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 from a
mono-crystal silicon wafer, coated with a
thin film of gold, deposited by a vapor deposition process (VDP), serving as a
substrate for the electrochemical deposition
of gold.
Limiting current density is achieved neither in citrate nor in thallium free
electrolyte. The rotation speed significantly influences
the process rate only at lower temperatures. At elevated temperatures gold
deposition occurs in a kinetic domain.
Tafel slopes confirmed that the electrochemical reaction occurs in two steps,
depending on both the electrode potential
and the presence of thallium ions in the electrolyte. The reaction kinetics
changes in the presence of thallium ions as
well. The mechanism of gold deposition is predominantly dependent on the
electrolyte composition. In the citrate, thallium
free solution, the adsorption of
Au(CN)– and CN– on the electrode surface is
presumed, resulting in the formation
of AuCNad species, which are afterwards being reduced to the metallic gold.
Thallium presence in the citrate solution
leads to the adsorption of Tl+ ion on the surface at a potential of –750 mV/SCE,
including it’s catalytic effect as an adatom.
AES and SEM analyses did not detect thallium presence in the deposited gold
layer. It was found that the presence
of thallium in the citrate solution shifts the deposition potential towards more
positive values.
Keywords: AES and SEM analysis, citrate solution, cyclic voltammetry, electrodeposition of gold, thallium ions