Fjf. Miranda et al., ELECTRODEPOSITION OF ZN-NI ALLOYS IN SULFATE ELECTROLYTES .1. EXPERIMENTAL APPROACH, Journal of the Electrochemical Society, 144(10), 1997, pp. 3441-3449
The mechanism of Zn-Ni alloy deposition in acidic sulfate electrolytes
is analyzed essentially from polarization curves and impedance plots,
using a rotating disk electrode. The anomalous deposition of the zinc
-rich phases gamma and delta occurs at high cathodic polarizations, ni
ckel deposition being inhibited and zinc deposition being stimulated.
At low polarizations, nickel-rich deposits are formed, on which the di
ffusion-controlled hydrogen evolution predominates, at pH 1.5. The tra
nsition is shown to be related with both an increase in the interfacia
l pH and the presence of sulfur in the deposit. Impedance data reveal
the reversibility of the charge-transfer reactions involved in hydroge
n evolution and in anomalous deposition. They also show the existence
of four relaxation processes: one inductive process due to zinc deposi
tion, and three capacitive processes associated to nickel deposition a
nd hydrogen evolution on a nickel-rich surface. They also reflect the
anion adsorption.