Electrodeposition of Silver in Cyanide-Free Solution Containing Pyrimidine Derivative as a Complexing Agent

Pyrimidine derivatives, for example, 2,4-pyrimidinedione (uracil), 1-methyluracil and 5-methyluracil (thymine) can bind with metal ions in alkaline solution. 5-methyluracil (thymine) as complexing agent in electroplating solution has not been investigated due to low solubility in water. The aims of this study were to determine the potential of 5-methyluracil (thymine) as complexing agent for cyanide-free silver electroplating solution. The influence of complexing agent and polyethyleneimine on the silver electrodeposition reaction were studied. Several methods which are electrochemical quartz crystal microbalance (EQCM) and electrochemical impedance spectroscopy (EIS) have been used to study the electrochemical behavior of cyanide-free silver electroplating solution. The surface morphology and brightness of silver deposits obtained from each cyanide-free silver electroplating solution were evaluated. A semi-bright deposit was obtained from thymine and uracil-complexing silver solution while matte deposit from 5,5-dimethylhydantoin-complexing silver solution. A bright silver deposit could be obtained in the presence of polyethyleneimine. The reduction current value decreases as the amount of polyethyleneimine added increases due to inhibition effect on the silver electrodeposition reaction. The results of electrochemical quartz crystal microbalance measurement showed that the addition of polyethyleneimine in thymine-complexing silver solution does not significantly affect the resonance frequency change.