Abstract
Natural additive agents such as glue and gelatin have been used for preventing impurities from precipitating during deposition and for surface leveling of deposited films in the electrowinning industry. The mechanism behind the effect of their agents on electrochemical deposition is not yet well understood.
We studied the effect of various additives on electrodeposition process in a zinc sulfate electrolytic bath.
We used polyethylene glycol (PEG M W 20000, 6000, 2000), polyacrylic acid (PAA M W 240000, 5000, 2000) and polyvinyl pyrrolidon (PVP M. W 360000, 40000, 10000), and their monomers as synthetic additives. We also used another eight types of additives including glycin, alanin, and proline as amino acid additives. Mass changes of deposits were monitored by quartz crystal microbalance (QCM) method. The surface morphology of zinc films was observed by FE-SEM.
Results are as follows:
1) Zinc deposition was inhibited in the presence of gelatin and polymer additives.
2) Amino acid and monomer additives did not inhibit the deposition. Corresponding surface morphology was similar to that in the absence of additives.
3) The inhibition effect of PAA was the highest of all tested additives.
4) Characteristic mass change was detected during the deposition in the presence of PEG, PAA and PVP.
5) From mass change measurements, inhibition by additives could be classified into four different modes
(A) The inhibition effect increases with deposition time. (PEG)
(B) The inhibition effect decreases with deposition time. (PAA)
(C) The inhibition effect was constant during deposition. (Gelatin)
(D) No inhibition. (Amino acid, Monomer)
