Abstract
It was shown by the Hull cell test that semi-bright tindeposits could be obtained from stannous sulfate bath in the presence of Pluronics (non-ionic surface active agents), and also the beneficial action of Pluronics was overshadowed by adding a small amount of halogen ions.
Polarization associated with electrodeposition of tin from the stannous sulfate bath (1M H2SO4, 0.43M SnSO4, Pluronics and/or halogen ions) was measured in order to make clear the mechanism of action of Pluronics and halogen ions added to the bath in the concentration ranges of 0.01-0.5% and 0.00003-0.3M respectively.
In the presence of Pluronics, at low current densities the polarization increased very little, then a sudden increase (300-400mV) occurred at a certain current density, and then it increased gradually until hydrogen was evolved.
The current density of the sudden increase point was examined as the function of the Pluronics concentration, the bath temperature and the ratio of the hydrophilic and hydrophobic portion of the pluronic molecule, presence of halogen ions rendered the sudden increase point to higher current densities. Such an activity of halogen ions were remarkable in the following order: I->Br->Cl->F-.
The result was tried to be explained by the fact that Pluronics tended to accumulate onto the metal-solution interface and adsorption of halogen ions on the interface was stronger than that of Pluronics and the adsorbed halogen ions made the electrode reaction more reversible.
