Abstract
Adsorption behavior of different polyethers (PE) on copper and tin was studied in combination with kinetic investigations. No pronounced effect of PE was detected in the Cu|Cu(II) system. In contrast, these substances show a high inhibition activity on the tin electrode. Halides enhance adsorption ability on copper electrode but suppress it on tin; this effect intensifies in the sequence: Cl− < Br− < I−. It is supposed that specifically adsorbed halides can act as species bridging the copper substrate with Cu(I)-polyether complexes, whereas the model of competitive adsorption is more suited for tin substrate. The inhibition degree of surfactants increases with the length of hydrocarbon chain. Underpotential deposition of Sn(II) is observed in the region of Cu(II) limiting current. The characteristic current minimum arises in the region where the free Sn phase becomes thermodynamically stable. Cl− ions broaden the range of current densities where yellow bronze can be obtained, but Br− ions show the opposite effect. Iodides retard the reduction of Cu(II) therefore tin prevails in the coatings. The deposits obtained present a mixture of pure copper, α-CuSn (fcc) phase and hcp phase of α-CuSn.
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