Codeposition of Copper and Tin

To understand the peculiarities of voltammograms, some regularities regarding the partial processes of Cu(II) and Sn(II) reduction are expedient to invoke. As noted earlier, most polyethers do not show a noticeable inhibition activity on copper substrate in the absence of halides. Such behavior is ako characteristic of other surfactants in mixed Cu(II) and Sn(II) solutions. However, when the Sn Sn equilibrium potential is approached, the specific voltammetric minimum develops. The effect of surfactants becomes detectable at rather low concentrations (some mgdm ). Its depth depends both on their molecular mass and concentration and on the intensity of forced convection. This minimum deepens and the effect of forced convection weakens when the molecular mass of surfactant grows. 

It was established that the formation of free tin phase followed by strong inhibitive adsorption is possible in this region. It is reasonable that this feature is absent in Sn(II)-free solutions. The minimum under discussion develops gradually on addition of small amounts of Sn(II), and its depth may be used as a measure of Sn(II) concentration in the presence of Sn(IV) [105]. Besides, anodic currents of Sn dissolution are observed in cyclic voltammograms at —0.24 V, when the reverse potential scan is applied (see below). An increase in current density arising at higher cathodic polarizations E -0.4 V) is concomitant with hydrogen evolution. 

We have seen from the aforementioned details that hahdes show quite opposite effects on copper and tin electrodes. According to the impedance data [88], the adsorption properties of the yellow bronze appear much closer to those of copper if compared with tin. Halides in rather low (micromolar) concentrations have a perceptible effect on the codeposition process as well [78, 82]. Chlorides that 

It should be emphasized that the first inhibition region is well pronounced under forced convection conditions and is easily reproduced when the record of voltammograms is performed with tight control of rotating and scan parameters. 

Attempts to interrupt the direct (cathodic) scan of the potential in the region of the first minimum and to fix it at -0.15 V causes rather fast (taking some seconds) rise of cathodic current from minimum value up to ij cu Such is not the case of the second characteristic minimum located at —0.24V where the cathodic 

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Survila, A., Mockus, Z. and Juskenas, R. (1998) Current oscillations observed during codeposition of copper and tin from sulfate solutions containing Laprol 2402C. Electrochim. Acta, 43, 909-917. 

It follows from the aforementioned discussion that polyethers play a peculiar role in codeposition of copper and tin. If halides are absent in the solution, surface complexes containing polyethers are not formed on copper and/or yellow bronze surface and the formation of bronze coatings is not accompanied by noticeable adsorption of surfactants. However, if a germ of pure tin phase is formed for some reason, its growth is immediately suppressed by significant inhibitive adsorption of polyether. 

Survila, A. and Zukauskaite, A. (1995) Codeposition of copper and tin by electrolysis of the solutions containing citrate complexes. Elektrokhimiya, 31 (11), 1254-1260. 

Jasulaitiene, V., and Juskenas, R. (2009) Codeposition of copper and tin from acid sulphate solutions containing polyether sintanol DS-10 and benzalde-hyde. /. Appl. Electrochem., 39 (10), 2021-2026. 

Kanapeckaite, S., Mockus, Z., and Jasulaitiene, V. (2010) Codeposition of copper and tin from acidic sulphate solutions containing polyethylene glycols. Effect of length of the hydrocarbon chain. J. Solid State Electrochem., 14 (4), 507-514. 

Figure 9.35 Effect of PEG-6000 on voltammograms of copper and tin codeposition. The concentrations of PEG (in mgdm" ) are given at the respective curves. Cu-coated RDE, 1250rpm.

Alloys of Cu, Sb, Pb, and Sn. This procedure for analysis of bearing metals relies on two successive depositions of pairs of metals. Each (mixed) deposit is dissolved, and then one of the components is selectively deposited (and determined) under different conditions and the other component determined by the difference. First, copper and antimony are codeposited from HCl, with hydrazine as a depolarizer. The (weighed) deposit is dissolved in nitric/ hydrofluoric acid, which retains antimony in solution as a fluoride complex, allowing deposition of pure copper (at —0.40 V). Tin and lead are codeposited (at —0.70 V) from the initial residual solution. After redissolution of the (weighed) deposit in nitric/hydrofluoric acids, lead is deposited ano-dically as PbOi- The Pb and Sn aspect of this procedure is useful for analysis of solders. An analogous procedure allows Ni and Co separation (via C02O3). 

It could be supposed that the first stages of Cu and Sn codeposition occurring at E < involve the underpotential deposition of tin on foreign (copper) lattice. In... 

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