Electrochemistry of tin has been studied for several decades. Nevertheless, the effect of the electrolyte additives on the electrochemical reaction and on the deposited structure is still an open field of research. In order to deposit a homogeneous, compact tin coating from an acidic solution, organic molecules are needed to be added into the electrolyte. One of the first additives introduced for this purpose in the tin electroplating is β-naphthol. A more stable form of this additive could be alkoxylated β-naphthol (ABN, C12H12O2), where the hydroxyl group is replaced with the more stable alkoxy group. Influence of the ABN additive on tin plating has not been described in the literature yet.
Within this scientific work as part of an ongoing PhD thesis within the Marie Sklodowska-Curie ITN, SELECTA (G.A. No 642642) the influence of the ABN additive in the acidic electrolyte on the electrochemical reaction and deposited structure of tin has been studied. For this purpose chloride based and methane sulfonic acid (MSA) electrolytes have been prepared. Reaction kinetics were studied by polarization measurements using a rotating disc electrode and Tafel measurements on stationary electrodes. Surface morphology and preferred crystal orientation were studied and by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). The influences of the electrolyte composition, ABN and complexing agent concentrations as well as the electrolyte temperature effect have been investigated.
The results from the reaction kinetics showed for both chloride and MSA electrolyte inhibition effect of the ABN additive. In the case of chloride electrolyte the ABN additive works as a very effective blocker of the electrode active sites. Very small ABN concentrations are needed for the suppressing of the electron transfer on the electrode- electrolyte interface as well as for the suppressing of the cathodic current density and H2 evolution. In the case of the MSA electrolyte, depending on the citrate concentration in the electrolyte, the ABN inhibition effect can be overlaid with the tin-citrate complexes.
The plating system was enlarged by adding iron as an alloying element. Influence of the electrolyte composition and plating parameters on the resulting coating composition have been investigated.