Tin plating in acid Sn(II) gluconate solutions containing excess of sulphate

摘要

Voltammetry, electrochemical impedance spectroscopy, SEM and XRD techniques were applied to study tin plating in acid 0.01M Sn(II) solutions containing different amounts (0.02-0.1M) of gluconate and 0.5M Na_2SO_4. Solution pH is the main factor that governs the rate of Sn(II) reduction. An increase in pH from 2 to 5 results in a 100-fold growth in electrode impedance and a four-fold reduction in limiting current density. Spongy tin deposits are obtained in the ligand insufficient solutions at low cathodic polarisations ΔE. To obtain compact fine grained tin coatings, ΔE and/or the gluconate concentration should be correspondingly increased. Sn(II) reduction proceeds under conditions of strong inhibition involving destructive ligand chemisorption and incorporation of its fragments into deposits.