M.A. Ameer

Kinetic studies of dissolution behaviour of bismuth and anodic oxide films in sulphuric acid

Abstract Preliminary investigations of the open circuit behaviour of bismuth by the impedance measurement technique indicates the dependence of the oxide growth and dissolution. processes on the medium. Slow oxide formation was observed in NaOH and at a higher rate in Na2SO4 in contrast to H2SO4 in which the dissolution process was observed to increase with increase of acid concentration. The oxide dissolves according to a zero order mechanism, which in practice produces a constant rate of change of reciprocal series capacitance with time. Results indicate that the anodically formed oxide film may be represented by a two layer model. The rates of dissolution of both layers increase with increase of formation voltage. The outer layer is more defective, partly due to contamination by anions during anodisation. Change in acid concentration affects the dissolution of both layers. Increase in temperature enhances the dissolution of both layers to the extent of apparently dissolving the anodicfilm completely at...

Cyclic Voltammetric Studies on Selected Tin-Silver Binary Alloys in Sodium Hydroxide Solution

Abstract The electrochemical corrosion and passivation behavior of four selected tin-silver alloys, xSn-Ag (x = 26, 50, 70, and 96.5 wt%) (II through V), in addition to their pure metallic components, Ag(I) and Sn(VI), were investigated in aqueous sodium hydroxide (NaOH) solution. The techniques used are linear sweep cyclic voltammetry and electrochemical impedance spectroscopy (EIS). In general, for all studied samples, the cyclic voltammograms show that increasing the scan rate shifts the passivation peak potential (Ep,a) positively and the reduction peak potential (Ep,c) negatively with a concomitant increase in both the passivation peak current density (ip,a) and the reduction peak current density (ip,c). EIS results investigate that the total resistance (RT) and the relative thickness (1/C) of the passive layers on the six tested electrodes are both found to increase with time of immersion, being more pronounced for sample II. Although this silver-rich alloy (74 wt%) has the most protectiveness among...

Dissolution of Oxalic Acid on Passive Bismuth

Abstract The action of oxalic acid on anodic films on bismuth was studied by impedance measurements. The dissolution of the acid on the anodic film is higher for films formed in concentrated sulpha...