Passivation Of Tin Research Articles

Anodic behaviour and passivation of tin in alkaline—stannate plating solutions

AbstractThe electrochemical behaviour of tin was studied in sodium hydroxide solutions as well as in alkaline—stannate plating solutions using potential—time and current—time measurements. Cyclic cathodic and anodic polarisation, as well as anodic decay curves were traced. Results indicate that the galvanostatic potential—time curves consisted of three main parts: an initial linear instantaneous rise of potential caused by the charging of the double layer, an intermediate rise caused by stannous and stannic hydroxides and oxides formation at their respective thermodynamic potentials, and a final steady potential associated with oxygen evolution.Current‐time measurements show that tin could be passivated in all solutions used and at different current densities. In all cases oxygen evolution was noticed at the end of passivation. Free surface area of tin electrode in various solutions used was calculated using the Müller formula. The porosity of the surface film was found to depend on the composition of the solution.

On the anodic passivity of tin in alkaline solutions

Abstract The anodic oxidation of tin was studied galvanostatically in NaOH solutions of different concentrations. Primary passivity is attained in all solutions when the metal is covered with a film of Sn(OH) 2 or SnO. Permanent passivity sets in when Sn(OH) 4 forms as a continuous layer on the electrode surface. In concentrated alkali solutions larger quantities of electricity are charged to the electrode to compensate for the chemical dissolution of the hydroxides. As a result of the competition between the anodic formation and chemical dissolution of Sn(OH) 4 , the potential of the tin electrode oscillates between the Sn/Sn(OH) 2 and Sn(OH) 2 /Sn(OH) 4 , values. For any one solution the oscillation phenomenon depends primarily upon the polarizing current. Permanent passivity is governed by the relation ( i - i 0 )τ n = const. where i 0 is the current below which no passivation takes place, τ the time elapsed till oxygen evolution and n is a constant. Interruption of the polarizing current when the electrode is at oxygen-evolution potential gives rise to a pH-independent arrest at potentials more positive than any of the known redox values for tin. This arrest is ascribed to the chemical dissolution of metastannic acid formed at oxygen-evolution potentials. The anodic behaviour of the tin electrode in solutions containing stannite and stannate is similar to that in solutions devoid of these ions. An increase in the tin content of the solution is equivalent to the elevation of the polarizing current; passivity sets in more readily in the concentrated solutions.

Anodic Behavior and Passivation of Tin In Solutions Containing Phosphoric Acid

Abstract A study has been made of the anodic behavior and passivation of tin in phosphoric acid solutions. Effects on passivation when the solution additionally contains nitric acid or potassium ni...