Abstract
The object of this study is to research the corrosion behavior of silver which is one of the components of lead alloy used in anode for cathodic protection.
The corrosion mechanism of silver was discussed by the analysis of Tafel's Equation, low potential region under constant current density, and current-potential curve determined by potentiostat.
The following results were obtained.
Silver was dissolved as Ag+ by the local anode reaction as shown in the following equation.
Ag_??_Ag++e
It was considered that the concentration of dissolved Ag+ in the solution was less than 10-6mol/l.
On the other hand, cathode reaction would be the reduction of dissolved oxygen.
Tafel's Equation was available only when the current density was below 4×10-3A/cm2. The results showed that the value of b in Tafel's Equation was 0.084V and exchange current density i0 was 1.6×10-7A/cm2 (assuming the standard potential value of Ag++e=Ag being -0.35V vs. spontaneous potential of silver in 0.5N sodium sulfate solution).
The value of α (transmission coefficient or symmetry factor) was 0.28 calculated by b of Tafel's Equation, which indicated that both barriers of potential energy of silver atom on electrode surface and that of Ag+ were not symmetrical.
