EIS analysis on the Effect of Sodium Dichromate on Corrosion Behavior of Platinum Anodes in Sodium Perchlorate production Cell

Sodium perchlorate is produced electrochemically using Pt/Nb anode due to their high service life and high oxygen evolution overpotential. Sodium chlorate, sodium chloride and sodium dichromate are the main components of the electrochemical cell for perchlorate production. In this research the effect of sodium dichromate concentration has been investigated on corrosion behavior of Pt/Nb anode. Platinum was electroplated on niobium substrate. The obtained samples were then exposed to accelerated life test in perchlorate production cell with 0, 1 and 3 gr/lit sodium dichromate for 3, 10, 40 and 70 hour at constant current density of 5.9 A/cm2. Cyclic voltammetry and electrochemical impedance spectroscopy tests was done on the samples at each time extension. The samples finally were characterized using SEM. The result showed that passivation of niobium substrate which tends Nb2O5 to form on it, is the main mechanism by which the sample is deactivated. In addition presence of sodium dichromate has a significant effect on corrosion of the anode, although it is known as a cathodic inhibitor. Finally it was observed that 3 gr/lit is the optimum concentration for sodium dichromate in which the anode has the highest corrosion resistance in sodium perchlorate production cell.