Potential decay behavior of iron in dilute nitric acid

Potential-time decay curves were used to investigate the passivation of iron in dilute nitric acid solutions of different concentrations. The effect of sulfate ions on the decay curves was also examined. It was observed that the decay curves formed an almost flat potential segment ending after reaching the Flade potential (the potential at the end of the plateau). The duration of the plateau was a function of both the initial holding potential and the acid concentration. The addition of sulfate ions affected the decay duration without interfering with the Flade potential. This is worth noting in view of the well-known dependence of the open-circuit potential decay on both pH and on the constituents of the solution. Received: 26 February 1997 / Accepted: 14 May 1997