Influence of Prepolarization on the Electrochemical Behavior of Iron-Carbon Alloys

Abstract

The influence of anodic and cathodic prepolarization of electrodes, containing respectively 0.03, 0.48, and 1.3 percent carbon, in de-aerated N and 0.1 N sulfuric acid at 25 C (77 F) on the subsequent open circuit potential-time curves has been determined. Anodic pretreatment always lowers and cathodic pretreatment raises the initial potential on these curves. Magnitude of the potential shift and time required to resume the rest potential are larger the higher the prepolarizing time. The influence of carbon content and acid concentration is complex. Special experiments have indicated the importance of specimen, and especially solution history, and have permitted an interpretation in terms of polarization diagrams. The most likely explanation is the influence of sulfide or noble metal or metalloid ions derived from the alloy or possibly the solution in altering the number of active anodic sites. This is achieved by an increase in the degree of hydrogen poisoning or by accumulation or plating out of metals or metalloids.