Electron Diffraction Studies of Active, Passive, and Transpassive Oxide Films Formed on Iron

Abstract

Iron foil specimens were anodically polarized by means of a potentiostat in , , and a sodium borate‐boric acid solution (pH, 8.5). Both passive, active, and transpassive regions of the polarization curve were studied for each solution. The oxide films were examined while still in contact with the iron foil by selected area transmission electron diffraction. Five iron planes were studied: {100}, {110}, {111}, {210}, and {211}, and the epitaxial relationship of the oxide to the iron substrate determined. Evidence was found indicating that in all of the electrolytes used the passive film contained , while the nonpassive films did not.