COMPOSITION OF ANODICALLY FORMED IRON-OXIDE FILMS

The results obtained showed that iron which is passivated in an iron-free borate buffer solution forms a substantially anhydrous “Fe3O4-γFe2O3” film. The presence of iron as ferrous ion in the solution leads to the additional formation of a mixed hydrated iron boron oxygen compound which is amorphous. The ferrous ion may be present due to the use of impure solutions or passivation in a stepwise process or with a potentiostat with a long rise time. Hydrated ferric oxides are not dehydrated by either vacuum treatment or by the electron bombardment used during measurements. Small amounts of water or hydrates may be present in or on the films due to adsorption from the solution. However, this water probably does not play a major role in the protectiveness of the film. Of more importance are the relative amounts and distribution of the anhydrous and deposited hydrated oxides. © 1979, The Electrochemical Society, Inc. All rights reserved.