Investigation of the Anodically Formed Passive Film on Iron by Secondary Ion Mass Spectroscopy

Abstract

This paper reports SIMS analysis of passive layers. Pure Fe disks are used in borate buffers of pH = 8.4. Preelectrolysis is carried out to remove trace impurities. Potential step control of the electrode is utilized. Two types of experiments are carried out. In one, passive layers are prepared and then exposed to chloride ions ~br various times. In the other, films are heated at various temperatures for preselected times. The passive layers subjected to these treatments are exposed to SIMS analysis. The distribution of OH-with depth, from SIMS analysis, shows an exponential-like decrease away from the electrode/solution interface for passive films exposed to 0.5M buffered chloride solutions for various times or heated at a given temperature for a predetermined period of time. The OH-peak heights at a fixed depth in passive layers decrease in a similar manner with increasing exposure time to chloride ions or with increasing annealing temperature for a given time period. C1-peak heights for films exposed to chloride ion-containing borate solutions increase rapidly for times up until breakdown, decrease sharply after breakdown, and then level off at times much longer than breakdown. O-peak heights decrease exponentially with depth for samples exposed to chloride ions and decrease linearly for specimens annealed at various temperatures for a number of different times. Corresponding Fe § peak height data display a linear decrease with depth for chloride-treated films and an almost constant value for layers subjected to thermal treatments. Positive SIMS O § peak heights increase sharply for thermally treated films over a surface region of approximately 7•, remain constant in the bulk regions, and decrease rapidly in the film]metal interfacial regions. Homogeneous films are indicated with a thickness of about 25~. Detailed mechanistic discussions of the two principal models of passivity show that the results are in greater agreement with the amorphous hydrated polymeric oxide model than with the crystalline oxide model, in which water is considered only in terms of adsorbed water on the surface of the passive film.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.122.253.228 Downloaded on 2014-10-19 to IP

Quantitative SIMS Analysis of Hydroxyl Ion Content in Thin Oxide Films

“…The results of this investigation have shown that SIMS is a very sensitive method for the direct determination of hydroxyl in thin oxide films on metals and alloys, provided that special attention is paid to the calibration of the technique. Contrary to earlier results (3,4,11), which were obtained without the benefit of the standardization procedures employed herein, this work shows that essentially no hydroxyl is present within the passive films formed on iron and nickel, while passive films on Fe-25% Cr contain only -1% averaged through the film.…”

A Photocurrent Spectroscopic Investigation of Passive Films on Ferritic Stainless Steels

“…It must be considered that the dehydration process can occur together with a partial crystallization of freshly formed amorphous films. The formation of amorphous films on alloys as well as on the main constituents of the alloys (Fe and Cr) has been reported in the literature (32)(33)(34)(35)(36)(37)(38)(39)(40)(41). On this basis it can be concluded that photoeffects are not revealed until the dehydration process (eventually accompanied by a partial crystallization) is well developed on the electrode surface.…”

Hydrogen Permeation Through the Passivation Film on Iron by Time‐Lag Method

“…1 On leave from: Corrosion Research Center, University of Minnesota, Minneapolis, Minnesota 55455. side of the specimen and to ionize any hydrogen coming through the exit surface. Before passivation, the exit side of the membrane specimen was cathodically reduced at -556 mVsnE for 20 min to remove the air-formed film (11) and then the potential was raised in steps to a desired value to form the passivating oxide film. The thickness of the oxide film was measured by ellipsometry (12).…”