Long term atmospheric oxidation of high purity iron.

High purity iron, cast and rolled more than 20 years ago, has largely maintained its bright surface finish over this period of time. The thickness of the passivating oxide film, measured by Auger electron spectroscopy and depth profiling, ranges from 70 to 100 angstroms, which is about 4 to 5 times the thickness of the film formed after only 24 hours oxidation. Short term (24 hr) oxide film thickness data from gaseous and anodic oxidation studies in the literature extrapolated to 20 years show good agreement with the long term results. These processes are of concern in optical fiber cables, in which hydrogen can significantly degrade transmission.