The Corrosion Resistance of Fe-Cr Alloys as Studied by ESCA
The chemistry of passive films formed on Fe-Cr alloys in acid, oxygenated neutral water and dry oxygen for different times at room temperature has been studied by ESCA. The composition of the film is dependent on the environments. In acid at the passivation potentials 0.1, 0.5 and 0.9 V vs. SCE an homogeneous film with about 60 pct. Cr is formed. A stationary state is reached after a few minutes. In water the initial composition of the passive layer corresponds to that of the alloy but is changed by dissolution and by enrichment of Cr in the outermost layer during prolonged exposure. After a few tens of hours a stationary state is reached and the film.consists of a top layer of Cr(OH)3 with Fe-Cr oxides beneath. Exposure in dry oxygen gives an oxide with the same average composition as the metal and due to low diffusivity at room temperature the composition does not change with time.
KeywordsPassive Film Passive Layer Outermost Layer Oxygenate Water Neutral Water
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