Charakterisierung der Prepassiv- und Passivschicht auf Eisen durch XPS,AES und Reflexionsspektroskopie

Characterization of the Prepassive and Passive Layer on Iron by XPS, AES and Reflectance Spectroscopy The prepassive and passive layers of iron, preferably produced in borate and carbonate/bicarbonate buffers of pH 8.4, cathodically and anodically of the Flade potential, were investigated by XPS, AES and reflexion spectroscopy. The XPS measurements revealed: The prepassive layer is thinner than the passive one. Both layers can be differentiated by the relative height of the XPS signals of oxygen at 530 and 531 eV which points to a higher fraction of OH groups in the surface layer of the passive region. Sputtering decreased the differences in the XP spectrum, i.e. the hydroxidic layer is localized at the electrolyte side. In the case of borate buffer the passive layer contains boron. In carbonate/bicarbonate buffer no iron carbonate layer is formed but also an oxidic/hydroxidic layer. Prepassive and passive layers show characteristic differences in reflection spectrum and aging behaviour.