Characterization of Native Oxide and Passive Film on Iron and Iron-Chromium Alloy

by Jingxing Feng

Institution: University of Cincinnati
Department: Engineering and Applied Science: Chemical Engineering
Degree: MS
Year: 2014
Keywords: Chemical Engineering
Record ID: 2024991
Full text PDF: http://rave.ohiolink.edu/etdc/view?acc_num=ucin1406811146


Passivation refers to the spontaneous formation of a thin protective oxide on a metal. Passive films determine the corrosion resistance of metals. Through systematic study of both iron and iron-chromium alloy thin films with reflectometry and electrochemistry, the structure and composition of native oxide and electrochemically passivated films are resolved. Analysis of polarized neutron reflectometry of pure iron thin films shows that native oxide is uniform, non-ferromagnetic, dense magnetite with a thickness of 33.7 ± 2.0 Å. Conditions for electrochemical passivation are explored including the passivation potential, passivation kinetics, and effect of solution pH. The optimized conditions to prepare smooth, dense passive oxide are found to be 800 mV vs. SCE, 15 minutes of passivation time in pH = 7 sodium sulfate solution.