Relation of the photocurrents to the corrosion rates of pure aluminum having various oxides

• Published in: Passivation of Metals and Semiconductors, and Properties of Thin Oxide Layers pp. 331 - 336
• Main Authors: Romanes, Maia C., Donovan, Kathleen A., David Burleigh, T.
• Format: Book Chapter
• Language: English
• Published: Elsevier B.V 2006
• ISBN: 0444522247; 9780444522245
• DOI: 10.1016/B978-044452224-5/50053-6

This chapter presents a study in which photoelectrochemistry (PEC) was used to characterize various oxide films on aluminum. The advantage of PEC is that it is a non-destructive, in-situ method that can provide information on semiconductor properties of aluminum oxide-hydroxide films. The secondary objective was to use photoelectrochemistry to understand how the oxides' defect density controls the corrosion resistance. This study investigated two different oxides, "thermal" and "plasma," grown on the surface of pure aluminum. The oxide samples were prepared by first sputter-depositing pure aluminum on an oxidized silicon wafer and then, the nascent aluminum was next exposed either to pure oxygen at room temperature (the thermal oxide) or exposed to oxygen in an RF plasma (the plasma oxide). The study found significant difference in corrosion resistance between plasma and thermal-grown oxides and the polarization resistance (Rp) was inversely related to the magnitude of the photocurrent. Fowler and Platband plots indicated two sources of photocurrents, a low energy (-2.4 eV) source and a high energy (-3.8 eV) source. Unlike the low energy defect, the high energy defect increases significantly with time in deaerated NaCl. Pitting was observed only in the higher 3.5% NaCl solution, and both the tendency to pit and the growth of the photocurrent appear to be connected to the number of high energy defects.