Microgravimetric Study of Early-Stage Aluminum Corrosion in Neutral Media

Early stages of aluminum corrosion in a NaCl solution as well as in pure water have been studied using the quartz crystal microbalance (QCM) sensors prepared as magnetron-sputtered (MS) and glued foil (GF) modifications. Structure, composition, and surface morphology of the samples were characterized by x-ray diffraction, atomic force microscopy, scanning electron microscope-energy dispersive spectroscopy, scanning transmission electron microscopy, and high angle annular dark field (HAADF). The QCM provided real time information in situ with nanogram resolution on the corrosion product layer formation and aluminum corrosion rate. Although the corrosion rate in pure water was negligible, a dramatic acceleration has been observed in the chloride solution. Although the MS and GF samples were of different crystallographic structures, both samples exhibited similar corrosion behavior at early stages. HAADF showed two-layer structure on the aluminum exposed to NaCl solution. Formation of a mixture of aluminum oxide and oxyhydroxide on the corroding surface has been concluded from x-ray photoelectron spectroscopy measurements. Thickness of the oxygen-containing layer estimated from the QCM data was in agreement with that determined by HAADF.