Scanning Kelvin Probe Force Microscopy

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Abstract
Scanning Kelvin probe force microscopy (SKPFM) is used to study the initial stages of atmospheric corrosion of an AlMg alloy and of physical vapor deposition (PVD) deposited 2 μm Al dots on pure Mg. The latter system is used as a model of a two-phase AlMg alloy. The influence of CO2CO2 was studied in situ in humid air using SKPFM. This method allows for the in situ investigation of the evolution of the Volta potential during exposure, the resolution being in the submicrometer range. The temperature was 22.0°C, and the relative humidity was 85 or 95%. The concentration of CO2CO2 was CO2,CO2, the corrosion attack is localized in nature whereas the presence of ambient levels of CO2CO2 results in a more general corrosion attack. The inhibitive effect of CO2CO2 on the atmospheric corrosion of AZ91D is explained by the formation of a passivating layer of Mg5(CO3)4(OH)2⋅5H2O.Mg5(CO3)4(OH)2⋅5H2O. In the absence of CO2,CO2, the increase in pH originating from the cathodic reaction results in the dissolution of aluminum in the passive layer. A corrosion mechanism is proposed explaining the behavior in the two environments. © 2004 The Electrochemical Society. All rights reserved.

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