Characterization of corrosion interfaces by the scanning Kelvin probe force microscopy technique

A variety of interfaces relevant to corrosion processes were examined by th e scanning Kelvin probe force microscopy (SKPFM) technique in order to stud y the influences of various parameters on the measured potential. SKPFM mea surements performed on AA2024-T3 after solution exposure showed that surfac e composition is not the only parameter that controls the Volta potential d ifference, which is measured by SKPFM. The influence of surface oxide struc ture and adsorption at the oxide surface can be probed by SKPFM and lateral potential gradients can be observed in the absence of significant differen ces in oxide composition. The influence of tip-sample separation distance o n the measured Volta potential difference was studied for different pure ox ide-covered metals. SKPFM measurements were made in air on pure Ni and Pt s amples withdrawn from solution at open circuit or under potential control. The Volta potential difference was found to be composed of a transient comp onent that slowly discharged and a more permanent component associated with the charge of adsorbed species. The Volta potential difference transients measured on the samples emersed under potential control decayed much slower than the open-circuit potential transient measured in solution upon releas e of the potential control. These different measurements validate the use o f SKPFM for the prediction of local corrosion sites and the study of surfac e modification during solution exposure. (C) 2001 The Electrochemical Socie ty.