Combining AFM imaging and elementally resolved spectroelectrochemistry for understanding stability and quality of passive films formed on Alloy 600

Abstract

Understanding elemental corrosion currents and visualizing corroding topographies provides a detailed insight into corrosion mechanisms at the nanoscale. Here, we develop a strategy to understand the elemental composition, corrosion resistivity, and local stability of passive materials. Specifically, we utilize a pulse voltammetry approach in a novel electrochemical atomic force microscopy (AFM) cell and complement this data by real-time dissolution currents based on spectroelectrochemical online analysis in an inductively coupled plasma mass spectroscopy (ICP-MS) flow cell. We study the oxide properties and their protective behavior when formed under different applied potentials using Alloy 600 as a model sample. Both AFM and ICP-MS data show that passive films formed on Alloy 600 at around +0.3 to +0.4 V in neutral 1 mM NaCl solution are most stable during anodic corrosion at +1.0 V, while AFM further demonstrates that local dissolution occurs, indicating locally varying defect levels in the passive film. In combination with both techniques, our approach provides real-time elementally resolved and localized information of passive film quality under corrosive conditions, and it may prove useful for other corroding materials.