University of the Punjab Conference Portal, 5th Symposium on Engineering Sciences

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Scanning Electrochemical Microscopy: A new way forward to identify and quantify regions of different electrochemical activity at high velocity oxyfuel sprayed Inconel 625 coatings
Akbar Niaz Butt

Last modified: 2014-03-27

Abstract


The scattered electrochemical activity at HVOF sprayed coatings is well known and studied by different researchers by using electrochemical techniques i.e., OCP vs. time measurement, potentiodynamic polarization, electrochemical noise and impedance spectroscopy. The real problem with existing techniques is that they do not give the precise position of the varied electrochemical activity over the surface. Furthermore results produced from the existing electrochemical techniques come with inherent errors of charging current, ohmic losses and other background currents. In the present study we used a more sophisticated technique; scanning electrochemical microscopy to spatially resolve and quantify regions of different electrochemical activity over HVOF sprayed Inconel 625 coatings. The SECM imaging was used to locate the positions of different electrochemical activity. Furthermore kinetics of charge transfer across substrate/electrolyte interface was studied to quantify different regions of electrochemical activities. In SECM analysis a 25µm diameter microelectrode was used to scan electrochemical activities of Inconel 625 coating in 0.1 M K2SO4 containing 1 mM ferrocenemethanol as a redox mediator. The bulk Inconel 625 alloy was used as a reference to establish comparison. The SECM images of the coatings showed segregated regions of low and high currents whereas the bulk alloy presented same current all over the surface. The electron rate constant was measured between 2.01 × 10-4 cm s−1 to 5.25 × 10-4 cm s−1 for the coating and 1.2 × 10-3 cm s−1 over the bulk alloy surface. These results clearly demonstrated that SECM can be used to visualize and quantify active regions having different electrochemical activity at HVOF sprayed coatings.