Development of Mg2+ Ion-Selective Microelectrodes for Potentiometric Scanning Electrochemical Microscopy Monitoring of Galvanic Corrosion Processes

Abstract

The fabrication of a solid-contact, micropipette-based magnesium ion-selective micro-tipped electrode (ISME) suitable for scanning electrochemical microscopy is reported and compared against a conventional micro-tipped ISME having a conventional aqueous internal reference electrode. Measurements showed that the solid-contact ISME had a lower internal resistance and a faster response time than the one with a liquid-contact. These advantages increased the spatial distribution and improved 2D images depicting concentration distributions of Mg2+. The ability of the microelectrode to image local ionic concentration has been tested over magnesium surfaces freely corroding or galvanically coupled to iron in aqueous chloride-containing solution. Scans of magnesium ion distribution, in the absence of corrosion currents, were also made over a micro-pipette source containing a concentrated magnesium chloride gel as a source of Mg2+ and over a current source in the absence of Mg2+. From these measurements it was concluded that the potentiometric measurements over corroding surfaces were dominated by the changes in Mg2+ distributions with small electric potential contributions due to corrosion current.