In Situ Monitoring of Molten Chloride Salt Chemistry and Corrosion Using a Microelectrode

Area of Science:

• Electrochemistry
• Materials Science
• Corrosion Science

Background:

• Localized electrochemical processes at high temperatures are crucial for material degradation.
• In situ monitoring requires robust electrode materials capable of withstanding harsh environments.
• Molten salt environments present unique challenges for electrochemical measurements.

Purpose of the Study:

• To evaluate a borosilicate glass-coated tungsten microelectrode for in situ monitoring of localized surface electrochemical processes.
• To analyze the diffusion of Eu3+ ions and assess microelectrode performance in molten salt at high temperatures.
• To investigate the potential for high-temperature scanning electrochemical microscopy (SECM) applications.

Main Methods:

• Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used to analyze ion diffusion and electrode characteristics.
• Approach curve tests were performed near insulating alumina and corroding Ni-20Cr surfaces.
• Open circuit potential (OCP) profiling was conducted to capture local redox potential gradients.

Main Results:

• The microelectrode overestimated diffusion coefficients due to intrinsic glass electrode current (IGEC).
• Effective capacitance of the borosilicate glass increased with temperature, necessitating IGEC subtraction for corrected diffusion values.
• Electrode response was sensitive to approach speed and temperature, inducing artifacts near alumina and influencing deposition near Ni-20Cr.

Conclusions:

• Borosilicate glass-coated tungsten microelectrodes show potential for localized electrochemical measurements in molten salts.
• Accurate measurements require careful optimization of operational parameters and correction for IGEC.
• The study highlights the feasibility of high-temperature SECM with appropriate microelectrode design and methodology.