Briefly describe Electrochemical Impedance Spectroscopy (EIS) and its use in corrosion monitoring.

• A. EIS applies a small AC signal over a range of frequencies to model the electrochemical system; it helps assess coating integrity, barrier properties, and corrosion processes
• B. EIS measures only voltage
• C. EIS determines only pH
• D. EIS is used only in non-corrosive environments

Answer: (A)

Electrochemical Impedance Spectroscopy works by applying a small alternating current signal over a range of frequencies to an electrochemical system and measuring the resulting response. By sweeping through frequencies, it reveals how different processes at the metal/coating interface respond to AC excitation, which allows the data to be interpreted with an equivalent circuit that includes elements representing coating resistance, pore resistance, the coating’s capacitance, charge-transfer resistance, and diffusion effects. This frequency-dependent view helps you see whether a coating is still acting as a barrier, where defects or defects are developing, and how corrosion-related processes are progressing.

In corrosion monitoring, that capability is especially valuable because you can quantify coating integrity and barrier properties over time without damaging the system, and you can detect changes that indicate the onset or acceleration of corrosion. EIS provides a non-destructive means to assess how well a coating protects the metal and to distinguish between different degradation mechanisms.

The other statements don’t fit because EIS measures impedance (a complex quantity that includes both magnitude and phase) rather than only voltage, it doesn’t determine pH, and it is not limited to non-corrosive environments; it is actively used to study coatings and corrosion in harsh and aggressive environments.