Overview
ISO/TR 16208:2014 - "Corrosion of metals and alloys - Test method for corrosion of materials by electrochemical impedance measurements" - is a Technical Report that explains the basic principles and practical use of electrochemical impedance spectroscopy (EIS) for corrosion assessment. The report focuses on how to set up electrochemical apparatus, connect potentiostats and electrodes, record impedance data (Bode and Nyquist), and analyse and present results. It is an introductory, application-focused guide and points to ISO 16773‑1/2 for more detailed methodology.
Key Topics
- Fundamentals of EIS: complex impedance representation (real/imaginary parts), magnitude |Z|, phase angle, and the use of Bode and Nyquist plots.
- Simple corroding system model: equivalent circuits for metal/solution interfaces including solution resistance (Rs), polarization/charge transfer resistance (Rp/Rct), and double-layer capacitance (Cdl) or constant phase element (CPE) for non-ideal capacitive behaviour.
- Instrumentation & apparatus: recommendations on potentiostats, reference, counter and working electrodes, test cells, Luggin capillaries and electrolyte choice.
- Specimen and solution preparation: considerations for preparing metal specimens and test electrolytes to ensure steady-state conditions during measurement.
- Dummy cell & instrument validation: use of dummy circuits (PCB-mounted components) to test and validate measurement chains and data processing.
- Data collection & analysis: presentation of measured impedance, use of Kramers–Kronig relations, interpretation of impedance spectra, and relationships between Rp and corrosion current (Icorr) where applicable.
- Reporting: essential content for a test report and informative annexes on dummy cell design and data analysis.
Applications
ISO/TR 16208:2014 is practical for professionals who need to apply EIS to corrosion problems, including:
- Corrosion engineers and materials scientists assessing metal corrosion rates, passive film integrity, and localized attack.
- Coating and surface-treatment developers evaluating barrier properties of coatings and coating degradation.
- Test laboratories performing routine EIS corrosion testing, quality control, and validation of instrumentation.
- R&D teams using impedance data to model electrochemical mechanisms or estimate polarization/charge-transfer resistance.
Keywords: ISO TR 16208:2014, electrochemical impedance spectroscopy, EIS, corrosion testing, Nyquist plot, Bode plot, CPE, potentiostat, polarization resistance.
Related Standards
- ISO 16773‑1 - Terms and definitions for EIS on high-impedance coated specimens
- ISO 16773‑2 - Collection of data for EIS on high-impedance coated specimens
- ISO 16773‑3 - Processing and analysis of data from dummy cells
Use ISO/TR 16208:2014 as a concise practical guide to performing and interpreting EIS corrosion measurements, and consult the ISO 16773 series for more detailed procedural and data‑collection requirements.