Overview
EN ISO 17475:2008 (ISO 17475:2005/Cor 1:2006) provides guidelines for conducting potentiostatic and potentiodynamic polarization measurements used in the study of corrosion of metals and alloys. The standard defines the principles and recommended procedures for electrochemical polarization testing to characterise anodic and cathodic reaction kinetics, determine the onset of localised corrosion (e.g., pitting, crevice attack), and evaluate repassivation behaviour.
Key topics and technical requirements
- Principle of measurement: Displacement of electrode potential from the open-circuit (corrosion) potential and measurement of the resulting net current to infer anodic or cathodic kinetics, passive behaviour, breakdown and repassivation potentials.
- Test modes:
- Potentiostatic - stepwise holding of potential for time-dependent studies.
- Potentiodynamic - continuous potential scan at a controlled rate.
- Instrumentation and accuracy:
- Potentiostat capable of precise potential control (example requirement: control to within ±1 mV).
- Electrode potential measurement using high-input-impedance instruments with millivolt sensitivity (capable of detecting ~1.0 mV changes).
- Current measurement instruments with low maximum error (example requirement: ≤ 0.5%).
- Cell and electrode arrangement:
- Working electrode (specimen), reference electrode, and one or more auxiliary (counter) electrodes.
- Use of Luggin capillary to minimise IR drop; tip positioned not closer than about two times its diameter from the working electrode.
- Option for double-junction reference electrode or salt bridge to avoid contamination.
- Practical considerations:
- Correct for solution ohmic drop in low-conductivity media.
- Select solution volume sufficient to avoid significant chemistry change (guidance: >100 ml per cm2 of specimen surface in many cases).
- Use inert cell materials and arrange auxiliary electrodes to give symmetrical current distribution.
- Control scan rate and hold times carefully-kinetics and film formation are time-dependent and affect measured breakdown/repassivation potentials.
Applications and users
- Applications:
- Characterising electrochemical kinetics of corrosion reactions.
- Assessing susceptibility to pitting, crevice corrosion and passive film breakdown.
- Measuring repassivation potential and comparing alloy/coating performance.
- Supporting materials selection, R&D, failure analysis and quality control.
- Primary users:
- Corrosion engineers, materials scientists, testing laboratories, coatings and alloy developers, and regulatory/standards bodies.
Related standards
Keywords: ISO 17475, EN ISO 17475:2008, corrosion testing, potentiostatic, potentiodynamic, polarization measurements, electrochemical test methods, pitting, repassivation, potentiostat.
