ISO 4905:2023

Overview

ISO 4905:2023 - "Corrosion of metals and alloys - Electrochemical test methods for high‑temperature corrosion testing of metallic materials in molten salts" defines standardized electrochemical test methods for evaluating corrosion behavior in high‑temperature molten salts. It specifies apparatus, test cell designs, instrumentation and general procedures for potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in molten‑salt environments, plus reporting requirements. Annexes provide example salts, temperatures and reference electrode types.

Key technical topics and requirements

• Apparatus components: heating unit/furnace with an isolated test chamber, gas feeding unit, electrochemical measurement unit (potentiostat/EIS), and electrochemical cell (Figures and schematics provided).
• Electrochemical systems: recommended three‑electrode configuration (working, reference, counter) for polarization tests; two‑electrode arrangements may be used for EIS.
• Instrumentation performance:
  • Potentiostat must control potential to within ±1 mV and support automatic potential scans for potentiodynamic tests.
  • Measurement instrument input impedance should be very high (order of magnitude shown in document) to avoid drawing current; current measuring instruments should have maximum error 0.5%.
• Temperature control and monitoring:
  • Furnace must provide a characterized isothermal zone; thermocouple calibration per ASTM E220, E230, E1350.
  • Permissible temperature tolerances (Table 1): ≤300 °C ±2 °C; 300–600 °C ±3 °C; 600–800 °C ±4 °C; 800–1 000 °C ±5 °C; 1 000–1 200 °C ±7 °C; >1 200 °C by agreement.
• Electrochemical cell & sample prep:
  • Use inert/non‑reactive cell materials (e.g., high‑purity alumina crucibles for sulfates/chlorides).
  • Working electrodes often flag‑shaped to minimize three‑phase interface effects; surface finish prepared with abrasives ~15 µm and degreased before testing.
  • Counter electrodes: Pt, Au or carbon; reference electrode types for chlorides, sulfates, carbonates are given in Annex B.
• Gas handling: controlled gas flow, humidification options, and measurement of water vapour when applicable.
• Procedure highlights: heat under inert gas, switch to test gas before melting, lower electrodes to fixed immersion depth after salt liquefies, then perform polarization/EIS measurements.
• Safety note: mandatory precautions when handling hazardous molten salts.

Practical applications and users

ISO 4905:2023 is relevant to:

• Corrosion engineers and materials scientists evaluating molten salt corrosion mechanisms.
• Test laboratories performing qualification of alloys for concentrated solar power, thermal energy storage, molten salt reactors, and industrial processes involving molten salts.
• Manufacturers and R&D teams assessing protective coatings, alloy selection and corrosion mitigation strategies. The standard supports reproducible electrochemical characterization, enabling comparative data across labs and industries.

Related standards

• ISO 17475 - electrochemical polarization in aqueous solutions (guidance)
• ISO 8044 - corrosion vocabulary
• ASTM E220, E230, E1350 - thermocouple calibration and testing

Keywords: ISO 4905:2023, electrochemical test methods, high‑temperature molten salts, potentiodynamic polarization, EIS, molten salt corrosion, electrochemical cell, potentiostat, thermocouple calibration.