ISO 23331:2021

Overview

ISO 23331:2021 specifies a standardized test method for the total electrical conductivity of conductive fine ceramics using the DC four‑terminal method. The procedure applies to conductive fine ceramics whose ionic transference number is 0.01 or less, over a conductivity range of 1 S·cm⁻¹ to 1 000 S·cm⁻¹ and temperatures up to 1 000 °C. Values are reported in SI units. The standard is targeted at industrial product quality control and material development for conductive ceramics used as electrodes in fuel cells, batteries and water electrolysis.

Key topics and technical requirements

• Measurement principle: DC four‑terminal method - four wire electrodes are wrapped on the test piece; the outer electrodes supply current and the inner electrodes measure voltage (minimizes contact resistance).
• Applicability limits: Ionic transference number ≤ 0.01; conductivity 1–1 000 S·cm⁻¹; temperature up to 1 000 °C.
• Test specimen: Typical dimensions ~4 × 3 × 35–40 mm (minimum length 20 mm when necessary); bulk density measured per ISO 18754; surface roughness < 0.20 µm (stylus instrument).
• Electrodes & wiring: Noble metal wires (Pt, Au, Ag) recommended; voltage terminal spacing ≥ 10 mm (preferably 20 mm); terminal width < 1 mm; current terminals placed ≥ 5 mm from voltage terminals; use of conductive paste allowed to reduce contact resistance.
• Apparatus requirements:
  • Furnace with hot zone uniformity (max variation 10 °C) and controlled heating rate (within 2 °C/h); controlled atmosphere (gas flow) to protect carbide/nitride ceramics.
  • Voltmeter suitable for low floating potentials and correcting lead‑wire effects.
  • Constant DC supply with precision to at least three significant digits.
  • Short, coaxially shielded lead wires and matched materials for electrodes/lead wires.
• Test procedure: Dimension measurement, controlled heating, gas composition maintenance, DC measurement and calculation of total conductivity using geometry, applied current and measured voltage.
• Quality controls: Minimum of three test pieces; calibration and uncertainty analysis; reporting of deviations (e.g., surface roughness, lead‑wire types).

Applications and users

ISO 23331:2021 is relevant for:

• Ceramic materials scientists and R&D teams developing conductive fine ceramics.
• QC and materials engineering in manufacturers of electrodes for fuel cells, batteries and water electrolysis.
• Test laboratories accredited under ISO/IEC 17025 performing electrical conductivity characterization.
• Suppliers validating material batches and optimizing sintering/processing for electronic conduction.

Keywords: ISO 23331:2021, conductive fine ceramics, total electrical conductivity, DC four‑terminal method, electrode materials, fuel cells, battery electrodes, water electrolysis.

Related standards

• ISO 18754 - Determination of density and apparent porosity (referenced)
• ISO/IEC 17025 - Laboratory competence
• ISO 13385‑1, ISO 3611 - Dimensional measuring equipment
• ISO 6145‑7, ISO 80000‑1 - Gas flow and units/quantities

For implementation, consult the full ISO 23331:2021 text for complete test procedures, calculations and reporting requirements.