ISO 14420:2020

Overview

ISO 14420:2020 specifies a standardized laboratory method to determine the coefficient of linear thermal expansion (CLTE) of carbonaceous and graphite materials used in aluminium production - specifically baked anodes and shaped carbon products. The method covers measurements between 20 °C and 300 °C using a push‑rod dilatometer, and defines specimen preparation, apparatus, calibration, measurement, evaluation and reporting requirements.

Keywords: ISO 14420:2020, coefficient of linear thermal expansion, baked anodes, shaped carbon products, aluminium production, dilatometer, thermal expansion testing.

Key topics and technical requirements

• Scope and principle
  • Determines average CLTE for solid carbonaceous/graphite materials between 20 °C and 300 °C.
  • Uses a push‑rod dilatometer with a low‑expansivity sample holder (e.g., flint glass) transmitting length change to an external measuring system.
• Apparatus accuracy
  • Length‑measurement device with error limits around ±0.5 µm for dilatometer output; vernier calliper per ISO 13385‑1 for initial lengths (error limit ±0.2%).
  • Furnace stability: temperature held within ±0.5% along specimen length.
  • Temperature measurement accuracy: thermocouple or equivalent within ±0.5%.
• Specimen preparation
  • Cylindrical or prismatic specimens; length ≥ 25 mm (preferably 50–120 mm).
  • Transverse dimensions at least twice the largest structural constituent and not smaller than 4 mm.
  • End surfaces machined to plane‑parallelism within 0.2 mm.
  • Optional stress relief by annealing at 1 000 °C in a non‑oxidizing atmosphere.
• Procedure
  • Calibration using calibrated reference samples.
  • Zeroing of the measuring system, heating to the upper temperature limit, recording length change, and correcting for sample‑holder/push‑rod expansion.
• Evaluation and precision
  • Average CLTE computed from measured length change, original length and temperature interval, accounting for apparatus expansion.
  • Reported precision (interlaboratory): repeatability r = 0.10 × 10^‑6 K^‑1; reproducibility R = 0.17 × 10^‑6 K^‑1.
• Test report content
  • Must include sample ID, reference to ISO 14420:2020, pre‑treatment, specimen count, temperature range, CLTE values (units 10^‑6 K^‑1), deviations and test date.

Applications and users

• Quality control and specification acceptance for baked anodes, carbon electrodes and shaped carbon products in aluminium smelting.
• Materials R&D for graphite/carbon product development and process optimization.
• Metrology and testing laboratories performing thermal‑expansion characterization.
• Process engineers, materials scientists and procurement teams specifying CLTE for thermal compatibility in potline components.

Related standards

• ISO 13385‑1 (dimensional measuring equipment - callipers)
• DIN 51909:2009 (basis for this document)
• ASTM E691 (precision assessment method referenced)

ISO 14420:2020 helps ensure consistent, comparable CLTE data for carbonaceous materials used in aluminium production, supporting reliable component design, quality control and materials selection.