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.
Open preview (PDF)Carbonaceous products for the production of aluminium — Baked anodes and shaped carbon products — Determination of the coefficient of linear thermal expansion
