Overview
ISO 6997:1985 specifies a conventional gravimetric heating method to determine the apparent oil content of calcined coke used in aluminium production. The test measures mass loss after heating a weighed sample in a non‑oxidizing atmosphere; the result is reported as percentage loss by mass. The method is intended as an indicator of oil-related mass loss (not the true chemical oil content) and provides two procedures: a normal/reference determination (A) and a simplified determination (B).
Key topics and requirements
- Test principle: Heat a test portion in a non‑oxidizing atmosphere at a fixed temperature and record mass loss. Calculate apparent oil content (%) = (m1 − m2) / m0 × 100, where m0 is the test portion mass, m1 the mass before heating and m2 after heating.
- Sample preparation:
- Sampling per ISO 6375.
- Crush ~200 g lab sample to pass a 4 mm sieve; dry at 105–110 °C until two consecutive weighings differ by ≤0.01 g.
- Apparatus:
- Porcelain crucibles (~150 ml) with lids.
- Electric oven controlled 105–110 °C (drying).
- Electric furnace up to 800 °C for crucible pre‑heating.
- Steel packing box resistant to 550 °C and screened petroleum coke (0.25–2 mm) for embedding crucibles.
- Non‑oxidizing atmosphere: A few drops of toluene are added to crucibles to ensure a reduced/ non‑oxidizing environment during heating.
- Procedures:
- A (normal/reference): Preheat crucibles at ~800 °C, place crucibles in steel box embedded in petroleum coke, heat in furnace to 550 ± 10 °C for 2 h (alternative protocol allows 2.5 h if introduced into a hot furnace).
- B (simplified): Place crucibles in furnace preheated to 500 ± 10 °C; when furnace temperature stabilizes, maintain 20 minutes.
- Weighing and cooling: Cool in a desiccator; weigh to 0.001 g accuracy.
- Precision (inter‑laboratory):
- A: mean ≈ 0.256%, repeatability r = 0.050, reproducibility R = 0.078.
- B: mean ≈ 0.237%, repeatability r = 0.036 (reproducibility variance reported negative for the small data set).
Applications and users
- Practical for quality control in aluminium smelting and anode production to monitor dust suppression treatment and handling losses.
- Used by: aluminium producers, refractory and electrode coke suppliers, materials testing laboratories, process engineers, and QA/QC technicians assessing coke handling performance.
- Useful as a routine, comparative indicator of oil-related mass loss rather than an exact chemical oil assay.
Related standards
- ISO 6375 - Sampling of cokes for aluminium production
- ISO 565 - Test sieves (sieving requirements)
- ISO 5725 - Precision of test methods (repeatability & reproducibility)
Keywords: ISO 6997:1985, calcined coke, apparent oil content, heating method, carbonaceous materials, aluminium production, gravimetric method, non‑oxidizing atmosphere, toluene, porcelain crucibles.
Open preview (PDF)Carbonaceous materials for the production of aluminium — Calcined coke — Determination of apparent oil content — Heating method