Overview
ISO 8006:1985 applies to carbonaceous materials used in aluminium production - specifically pitch for electrodes (tar pitch, petroleum pitch, etc.) - and specifies a gravimetric method for the determination of ash. The method is intended for products that yield an ash content greater than or equal to 0.05 % (m/m). The procedure uses a tared platinum crucible and controlled oxidizing incineration in a furnace at 700 ± 10 °C until constant mass is achieved.
Key Topics
- Scope and applicability: Designed for electrode pitch materials in the aluminium industry with ash ≥ 0.05 % (m/m).
- Apparatus:
- Platinum crucible (low form), capacity ~50 ml.
- Electric furnace adjustable up to 700 ± 10 °C with air circulation.
- Drying oven adjustable to 150 ± 5 °C and desiccator with P2O5.
- Analytical balance with precision to 0.0002 g for weighing crucible and residues.
- Sampling and preparatory tests: Sampling is to follow ISO 6257; if results must be reported on a dry basis, determine moisture according to ISO 5939 (Dean and Stark azeotropic method).
- Procedure summary:
- Preheat/crucible conditioning (e.g., 1 h at 700 ± 10 °C) and cooling in desiccator.
- Weigh crucible (m1) to 0.0002 g precision, add ~5 g test portion (mo) and place in furnace.
- Heat in stages (e.g., starting ≈300 ± 10 °C, then 350, 400, 450 °C with controlled ramping and holds of not less than 30 min - to avoid rapid volatilization) before final heating at 700 ± 10 °C until incineration is complete and constant mass is reached.
- Cool first to ~100–150 °C in air, then to ambient in a desiccator with P2O5 and weigh (m2).
- Calculation: Express ash on the as‑received sample as percentage by mass to 0.01 % (m/m) using the equation:
x = ((m2 - m1) / mo) × 100
where m1 = mass of empty crucible, m2 = mass of crucible + ash residue, mo = mass of test portion.
- Performance: Precision (repeatability and reproducibility) is addressed per ISO 5725; graphical and statistical correlation between repeatability and reproducibility are reported in the standard.
Applications
- Quality control of electrode pitch suppliers and incoming raw materials for aluminium smelting operations.
- Material certification and batch release testing to confirm ash limits and compliance with procurement specifications.
- Useful for laboratories conducting routine ash determinations as part of process control, acceptance testing, or comparative material assessment.
Related Standards
- ISO 6257 - Sampling of pitch for electrodes (referenced for correct sample selection).
- ISO 5939 - Determination of water in carbonaceous products (Dean and Stark azeotropic method) for dry-basis reporting.
- ISO 5725 - Precision of test methods (repeatability and reproducibility) for interlaboratory performance assessment.
ISO 8006:1985 is a practical, standardized gravimetric procedure that supports reproducible ash determination and helps maintain consistent quality in carbonaceous materials used for electrode manufacture in the aluminium industry.