Overview
ISO 6376:1980 specifies a gravimetric method for determining the content of toluene‑insoluble material in electrode pitch used in the production of aluminium. The standard defines a practical laboratory procedure: dissolve a measured test portion of pitch in hot toluene, reflux for a specified time, collect and dry the insoluble fraction, and express the result as a percentage by mass. ISO 6376 was developed by ISO/TC 47 (Chemistry) and is also approved by IUPAC.
Key topics and technical requirements
- Scope: Measurement of toluene‑insoluble content in carbonaceous pitch for aluminium electrodes.
- Principle: Gravimetric determination of the insoluble fraction after boiling in toluene.
- Sample preparation:
- Hard pitches: grind to pass a 200 µm sieve (see ISO 565).
- Soft pitches: use as received.
- Reagents: Analytical‑grade toluene and acetone. Safety warning: toluene is toxic and highly flammable-perform in a fume cupboard.
- Apparatus:
- 500 ml conical flask with ground glass socket.
- Reflux condenser (effective length ~300 mm).
- Glass filter crucible with sintered glass disc (porosity grade P16, disc ~30 mm).
- Electric oven controllable at 105–110 °C.
- Procedure essentials:
- Test portion ≈ 1 g (weighed to 0.001 g).
- Add ~100 ml hot (~80 °C) toluene, dissolve and reflux for about 30 minutes.
- Filter under gentle suction, rinse with hot toluene and acetone to remove soluble residues.
- Dry the crucible and residue ~1 hour at 105–110 °C, cool in a desiccator and weigh.
- Result calculation: Percentage of toluene‑insoluble material = (mass of dried insoluble residue ÷ mass of test portion) × 100.
- Precision: Repeatability ~0.5% ; reproducibility ~1%.
Applications and users
ISO 6376:1980 is used by:
- Quality control laboratories in aluminium smelting and electrode manufacturing.
- Suppliers of carbonaceous materials (pitch producers) validating resin content.
- Research and development teams studying pitch formulations and electrode performance.
Practical uses include verifying pitch composition, monitoring production consistency, and ensuring feedstock meets specifications for anode and electrode manufacture.
Related standards
Keywords: ISO 6376:1980, carbonaceous materials, pitch for electrodes, toluene‑insoluble, gravimetric method, aluminium production, electrode pitch, determination of insoluble material.