Overview
ISO 7404-2:2025 - "Coal - Methods for petrographic analysis - Part 2: Method of preparing coal samples" specifies standardized methods for preparing a polished particulate block (or a polished, embedded lump) from crushed coal for examination by reflected light microscopy. The third edition updates procedures with input from the International Committee for Coal and Organic Petrology (ICCP) and clarifies that ion‑milling is not acceptable for sample preparation.
Key topics and requirements
- Scope & principle: Produce a relief‑free, scratch‑free polished surface by crushing, sizing, binding, curing, grinding and polishing a representative coal sample for petrographic analysis and vitrinite reflectance measurement.
- Sample sizing: Use a 1.00 mm test sieve (ISO 3310‑1) and crush the required mass (0.3–0.45 kg) to pass the sieve with minimal fines.
- Binders: Requirements include chemical inertness, good wetting/penetration, compatible hardness and minimal curing shrinkage. Liquid resins should cure preferably below 60 °C (not exceeding 100 °C). Thermoplastics such as PMMA require ~120 °C and can be unsuitable for low‑rank coals.
- Abrasives & polishing:
- Grinding papers: e.g., silicon carbide grades ≈ 53.5 µm (240 grit), 23.6 µm (400 grit), 16.0 µm (600 grit).
- Polishing abrasives: metal oxides, colloidal silica or diamond pastes; final polishing particle size ≤ 0.05 µm; penultimate polishing ~0.3 µm recommended.
- Use nap‑minimal lap cloths (cotton, silk or synthetic).
- Apparatus: pressure capable press (up to 21 MPa), moulds sized to give a polished face ≥ 500 mm², contra‑rotating specimen holder grinder/polisher, ultrasonic or water cleaning between stages, desiccator storage, and reflected‑light microscope (approx. 100×–250×).
- Prohibitions/clarifications: Ion‑milling equipment is explicitly not acceptable for preparing samples for reflected light microscopy.
- Supporting documents: normative references include ISO 7404‑1 (vocabulary), ISO 18283 (manual sampling), ISO 3310‑1 (test sieves), and the ICCP Handbook.
Applications and users
ISO 7404‑2:2025 is used where accurate petrographic description and vitrinite reflectance are required:
- Coal and coke laboratories performing petrographic/reflectance analyses
- Mining and exploration geoscientists characterizing seams and variability
- Quality control teams in coal preparation and blending operations
- Research institutions studying coal rank, macerals and coal petrography
- Shipping and cargo inspection where petrographic characterisation of bulk coal is needed
Adoption ensures reproducible, comparable sample preparation for reflected‑light petrographic work and rank determinations across labs.
Related standards
- ISO 7404‑1 - Vocabulary for coal petrographic analysis
- ISO 18283 - Coal and coke - Manual sampling
- ISO 3310‑1 - Test sieves - Technical requirements
Keywords: ISO 7404-2:2025, coal petrographic analysis, polished particulate block, reflected light microscopy, sample preparation, vitrinite reflectance, binder, grinding and polishing.
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