ISO 7404-5:2025

Overview

ISO 7404-5:2025 - "Coal - Methods for petrographic analysis - Part 5: Method of determining microscopically the reflectance of vitrinite" specifies a microscope-based procedure to measure vitrinite reflectance on well‑polished coal surfaces immersed in oil. The method is applicable across the full range of low-, medium- and high‑rank coals and to single‑seam coals or coal blends. Measurements are performed at 546 nm and compared against calibrated reflectance standards. Automated interpretation of reflectance data is explicitly outside the scope.

Key topics and technical requirements

• Measurement principle: Near‑normal incidence light reflected from vitrinite in oil is measured (photomultiplier or equivalent) at 546 nm and compared with standards.
• Immersion medium: Non‑drying, non‑corrosive oil with refractive index 1.5180 ± 0.0004 at 23 °C and 546 nm; avoid old or contaminated oil.
• Calibration standards: Use at least two polished, durable, isotropic standards with well‑spaced reflectances; additional standards needed for reflectance > 2.0%.
• Measurement types: Supports maximum and random reflectance determinations - the chosen type must be reported.
• Sample preparation & apparatus: Polished surfaces and optical alignment as described; see ISO 7404-2 for sample preparation procedures.
• Quality checks: Procedures for apparatus stability, linearity, parasitic reflections and calibration verification are specified.
• Analyst identification: Vitrinite must be identified by the analyst; results derived solely from automated interpretation are excluded.
• Reporting & precision: Requirements for reporting results, repeatability and reproducibility data, and test reporting are included.

Applications and users

Practical uses of ISO 7404-5:2025:

• Determination of coal rank for geological or technical classification.
• Characterization of coal blends, including correction for vitrinite content or estimation of component proportions when components differ in vitrinite reflectance.
• Quality control in coal production, trading and transport (cargo characterization).
• Feedstock assessment for coking, combustion, gasification and coal conversion processes.
• Research and accreditation (e.g., ICCP Single Coal Accreditation Program) for petrographers and analytical laboratories.

Typical users:

• Coal petrologists and petrographic laboratories
• Power and steel industry quality/control teams
• Coal traders and commodity analysts
• Academic and geological researchers

Related standards

• ISO 7404 series (petrographic methods)
• ISO 7404-1 (Vocabulary)
• ISO 7404-2 (Sample preparation)

Keywords: ISO 7404-5:2025, vitrinite reflectance, coal petrographic analysis, immersion oil, reflectance standards, coal rank, coal blends, photomultiplier, polished surfaces.