ISO 7404-5:2009

Overview

ISO 7404-5:2009 - Methods for the petrographic analysis of coals - Part 5 specifies the microscopic method for determining vitrinite reflectance. Measurements are made on well‑polished coal surfaces immersed in oil, using a reflected‑light microscope with a photometer at 546 nm. The procedure applies across the full range of low-, medium- and high‑rank coals and to both single‑seam coals and coal blends. Note: reflectance results derived solely from automated interpretation systems are outside the scope of this standard.

Key topics and requirements

• Measurement principle: compare light intensity reflected from vitrinite with calibrated reflectance standards under oil immersion at near‑normal incidence (546 nm) using a photomultiplier or equivalent detector.
• Sample preparation: polished surfaces prepared according to ISO 7404‑2 (sample preparation) are required; vitrinite must be identified microscopically by the analyst.
• Immersion oil: non‑drying, non‑corrosive oil with refractive index 1.5180 ± 0.0004 at 23 °C and 546 nm; avoid aged or toxic oils.
• Calibration standards: use at least two well‑spaced, individually calibrated reflectance standards (e.g., optical glasses, YAG, GGG); include a zero (non‑reflecting) standard. Standards should be calibrated against ICCP master standards where possible.
• Apparatus: reflected‑light microscope with stable light source, polarizer (for maximum reflectance), measuring aperture (<80 µm area), strain‑free objective and photometer; internal stray light control is mandatory.
• Sampling and readings: take an adequate number of readings across different vitrinite particles to ensure representative results; specify maceral types measured and whether random or maximum reflectance values are reported.
• Reporting and precision: the standard outlines required report elements, result presentation and precision considerations (see ISO text for details).

Applications

• Coal rank determination: vitrinite reflectance is a primary indicator of coal metamorphic rank.
• Blend characterization and QC: identify components of coal blends, correct for differing vitrinite contents, and estimate proportions of component coals.
• Technological and commercial uses: informs coking/combustion performance, metallurgical coal assessment, cargo/bulk sample characterization and quality control in mining, trading and processing.
• Research and accreditation: used in petrographic research; petrologists may participate in ICCP/SCAP proficiency schemes for accreditation.

Who should use this standard

• Coal petrologists and mineralogists
• Laboratory analysts performing petrographic coal testing
• Mine geologists, coal producers and blending engineers
• Quality assurance teams and regulatory bodies
• Research institutions studying coal rank and maceral properties

Related standards

• ISO 7404‑1 - Vocabulary (petrographic terms)
• ISO 7404‑2 - Methods of preparing coal samples
• ISO 7404‑3 - Maceral group composition
• ISO 7404‑4 - Microlithotype and minerite composition

Keywords: ISO 7404-5, vitrinite reflectance, petrographic analysis, coal rank, microscopic reflectance, immersion oil, reflectance standards, coal blends.