Overview
ISO 23873:2025 - Hard coal - Method for the measurement of the swelling properties using a dilatometer specifies a standardized laboratory procedure to measure the swelling (dilatation and contraction) behaviour of hard coal when heated. The method records piston movement on a compacted pencil of powdered coal in a steel retort heated at a controlled rate, producing a characteristic dilatation curve used to quantify properties such as softening temperature, maximum contraction and maximum dilatation. This second edition (2025) unifies earlier Ruhr and Audibert-Arnu procedures into a single acceptable method.
Key technical topics and requirements
- Principle: A coal pencil is heated in a dilatometer; piston displacement is continuously recorded to determine swelling properties.
- Sample preparation: Test pieces are prepared as compressed pencils from powdered coal (mould, ram, press and load cell specifications provided).
- Temperature control & calibration:
- Heating rate: 3 °C/min (typical test rate up to 550 °C).
- Controller precision: maintain 3 °C/min ± 0.05 °C/min between 250 °C and 550 °C, with ±1 °C precision.
- Temperature recorder: independent instrument with equivalent precision to the controller.
- Calibration uses reference metals (lead, Zn) and graphite pencils positioned 30 mm above the retort base.
- Apparatus: Detailed specifications for mould dimensions, retort holes (∅ 15.0 ± 0.1 mm), furnace block, piston and recording mechanism are included.
- Measured results: Definitions and methods for reporting softening temperature, temperature of maximum contraction/dilatation, and percentage dilatation relative to initial test-piece length.
- Quality aspects: Requirements on number of tests, apparatus inspection, furnace temperature uniformity, precision (repeatability and reproducibility), and cleaning procedures.
Practical applications and users
ISO 23873:2025 is used where reliable, comparable measurements of coal swelling are required:
- Coal and coke testing laboratories performing quality control and acceptance testing.
- Coke oven operators and steel producers assessing coking performance and blend selection.
- Coal suppliers and buyers for specification compliance and material characterization.
- Research institutions studying thermal behavior of coals and carbonization processes.
- Process engineers concerned with thermal expansion effects in coal-handling or pyrolysis equipment.
Benefits include standardized data for coal selection, blending, process control, and R&D-helping predict coke quality and manage furnace or oven performance.
Related standards
- ISO 1213-2 - Coal and coke - Vocabulary (terms for sampling, testing and analysis)
- ISO 13909-4 - Mechanical sampling - Preparation of test samples of coal
- ISO 18283 - Manual sampling
Keywords: ISO 23873:2025, hard coal, dilatometer, swelling properties, coal testing, dilatation, softening temperature, coke quality.