Overview - ISO/TR 9686:2017 (Direct reduced iron, HF combustion + IR)
ISO/TR 9686:2017 specifies a laboratory method for the determination of carbon and/or sulfur mass fractions in direct reduced iron (DRI) using high-frequency (HF) combustion followed by infrared (IR) measurement of CO2 and SO2. The method applies to carbon levels from 0.05 % to 2.5 % and sulfur levels from 0.001 % to 0.05 %. It describes sample preparation, reagents, crucible preparation, calibration, blank tests and instrument operation for commercial HF combustion/IR analyzers.
Key topics and technical requirements
- Principle: Combustion of a weighed test portion in oxygen in a refractory crucible within an HF furnace; CO2 and SO2 measured by IR absorption.
- Scope limits: Carbon 0.05–2.5 % (mass fraction); sulfur 0.001–0.05 % (mass fraction).
- Sample: Laboratory sample milled to −160 µm and predried at 105 °C ± 2 °C (per ISO 10835 / ISO 7764). Typical test portion: 0.400 g.
- Reagents & materials: Oxygen (≥ 99.5 %), magnesium perchlorate, ascarite (for C), tungsten accelerator (low C/S content), tin capsules, barium carbonate for carbon calibration and potassium sulfate standard solutions for sulfur calibration.
- Crucibles: Ceramic combustion crucibles must be pre‑ignited (≥ 1 350 °C for general use; 1 100 °C if only sulfur is determined) and precisely dimensioned for the instrument.
- Calibration & blanks: Multi-point calibration using prepared standards (BaCO3 for carbon; K2SO4 solutions for sulfur). At least three blank burns are recommended to establish zero adjustment.
- Instrumentation & operation: Uses commercial HF combustion/infrared sulfur analysers; follow manufacturer instructions for oxygen flow (typically ~2.0 L/min during combustion), filter maintenance and stabilization.
- Safety: Addresses combustion hazards, oxygen handling and high-frequency radiation screening.
Applications and users
ISO/TR 9686:2017 is intended for:
- Steelmakers, iron producers and DRI manufacturing labs monitoring carbon and sulfur content for process control and product specification.
- Quality control and metallurgical laboratories performing routine compositional analysis of direct reduced iron.
- Equipment manufacturers and analytical service providers implementing or validating HF combustion + IR analyzers for DRI.
Practical benefits include fast, direct measurement of C and S in DRI, clear calibration procedures, and guidance on sample preparation and instrument setup.
Related standards and annex material
- Related ISO references cited for sampling and glassware: ISO 10835, ISO 7764, ISO 7550, ISO 1042.
- Annexes provide crucible loading sequences, calibration flowsheets, features of commercial analyzers, repeatability/tolerance derivations and international precision data.
- Note: ISO/TR 9686:2017 replaces ISO 9686:2006 and is published as a Technical Report (not a referee method).
Keywords: ISO/TR 9686:2017, direct reduced iron, HF combustion, infrared measurement, carbon determination, sulfur determination, DRI analysis, barium carbonate calibration, potassium sulfate standard.