Overview
EN ISO 15351:2010 (ISO 15351:1999 adopted by CEN) specifies a thermal conductimetric method after fusion in a current of inert gas for the determination of nitrogen in steel and iron (routine method). The specified procedure uses fusion of a test portion in a single-use graphite crucible under high‑purity helium, extraction of nitrogen as N2, separation from other gaseous species and measurement by a thermal conductivity detector. Applicable range: 0.002 % (m/m) to 0.6 % (m/m) nitrogen.
Key topics and technical requirements
- Principle: Fusion at very high temperature (e.g., ~2 200 °C) under inert gas; nitrogen is carried as N2 and measured by thermal conductimetry.
- Analytical range: 0.002–0.6 % (m/m) nitrogen in steel and iron.
- Reagents & gases: Use analytical-grade reagents and high-purity helium (total impurities ≤ 0.0005 % m/m). Oxidation catalysts (CuO or Pt) and drying/CO2 traps (magnesium perchlorate, anhydrous CaSO4, ascarite) are specified for gas purification.
- Apparatus: Single-use graphite crucibles, graphite crucible tongs, glass‑wool filters and a commercial inert‑gas fusion / nitrogen analyser. Follow manufacturer instructions; features of typical instruments are summarized in the standard.
- Sampling and sample prep: Sampling per ISO 14284; degrease samples (e.g., acetone) and evaporate solvent. Typical test portion masses: ≈1 g for N ≤ 0.1 % and ≈0.5 g for N > 0.1 % (instrument dependent).
- Calibration & quality control: Calibration with multiple certified reference materials (CRMs) covering the measurement range; CRM traceability per ISO Guide 31 and ISO Guide 35. Blank tests and routine checks (degassing crucibles, reagent/filter replacement, stability runs) are required.
- Safety & precision: Warning about burn hazards when handling hot crucibles. Method precision depends strongly on CRM accuracy and homogeneity; ISO 5725 series referenced for precision assessment.
Applications and users
- Routine quantification of nitrogen content in steel and iron for:
- Quality control in steel mills and foundries
- Metallurgical laboratories and chemical analysis labs
- Material certification, R&D on alloy composition and processing
- Instrument manufacturers validating inert‑gas fusion analyzers
- Useful where rapid, routine, and trace‑to‑intermediate nitrogen analysis (0.002–0.6 % N) is required.
Related standards
- ISO 14284 - Sampling and preparation of samples for chemical composition.
- ISO Guide 31 / ISO Guide 35 - Requirements for reference materials and certification.
- ISO 10702 - Titrimetric method for nitrogen after distillation (alternative method).
- ISO 5725 series - Accuracy (trueness and precision) of measurement methods.
Keywords: EN ISO 15351:2010, nitrogen determination, thermal conductimetric method, inert gas fusion, steel and iron analysis, helium fusion, graphite crucible, certified reference material (CRM).