ISO 21068-3:2024

Overview

ISO 21068-3:2024 - Chemical analysis of raw materials and refractory products containing silicon carbide, silicon nitride, silicon oxynitride and sialon - Part 3 specifies validated analytical techniques for the determination of total nitrogen, oxygen, and metallic and oxidic constituents. This second edition (2024) updates and consolidates established laboratory methods (including methods adopted from ISO 12698-1:2007), and replaces the 2008 edition. It is applicable to SiC raw materials and, with verification, to a range of refractory product matrices.

Key topics and technical requirements

• Scope and applicability: Methods target SiC raw materials and refractory products containing SiC, Si3N4, Si2ON2 and SiAlON-type materials; verification is recommended for some product matrices.
• Nitrogen and oxygen analysis:
  • Combined determination using analysers with thermal conductivity (TC) and infrared (IR) absorption detection.
  • Total nitrogen by fusion decomposition and by Kjeldahl distillation.
  • Calculation of silicon‑nitride equivalent (SiN content) from total nitrogen.
• Metallic and oxidic constituents:
  • Soluble iron by hydrochloric acid extraction followed by ICP‑OES measurement.
  • Free (metallic) aluminium via a hydrogen‑generating method.
  • Acid‑soluble aluminium and magnesium procedures.
• Impurity determination and sample preparation:
  • Alkaline melt fusion and acid pressure decomposition for elemental analysis.
  • Techniques for elemental impurities by XRF (fused bead) and DCArc‑OES (direct solid sampling).
• Quality and traceability: precision data, calibration, reagents, apparatus, and test reporting requirements are provided to ensure reproducible results.

Applications and users

ISO 21068-3:2024 is intended for:

• Quality control laboratories at refractory manufacturers and SiC raw material suppliers.
• R&D teams developing nitride- or oxynitride-bonded refractory compositions.
• Third‑party testing and conformity assessment bodies performing material characterization.
• Failure analysis and process optimization where accurate nitrogen, oxygen, and impurity profiling impacts performance (e.g., high-temperature corrosion resistance, densification, and electrical behavior).

Practical uses include incoming raw material verification, batch release testing, formulation control, and supporting specification compliance for industrial refractories.

Related standards

• ISO 21068 series (other parts cover additional chemical and mineralogical methods).
• ISO 21068-1, ISO 21068-2, ISO 21068-4 (XRD methods referenced in the series).
• ISO 10081 (shaped refractories) and ISO 1927-1 (unshaped refractories) for product classification and matrix context.

Keywords: ISO 21068-3:2024, chemical analysis, silicon carbide, silicon nitride, sialon, nitrogen determination, oxygen analysis, ICP‑OES, XRF, DCArc‑OES, refractory materials.