Overview
ISO 16169:2018 specifies laboratory procedures for preparing fused cast beads from silicon carbide (SiC) and similar reduced materials for chemical analysis by X‑ray fluorescence (XRF) using ISO 12677. The standard defines reagents, apparatus, sample handling, loss on drying/ignition (LOD/LOI) guidance and three fused‑bead preparation procedures tailored to the challenges of non‑oxide, exothermic materials. Annex A gives modifications for other reduced materials (e.g., boron carbide, boron nitride, ferroalloys, sialons, silicon nitride).
Key topics and technical requirements
- Purpose: Produce homogeneous borate‑based fused beads suitable for XRF analysis in accordance with ISO 12677.
- Materials covered: Silicon carbide and similar reduced materials; principles extendable via Annex A.
- Three preparation methods:
- Method 1 - Oxidation with alkali nitrate (fast, higher dilution; Na/K/Al interferences possible).
- Method 2 - Oxidation on a bed of fused lithium tetraborate (higher sample:flux ratio; slower for high SiC).
- Method 3 - Oxidation on Li‑tetraborate bed at ~840 °C in oxygen (similar benefits to Method 2, longer cycle times; can take up to ~30 h).
- Reagents and flux: Lithium tetraborate (Li2B4O7) flux grade, KNO3, NaNO3, LiBr/LiI, Li2CO3, optional V2O5 catalyst and oxygen for some methods. Flux pre‑ignition and LOI corrections are required.
- Apparatus: Fusion unit or furnace capable of forming homogeneous borate beads, laboratory furnace for pre‑oxidation (≈950 ± 50 °C), ceramic crucibles and platinum alloy dishes (care to avoid corrosion/exothermic attack).
- Sample prep controls: Grinding and sampling per ISO 21068‑1 and ISO 8656‑1; LOD/LOI guidance (ISO 21068‑2); duplicate fusions recommended; blank fluxes and calibration checks essential to manage matrix effects and mass‑absorption corrections.
- Analytical considerations: Potential exothermic reactions, protective flux strategies, use of TGA/DTA to select LOI temperature, XRD recommended to characterise mineralogy and support XRF interpretation.
Practical applications and users
- Quality control and production testing in the refractories, advanced ceramics and silicon carbide manufacturing sectors.
- Analytical and materials laboratories performing XRF chemical analysis of SiC raw materials, refractory products and related reduced‑material alloys.
- R&D groups needing reproducible fused bead preparation for calibration, method development or inter‑laboratory comparison.
Related standards
- ISO 12677 - Chemical analysis by XRF (fused cast‑bead method).
- ISO 21068‑1 / ISO 21068‑2 - Sample preparation and determination of LOI/total carbon for SiC‑containing materials.
- ISO 8656‑1 - Sampling of raw materials and unshaped refractory products.
Keywords: ISO 16169:2018, fused cast‑bead, silicon carbide, XRF, lithium tetraborate flux, loss on ignition, sample preparation, refractory analysis, ISO 12677.