Overview
ISO/TS 23690:2023 - Nanotechnologies - Multiwall carbon nanotubes - Determination of carbon impurity content by thermogravimetric analysis (TGA) specifies a mild oxidation TGA method to quantify carbon impurities (amorphous carbon and other non‑CNT carbon species) that are less thermally stable than multiwall carbon nanotubes (MWCNTs). The procedure uses a carbon dioxide (CO2) atmosphere to selectively oxidize impurities prior to MWCNT oxidation, enabling quantitative purity assessment for MWCNTs produced by chemical vapour deposition (CVD).
Key topics and technical requirements
- Principle: TGA/DTG exploits different reactivities of carbon impurities and MWCNTs in CO2; oxidation of impurities is endothermic and helps separate mass‑loss stages.
- Scope limits: Applicable primarily to CVD‑prepared MWCNTs and to samples showing a single‑stage TG curve; not for functionalized MWCNTs or samples containing encapsulants.
- Sample preparation: Dry at 150 °C for 2 h in a vacuum drying furnace, cool in a desiccator before analysis.
- Apparatus & reagents:
- Thermogravimetric analyser capable up to 1 000 °C, balance sensitivity ≤1 μg, temperature controller ≤0.01 °C.
- Crucibles: alumina, platinum, quartz, etc.
- High‑purity gases: inert (N2 or Ar) and CO2, both ≥99.999 % purity.
- Typical test conditions:
- Sample mass: ~3–5 mg.
- Recommended heating rate: 10 °C·min⁻¹ (instrument range 1–50 °C·min⁻¹).
- Gas flows: inert 10–20 ml·min⁻¹; CO2 20–40 ml·min⁻¹.
- Baseline correction using empty crucibles; pre‑flow stabilization ≥15 min.
- Data analysis: Determine mass percentage at 300 °C (w300) and at the extrapolated onset temperature Te of MWCNT oxidation (we); carbon impurity content = w300 − we. Guidance on TG/DTG curve analysis, repeatability and reproducibility is included.
- Quality control: Calibration per manufacturer, triple repeat measurements, and measurement uncertainty evaluation (Type A and B) are specified.
Applications and users
ISO/TS 23690:2023 is intended for:
- MWCNT manufacturers performing quality control and purity specification.
- Analytical laboratories and research groups characterizing CNT samples by thermogravimetric analysis (TGA).
- Regulatory bodies and product developers needing standardized purity metrics for nanomaterials.
- R&D teams optimizing CVD production and post‑treatment processes.
Practical benefits include reproducible quantification of non‑CNT carbon content to support product specifications, batch release testing, process optimization, and materials comparison.
Related standards and further reading
- Terminology and definitions referenced from ISO/TS 80004‑3 (nanotechnology - carbon nanotube terminology).
- ISO/TS 23690 contains informative annexes with repeatability/reproducibility case studies and detailed TG curve analysis guidance to aid implementation.