Overview
ISO 19618:2025 specifies a standardized laboratory method for determining normal spectral emissivity and normal quasi‑total emissivity of fine ceramics and ceramic matrix composites using a blackbody reference and a Fourier transform infrared (FTIR) spectrometer at elevated temperatures. The method applies to opaque, highly non‑reflective materials in the wavelength range 1.67 μm to 25 μm and an approximate temperature range of 350 K to 1 100 K. Measurements are made by directly comparing the specimen’s infrared radiance spectrum to that of a traceable blackbody under controlled conditions.
Key topics and technical requirements
- Measurement principle: Direct comparison of specimen and blackbody radiance with an FTIR interferometer; emissivity derived from spectral radiance ratios and numerical integration (normal quasi‑total emissivity).
- Instrument and environment:
- FTIR with external optical path and Michelson interferometer; optical path purged with dry N2 or dry air (dew point < 220 K) or evacuated.
- Spectral resolution requirement (documented) and acquisition/integration counts (e.g., >100 acquisitions).
- Wavelength (wavenumber) calibration using a polystyrene calibration film.
- Reference blackbody: Total emissivity > 0.95 and aperture > 3× the FTIR measurement spot area; traceable to SI units.
- Specimen heating and temperature control: Heating devices (resistance, heat‑pipe, heat‑transfer media) with specimen temperature control to within ±3 K over the measurement area.
- Temperature sensors: Thermocouples per IEC 60584‑2 or platinum RTDs per IEC 60751; minimal sensor diameter to reduce conduction artifacts; sensor attached by bonding or embedded methods.
- Specimen geometry and preparation: Plain plates, area > 3× measurement spot, typical thickness 2–6 mm, lateral dimensions 10–50 mm; flat smooth back face for good thermal contact; document machining parameters and thermal history.
- Quality checks: Linearity and stability verification, background radiance measurement (gold‑coated mirror, reflectivity > 0.95), system validation and test reporting as required by Clauses 7–11.
Applications and who uses it
- Materials scientists and research laboratories measuring infrared emissivity of advanced ceramics.
- Ceramic manufacturers and quality‑control labs validating thermal‑radiative properties for high‑temperature components.
- Engineering teams in aerospace, power generation, automotive, and defense assessing coating and composite performance at elevated temperatures.
- Metrology and calibration labs establishing traceable emissivity datasets for thermal modeling and infrared thermography.
Related standards
- IEC 60584‑2 (thermocouple tolerances)
- IEC 60751 (industrial platinum resistance thermometers)
- ISO 19618:2025 aligns emissivity measurement practice with SI‑traceable blackbody reference methodology.
Keywords: ISO 19618:2025, normal spectral emissivity, FTIR spectrometer, blackbody reference, fine ceramics, ceramic matrix composites, emissivity measurement, infrared spectrometer, elevated temperatures.