Overview
ISO 19618:2017 specifies a laboratory measurement method for determining normal spectral emissivity and normal quasi‑total emissivity of fine ceramics (advanced/technical ceramics), ceramic matrix composites, and continuous fibre‑reinforced ceramic matrix composites. The method uses a blackbody reference and a Fourier transform infrared (FTIR) spectrometer to measure infrared radiance at elevated temperatures. It 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.
Key topics and technical requirements
- Principle: Direct comparison of specimen radiance to an internationally traceable blackbody using FTIR; spectral data are Fourier‑transformed from interferograms and integrated to obtain quasi‑total emissivity.
- Apparatus: FTIR with an external optical path, specimen heating device, blackbody furnace (total emissivity > 0.95), temperature sensors (thermocouples per IEC 60584‑2 or RTDs per IEC 60751), and a high‑reflectance mirror for background measurement.
- Measurement conditions:
- Wavelength coverage: 1.67 μm–25 μm.
- Temperature control: specimen surface controlled to within ±3 K.
- Spectral resolution: better than 16 cm⁻¹; acquisitions/integrations >100.
- Measurement spot and blackbody aperture: aperture >3× measurement spot area.
- Preparation and validation:
- Wavelength calibration using polystyrene film.
- Linearity checks using multi‑temperature blackbody ratios and neutral density filters.
- Stability verification: repeat blackbody measurements within 10 min must be within ±1%.
- System validation against literature data for standard materials (e.g., alumina).
- Calculations: Use Planck’s blackbody radiation function to compute theoretical radiance and calculate spectral and quasi‑total emissivity.
Practical applications and users
ISO 19618:2017 is intended for:
- Materials researchers and laboratories measuring high‑temperature radiative properties of advanced ceramics.
- Quality control and R&D in ceramic manufacturers and composite fabricators.
- Thermal engineers and modelling teams needing accurate emissivity inputs for radiative heat transfer simulations.
- Aerospace, power generation, and high‑temperature industrial sectors where ceramic components’ thermal emissivity affects performance and safety.
Using this standard helps ensure traceable, repeatable emissivity data for thermal design, coating evaluation, life‑prediction studies, and energy balance calculations.
Related standards and references
- IEC 60584‑2 - Thermocouples (tolerances)
- IEC 60751 - Industrial platinum resistance thermometers (RTDs)
- Planck’s blackbody radiation function (used in Annex A)
- ISO/TC 206 (Technical Committee on Fine Ceramics) - committee responsible for the standard
ISO 19618:2017 provides a robust, ISO‑consistent procedure for obtaining reliable emissivity data of fine ceramics using FTIR and blackbody referencing - essential input for accurate thermal analysis and materials characterization.