Overview
ISO 23738:2021 specifies a standardized measurement method for the spectral reflectance of fine ceramic thin films under humid conditions. It defines procedures to measure how humidity alters the optical reflectance of advanced/technical ceramic coatings using a general-purpose spectrophotometer and an environmental mini‑chamber. The standard supports repeatable evaluation of humidity‑induced refractive index and reflectance changes caused by water adsorption in voided thin‑film structures.
Key topics and technical requirements
- Scope: Measurement of spectral reflectance of single- or multi‑layer fine ceramic thin films in environments with variable relative humidity.
- Measurement environment: Room ambient control (23 ± 2 °C; RH < 70 %) to avoid condensation around the mini‑chamber.
- Apparatus configuration:
- Spectrophotometer: Double‑beam recommended; wavelength accuracy ±0.2 nm (UV‑vis) and ±1.0 nm (NIR); repeatability ±0.1 nm (UV‑vis) and ±0.5 nm (NIR); desirable 300–2 500 nm range.
- Environmental mini‑chamber: Airtight chamber with quartz window, inlet/evacuation valves and feedthroughs to maintain vacuum, high and low humidity without removing the specimen.
- Vacuum pump: Ultimate pressure < 40 Pa.
- Temperature/humidity chamber: Controls sample RH to specified levels (recommended 23 ± 2 °C with 40 % and 80 % RH test points).
- Control procedures:
- Vacuum: evacuate mini‑chamber ≥ 30 min.
- High humidity: expose at (23 ± 2) °C and (80 ± 2) % RH for ~20 min.
- Low humidity: expose at (23 ± 2) °C and (40 ± 2) % RH for ~20 min.
- Measurement settings:
- Wavelength interval 0.2 nm; incidence angle ~5°.
- Scanning speed: < 120 nm/min for < 850 nm; < 150 nm/min for > 850 nm.
- Calibration:
- Wavelength calibration using optical glass filters.
- Baseline correction to set 100 % reflectance (without mini‑chamber).
- Definitions: Terms such as spectral reflectance, environmental mini‑chamber, half‑maximum reflectance wavelength, monochromator and integrating sphere are specified.
Applications and users
- Practical applications:
- Evaluation of anti‑reflective coatings, infrared and X‑ray sensor cut filters, band‑pass filters and other optical components made from fine ceramics.
- Reliability testing for humidity sensitivity of optical thin films used in sensors, imaging, optics and photonics.
- Who should use it:
- Optical engineers, materials scientists, thin‑film manufacturers, quality assurance and calibration laboratories, R&D teams and test houses performing humidity‑dependent optical characterization.
Related standards
- ISO 17861 - spectral transmittance of fine ceramic thin films under humid conditions
- ISO 9211 - optical coatings
- ISO 8980‑3 - ophthalmic optics transmittance test methods
Keywords: ISO 23738:2021, fine ceramics, spectral reflectance, thin films, humid conditions, spectrophotometer, environmental mini‑chamber, measurement method.