ISO 23738:2021 Fine ceramics (advanced ceramics, advanced technical ceramics) — Measurement method of spectral reflectance of fine ceramic thin films under humid conditions.
4 Principle Fine ceramic thin films sometimes possess a voided micro columnar structure. Due to this structure, moisture in the air is adsorbed onto the surfaces of columns with voids between them. The quantity of adsorbed water is affected by the hydrostatic vapour pressure and temperature in the environment. Depending on the quantity of water that is adsorbed, the refractive index of a thin film changes, resulting in a change in its spectral reflectance. To evaluate what effects the adsorption of water on the surface of voids in fine ceramic thin films has on the spectral reflectance of thin films, it is necessary to measure the optical properties under a vacuum, a high-humidity environment and a low-humidity environment. Comparing the results measured under a vacuum, a high-humidity environment and a low-humidity environment facilitates an evaluation of changes in the spectral reflectance due to the environmental humidity.
5 Measurement room ambient environment
The tests shall be carried out in a measurement laboratory under a room atmosphere in which the temperature and humidity changes are negligible. In particular, to prevent the condensation of water in the environmental mini-chamber, the ambient temperature shall be controlled to restrict it to a certain range.
a) Measurement room temperature: (23 ± 2) °C.
b) Measurement room relative humidity: below 70 %.
7 Measuring apparatus 7.1 Apparatus configuration a) Spectrophotometer: an instrument that utilizes a double-beam method with a wavelength accuracy of ±0,2 nm or less in UV-visible light and ±1,0 nm or less in the near-infrared domain. The repeatability of the wavelength setting is ±0,1 nm or less in UV-visible light and ±0,5 nm or less in the near-infrared domain, with a desirable measurement range of 300 nm to 2 500 nm. The use of a double-beam spectrophotometer is strongly recommended. However, the use of an integrating sphere is not mandatory. b) Environmental mini-chamber: an airtight container that maintains test pieces under a vacuum, a high-humidity environment and a low-humidity environment for the measurement of the spectral reflectance under each condition. The chamber consists of an optical feedthrough that comprises a transparent quartz glass plate, a backside window, and two valves for the inlet of environmental air and evacuation. A test piece is fixed inside the chamber for the measurement of light reflectance. It is necessary to confirm that there is no vacuum leak from the chamber when the valves are closed. The spectrometry device configuration is shown in Figure 1. An example of the blueprint is shown in Annex A.ISO 23738 pdf download.