Materials for reflective coatings of window glass applications

Special glass with reflective coatings has found wide applications in architecture. Thin coatings deposited on glass panes modulate the glass optical properties. Some of the coatings operate as a mirror for long-wave infrared radiation of building interiors. The thin films have high transmittance in visible range and very high reflectance in long-wave infrared range. These coatings limit absorption of infrared radiation in the glass. They have low emissivity. It means radiation heat losses of the coated glazing are reduced. The design of coatings for window glazing applications should be based on the study of optical spectral properties of glass and thin film materials. Optical properties of thin films are determined by spectral characteristics as reflectance, transmittance and absorptance for wavelength in a defined spectral range. Visible and long-wave infrared ranges are important for architectural glass. The article presents results of a study focused on the selection of convenient materials for thin reflective films and optimisation of their composition in coatings. Data from spectral measurements of transmittance and reflectance of selected types of architectural glass were compared with spectral characteristics of the designed coated glass simulated and optimised in the computer program FILM*CALC. The experimental vacuum deposition of the designed thin reflective coating on the glass substrate was carried out and spectrally measured. Apart from the spectral measurements the effect of the special glass reflectance was thermally evaluated in a testing box with the temperature sensor. Results from experiments, computer simulations and spectral measurements brought design recommendations for the optimised composition of thin infrared reflective coatings for window glazing applications.