Influence of Fe2O3 on the structure and near-infrared emissivity of aluminosilicate glass coatings

The present paper reports on the development of a vitreous material with high near-infrared (NIR) emissivity. Silica-based glasses (SiO2, Na2O, Al2O3, K2O) with different Fe2O3 (hematite) contents are deposited on ceramic tiles as coatings and annealed at 1250 degrees C. Using the indirect radiometric measurement method, the emissivity of the materials was determined at room temperature, where the spectral directional reflectance of the coatings was measured. The samples possessing high emissivity values of 0.78-0.80 in the near-infrared are those with the highest Fe2O3 contents. Colorimetric test (L*a*b*), has revealed that the glass coating goes darker red by adding more amount of Fe2O3. XRD analysis has shown the magnetite, hematite, and nepheline crystallization phases in the glasses with Fe2O3 contents above 30 wt%. Readable aspects of FTIR absorbance spectra were found, which gave information about the structure variations of these glasses as a function of Fe2O3 content, also, SEM photographs displayed morphology of the prepared glass coatings.