Eggshell powder-derived calcium sodium borosilicate-based glass coating production: characterization and coating performance

Eggshells (ES) have economic importance due to organic (3–4%wt.) and inorganic (96–97%wt.) such as Calcite (CaCO₃) content, leading to alternative calcium oxide (CaO) sources for the glass and ceramic industry. Experiments began with the grinding and calcination of eggshells. After obtaining eggshell powders (ESP), two precursor glasses (PGs) were prepared from different CaO sources; CaCO₃ which is an industrial CaO source, and calcined eggshell powder (C-ESP). The batches were melted at 1200 °C for 1 h. The PGs were applied on low-carbon steel plates by the wet spray method and fired at 760 °C for 4 min. The samples were characterized for their chemical composition, phase formation, thermal features, and microstructure by XRF, XRD, TG-DSC, and SEM-EDS analysis. The color and brightness values, surface roughness, and morphology of the coatings were examined. Finally, phase formation was examined in the controlled crystallization of the precursor glasses, and calcium fluoride (CaF₂) phase formation was observed in both types of glass. The chemical and thermal properties of the precursor glasses and the final properties of the coated products from the two sources showed consistent results. It was shown that utilizing calcined ESP as a CaO source is appropriate for producing industrial glass-ceramic coatings.