Effects of B ₂ O ₃ content and sintering temperature on crystallization and microstructure of CBS glass-ceramic coatings

Borosilicate glass-ceramics precursors with varying compositional ratios in the CaO-SiO ₂ -B ₂ O ₃ (CBS) system were synthesized by sol-gel method. The precursors were calcined at 1200 °C for 2 h to form glass powders. The glass-ceramics were prepared by overlaying glass slurries on the substrates before sintering at different temperatures. The as-prepared glasses and glass-ceramics were characterized by differential scanning calorimetry and X-ray diffraction. The crystallization activation energies (E _c ) were calculated using the Kissinger method from DSC results. The morphology and crystallization behavior of the glass-ceramics were monitored by scanning electron microscopy. Both glass transition and crystallization temperatures decreased, however, the metastable zone increased. The E _c values of CBS glasses and glass-ceramics were 254.1, 173.2 and 164.4 kJ/mol with increasing B ₂ O ₃ content, whereas that of the calcined G3 glass was 104.9 kJ/mol. Finally, the coatings were prepared at a low temperature (700 °C). The crystals that grew on the surface of multilayer coatings demonstrated heterogeneous surface nucleation and crystallization after heat-treatment from 700 °C to 850 °C for 4 h.