Effects of B2O3 content and sintering temperature on crystallization and microstructure of CBS glass–ceramic coatings

Abstract

Borosilicate glass–ceramics precursors with varying compositional ratios in the CaO–SiO2–B2O3 (CBS) system were synthesized by sol–gel method. The precursors were calcined at 1200°C for 2h 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 (Ec) 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 Ec values of CBS glasses and glass–ceramics were 254.1, 173.2 and 164.4kJ/mol with increasing B2O3 content, whereas that of the calcined G3 glass was 104.9kJ/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 4h.