Combined sodium and fluorine promote diopside continuous growth to achieve one-step crystallization in CaO-Al2O-SiO2-Fe2O3 glass-ceramics

In CaO-Al2O-SiO2-Fe2O3 (CASF) glass-ceramics, a dense silicon and aluminum tetrahedral network barrier layer is formed around the diopside nucleus, which hinders the continuous growth of the crystal. In this work, the continuous growth of the diopside crystals was achieved by introducing sodium and fluorine. A combination of FTIR, XRD, SEM and EDS were used to analyze the evolution mechanism of the precursor glass network structure and the growth process of the diopside. The modification mechanism of sodium and fluorine action on the glassy structure was revealed by Si-29 NMR. The results showed that sodium and fluorine can selectively destroy the [SiO4]/[AlO4] network structure. The Ca2+ diffusion channels formed around diopside, which facilitated the continuous growth of the crystals. The diopside crystals can grow to an expected size, approximately 1 mu m, when the value of NBO/T reaches 1.44.