Crystallization kinetics and microstructures of NaF-CaF_2-Al_2O_3-SiO_2 glass-ceramics
The Yb3+-doped transparent oxyfluoride glass in NaF-CaF2-Al2O3-SiO2 system was prepared by conventional melt-quenching method and the transparent oxyfluoride glass-ceramics was obtained by optimized heat treating. The influences of introducing alkali metals oxides and alkaline earth oxides on glass-forming ability were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). The crystallization mechanism of NaF-CaF2-Al2O3-SiO2 system glass was analyzed by kinetics method, and the influences of heat treating conditions on the crystallization behavior and the microstructures of this system glass-ceramic were studied. The results show that the glass-forming ability is weakened with introducing alkali metals oxides, while the crystallization stability is improved by introducing alkaline earth oxides. In addition, the main crystal phase of the glass-ceramics is CaF2 and its crystallization activation energy is 345.8 kJ/mol. The size of CaF2 grains increases with increasing crystallization temperature and the amount of crystals increases with increasing holding time. A novel transparent Yb3+-doped glass-ceramics is obtained by optimizing heat treating, in which the grain size is less than 50 nm and the crystallization degree is about 30%.