Abstract:
Glass-ceramics belonging to SiO
2-Na
2O-B
2O
3-BaO-CaO-ZrO
2-TiO
2 system were prepared by a melting-heat treatment method. The differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to research the effects of the CaO content (CaO, TiO
2 and ZrO
2 mole ratio is
x∶2∶1,
x=0.5-6) on crystalline phases and microstructure of samples when the concentration of nucleating agents (CaO, TiO
2 and ZrO
2) is 45%. The leaching resistance of zirconolite-barium borosilicate glass-ceramics of C
2 (
x=2) was characterized by product consistency test (PCT). The results show that the glass network structure is mainly formed of SiO
4, BO
3 and BO
4, the increase of calcium concentration leads to more B ions exist in the form of BO
4 tetrahedral units in the glass network. The glass transition temperature
Tg gradually increases and the exothermic peak temperature gradually decreases while the strength of exothermic peak increases with the CaO content. The other crystalline phase (ie. TiO
2 and ZrO
2) forms in addition to CaZrTi
2O
7 phase with
x<2 while only CaZrTi
2O
7 phase forms with
x=2 and 4. The stellate CaZrTi
2O
7 and columnar CaTiO
3 phases are observed for the sample with
x=6. The PCT experiment of glass-ceramics shows that the normalized leaching rates of B, Na and Ca gradually decrease with increasing leaching time and remain almost unchanged after 28 d, about 8.4, 7.8, 2.2 mg/(m
2•d), respectively, which are the same order of magnitude of borosilicate glass waste.