Yanhong Hu

Investigation on phase evolution of the ZnO-B2O3-SiO2 glass ceramics

ZnO-B2O3-SiO2-Al2O3-Na2O glass doped with nucleating agent TiO2 was prepared with melting-quenching method and the effect of nucleating agent on the crystallization behavior and phase evolution of this glass was investigated by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The experimental results show that the glass transition temperature and the first crystallization temperature decrease from 630 °C and 765 °C to 595 °C and 740 °C, respectively, with introduction of TiO2 into glass. There is no diffraction peaks in the XRD pattern but it is no longer transparent for the base glass without nucleating agent after heat treatment, which suggests the serious phase separation occurred, and the observation by SEM indicates that the phase separation is developed by nucleation and growth mechanism. However, there are two different crystals ZnAl2O4 and NaAlSiO4 present in the glass containing TiO2 after heat treating at 575 °C for 2 h and 740 °C for 6 h, respectively. What is interesting is that NaAlSiO4 disappears as the crystallization time at 740 °C increases from 6 h to 12 h, and more ZnAl2O4 crystal is formed, namely, the further formation of ZnAl2O4 is at cost of NaAlSiO4 with increasing crystallization time. And observation of the morphology of glass ceramics shows great difference with increasing crystallization time. Moreover, the ability of ZnO-B2O3-SiO2-Al2O3-Na2O glass ceramics against attacking of 1M HCl solution is increased by the crystals precipitated in heat treatment process.