Phase evolution and microstructure analysis of CaZrTi2O7 zirconolite in glass

The internal crystallization of CaZrTi2O7 zirconolite in a sodium alumino-borosilicate glass has been investigated with powder X-ray diffraction (XRD), scanning electron microscopy and energy dispersion spectroscopy (SEM-EDS), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) techniques. The samples have been prepared using a soft chemistry route and ceramic phase evolution has been observed with sintering time. Zirconolite as the dominant phase at 1 h sintering gradually changes to baddeleyite structured materials for longer sintering times. XRD shows that one dominant phase belongs to zirconolite at 3 h sintering, however, SEM-EDS reveals that the dominant ceramic phase is actually baddeleyite phase, which is enclosed by zirconolite phase. TEM and SAED patterns also confirm the crystallization of zirconolite phase in glass. The addition of CaO enhances the formation of zirconolite (i.e. impedes baddeleyite phase) with CaO to glass weight ratio ≤ 35:100.