3. Results and discussion
Fig. 1 shows the XRD patterns of glass–ceramics held at 700 °C for 30 days. The XRD pattern of glass#2ZnO held at 700 °C for 24 h is also included for comparison. The crystalline phases in glass–ceramics, held at 700 °C for 30 days, include (Ca0.9Zn0.03)2(Al0.63Zn0.37)(Si0.69Al0.31)2O7 (referred to as ‘solid solution phase’), Ca2ZnSi2O7, Sr2SiO4 and Bi4B2O9; whereas, the diffraction peaks corresponding for two hardystonite phases, i.e., solid solution phase and Ca2ZnSi2O7, present in the glass#2ZnO sample held at 700 °C for 24 h. This indicates that these two hardystonite phases are primary phases in glass–ceramics.