Structural analysis and thermal behavior of diopside–fluorapatite–wollastonite-based glasses and glass–ceramics

Glass–ceramics in the diopside (CaMgSi2O6)–fluorapatite (Ca5(PO4)3F)–wollastonite (CaSiO3) system are potential candidates for restorative dental and bone implant materials. The present study describes the influence of varying SiO2/CaO and CaF2/P2O5 molar ratio on the structure and thermal behavior of glass compositions in the CaO–MgO–SiO2–P2O5–Na2O–CaF2 system. The structural features and properties of the glasses were investigated by nuclear magnetic resonance (NMR), infrared spectroscopy, density measurements and dilatometry. Sintering and crystallization behavior of the glass powders were studied by hot-stage microscopy and differential thermal analysis, respectively. The microstructure and crystalline phase assemblage in the sintered glass powder compacts were studied under non-isothermal heating conditions at 825 °C. X-ray diffraction studies combined with the Rietveld-reference intensity ratio (R.I.R) method were employed to quantify the amount of amorphous and crystalline phases in the glass–ceramics, while scanning electron microscopy was used to shed some light on the microstructure of resultant glass–ceramics. An increase in CaO/SiO2 ratio degraded the sinterability of the glass powder compacts, resulting in the formation of akermanite as the major crystalline phase. On the other hand, an increase in P2O5/CaF2 ratio improved the sintering behavior of the glass–ceramics, while varying the amount of crystalline phases, i.e. diopside, fluorapatite and wollastonite.