The role of TiO2, ZrO2, BaO and SiO2 on the mechanical properties and crystallization behavior of fluorapatite–mullite glass–ceramics

The effect of TiO2, ZrO2, BaO and extra addition of silica on the crystallization behavior, microstructure and mechanical properties of an apatite–mullite based glass–ceramic system were investigated by means of X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The precipitated crystalline phases were fluorapatite [Ca10(PO4)6F2] and mullite [Al6Si2O13], which apart from the extra bearing SiO2 specimen were rod-like in the other specimens. The rod-like crystalline phasesʹ lengths were small, i.e. < 20 μm, in the TiO2 and BaO containing glass–ceramics, but small addition of ZrO2 enhanced the length of crystalline phases to approximately 50 μm. The flexural strength and fracture toughness of the prepared glasses and glass–ceramics were also studied. The results showed that the additive oxides affected both parameters differently. The highest fracture strength and fracture toughness values belonged to the TiO2 and BaO containing glass–ceramics which contained smaller crystal size. The mechanical properties of the prepared glass–ceramic samples did not differ strongly and/or were even decreased by addition of ZrO2 and extra amount of SiO2.