Devitrification studies of wollastonite–tricalcium phosphate eutectic glass

The present paper describes and discusses the devitrification and crystallization process of wollastonite–tricalcium phosphate (W–TCP) eutectic glass. This process was studied in situ from room temperature up to 1375 °C, by neutron diffractometry in vacuum. The data obtained were combined and compared with those performed in ambient atmosphere by differential thermal analysis and with those of samples fired in air at selected temperatures, and then cooled down and subsequently studied by laboratory XRD and field emission scanning electron microscopy fitted with energy X-ray dispersive spectroscopy. The experimental evidence indicates that the devitrification of W–TCP eutectic glass begins at ∼870 °C with the crystallization of a Ca-deficient apatite phase, followed by wollastonite-2M (CaSiO3) crystallization at ∼1006 °C. At 1375 °C, the bio-glass-ceramic is composed of quasi-rounded colonies formed by a homogeneous mixture of pseudowollastonite (CaSiO3) and α-tricalcium phosphate (Ca3(PO4)2). This microstructure corresponds to irregular eutectic structures. It was also found that it is possible to obtain from the eutectic composition of the wollastonite–tricalcium phosphate binary system a wide range of bio-glass-ceramics, with different crystalline phases present, through appropriate design of thermal treatments.