Phase transitions in single phase Si–Ca–P-based ceramic under thermal treatment

The influence of thermal treatment on phase transformations of Si–Ca–P (Nurse's Ass) single phase ceramic was investigated. The results showed that the phase evolution during the synthesis of ceramic was influenced by the type of raw materials used. While annealing within the 1000–1500 °C range for 2 h, the interdiffusion of silica and phosphorous took place. Different polymorphs appeared at lower temperatures than that observed in pure compounds, and different intermediate phases also appeared in the samples. The obtained results allowed us to conclude that the formation of a single phase ceramic with a Ca2SiO4/Ca3(PO4)2 molar ratio equal to 2/1 is a complex slow process. In order to optimise the synthesis conditions, two-step synthesis conditions were used: firstly, heating at 1550 °C/3 h then liquid-nitrogen was quenched, ground and pressed; secondly, heating at 1300 °C/3 h and subsequent annealing at 1200 °C for 24 h.