Synthesis of spherical shape borate-based bioactive glass powders prepared by ultrasonic spray pyrolysis

Abstract Spherical shape borate-based bioactive glass powders with fine size were directly prepared by high temperature spray pyrolysis. The powders prepared at temperatures between 1200 and 1400 °C had mixed phase with small amounts of fine crystal and an amorphous rich phase. Glass powders with amorphous phase were prepared at a temperature of 1500 °C. The mean size of the glass powders prepared by spray pyrolysis was 0.76 μm. The glass powders prepared at a temperature of 1200 °C had two distinct exothermic peaks ( T c 1 and T c 2 ) at temperatures of 588 and 695 °C indicating crystallization. The glass transition temperature ( T g ) of the powders prepared at a temperature of 1200 °C was 480 °C. Phase-separated crystalline phases with spherical shape were observed from the surface of the pellet sintered at a temperature of 550 °C. Crystallization of the pellet was completely occurred at temperatures of 750 and 800 °C. The pellets sintered at temperatures below 700 °C had single crystalline phase of CaNa 3 B 5 O 10 . The pellet sintered at a temperature of 800 °C had two crystalline phases of CaNa 3 B 5 O 10 and CaB 2 O 4 .