Effect of sintering time on crystallization, densification and in-vitro characteristics of bioactive glass ceramics

In order to improve the chemical stability and modify the biodegradability of bio-glass ceramics materials for certain applications, a correlation between structural and biological properties of bio-glass ceramics is very essential and these properties are found to be greatly dependent on the composition and synthetic parameters of the material. In the present work, an attempt has been made to study the effect of sintering time on crystallization, densification and invitro properties of a new glass ceramics system. For that purpose, glass of the composition (% wt) (34SiO2-46CaO14.5P2O5-4Na2O-1CaF2-.5MgF2) was prepared by melting the thoroughly mixed powders of the ingredients in muffle furnace and then quenching the melt in water. Sintering was carried out at 1000 C, in accordance with the average of three exothermal peaks of differential thermal analysis (DTA), for three different time intervals 5h, 10h and 15 hours respectively. The main crystalline phases formed after controlled heat-treatment of the glass were hydroxyfluoroapatite (HFA), tricalcium phosphate (TCP) and wollastonite (W) respectively as conformed by the X-Ray diffraction (XRD). Scanning electron microscope, bulk density and diameter shrinkage co-efficient data illustrated that the rate of densification was higher for 5-10 hours sintering time interval than that for 10-15 hours. At 15 hours sintering time, decomposition of HFA into TCP and W was also observed. The samples were immersed in simulated body fluid (SBF) for 30 days at ambient temperature. Fourier transformation infrared spectroscopy (FTIR) and energy dispersive analysis by X-rays (EDX) revealed the presence of Hydroxycarbonate apatite (HCA) showing that the glass ceramics under investigation were bioactive and their bioactivity depends on the sintering time.