THERMAL-BEHAVIOR OF BIOACTIVE ALKALINE-EARTH SILICOPHOSPHATE GLASSES

The thermal behaviour (sinterability and first crystallization) of a series of alkaline-earth silicophosphate glasses has been studied by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The samples were prepared from a base bioactive glass of the system CaO-P2O5-SiO2-CaF2, by (a) slightly changing the F/O ratio; (b) replacing part of the CaO by SrO or MgO; and (c) increasing the total alkaline earth concentration by MgO additions. The results show that the addition of MgO is the most effective way of improving sinterability. In these samples, a decrease of the glass transition temperature, together with an increase in the temperature of the first crystallization, is observed. The difference between both temperatures is proposed to be an adequate indicator of the sinterability. The initial stages of the first crystallization (which produces an oxo-fluorapatite), and its composition dependence, are discussed in terms of the results of sinterability, and the classical theory of nucleation.