Sol-gel synthesis of the P2O5-CaO-Na2O-SiO2 system as a novel bioresorbable glass

A series of phosphate-based sol-gel glasses in the system P2O5-CaO-Na2O-SiO2 were synthesised using PO(OH)(3-x)(OC2H5)(x) (x = 1, 2) as a phosphorus precursor and alkoxides of sodium, calcium and silicon in an ethylene glycol solution. It has been found that the upper limit for gel formation is about 22 mol% phosphorus and that the gelation time increases with increasing phosphorus content of the sol. X-ray diffraction (XRD) along with X-ray fluorescence chemical analysis (XRF) have been performed on samples containing 45 mol% of P2O5 and 0, 10, 15 and 25 mol% of SiO2 with varying amount of modifier oxides (CaO, Na2O). All the samples are predominantly amorphous up to 400 degrees C and some of them, depending on the composition, retain their amorphous structure up to 600 and 800 degrees C. To the knowledge of the authors, this is the first time that phosphate-based glasses having these compositions have successfully been synthesised via the sol-gel method.