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

Abstract

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 °C and some of them, depending on the composition, retain their amorphous structure up to 600 and 800 °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.