Density–structure correlations in Na2O–CaO–P2O5–SiO2 bioactive glasses

Relations for Na2O–CaO–SiO2 glasses have been developed to calculate the density of Na2O–CaO–P2O5–SiO2 bioactive glasses. The calculation makes use of NMR results of O’Donnell et al. indicating that P2O5 forms a separate phase, containing Na3PO4 and Ca3(PO4)2, in the investigated glasses. The volume of the silicate units is the same as that found in Na2O–CaO–SiO2, Na2O–SiO2, and CaO–SiO2 glasses. Similarly, the volume of PO4 units is equivalent to that in Na3PO4 and Ca3(PO4)2. Calculated densities are consistent with the experimental data.