Effect of P2O5 content in two series of soda lime phosphosilicate glasses on structure and properties – Part II: Physical properties

The effect of the variation in phosphate (P2O5) content on the properties of two series of bioactive glasses in the quaternary system SiO2–Na2O–CaO–P2O5 was studied. The first series (I) was a simple substitution of P2O5 for SiO2 keeping the Na2O:CaO ratio fixed (1:0.87). The second series (II) was designed to ensure charge neutrality in the orthophosphate (PO43-), therefore as P2O5 was added the Na2O and CaO content was varied to provide sufficient Na+ and Ca2+ cations to charge balance the orthophosphate present. Network connectivity’s of the glasses were calculated, and densities and thermal expansion coefficients predicted using the Appen and Doweidar models, respectively. Theoretical densities were measured using the Archimedes principle. Characteristic temperatures, namely the glass transition temperature, Tg, and crystallization temperatures, Tx, were obtained using differential analysis (DTA). Two crystallization exotherms were observed for both glass series (Txi and Txii). Both Tg and Tx decreased with P2O5 addition for both series. The working range of the glasses, Tx–Tg was shown to increase to a maximum at around 4 mol% P2O5 then decrease at higher P2O5 contents for both series. Thermal expansion coefficients were measured using dilatometry increasing with P2O5 addition and showed good agreement with the Appen values. Dilatometric softening points, Ts, were also measured, which increased with P2O5 addition. X-ray diffraction (XRD) was performed on the glasses to confirm their amorphous nature. The glass containing 9.25 mol% P2O5 from series I exhibited well-defined peaks on the XRD trace, indicating the presence of a crystalline phase.