The Effects of Silicon Oxide on the Structure, Physical Chemistry Properties, and Bioactivity of Phosphate Glasses Containing Sodium, Strontium, and Titanium Oxides

Glasses with molar compositions 40Na2O - 10SrO - (20-x)TiO2 - xSiO2 - 30P2O5 (0 ≤ x ≤ 10), corresponding to the chemical formula Na4Sr0.5Ti(1-y)Siy(PO4)3 ( 0 ≤ y ≤ 0.5) with O/P = 4, have been prepared by the classical melt - quenching technique and structurally characterized by XRD, DSC, FTIR, Raman, NMR and density measurements. The introduction of SiO2 in the phosphate glass weakens slightly the glass network, as shown by the low increase of the molar volume (VM) and the decrease of the glass transition temperature (Tg). This behaviour is due to the existence of more ionic P-O-Si bonds than the P-O-P bonds. Spectroscopy studies reveal that SiO2 behaves as network former like P2O5 oxide and the glass structure contains P-O, P-O-P, Si-O, Si-O-Si, Ti-O, Ti-O-Ti, P-O-Ti and P-O-Si linkages. The preliminary results of the in vitro bioactivity tests show the existence of ionic exchanges between the SBF solution and the studied glasses. X-ray powder diffraction and FTIR spectroscopy confirmed the formation of Ca-P layer on the surfaces of the tested compositions.