Strontium containing bioactive glasses: Glass structure and physical properties

The influence of substituting strontium for calcium in the following glass series 49.46 SiO2–1.07 P2O5–(23.08-X) CaO–X SrO–26.38 Na2O was studied on the physical properties. Solid state nuclear magnetic resonance and vibrational spectroscopy showed that the glasses were predominantly composed of Q2 silicate chains. Addition of strontium did not result in any structural alteration of the glass network due to the similar role of SrO compared with that of CaO. The density increased with strontium content whilst the oxygen density decreased indicating a more expanded glass network. The glass transition temperature reduced with strontium substitution in a linear fashion and there was no evidence of a mixed alkaline earth effect with a lower than expected glass transition temperature. Dilatometric softening points also reduced with increasing strontium content, whilst the thermal expansion coefficients increased. The results are consistent with a weaker network as a result of the lower charge to size ratio of Sr2+ compared to Ca2+.