Zinc addition to sodium-calcium-silicate bioglasses. Theoretical vs experimental results

The glass composition Na2O•CaO•2SiO2 was modified upon addition of ZnO to obtain the series of glasses Na2O•CaO•(2-x)SiO2•xZnO (x=0.15 and 0.19), where x= 0.19 is the maximum zinc content which does not produce phase separation. The glasses were investigated by means of density and thermal measurements (glass transition, Tg, and crystallisation, Tc, temperature); moreover the phases separated upon crystallisation were identified. The results of molecular dynamics (MD) simulations combined with the analysis of the crystal structure of the main phases separated [(Na4Ca4(SiO3)6 and Na2ZnSiO4)] provide insight into the structural role of zinc in the glass network, its limits of solubility and its effect on the short- and medium-range order of the glass structure.