Thermal properties, viscosities and densities of (50-x)Na2O-xCaO-50P2O5 glasses

Phosphate based glasses (PBG) are currently of huge interest in the biomaterials field and findings have shown that their durability can be increased by doping with selected metal cations. In this study various compositions in the system (50-x)Na2O-xCaO-50P(2)O(5) glasses, 0 <= x5 <= 50, were investigated to determine their characteristic temperatures (glass transition temperature (T-g), onset and peak temperatures of crystallisation (T-x and T-p), melting point and liquidus temperature (T-m and T-L)), and also the temperature dependence of viscosity and density. The glass compositions were confirmed via EDX and the amorphous nature of the glasses was confirmed via XRD. T-g increased with increasing CaO mol% from 280 +/- 0.5 degrees C to 521 +/- 0.1 degrees C. The temperature dependence of viscosity revealed an increase in the temperature window for extrusion (from 26 +/- 0.66 degrees C to 42 +/- 0.31 degrees C) and fibre drawing (from 363 +/- 1.0 degrees C to 539 +/- 0.9 degrees C). The density was also seen to increase from 2.5 to 2.64 gm'. The increases in properties were attributed to the crosslinking of Ca2+ cations between phosphate chains which strengthened the glass network. For x.20 mol% the activation energy for viscous flow is affected by the phosphate chain length. For 30 >= x >= 50 mol% the crosslinking effect of Ca2+ counters the effect of decreasing chain length, resulting in increasing activation energy for viscous flow.