Analysis of the structural changes of a phosphate glass during its dissolution in simulated body fluid

The structural changes of two calcium-sodium metaphosphate glasses during its dissolution in simulated body fluid (SBF) have been analyzed by Fourier transform Raman spectroscopy (FT-Raman), scanning electron microscopy (SEM) and environmental scanning electron microscopy (ESEM). The results showed that no structural changes could be detected during the first week of dissolution. However, after approximately 4 weeks of dissolution the analysis of the glass surface revealed the presence of a thin orthophosphate layer. The elemental analysis of this layer by X-ray dispersive energy showed the presence of calcium phosphate ions, while almost no sodium was detected. The observation of the glasses by ESEM showed the formation of small crystals when the water vapor pressure of the chamber was decreased. This indicates that the layer analyzed by SEM and FT-Raman was related to a hydrated calcium phosphate layer.