Structure and microstructure of glasses from a NaCaPO4–SiO2–BPO4 system

The present investigations are devoted to silicate–phosphate glasses of the NaCaPO4–SiO2–BPO4 system. Glasses belonging to this system are characterized by a glass phase separation phenomenon, i.e. occurrence of spherical amorphous inclusions dispersed in an amorphous matrix, which have been detected by SEM. SEM investigation has also shown that the introduction of boron ions into the structure of silicate–phosphate glasses leads to homogenization of their microstructure. Based on EDX analyses, it has been found that the introduction of boron ions results in an inversion of the matrix and chemical composition of inclusions. Structural investigations (middle infrared spectroscopy – MIR) of the obtained glasses as well as of the corresponding crystalline materials have shown that the glasses studied exhibit a domain composition. The structure of the domains is close to that of the corresponding crystalline phases. Spectroscopic investigations involving spectra decomposition into component bands have made it possible to establish the homogenising effect of boron ions on the structure of silicate–phosphate glasses.11B MAS NMR research revealed that in the structure of the NaCaPO4–SiO2–BPO4 silicate–phosphate glasses boron ions show coordination numbers of 3 and 4. 29Si MAS NMR studies have shown the total separation of silicate and sodium–calcium–phosphate phases.