Structure and microstructure of the glasses from NaCaPO4-SiO2 and NaCaPO4-SiO2-AlPO4 systems

Structure and microstructure of silico-phosphate glasses belong to NaXPO4-SiO2 and NaXPO4-SiO2-AlPO4 (where X = Ca or/and Mg) systems were investigated. Scanning electron microscopic studies combined with EDX were made it possible to show the occurrence of phase separation in the obtained materials. It was found that alumina has a homogenising effect on the microstructure of silico-phosphate glasses. Addition of a small amount of alumina (5 mol. % of AlPO4) causes the chemical compositions inversion of the matrix and the inclusions. Structural investigations of the obtained glasses as well as of the corresponding crystalline materials showed that the studied glasses exhibit domain composition. Structure of the domains is close to that of the corresponding crystalline phases. Spectroscopic investigations involving spectra decomposition into component bands were made it possible to establish the homogenising effect of aluminium on the structure of silicate-phosphate glasses. Presence of alumina leads to elimination of PO bonds as well as replacement of Si-O-P by the Al-O-P ones.