The effect of inversion of matrix and inclusions composition in liquation phospho-silicate glasses

Silico-phosphate glasses of XCaPO4–SiO2 and XCaPO4–AlPO4–SiO2 (X = Na+ and/or K+) system have been the subject of the presented investigations. Glasses belonging to those systems are characterized by a liquation phenomenon—spherical amorphous inclusions dispersed in an amorphous matrix. Thorough EDX investigations have shown that introduction of aluminum ions into the structure of phospho-silicate glasses results in inversion of matrix and inclusions composition, when XCaPO4 exceeds 25–35% mol. Such a substantial influence of aluminum ions on phospho-silicate glasses texture as well as matrix and inclusions composition (inversion) must be a result of structural changes.27Al MAS NMR research stated that aluminum ions in structures of XCaPO4–AlPO4–SiO2 phospho-silicate glasses always acts as a glass-forming ion–i.e. aluminum always occupies fourfold coordinated sites.23Na and 31P MAS NMR research has shown that the inversion of matrix and inclusions composition, brought about by introduction of aluminum ions into the structure of phospho-silicate glasses, is an outcome of a change in phosphorous and alkaline ions coordination.