Phase separation in the glasses of the (8-x)Na2O • xFe2O3 • 22B2O3 • 70SiO2 system

Glasses with the (8-x)Na2O center dot xFe(2)O(3) a (TM) 22B(2)O(3) a (TM) 70SiO(2) compositions, where the Fe2O3 content varies from 2 to 6 mol %, which were heat-treated at the temperatures of 550 and 700A degrees D for 144 and 2 h, respectively, have been studied by dilatometry, electron microscopy, and X-ray powder diffractometry. It has been shown that, with an increase in the total concentration of Fe2O3 in the glass, there is a trend to the transition from an interconnected to a droplet-matrix phase-separated structure. The crystal line phases of Fe3O4, FeSiO3, and beta-Fe2O3 are formed depending on composition, while the latter is observed only in the glass with the equivalent contents of Na2O and Fe2O3. There is a minimum on the glass transition temperature dependence of the composition at equimolar (4 mol %) contents of Na2O and Fe2O3.