Phase composition, structure, and hydrolytic durability of glasses in the Na2O-Al2O3-(Fe2O3)-P2O5 system at replacement of Al2O3 by Fe2O3

Abstract

Samples of sodium aluminum iron phosphate glasses of the composition (mol %) 40 Na2O, (20 − x) Al2O3, x Fe2O3, 40 P2O5 (series I) and 35 Na2O, (20 − x) Al2O3, x Fe2O3, 45 P2O5 (series II) were synthesized. The phase composition and structure of the samples obtained were determined by X-ray diffraction and IR spectroscopy. At equimolar replacement of Al2O3 by Fe2O3, the structure of the quenched glasses of series I does not change appreciably, in contrast to glasses of series II. Annealing of the glasses leads to their partial devitrification with segregation of crystalline aluminum iron phosphate phases. Glasses of series I with up to 10 mol % Al2O3 replaced by Fe2O3 exhibit the highest hydrolytic durability: The leach rates of Na, Al, Fe, and P from the samples are within (4–10) × 10−8 g cm−2 day−1, meeting the requirements of GOST (State Standard) R 50 926-96. Thus, glasses with approximately equal molar concentrations of Al2O3 and Fe2O3 are the most resistant to crystallization and hydrolysis.