Abstract
The relationship between the composition and structure for the glasses of general composition (40-y)Na2O-yFe2O3-5Al2O3-55P2O5 (5≤y≤20), has been studied. The chemical durability and density of these glasses increase with increasing Fe2O3 content. The dissolution rate (DR), calculated from the weight loss in distilled water at 90°C for up to 20 days was ≈ 3.10−9 g/cm2/mn which is 30 times lower than that of window glass. The structure and valence states of the iron ions in the glasses were investigated using, X-ray diffraction, 57Fe Mössbauer spectrometry, potentiometric analysis, and infrared spectroscopy. Both Mössbauer spectrometry and potentiometric analysis allow to estimate both Fe2+ and Fe3+ contents in all these glasses. X-ray diffraction indicates that the local structure of iron phosphate glasses is related to the short range structures of NaFeP2O7. Infrared spectra indicate the formation of P–O–Fe bonds in the pyrophosphate glasses that replace P–O–Na bonds. The presence of a small content of Al2O3 in the glass seems to play a role as a network modifier. The addition of Fe2O3 to Al2O3 in phosphate glasses favours the enhancement of the formation of pyrophosphate units because iron ions have stronger effect on the depolymerization of metaphosphate chains than the aluminium ions. Finally, the I.R spectra indicate that the presence of P-O-Fe bands of these glasses containing more than 15 mol%Fe2O3 is consistent with their good chemical durability.
Published Version
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