Chemical durability and structure of zinc–iron phosphate glasses

The chemical durability of zinc–iron phosphate glasses with the general composition (40−x)ZnO–xFe2O3–60P2O5 has been measured. The chemical durability and density of these glasses increase with increasing Fe2O3 content. Glasses containing more than 30 mol% Fe2O3 had an excellent chemical durability. The dissolution rate (DR), calculated from the weight loss in distilled water at 90 °C for up to 32 days, was ∼10−9 g/cm2/min which is 100 times lower than that of window glass and 300 times lower than that of a barium ferro, aluminoborate glass. The structure and valence states of the iron ions in these glasses were investigated using Mössbauer spectroscopy, X-ray diffraction, infrared spectroscopy and differential thermal analysis. X-ray diffraction indicates that the local structure of the zinc–iron phosphate is related to the short range structures of crystalline Zn2P2O7, Fe3(P2O7)2 and Fe(PO3)3. Both Fe(II) and Fe(III) ions are present in all of these glasses. The presence of an Fe–O–P related band in the infrared (IR) spectra of the glasses containing more than 30 mol% Fe2O3 is consistent with their excellent chemical durability.