Influence of ZrO2 content on the chemical durability and structure of P2O5-Fe2O3-Al2O3-Na2O-ZrO2 glass ceramics

Staring with the composition of 62.5P2O5–16.5Fe2O3–8Al2O3–13Na2O (PFAN), a series of samples have been prepared by doping ZrO2 (from 1 to 12 mol%) through the melting-quenching method. Samples with ZrO2 content from 2 to 12 mol% are glass ceramics, in which zirconium pyrophosphate (ZrP2O7) is the only crystalline phase. The weight fraction of ZrP2O7 increases linearly with the increase of ZrO2. Raman spectra indicate that the Q1 and Q2 units are the dominating structures in glass phase. The standard product consistency test (PCT) show that the chemical durability has been significantly improved with additional ZrO2, which is due to that the formation of ZrP2O7, the increase of Q1 units, and the dissolution of Zr4+ ions in the glass phase. X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy show that the valance state of iron ions does not change much with ZrO2 content, that the Fe2+/(Fe2++Fe3+) ratio stay around 0.4 to 0.5.