Effect of boron addition on the structure and properties of iron phosphate glasses

Effects of boron addition on the glass forming characteristics, structure and properties of iron phosphate glasses with nominal compositions of xB2O3–(40−x)Fe2O3–60P2O5 (x = 2–20, mol%) and xB2O3–(100−x)[Fe2O3–60P2O5] (x = 2–20, mol%) have been investigated by DTA, XRD, IR and Mössbauer spectroscopy. Although there were some weak local surface crystallizations on especially most of the glasses in group B, all of the compositions formed glass. DTA spectra showed two exothermic peaks corresponding to crystallizations along with an endothermic glass transition peak. Tg increased with increasing B2O3 content for the glasses in the first series which indicates that the addition of B2O3 increases the thermal stability of glasses in this series while the opposite is observed in the second series. The dissolution rates of boron containing bulk glasses were found to be around 10−9 gr/cm2 min which are comparable to that of the base iron phosphate glass. When the B2O3 content was above 14%, new bands related to BO4 tetrahedral groups have been observed in the IR spectra. The Mössbauer isomer shift values of boron doped glasses were found to be a little lower than that of base glass but both iron ions had distorted octahedral coordination in all glasses. The fraction of Fe2+ ions in glasses (Fe2+/∑(Fe2+ + Fe3+)) was found to be 23% for the base glass while it was 10–22% for the boron doped glasses.