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. T_g 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.