Influence of aluminum on structural properties of iron-polyphosphate glasses

An Insight into the Correlation between Chemical Composition Changes of Aluminum-Iron-Polyphosphate Glasses and Thermal Properties

“…Additionally, part of iron atoms is reduced to ferrous (about 20–30%). In this redox state, iron acts as the glass network modifier, making the network more flexible [ 12 ]. Moreover, the ionicity of the Fe 2+ -O bonds is higher than Fe 3+ -O and Al 3+ -O, which have, among them, the most covalent character [ 38 ].…”

“…The indicator of the glass network polymerization may be the number of P-O-P bridges, which is proportional to the integral intensity of the appropriate band in Raman spectroscopy. Based on the data presented in [ 12 ], a correlation between the integral intensity and T g temperature can be observed. The correlation is presented in Figure 7 .…”

“…This comprises the number and the energy of the broken chemical bonds. Thus, the parameter change is related to the differences in the bond’s ionicity, the lower ionicity, the lower value of ∆Cp [ 12 , 39 ]. As was mentioned above, the increase in Al 2 O 3 enhances the mean covalent character of the cation-oxygen bonds, and as a result, the network becomes more rigid.…”

“…During melting at temperatures above 1300 °C, there was evidenced evaporation of P 2 O 5 [ 22 ]. To compensate for P 2 O 5 losses, an approximately 20% overweight of NH 4 H 2 PO 4 was used [ 12 ].…”

“…Both aluminum and iron ions can play an intermediate role in the phosphate glass network. It means that they can be network modifiers leading to network depolymerization or, under specific conditions, may act as network formers [ 12 ]. Depending on the glass composition, aluminum and iron could take different coordination numbers, which, in consequence, determine different glass properties.…”