The influence of air and temperature on the reaction mechanism and molecular structure of Fe-silicate inorganic polymers

Fe-rich inorganic polymers are rising in importance because of their low CO 2 emissions during production and their potential in upcycling metallurgical residues. Here, the oxidation of Fe during formation of the binder from 0.4CaO-1.2FeO x-SiO 2 slag is investigated in more detail using 57Fe Mössbauer spectroscopy. It was shown that the oxidation at early stages is not influenced by (O 2 in the) air. Later, the quadrupole split Fe 2+ state in the binder transforms to Fe 3+ when the samples are crushed and exposed to air as powder for 28 days at room temperature or 1 h at ≥200 °C. This transformation does not affect the connectivity of the silicate network according to infrared spectroscopy. During heating of the inorganic polymer powder, the Mössbauer spectra remain stable until 400–500 °C. At 400 °C the Fe 2+ in the slag starts to be oxidized, showing the formation of new Fe 3+ components.