Molecular structure of CaO–FeO_x–SiO₂ glassy slags and resultant inorganic polymer binders

The molecular structures of CaO–FeO_x–SiO₂ slags and their inorganic polymer counterparts were determined using neutron and X-ray scattering with subsequent pair distribution function (PDF) analysis. The slags were synthesized with approximate molar compositions: 0.17CaO–0.83FeO–SiO₂ and 0.33CaO–0.67FeO–SiO₂ (referred to as low-Ca and high-Ca, respectively)_. The PDF data on the slags reasserted the predominantly glassy nature of this iron-rich industrial byproduct. The dominant metal-metal correlation was Fe–Si (3.20-3.25 Å), with smaller contributions from Fe–Ca (3.45-3.50 Å) and Fe–Fe (2.95-3.00 Å). After inorganic polymer synthesis, a rise in the amount of Fe³⁺ was observed via the shift of the Fe–O bond length to shorter distances. This shortening of the Fe–O distance in the binder is also evidenced by the apparent rise of the Fe–Fe correlation at 2.95-3.00 Å, although this feature may also suggest a potential aggregation of FeO_x clusters. In general, the atomic arrangements of the reaction product was shown to be very similar to the precursor structure and the dominance of the Fe–Si correlation suggests the participation of Fe in the silicate network. The binder was shown to be glassy, as no distinct atom-atom correlations were observed beyond 8 Å.