Understanding Fe incorporation in layered double hydroxide (LDH) phases is important for revealing the steel/cement interface interaction in low carbon cement. In this study, synchrotron-based characterization is combined with density functional theory (DFT) calculations to unravel the atomistic mechanisms controlling Fe(III) incorporation in MgAl LDHs as a function of composition and local structure. XAS measurements reveal that Fe incorporation is strongly suppressed under trivalent-cation-rich compositions, leading to a preferential association of Fe with edge or defect-related environments. The spectra indicate that Fe(III) is incorporated into the LDH lattice in a well-defined octahedral environment under Mg-rich compositions. DFT calculations of substitution energies support these findings by showing that Fe(III) substitution for Al(III) in the main layers is strongly composition-dependent: Fe(III) incorporation is most unfavorable at Al-rich compositions but becomes progressively more favorable in Mg-rich environments. In Al-rich LDHs, Fe shortens neighboring AlO bonds, introducing local strain and lowering mechanical stability, while in Mg-rich LDHs the more flexible MgO framework accommodates Fe(III) more effectively. Overall, this study defines molecular-level constraints governing Fe(III) incorporation into LDH phases in low-carbon cements. The results offer transferable insights concerning the influence of LDH composition on the interfacial phase assemblages relevant to steel corrosion protection.
Contact
Prof. Dr. Sergey Churakov
PSI Center for Nuclear Engineering and Sciences
Paul Scherrer Institute PSI
+41 56 310 41 13
sergey.churakov@psi.ch
[English]