Solving the Structure of Metakaolin

Abstract

Metakaolin has been used extensively as a cement additive and paint extender, and recently as a geopolymer precursor. This disordered layered aluminosilicate is formed via the dehydroxylation of kaolinite. However, an accurate representation of its atomic structure has bever before been presented. Here, a novel synergy between total scattering and density functional modeling is presented to solve the structure of metakaolin. The metastable structure is elucidated by iterating between least-squares real-space refinement using neutron pair distribution function data, and geometry optimization using density functional modeling. The resulting structural representation is both energetically feasible and in excellent agreement with experimental data. This accurate structure of metakaolin provides new insight into the local environment of the aluminum atoms, with evidence of the existence of tri-coordinated aluminum. By the availability of this detailed atomic description, there exists the opportunity to tailor chemical and mechanical processes involving metakaolin at the atomic level to obtain optimal performance at the macro-scale.