New insight into the crystal structure of ettringite: Ca6[Al(OH)6]2(SO4)3 · 26H2O
Ettringite, ideal chemical formula Ca6[Al(OH)6]2(SO4)3 x 26H2O, is an important crystalline compound in the chemistry of Portland cement: it controls the rate of set of the highly reactive calcium aluminate phase (i.e., C3A), during the early hydration stages, and its formation plays an important role in degradation processes occurring in mature cement pastes due to sulphate attack. The structure of a synthetic ettringite-type compound was also investigated by neutron powder diffraction. The authors were able to locate the proton sites. However, all the sites were modelled isotropically, with unusually different displacement factors for atoms of the same ionic groups, and some of the refined site occupancy factors showing partial occupancies without a robust explanation. The aim of the present study is a re-investigation of the crystal structure of a natural ettringite at ambient and low-T (20 K) by means of single-crystal neutron diffraction, in order to define the reliable location of all the proton sites, their displacement regime along with the real topological configuration of the H2O and OH-groups, for a full description of the atomic relationship via the H-bond.
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GATTA Giacomo Diego and FERNANDEZ DIAZ Maria Teresa. (2016). New insight into the crystal structure of ettringite: Ca6[Al(OH)6]2(SO4)3 · 26H2O. Institut Laue-Langevin (ILL) doi:10.5291/ILL-DATA.5-11-419
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