STRUCTURE OF ALPHA-DICALCIUM SILICATE HYDRATE

Ca2(SiO3OH)(OH), M(r) = 190.26, orthorhombic, P2(1)2(1)2(1), a = 9.487 (4), b = 9.179 (4), c = 10.666 (7) angstrom, V = 928.8 (8) angstrom, Z = 8, D(x) = 2.72 g cm-3, lambda(Mo Kalpha) = 0.71069 angstrom, mu = 25.07 cm-1, F(000) = 768, T = 293 K, final R = 0.054 for 1677 unique n on-zero reflections having I > 3sigma(I). The crystal was hydrothermal ly synthesized from a mixture of CaO and quartz at 403 K. The structur e was redetermined by means of Patterson synthesis and refined by leas t-squares calculations. Hydrogen bonds were assigned by the balance of electrostatic valences of O atoms. The structure consists of Ca2+, (S iO3OH)3- and OH- ions. Calcium ions are coordinated by six or seven O atoms. Calcium polyhedra are linked together with shared edges to form a waved polyhedral sheet parallel to {001}. These sheets are bridged along the [001] direction by isolated SiO3OH tetrahedra and hydrogen b onds.