title: Structure determination of Mg3(OH)5Cl.4H2O (F5 phase) from laboratory powder diffraction data and its impact on the analysis of problematic magnesia floors.
abstract: The crystal structure with the idealized formula Mg(3)(OH)(5)Cl.4H(2)O, the so-called F5 phase according to 5Mg(OH)(2).MgCl(2).8H(2)O in the system MgCl(2)-MgO-H(2)O, has been solved ab initio from high-quality laboratory powder diffraction data at room temperature. The F5 phase is structurally related to 3Mg(OH)(2).MgCl(2).8H(2)O (F3 form). The F5 phase consists of infinite triple chains with one Mg(OH)(6) and two Mg(OH)(4)(OH(2))(2) octahedra as building units intercalated by chlorides, which are partly substituted by disordered hydroxides in the real structure. The F5 phase is of technological importance as the most important binder phase in Sorel cements. Knowledge of the crystal structure enables the full quantitative phase analysis of magnesia cements for the first time, which turns out to be very helpful in the search for possible causes of broken or bleached magnesia floors. Two real-life examples are given.
authors.affiliation: Max-Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
authors.forename: Kunihisa
authors.initials: K
authors.lastname: Sugimoto
authors.forename: Robert E
authors.initials: RE
authors.lastname: Dinnebier
authors.forename: Thomas
authors.initials: T
authors.lastname: Schlecht