2Mg(OH)2·MgCl2·2H2O and 2Mg(OH)2·MgCl2·4H2O, Two High Temperature Phases of the Magnesia Cement System

Abstract In the course of investigations relating to magnesia cement the basic magnesium salt hydrates 2Mg(OH) 2 · MgCl 2 · 2H 2 O (2‐1‐2 phase) and 2Mg(OH) 2 · MgCl 2 · 4H 2 O (2‐1‐4 phase) were found as stable phases in the system MgO‐MgCl 2 ‐H 2 O at a temperature of T = 120 °C and were characterized by thermal analysis, Raman spectroscopy and X‐ray powder diffraction. The crystal structures of the 2‐1‐2 and 2‐1‐4 phases were determined from high resolution laboratory X‐ray powder diffraction data.Both phases crystallize in space group C 2/ m with Z = 2 (2‐1‐2: a = 15.3285(3) Å, b = 3.2208(5) Å, c = 8.1096(2) Å, β = 91.99(1)°, V = 400.13(2) Å 3 ; 2‐1‐4: a = 15.1264 Å, b = 3.1715(2) Å, c = 10.5230(1) Å, β = 101.55(1)°, V = 494.60(1) Å 3 ). The main building unit of both crystal structures is made up by infinite triple chains of edge‐linked distorted MgO 6 octahedra. In case of the 2‐1‐4 phase, the parallel stacks are in addition separated by interstitial one dimensional zig‐zag chains of disordered Cl – ions and H 2 O molecules.