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Keywords:

  • Magnesia cement;
  • Magnesium oxide chloride cement;
  • System MgO-MgCl2-H2O;
  • X-ray powder diffraction;
  • 2-1-4 Phase;
  • 2-1-2 Phase

Abstract

In the course of investigations relating to magnesia cement the basic magnesium salt hydrates 2Mg(OH)2·MgCl2·2H2O (2-1-2 phase) and 2Mg(OH)2·MgCl2·4H2O (2-1-4 phase) were found as stable phases in the system MgO-MgCl2-H2O 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 C2/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) Å3; 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) Å3). The main building unit of both crystal structures is made up by infinite triple chains of edge-linked distorted MgO6 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 H2O molecules.