The solubility equilibria of the ternary system Mg­(OH)2–MgCl2–H2O were determined at temperatures from 298 to 393 K applying equilibration periods of up to 3.5 years. As a result, four thermodynamically stable magnesium chloride hydroxide hydrates (Sorel phases) exist in the ternary system within the investigated temperature range. These are the 3-1-8 phase [3Mg­(OH)2·MgCl2·8H2O], the 9-1-4 phase [9Mg­(OH)2·MgCl2·4H2O], the 2-1-4 phase [2Mg­(OH)2·MgCl2·4H2O], and the 2-1-2 phase [2Mg­(OH)2·MgCl2·2H2O]. The also known 5-1-8 phase [5Mg­(OH)2·MgCl2·8H2O] was found to be metastable in the solid–liquid system. With this work, a reliable solubility data set is now available, for example, to prove the long-term stability of magnesia building materials in the presence of salt-bearing media, a challenging demand on the material in a special application as a barrier construction material in salt formation.

Abstract. In the course of investigations relating to magnesia oxysulfate cement the basic magnesium salt hydrate 3Mg(OH) 2 ·MgSO 4 ·8H 2 O (3-1-8 phase) was found as a metastable phase in the system Mg(OH) 2 -MgSO 4 -H 2 O at room temperature (the 5-1-2 phase is the stable phase) and was characterized by thermal analysis, Raman spectroscopy, and X-ray powder diffraction. The complex crystal structure of the 3-1-8 phase was determined from high resolution laboratory X-

Mg(OH)2-MgSO4-H2O. -3Mg(OH)2·MgSO4·8H2O (3-1-8 phase) and 5Mg(OH)2·MgSO4·2H2O (5-1-2 phase) are obtained from OHsupersaturated MgSO4 solutions which are obtained by suspending highly reactive MgO in differently concentrated MgSO4 solutions followed by filtration and storage at 25 (3-1-8 phase) or 40°C (5-1-2 phase). The 3-1-8 phase is metastable, the 5-1-2 phase stable at room temperature. The former is characterized by thermal analysis, Raman spectroscopy, and high--resolution synchrotron powder XRD (space group C2/c, Z = 4). Its crystal structure consists of parallel double chains of edge-linked distorted Mg (OH2)2(OH)4 octahedra along the [-110] and [110] directions forming a pattern of crossed rods. Isolated SO4 tetrahedra and interstitial H 2 O molecules separate the stacks of parallel double chains. -(DINNEBIER*, R. E.; PANNACH, M.; FREYER, D.; Z. Anorg. Allg. Chem. 639 (2013) 10, 1827-1833, http://dx.doi.org/10.1002/zaac.201300128 ; MPI Festkoerperforsch., D-70569 Stuttgart, Germany; Eng.) -J. Schramke 43-004

The solid/liquid equilibria in the ternary system Ni(OH)2–NiCl2–H2O at temperatures of 25 and 200 °C have been investigated by applying equilibration periods of up to 45 months (3 years and 9 months). The equilibration process was studied by isothermal saturation methods using different solids as starting materials. At 200 °C, Ni2Cl(OH)3 and NiCl(OH) occur as stable phases, whereas a solid solution, NiClx(OH)2–x (ss‐type‐OH), appears as an intermediate phase. At 25 °C, two nickel(II) chloride hydroxide hydrates, Ni3Cl2+x(OH)4–x·4H2O and Ni3Cl(OH)5·4H2O, are formed. The latter phase was characterized for the first time and a structural model was created from a Rietveld refinement of the powder X‐ray diffraction pattern. A systematic investigation of the solubilities at 25 °C revealed that Ni2Cl(OH)3 is the solid phase in both dilute and concentrated NiCl2 solutions at this temperature. In general, all stable and metastable phases in the system Ni(OH)2–NiCl2–H2O exhibit very low solubility, but during the very slow phase transformations high hydroxide supersaturations occur that are persistent for years.

During evaporation of natural and synthetic K-Mg-Cl brines, the formation of almost square plate-like crystals of potassium carnallite (potassium chloride magnesium dichloride hexahydrate) was observed. A single-crystal structure analysis revealed a monoclinic cell [a = 9.251 (2), b = 9.516 (2), c = 13.217 (4) Å , = 90.06 (2) and space group C2/c]. The structure is isomorphous with other carnallite-type compounds, such as NH 4 ClÁMgCl 2 Á6H 2 O. Until now, natural and synthetic carnallite, KClÁMgCl 2 Á6H 2 O, was only known in its orthorhombic form [a = 16.0780 (3), b = 22.3850 (5), c = 9.5422 (2) Å and space group Pnna].