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Structure, thermal expansion and incompressibility of MgSO4·9H2O, its relationship to meridianiite (MgSO4·11H2O) and possible natural occurrences

ABSTRACT: We have employed neutron and X-ray powder diffraction and density functional theory calculations to determine the structure and thermoelastic properties of a new hydrate in the MgSO4–H2O binary system, magnesium sulfate enneahydrate. We show that this 9-hydrate could occur naturally in certain hypersaline lakes on Earth and indicate where it may be formed as a more persistent mineral elsewhere in the solar system. Since being discovered initially in mixed-cation systems, a method of forming end-member MgSO4·9H2O has been found. We have obtained powder diffraction data from protonated analogues (using X-rays) and deuterated analogues (using neutrons) of this compound over a range of temperatures and pressures. From these data we have determined the crystal structure, including all hydrogen positions, the thermal expansion over the range 9–260?K at ambient pressure, the incompressibility over the range 0–1.1?GPa at 240?K and studied the transitions to other stable and metastable phases. MgSO4·9D2O is monoclinic, space group P21/c, Z = 4, with unit-cell parameters at 9?K, a = 6.72764?(6), b = 11.91154?(9), c = 14.6424?(1)?Å, ? = 95.2046?(7)° and V = 1168.55?(1)?Å3. The structure consists of two symmetry-inequivalent Mg(D2O)6 octahedra on sites of

SUBMITTER: Fortes A

PROVIDER: S-EPMC5289306 | biostudies-literature | 2017 Jan

REPOSITORIES: biostudies-literature

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