Sodium sulfate heptahydrate: a synchrotron energy-dispersive diffraction study of an elusive metastable hydrated salt
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Date
2008Author
Hamilton, Andrea
Hall, Christopher
Metadata
Abstract
We describe an unusual application of synchrotron energy-dispersive diffraction with hard X-rays to
obtain structural information on metastable sodium sulfate heptahydrate. This hydrate was often
mentioned in nineteenth and early twentieth century scientific literature but rarely in modern
publications, and it had not been characterised structurally. Using a unique three-detector fixed-angle
X-ray geometry, a good quality powder diffraction pattern was obtained directly from a stirred
suspension of hydrate crystals in saturated aqueous sodium sulfate solution at about 14 degrees celcius. The
suspension of crystals was contained in the 22 mm dia sealed cylindrical bottle in which crystallization
occurred. Indexing showed that the heptahydrate has a tetragonal unit cell with a = 7.1668 A and
c = 22.2120 A with a few weak unindexed reflections arising from the 2a supercell. New gravimetric
data and the cell dimensions confirm the heptahydrate composition originally proposed by Loewel