Powder Neutron Diffraction Study of the Thermal Expansion of Mirabilite, Na2SO4.10H2O

Details Powder Neutron Diffraction Study of the Thermal Expansion of Mirabilite, Na2SO4.10H2O Powder Neutron Diffraction Study of the Thermal Expansion of Mirabilite, Na2SO4.10H2O

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p23e0116b&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #P23E-0116

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Computation

5134 Thermal Properties, 5422 Ices, 6218 Jovian Satellites

Scientific paper

The presence of salts such as MgSO4 and Na2SO4 in chondritic meteorites has led to the suggestion that the water-rich icy moons of the Gas Giant planets are likely to be dominated by multiply hydrated salts such as Fritzsche's salt (MgSO4.11H2O), epsomite (MgSO4.7H2O) and mirabilite (Na2SO4.10H2O). Moreover, hydrated sulfates are likely to be important rock-forming minerals and water storage reservoirs on Mars. When constructing models of icy moons to explore their structure and evolution, it is therefore extremely important to know the phase behaviour and physical properties of the constituent materials under the appropriate pressure and temperature regimes (0 < P < 5 GPa, and 100 < T < 300 K). We are therefore engaged in a programme of study to measure the physical characteristics of candidate materials using a combination of neutron diffraction and computational chemistry. Neutrons are powerful probes of low molecular-weight solids, hydrogen-bearing species in particular, and their penetrative power allows one to study materials even in complex sample environments, such as pressure cells and cryostats. In practice, we measure the variation in molar volume of a solid as a function of pressure and temperature; this leads to derivatives in P and T, such as thermal expansivity and compressibility. Furthermore, we can observe phase transitions in situ, and collect diffraction data which may lead to a successful solution of the new polymorph's structure. In this contribution, we present the results of work to investigate the structure and thermoelastic properties of mirabilite. We have determined the ambient pressure thermal expansion tensor and investigated the low- temperature structural disorder of deuterated mirabilite from 4 - 300K. The volume expansion is positive and this is echoed by the expansion of the a and c axes. However, the b axis shows a small negative thermal expansion below 50K. Very similar behaviour is seen in MgSO4.7H2O and MgSO4.11H2O (Fortes et al. 2006) and a number of hydrous and anhydrous sulfates. Observed changes in the β angle appear to be related to the structural disorder which is frozen-in at low temperatures (<150k).

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