Thermoelastic properties of salt hydrates and implications for geological structures

• Main Author: Brand, H.
• Published: University College London (University of London) 2009
• Subjects: 550
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.564742

This thesis reports the results of neutron diffraction studies and first principles ab initio simulations of two salt hydrates in the Na2SO4 – H2O and MgSO4 – H2O systems, namely mirabilite (Na2SO4·10H2O) and meridianiite (MgSO4·11H2O). Neutron diffraction experiments of deuterated mirabilite were carried on the High Resolution Powder Diffractometer (HPRD) at the ISIS spallation neutron source to measure its thermal expansion from 4.2 - 300 K and its incompressibility from 0 – 0.55 GPa. A detailed analysis of both the thermal expansion and incompressibility data is presented including determination of the thermal expansion tensor and elastic strain tensor. First principles ab initio calculations were also carried out on both materials to complement the experimental studies and to extend the study to higher pressures outside the experimental range. Mirabilite was simulated from 0 – 61 GPa; at least two new phases were detected resulting from first-order phase transformations. Meridianiite was simulated from 0 – 11GPa; this material shows one transition to a higher pressure phase (probably second-order).Finally, a simple model has been developed, incorporating the density of mirabilite determined in the experiments, to study the size and ascent speed of diapiric salt hydrate structures as they interact with, and travel through, a more viscous overburden layer within the upper crust of Earth, Mars and Ganymede, a large icy satellite of Jupiter.