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The thermoelastic properties Of MgSO4 center dot 7D(2)O (epsomite) from powder neutron diffraction and ab initio calculation

Fortes, AD; Wood, IG; Alfredsson, M; Vocadlo, L; Knight, KS; (2006) The thermoelastic properties Of MgSO4 center dot 7D(2)O (epsomite) from powder neutron diffraction and ab initio calculation. EUR J MINERAL , 18 (4) 449 - 462. 10.1127/0935-1221/2006/0018-0449.

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Abstract

time-of-flight powder neutron diffraction has been used to measure the molar volume of MgSO4.7D(2)O (i) from 1.8 - 300 K at ambient pressure, (ii) from 50 - 290 K at 1.4, 3.0, and 4.5 kbar, (iii) from 0 - 5.5 kbar at 290 K, and (iv) from 0 - 4.5 kbar at 50 K. The data have allowed us to determine the temperature dependence of the incompressibility, (partial derivative K/partial derivative T)(p), (thermodynamically equivalent to the pressure dependence of the thermal expansion, (partial derivative alpha/partial derivative P)(T)) of epsomite throughout its stability field. We observed that the a-axis exhibits negative thermal expansion, alpha(a), from 30 - 250 K at room pressure, turning positive above 250 K and being zero below 30 K. However, each of the crystallographic axes exhibits a sharp change in (partial derivative alpha/partial derivative T) at similar to 125 K, and this appears to correspond to significant changes in the axial incompressibilities with the a- and c-axes softening, and the b-axis stiffening considerably below similar to 125 K.Our thermoelastic results are in agreement with ab initio calculations at zero Kelvin; however the calculations offer no obvious insight into the mechanism responsible for the change in behaviour at low temperature.

Type:Article
Title:The thermoelastic properties Of MgSO4 center dot 7D(2)O (epsomite) from powder neutron diffraction and ab initio calculation
DOI:10.1127/0935-1221/2006/0018-0449
Keywords:epsomite, neutron diffraction, high-pressure, incompressibility, thermal expansion, DENSITY-FUNCTIONAL THEORY, CRYSTAL-STRUCTURE, THERMAL-EXPANSION, REFINEMENT, OCEAN, SURFACE, TEMPERATURE, MGSO4.7H2O, DIHYDRATE, EUROPA
UCL classification:UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Earth Sciences

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