HR: 1340h
AN: MR43C-1528    [Abstracts]
TI: Heat Capacity of γ-Fe₂SiO₄ and Thermodynamic Calculation of Fayalite - γ-Fe₂SiO₄ Phase Transition Boundary
AU: * Yong, W
EM: wenjuny@umich.edu
AF: Department of Geological Sciences, University of Michigan, 2534 C.C. Little Building,1100 N. University, Ann Arbor, MI 48104, United States
AU: Dachs, E
EM: Edgar.Dachs@sbg.ac.at
AF: Fachbereich Materialwissenschaften, Universität Salzburg, Hellbrunnerstr. 34, Salzburg, A- 5020, Austria
AU: Withers, A C
EM: withe012@umn.edu
AF: Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, United States
AU: Essene, E J
EM: essene@umich.edu
AF: Department of Geological Sciences, University of Michigan, 2534 C.C. Little Building,1100 N. University, Ann Arbor, MI 48104, United States
AB: The low-temperature heat capacity (Cp) of γ-Fe₂SiO₄ was measured between 5 and 303 K using the heat capacity option of a physical properties measurement system (PPMS). Fayalite powder was used as the starting material to synthesize the γ-Fe₂SiO₄ at 8.5 GPa and 1273 K by a 1,000-ton Walker-type multi-anvil device at the university of Minnesota. The heat capacity data were measured at more than 100 different temperatures with both logarithmic spacing and linear spacing. The measured heat capacity data show a broad lambda-transition at 11.8 K, probably related to a paramagnetic-antiferromagnetic transition just like the 65 K transition in fayalite. The difference in the Cp between fayalite and γ-Fe₂SiO₄ is reduced as the temperature increases in the range of 50-300 K. The Cp and entropy of γ- Fe₂SiO₄ at standard temperature and pressure (S°298) are 131.1±0.6 J mol^-1K^-1 and 140.2±0.4 J mol^-1K^-1, respectively. The Gibbs free energy at standard pressure and temperature (G°f,298) is calculated to be 1,369.3±2.7 J mol^-1 based on the new entropy data. Based on current thermodynamic data, the calculated phase boundary for the fayalite – γ- Fe₂SiO₄ transition at high temperatures and pressures is consistent with the results of previous experimental studies.
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3630 Experimental mineralogy and petrology
DE: 3939 Physical thermodynamics
DE: 8411 Thermodynamics (0766, 1011, 3611)
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting