Heat capacity of γ-Fe2SiO4 between 5 and 303 K and derived thermodynamic properties |
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Authors: | Wenjun Yong E Dachs A C Withers E J Essene |
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Institution: | 1. Department of Geological Sciences, University of Michigan, Ann Arbor, MI, 48109-1005, USA 2. Fachbereich Materialwissenschaften, Universit?t Salzburg, Hellbrunnerstr. 34, 5020, Salzburg, Austria 3. Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN, 55455, USA
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Abstract: | A multi-anvil device was used to synthesize 24 mg of pure γ-Fe2SiO4 crystals at 8.5 GPa and 1,273 K. The low-temperature heat capacity (C
p) of γ-Fe2SiO4 was measured between 5 and 303 K using the heat capacity option of a physical properties measurement system. The measured
heat capacity data show a broad λ-transition at 11.8 K. The difference in the C
p between fayalite and γ-Fe2SiO4 is reduced as the temperature increases in the range of 50–300 K. The gap in C
p data between 300 and 350 K of γ-Fe2SiO4 is an impediment to calculation of a precise C
p equation above 298 K that can be used for phase equilibrium calculations at high temperatures and high pressures. The C
p and entropy of γ-Fe2SiO4 at standard temperature and pressure (S°298) are 131.1 ± 0.6 and 140.2 ± 0.4 J mol−1 K−1, respectively. The Gibbs free energy at standard pressure and temperature (ΔG°
f,298) is calculated to be −1,369.3 ± 2.7 J mol−1 based on the new entropy data. The phase boundary for the fayalite–γ-Fe2SiO4 transition at 298 K based on current thermodynamic data is located at 2.4 ± 0.6 GPa with a slope of 25.4 bars/K, consistent
with extrapolated results of previous experimental studies. |
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Keywords: | γ -Fe2SiO4 Fayalite Heat capacity Entropy Thermodynamic property Gibbs free energy |
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