Heat capacity,entropy and phase equilibria of stishovite |
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| Authors: | Email author" target="_blank">Wenjun?YongEmail author Edgar?Dachs Artur?Benisek Richard?A?Secco |
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| Institution: | 1.Department of Earth Sciences,University of Western Ontario,London,Canada;2.Fachbereich Materialforschung & Physik, Abteilung Mineralogie,Universit?t Salzburg,Salzburg,Austria |
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| Abstract: | The low-temperature heat capacity (C
P) of stishovite (SiO2) synthesized with a multi-anvil device was measured over the range of 5–303 K using the heat capacity option of a physical
properties measurement system (PPMS) and around ambient temperature using a differential scanning calorimeter (DSC). The entropy
of stishovite at standard temperature and pressure calculated from DSC-corrected PPMS data is 24.94 J mol−1 K−1, which is considerably smaller (by 2.86 J mol−1 K−1) than that determined from adiabatic calorimetry (Holm et al. in Geochimica et Cosmochimica Acta 31:2289–2307, 1967) and about 4% larger than the recently reported value (Akaogi et al. in Am Mineral 96:1325–1330, 2011). The coesite–stishovite phase transition boundary calculated using the newly determined entropy value of stishovite agrees
reasonably well with the previous experimental results by Zhang et al. (Phys Chem Miner 23:1–10, 1996). The calculated phase boundary of kyanite decomposition reaction is most comparable with the experimental study by Irifune
et al. (Earth Planet Sci Lett 77:245–256, 1995) at low temperatures around 1,400 K, and the calculated slope in this temperature range is mostly consistent with that determined
by in situ X-ray diffraction experiments (Ono et al. in Am Mineral 92:1624–1629, 2007). |
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