Heat capacity,entropy, and phase equilibria of dmitryivanovite |
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Authors: | Email author" target="_blank">Wenjun?YongEmail author Edgar?Dachs Artur?Benisek Anthony?C?Withers 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;3.Department of Earth Sciences,University of Minnesota,Minneapolis,USA |
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Abstract: | The heat capacity (C
p
) of dmitryivanovite synthesized with a cubic press was measured in the temperature range of 5–664 K using the heat capacity
option of a physical properties measurement system and a differential scanning calorimeter. The entropy of dmitryivanovite
at standard temperature and pressure (STP) was calculated to be 110.1 ± 1.6 J mol−1 K−1 from the measured C
p
data. With the help of new phase equilibrium experiments done at 1.5 GPa, the phase transition boundary between krotite and
dmitryivanovite was best represented by the equation: P (GPa) = −2.1825 + 0.0025 T (K). From the temperature intercept of this phase boundary and other available thermodynamic data
for krotite and dmitryivanovite, the enthalpy of formation and Gibbs free energy of formation of dmitryivanovite at STP were
calculated to be −2326.7 ± 2.1 and −2,208.1 ± 2.1 kJ mol−1, respectively. It is also inferred that dmitryivanovite is the stable CaAl2O4 phase at STP and has a wide stability field at high pressures whereas the stability field of krotite is located at high temperatures
and relatively low pressures. This conclusion is consistent with natural occurrences (in Ca–Al-rich inclusions) of dmitryivanovite
and krotite, where the former is interpreted as the shock metamorphic product of originally present krotite. |
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