Thermodynamic properties of α-quartz, coesite, and stishovite and equilibrium phase relations at high pressures and high temperatures

摘要: Isobaric heat capacities of α -quartz, coesite, and stishovite were measured by differential scanning calorimetry at 183–703 K. The capacity data coesite represent a significant revision the previous data. entropies also calculated using Kieffer's model. By high-temperature solution calorimetry, transition enthalpy for β-quartz-coesite 979 K was to be 1.27±0.39 kJ/mol. enthalpies α-quartz-coesite coesite-stishovite transitions 298 3.40±0.56 33.62±1.01 kJ/mol, respectively, drop-solution calorimetry. obtained in this study is about 10–15 kJ/mol smaller than those studies. Phase relations SiO2 high pressures temperatures these new thermodynamic boundary consistent with determined experimentally. For transition, having slope 2.5±0.3 MPa/K disagrees that Yagi Akimoto but generally Zhang et al.'s situ X ray diffraction study.