Calorimetric study of the coesite-stishovite transformation and calculation of the phase boundary |
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| Authors: | Jun Liu Letitia Topor Jianzhong Zhang Alexandra Navrotsky Robert C Liebermann |
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| Institution: | 1. Center for High Pressure Research and Department of Earth and Space Sciences, University at Stony Brook, 11794, NY, USA
2. Center for High Pressure Research and Department of Geological and Geophysical Sciences, Princeton University, 08544, NJ, USA
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| Abstract: | High temperature drop-solution calorimetry in molten 2 PbO · B2O3 at 1044 K for coesite and stishovite polymorphs of silica was carried out to determine the enthalpy of the coesite-stishovite transition. These experiments were performed on high-purity, single-phase samples of coesite and stishovite. Our new value for the enthalpy of the coesitestishovite transition (ΔH 298 0 ) is 29.85 ± 0.78 kJ/mol, which is about 35% lower than previously reported by Akaogi and Navrotsky (1984) and Holm et al. (1967), but which compares well with new measurements by Akaogi et al. (1994b). Using these new data, we have calculated the equilibrium phase boundary between coesite and stishovite and obtained a slope, dP/dT=0.0031 (2) GPa/K. This calculated slope is in good agreement with that determined 0.0026 (2) GPa/K] from the in-situ X-ray diffraction study of Zhang et al. (1996). |
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