The ZnSiO3 clinopyroxene-ilmenite transition: Heat capacity,enthalpy of transition,and phase equilibria期刊界 All Journals 搜尽天下杂志传播学术成果专业期刊搜索期刊信息化学术搜索

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The ZnSiO3 clinopyroxene-ilmenite transition: Heat capacity,enthalpy of transition,and phase equilibria

Authors:

M Akaogi H Yusa E Ito T Yagi K Suito J T Iiyama

Institution:

1. Department of Earth Sciences, Kanazawa University, 920, Kanazawa, Japan
2. Institute for Study of the Earth's Interior, Okayama University, Misasa, 682-02, Tottori, Japan
3. Institute for Solid State Physics, University of Tokyo, 106, Tokyo, Japan
4. Department of Material Physics, Osaka University, 560, Osaka, Japan
5. Department of Earth Sciences, Chiba University, 260, Chiba, Japan

Abstract:

ZnSiO₃ clinopyroxene stable above 3 GPa transforms to ilmenite at 10–12 GPa, which further decomposes into ZnO (rock salt) plus stishovite at 20–30 GPa. The enthalpy of the clinopyroxene-ilmenite transition was measured by high-temperature solution calorimetry, giving ΔH⁰=51.71 ±3.18 kJ/mol at 298 K. The heat capacities of clinopyroxene and ilmenite were measured by differential scanning calorimetry at 343–733 and 343–633 K, respectively. The C _p of ilmenite is 3–5% smaller than that of clinopyroxene. The entropy of transition was calculated using the measured enthalpy and the free energy calculated from the phase equilibrium data. The enthalpy, entropy and volume changes of the pyroxene-ilmenite transition in ZnSiO₃ are similar in magnitude to those in MgSiO₃. The present thermochemical data are used to calculate the phase boundary of the ZnSiO₃ clinopyroxene-ilmenite transition. The calculated boundary,

$P(Gpa) = 8.9( \pm 0.6) + 1.7(\bar + 0.5)$

Keywords:
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