Properties of molten CaCO3 at high pressure
Properties of molten CaCO3 at high pressure
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DOI：
10.7185/geochemlet.1813
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发表时间：
2018-04
期刊：
影响因子：
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通讯作者：
J. Hudspeth;C. Sanloup;Y. Kono
中科院分区：
文献类型：
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作者：
J. Hudspeth;C. Sanloup;Y. Kono
我们在这里报告了使用巴黎-爱丁堡压力机高达8.7 GPa的原位x射线衍射研究熔融CaCO3的结构。在中等范围内，随着分子间贡献的缩小，观察到变化，反映了碳酸盐分子的高填充效率。熔体的密度由径向分布函数得到，假设C-O贡献的配位数为3。体积模量值在实验压力-温度范围内增加了2倍，达到与所研究的最高压力下的底层晶相相似的值。这是压缩CaCO3熔体的第一次直接密度测量；它们与最近的从头算预测（Li et al., 2017）非常吻合，这意味着所报道的熔化曲线变平，随后在8 GPa以上出现略负的曲线，不可能是由于晶体-熔体密度反演。相反，熔合焓可能是原因，我们注意到在这方面，方解石- v晶体中氧的特殊高扩散率，这进一步暗示了碳酸盐熔体在深度的迁移率。
We report here the structure of molten CaCO3 studied by in situ X-ray diffraction using a Paris-Edinburgh press up to 8.7 GPa. Variations are observed in the medium range order with shrinkage of the intermolecular contributions, reflecting higher packing efficiency of the carbonate molecules. Density of the melt is obtained from the radial distribution functions, assuming a constant coordination number of 3 for the C-O contribution. Bulk modulus values increase by a factor of 2 over the experimental pressure-temperature range, reaching a value similar to that of underlying crystalline phases at the highest pressure investigated. Those are the first direct density measurements of compressed CaCO3 melt; they agree well with recent ab initio predictions (Li et al., 2017), which implies that the reported flattening of the melting curve followed by a slightly negative curve above 8 GPa cannot be due to crystal-melt density inversion. Instead, the enthalpy of fusion is likely responsible, and we note the peculiar high diffusivity of oxygen in crystalline calcite-V in this regard, with further implications for the mobility of carbonate melts at depth.