The Thermodynamic Properties of MgCO3-CaCO3-FeCO3-Na2CO3-K2CO3-Li2CO3 Liquids: New Measurements

本提案的目标是为MgCO3-FeCO3-CaCO3-Na2CO3-K2CO3-Li2CO3体系中的各种液体提供各种热力学性质（热容量，密度，热膨胀，可压缩性）的首次测量。这些碳酸盐液体的基本热力学数据，特别是含有CaCO3和MgCO3的液体，将为含碳酸盐的地幔岩石的部分熔融提供热力学模型。需要这样的模型来严格评估复杂的全球碳循环，其中包括碳酸化海洋地壳的俯冲，使各种地幔岩性交代的碳酸盐岩熔体的形成，这些碳酸化岩石的部分熔化，以及随后的火山向大气中释放二氧化碳。多组分碳酸盐液体的热力学性质测量不仅引起了地球科学家的兴趣，而且引起了对熔融碳酸盐燃料电池从氢中获取能量感兴趣的材料科学家的兴趣。我们计划将10-50 mol %的CaCO3和MgCO3（以及10-30 mol %的FeCO3）添加到各种低熔点的混合碱（Li-Na-K）碳酸盐液体中，并进行热容量（通过差示扫描量热法；DSC），密度（通过双bob阿基米德法）和声速（通过声干涉测量法）的测量，以获得熔体压缩性。另一个目标是进行一系列相平衡实验，以确定各种碳酸盐相(如K2Ca（CO3)2、Na2Ca(CO3)2、Na2CO3、CaCO3、MgCO3、KLiCO3等）在P-T空间中的熔合曲线。根据这两组实验数据，我们建议使用熔合曲线分析来约束不同碳酸盐相的熔合焓以及它们各自的液体值（它们的熔体压缩性的压力依赖关系）。

The goal of this proposal is to provide the first measurements of various thermodynamic properties (heat capacity, density, thermal expansion, compressibility) for a wide range of liquids in the MgCO3-FeCO3-CaCO3-Na2CO3-K2CO3-Li2CO3 system. These fundamental thermodynamic data for carbonate liquids, especially those containing CaCO3 and MgCO3, will permit thermodynamic models of partial melting for carbonate-bearing mantle rocks. Such models are needed to rigorously evaluate the complex global carbon cycle, which includes the subduction of carbonated oceanic crust, the formation of carbonatite melts that metasomatize diverse mantle lithologies, the partial melting of these carbonated rocks, and the subsequent volcanic outgassing of CO2 to the atmosphere. Thermodynamic property measurements on multi-component carbonate liquids are of interest not only to earth scientists, but also to material scientists interested in molten carbonate fuel cells to derive energy from hydrogen. We plan to add 10-50 mol % CaCO3 and MgCO3 (and 10-30 mol % FeCO3) to various mixed alkali (Li-Na-K) carbonate liquids with low melting temperatures, and to perform measurements of heat capacity (by differential scanning calorimetry; DSC), density (by the double-bob Archimedean method), and sound speed (by acoustic interferometry) to obtain melt compressibility. An additional objective is to perform a series of phase equilibrium experiments to locate the fusion curves of various carbonate phases (e.g., K2Ca(CO3)2, Na2Ca(CO3)2, Na2CO3, CaCO3, MgCO3, KLiCO3, etc.) in P-T space. From these two sets of experimental data, we propose to use fusion curve analysis to constrain the enthalpies of fusion of the various carbonate phases as well as their respective liquid values (the pressure dependence of their melt compressibility).