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).