K-Fe Sulfides and Fe-Ni Phosphides at Core Pressures and Temperatures

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EAR-0073433PrewittThe density of the Earth's core is about 10% less than that of pure nickel-iron at core pressures and temperatures. Several elements have been proposed to account for the low density of the core, including sulfur, silicon, carbon, potassium, hydrogen, and oxygen. Because potassium and phosphorous are depleted in the Earth's mantle, it has been proposed that this depletion may result from incorporation of these elements in Earth's core. However, phases with compositions including these elements are known only from syntheses at relatively low pressures and from meteorites, and there has been little or no experimental work at higher pressures and temperatures, especially those approaching core conditions. Therefore, we will investigate the high-pressure, high-temperature chemistry and structures of two different classes of phases that could be present under core conditions, potassium-iron sulfides and iron-nickel phosphides. From these experiments, we expect to provide information on the synthesis of these materials, their phase relations, and their structural characteristics. We also will investigate the partitioning of K and P between bulk silicate earth and metallic liquids in the presence or absence of S and/or C. Experimental techniques will include synthesis of appropriate materials under controlled vapor pressures, temperature, and overall pressure, characterization of products with electron and ion microprobes, and in-situ structural measurements at high-pressures and temperatures using x-ray diffraction in our laboratory and at national synchrotron sources, and by a variety of spectroscopic techniques.