Melting in the Fe-Si System at High Pressures and Temperatures

It has long been known that the Earth's core consists mainly of iron and nickel with several weight percent of a light element. Geochemical and cosmochemical constraints suggest Si as a strong candidate for this light element contribution. Therefore it is important to understand the phase diagram, including melting relations, in the Fe-Si binary at high pressures and temperatures. We have conducted melting experiments in the Fe-Si system using double-sided laser heating in diamond anvil cells. Temperatures were measured using standard spectroradiometric techniques, and also using a new system for obtaining 2D temperature distributions over the laser heated spots. Melting was established by a variety of criteria, including: analysis of temperature, laser power and emissivity data during heating; optical examination; and electron microscopy of the recovered samples. Electron microprobe analysis of recovered samples also indicated the direction of partitioning of Si between solid and liquid. Our melting temperatures are comparable to earlier results obtained from multi-anvil press experiments.