Fluorescence x-ray absorption fine structure studies of Fe-Ni-S and Fe-Ni-Si melts to 1600 K

We report Ni K-edge fluorescence x-ray absorption fine structure spectra (XAFS) for Fe₀.₇₅Ni₀.₀₅S₀.₂₀ and Fe₀.₇₅Ni₀.₀₅S₀.₂₀ ternary alloys from room temperature up to 1600 K. A high-temperature furnace designed for these studies incorporates two x-ray transparent windows and enables both a vertical orientation of the molten sample and a wide opening angle, so that XAFS can be measured in the fluorescence mode with a detector at 90° with respect to the incident x-ray beam. An analysis of the Ni XAFS data for these two alloys indicates different local structural environments for Ni in Fe₀.₇₅Ni₀.₀₅S₀.₂₀ and Fe₀.₇₅Ni₀.₀₅S₀.₂₀ melts, with more Ni-Si coordination than Ni-S coordination persisting from room temperature through melting. These results suggest that light elements such as S and Si may impact the structural and chemical properties of Fe-Ni alloys with a composition similar to the earth’s core.