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The Core Composition of Terrestrial Planets: A Study of the Ternary Fe-Ni-Si System

Wann, ETH; (2016) The Core Composition of Terrestrial Planets: A Study of the Ternary Fe-Ni-Si System. Doctoral thesis , UCL (University College London). Green open access

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Abstract

The exact composition of the cores of terrestrial planets is not known, but it is generally agreed that they are composed of iron alloyed with a fraction of nickel plus a small percentage of a light element, likely Si, S, O, C or H. Silicon has long been a popular choice and is still regarded as a very likely candidate, based on density deficit and cosmochemical arguments. Although much work has been carried out on the Fe-Si system, studies on the Fe-Ni-Si system have only recently been carried out. The majority of studies have concentrated on specific candidate core compositions, based on core formation models or matching the observed density deficit. This can be problematic when core formation models depend on core composition. In this thesis, the Fe-Ni-Si system is investigated as a whole, starting with the end-member binary systems, FeSi and NiSi. This provides a more methodical approach to solving the core composition problem. Both ab initio calculations and high-pressure, high-temperature experiments have been used in this work. Ab initio calculations at 0 K were used to find the transition pressure of the "-FeSi to CsCl-FeSi phase transition, and also to test the stability of newly discovered NiSi-structured phases in FeSi. Lattice dynamics calculations at high temperatures and pressures have been carried out to determine the Clapeyron slope of the "-FeSi to CsCl transition, in both FeSi and NiSi systems. Laser-heated diamond anvil cell experiments were used to measure the melting curves of NiSi and the Fe-FeSi eutectic, and in-situ neutron di↵raction experiments were used to determine the equation of state of MnP-structured NiSi at high-pressure and high-temperature. Finally, X-ray diffraction experiments were used to measure the thermal expansion of a range of (Fe,Ni)Si alloys.

Type: Thesis (Doctoral)
Title: The Core Composition of Terrestrial Planets: A Study of the Ternary Fe-Ni-Si System
Open access status: An open access version is available from UCL Discovery
Language: English
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1475909
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