New models for the Earth's core: the neglected role of nickel - ab initio calculations and high P-T experiments on Fe-Ni alloys

Lead Research Organisation: University College London
Department Name: Earth Sciences

Abstract

Determining the properties of the Earth's core is vital for understanding the evolution and dynamics of the whole planet. For over 80 years, the Earth's core has been considered to consist of an iron-nickel alloy; more recently it has been suggested that it must also contain a few percent of light alloying elements such as silicon or sulphur. The pressure range in the core is ~135

Publications

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Côté A (2012) Ab initio simulations of iron-nickel alloys at Earth's core conditions in Earth and Planetary Science Letters

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Dobson D (2016) The phase diagram of NiSi under the conditions of small planetary interiors in Physics of the Earth and Planetary Interiors

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Hunt SA (2017) The thermal expansion of (Fe Ni )Si. in Journal of physics. Condensed matter : an Institute of Physics journal

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Lord O (2014) The NiSi melting curve to 70GPa in Physics of the Earth and Planetary Interiors

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Lord O (2014) The melting curve of Ni to 1 Mbar in Earth and Planetary Science Letters

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Lord OT (2015) The equation of state of the phase of NiSi. in Journal of applied crystallography

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Martorell B (2016) The elastic properties of hcp-Fe 1-x Si x at Earth's inner-core conditions in Earth and Planetary Science Letters

 
Description 1. At the pressures and temperatures of the Earth's core, nickel has little or no affect on the properties of iron. However, at lower pressures and temperatures, in, say, the cores of terrestrial planets, nickel may have a significant effect. NiSi has complex phase diagram, very different from that of FeSi, at low pressures, but identical at the conditions of the Earth's inner core. 2. The elastic properties of iron are significantly affected by pre-melting phenomena (i.e., dramatic changes in properties above 95% of the melting temperature). This could explain the ongoing problem of the seismological and mineralogical mismatch in wave velocities in the Earth's inner core. 3. We have determined the Clapeyron slope for the phase boundary between epsilon-FeSi and CsCl structures for both FeSi and NiSi. We find that both are negative with increasing temperature and place much-needed constraints on the very variable experimental data.
Exploitation Route Pre-melting phenomena need to be tested with the right compositions for the Earth's core specifically, and over a range of relevant materials more generally. Further work needs to be carried out on the complexities of the Fe-Ni phase diagram.
Sectors Other

 
Description Box Office Blunders 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact A UCL Earth Sciences workshop which seeks out the scientific blunders in the blockbuster film, "The Core". This highly interactive workshop introduces secondary school students to the physics of the interior of the Earth, as well as giving a brief insight into the techniques used by scientists to probe the deep depths of the planet beneath our feet.

The perception of what actually goes on inside the Earth was significantly altered as a result of this activity
Year(s) Of Engagement Activity 2012,2013,2014,2015,2016
URL http://www.ucl.ac.uk/EarthSci/impact/bob/index.html
 
Description Rocks and Minerals 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Rocks and Minerals: learn about the different types of rocks and minerals that make up our planet and those in our solar system. KS2
We run a series of Rocks and Minerals workshops for children in Key Stage 2, Years 3 and 4 (ages 7-9) to meet their curriculum needs via the statutory requirement: compare and group together different kinds of rocks on the basis of their appearance and simple physical properties. The children have a guided hands-on experience, learning also about the Earth as a whole through discussion and questions at the end of each session. We have three stations with sedimentary rocks, igneous and metamorphic rocks, and minerals. We find that the children are fascinated by, for example, the beauty yet poisonous nature of bismuth, the remarkable intergrowth of pyrite (which they always think is gold) and the age of a meteorite.
Year(s) Of Engagement Activity 2015,2016,2017,2018,2019
URL https://www.ucl.ac.uk/earth-sciences/impact/for-public/public-list/school-visits
 
Description Volcanoes and Earthquakes 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact We run a series of Volcanoes and Earthquakes workshops for children in Key Stage 3 and 4. This meets their curriculum needs via the statutory requirement: volcanoes and earthquakes. In this activity the children are taught about the origin and global impact of volcanoes; they then build a volcano themselves, analysing its formation and structure. Earthquakes are taught by demonstration in conjunction with the use of an IPhone and the iSeismometer app.
Year(s) Of Engagement Activity 2015,2016