Sound wave propagation and thermal relaxation in Fe and Fe-alloys at extreme conditions

Axe 5 - Matériaux en conditions extrêmes

Thèse d'Eric Edmund

Projet de recherche commencé le 1er octobre 2015.

Soutenance le 24 octobre, 9h30
Salle de conférence 401 - 4e étage - Tour 23 - Couloir 22-23
Campus Pierre et Marie Curie
Sorbonne Université

Cotutelle

• Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC)
  Porteur de projet : Daniele Antonangeli
  Co-encadrant : Frederic Decremps
• Institut des Sciences de la Terre de Paris (ISTeP)
  Co-encadrant : Lapo Boschi

Résumé du projet

For nearly 40 years, there has been a robust seismological model (PREM - Preliminary Reference Earth Model) which reports the elastic properties (compressional velocity - Vp, shear velocity - Vs, and density) of the Earth's interior, and yet there is still no clear consensus on the composition of the material which can match such properties at the pressures and temperatures of the core, the metallic portion of the planet. While iron has elastic properties which are close to those of the solid inner core, iron alone is too heavy to match the density of the inner core. In light of this, and based on a series of cosmochemical and geochemical arguments, Si has been proposed for many years in varying quantities as a material which could explain the difference in material properties between Fe and PREM. Furthermore, Fe-Si alloys are important technological materials which are common in a wide variety of different industries.

Using a combination of Synchrotron X-ray Diffraction and Picosecond Acoustics, density and Vp of Fe-Si and Fe-Ni-Si alloys have been measured to pressures and temperatures exceeding 1 Mbar and 2000 K. This is the the first systematic experimental study of Fe alloys performed under quasihydrostatic conditions, using a direct method for the measurement of acoustic travel time at extreme conditions. Noteworthy, these studies were performed on well-characterized samples of high quality, synthesized by novel methods.

Obtained data allows an accurate determination of Velocity-Density relations, both P-V and P-V-T equations of state, and axial ratios of a variety of technologically and geophysically important Fe-Si and Fe-Ni-Si alloys. These results are used to discuss the elastic properties of Fe-Si alloys at high pressure - high temperature conditions in relation to Si concentration and Si ordering, and to place tight constraints on Si abundance in the Earth's inner core.

Publication

• E. Edmund, D. Antonangeli, F. Decremps, F. Miozzi, G.Morard, E. Boulard, A. N. Clark, S. Ayrinhac, M. Gauthier, M. Morand, M. Mezouar
  Velocity‐Density Systematics of Fe‐5wt%Si: Constraints on Si Content in the Earth's Inner Core
  JGR Solid Earth    
  DOI : 10.1029/2018JB016904Universite de Paris VI

Interventions et conférences

• High-Pressure Mineral Physics Seminar (HPMPS-9)
  24-28 Sep 2017 Saint Malo, France
  https://hpmps-9.sciencesconf.org/161871
• 20th EGU General Assembly, EGU2018
  4-13 April 2018 in Vienna, Austria
  http://adsabs.harvard.edu/abs/2018EGUGA..2013148E