Axial Compressibility and Thermal Equation of State of Hcp Fe-5wt%Ni-5wt%Si

Eric Edmund (1) , Francesca Miozzi (1) , Guillaume Morard (1) , Eglantine Boulard (1) , Alisha Clark , Frédéric Decremps (1) , Gaston Garbarino (2) , Volodymyr Svitlyk (3) , Mohamed Mezouar (2) , Daniele Antonangeli (1)

1 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie
2 ESRF - European Synchrotron Radiation Facility
3 Institut für Anorganische und Analytische Chemie

Knowledge of the elastic properties and equations of state of iron and iron alloys are of fundamental interest in Earth and planetary sciences as they are the main constituents of telluric planetary cores. Here, we present results of X-ray diffraction measurements on a ternary Fe-Ni-Si alloy with 5 wt% Ni and 5 wt% Si, quasi-hydrostatically compressed at ambient temperature up to 56 GPa, and under simultaneous high pressure and high temperature conditions, up to 74 GPa and 1750 K. The established pressure dependence of the c/a axial ratio at ambient temperature and the pressure-volume-temperature (P-V-T) equation of state are compared with previous work and literature studies. Our results show that Ni addition does not affect the compressibility and axial compressibility of Fe-Si alloys at ambient temperature, but we suggest that ternary Fe-Ni-Si alloys might have a reduced thermal expansion in respect to pure Fe and binary Fe-Si alloys. In particular, once the thermal equations of state are considered together with velocity measurements, we conclude that elements other than Si and Ni have to be present in the Earth's inner core to account for both density and seismic velocities.

Mots clés: high temperature; high pressure; silicon; nickel; Earth's core; telluric planetary cores; equation of state; iron alloys

Domaines: Science des matériaux [cond-mat.mtrl-sci]; Minéralogie

Eric Edmund, Francesca Miozzi, Guillaume Morard, Eglantine Boulard, Alisha Clark, et al.. Axial Compressibility and Thermal Equation of State of Hcp Fe-5wt%Ni-5wt%Si. Minerals, 2020, 10 (2), pp.98. ⟨10.3390/min10020098⟩. ⟨hal-02526718⟩