Location of Thesis Examination

1027 B&GS

Date of Public Lecture

12-16-2013

Location of Public Lecture

Room 1084 B&GS

Degree

Doctor of Philosophy

Program

Geophysics

Supervisor

Dr. Richard A. Secco

Abstract

The electrical resistivity of Fe17wt%Si alloy was measured within the solid and the liquid phases up to 5 GPa in 200 ton and 1000 ton cubic anvil presses. Special attention was paid in the investigation to the challenges in resistance measurements in connection with the contaminations originating from the electrode materials and also the dominant role of the electrode resistances in the final results. The current results on Fe17Si alloys yielded insights to the manifestations of the magnetic, order-disorder and melting transitions on the electrical resistivity at high P, T. A drop in electrical resistivity in Fe17Si was observed at the melting boundary at high pressures up to 5 GPa as reported by Baum et al. (1967) at 1 atm. The liquid resistivity results from the present study provide insight on the effect of Si on the electrical resistivity of Fe-Si alloy specifically that the difference in resistivity between Fe and Fe17Si decreased with increasing pressure. The model of saturation resistivity (Mooij, 1973) describes saturation of electron-scattering where the electron mean free path approaches the interatomic distance (Ioffe-Regel criteria); the temperature coefficient of resistivity (TCR) has been shown to change sign due to compositionally-induced changes to the mean free path and interatomic distance. The results of the present study show that pressure can also provide a mechanism for resistivity saturation and change of TCR sign most likely due to reduction in interatomic distance. The present electrical resistivity results of Fe17Si were interpreted in terms of the resistivity saturation model in order to estimate the electrical resistivity of the Earth’s outer core. This yielded a range of 9.0×10-7Ωm to 9.4×10-7Ωm which is in agreement with the very recently reported studies on the electrical resistivity of the Earth’s core. Using Wiedemann-Franz law, electrical thermal conductivities were calculated to be 103 Wm−1K−1 to 109Wm−1K−1.

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