Degree
Doctor of Philosophy (PhD)
Department
Engineering Science
Document Type
Dissertation
Abstract
In this dissertation, we report the results of the first-principles molecular dynamics (FPMD) simulations and data analysis on the thermodynamic, structural, and transport properties of iron-rich metallic liquids considering several light and heavy elements under wide ranges of pressure and temperature that are relevant to the earth’s core. Our simulations of pure liquid iron cover the pressure range from 0 GPa at 2000 K to 380 GPa at 7000 K perhaps representing the most extensive computational study to date. We studied four molten iron-rich alloys corresponding to 2.67 atom% of Ni, Co, Mo, and W at pressures up to 380 GPa and at temperatures 4000 to 7000 K. We also simulated H- and C-bearing metallic systems at similar pressure-temperature conditions. The calculated pressure-temperature-volume (P-V-T) results of all liquid alloys can be accurately described with a three-term form of the equation of state consisting of the reference pressure-volume isotherm, the thermal pressure, and the impurity pressure. Moreover, pressure is corrected for the difference in calculation and recent experimental results by adding the fourth term to the equation of state. The resulting density-pressure profile of pure iron liquid along a geotherm shows that the outer core suffers from a density deficient of ~ 6.8%. Our results show that the addition of Mo and W in liquid iron in any amount widens the density gap whereas the addition of H and C reduces the gap. Both Ni and Co do not affect the liquid density significantly and they behave as host iron atoms showing similar bond distances and local coordination. The calculated mean iron coordination number of Mo and W is somewhat larger than that of Ni and Co and host iron atoms thus implying a substitutional incorporation mechanism, whereas both H and C are undercoordinated consistent with their interstitial incorporation. Our results from extended FPMD simulations for pure iron and FeW liquids show that the diffusion coefficient of Fe varies modestly over the outer core regime taking values of ~3 to 5 x 10-9 m2s-1. The heavy impurity (W) atoms tend to diffuse slower than host iron atoms by almost a factor of two, unlike highly mobile H atoms. The calculated viscosity of pure and alloyed iron liquids remains almost unchanged taking a low value of 12±2 mPa.s at the outer core conditions. It implies that outer core convection may involve small-scale turbulent circulation and barodiffusion possibly causing heavy elements to accumulate near the inner core boundary.
Date
1-23-2023
Recommended Citation
Banjara, Dipendra, "First-Principles Molecular Dynamics Study of Liquid Iron-Rich Alloys Under Conditions of the Earth’s Core" (2023). LSU Doctoral Dissertations. 6041.
https://repository.lsu.edu/gradschool_dissertations/6041
Committee Chair
Karki, Bijaya B.
DOI
10.31390/gradschool_dissertations.6041