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Boiling of silicate liquids, II: a molecular dynamic and thermodynamic analysis

Applicant Connolly James A. D.
Number 162450
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geochemie und Petrologie ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geochemistry
Start/End 01.01.2016 - 31.12.2017
Approved amount 243'600.00
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All Disciplines (5)

Discipline
Geochemistry
Astronomy, Astrophysics and Space Sciences
Material Sciences
Geophysics
Physical Chemistry

Keywords (6)

Thermodynamics; Molecular Dynamics; Silicate vaporization; Phase Equilibria; Equation of state; Giant impacts

Lay Summary (German)

Lead
Thermodynamic properties of liquid-saturated silicate vapor are of importance in planet and satellite forming processes associated with giant impacts. Silicate liquid-vapor phase fields lie at ~3000 K at 0.1 MPa and terminate at a critical point that is variously estimated to lie at 5000-15000 K and 0.2-4 GPa. The estimated conditions are inaccessible by present experimental techniques; therefore, this study will constrain these conditions through molecular dynamic super-computer simulations.
Lay summary
Für die Riesen-Impact-Hypothese der Mondentstehung dynamische Modellierung deutet darauf hin, dass die Staubscheibe würde in erster Linie des Schlagzusammengesetzt sein, doch die Erde und Mond sind chemisch ähnlich. Es wurde vorgeschlagen, Mond-Erde-System wurde von einer frühen Phase der Massenaustausch zwischen Proto-Erde und seine Staubscheibe homogenisiert. Das Silikat-Flüssig-kritischen Punkt definiert die niedrigste Temperatur, bei der solche Austausch könnte ohne chemische Fraktionierung zu nehmen. Kenntnis der Bedingungen des kritischen Punktes, der geschätzt wird, um bei Temperaturen von 5.000 bis 14.000 K und Drücken von 0,1-1 GPa liegt, ist für die Durchführbarkeit der Einführung nach einem Aufprall Homogenisierung. Diese Studie wird Super-Computer molekulardynamische Berechnungen verwenden, um das Siliciumdioxid Siedelinie und seinen kritischen Punkt beschränken.
Direct link to Lay Summary Last update: 03.01.2016

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
Bulk properties and near-critical behaviour of SiO2 fluid
Green Eleanor C. R., Artacho E., Connolly J. A. D. (2018), Bulk properties and near-critical behaviour of SiO2 fluid, in Earth and Planetary Science Letters, 491, 11-20.
Uncertainty of mantle geophysical properties computed from phase equilibrium models
Connolly James A. D., Khan Amir (2016), Uncertainty of mantle geophysical properties computed from phase equilibrium models, in GEOPHYSICAL RESEARCH LETTERS, 43(10), 5026-5034.

Collaboration

Group / person Country
Types of collaboration
Emilio Artacho/NanoGUNE Research Center, San Sebastian, Spain Spain (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication

Associated projects

Number Title Start Funding scheme
146872 Boiling of silicate liquids: a molecular dynamic and thermodynamic analysis 01.01.2014 Project funding (Div. I-III)
146872 Boiling of silicate liquids: a molecular dynamic and thermodynamic analysis 01.01.2014 Project funding (Div. I-III)

Abstract

We seek an extension of a project that was funded, but curtailed, apparently because one of the six reviewers of the original proposal doubted the feasibility of the proposed first principle molecular dynamic (FPMD) calculations. We have now demonstrated the feasibility of the calculations and seek an extension now, 15 months into the project, to assure that there is no lapse in the funding for the postdoctoral researcher responsible for the FPMD calculations. Because neither the project goals nor its methods have changed, this proposal differs from the original primarily in that it has been updated to account for interim results.The thermodynamic properties of liquid-saturated silicate vapor are of importance to understanding planet and satellite forming processes associated with giant impacts. These include the relationship between impact energy and the consequent melting and thermal evolution (e.g., Benz et al. 1986, Stevenson 1987, Canup 2008), development of the instability that causes debris disks to spread beyond the Roche limit at which point satellites may coalesce (e.g., Thompson & Stevenson 1988, Machida & Abe 2004, Ward 2012), and chemical fractionation caused by the escape of a silicate atmosphere (Genda & Abe 2003) or interactions between the protoplanet and its disk (Pahlevan et al. 2011). Silicate liquid-vapor phase fields lie at ~3000 K at 0.1 MPa and terminate at a critical point or, more generally, a maxcondentherm that is variously estimated to lie at 5000-15000 K and 0.2-4 GPa (e.g., Stevenson 1987, Melosh 1990, Guillot & Sator 2007, Melosh 2007). Such conditions, which can be realized during giant impacts (e.g., Canup 2004, Reufer et al. 2012), preclude direct experimental observation except at pressures on the order of a 1-10 Pa (e.g., Mysen & Kushiro 1988, Nagahara et al. 1994) or, most recently, by extraordinarily complex shock-wave experiments (Kraus et al. 2012).Thus an equation of state (EoS) is required to predict liquid-vapor phase equilibria and thermodynamic properties from the limited experimental data. To date, the only EoS suitable for this purpose is the MANEOS for SiO2 (Melosh 2007), but the MANEOS makes no provision for compositional degrees of freedom and does not provide the information on fluid speciation. Such information is essential for the evaluation of chemical (isotopic) fractionation effects. We propose to remedy these deficiencies by parameterizing a van der Waals-type equation of state to characterize silicate fluids in MgO-FeO-SiO2 system. Herein we demonstrate the feasibility of this approach by using the Modified Redlich-Kwong EoS (MRK, deSantis et al. 1974) to predict properties and phase equilibria in the Si-O system to pressures (~1 GPa) that are adequate to complement the high-pressure predictive capacity of empirical Hugoniot equations and/or the MANEOS. To calibrate the EoS we propose a FPMD study of silica fluids. This study will not only constrain the p-v-T state and viscosity of low density silica liquid, but also locate the boiling curve at elevated pressure and address the issue of non-stoichiometric boiling. Our preliminary FPMD results suggest silica liquid does become increasingly molecular with increasing temperature along its boiling curve. The FPMD results are also in remarkably good agreement with both p-v-T relations and Si-O coordination numbers independently predicted by the MRK EoS formulation.
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