4:00 PM - 4:15 PM
[SIT20-09] The iron charge disproportionation reaction in silicate melts: The effects of oxygen fugacity
Keywords:Ab initio free energy calculations, Iron charge disproportionation reaction, Magma ocean
It is widely thought that the accretion of materials during the growth of the proto-Earth caused a large-scale melting, resulting in the formation of magma ocean (MO). Recently, high-pressure experiments have continuously reported that the charge disproportionation (CD) reaction of iron facilitates in molten silicates under high pressure as suggested in solids [Armstrong et al., 2019; Kuwahara et al., 2023; Zhang et al., 2024]. This implies that the iron CD reaction might lead to the nucleation of metal droplets in the MO, which might have had some contribution to the formation of a metallic proto-core through their gravitational separation from silicate melt. A considerable discrepancy is however seen in the pressure dependence of the iron CD reaction reported in the experimental outputs. And although theoretical assessment are worthy as well, no studies have been conducted on this reaction so far.
In this study, the thermodynamic stability and pressure dependence of the iron CD reaction in MO are directly evaluated from the Gibbs free energies of molten silicates containing divalent and trivalent iron ions and liquid iron calculated by a non-empirical first principles way. These are performed using the originally developed thermodynamic integration molecular dynamics program [Taniuchi and Tsuchiya, 2018] over a wide pressure range under different temperature conditions. In this presentation, in addition to the pressure and temperature effects on the iron CD reaction, I will particularly focus on the effects of oxygen fugacity, which are thought to be a key parameter to control the CD reaction, the and try to rationalize the predicted results from the microscopic point of view.
In this study, the thermodynamic stability and pressure dependence of the iron CD reaction in MO are directly evaluated from the Gibbs free energies of molten silicates containing divalent and trivalent iron ions and liquid iron calculated by a non-empirical first principles way. These are performed using the originally developed thermodynamic integration molecular dynamics program [Taniuchi and Tsuchiya, 2018] over a wide pressure range under different temperature conditions. In this presentation, in addition to the pressure and temperature effects on the iron CD reaction, I will particularly focus on the effects of oxygen fugacity, which are thought to be a key parameter to control the CD reaction, the and try to rationalize the predicted results from the microscopic point of view.