Low-Dimensional Network Formation in Molten Sodium Carbonate

Abstract

Molten carbonates are highly inviscid liquids characterized by low melting points and high solubility of rare earth elements and volatile molecules. An understanding of the structure and related properties of these intriguing liquids has been limited to date. We report the results of a study of molten sodium carbonate (Na2CO3) which combines high energy X-ray diffraction, containerless techniques and computer simulation to provide insight into the liquid structure. Total structure factors (Fx(Q)) are collected on the laser-heated carbonate spheres suspended in flowing gases of varying composition in an aerodynamic levitation furnace. The respective partial structure factor contributions to Fx(Q) are obtained by performing molecular dynamics simulations treating the carbonate anions as flexible entities. The carbonate liquid structure is found to be heavily temperature-dependent. At low temperatures a low-dimensional carbonate chain network forms, at T = 1100 K for example ~55% of the C atoms form part of a chain. The mean chain lengths decrease as temperature is increased and as the chains become shorter the rotation of the carbonate anions becomes more rapid enhancing the diffusion of Na+ ions.

Polymerized 4-Fold Coordinated Carbonate Melts in the Deep Mantle

“…This is in stark contrast to silicate glasses that lose their medium-range order with increased P (Sato and Funamori, 2008), but consistent with ab initio calculations on carbon-bearing silicate melts reporting Pinduced polymerization of carbonate species into dimers and with the silicate network (Ghosh et al, 2017;Solomatova and Asimow, 2019). A second noticeable feature is the decrease of the contribution at 4 Å −1 attributed in molten carbonates to the O-O bond (Wilding et al, 2016). On radial distribution functions, g(r) (Figure 3B), the C-O contribution is clearly visible at 1.2-1.3 Å with none or little overlap with the second contribution (Fe-O and O-O) at ∼2 Å in the glass, and with some overlap in the melt.…”

Aerodynamic levitation, supercooled liquids and glass formation

“…A snapshot of a molecular dynamics configuration of liquid na 2 cO 3 taken at T = 1100 K showing the formation of chains through the formation of bonds between c (red), and O (blue) atoms. na atoms are shown as dots [93].…”

Structure and diffusion of molten alkali carbonate salts at the liquid-vacuum interface

“…1). This study uses the interaction parameters developed by Tissen and Janssen , sometimes called the JT model, which have been employed for many similar studies of molten alkali carbonate salts and as such provides a robust body of literature for validation and reference Tissen, Janssen & Eerden, 1994;(Koishi et al, 2000;Ottochian et al, 2016;Wilding et al, 2016;Roest et al, 2017;Du et al, 2017;Du et al, 2019;Ding et al, 2018;Gutiérrez et al, 2018). The JT model employs coulombic interactions with long-ranged interactions described by Ewald summation and Born-type repulsion parameterized from quantum mechanical calculations .…”