Ion solvation and association and water structure in an aqueous cerium (III) chloride solution in the gigapascal pressure range

Abstract

X-ray diffraction measurements are performed on a 1 m (= mol kg -1 ) CeCl3 aqueous solution over a temperature range of 300 K to 600 K and a pressure range of 0.1 MPa to 4 GPa. The experimental interference functions are analyzed by an empirical potential structure refinement (EPSR) modeling.The Ce 3+ coordinates water molecules in a tricapped trigonal prism configuration under the ambient condition. The number of water molecules around Ce 3+ changes from 8.8 at 0.1 MPa/300 K to 11.5 at 4 GPa/600 K. The number of water molecules around Clchanges drastically from 10 under the ambient condition to 17 at 4 GPa/600 K. The tetrahedral-like network structure of water under the ambient condition is transformed toward a simple liquid-like packing in the GPa pressure range. The corresponding coordination number is increased from 4.3 in the ambient condition to 9.7 at 4 GPa/600 K. The Ce 3+ -Classociation decreases with increasing pressure.

An X-ray and Neutron Scattering Study of Aqueous MgCl2 Solution in the Gigapascal Pressure Range

“…This structural difference of solvent water is ascribed to the solute concentrations, i.e., more water molecules are present in a 2 m MgCl 2 solution than in a 3 m NaCl solution. A similar change in solvent water's structure has also been observed for a 1 m CeCl 3 solution [11]. When the solution is heated to 500 K at 1 GPa, the O W -O W pdfs show a drastic change in the second and third peaks evolved at 5.6 and 8.2 Å, respectively, showing the transformation to a random dense-packing structure.…”

“…From our previous studies of aqueous 3 m NaCl [5,7], 3 m RbCl [8], 2 m CaCl 2 [10], and 1 m CeCl 3 [11] solutions in the GPa pressure range, we found that the tetrahedral network structure of solvent water at 0.1 MPa/300 K transforms to a random dense-packing structure in the GPa pressure range. As seen in the pdfs of Ow-Ow in Figure 7 (left frame), three peaks are observed at 2.8, 4.1, and 6.8 Å, characteristic for the tetrahedral network structure of water, at 0.1 MPa/300 K. The structure parameters are summarized in Table 4.…”

“…From our previous studies of aqueous 3 m NaCl [5,7], 3 m RbCl [8], 2 m CaCl2 [10], and 1 m CeCl3 [11] solutions in the GPa pressure range, we found that the tetrahedral network structure of solvent water at 0.1 MPa/300 K transforms to a random dense-pack-…”

“…Due to the development of a highpressure cell and data acquisition techniques at synchrotron and pulsed neutron sources, high-pressure and high-temperature X-ray-and neutron-scattering measurements in the GPa pressure range became possible. Many studies have been conducted on aqueous solutions of electrolytes, such as NaCl [5][6][7], RbCl [8], CaCl 2 [9,10], and CeCl 3 [11].…”