R. D. Oparin

Structure formation of aqueous electrolyte solutions under extreme conditions by the extended RISM-approach. A possibility of predicting

Abstract In the present study the possibility to use the extended RISM-approach in conjunction with the modified TIPS-water model for predicting structural properties of aqueous electrolyte solutions under extreme conditions (high pressure and high temperatures) is considered. The structural characteristics are computed by the site-site Ornstein-Zernike integral equation in the framework of hypernetted chain closure for aqueous LiCl and NaCl solutions with different state parameters. The effect of temperature and pressure on structure formation of these systems is under observation during the research. The obtained results are compared with experimental structural work data and computer simulations for the same objects. The agreement between our data and those available from the literature proves the possibility to use the extended RISM-approach for predicting structural parameters of liquid state systems in state parameter regions, which are problematic for making experiments.

Effect of electrolyte additions and temperature on the structure self-organization of the water subsystem in water-supercritical Co2-NaCl ternary mixtures

The effect of electrolyte additions (6, 15, 23 wt % NaCl) and temperature (T 313–633 K, p 250 bar) on the structural state of the water subsystem in the water-rich phase of the water-supercritical CO2-NaCl ternary system was studied by IR spectroscopy and the method of integral equations. With increasing salt concentration, the breaking effect of temperature on the structure of the water subsystem becomes weaker, and the fractions of H-bonded water n-mers are redistributed. In systems with a nonzero NaCl concentration, tetramers exist throughout the examined temperature range, and trimers become the main structural unit of the water subsystem at temperatures close to the critical point. The prevalent structural components of the system with 0 wt % NaCl near the critical point are dimers. The O⋯H bonds between water molecules and Cl⋯H bonds in the nearest surroundings of the anions make approximately equal contributions to the overall pattern of H bonds in the water subsystem.

Influence of isobaric heating of hydrogen bonding in precritical water

IR spectroscopy and statistical mechanic calculations were used to study the influence of isobaric heating (p 250 bar, T 493–633 K) on H-bond distribution in precritical water. As the temperature rises, the intermolecular water H-bond network is much destroyed, and the fractions of H-bonded n-mers are redistributed. At temperatures close to critical, water has a cluster-like structure with prevalence of dimers and trimers.

Relationship between the Structural State of Water and the Character of Ion Hydration in Concentrated 1:1 Aqueous Solutions of Electrolytes in Extreme Conditions

AbstractIt is suggested that the association parameter A be used as an indicator demonstrating the effect of extremal conditions on the structure of water in the series of solutions

STRUCTURAL PROPERTIES OF CONCENTRATED AQUEOUS SOLUTIONS OF LITHIUM CHLORIDE NEAR THE CRITICAL POINT OF WATER AS CALCULATED BY THE INTEGRAL EQUATION METHOD

LiCl{\kern 1pt} \to {\kern 1pt} NaCl{\kern 1pt} \to {\kern 1pt} KCl

Structural Parameters of Concentrated Aqueous Solutions of Lithium Chloride under Extreme Conditions, Determined by the Method of Integral Equations: Effect of Isothermal Compression

. Analysis of the diagrams “A parameter–external conditions” permitted us to establish that compression has a weak effect on association of water molecules in the systems, in which case the effect of the ion field on the mutual ordering of solvent molecules does not change. In conditions of strong compression in NaCl–H2O, positive hydration of Na+ changes to negative. On the contrary, at elevated temperatures, the probability of association of bulk water molecules increases and the effect of ions on the structure of the solvent decreases. Positive hydration of Li+ and negative hydration of K+ become less pronounced, and Na+ has no ordering effect on the structure of the solvent any longer.

Structural parameters of concentrated aqueous solutions of LiCl under extreme conditions, as calculated by the method of integral equations. Effect of temperature

The structure of water and the influence of halide ions on the structure formation of concentrated LiX : H2O (1 : 5; X = Cl, Br, I) solutions at low temperatures were studied by the method of integral equations. Based on the results obtained, supercooling of pure water is expected to significantly enhance the tetrahedral ordering of its molecules, strengthen hydrogen bonding in the system, and decrease the number of the nearest-neighbor water molecules. The effects for the solutions on lowering the temperature include a partial restoration of the tetrahedral network of H-bonds of the solvent molecules, insignificant increase in the number of the nearest-neighbor water molecules, enhancement of the coordination ability of Li+ cation, strengthening of hydrogen bonding between anions and water molecules in the first hydration shell, increase in the number of solvent-separated ion pairs, and weakening of the temperature effect on these structural parameters in the following order of solutions: LiCl > LiBr > LiI. The probability of contact ion pair formation in the systems studied should appreciably decrease. The temperature should to a greater extent influence the associative ability of larger anions.

Features of Cation Hydration in Concentrated Aqueous Solutions of MeCl (Me = Li, Na, K, Rb): A Study by the Method of Integral Equations

AbstractThe integral equation method was used to study structure formation in concentrated aqueous solutions of lithium chloride in the near-critical region (P = 20 MPa, T = 298-623 K). It is found that when the LiCl–H2O system passes from a concentrated state to a melt-like one (