New high-pressure polymorphs in sodium halides

Static compression experiments to 50 GPa, employing X-ray diffraction through a diamond cell, were made on NaF, NaBr and NaI. NaF was found to transform from its initial B1 (NaCl-type) to the B2 (CsCl-type) structure at 27 ± 1GPa on the ruby fluorescence scale with a volume change at the transition of ?8.9%. New high-pressure polymorphs showing birefringence under microscope were found both for NaBr and NaI at 29 ± 1 GPa and 26 ± 1 GPa, respectively. X-ray diffraction patterns of these high-pressure polymorphs could not be indexed as the B2 structure. The GeS-type structure (the distorted NaCl structure) was tentatively assigned to the high-pressure polymorph of NaI.     

Small-angle neutron scattering study of temperature vs. salt dependence of clouding in charged micellar system

Clouding is studied by small-angle neutron scattering (SANS) on a charged micellar system of sodium dodecyl sulphate (SDS) and tetrabutylammonium bromide (TBAB) with varying temperature and salt NaCl. We show that the clouding occurs as a result of increase in the attractive potential between the micelles mediated by the dehydrated TBA(+) counterions on increasing temperature and in the presence of salt. Both micelles and clusters coexist at cloud point temperature (CP) and beyond CP. The addition of salt can be used to obtain CP at room temperature (30° C). The relative effect of different salts on clouding has been found in the order CaCl(2) > MgSO(4) > Na(2)SO(4) > NaF > NaCl > KCl > CsCl > NaBr > NaNO(3). This order is explained on the basis of two important roles played by salt ions: i) counterion condensation that increases the size of the micelles and ii) dehydration of TBA(+) counterions by salt ions for bridging the micelles.     

Surface segregation during the uptake of NO3 on coatings composed of NaI · 2H2O/NaBr · 2H2O and MgBr2 · 6H2O/MgCl2 · 6H2O binary salts: Solubility or deliquescence?

The uptake of NO₃ radicals on the surface of coatings prepared from the individual salts of NaI and NaBr dehydrates, hexahydrates of MgBr₂, and MgCl₂ and NaI · 2H₂O/NaBr · 2H₂O and MgBr₂ · 6H₂O/MgCl₂ · 6H₂O binary salts at various mole fractions of the doping salts, NaI · 2H₂O and MgBr₂ · 6H₂O in the initial aqueous solution was measured in a flow reactor by kinetic mass spectrometry. The dependences of the rates of the consumption of the reactant and of the formation of the products on the mole fraction of the doping salt made it possible to determine a quantitative relationship between the surface density of the doping salt and its mole fraction in the initial solution. A joint analysis of these dependences and the previously obtained data led to the conclusion that the deliquescence of the studied individual salts produces the predominant effect on the ratio between their surface densities.     

The effect of hydration of ions of inorganic salts on the shape of the Raman stretching band of water

The shape of the Raman stretching band of water molecules in aqueous solutions of electrolytes KBr, KCl, KI, NaCl, and NaI is studied. It is confirmed that the characteristics of the stretching band strongly depend on the concentration and type of salt. The behavior of different parameters of the band is explained in terms of the theory of hydration of salts.     

Dynamic properties of aqueous electrolyte solutions from non-polarisable,polarisable, and scaled-charge models

We investigated the dynamic properties of alkali halide solutions (NaCl, NaF, NaBr, NaI, LiCl, and KCl) using molecular dynamics simulations and several non-polarisable, polarisable, and scaled-charge models. The concentration dependence of shear viscosity was obtained with low statistical uncertainties to allow for calculation of the viscosity Jones-Dole B-coefficients. No prior values are available for the B-coefficients from molecular simulations of fully atomistic models for electrolyte solutions. In addition, we obtained diffusion coefficients with rigorous finite-size corrections to access ion mobilities; these provide insights on single ion hydration behaviour. We find that all models studied, even polarisable and scaled-charge models, quantitatively over-predict water structuring but qualitatively follow the experimentally determined Hofmeister series. All ion models considered are kosmotropes based on their calculated B-coefficient and diffusion coefficients, even for ions experimentally found to be chaotropes. These observations indicate that the water-ion interactions in these models are not adequately represented; additional interactions such as charge transfer must be incorporated in future models in order to better represent electrolyte solution properties.     

The thermochemical properties of transition metal complex salts with 1,5-diaminotetrazole

A method for determining the enthalpies of formation of coordination compounds of Cu(II), Co(II), Zn, and Cd perchlorates was developed. The enthalpies of solution of complex salts in water were measured. The enthalpy of combustion of the 1,5-diaminotetrazole ligand was determined, and the enthalpy of its formation in the standard state calculated. The experimental data were used to calculate the enthalpies of formation of the coordination compounds studied in the standard state.     

Shanker formulation needs modification at high pressures

It is found that the Shanker formulation widely used in the literature to study the thermal expansion of solids (at constant pressure) works under the effect of pressure (at constant temperature) up to a limited range (≈30 kbar). Large deviations occur, when the pressure range is increased, demonstrating the failure of the relation under high pressure (at constant temperature). We, therefore, propose the modification in the formulation on an empirical basis. The modified relation is used to study the compression behavior of ionic solids viz. NaF, NaCl, NaBr and NaI crystals. The results obtained with the modified relation are compared with the experimental data in the light of the results obtained from Shanker formulation and Birch-Murnaghan equation of state. A good agreement between theory and experiment demonstrates the validity of the modification presented in the present note.     

Thermochemistry of complex salts of transition metals with tetrazolyl ligands

A combined use of precise combustion calorimetry and reaction calorimetry made it possible to obtain the standard enthalpy of formation of complex salts of transition metals (nickel, zinc, and cadmium) with 2-(1H-1,2,3,4-tetrazol-1-yl)acetohydrazide ligands. The enthalpy of combustion of the ligand was determined using combustion calorimetry, based on which its standard enthalpy of formation was calculated. For measurements by reaction calorimetry, a thermochemical cycle was designed to determine the standard enthalpy of formation of complex salts. The enthalpies of solution in water and in a 0.1 N hydrochloric acid solution of the ligand and complex transition metal salts were measured. Based on these data, the enthalpy of formation of the salts and the enthalpy of formation of three new complex ions were calculated.     

On the problem of water adsorption on alkali halide cleavage planes,investigated by secondary ion mass spectroscopy

In the epitaxial growth of thin metallic films, atomic beam scattering and other work on (001) cleavage planes of alkali halides, the problem of water adsorption (physically or chemically) and its consequences often arose. In this paper (001) planes of LiF, NaF and NaCl were investigated in a UHV apparatus by secondary ion mass spectroscopy (SIMS) under a variety of conditions: air and vacuum cleaved, with and without heat annealing, with and without exposure to water at various crystal temperatures. The main results are: cleaved crystal surfaces are free of water and hydroxide layers even in the submonolayer region under UHV conditions. Water vapour at a partial pressure of 10^?9 Torr will only adsorb on cooled cleavage planes: for LiF below 200 K, for NaF below 250 K and for NaCl below 260 K, the adsorption energy for the fluorides being in the 200 meV region. Thicker layers of adsorbed water on LiF (001) will grow according to the Weber-Volmer mechanism. The formation of hydroxide layers on the fluorides is possible only under extremely forced conditions. Direct evidence is given that the “active sites” for the adsorption of H₂O consist in surplus Li metal atoms on the surface. Heat treatment in UHV at temperatures up to the melting point for several hours removes these active sites and yields crystal surfaces which do not adsorb water even if cooled. Cleavage planes of the water soluble NaCl showed a somewhat different behaviour.     

Lattice model calculation of hugoniot curves and the grüneisen parameter at high pressure for the alkali halides

A seven parameter shell model of the interatomic forces in the NaCl lattice is used to make a detailed lattice dynamics calculation at arbitrary volume, for fourteen alkali halides. The calculated normal mode spectrum gives an explicit vibrational contribution to the pressure and the elastic constants in the quasiharmonic approximation. The seven parameters are chosen to fit low pressure ultrasonic data and the low and high frequency dielectric constants. Prediction of the Grüneisen parameter γ, (?lnγ/?lnV), and δ_s = (?1/βB_s)(dB_s/dT) are in reasonable agreement with experiment. The calculated γ decreases monotonically with volume. Calculated Hugoniots are in good agreement with experiment for NaCl, NaBr and NaI, and in fair agreement for LiBr, LiI and NaF.     

The photoelectron spectra of gaseous alkali halides

The He I photoelectron spectra of the gaseous forms of CsF, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, NaI, KI, RbI, and CsI have been obtaine using a high-temperature spectrometer equipped with an internally-located, laser-beam heated sample oven. The spectral bands have been assigned molecul origins by use of MO calculations, spin—orbital splitting considerations, band intensity relations, polymer formation tendencies, and mass spectromet     

Molecules on kepler orbits: An experimental study

We have demonstrated experimentally that polar molecules revolve around the inner electrode of a charged cylindrical capacitor in helical trajectories that result from a superposition of a translational motion along and an orbital motion around the cylinder axis. In this way molecular beams can be guided over any given distance. The results have been obtained for nozzle beams of NaCl, NaBr, and NaI seeded in Kr. The capacitor bent into a toroid may be used as a storage ring for polar molecules in high field seeking rotational states.     

The adsorption of water vapour by lithium fluoride,sodium fluoride and sodium chloride

Water vapour adsorption isotherms have been determined volumetrically on samples of LiF, NaF and NaCl at 278.15, 288.15 and 298.15 K. The surface areas of the samples were determined by krypton adsorption at 77.5 K. Infrared measurements showed the presence of occluded solvents and complete removal of these species was effected under vacuum at the following temperatures; LiF, 823 K; NaF, 723 K; NaCl, 623 K. Except in the case of NaF, for which a BET Type II isotherm was obtained, the krypton isotherms exhibited single sharp steps at the following values of $\text{P}\text{P}{}_0$; LiF, 0.57; NaCl, 0.15. Similarly with water adsorption, the NaF and NaCl isotherms exhibited a single sharp step at the$\text{P}\text{P}{}_0$ values of 0.30 for NaF and 0.35 for NaCl. The isotherm for LiF outgassed at room temperature was of Type II, whilst for LiF outgassed at 673 K it was of Type III. Throughout the water runs no irreversible uptake was observed. The sharp steps in the krypton and water isotherms were attributed to phase transformations in the monolayer. Isosteric heats of adsorption for water vapour were generally invariant with coverage and close to the enthalpy of liquefaction of water. Theoretical adsorption potential energy calculations were carried out for adsorption of a water molecule above four sites on the (100) planes of the three adsorbents. The total adsorption potential was obtained as a sum of the dispersion, electrostatic, induction and repulsion interactions, and for each solid the most favourable adsorption site was above the cation. For adsorption directly above ions, the greatest contribution to the attractive potential was furnished by the electrostatic interaction. Except for the cation values of LiF and NaCl, the theoretical isosteric heats calculated from the potential curves were significantly lower than the experimental isosteric heats. All the samples possessed active sites depending on the adsorbate and outgassing temperature as follows; LiF (Kr, 298 K) 36%, LiF (Kr, 673 K) 15%, NaF (H₂O, 298 K) 18%, NaCl (Kr, 623 K) 20%, NaCl (H₂O, 623 K) 25%.     

Self-consistent field theory investigation of the behavior of hyaluronic acid chains in aqueous salt solutions

In this work we continue to develop a field-theoretic methodology, which combines the technique of Gaussian equivalent representation for the calculation of functional integrals with the continuous Gaussian thread model of flexible polymers for solving statistical–mechanical problems of polyelectrolyte solutions. We present new analytic expressions for the osmotic pressure, the potential of mean force, and the monomer–monomer pair distribution function, and employ them to investigate the structural and thermodynamic quantities of the polyelectrolyte system. We demonstrate the applicability of the method for systems of polyelectrolyte chains in which the monomers interact via a Yukawa-type pair potential. As a specific example, the present work focuses on aqueous solutions of hyaluronic acid with added salts NaCl and CaCl₂. Hyaluronic acid is a high molecular weight linear polysaccharide, which has a multitude of roles in biological tissues. We conclude that the effect of sodium chloride and calcium chloride on the osmotic properties of hyaluronic acid solutions can be accounted for by their contributions to the ionic strength. Nevertheless, the effects of coiling and self-association can be stimulated in solution by added salt.     

Conductance studies of NaBPh4, NBu4I, NaI, NaCl, NaBr, NaClO4 and the limiting ionic conductance in water + propan-1-ol mixtures at 298.15 K

The electrical conductivities of NaBPh₄, NBu₄I, NaI, NaCl, NaBr and NaClO₄ have been studied in the mixtures of propan-1-ol with water. The obtained results were analysed using the Fuoss–Justice equation. The individual limiting ionic conductivities of Na⁺, NBu₄⁺, BPh₄⁻, I⁻, Cl⁻, Br⁻, ClO₄⁻ ions have been determined using the Fuoss–Hirsch assumption. The dependencies of the limiting molar conductances Λ_o and Walden products Λ_oη versus mixed solvent composition have been discussed.     

The electrical conductivity of chloride melts

The interrelationship between electrical conductivity, molar volume and enthalpy of mixing was studied for molten chlorides and their mixtures. The dependence of electrical conductivity and activation energy on the molar volume is different for various groups of salts. The dependence of specific conductivity on molar volume obtained for molten alkali chlorides was found to be similar to other chloride salts. The specific conductivity of binary mixtures that lack strong chemical interactions between the components can also be described by the proposed empirical equation. The enthalpy of mixing should be taken into consideration for these chemical interactions.     

Heat of formation of solid solution of alkali halides

Based on a semicontinuum model, the electrostatic, the polarisation, and the repulsive energy change of a lattice is calculated numerically, as a function of the relaxation of the nearest neighbouring ions of a substitutional impurity in an alkali halide crystal. It is found that for a particular displacement, the total energy change of the lattice is a minimum. Thus the heat of formation of a dilute solid solution is obtained. Here, we report calculations on the heat of formation of the following systems-Na⁺ in LiCl, Li⁺ in NaCl, K⁺ in NaCl, Na⁺ in KCl, Rb⁺ in NaCl, Na⁺ in RbCl, F^? in NaCl, Cl^? in NaF. Br^? in NaCl and Cl^? in NaBr.     

Effect of cubic hydrostatic compression on the elastic properties of single crystals of halides of sodium and potassium

Experimental studies (by the ultrasonic pulse method) and theoretical investigations (with the model of polarizable ions) were made of changes in the elastic moduli of single crystals of NaCl, NaBr, NaI, KCl, KBr, and KI in cubic hydrostatic compression in the pressure range up to 10⁸ Pa at a temperature of 298°K. The experimental unit and method of measurement are described. Theoretical values of the derivatives of the elastic moduli with respect to pressure are presented for the compounds studied and are compared with existing empirical data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 71–75, October, 1985.     

A Monte Carlo calculation of thermodynamic properties for the liquid NaCl+KCl mixture

The mixing process NaCl+KCl →(Na, K)Cl in the liquid state at T=1083 K and zero pressure is simulated by means of Monte Carlo calculations. A cubic box with periodic boundary conditions containing 216 ions interacting according to a pair potential of the Huggins-Mayer form served as a model of the system. Thermodynamic properties are calculated for the mixture and the pure salt models and compared with experiments. Radial and angular distribution functions are obtained. A perturbation theory of the heats of mixing of molten salts and the ‘random mixture approximation’ are commented on in the light of the Monte Carlo results.