Concentrated LiCl Solutions Research Articles

Application of luminescence methods in the study of the structure of aqueous electrolyte solutions

Abstract Luminescence methods have been applied to the study of solutions of concentrated aqueous electrolytes of LiCl, CaCl 2 , LiBr, CsCl with addition to those of LnCl 3 , NiCl 2 , MnCl 2 . The rate constants of energy transfer from Tb(III) ions to Er(III) ions to Er(III), Ni(II), Mn(II) were measured in solutions of different electrolytes. So as the energy transfer rate depends on the distance between the energy donor and acceptor, it can be shown from this study, that the labile nanostructures of lanthanide ions are formed in concentrated aqueous solutions of LiCl and to a lesser degree in solutions of CaCl 2 . The concentration of lanthanide ions in labile nanostructures is close to that of a saturated aqueous solution of LnCl 3 . The labile nanostructures consist of no less than several tens of lanthanide ions which exchange with ions of the solution during the time of less than one μs. The mixed labile nanostructures of lanthanide and Ni(II) or Mn(II) ions are also formed in concentrated LiCl solutions, but they are less stable. The dependence of labile nanostructure stability on temperature and on the addition to the electrolyte solution of other multicharge cations was also studied. The nature of the phenomenon of the labile nanostructure formation is discussed.

Measured and predicted ternary diffusion coefficients for concentrated aqueous LiCl + KCl solutions over a wide range of compositions

Taylor dispersion and differential refractometry are used to measure mutual diffusion (chemical interdiffusion) in ternary LiCl + KCl + H2O solutions at 25 °C. Ternary diffusion coefficients are reported for 23 different compositions at total electrolyte concentrations of 0.5, 1.0, 2.0 and 3.0 mol dm−3. The results show that LiCl concentration gradients drive substantial coupled flows of KCl, but only weak flows of LiCl are produced by KCl gradients. In dilute solutions, aqueous K+ ions are nearly twice as mobile as Li+ ions and KCl diffuses significantly more rapidly than LiCl. In concentrated LiCl solutions, however, KCl diffuses more slowly than LiCl. The measured diffusion coefficients are in close agreement with values predicted by a model of mixed electrolyte diffusion which includes electrostatic coupling, ionic hydration, solvent counterflow, and changes in the viscosity and the thermodynamic driving forces for diffusion. The average magnitude of the difference between the measured and predicted diffusion coefficients is 0.03×10−5 cm2 s−1.

Thermal and Mechanical Properties of Collagen/Poly (vinyl alcohol) and Chitosan/Poly (vinyl alcohol) Blends: Effect of Crosslinking with Glutaraldehyde.

Collagen/poly (vinyl alcohol) (PVA) and chitosan/PVA blends were cast into films from mixed polymer solutions in aqueous acetic acid. Transition behavior of two series of binary blends was examined by DSC measurements. Composition-dependent shift in the glass transition temperature (Tg) of PVA was observed for chitosan/PVA blends and the melting point of PVA was depressed systematically with increasing chitosan content. On the other hand, the less significant shift in Tg of PVA was observed for collagen/PVA blends. These results suggest that the chitosan is compatible with PVA, while collagen is incompatible with PVA. An attempt was made to introduce crosslinks into both series of blends with the aid of glutaraldehyde. Enhancement of the compatibility was achieved for collagen/PVA blends and the mixing state was improved by the introduction of the crosslinking in consequence of the bridge formation between PVA and collagen molecules. On the other hand, chitosan/PVA blends lost their high compatibility due to the preferential crosslinking among chitosan chains. Elongation/contraction behavior of the crosslinked collagen/PVA blends during the alternate immersion in water and concentrated LiCl solution was examined. Further, the moduli of crosslinked collagen/PVA and chitosan/PVA blend hydrogels were also discussed in terms of the degree of crosslinking and the higher order structure of collagen in the hydrogel.

Mutual diffusion in solutions of alkali metal halides Aqueous LiF, NaF and KF at 25[deg

A Taylor dispersion tube has been used to measure mutual diffusion coefficients (interdiffusion coefficients) for binary aqueous solutions of LiF (from 0.002 to 0.050 mol dm−3), NaF (0.002 to 0.900 mol dm−3) and KF (0.002 to 8.00 mol dm−3) at 25 °C. The Taylor results together with previously reported activity and density data are used to evaluate resistance coefficients for the mutual diffusion of aqueous NaF and KF. Diffusion coefficients, resistance coefficients and relative viscosities of the fluoride solutions are compared with the corresponding quantities for aqueous solutions of LiCl, LiBr, NaF, NaCl, NaBr, NaI, KCl, KBr, KI, RbCl and CsCl. In contrast to the resistance coefficients of aqueous KCl, KBr, KI, RbCl and CsCl solutions which are relatively insensitive to changes in composition, the resistance coefficients of concentrated LiCl, LiBr, NaCl, NaBr, NaI and KF solutions increase sharply with increasing salt concentration as a consequence of the higher viscosities of these solutions.

Reduction of Gold in Concentrated LiCl

Reduction of gold from concentrated solutions of LiCl containing low gold concentration was investigated using electrochemical and microscopic techniques. Cyclic voltammetric measurements in solutions containing 0.5 mM Au in 6 M LiCl show two reduction peaks on both platinum and HOPG electrodes, indicating that the reduction of gold occurs in two steps. Chronocoulometric measurements on platinum electrodes give evidence of a two‐electron reaction in the region of the first reduction peak, whereas in the region of second peak a three‐electron reaction is approached. The morphology of deposited gold on highly oriented pyrolytic graphite (HOPG) substrates from solutions containing in 6 M LiCl was characterized using in situ scanning tunneling microscopy (STM). In situ STM images in the potential range of the first reduction peak show the formation of gold clusters weakly bound to the HOPG substrate. In the region of the second reduction peak an increase in the z‐range of the STM images was observed due to the formation of the three‐dimensional gold bulk phase. However no stable gold clusters could be imaged in situ in this potential range due to reproportionation of freshly deposited gold and Au(III) from the electrolyte to form Au(I).

Testing of mode-coupling theory through impulsive stimulated thermal scattering

Abstract Impulsive stimulated thermal scattering, a time-domain light scattering technique spanning ps-ms time scales, allows a number of experimental tests of mode-coupling theory (MCT) predictions. Time-dependent acoustic responses and also slower relaxational responses to sudden heating are observed. From the acoustic responses, mechanical modulus spectra are deduced which permit testing of MCT predictions for α and β relaxation dynamics. From the relative intensities of acoustic and relaxational signals, the prediction of a cusp in the temperature-dependence of the nonergodicity parameter (Debye-Waller factor) can be tested. ISTS results from a concentrated (13 m%) aqueous LiCl solution, the molten salt [Ca(NO3)2]0.4[KNO3]0.6, and salol are reviewed.

Luminescent-Kinetic Method of Investigation of Structure of Concentrated Water Solutions of Chloride Salts

Abstract Energy transfer from Tb3+ to Er3+ ions in concentrated water solutions of AlCl3, MgCl2, CaCl2, ZnCl2, CsCl, NaCl and LiCl is examined. The analysis of energy transfer rate dependence on concentration of electrolyte and Er3+ shows that Ln3+ ions are separated into their own phase in two electrolytes: LiCl and CaCl2. I.e. Ln3+ ions self-assemblies occur only in solutions of those chlorides, whose cations possess negative entropy variation under their hydration, but this variation ought to be less than for Ln3+ hydration. Thus, Ln3+ ions phase detection is a probe for detection of solution ordering. The conclusion is confirmed by two experiments on disordering of LiCl solutions.

Time-resolved measurements of scaling behavior in LiCl/H 2O near the liquid-glass transition

Time-domain light scattering experiments on ps-μs timescales permit determination of the complex compressibility modulus in liquids and glasses in the MHz-GHz frequency window. Analysis of mechanical and electrical modulus spectra for a concentrated aqueous LiCl solution yields results consistent with some predictions of mode-coupling theory: simple scaling for α-relaxation peaks and property-independent power-law functional forms for the spectra which are independent of the property described. Preliminary data from salol, recorded with an improved experimental system, are also presented.

Orientational relaxation in hydrogen-bonded systems: aqueous solutions of electrolytes

A model of the rotational motion of water molecules within ion hydration sheaths is proposed in the present paper. This model is based on the concept of a ‘boundary’ ion, according to which the parameters of the structural surroundings, as well as the translational, rotational and librational motions of water molecules within the first sphere, are the same as those for water molecules in water. The wide-band absorption spectra, α(ν)(0 < ν/cm–1 < 400), and the complex dielectric permittivity spectrum measured for the concentrated electrolyte solutions, are described on the basis of the model proposed in this paper. It is shown that the confined rotator/extended diffusion (CR/ED) model, which has been advanced previously for liquid water, is applicable for spectral calculations of the electrolyte solutions studied in the present paper.The typical characteristics of ions having hydrophilic and hydrophobic hydration, as well as the distinctions between the hydration sheaths of ions with negative and positive hydrations, are discussed. A new method is proposed to study the molecular nature of these phenomena at the level of elementary processes. The complex dielectric permittivity of the concentrated LiCl, NaCl, Nal, KCl and KBr solutions has been measured in the range 7–25 GHz at 25 °C. For electrolyte solutions, the wide band (0 ⩽v/cm–1⩽ 1000) dielectric spectra and the parameters of the proposed model are calculated.

Time-resolved spectroscopy and scaling behavior in LiCl/H2O near the liquid-glass transition.

Time-domain light scattering experiments on ps-\ensuremath{\mu}s time scales have been conducted on a concentrated aqueous LiCl solution. Analysis of mechanical and electrical modulus spectra confirms some results of mode-coupling theory: Simple scaling for \ensuremath{\alpha} peaks and property-independent power laws. This is made without any assumptions about the data which are not derived from theory. A new characteristic time scale, reflecting the short- and intermediate-range ordering dynamics, is also observed.

Raman study of the effect of LiCl and CsCl on the resonance intermolecular coupling and the Fermi resonance of water

AbstractChanges in the isotropic and anisotropic component contours of the H2O and D2 stretching bands in aqueous solutions of LiCl and CsCl were studied within the entire accessible concentration range. The isotropic component contours were resolved into three constituents and the anisotropic contours into four. The resonance intermolecular coupling constants, V1 for the ν1 vibration and V2 for the 2ν2 overtone, and the Fermi resonance constant, W, of water were determined for solutions of various electrolyte concentrations. The added electrolytes were found to lower the V1 and V2 values. The Fermi resonance coupling constant decreased in aqueous LiCl solutions and was constant in CsCl solutions. The unperturbed ν1 and 2ν2 band positions of the LiCl solutions did not change. In the CsCl solutions, ν1 shifted to lower frequencies and 2ν2 to higher frequencies. A new component was found to appear in the anisotropic component for concentrated LiCl solutions, at 3550 cm−1 for H2O and 2590 cm−1 for D2O.

Extractive Separation of Lithium Isotopes Using Benzo-15-Crown-5. Effect of Salt Concentration

Abstract In an extractive separation of lithium isotopes with benzo-15-crown-5, the greater separation factor is obtained from more concentrated LiCl solution. The intrinsic separation factor of benzo-15-crown-5 is determined to be α = 1.045 at 20°C.

Trapped electrons in concentrated aqueous LiCl glasses at 4K—An optical absorption study

Absorption spectral characteristics of visible absorbing electrons, e - vis, in LiCl glasses have been studied by γ-radiolysis at 4K. Increasing the LiCl concentration causes a decrease of the absorption peak energy. The mean radius of charge density distribution and the mean kinetic energy of e - vis in the ground state have been calculated from the absorption spectra by applying the sum rules. The former increases and the latter concomitantly decreases with increasing the salt concentration. On the basis of these results, the trap structure is discussed in relation to the glass structure of concentrated LiCl solutions.

Studies on the interaction between alkali metal cations and polyion by sound velocity

The sound velocities in polyelectrolyte solutions were measured at various concentrations of added salts. When aqueous solutions of tetra ( n-butyl)ammonium polyacrylate were titrated with concentrated solutions of LiCl, NaCl, KCl or CsCl, the sound velocity, i.e., the adiabatic compressibility of the solution, did not change linearly with added salt concentration, but showed a breaking point. The degrees of counterion binding on polyacrylate ion estimated from the breaking points were 0.25–0.30, independent of cation species. In polystyrenesulfonate, moreover, no Na + binding was detected from such sound velocity measurements.

Liquidus temperatures of some systems salt-dimethyl sulphoxide and solvate formation. Preferential solvation by dimethyl sulphoxide

Liquidus temperatures were measured for concentrated solutions of LiCl, CaCl2, ZnCl2, Zn(NO3)2, NaNO3 and Mg(NO3)2 in dimethyl sulphoxide. Crystalline solvates of salts with dimethyl sulphoxide which separated from these solutions were isolated and subjected to chemical and infrared spectroscopic analyses. It has been proved that in concentrated solutions in the mixed solvent water-dimethyl sulphoxide, the salts are preferentially solvated by dimethyl sulphoxide.

Temperature jump in electric double-layer study: Part II. Excess entropy of EDl formation at the interface of mercury and electrolyte solutions of various concentrations

The method of laser-produced temperature jump has been used for measuring the temperature coefficients of potential drop, (∂/ω∂ T α at the boundary between mercury and aqueous solutions of NaF, KF, LiCl< CKl and CsCl within a wide range of electrolyte concentrations. The dependence of excess entropy os electric double-layer (α S°) formation on electrode charge and salt concentration have been found. In dilute solutions, (∂ω/∂ T) α and α S° are eequal to the sum of two quantities corresponding to the compact and diffuse parts of the electric double-layer (EDL). The first is determined by orientational polarization of the aqueous monolayer in the inner EDL region and does not depend on salt concentration. The other correspondds to the value calculated from Gouy-Chapman theory for the case when specific adsorption is absent. The measured EDL relaxation times are due tothe reorientation of water dipoles and do not depend on electrolyte concentration (up to 14 M) or the structure of the diffuse layer. Negative adsorption in concentrated LiCl solutions at qš0 produces positive and by an order of magnitude higher temperature coeeficients of surface excess of (∂_/∂ T) q as compared with the values expected according to Graham's theory, where we have (∂_/∂ T q, < O.

Dissolution of Copper Chloride in Concentrated LiCl Solution

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Anodic Dissolution of Copper in Concentrated LiCl Solution at pH Between 3 and 7

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Photoelectron emission from metal into concentrated electrolytes: Part II. Thermalization path-length of low-energy electrons and eaq− bulk reactions

Laser-induced photoelectron emission from metal into electrolyte solutions has been used for determining thermalization path-lengths ( l) of low-energy (0.5 eV⩽ E⩽2.7 eV) electrons, as well as absolute rate constants of reactions e aq −+N 2O and e aq −+ e aq − ( K a and K c, respectively) in aqueous solutions with varying concentration of KCl (0.25 M-4.15 M), CsCl (0.5 M-6.8 M), and LiCl (0.5 M-14 M). Two regions of l ( E) dependences have been observed in all solutions: l remains approximately constant at E≲2.2 eV and does not depend on composition of solution. viz. l=2.7±0.6 nm. Increase of l takes place in the range 2.2–2.7 eV, diminishing with electrolyte concentration. The observed l ( E) dependence is attributed to different mechanisms of energy losses. At E≲2 eV the resonance electron scattering from water molecules provides the main mechanism of thermalization. The dipol e mechanism of slowing down is preferred at E>2.2 eV. The decrease of l, observed in this energy range at higher electrolyte concentration, can be connected with electron scattering from ions. K a and K c are shown to be inversely proportional to viscosity (η) of solution, expect for concentrated LiCl solutions for which K aη increases with c at c>10 M, whilst K cη decreases at c≳5 M. The results obtained lead to the conclusion that the reaction ( e aq −+N 2O) is a diffusion-controlled one, the reaction diameter being independent of the properties of solution. Changes in K aη take place only when all water molecules are included in hydration shells of ions. The decrease in K c with rise in c is attributed to transition from the diffusion region into the kinetic one at c≳5 M, at which association of ions leads to changes in e aq − cluster structure.

Photoelectron emission from metal into concentrated electrolyte: Part I. Photoemission threshold

Current-voltage characteristics of photoemission from mercury into concentrated solutions of LiCl (1.0–14.06 M) KCl (1.0–4.15 M), and CsCl (1.0–6.8 M) have been measured. It is shown that a “ 5 2 -law” is valid for all solutions, and quantum yield of photoemission does not depend on the nature and concentration of the electrolyte. The photoemission method is applicable for studies in high-concentration electrolytes. In order to remove the diffusional potential drop, the photoemission threshold was measured against a calomel electrode with the same electrolyte content, and then recalculated to 1 M solution of the corresponding salt by means of the Nernst equation, thus avoiding concentrational potential drop. Photoemission threshold values thus obtained are approximately constant for solutions with salt concentration up to 7 M, shifting, with further increasing concentration, towards the cathode region up to 0.25 eV at 14 M of LiCl. The shift has been attributed to displacement of the bottom of the delocalized (quasi-free) electron band from V o towards vacuum level with increasing concentration of the electrolyte, when the greater part of the water molecules is bound in hydrated ion shells. A comparison between the changes in V o values and absorption spectra of the hydrated electron indicate that the change in solution content mentioned increases the medium reorganization energy in the process of localized state formation.