NaBr Solutions Research Articles

Water DynamicsThe Effects of Ions and Nanoconfinement

Hydrogen bond dynamics of water in highly concentrated NaBr salt solutions and reverse micelles are studied using ultrafast 2D-IR vibrational echo spectroscopy and polarization-selective IR pump-probe experiments performed on the OD hydroxyl stretch of dilute HOD in H(2)O. The vibrational echo experiments measure spectral diffusion, and the pump-probe experiments measure orientational relaxation. Both experimental observables are directly related to the structural dynamics of water's hydrogen bond network. The measurements performed on NaBr solutions as a function of concentration show that the hydrogen bond dynamics slow as the NaBr concentration increases. The most pronounced change is in the longest time scale dynamics which are related to the global rearrangement of the hydrogen bond structure. Complete hydrogen bond network randomization slows by a factor of approximately 3 in approximately 6 M NaBr solution compared to that in bulk water. The hydrogen bond dynamics of water in nanoscopically confined environments are studied by encapsulating water molecules in ionic head group (AOT) and nonionic head group (Igepal CO 520) reverse micelles. Water dynamics in the nanopools of AOT reverse micelles are studied as a function of size by observing orientational relaxation. Orientational relaxation dynamics deviate significantly from bulk water when the size of the reverse micelles is smaller than several nm and become nonexponential and slower as the size of the reverse micelles decreases. In the smallest reverse micelles, orientational relaxation (hydrogen bond structural randomization) is almost 20 times slower than that in bulk water. To determine if the changes in dynamics from bulk water are caused by the influence of the ionic head groups of AOT or the nanoconfinement, the water dynamics in 4 nm nanopools in AOT reverse micelles (ionic) and Igepal reverse micelles (nonionic) are compared. It is found that the water orientational relaxation in the 4 nm diameter nanopools of the two types of reverse micelles is almost identical, which indicates that confinement by an interface to form a nanoscopic water pool is a primary factor governing the dynamics of nanoscopic water rather than the presence of charged groups at the interface.

The Interaction Between Alloyed Molybdenum and Dissolved Bromide in the Pitting Corrosion of Stainless Steels

Artificial pit electrodes of types 304 and 316 stainless steels (304SS and 316SS) have been used to determine transition potentials for salt-film formation (E T ) as a function of the anodic limiting current density (i lim ), a procedure introduced by Laycock and Newman. Plots of E T vs log i lim are normally straight lines, and when extrapolated to a current density typical of an initiating pit, provide a model of the pitting potential. NaBr and NaCl solutions were compared using this procedure. It was found that the slope of the E T vs log i lim plot was higher for 316SS than 304SS in chloride solution, but higher for 304SS than 316SS in bromide solution. Thus, in bromide solutions, the anodic kinetics of 304SS and 316SS become the same at an anodic current density of several A/cm 2 . This set of observations can explain the absence of the usual beneficial effect of alloyed Mo on the stable pitting potential in bromide solution. On the other hand, metastable pits, which grow more slowly than stable pits, do show an inhibiting effect of alloyed Mo, in bromide as well as in chloride. The literature on comparative effects of halides on aqueous molybdenum chemistry has been reviewed, but no definite conclusions can be drawn. It is considered unlikely that the possible breakup of large polymolybdates by bromide is the underlying reason for the kinetic effects observed. Complexation of a low oxidation state of Mo is more likely.

Hydrogen bond dynamics in aqueous NaBr solutions.

Hydrogen bond dynamics of water in NaBr solutions are studied by using ultrafast 2D IR vibrational echo spectroscopy and polarization-selective IR pump-probe experiments. The hydrogen bond structural dynamics are observed by measuring spectral diffusion of the OD stretching mode of dilute HOD in H(2)O in a series of high concentration aqueous NaBr solutions with 2D IR vibrational echo spectroscopy. The time evolution of the 2D IR spectra yields frequency-frequency correlation functions, which permit quantitative comparisons of the influence of NaBr concentration on the hydrogen bond dynamics. The results show that the global rearrangement of the hydrogen bond structure, which is represented by the slowest component of the spectral diffusion, slows, and its time constant increases from 1.7 to 4.8 ps as the NaBr concentration increases from pure water to approximately 6 M NaBr. Orientational relaxation is analyzed with a wobbling-in-a-cone model describing restricted orientational diffusion that is followed by complete orientational randomization described as jump reorientation. The slowest component of the orientational relaxation increases from 2.6 ps (pure water) to 6.7 ps (approximately equal to 6 M NaBr). Vibrational population relaxation of the OD stretch also slows significantly as the NaBr concentration increases.

Interfacial Interactions of DCl with Salty Glycerol Solutions of KI, NaI, LiI, and NaBr

Gas−liquid scattering experiments are used to explore the role of interfacial ions in controlling collisions and reactions of DCl molecules with ∼2.5 M KI, NaI, LiI, and NaBr glycerol solutions. DCl molecules that thermalize upon collision with the surface of each solution follow one of three pathways: they may desorb immediately as DCl, undergo D → H exchange in the near-interfacial region and desorb as HCl, or dissolve and dissociate in the bulk. We find that each salt amplifies the differences among the channels: the fraction of DCl molecules that desorb intact increases from 9% for pure glycerol to 18% on average for the salt solutions, interfacial DCl → HCl exchange increases from 3 to 7%, and bulk dissolution drops from 87 to 75%. Dissolved ions may enhance nonreactive DCl desorption and interfacial D → H exchange by tying up glycerol OH groups, which will impede both DCl−OH bonding and migration of D+ and H+ away from Cl- after DCl ionization. Despite differences in the sizes of the ions and thei...

NaBr 및 NaF 용액에 대한 Sn-3.0Ag-0.5Cu 솔더 합금의 Electrochemical Migration 특성

Electrochemical migration characteristics of Pb-free solder alloys are quantitatively correlated with corrosion characteristics in harsh environment conditions. In-situ water drop test and corrosion resistance test for Sn-3.0Ag-0.5Cu solder alloys were carried out in NaBr and NaF solutions to obtain the electrochemical migration lifetime and pitting potential, respectively. Sn-3.0Ag-0.5Cu solder alloy shows similar ionization and electrochemical migration behavior with pure Sn because of Ag and Cu do not migrate due to the formation of resistant intermetallic compounds inside solder itself. Electrochemical migration lifetime in NaBr is longer than in NaF, which seems to be closely related to higher pitting potential in NaBr than NaF solution. Therefore, it was revealed that electrochemical migration lifetime of Sn-3.0Ag-0.5Cu solder alloys showed good correlation to the corrosion resistance, and also the initial ionization step at anode side is believed to be the rate-determining step during electrochemical migration of Pb-free solders in these environments.

Calculating models of mass action concentrations for NaBr(aq), LiNO 3(aq), HNO 3(aq), and KF(aq) binary solutions

The calculating models of mass action concentrations for electrolyte aqueous solutions NaBr-H 2O, LiNO 3-H 2O, HNO 3-H 2O, and KF-H 2O have been developed at 298.15 K and their molalities ranging from 0.1 mol/kg to saturation according to the ion and molecule coexistence theory as well as mass action law. The calculated mass action concentration is based on pure species as the standard state and the mole fraction as the concentration unit, and the reported activities are usually based on infinite dilution as the standard state and molality as the concentration unit. Hence, the calculated mass action concentration must be transformed to the same standard state and concentration unit. The transformation coefficients between calculated mass action concentrations and reported activities of the same component fluctuate in a very narrow range. Thus, the transformed mass action concentrations not only agree well with reported activities, but also strictly obey mass action law. The calculated results show that the new developed models can embody the intrinsic structure of investigated four electrolyte aqueous solutions. The results also indicate that mass action law has its widespread applicability to electrolyte binary aqueous solutions.

Enthalpic interaction coefficients of glycine in aqueous sodium halide solutions at 298.15 K

The enthalpies of dilution have been measured for glycine in aqueous NaCl and NaBr solutions at 298.15 K using a flow microcalorimetry. The enthalpic interaction coefficients of glycine in the studied aqueous sodium halide solutions have been calculated according to the McMillan–Mayer model. Combining the previous studies for other sodium halides, the effect of the anions on enthalpic pairwise interaction coefficients between the glycine molecules has been rationalized in terms of the concepts of electrostatic interaction and structural interaction. The experimental data of the present work and those of the literature are combined, to put forward the general chemical principal, namely the more strongly solutes are solvated the less will be their tendency to interact with other solutes.

Br2 Production from the Heterogeneous Reaction of Gas-Phase OH with Aqueous Salt Solutions: Impacts of Acidity, Halide Concentration, and Organic Surfactants

This study reports the first laboratory measurement of gas-phase Br2 production from the reaction between gas-phase hydroxyl radicals and aqueous salt solutions. Experiments were conducted at 269 K in a rotating wetted-wall flow tube coupled to a chemical-ionization mass spectrometer for analysis of gas-phase components. From both pure NaBr solutions and mixed NaCl/NaBr solutions, the amount of Br2 released was found to increase with increasing acidity, whereas it was found to vary little with increasing concentration of bromide ions in the sample. For mixed NaCl/NaBr solutions, Br2 was formed preferentially over Cl2 unless the Br- levels in the solution were significantly depleted by OH oxidation, at which point Cl2 formation was observed. Presence of a surfactant in solution, sodium dodecyl sulfate, significantly suppressed the formation of Br2; this is the first indication that an organic surfactant can affect the rate of interfacial mass transfer of OH to an aqueous surface. The OH-mediated oxidation of bromide may serve as a source of active bromine in the troposphere and contribute to the subsequent destruction of ozone that proceeds in marine-influenced regions of the troposphere.

Experimental Study of the Effect of Temperature, Pressure and Concentration on the Viscosity of Aqueous NaBr Solutions

The viscosity of 10 (0.049, 0.205, 0.464, 0.564, 0.820, 1.105, 1.496, 2.007, 2.382, and 2.961 mol ċ kg−1) binary aqueous NaBr solutions has been measured with a capillary-flow technique. Measurements were made at pressures up to 40 MPa. The range of temperature was 288–595 K. The total uncertainty of viscosity, pressure, temperature and composition measurements were estimated to be less than 1.6%, 0.05%, 15 mK, and 0.02%, respectively. The effect of temperature, pressure, and concentration on viscosity of binary aqueous NaBr solutions were studied. The measured values of the viscosity of NaBr(aq) were compared with data, predictions and correlations reported in the literature. The temperature and pressure coefficients of viscosity of NaBr(aq) were studied as a function of concentration and temperature. The viscosity data have been interpreted in terms of the extended Jones–Dole equation for the relative viscosity (η/η0) to calculate accurately the values of viscosity A- and B-coefficients as a function of temperature. The derived values of the viscosity A- and B-coefficients were compared with the results predicted by the Falkenhagen–Dole theory of electrolyte solutions and calculated with the ionic B-coefficient data. The physical meaning parameters V and E in the absolute rate theory of the viscosity and hydrodynamic molar volume V k were calculated using the present experimental viscosity data. The TTG model has been used to compare predicted values of the viscosity of NaBr(aq) solutions with experimental values at high pressures.

Limiting ionic partial molar volumes of R4N+ and Br− in aqueous ethanol at 298.15 K

The densities of tetraalkyl ammonium bromide, R4NBr (R=CH3 through n-C4H9), NaBPh4 and NaBr solutions in (0, 10, 30, 50, 70, 90, and 100) mass% ethanol+water have been measured over the whole composition range at 298.15 K. From the densities, apparent and limiting partial molar volumes of the electrolytes and ions in these mixtures have been evaluated.

The Durability of the Enantio-Differentiating Ability of a Tartaric Acid–NaBr-Modified Reduced Nickel Catalyst Pre-Modified in Tetrahydrofuran

The enantio-differentiating hydrogenation of methyl acetoacetate was carried out over a (R,R)-tartaric acid–NaBr-modified reduced Ni catalyst. The reduced Ni was pre-modified in a tetrahydrofuran solution of tartaric acid and NaBr at atmospheric pressure or at a high hydrogen pressure. The enantio-differentiating ability of 70–90% was maintained during 40 runs over the reduced nickel catalyst pre-modified at 9 MPa hydrogen and 373 K. The results indicated that the durability of a high enantio-differentiating ability of an in-situ-modified catalyst would be attributed to the modification conditions at the high hydrogen pressure of 9 MPa and the high temperature of 373 K in the autoclave.

Rate controls on the chemical weathering of natural polymineralic material. I. Dissolution behaviour of polymineralic assemblages determined using batch and unsaturated column experiments

Chemical weathering rates for a mudstone obtained from a mining environment were investigated using a combination of batch reactors and hydrologically unsaturated column experiments. Results of tracer tests were combined with relationships between solute concentrations, mass fluxes, flow rates and residence times, and used to calculate element release rates and infer rate-controlling mechanisms for the two different experimental environments. Elements that eluted from column experiments exhibited either: (1) concentrations independent of flow rate and column length coupled with mass flux increasing with flow rate, or (2) an inverse relationship between concentration and flow rate coupled with mass flux increasing with both column length and flow rate. The former is attributed to equilibrium-controlled release of particular elements (Si, Al), while the latter is ascribed to transport-controlled release of others (Mg, Mn, Ca, Na, K, S). Tracer tests using NaBr solutions revealed that some elements were also affected by ion exchange (Mg, Mn, Ca, Na), but these effects were temporary and did not mask underlying dissolution rate-controlling mechanisms. Analysis of characteristic diffusive lengths was used to distinguish between transport rates limited by the transfer of solutes between immobile and mobile water within the columns, and rates limited by slow diffusion across partially reacted mineral layers. The analysis suggests that transfer between immobile and mobile water limited the element release rates, with diffusion hindered by low diffusion coefficients within the unsaturated medium, and by low interfacial areas between mobile and immobile fluids. Results of the batch experiments showed different characteristics. Element concentrations either rose to a plateau or increased linearly with time. Rate-controlling mechanisms associated with these characteristics were equilibrium (Fe) and surface kinetic reactions (Si, Mg, Mn, Ca, K, S), respectively. Surface area-normalized element release rates for Mg, Mn, Ca and S are consistently a factor of 4 higher than those from the column experiments. This is a significant difference and cannot be attributed to differences in mineral preparation or to factors influencing individual minerals. It must, therefore, reflect the difference in the rate-controlling mechanism, that is, transport vs. surface-kinetic control. These results suggest that some proportion of the commonly recorded discrepancy between laboratory and field weathering rates is due to hydrological differences between the two environments, and that hydrological characterization of weathering environments is, therefore, as important as physical–geochemical characterization of reacting solids. An important practical implication of the work is that substantial reservoirs of solutes are held in immobile water in the unsaturated environment, and that these could be released by soil disturbance or flooding.

Towards accurate values of individual ion activities: Additional data for NaCl, NaBr and KCl, and new data for NH 4Cl

Ion-selective electrodes (ISEs) were used to measure the activity coefficients at 298.15 K of individual ions in aqueous solutions of NaCl, NaBr, KCl and NH 4Cl up to 3m. The possible effect of the standard solution used in the reference electrode was tested. The emf responses of ISEs were measured against a single-junction reference electrode filled with either a 4 M KCl solution, saturated with AgCl, or a 2 M NH 4Cl solution. For the first three systems, ISEs for both the cation and the anion were used. For NH 4Cl, only the response of a chloride ISE was measured. The number of experimental points measured in the dilute region was increased and the effect of the maximum composition used to determine electrode parameters was studied. It was found that the reference solution used for the measurements has a minor effect on the measured values of the individual ionic activities while the maximum sample composition to which the normalization condition is applied has a larger effect. The ionic activity coefficients may fail to satisfy the necessary condition of reproducing the mean ionic activity coefficient if the maximum normalization concentration exceeds 0.01m. Otherwise, values of the ionic activities reproduce well literature values for the mean ionic activity coefficients.

Conductivity and association of NaCl, NaBr, NaI, NaNO 3, NaClO 4 and NaSCN in ethanol at 213.15–333.15 K

Based on Krumgalz conductivity data of dilute (1×10−6–5×10−2 mol kg−1) electrolyte solutions of NaCl, NaBr, NaI, NaNO3, NaClO4 and NaSCN in ethanol in the temperature range 213.15–333.15 K (at 10 K intervals), the standard Gibbs energy, enthalpy and entropy of ion-pair formation, as well as contributions of the electrostatic and the non-electrostatic interactions to these functions, have been calculated.

Excess volumes of mixing of 1:1 electrolyte solutions at 308.15 K in aqua–DMF mixed solvent system

Excess volumes of mixing for six possible binary combinations of solutions of NaCl, KCl, NaBr and KBr have been determined at constant ionic strength of 1.000 and 2.000 mol kg − 1 at 308.15 K in water + N, N-dimethylformamide mixed solvent system using a dilatometer. Data were examined using the Friedman model and the mixing parameters related to the pair, triplet, and higher interactions, i.e., v 0, v 1, and v 2 were calculated. Data follow the cross square rule (CSR) at I = 2.000 mol kg − 1 but not at I = 1.000 mol kg − 1. The deviation from CSR is considered to arise from preferential solvation of the ions and ion clusters in the mixed solvent system. It is observed that the higher number of DMF molecules is in the solvation shell of an ion the larger is the deviation from CSR.

Is There an Anionic Hofmeister Effect on Water Dynamics? Dielectric Spectroscopy of Aqueous Solutions of NaBr, NaI, NaNO3, NaClO4, and NaSCN

A systematic study of the dielectric relaxation spectra of aqueous solutions of NaBr, NaI, NaNO(3), NaClO(4), and NaSCN has been made over a wide range of frequencies (0.2 < or = nu/GHz < or = 89) and solute concentrations (0.05 < or = c/M < or = 1.5) at 25 degrees C. The spectra could be adequately described by a single Cole-Cole (CC) process, symmetrically broadened relative to that of pure water. However, similar quality fits were also obtained with a three-Debye-process (3D) model consisting of a small ion-pair contribution at lower frequencies and two solvent relaxations at higher frequencies. Assuming the ions to be solvent separated, the 3D model provided estimates of their association constants and their rate constants for formation and dissociation. The bulk water relaxation times obtained from both models showed almost no dependence on the nature of the anion. Nevertheless, there were subtle differences in the concentration dependences of the relaxation times which correlated with some, but not all, of the anion properties that are believed to be relevant for explaining the anionic Hofmeister series.

Excess Volume of Mixing of 1:1 Electrolyte Solutions at 298.15 K in the Aquo-1,4-Dioxane Mixed-Solvent System

Excess volumes of mixing for six possible binary combinations of solutions of NaCl, KCl, NaBr and KBr have been determined at constant ionic strengths of 1.000 and 2.000 mol-kg− 1 at 298.15 K using a dilatometer in the water + 1,4-dioxane mixed-solvent system. Pitzer’s ion-interaction model has been utilized to obtain binary and triplet interaction parameters, i.e., θV and ψV. The data were also analyzed by the Friedman Model and it is suggested that interactions between solvated ions are dictated not only by coulombic interactions but also by appreciable asymmetric effects. The data are dependent on the nature of the common ion and do not support Young’s cross-square rule. The deviation from the cross-square rule is considered to arise from preferential solvation of the ions and ion clusters in the mixed-solvent system as reflected by the appreciable contribution of triplet interactions.

Photochemistry of an Azido-Functionalized Cryptand: Controlling the Reactivity of an Extremely Long-Lived Singlet Aryl Nitrene by Complexation to Alkali Cations

Photolysis of the cryptand 1, bearing an intraannular azido substituent, results in a complex photochemistry. Low-temperature photolysis yields the triplet nitrene (3)2, which has been characterized by EPR spectroscopy. Small differences in ZFS parameters are detected between the uncomplexed nitrene-functionalized ligand (in EtOH: D' = 0.93 cm(-1)) and its sodium (NaBr@(3)2 in EtOH: D' = 0.88 cm(-1)) and potassium (KBr@(3)2 in MTHF: D' = 0.89 cm(-1)) complexes. If the photolysis of the free ligand is conducted at ambient temperature, a derivative of o-aminobenzaldehyde 4 is found to be the main product, which is formed by reaction of the o-iminoquinone methide 9 with water. The latter can be detected by UV/vis spectroscopy. Its lifetime is tau = 254 s in acetonitrile solution at ambient temperature. In the presence of diethylamine, the methyleneazepine derivative 5 is formed, which is indicative of didehydroazepine formation (7). Room-temperature photolysis of acetonitrile solutions of the sodium or potassium complexes also results in formation of the o-aminobenzaldehyde derivative. In the presence of diethylamine, however, no methyleneazepine 5 is found. Formation of the aniline derivative 8 instead points to free radical processes. Laser flash photolysis (LFP) of acetonitrile solutions of 1 leads to the detection of a short-lived (tau = 1.4 mus, lambda(max) = 445 nm plus weak absorption at lambda > 500 nm) intermediate A, which decays to transient B (tau = 8 ms, lambda(max) = 295 and ca. 350-400 nm). LFP of acetonitrile solutions of complexes NaBr@1 and KBr@1 gives similar transient spectra. In the presence of sodium and potassium cations, the lifetime of the short-lived transient A is reduced (Na(+): A', tau = 200 ns; K(+): A", tau = 160 ns). Transients A' and A" decay to long-lived transients B' + C' (B" + C"). Based on the results of our product studies, a comparison with the low-temperature results, and quantum mechanical calculations, the transients A, A', and A" are identified as singlet nitrenes (1)2, NaBr@(1)2, and KBr@(1)2, while the long-lived transients B, B', and B" are assigned to didehydroazepines 7, NaBr@7, and KBr@7. Transients C' and C" can be assigned to aminyl radicals NaBr@16 and KBr@16.

Effect of NaBr, KCl, KBr, and MgCl2 on Viscosities of Aqueous Glycine and l-Alanine Solutions at 298.15 K

Viscosities, η, of glycine and l-alanine are measured in aqueous solutions of NaBr, KCl, KBr, and MgCl2 up to high concentrations at 298.15 K. This study suggests that 1:1 electrolytes enhance the structure-making ability of the amino acids whereas MgCl2 does not. The viscosities of the above solutions are correlated using a simple model with two interaction parameters.

The electronic structures of crystalline and aqueous solutions of NaBr and NaBrO3 using in-situ Na K and Br L edge x-ray absorption spectroscopy

The electronic structures of crystalline and aqueous solutions of NaBr and NaBrO3 were studied using in-situ Na K and Br L edge x-ray absorption spectra measured under ambient conditions. Analyses of Na K-edge x-ray absorption spectra show that NaBr and NaBrO3 strongly dissociate in aqueous solution and form Na+ hydration structures, [Na(H2O)n]+ (n = 0–6). However, the size of the anions significantly affects the formation of the Na+ hydration structures in aqueous solutions. The ligand field potential (10 Dq) observed in the Br L-edge x-ray absorption spectra allows in determining their dependence not only on the coordination structure between the Br and the first near neighbor but also the second near neighbor in crystalline state, and, the hydration structure and the counter cations in aqueous solutions. DV-Xα molecular-orbital calculations predict that the transitions in the Br L-edge NEXAFS occur from Br 2p to the unoccupied states containing mainly 4d orbitals of Br for both crystalline and aqueous solution. However, 5s and 5p of Br and 3p of Na in addition to the 4d orbitals of neighbor Br for crystalline NaBr and 5s and 5p of Br, 2p of O and 1s of H for aqueous NaBr also contribute to the unoccupied states.